The predictions of our previous analyses about possible low-mass (lower than 50 GeV) relic neutralinos are discussed in the light of the most recent results from WIMP direct detection experiments. It is proved that these light neutralinos are quite compatible with the new annual-modulation data of the DAMA Collaboration; our theoretical predictions are also compared with the upper bounds of the CDMS and EDELWEISS Collaborations.

(ABRIDGED) The canonical picture of a supernova impostor is a -11 < M_V 40Msun) star during which the star ejects a dense shell of material. Dust formed in the ejecta then obscures the star. In this picture, the geometric expansion of the shell leads to clear predictions for the evolution of the optical depths and hence the evolution of the optical through mid-IR emissions. Here we review the theory of this standard model and then examine the impostors SN1954J, SN1997bs, SN1999bw, SN2000ch, SN2001ac, SN2002bu, SN2002kg and SN2003gm, as well as the potential archetype eta Carinae. SN1999bw, SN2000ch, SN2001ac, SN2002bu and SN2003gm all show mid-IR emission indicative of dust, and the luminosities of SN1999bw, SN2001ac, SN2002bu and SN2003gm are dominated by dust emission. The properties of these sources are broadly inconsistent with the predictions of the canonical model. There are probably two classes of sources. In one class (eta Carinae, SN1954J, SN1997bs, and (maybe) SN2003gm), the optical transient is a signal that the star is entering a phase with very high mass loss rates that must last far longer than the visual transient. The second class (SN1999bw, SN2001ac, SN2002bu and (maybe) SN2003gm) has the different physics of SN2008S and the 2008 NGC300 transient, where they are obscured by dust re-forming in a pre-existing wind after it was destroyed by an explosive transient. There are no cases where the source at late times is significantly fainter than the progenitor star. All these dusty transients are occurring in relatively low mass (M 40Msun) stars radiating near the Eddington limit like eta Carinae. The durations and energetics of these transients cannot be properly characterized without near/mid-IR observations.

We present the detection of Ly-alpha, [OIII] and H-alpha emission associated with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards the quasar SDSS J113520-001053. This is the largest HI column density ever measured along a QSO line of sight, though typical of what is seen in GRB-DLAs. This absorption system also classifies as ultrastrong MgII system with W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally larger than) the mean values found in the general QSO-DLA population. The [OIII]-Ha emitting region has a very small impact parameter with respect to the QSO line of sight, b=0.1″, and is unresolved. From the Ha line, we measure SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More strikingly, the blue and red Ly-a peaks arise from distinct regions extended over a few kpc on either side of the star-forming region. We propose that this is the consequence of Ly-a transfer in outflowing gas. The presence of starburst-driven outflows is also in agreement with the large SFR together with a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV continuum luminosity of the galaxy, we estimate an age of at most a few 10^7 yr, again consistent with a recent starburst scenario. We interpret the data as the observation of a young, gas rich, compact starburst galaxy, from which material is expelled through collimated winds powered by the vigorous star formation activity. We substantiate this picture by modelling the radiative transfer of Ly-a photons in the galactic counterpart. Though our model (a spherical galaxy with bipolar outflowing jets) is a simplistic representation of the true gas distribution and velocity field, the agreement between the observed and simulated properties is particularly good. [abridged]

We present moderate resolution (R $\sim$ 3575) optical spectra of 19 known or suspected members of the AB Doradus and $\beta$ Pictoris Moving Groups, obtained with the DeVeny Spectrograph on the 72-inch Perkins telescope at Lowell Observatory. For 4 of 5 recently proposed members, signatures of youth such as Li\,I 6708 \AA\, absorption and H$\alpha$ emission further strengthen the case for youth and membership. Effective temperatures are determined via line ratio analyses for the 11 F, G and early K stars observed, and via spectral comparisons for the 8 late-K and M stars observed. We assemble updated candidate membership lists for these Moving Groups that account for known binarity. We then use temperature, luminosity, and distance estimates to predict angular diameters for these stars; the motivation is to identify stars that can be spatially resolved with long-baseline optical/infrared interferometers in order to improve age estimates for these Groups and to constrain evolutionary models at young ages. Considering the portion of the sky accessible to northern hemisphere facilities (DEC $> -30$), 6 stars have diameters large enough to be spatially resolved ($\theta > 0.4$ mas) with the CHARA Array; this subsample includes the low mass M2.5 member of AB Dor, GJ 393, which is likely to still be pre-main sequence. For southern hemisphere facilities (DEC $< +30$), 18 stars have diameters larger than this limiting size, including the low mass debris disk star AU Mic (0.72 mas). However, the longest baselines of southern hemisphere interferometers (160-m) are only able to resolve the largest of these, the B6 star $\alpha$ Gru (1.17 mas); proposed long-baseline stations may alleviate the current limitations.

There is mounting evidence that a significant fraction of Black Holes (BHs) today live in late-type galaxies, including bulge-less galaxies and those hosting pseudobulges, and are significantly undermassive with respect to the scaling relations followed by their counterpart BHs in classical bulges of similar stellar (or even bulge) mass. Here we discuss the predictions of two state-of-the-art hierarchical galaxy formation models in which BHs grow via mergers and, in one, also via disk instability. Our aim is to understand if the wealth of new data on local BH demography is consistent with standard models. We follow the merger trees of representative subsamples of BHs and compute the fractional contributions of different processes to the final BH mass. We show that the model in which BHs always closely follow the growth of their host bulges, also during late disk instabilities (i.e., bars), produces too narrow a distribution of BHs at fixed stellar mass to account for the numerous low-mass BHs now detected in later-type galaxies. Models with a looser connection between BH growth and bar instability instead predict the existence of a larger number of undermassive BHs, in better agreement with the observations. The scatter in the updated local BH-bulge mass relation (with no restriction on galaxy type) appears to be quite large when including later-type systems, but it can still be managed to be reproduced within current hierarchical models. However, the fuelling of BHs during the late bar-instability mode needs to be better quantified/improved to properly fit the data. We conclude discussing how the possibly large number of BHs in later type galaxies demands for an in-depth revision of the local BH mass function and its modelling.

The neutron-star Low-Mass X-ray Binary Aquila X-1 was observed seven times in total with the Suzaku X-ray observatory from September 28 to October 30 in 2007, in the decaying phase of an outburst. In order to constrain the flux-dependent accretion geometry of this source over wider energy bands than employed in most of previous works, the present study utilized two out of the seven data sets. The 0.8-31 keV spectrum on September 28, taken with the XIS and HXD-PIN for an exposure of 13.8 ks, shows an absorbed 0.8-31 keV flux of $3.6\times 10^{-9}$ erg s$^{-1}$ cm$^{-2}$, together with typical characteristics of the soft state of this type of objects. The spectrum was successfully explained by an optically-thick disk emission plus a Comptonized blackbody component. Although these results are in general agreement with previous studies, the significance of a hard tail recently reported using the same data was inconclusive in our analysis. The spectrum acquired on October 9 for an exposure of 19.7 ks was detected over a 0.8-100 keV band with the XIS, HXD-PIN, and HXD-GSO, at an absorbed flux of $8.5\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ (in 0.8-100 keV). It shows characteristics of the hard state, and was successfully explained by the same two continuum components but with rather different parameters including much stronger thermal Comptonization, of which the seed photon source was identified with blackbody emission from the neutron-star surface. As a result, the accretion flow in the hard state is inferred to take a form of an optically-thick and geometrically-thin disk down to a radius of $21\pm 4$ km from the neutron star, and then turn into an optically-thin nearly-spherical hot flow.

We investigate the alignment of the spin of dark matter halos relative (i) to the surrounding large-scale filamentary structure, and (ii) to the tidal tensor eigenvectors using the Horizon 4pi dark matter simulation which resolves over 43 million dark matter halos at redshift zero. We detect a clear mass transition: the spin of dark matter halos above a critical mass tends to be perpendicular to the closest filament, and aligned with the intermediate axis of the tidal tensor, whereas the spin of low-mass halos is more likely to be aligned with the closest filament. Furthermore, this critical mass of 5 10^12 is redshift-dependent and scales as (1+z)^-2.5. We propose an interpretation of this signal in terms of large-scale cosmic flows. In this picture, most low-mass halos are formed through the winding of flows embedded in misaligned walls; hence they acquire a spin parallel to the axis of the resulting filaments forming at the intersection of these walls. On the other hand, more massive halos are typically the products of later mergers along such filaments, and thus they acquire a spin perpendicular to this direction when their orbital angular momentum is converted into spin. We show that this scenario is consistent with both the measured excess probabilities of alignment w.r.t. the eigen-directions of the tidal tensor, and halo merger histories. On a more qualitative level, it also seems compatible with 3D visualization of the structure of the cosmic web as traced by “smoothed” dark matter simulations or gas tracer particles. Finally, it provides extra support to the disc forming paradigm presented by Pichon et al (2011) as it extends it by characterizing the geometry of secondary infall at high redshift.

We present a new method for confirming transiting planets based on the combination of transit timingn variations (TTVs) and dynamical stability. Correlated TTVs provide evidence that the pair of bodies are in the same physical system. Orbital stability provides upper limits for the masses of the transiting companions that are in the planetary regime. This paper describes a non-parametric technique for quantifying the statistical significance of TTVs based on the correlation of two TTV data sets. We apply this method to an analysis of the transit timing variations of two stars with multiple transiting planet candidates identified by Kepler. We confirm four transiting planets in two multiple planet systems based on their TTVs and the constraints imposed by dynamical stability. An additional three candidates in these same systems are not confirmed as planets, but are likely to be validated as real planets once further observations and analyses are possible. If all were confirmed, these systems would be near 4:6:9 and 2:4:6:9 period commensurabilities. Our results demonstrate that TTVs provide a powerful tool for confirming transiting planets, including low-mass planets and planets around faint stars for which Doppler follow-up is not practical with existing facilities. Continued Kepler observations will dramatically improve the constraints on the planet masses and orbits and provide sensitivity for detecting additional non-transiting planets. If Kepler observations were extended to eight years, then a similar analysis could likely confirm systems with multiple closely spaced, small transiting planets in or near the habitable zone of solar-type stars.

Germanium detectors with sub-keV sensitivities open a window to search for low-mass WIMP dark matter. The CDEX-TEXONO Collaboration is conducting the first research program at the new China Jinping Underground Laboratory with this approach. The status and plans of the laboratory and the experiment are discussed.

Jupiter and Saturn formed in a few million years (Haisch et al. 2001) from a gas-dominated protoplanetary disk, and were susceptible to gas-driven migration of their orbits on timescales of only ~100,000 years (Armitage 2007). Hydrodynamic simulations show that these giant planets can undergo a two-stage, inward-then-outward, migration (Masset & Snellgrove 2001, Morbidelli & Crida 2007, Pierens & Nelson 2008). The terrestrial planets finished accreting much later (Klein et al. 2009), and their characteristics, including Mars’ small mass, are best reproduced by starting from a planetesimal disk with an outer edge at about one astronomical unit from the Sun (Wetherill 1978, Hansen 2009) (1 AU is the Earth-Sun distance). Here we report simulations of the early Solar System that show how the inward migration of Jupiter to 1.5 AU, and its subsequent outward migration, lead to a planetesimal disk truncated at 1 AU; the terrestrial planets then form from this disk over the next 30-50 million years, with an Earth/Mars mass ratio consistent with observations. Scattering by Jupiter initially empties but then repopulates the asteroid belt, with inner-belt bodies originating between 1 and 3 AU and outer-belt bodies originating between and beyond the giant planets. This explains the significant compositional differences across the asteroid belt. The key aspect missing from previous models of terrestrial planet formation is the substantial radial migration of the giant planets, which suggests that their behaviour is more similar to that inferred for extrasolar planets than previously thought.

A study of late-type low-mass eclipsing binaries provides us with important information about the most common stars in the Universe. We obtain the first light curves and perform period analyses of two neglected eclipsing binaries GK Boo and AE For to reveal their basic physical properties. We performed both a period analysis of the times of the minima and a BVR light curve analysis. Many new times of minima for both the systems were derived and collected from the data obtained by automatic and robotic telescopes. This allowed us to study the long-term period changes in these systems for the first time. From the light curve analysis, we derived the first rough estimates of the physical properties of these systems. We find that the analyzed systems are somewhat similar to each other. Both contain low-mass components of similar types, both are close to the Sun, both have short orbital period, and both contain another low-mass companions on longer orbits of a few years. In the case of GK Boo, both components are probably of K3 spectral type, while the distant companion is probably a late M star. The light curve of GK Boo is asymmetric, which probably causes the shift in the secondary minima in the O-C diagram. System AE For comprises two K7 stars, and the third body is a possible brown dwarf with a minimal mass of only about 47 Jupiter Mass. We succeed in completing period and light curve analyses of both systems, although a more detailed spectroscopic analysis is needed to confirm the physical parameters of the components to a higher accuracy.

We present new upper limits for black hole masses in extremely late type spiral galaxies. We confirm that this class of galaxies has black holes with masses less than 10^6 Msolar, if any. We also derive new upper limits for nuclear star cluster (NC) masses in massive galaxies with previously determined black hole masses. We use the newly derived upper limits and a literature compilation to study the low mass end of the global-to-nucleus relations. We find the following (1) The M_BH-sigma relation cannot flatten at low masses, but may steepen. (2) The M_BH-M_bulge relation may well flatten in contrast. (3) The M_BH-Sersic n relation is able to account for the large scatter in black hole masses in low-mass disk galaxies. Outliers in the M_BH-Sersic n relation seem to be dwarf elliptical galaxies. When plotting M_BH versus M_NC we find three different regimes: (a) nuclear cluster dominated nuclei, (b) a transition region, and (c) black hole-dominated nuclei. This is consistent with the picture, in which black holes form inside nuclear clusters with a very low-mass fraction. They subsequently grow much faster than the nuclear cluster, destroying it when the ratio M_BH/M_NC grows above 100. Nuclear star clusters may thus be the precursors of massive black holes in galaxy nuclei.

We present the optical to near-infrared spectrum of MAXI J1659-152, during the onset of its 2010 X-ray outburst. The spectrum was obtained with X-shooter on the ESO – Very Large Telescope (VLT) early in the outburst simultaneous with high quality observations at both shorter and longer wavelengths. At the time of the observations, the source was in the low-hard state. The X-shooter spectrum includes many broad (~2000 km/s), double-peaked emission profiles of H, HeI, HeII, characteristic signatures of a low-mass X-ray binary during outburst. We detect no spectral signatures of the low-mass companion star. The strength of the diffuse interstellar bands results in a lower limit to the total interstellar extinction of Av ~ 0.4 mag. Using the neutral hydrogen column density obtained from the X-ray spectrum we estimate Av ~1 mag. The radial-velocity structure of the interstellar NaI D and CaII H & K lines results in a lower limit to the distance of ~ 4 +/- 1 kpc, consistent with previous estimates. With this distance and Av, the dereddened spectral energy distribution represents a flat disk spectrum. The two subsequent 10 minute X-shooter spectra show significant variability in the red wing of the emission-line profiles, indicating a global change in the density structure of the disk, though on a timescale much shorter than the typical viscous timescale of the disk.

We describe a new method that allows us to quantitatively characterize galactic satellites from analysis of disturbances in outer gas disks, without requiring knowledge of their optical light. We have demonstrated the validity of this method, which we call Tidal Analysis, by applying it to local spirals with known optical companions, including M51 and NGC 1512. These galaxies span the range from having a low mass companion (~ one-hundredth the mass of the primary galaxy) to a fairly massive companion (~ one-third the mass of the primary galaxy). This approach has broad implications for many areas of astrophysics – for the indirect detection of dark matter (or dark-matter dominated dwarf galaxies), and for galaxy evolution in its use as a decipher of the dynamical impact of satellites on galactic disks. Here, we present some preliminary results on the emergent SEDs and images, calculated along the time sequence of these dynamical simulations using the 3-D self-consistent Monte Carlo radiative transfer code RADISHE. We explore star formation prescriptions and how they affect the emergent SEDs and images. Our goal is to identify SED colors that are primarily affected by the galaxy’s interaction history, and not significantly affected by the choice of star formation prescription. If successful, we may be able to utilize the emergent UV-IR SED of the primary galaxy to understand its recent interaction history.

We interpret the observed radial-velocity curve of the optical star in the low-mass X-ray binary 2S 0921-630 using a Roche model, taking into account the X-ray heating of the optical star and screening of X-rays coming from the relativistic object by the accretion disk. Consequences of possible anisotropy of the X-ray radiation are considered.We obtain relations between the masses of the optical and compact (X-ray) components, mv and mx, for orbital inclinations i=60, 75, 90 degrees. Including X-ray heating enabled us to reduce the compact object’s mass by near 0.5-1Msun, compared to the case with no heating. Based on the K0III spectral type of the optical component (with a probable mass of mv=2.9Msun, we concluded that mx=2.45-2.55Msun (for i=75-90 degrees). If the K0III star has lost a substantial part of its mass as a result of mass exchange, as in the V404 Cyg and GRS 1905+105 systems, and its mass is $m_v=0.65-0.75Msun, the compact object’s mass is close to the standard mass of a neutron star, mx=1.4Msun (for i=75-90 degrees). Thus, it is probable that the X-ray source in the 2S 0921-630 binary is an accreting neutron star.

We have observed the HN13C J=1-0 and DNC J=1-0 lines toward 18 massive clumps, including infrared dark clouds (IRDCs) and high-mass protostellar objects (HMPOs), by using the Nobeyama Radio Observatory 45 m telescope. We have found that the HN13C emission is stronger than the DNC emission toward all the observed sources. The averaged DNC/HNC ratio is indeed lower toward the observed high-mass sources (0.009\pm0.005) than toward the low-mass starless and star-forming cores (0.06). The kinetic temperature derived from the NH3 (J, K) = (1, 1) and (2, 2) line intensities is higher toward the observed high-mass sources than toward the low-mass cores. However the DNC/HNC ratio of some IRDCs involving the Spitzer 24 {\mu}m sources is found to be lower than that of HMPOs, although the kinetic temperature of the IRDCs is lower than that of the HMPOs. This implies that the DNC/HNC ratio does not depend only on the current kinetic temperature. With the aid of chemical model simulations, we discuss how the DNC/HNC ratio decreases after the birth of protostars. We suggest that the DNC/HNC ratio in star-forming cores depends on the physical conditions and history in their starless-core phase, such as its duration time and the gas kinetic temperature.

The physical mechanisms that set the initial rotation rates in massive stars are a crucial unknown in current star formation theory. Observations of young, massive stars provide evidence that they form in a similar fashion to their low-mass counterparts. The magnetic coupling between a star and its accretion disk may be sufficient to spin down low-mass pre-main sequence (PMS) stars to well below breakup at the end stage of their formation when the accretion rate is low. However, we show that these magnetic torques are insufficient to spin down massive PMS stars due to their short formation times and high accretion rates. We develop a model for the angular momentum evolution of stars over a wide range in mass, considering both magnetic and gravitational torques. We find that magnetic torques are unable to spin down either low or high mass stars during the main accretion phase, and that massive stars cannot be spun down significantly by magnetic torques during the end stage of their formation either. Spin-down occurs only if massive stars’ disk lifetimes are substantially longer or their magnetic fields are much stronger than current observations suggest.

We present a candidate orbital period for the low mass X-ray binary XB 1832-330 in the globular cluster NGC 6652 using a 6.5 hour Gemini South observation of the optical counterpart of the system. Light curves in g’ and r’ for two LMXBs in the cluster, sources A and B in previous literature, were extracted and analyzed for periodicity using the ISIS image subtraction package. A clear sinusoidal modulation is evident in both of A’s curves, of amplitude ~0.11 magnitudes in g’ and ~0.065 magnitudes in r’, while B’s curves exhibit rapid flickering, of amplitude ~1 magnitude in g’ and ~0.5 magnitudes in r’. A Lomb-Scargle test revealed a 2.15 hour periodic variation in the magnitude of A with a false alarm probability less than 10^-11, and no significant periodicity in the light curve for B. Though it is possible saturated stars in the vicinity of our sources partially contaminated our signal, the identification of A’s binary period is nonetheless robust.

As part of our continuing effort to identify new, low-mass members of nearby, young moving groups (NYMGs), we present a list of young, low-mass candidates in the northern hemisphere. We used our proven proper motion selection procedure and ROSAT-X-ray and GALEX-UV activity indicators to identify 204 young stars as candidate members of the Beta Pictoris and AB Doradus NYMGs. Definitive membership assignment of a given candidate will require a measurement of its radial velocity and distance. We present a simple system of indices to characterize the young candidates and help prioritize follow up observations. New group members identified in this candidate list will be high priority targets for: 1) exoplanet direct imaging searches, 2) the study of post-T-Tauri astrophysics, 3) understanding recent local star formation, and 4) the study of local galactic kinematics. Information available now allows us to identify 8 likely new members in the list. Two of these, a late-K and an early-M dwarf, we find to be likely members of the Beta Pic group. The other six stars are likely members of the AB Dor moving group. These include an M dwarf triple system, and three very cool objects that may be young brown dwarfs, making them the lowest-mass, isolated objects proposed in the AB Dor moving group to date.

The galaxies hosting the most energetic explosions in the universe, the gamma-ray bursts (GRBs), are generally found to be low-mass, metal poor, blue and star forming galaxies. However, the majority of the targets investigated so far (less than 100) are at relatively low redshift, z < 2. We know that at low redshift, the cosmic star formation is predominantly in small galaxies. Therefore, at low redshift, long-duration GRBs, which are associated with massive stars, are expected to be in small galaxies. Preliminary investigations of the stellar mass function of z < 1.5 GRB hosts does not indicate that these galaxies are different from the general population of nearby star-forming galaxies. At high-z, it is still unclear whether GRB hosts are different. Recent results indicate that a fraction of them might be associated with dusty regions in massive galaxies. Remarkable is the a super-solar metallicity measured in the interstellar medium of a z = 3.57 GRB host.

Amplifying the phonon signal in a semiconductor dark matter detector can be accomplished by operating at high voltage bias and converting the electrostatic potential energy into Luke-Neganov phonons. This amplification method has been validated at up to |E|=40V/cm without producing leakage in CDMSII Ge detectors, allowing sensitivity to a benchmark WIMP with mass = 8GeV and cross section 1.8e-42cm^2 assuming flat electronic recoil backgrounds near threshold. Furthermore, for the first time we show that differences in Luke-Neganov gain for nuclear and electronic recoils can be used to discriminate statistically between low-energy background and a hypothetical WIMP signal by operating at two distinct voltage biases. Specifically, 99% of events have p-value<1e-8 for a simulated 20kg-day experiment with a benchmark WIMP signal with mass =8GeV and cross section =3.3e-41cm^2.

The Gamma ray Burst Monitor (GBM) on board Fermi has been providing continuous data to the astronomical community since 2008 August 12. In this paper we present the results of the analysis of the first three years of these continuous data using the Earth occultation technique to monitor a catalog of 209 sources. From this catalog, we detect 102 sources, including 41 low-mass X-ray binary/neutron star systems, 33 high-mass X-ray binary neutron star systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the Crab Nebula, and the Sun. Nine of these sources are detected in the 100-300 keV band, including seven black-hole binaries, the active galaxy Cen A, and the Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM provides complementary data to other sky-monitors below 100 keV and is the only all-sky monitor above 100 keV. Up-to-date light curves for all of the catalog sources can be found at http://heastro.phys.lsu.edu/gbm/.

(Abridged) X1822-371 is the prototypical accretion disc corona X-ray source, a low-mass X-ray binary viewed at very high inclination, thereby allowing the disc structure and extended disc coronal regions to be visible. We study the structure of the accretion disc in X1822-371 by modelling the phase-resolved spectra both in optical and X-ray regime. We analyse high time resolution optical ESO/VLT spectra of X1822-371 to study the variability in the emission line profiles. In addition, we use data from XMM-Newton space observatory to study phase-resolved as well as high resolution X-ray spectra. We apply the Doppler tomography technique to reconstruct a map of the optical emission distribution in the system. We fit multi-component models to the X-ray spectra. We find that our results from both the optical and X-ray analysis can be explained with a model where the accretion disc has a thick rim in the region where the accretion stream impacts the disc. The behaviour of the H_beta line complex implies that some of the accreting matter creates an outburst around the accretion stream impact location and that the resulting outflow of matter moves both away from the accretion disc and towards the centre of the disc. Such behaviour can be explained by an almost isotropic outflow of matter from the accretion stream impact region. The optical emission lines of HeII 4686 and 5411 show double peaked profiles, typical for an accretion disc at high inclination. However, their velocities are slower than expected for an accretion disc in a system like X1822-371. This, combined with the fact that the HeII emission lines do not get eclipsed during the partial eclipse in the continuum, suggests that the line emission does not originate in the orbital plane and is more likely to come from above the accretion disc, for example the accretion disc wind.

Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC602/N90 is characterized by the HII nebular ring N90 and the young cluster of pre–main-sequence (PMS) and early-type main sequence stars NGC602. We present a thorough cluster analysis of the stellar sample identified with HST/ACS camera in the region. We show that apart from the central cluster, low-mass PMS stars are congregated in thirteen additional small compact sub-clusters at the periphery of NGC602. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction (~60%) of the total population being clustered, while the remaining is diffusely distributed in the inter-cluster area. From the corresponding color-magnitude diagrams we disentangle an age-difference of ~2.5Myr between NGC602 and the compact sub-clusters which appear younger. The diffuse PMS population appears to host stars as old as those in NGC602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings we propose a scenario, according to which the region NGC602/N90 experiences an active clustered star formation for the last ~5Myr. The central cluster NGC602 was formed first and rapidly started dissolving into its immediate ambient environment, possibly ejecting also massive stars found away from its center. Star formation continued in sub-clusters of a larger stellar agglomeration, introducing an age-spread of the order of 2.5Myr among the PMS populations.

We have made an extensive survey of emission-line stars in the IC 1396 HII region to investigate the low-mass population of pre-main sequence (PMS) stars. A total of 639 H-alpha emission-line stars were detected in an area of 4.2 deg^2 and their i’-photometry was measured. Their spatial distribution exhibits several aggregates near the elephant trunk globule (Rim A) and bright-rimmed clouds at the edge of the HII region (Rim B and SFO 37, 38, 39, 41), and near HD 206267, which is the main exciting star of the HII region. Based on the extinction estimated from the near-infrared (NIR) color-color diagram, we have selected pre-main sequence star candidates associated with IC 1396. The age and mass were derived from the extinction corrected color-magnitude diagram and theoretical pre-main sequence tracks. Most of our PMS candidates have ages of < 3 Myr and masses of 0.2-0.6 Mo. Although it appears that only a few stars were formed in the last 1 Myr in the east region of the exciting star, the age difference among subregions in our surveyed area is not clear from the statistical test. Our results may suggest that massive stars were born after the continuous formation of low-mass stars for 10 Myr. The birth of the exciting star could be the late stage of slow but contiguous star formation in the natal molecular cloud. It may have triggered to form many low-mass stars at the dense inhomogeneity in and around the HII region by a radiation-driven implosion.

Protostellar feedback, both radiation and bipolar outflows, dramatically affects the fragmentation and mass accretion from star-forming cores. We use ORION, an adaptive mesh refinement gravito-radiation-hydrodynamics code, to simulate the formation of a cluster of low-mass stars, including both radiative transfer and protostellar outflows. We ran four simulations to isolate the individual effects of radiation feedback and outflow feedback as well as the combination of the two. Outflows reduce protostellar masses and accretion rates each by a factor of three and therefore reduce protostellar luminosities by an order of magnitude. Thus, while radiation feedback suppresses fragmentation, outflows render protostellar radiation largely irrelevant for low-mass star formation above a mass scale of 0.05 M_sun. We find initial fragmentation of our cloud at half the global Jeans length, ~ 0.1 pc. With insufficient protostellar radiation to stop it, these 0.1 pc cores fragment repeatedly, forming typically 10 stars each. The accretion rate in these stars scales with mass as predicted from core accretion models that include both thermal and turbulent motions. We find that protostellar outflows do not significantly affect the overall cloud dynamics, in the absence of magnetic fields, due to their small opening angles and poor coupling to the dense gas. The outflows reduce the mass from the cores by 2/3, giving a core to star efficiency ~ 1/3. The simulation with radiation and outflows reproduces the observed protostellar luminosity function. All of the simulations can reproduce observed core mass functions, though they are sensitive to telescope resolution. The simulation with both radiation and outflows reproduces the galactic IMF and the two-point correlation function of the cores observed in rho Oph.

We present a study of protoplanetary disks in spatially resolved low-mass binary stars in the Orion Nebula Cluster (ONC) to assess the impact of binarity on the properties of circumstellar disks. This is currently the largest such study in a clustered high-stellar-density star-forming environment. We particularly aim to determine the presence of magnetospheric accretion and dust disks for each binary component, and measure the overall disk frequency. We carried out spatially resolved adaptive-optics-assisted observations to acquire near-IR photometry and spectroscopy of 26 binaries in the ONC, and determine stellar parameters such as effective temperatures, spectral types, luminosities, and masses, as well as accretion properties and near-infrared excesses for the individual binary components. A fraction of 40(+10/-9)% of the binary components in the sample can be inferred to be T Tauri stars possessing an accretion disk, marginally fewer than the disk fraction of single stars. We find that disks in wide binaries of >200AU separation are consistent with random pairing, while the evolution of circumprimary and circumsecondary disks is observed to be synchronized in close binaries (separations <200AU). Circumbinary disks appear to be unsuitable to explain this difference. Furthermore, we identify several mixed pairs of accreting and non-accreting components, suggesting that these systems are common and that there is no preference for either the more or less massive component to evolve faster. The derived accretion luminosities and mass accretion rates of the ONC binary components are of similar magnitude as those for both ONC single stars and binaries in the Taurus star-forming region. The paper concludes with a discussion of the (presumably weak) connection between the presence of inner accretion disks in young binary systems and the existence of planets in stellar multiples.(abridged)

We present a study of protoplanetary disks in spatially resolved low-mass binary stars in the well-known Orion Nebula Cluster (ONC) in order to assess the impact of binarity on the properties of circumstellar disks and its relation to the cluster environment. This is the currently largest such study in a clustered high stellar density star forming environment. We particularly aim at determining the presence of magnetospheric accretion and dust disks for each binary component, and at measuring the overall disk frequency. We carried out spatially resolved Adaptive Optics assisted near-IR photometry and spectroscopy of 26 binaries in the ONC, and determine stellar parameters such as effective temperatures and spectral types, luminosities, masses, as well as accretion properties and near-infrared excess for individual binary components. A fraction of 40(+10/-9)% of the binary components in the sample can be inferred to be T Tauri stars possesing an accretion disk. This is marginally lower than the disk fraction of single stars of ~50% in the ONC. We find that disks in wide binaries of >200AU separation are consistent with random pairing, while the evolution of circumprimary and circumsecondary disks is observed to be synchronized in closer binaries. Circumbinary disks appear to be not suited to explain this difference. Further, we identify several mixed pairs of accreting and non-accreting components, suggesting that these systems are common, and without preference for the more or less massive component to evolve faster. The derived mass accretion rates of the ONC binary components are of similar magnitude as those for ONC single stars and for binaries in the Taurus star forming region. The paper concludes with a discussion of the (presumably weak) connection between the presence of inner accretion disks in young binary systems and the existence of planets in stellar multiples.(abridged)

We present a study of protoplanetary disks in spatially resolved low-mass binary stars in the well-known Orion Nebula Cluster (ONC) in order to assess the impact of binarity on the properties of circumstellar disks and its relation to the cluster environment. This is the currently largest such study in a clustered high stellar density star forming environment. We particularly aim at determining the presence of magnetospheric accretion and dust disks for each binary component, and at measuring the overall disk frequency. We carried out spatially resolved Adaptive Optics assisted near-IR photometry and spectroscopy of 26 binaries in the ONC, and determine stellar parameters such as effective temperatures and spectral types, luminosities, masses, as well as accretion properties and near-infrared excess for individual binary components. A fraction of 40(+10/-9)% of the binary components in the sample can be inferred to be T Tauri stars possesing an accretion disk. This is marginally lower than the disk fraction of single stars of ~50% in the ONC. We find that disks in wide binaries of >200AU separation are consistent with random pairing, while the evolution of circumprimary and circumsecondary disks is observed to be synchronized in closer binaries. Circumbinary disks appear to be not suited to explain this difference. Further, we identify several mixed pairs of accreting and non-accreting components, suggesting that these systems are common, and without preference for the more or less massive component to evolve faster. The derived mass accretion rates of the ONC binary components are of similar magnitude as those for ONC single stars and for binaries in the Taurus star forming region. The paper concludes with a discussion of the (presumably weak) connection between the presence of inner accretion disks in young binary systems and the existence of planets in stellar multiples.(abridged)

In the quest for the formation and evolution of galaxy clusters, Rakos and co-workers introduced a spectrophotometric method using the modified Str\”omgren photometry. But with the considerable debate toward the project’s abilities, we re-introduce the system after a thorough testing of repeatability of colors and reproducibility of the ages and metallicities for six common galaxies in the three A779 data sets. A fair agreement has been found between the modified Str\”omgren and Str\”omgren filter systems to produce similar colors (with the precision of 0.09 mag in (uz-vz), 0.02 mag in (bz-yz), and 0.03 mag in (vz-vz)), ages and metallicities (with the uncertainty of 0.36 Gyr and 0.04 dex from the PCA and 0.44 Gyr and 0.2 dex using the GALEV models). We infer that the technique is able to relieve the age-metallicity degeneracy by separating the age effects from the metallicity effects, but still unable to completely break. We further extend this paper to re-study the evolution of galaxies in the low mass, dynamically poor A779 cluster by correlating the luminosity (mass), density, radial distance with the estimated age, metallicity, and the star formation history. Our results distinctly show the bimodality of the young, low-mass, metal-poor population with the mean age of 6.7 Gyr (\pm 0.5 Gyr) and the old, high-mass, metal-rich galaxies with the mean age of 9 Gyr (\pm 0.5 Gyr). The method also observes the color evolution of the blue cluster galaxies to red, and the downsizing phenomenon. Our analysis shows that the modified Str\”omgren photometry is very well suited for studying low- and intermediate-z clusters, as it is capable of observing deeper with better spatial resolution at spectroscopic redshift limits, and the narrowband filters estimate the age and metallicity with lesser uncertainties compared to other methods that study stellar population scenarios.

Rapidly rotating Neutron Stars in Low Mass X-ray Binaries (LMXBs) may be an interesting source of Gravitational Waves (GWs). In particular, several modes of stellar oscillation may be driven unstable by GW emission, and this can lead to a detectable signal. Here we illustrate how current X-ray and ultra-violet (UV) observations can constrain the physics of the r-mode instability. We show that the core temperatures inferred from the data would place many systems well inside the unstable region predicted by standard physical models. However, this is at odds with theoretical expectations. We discuss different mechanisms that could be at work in the stellar interior, and we show how they can modify the instability window and make it consistent with the inferred temperatures.

The transit timing variation (TTV) method allows the detection of non-transiting planets through their gravitational perturbations. Since TTVs are strongly enhanced in systems close to mean-motion resonances (MMR), even a low mass planet can produce an observable signal. This technique has thus been proposed to detect terrestrial planets. In this letter, we analyse TTV signals for systems in or close to MMR in order to illustrate the difficulties arising in the determination of planetary parameters. TTVs are computed numerically with an n-body integrator for a variety of systems close to MMR. The main features of these TTVs are also derived analytically. Systems deeply inside MMR do not produce particularly strong TTVs, while those close to MMR generate quasiperiodic TTVs characterised by a dominant long period term and a low amplitude remainder. If the remainder is too weak to be detected, then the signal is strongly degenerate and this prevents the determination of the planetary parameters. Even though an Earth mass planet can be detected by the TTV method if it is close to a MMR, it may not be possible to assert that this planet is actually an Earth mass planet. On the other hand, if the system is right in the center of a MMR, the high amplitude oscillation of the TTV signal vanishes and the detection of the perturber becomes as difficult as it is far from MMR.

To investigate the universality hypothesis of the initial mass function in the substellar regime, the population of the rho Ophiuchi molecular cloud is analysed by including a new sample of low-mass spectroscopically confirmed members. We have conducted a large spectroscopic follow-up of young substellar candidates uncovered in our previous photometric survey. It is shown that the study of the substellar population of the rho Ophiuchi molecular cloud is hampered only by the high extinction in the cluster ruling out an apparent paucity of brown dwarfs. The spectral types and extinction are derived for a newly found population of substellar objects, and its masses estimated by comparison to evolutionary models. A thoroughly literature search is conducted to provide an up-to-date census of the cluster, which is then used to derive the luminosity and mass functions, as well as the ratio of brown dwarfs to stars in the cluster. These results are compared to other young clusters. The discovery of 16 new members of rho Ophiuchi, 13 of them in the substellar regime, reveals the low mass end of its population and shows the success of our photometric candidate selection with the WIRCam survey. The study of the brown dwarf population of the cluster reveals a high disk fraction of 76 (+5-8)%. Taking into account the characteristic peak mass of the derived mass function and the ratio of brown dwarfs to stars, we conclude that the mass function of rho Ophiuchi is similar to other nearby young clusters.

Our aim is to determine precisely the abundance distribution of HDO towards the low-mass protostar IRAS16293-2422 and learn more about the water formation mechanisms by the determination of the HDO/H2O abundance ratio. A spectral survey of the source IRAS16293-2422 has been carried out in the framework of the CHESS Herschel Key program with the HIFI instrument, allowing the detection of numerous HDO lines. Other transitions were previously observed with ground-based telescopes in the framework of TIMASSS. The spherical Monte Carlo radiative transfer code RATRAN has been used to reproduce the observed line profiles of HDO assuming an abundance jump, corresponding to the sublimation of the molecules trapped on the icy grain mantles in the hot corino. To determine the H2O abundance throughout the envelope, a similar study has been applied to the H2-18O observed lines, as the H2O main isotope lines are contaminated by the outflows. We derive an inner HDO abundance of 1.7e-7 and an outer HDO abundance of 8e-11. To reproduce the HDO absorption lines, it is necessary to add an absorbing layer in front of the envelope. It may correspond to a water-rich layer created by the photodesorption of the ices at the edges of the molecular cloud. The HDO/H2O ratio is ~1.4-5.8% in the hot corino whereas it is ~0.2-2.2% in the outer envelope. It is estimated at ~4.8% in the added absorbing layer. Although it is clearly higher than the cosmic D/H abundance, the HDO/H2O ratio remains lower than the D/H ratio derived for other deuterated molecules observed in the same source. The similar ratios derived in the hot corino and in the added absorbing layer suggests that water formed before the gravitational collapse of the protostar, contrary to formaldehyde and methanol which formed later once the CO molecules have depleted on the grains.

The Infrared Array Camera (IRAC) on the Spitzer Space Telescope has revealed that a number of high-mass protostars are associated with extended mid-infrared emission, particularly prominent at 4.5-micron. These are called “Green Fuzzy” emission or “Extended Green Objects”. We present color analysis of this emission toward six nearby (d=2-3 kpc) well-studied high-mass protostars and three candidate high-mass protostars identified with the Spitzer GLIMPSE survey. In our color-color diagrams most of the sources show a positive correlation between the [3.6]-[4.5] and [3.5]-[5.8] colors along the extinction vector in all or part of the region. We compare the colors with those of scattered continuum associated with the low-mass protostar L 1527, modeled scattered continuum in cavities, shocked emission associated with low-mass protostars, modeled H2 emission for thermal and fluorescent cases, and modeled PAH emission. Of the emission mechanisms discussed above, scattered continuum provides the simplest explanation for the observed linear correlation. In this case, the color variation within each object is attributed to different foreground extinctions at different positions. Alternative possible emission mechanisms to explain this correlation may be a combination of thermal and fluorescent H2 emission in shocks, and a combination of scattered continuum and thermal H2 emission, but detailed models or spectroscopic follow-up are required to further investigate this possibility. Our color-color diagrams also show possible contributions from PAHs in two objects. However, none of our sample show clear evidence for PAH emission directly associated with the high-mass protostars, several of which should be associated with ionizing radiation. This suggests that those protostars are heavily embedded even at mid-infrared wavelengths.

The radius of neutron stars can in principle be measured via the normalisation of a blackbody fitted to the X-ray spectrum during thermonuclear (type-I) X-ray bursts, although few previous studies have addressed the reliability of such measurements. Here we examine the apparent radius in a homogeneous sample of long, mixed H/He bursts from the low-mass X-ray binaries GS 1826-24 and KS 1731-26. The measured blackbody normalisation (proportional to the emitting area) in these bursts is constant over a period of up to 60s in the burst tail, even though the flux (blackbody temperature) decreased by a factor of 60-75% (30-40%). The typical rms variation in the mean normalisation from burst to burst was 3-5%, although a variation of 17% was found between bursts observed from GS 1826-24 in two epochs. A comparison of the time-resolved spectroscopic measurements during bursts from the two epochs shows that the normalisation evolves consistently through the burst rise and peak, but subsequently increases further in the earlier epoch bursts. The elevated normalisation values may arise from a change in the anisotropy of the burst emission, or alternatively variations in the spectral correction factor, f_c, of order 10%. Since burst samples observed from systems other than GS 1826-24 are more heterogeneous, we expect that systematic uncertainties of at least 10% are likely to apply generally to measurements of neutron-star radii, unless the effects described here can be corrected for.

The role of neutrinos in stars is introduced for students with little prior astrophysical exposure. We begin with neutrinos as an energy-loss channel in ordinary stars and conversely, how stars provide information on neutrinos and possible other low-mass particles. Next we turn to the Sun as a measurable source of neutrinos and other particles. Finally we discuss supernova (SN) neutrinos, the SN 1987A measurements, and the quest for a high-statistics neutrino measurement from the next nearby SN. We also touch on the subject of neutrino oscillations in the high-density SN context.

We investigate for the first time the effects of a Warm Dark Matter (WDM) power spectrum on the statistical properties of galaxies using a semi-analytic model of galaxy formation. The WDM spectrum we adopt as a reference case is suppressed – compared to the standard Cold Dark Matter (CDM) case – below a cut-off scale ~ 1 Mpc corresponding (for thermal relic WDM particles) to a mass m_X=0.75 keV. This ensures consistency with present bounds provided by the microwave background WMAP data and by the comparison of hydrodynamical N-body simulations with observed Lyman-{\alpha} forest. We run our fiducial semi-analytic model with such a WDM spectrum to derive galaxy luminosity functions (in B, UV, and K bands) and the stellar mass distributions over a wide range of cosmic epochs, to compare with recent observations and with the results in the CDM case. The predicted color distribution of galaxies in the WDM model is also checked against the data. When compared with the standard CDM case, the luminosity and stellar mass distributions we obtain assuming a WDM spectrum are characterized by: i) a flattening of the faint end slope and ii) a sharpening of the cutoff at the bright end for z \lesssim 0.8. We discuss how the former result is directly related to the smaller number of low-mass haloes collapsing in the WDM scenario, while the latter is related to the smaller number of satellite galaxies accumulating in massive haloes at low redshift, thus suppressing the accretion of small lumps on the central, massive galaxies. These results shows how a adopting a WDM power spectrum may contribute to solve two major problems of CDM galaxy formation scenarios, namely, the excess of predicted faint (low mass) galaxies at low and – most of all – high redshifts, and the excess of bright (massive) galaxies at low redshifts.

H and He features in photospheric spectra have seldom been used to infer quantitatively the properties of Type IIb, Ib and Ic supernovae (SNe IIb, Ib and Ic) and their progenitor stars. Most radiative transfer models ignored NLTE effects, which are extremely strong especially in the He-dominated zones. In this paper, a comprehensive set of model atmospheres for low-mass SNe IIb/Ib/Ic is presented. Long-standing questions such as how much He can be contained in SNe Ic, where He lines are not seen, can thus be addressed. The state of H and He is computed in full NLTE, including the effect of heating by fast electrons. The models are constructed to represent iso-energetic explosions of the same stellar core with differently massive H/He envelopes on top. The synthetic spectra suggest that 0.06 – 0.14 M_sun of He and even smaller amounts of H suffice for optical lines to be present, unless ejecta asymmetries play a major role. This strongly supports the conjecture that low-mass SNe Ic originate from binaries where progenitor mass loss can be extremely efficient.

We study relations between the X-ray luminosity, orbital period and absolute near-infrared magnitude of persistent low-mass X-ray binaries (LMXBs). We show that often optical and near-infrared spectral energy distribution of LMXBs can be adequately described by a simple model of an accretion disc and a secondary star reprocessing X-ray emission of a central compact object. This gives us an evidence that using an X-ray luminosity and an absolute infrared magnitude of a persistent LMXB one can make reliable estimate of its orbital period. Using a sample of well-known LMXBs, we have constructed a correlation of L_X, P_orb and M_K values which can be approximated by a straight line with the RMS scatter at the level of ~0.3 mag. Such a correlation, being to some extent an analogous to the correlation, found by van Paradijs & McClintock 1994, might be helpful for future population studies especially in the light of forthcoming surveys of the Galaxy in X-ray and infrared spectral domains.

Context. This is the fourth paper in a series showing the results of planet population synthesis calculations. Aims. Our goal in this paper is to systematically study the effects of important disk properties, namely disk metallicity, mass and lifetime on fundamental planetary properties. Methods. For a large number of protoplanetary disks we calculate a population of planets with our core accretion formation model including planet migration and disk evolution. Results. We find a large number of correlations: Regarding the planetary initial mass function, metallicity, disk mass and disk lifetime have different roles: For high [Fe/H], giant planets are more frequent. For high disk masses, giant planets are more massive. For long disk lifetimes, giant planets are both more frequent and massive. At low metallicities, very massive giant planets cannot form, but otherwise giant planet mass and metallicity are uncorrelated. In contrast, planet masses and disk gas masses are correlated. The sweet spot for giant planet formation is at 5 AU. In- and outside this distance, higher planetesimals surface densities are necessary. Low metallicities can be compensated by high disk masses, and vice versa, but not ad infinitum. At low metallicities, giant planets only form outside the ice line, while at high metallicities, giant planet formation occurs throughout the disk. The extent of migration increases with disk mass and lifetime and usually decreases with metallicity. No clear correlation of metallicity and the semimajor axis of giant planets exists because in low [Fe/H] disks, planets start further out, but migrate more, whereas for high [Fe/H] they start further in, but migrate less. Close-in low mass planets have a lower mean metallicity than Hot Jupiters. Conclusions. The properties of protoplanetary disks are decisive for the properties of planets, and leave many imprints.

We present the first measurement of the evolution of the galaxy group stellar mass function (GrSMF) to redshift z>~1 and low masses (M*>10^12 Msun). Our results are based on early data from the Carnegie-Spitzer-IMACS (CSI) Survey, utilizing low-resolution spectra and broadband optical/near-IR photometry to measure redshifts for a 3.6um selected sample of 37,000 galaxies over a 5.3 deg^2 area to z~1.2. Employing a standard friends-of-friends algorithm for all galaxies more massive than log(M*/Msun)=10.5, we find a total of ~4000 groups. Correcting for spectroscopic incompleteness (including slit collisions), we build cumulative stellar mass functions for these groups in redshift bins at z>0.35, comparing to the z=0 and z>0 mass functions from various group and cluster samples. Our derived mass functions match up well with z>0.35 X-ray selected clusters, and strong evolution is evident at all masses over the past 8 Gyr. Given the already low level of star formation activity in galaxies at these masses, we therefore attribute most of the observed growth in the GrSMF to group-group and group-galaxy mergers, in accordance with qualitative notions of hierarchical structure formation. Given the factor 3-10 increase in the number density of groups and clusters with M*>10^12 Msun since z=1 and the strong anticorrelation between star formation activity and environmental density, this late-time growth in group-sized halos may therefore be an important contributor to the structural and star-formation evolution of massive galaxies over the past 8 Gyr.

(abridged) We investigate the properties of young stars and their disks in the NGC 6357 complex, concentrating on the most massive star cluster within the complex: Pismis 24. We discover two new young clusters in the NGC 6357 complex. We give a revised distance estimate for Pismis 24 of 1.7+-0.2 kpc. We find that the massive star Pis 24-18 is a binary system, with the secondary being the main X-ray source of the pair. We derive the cluster mass function and find that up to the completeness limit at low masses it agrees well with the IMF of the Trapezium cluster. We derive a median age of 1 Myr for the Pismis 24 cluster members. We find five proplyds in HST archival imaging of the cluster, four of which are newly found. In all cases the proplyd tails are pointing directly away from the massive star system Pis 24-1. One proplyd shows a second tail, pointing away from Pis 24-2, suggesting this object is being photoevaporated from two directions simultaneously. We find that the global disk frequency (~30%) in Pismis 24 is much lower than some other clusters of similar age, such as the Orion Nebula Cluster. When comparing the disk frequencies in 19 clusters/star-forming regions of various ages and different (massive) star content, we find that the disks in clusters harboring extremely massive stars (typically earlier than O5), like Pismis 24, are dissipated roughly twice as quickly as in clusters/star-forming regions without extremely massive stars. Within Pismis 24, we find that the disk frequency within a projected distance of 0.6 pc from Pis 24-1 is substantially lower than at larger radii (~19% vs. ~37%). We argue for a combination of photoevaporation and irradiation with ionizing UV photons from nearby massive stars, causing increased MRI-induced turbulence and associated accretion activity, to play an important role in the dissipation of low-mass star disks in Pismis 24.

Recent observations have constrained the galaxy UV luminosity function up to z~10. However, these observations alone allow for a wide range of reionization scenarios due to uncertainties in the abundance of faint galaxies and the escape fraction of ionizing photons. We show that requiring continuity with post-reionization (z<6) measurements, where the Lya forest provides a complete probe of the cosmological emissivity of ionizing photons, significantly reduces the permitted parameter space. Models that are simultaneously consistent with the measured UV luminosity function, the Thomson optical depth to the CMB, and the Lya forest data require either: 1) extrapolation of the galaxy luminosity function down to very faint UV magnitudes M_lim ~10 from z=4 (where the best fit is 4%) to z=9; or 3) more likely, a hybrid solution in which undetected galaxies contribute significantly and f_esc increases more modestly. Models in which star formation is strongly suppressed in low-mass, reionization-epoch haloes of mass up to ~10^10 M_sun (e.g., owing to a metallicity dependence) are only allowed for extreme assumptions for the evolution of f_esc. However, variants of such models in which the suppression mass is reduced (e.g., assuming an earlier or higher metallicity floor) are in better agreement with the data. Concordance scenarios satisfying the available data predict a consistent redshift of 50% ionized fraction z_reion(50%) ~ 10. On the other hand, the duration of reionization is sensitive to the relative contribution of bright versus faint galaxies, with scenarios dominated by faint galaxies predicting a more extended reionization event. Scenarios relying heavily on high-redshift dwarfs are disfavored by kinetic Sunyaev-Zeldovich measurements, which prefer a short reionization history.

We present high speed photometric observations of 20 faint cataclysmic variables, selected from the Sloan Digital Sky Survey and Catalina catalogues. Measurements are given of 15 new directly measured orbital periods, including four eclipsing dwarf novae (SDSS0904+03, CSS0826-00, CSS1404-10 and CSS1626-12), two new polars (CSS0810+00 and CSS1503-22) and two dwarf novae with superhumps in quiescence (CSS0322+02 and CSS0826-00). Whilst most of the dwarf novae presented here have periods below 2 h, SDSS0805+07 and SSS0617-36 have relatively long orbital periods of 5.489 and 3.440 h, respectively. The double humped orbital modulations observed in SSS0221-26, CSS0345-01, CSS1300+11 and CSS1443-17 are typical of low mass transfer rate dwarf novae. The white dwarf primary of SDSS0919+08 is confirmed to have non-radial oscillations and quasi-periodic oscillations were observed in the short-period dwarf nova CSS1028-08 during outburst. We further report the detection of a new nova-like variable (SDSS1519+06). The frequency distribution of orbital periods of CVs in the Catalina survey has a high peak near ~80 min orbital period, independently confirming that found by Gaensicke et al (2009) from SDSS sources. We also observe a marked correlation between the median in the orbital period distribution and the outburst class, in the sense that dwarf novae with a single observed outburst (over the 5-year baseline of the CRTS coverage) occur predominantly at shortest orbital period.

We study the effect of local stellar radiation and UVB on the physical properties of DLAs and LLSs at z=3 using cosmological SPH simulations. We post-process our simulations with the ART code for radiative transfer of local stellar radiation and UVB. We find that the DLA and LLS cross sections are significantly reduced by the UVB, whereas the local stellar radiation does not affect them very much except in the low-mass halos. This is because clumpy high-density clouds near young star clusters effectively absorb most of the ionizing photons from young stars. We also find that the UVB model with a simple density threshold for self-shielding effect can reproduce the observed column density distribution function of DLAs and LLSs very well, and we validate this model by direct radiative transfer calculations of stellar radiation and UVB with high angular resolution. We show that, with a self-shielding treatment, the DLAs have an extended distribution around star-forming regions typically on ~ 10-30 kpc scales, and LLSs are surrounding DLAs on ~ 30-60 kpc scales. Our simulations suggest that the median properties of DLA host haloes are: Mh = 2.4*10^10 Msun, SFR = 0.3 Msun/yr, M* = 2.4*10^8 Msun, and Z/Zsun = 0.1. About 30 per cent of DLAs are hosted by haloes having SFR = 1 – 20 Msun/yr, which is the typical SFR range for LBGs. More than half of DLAs are hosted by the LBGs that are fainter than the current observational limit. Our results suggest that fractional contribution to LLSs from lower mass haloes is greater than for DLAs. Therefore the median values of LLS host haloes are somewhat lower with Mh = 9.6*10^9 Msun, SFR = 0.06 Msun/yr, M* = 6.5*10^7 Msun and Z/Zsun = 0.08. About 80 per cent of total LLS cross section are hosted by haloes with SFR < 1 Msun/yr, hence most LLSs are associated with low-mass halos with faint LBGs below the current detection limit.

We report the first detection of the intrinsic velocity dispersion of the Arches cluster – a young (~2 Myr), massive (~10,000 Solar Mass) starburst cluster located near the Galactic center. This was accomplished using proper motion measurements within the central region of the cluster, obtained with the laser guide star adaptive optics system at Keck Observatory over a 3 year time baseline (2006-2009). This uniform dataset results in proper motion measurements that are improved by a factor ~5 over previous measurements from heterogeneous instruments, yielding internal velocity dispersion estimates 0.15 +/- 0.01 mas/yr, which corresponds to 5.4 +/- 0.4 km/s at a distance of 8.4 kpc. Projecting a simple model for the cluster onto the sky to compare with our proper motion dataset, in conjunction with surface density data, we estimate the total present-day mass of the cluster to be 15,000 (+7400 -6000) Solar masses. The mass in stars observed within a cylinder of radius R=0.4 pc is found to be 9000 (+4000 -3500) Solar Masses at formal 3-sigma confidence. This mass measurement is free from assumptions about the mass function of the cluster, and thus may be used to check mass estimates from photometry and simulation. When we conduct this check, we find that the present-day mass function of the Arches cluster is likely either top-heavy or truncated at low-mass, or both. Collateral benefits of our data and analysis include: 1. cluster membership probabilities, which may be used to extract a clean cluster sample for future photometric work; 2. a refined estimate of the bulk motion of the Arches cluster with respect to the field, which we find to be 172 +/- 15 km/s, which is slightly slower than suggested by previous VLT-Keck measurements; and 3. a velocity dispersion estimate for the field itself, which is likely dominated by the inner galactic bulge and the nuclear disk.

In this paper we consider a new mechanism for stopping the inward migration of a low-mass planet embedded in a gaseous protoplanetary disc. It operates when a low-mass planet (for example a super-Earth), encounters outgoing density waves excited by another source in the disc. This source could be a gas giant in an orbit interior to that of the low-mass planet. As the super-Earth passes through the wave field, angular momentum is transferred to the disc material and then communicated to the planet through coorbital dynamics, with the consequence that its inward migration can be halted or even reversed. We illustrate how the mechanism we consider works in a variety of different physical conditions employing global two-dimensional hydrodynamical calculations. We confirm our results by performing local shearing box simulations in which the super-Earth interacts with density waves excited by an independent harmonically varying potential. Finally, we discuss the constraints arising from the process considered here, on formation scenarios for systems containing a giant planet and lower mass planet in an outer orbit with a 2:1 commensurability such as GJ876.

The low mass X-ray binary IGR J17480-2446 in the globular cluster Terzan 5 harbors an 11 Hz accreting pulsar. This is the first object discovered in a globular cluster with a pulsar spinning at such low rate. The accreting pulsar is anomalous because its characteristics are very different from the other five known slow accreting pulsars in galactic low mass X-ray binaries. Many features of the 11 Hz pulsar are instead very similar to those of accreting millisecond pulsars, spinning at frequencies >100 Hz. Understanding this anomaly is very valuable because IGR J17480-2446 can be the only accreting pulsar discovered so far which is in the process of becoming an accreting millisecond pulsar. We first verify that the neutron star in IGR J17480-2446 is indeed spinning up by carefully analysing X-ray data with coherent timing techniques that account for the presence of timing noise. We then study the present Roche Lobe Overflow epoch and the two previous spin-down epochs dominated by magneto dipole radiation and stellar wind accretion. We find that IGR J17480-2446 is very likely a mildly recycled pulsar and suggest that it has started a spin-up phase in an exceptionally recent time, that has lasted less than a few 10^7 yr. We also find that the total age of the binary is surprisingly low (<10^8 yr) when considering typical parameters for the newborn neutron star and propose different scenarios to explain this anomaly.

Recent spectroscopic measurements in open clusters younger than the Sun, with [Fe/H]>=0, showed that the abundances of neutron-rich elements have continued to increase in the Galaxy after the formation of the Sun, roughly maintaining a solar-like distribution. Such a trend requires neutron fluences larger than those so far assumed, as these last would have too few neutrons per iron seed. We suggest that the observed enhancements can be produced by nucleosynthesis in AGB stars of low mass (M 1.5M\odot). Adopting such a stronger neutron source as a contributor to the abundances at the time of formation of the Sun, we show that this affects also the solar s-process distribution, so that its main component is well reproduced, without the need of assuming ad-hoc primary sources for the synthesis of s elements up to A \sim 130, contrary to suggestions from other works. The changes in the expected abundances that we find are primarily due to the following reasons. i) Enhancing the neutron source increases the efficiency of the s process, so that the ensuing stellar yields now mimic the solar distribution at a metallicity higher than before ([Fe/H]>=-0.1). ii) The age-metallicity relation is rather flat for several Gyr in that metallicity regime, so that those conditions remain stable and the enhanced nuclear yields, which are necessary to maintain a solar-like abundance pattern, can dominate the composition of the interstellar medium from which subsequent stars are formed.

We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The central part of Orion B9 was mapped at 350 micron with APEX/SABOCA. A sample of nine cores in the region were observed in C17O(2-1), H13CO+(4-3) (towards 3 sources), DCO+(4-3), N2H+(3-2), and N2D+(3-2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-micron dust continuum data. Many of the LABOCA cores show evidence of substructure in the higher-resolution SABOCA image. In particular, we report on the discovery of multiple very low-mass condensations in the prestellar core SMM 6. Based on the 350-to-870 micron flux density ratios, we determine dust temperatures of ~7.9-10.8 K, and dust emissivity indices of ~0.5-1.8. The CO depletion factors are in the range ~1.6-10.8. The degree of deuteration in N2H+ is ~0.04-0.99, where the highest value (seen towards the prestellar core SMM 1) is, to our knowledge, the most extreme level of N2H+ deuteration reported so far. The level of HCO+ deuteration is about 1-2%. We also detected D2CO towards two sources. The detection of subcondensations within SMM 6 shows that core fragmentation can already take place during the prestellar phase. The origin of this substructure is likely caused by thermal Jeans fragmentation of the elongated parent core. A low depletion factor and the presence of gas-phase D2CO in SMM 1 suggest that the core chemistry is affected by the nearby outflow. The very high N2H+ deuteration in SMM 1 is likely to be remnant of the earlier CO-depleted phase.

We report the identification of the double degenerate system NLTT 16249 that comprises a normal, hydrogen-rich (DA) white dwarf and a peculiar, carbon-polluted white dwarf (DQ) showing photospheric traces of nitrogen. We disentangled the observed spectra and constrained the properties of both stellar components. In the evolutionary scenario commonly applied to the sequence of DQ white dwarfs, both carbon and nitrogen would be dredged up from the core. The C/N abundance ratio (~ 50) in the atmosphere of this unique DQ white dwarf suggests the presence of unprocessed material (14N) in the core or in the envelope. Helium burning in the DQ progenitor may have terminated early on the red-giant branch after a mass-ejection event leaving unprocessed material in the core although current mass estimates do not favor the presence of a low-mass helium core. Alternatively, some nitrogen in the envelope may have survived an abridged helium-core burning phase prior to climbing the asymptotic giant-branch. Based on available data, we estimate a relatively short orbital period (P <~ 13 hrs) and on-going spectroscopic observations will help determine precise orbital parameters.

We derive bounds on the dark matter annihilation cross-section for low-mass (5-20 GeV) dark matter annihilating primarily to up or down quarks, using the Fermi-LAT bound on gamma-rays from Milky Way satellites. For models in which dark matter-Standard Model interactions are mediated by particular contact operators, we show that these bounds can be directly translated into bounds on the dark matter-proton scattering cross-section. For isospin-violating dark matter, these constraints are tight enough to begin to constrain the parameter-space consistent with experimental signals of low-mass dark matter. We discuss possible models that can evade these bounds.

Recently, Gillessen et al. discovered an ionized cloud of gas plunging toward the supermassive black hole, SgrA*, at the centre of the Milky Way. The cloud is being tidally disrupted along its path to closest approach at ~3100 Schwarzschild radii from the black hole. Here, we show that this cloud of gas naturally originates from a proto-planetary disk surrounding a low-mass star, which was scattered a century ago from the observed ring of young stars orbiting Sgr A*. As the young star approaches the black hole, its disk experiences both photo-evaporation and tidal disruption, producing a cloud with the observed properties. Our model implies that planets form in the Galactic centre, and that tidal debris from proto-planetary disks can flag low mass stars which are otherwise too faint to be detected.

We determine the observational signatures of protostellar cores by coupling two-dimensional radiative transfer calculations with numerical hydrodynamical simulations that predict accretion rates that both decline with time and feature short-term variability and episodic bursts caused by disk gravitational instability and fragmentation. We calculate the radiative transfer of the collapsing cores throughout the full duration of the collapse, using as inputs the core, disk, and protostellar masses, radii, and mass accretion rates predicted by the hydrodynamical simulations. From the resulting spectral energy distributions, we calculate standard observational signatures (bolometric luminosity, bolometric temperature, ratio of bolometric to submillimeter luminosity) to directly compare to observations. We show that the accretion process predicted by these models reproduces the full spread of observed protostars in both Lbol – Tbol and Lbol – core mass space, including very low luminosity objects, provides a reasonable match to the observed protostellar luminosity distribution, and resolves the long-standing luminosity problem. These models predict an embedded phase duration shorter than recent observationally determined estimates (0.12 Myr vs. 0.44 Myr), and a fraction of total time spent in Stage 0 of 23%, consistent with the range of values determined by observations. On average, the models spend 1.3% of their total time in accretion bursts, during which 5.3% of the final stellar mass accretes, with maximum values being 11.8% and 35.5% for the total time and accreted stellar mass, respectively. Time-averaged models that filter out the accretion variability and bursts do not provide as good of a match to the observed luminosity problem, suggesting that the bursts are required.

The existence of 10$^9$ M$_{\odot}$ black holes (BH) in massive galaxies by $z \sim 7$ is one of the great unsolved mysteries in cosmological structure formation. One leading model argues that they originate from much smaller seeds at high redshift and then accrete at the Eddington limit down to the epoch of reionization, which requires that they have constant access to rich supplies of fuel. Because early numerical simulations suggested that many first stars had masses $\gtrsim 100$ M$_{\odot}$, the supermassive black hole (SMBH) seeds in this model were 100 – 300 M$_{\odot}$ black holes formed by Pop III stars at $z \sim 20$. However, there is growing numerical and observational evidence that most Pop III stars were tens of solar masses, not hundreds, and consequently that 20 – 140 M$_{\odot}$ black holes may have been much more plentiful at high redshift. We have examined low-mass Pop III black holes as potential seeds of SMBH and find that the mass range for possible seeds is severely constrained. Progenitors of black holes above $\sim $100 M$_{\odot}$ disperse their fuel supply prior to the birth of the BH. Natal kicks imparted to 20 – 40 M$_{\odot}$ Pop III BHs during formation eject these BHs from their halos and hence their fuel supply, precluding them from constant Eddington-limit growth. Inefficient radiative feedback and halo mass statistics favor early rapid accretion by 40 – 140 M$_{\odot}$ BH, and these may be the characteristic masses of Pop III SMBH seeds.

Radiative feedback is among the most important consequences of clustered star formation inside molecular clouds. At the onset of star formation, radiation from massive stars heats the surrounding gas, which suppresses the formation of many low-mass stars. When simulating pre-main-sequence stars, their stellar properties must be defined by a prestellar model. Different approaches to prestellar modeling may yield quantitatively different results. In this paper, we compare two existing prestellar models under identical initial conditions to gauge whether the choice of model has any significant effects on the final population of stars. The first model treats stellar radii and luminosities with a ZAMS model, while separately estimating the accretion luminosity by interpolating to published prestellar tracks. The second, more accurate prestellar model self-consistently evolves the radius and luminosity of each star under highly variable accretion conditions. Each is coupled to a raytracing-based radiative feedback code that also treats ionization. The impact of the self-consistent model is less ionizing radiation and less heating during the early stages of star formation. This may affect final mass distributions. We noted a peak stellar mass reduced by 8% from 47.3 Msun to 43.5 Msun in the evolutionary model, relative to the track-fit model. Also, the difference in mass between the two largest stars in each case is reduced from 14 Msun to 7.5 Msun. The HII regions produced by these massive stars were also seen to flicker on timescales down to the limit imposed by our timestep (< 560 years), rapidly changing in size and shape, confirming previous cluster simulations using ZAMS-based estimates for prestellar ionizing flux.

Radiative feedback is among the most important consequences of clustered star formation inside molecular clouds. At the onset of star formation, radiation from massive stars heats the surrounding gas, which suppresses the formation of many low-mass stars. When simulating pre-main-sequence stars, their stellar properties must be defined by a prestellar model. Different approaches to prestellar modeling may yield quantitatively different results. In this paper, we compare two existing prestellar models under identical initial conditions to gauge whether the choice of model has any significant effects on the final population of stars. The first model treats stellar radii and luminosities with a ZAMS model, while separately estimating the accretion luminosity by interpolating to published prestellar tracks. The second, more accurate prestellar model self-consistently evolves the radius and luminosity of each star under highly variable accretion conditions. Each is coupled to a raytracing-based radiative feedback code that also treats ionization. The impact of the self-consistent model is less ionizing radiation and less heating during the early stages of star formation. This may affect final mass distributions. We noted a peak stellar mass reduced by 8% from 47.3 Msun to 43.5 Msun in the evolutionary model, relative to the track-fit model. Also, the difference in mass between the two largest stars in each case is reduced from 14 Msun to 7.5 Msun. The HII regions produced by these massive stars were also seen to flicker on timescales down to the limit imposed by our timestep (< 560 years), rapidly changing in size and shape, confirming previous cluster simulations using ZAMS-based estimates for prestellar ionizing flux.

We performed the photometric B, V and R observations of nine disk galaxies that were suspected in having abnormally low total mass-to-light (M/L) ratios for their observed color indices. We use our surface photometry data to analyze the possible reasons for the anomalous M/L. We infer that in most cases this is a result of errors in photometry or rotational velocity, however for some galaxies we cannot exclude the real peculiarities of the galactic stellar population. The comparison of the photometric and dynamical mass estimates in the disk shows that the low M/L values for a given color of disks are probably real for a few our galaxies: NGC 4826 (Sab), NGC 5347 (Sab), and NGC 6814 (Sb). The small number of such galaxies suggests that the stellar initial mass function is indeed universal, and that only a small fraction of galaxies may have a non-typical low-mass star depleted initial mass function. Such galaxies require more careful studies for understanding their star formation history.

Context: Ideal MHD simulations have revealed catastrophic magnetic braking (MB) in the protostellar phase, which prevents the formation of a centrifugal disk around a nascent protostar. Aims: We determine if non-ideal MHD, including the effects of ambipolar diffusion and Ohmic dissipation determined from a detailed chemical network model, allows for disk formation at the earliest stages of star formation (SF). Methods: We employ the axisymmetric thin-disk approximation in order to resolve a dynamic range of 9 orders of magnitude in length and 16 in density, while also calculating partial ionization using up to 19 species in a detailed chemical equilibrium model. MB is applied using a steady-state approximation, and a barotropic relation is used to capture the thermal evolution. Results: We resolve the formation of the first and second cores, with expansion waves at the periphery of each, a magnetic diffusion shock, and prestellar infall profiles at larger radii. Power-law profiles in each region can be understood analytically. After the formation of the second core, centrifugal support rises rapidly and a low-mass disk of radius ~10 R_Sun is formed, when the second core has mass ~0.001 M_Sun. The mass-to-flux ratio is ~10,000 times the critical value in the central region. Conclusions: A centrifugal disk can indeed form in the earliest stage of SF, due to a shut-off of MB caused by magnetic field dissipation in the first core region. There is enough angular momentum loss to allow the second collapse to occur directly, and a low-mass stellar core to form with a surrounding disk. The disk mass and size will depend upon how the angular momentum transport mechanisms within the disk can keep up with mass infall onto the disk. We estimate that the disk will remain <~10 AU, undetectable even by ALMA, in the early Class 0 phase.

To investigate the composition and evolution of circumstellar ice around low-mass YSOs, we observed ice absorption bands in the near infrared (NIR) towards eight YSOs ranging from class 0 to class II, among which seven are associated with edge-on disks. We performed slit-less spectroscopic observations using the grism mode of the Infrared Camera (IRC) on board AKARI, which enables us to obtain full NIR spectra from 2.5 $\mu$m to 5 $\mu$m. The spectra were fitted with polynomial baselines to derive the absorption spectra. The molecular absorption bands were then fitted with the laboratory database of ice absorption bands, considering the instrumental line profile and the spectral resolution of the grism dispersion element. Towards the class 0-I sources (L1527, IRC-L1041-2, and IRAS04302), absorption bands of H$_2$O, CO$_2$, CO, and XCN are clearly detected. Column density ratios of CO$_2$ ice and CO ice relative to H$_2$O ice are 21-28% and 13-46%, respectively. If XCN is OCN$^-$, its column density is as high as 2-6% relative to H$_2$O ice. The HDO ice feature at 4.1 $\mu$m is tentatively detected towards the class 0-I sources and HV Tau. Non-detections of the CH-stretching mode features around 3.5 $\mu$m provide upper limits to the CH$_3$OH abundance of 26% (L1527) and 42% (IRAS04302) relative to H$_2$O. We tentatively detect OCS ice absorption towards IRC-L1041-2. Towards class 0-I sources, the detected features should mostly originate in the cold envelope, while CO gas and OCN$^-$ could originate in the region close to the protostar, where there are warm temperatures and UV radiation. We detect H$_2$O ice band towards ASR41 and 2MASSJ1628137-243139, which are edge-on class II disks. We also detect H$_2$O ice and CO$_2$ ice towards HV Tau, HK Tau, and UY Aur, and tentatively detect CO gas features towards HK Tau and UY Aur.

Within the next few years, GAIA and several instruments aiming at imag- ing extrasolar planets will see first light. In parallel, low mass planets are being searched around red dwarfs which offer more favourable conditions, both for radial velocity de- tection and transit studies, than solar-type stars. Authors of the model atmosphere code which has allowed the detection of water vapour in the atmosphere of Hot Jupiters re- view recent advancement in modelling the stellar to substellar transition. The revised solar oxygen abundances and cloud model allow for the first time to reproduce the pho- tometric and spectroscopic properties of this transition. Also presented are highlight results of a model atmosphere grid for stars, brown dwarfs and extrasolar planets.

[Shortened] In preparation for the HERMES chemical tagging survey of about a million Galactic FGK stars, we estimate the number of independent dimensions of the space defined by the stellar chemical element abundances [X/Fe]. [...] We explore abundances in several environments, including solar neighbourhood thin/thick disk stars, halo metal-poor stars, globular clusters, open clusters, the Large Magellanic Cloud and the Fornax dwarf spheroidal galaxy. [...] We find that, especially at low metallicity, the production of r-process elements is likely to be associated with the production of alpha-elements. This may support the core-collapse supernovae as the r-process site. We also verify the over-abundances of light s-process elements at low metallicity, and find that the relative contribution decreases at higher metallicity, which suggests that this lighter elements primary process may be associated with massive stars. [...] Our analysis reveals two types of core-collapse supernovae: one produces mainly alpha-elements, the other produces both alpha-elements and Fe-peak elements with a large enhancement of heavy Fe-peak elements which may be the contribution from hypernovae. [...] The extra contribution from low mass AGB stars at high metallicity compensates the dimension loss due to the homogenization of the core-collapse supernovae ejecta. [...] the number of independent dimensions of the [X/Fe]+[Fe/H] chemical space in the solar neighbourhood for HERMES is about 8 to 9. Comparing fainter galaxies and the solar neighbourhood, we find that the chemical space for fainter galaxies such as Fornax and the Large Magellanic Cloud has a higher dimensionality. This is consistent with the slower star formation history of fainter galaxies. [...]

Context. High contrast imaging is a powerful technique to search for gas giant planets and brown dwarfs orbiting at separation larger than several AU. Around solar-type stars, giant planets are expected to form by core accretion or by gravitational instability, but since core accretion is increasingly difficult as the primary star becomes lighter, gravitational instability would be the a probable formation scenario for yet-to-be-found distant giant planets around a low-mass star. A systematic survey for such planets around M dwarfs would therefore provide a direct test of the efficiency of gravitational instability. Aims. We search for gas giant planets orbiting around late-type stars and brown dwarfs of the solar neighborhood. Methods. We obtained deep high resolution images of 16 targets with the adaptive optic system of VLT-NACO in the Lp band, using direct imaging and angular differential imaging. This is currently the largest and deepest survey for Jupiter-mass planets around Mdwarfs. We developed and used an integrated reduction and analysis pipeline to reduce the images and derive our 2D detection limits for each target. The typical contrast achieved is about 9 magnitudes at 0.5″ and 11 magnitudes beyond 1″. For each target we also determine the probability of detecting a planet of a given mass at a given separation in our images. Results. We derived accurate detection probabilities for planetary companions, taking into account orbital projection effects, with in average more than 50% probability to detect a 3MJup companion at 10AU and a 1.5MJup companion at 20AU, bringing strong constraints on the existence of Jupiter-mass planets around this sample of young M-dwarfs.

We report the results from spectroscopic observations of 113 ultra-wide, low-mass binary systems, composed largely of M0–M3 dwarfs, from the SLoWPoKES catalog of common proper motion pairs identified in the Sloan Digital Sky Survey. Radial velocities of each binary member were used to confirm that they are co-moving and, consequently, to further validate the high fidelity of the SLoWPoKES catalog. Ten stars appear to be spectroscopic binaries based on broad or split spectral features, supporting previous findings that wide binaries are likely to be hierarchical systems. We measured the H{\alpha} equivalent width of the stars in our sample and found that components of 81% of the observed pairs has similar H{\alpha} levels. The difference in H{\alpha} equivalent width amongst components with similar masses was smaller than the range of H{\alpha} variability for individual objects. We confirm that the Lepine et al. {\zeta}(CaH2+CaH3, TiO5) index traces iso-metallicity loci for most of our sample of M dwarfs. However, we find a small systematic bias in {\zeta}, especially in the early-type M dwarfs. We use our sample to recalibrate the definition of {\zeta}. While representing a small change in the definition, the new {\zeta} is a significantly better predictor of iso-metallicity for the higher mass M dwarfs.

We have used the Robert C. Byrd Green Bank Telescope to time nine previously known pulsars without published timing solutions in the globular clusters M62, NGC 6544, and NGC 6624. We have full timing solutions that measure the spin, astrometric, and (where applicable) binary parameters for six of these pulsars. The remaining three pulsars (reported here for the first time) were not detected enough to establish solutions. We also report our timing solutions for five pulsars with previously published solutions, and find good agreement with past authors, except for PSR J1701-3006B in M62. Gas in this system is probably responsible for the discrepancy in orbital parameters, and we have been able to measure a change in the orbital period over the course of our observations. Among the pulsars with new solutions we find several binary pulsars with very low mass companions (members of the so-called “black widow” class) and we are able to place constraints on the mass-to-light ratio in two clusters. We confirm that one of the pulsars in NGC 6624 is indeed a member of the rare class of non-recycled pulsars found in globular clusters. We also have measured the orbital precession and Shapiro delay for a relativistic binary in NGC 6544. If we assume that the orbital precession can be described entirely by general relativity, which is likely, we are able to measure the total system mass (2.57190(73) M_sun) and companion mass (1.2064(20) M_sun), from which we derive the orbital inclination [sin(i) = 0.9956(14)] and the pulsar mass (1.3655(21) M_sun), the most precise such measurement ever obtained for a millisecond pulsar. The companion is the most massive known around a fully recycled pulsar.

We have used the Robert C. Byrd Green Bank Telescope to time nine previously known pulsars without published timing solutions in the globular clusters M62, NGC 6544, and NGC 6624. We have full timing solutions that measure the spin, astrometric, and (where applicable) binary parameters for six of these pulsars. The remaining three pulsars (reported here for the first time) were not detected enough to establish solutions. We also report our timing solutions for five pulsars with previously published solutions, and find good agreement with past authors, except for PSR J1701-3006B in M62. Gas in this system is probably responsible for the discrepancy in orbital parameters, and we have been able to measure a change in the orbital period over the course of our observations. Among the pulsars with new solutions we find several binary pulsars with very low mass companions (members of the so-called “black widow” class) and we are able to place constraints on the mass-to-light ratio in two clusters. We confirm that one of the pulsars in NGC 6624 is indeed a member of the rare class of non-recycled pulsars found in globular clusters. We also have measured the orbital precession and Shapiro delay for a relativistic binary in NGC 6544. If we assume that the orbital precession can be described entirely by general relativity, which is likely, we are able to measure the total system mass (2.57190(73) M_sun) and companion mass (1.2064(20) M_sun), from which we derive the orbital inclination [sin(i) = 0.9956(14)] and the pulsar mass (1.3655(21) M_sun), the most precise such measurement ever obtained for a millisecond pulsar. The companion is the most massive known around a fully recycled pulsar.

Conceptually reconstructing the physical conditions in relativistic jets, given the observed electromagnetic spectrum, poses a complex inverse problem. We aim to obtain a better understanding of the mechanisms operating in relativistic jets through the modeling of their broadband electromagnetic spectrum. We develop an inhomogeneous jet model where the injection of relativistic primary and secondary particles takes place in a spatially extended region. We calculate the contribution of all particles species to the jet emissivity due to several processes, and assess the effect of gamma-ray absorption in internal and external photon fields. A number of specific models with different parameters are computed to explore the possibilities of this scenario. We obtain a variety of spectral shapes depending on the model parameters, some of them predicting significant gamma-ray emission. The observed broadband spectrum of the low-mass microquasar XTE J1118+480 can be satisfactorily reproduced by the model. Our results indicate that outbursts similar to those displayed in the past by XTE J1118+480 might be detected with present-day gamma-ray instruments.

Conceptually reconstructing the physical conditions in relativistic jets, given the observed electromagnetic spectrum, poses a complex inverse problem. We aim to obtain a better understanding of the mechanisms operating in relativistic jets through the modeling of their broadband electromagnetic spectrum. We develop an inhomogeneous jet model where the injection of relativistic primary and secondary particles takes place in a spatially extended region. We calculate the contribution of all particles species to the jet emissivity due to several processes, and assess the effect of gamma-ray absorption in internal and external photon fields. A number of specific models with different parameters are computed to explore the possibilities of this scenario. We obtain a variety of spectral shapes depending on the model parameters, some of them predicting significant gamma-ray emission. The observed broadband spectrum of the low-mass microquasar XTE J1118+480 can be satisfactorily reproduced by the model. Our results indicate that outbursts similar to those displayed in the past by XTE J1118+480 might be detected with present-day gamma-ray instruments.

In order to understand environmental effects on star formation in high-redshift galaxies, we investigate the physical relationships between the star formation activity, stellar mass, and environment for z ~1.2 galaxies in the 2 deg^2 COSMOS field. We estimate star formation using the [OII] emission line and environment from the local galaxy density. Our analysis shows that for massive galaxies M_*>10^10 M_sun, the fraction of [OII] emitters in high-density environments is 1.7 times higher than in low-density environments, while the [OII] emitter fraction does not depend on environment for low-mass M_* 10^10 M_sun. In addition, massive galaxies are more likely to have companions in high-density environments. However, although the “number” of star forming galaxies increases for massive galaxies with close companions and in dense environments, the “average” star formation rate of star forming galaxies at a given mass is independent of environment and the presence/absence of a close companion. These results suggest that interactions and/or mergers in high-density environment could induce star formation in massive galaxies at z~1.2, increasing the fraction of star-forming galaxies with M_* > 10^10 M_sun.

A candidate diffuse stellar substructure was previously reported in the halo of the nearby dwarf starburst galaxy NGC 4449 by Karachentsev et al. We map and analyze this feature using a unique combination of deep integrated-light images from the Black Bird 0.5-meter telescope, and high-resolution wide-field images from the 8-meter Subaru telescope, which resolve the nebulosity into a stream of red giant branch stars, and confirm its physical association with NGC 4449. The properties of the stream imply a massive dwarf spheroidal progenitor, which after complete disruption will deposit an amount of stellar mass that is comparable to the existing stellar halo of the main galaxy. The ratio between luminosity or stellar-mass between the two galaxies is ~1:50, while the indirectly measured dynamical mass-ratio, when including dark matter, may be ~1:10-1:5. This system may thus represent a “stealth” merger, where an infalling satellite galaxy is nearly undetectable by conventional means, yet has a substantial dynamical influence on its host galaxy. This singular discovery also suggests that satellite accretion can play a significant role in building up the stellar halos of low-mass galaxies, and possibly in triggering their starbursts.

We map and analyze a stellar stream in the halo of the nearby dwarf starburst galaxy NGC 4449, detecting it in deep integrated-light images using the Black Bird Observatory 0.5-meter telescope, and resolving it into red giant branch stars using Subaru/Suprime-Cam. The properties of the stream imply a massive dwarf spheroidal progenitor, which will continue to disrupt and deposit an amount of stellar mass that is comparable to the existing stellar halo of the main galaxy. The ratio between luminosity or stellar-mass between the two galaxies is ~1:50, while the dynamical mass-ratio when including dark matter may be ~1:10-1:5. This system may thus represent a “stealth” merger, where an infalling satellite galaxy is nearly undetectable by conventional means, yet has a substantial dynamical influence on its host galaxy. This singular discovery also suggests that satellite accretion can play a significant role in building up the stellar halos of low-mass galaxies, and possibly in triggering their starbursts.

Although hydrogen cyanide has become quite a common molecular tracing species for a variety of astrophysical sources, it, however, exhibits dramatic non-LTE behaviour in its hyperfine line structure. Individual hyperfine components can be strongly boosted or suppressed. If these so-called hyperfine line anomalies are present in the HCN rotational spectra towards low or high mass cores, this will affect the interpretation of various physical properties such as the line opacity and excitation temperature in the case of low mass objects and infall velocities in the case of their higher mass counterparts. This is as a consequence of the direct effects that anomalies have on the underlying line shape, be it with the line structural width or through the inferred line strength. This work involves the first observational investigation of these anomalies in two HCN rotational transitions, J=1!0 and J=3!2, towards both low mass starless cores and high mass protostellar objects. The degree of anomaly in these two rotational transitions is considered by computing the ratios of neighboring hyperfine lines in individual spectra. Results indicate some degree of anomaly is present in all cores considered in our survey, the most likely cause being line overlap effects among hyperfine components in higher rotational transitions.

We explore the circumgalactic medium (CGM) of two simulated star-forming galaxies with luminosities $L \approx 0.1$ and $1 L^\star$ generated using the smooth particle hydrodynamic code {\sc GASOLINE}. For each galaxy, we have implemented two prescriptions for supernovae feedback: a “low feedback” (LF) model which has strength comparable to other implementations in the literature and a “high feedback” (HF) model that has a higher incidence of massive stars and an $\approx 2\times$ higher energy input per supernova. Aside from the the low mass halo using LF, each galaxy exhibits a metal-enriched CGM that extends to approximately the virial radius. A significant portion of this gas has been shock-heated to $T \sim 10^{5.5}\,$K and is predicted to give rise to substantial \iovi\ absorption. These models also predict a reservoir of cool \ihi\ clouds that show strong \lya\ absorption to several hundred kpc. Comparing these models to recent surveys with the {\it Hubble Space Telescope}, we find that only the HF models have sufficient \iovi\ and \ihi\ gas in the CGM to reproduce the observed distributions. In separate analysis, these same HF models also offer better agreement to other galaxy observables (e.g.\ the stellar mass-halo mass relation). We infer that the CGM holds the dominant reservoir of baroyns for galaxy halos.

We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs to pure hydrogen atmosphere white dwarf models. Our photometric dataset is obtained from a 121 orbit Hubble Space Telescope program using the Wide Field Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images. These images cover more than 60 square arcmins and extend over a radial range of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Using a likelihood analysis, we obtain a best fitting unreddened distance modulus of (m – M)o=13.36+/-0.02+/-0.06 corresponding to a distance of 4.70+/-0.04+/-0.13 kpc, where the first error is random and the second is systematic. We also search the white dwarf photometry for infrared excess in the F160W filter, indicative of debris disks or low mass companions, and find no convincing cases within our sample.

Observations of a large population of Millisecond Pulsars (MSPs) show a wide divergence in the orbital periods (from approximately hours to a few months). In the standard view, Low-Mass X-Ray Binaries (LMXBs) are considered as progenitors for some MSPs during the recycling process. We present a systematic study that combines different types of compact objects in binaries such as Cataclysmic Variables (CVs), LMXBs and MSPs. We plot them together in the so called Corbet diagram. Larger and different samples are needed to better constrain the result as a function of the environment and formations. A scale diagram showing the distribution of MSPs for different orbital periods and the aspects for their progenitors relying on Accretion Induced Collapse (AIC) of white dwarfs in binaries. Thus massive CVs (M >1.1M\odot) can play a vital role on binary evolution, as well as of the physical processes involved in the formation and evolution of neutron stars and their magnetic fields, and could turn into binary MSPs with different scales of orbital periods; this effect can be explained by the AIC process. This scenario also suggests that some fraction of isolated MSPs in the Galactic disk could be formed through the same channel, formingthe contribution of some CVs to the single-degenerate progenitors of Type Ia supernova. Furthermore, we have refined the statistical distribution and evolution by using updated data. This implies that the significant studies of compact objects in binary systems can benefit from the Corbet diagram.

We discuss a hydrodynamical model for the dispersal of protoplanetary discs around young, low mass (100) luminosity ratios, the FUV constricts the X-ray flow and may dominate the mass-loss. Simulations of low mass discs with inner holes demonstrate a further stage of disc clearing, which we call `thermal sweeping’. This process occurs when the mid-plane pressure drops to sufficiently low values. At this stage a bound, warm, X-ray heated region becomes sufficiently large and unstable, such that the remaining disc material is cleared on approximately dynamical time-scales. This process significantly reduces the time taken to clear the outer regions of the disc, resulting in an expected transition disc population that will be dominated by accreting objects, as indicated by recent observations.

HYPERION is a new three-dimensional dust continuum Monte-Carlo radiative transfer code that is designed to be as generic as possible, allowing radiative transfer to be computed through a variety of three-dimensional grids. The main part of the code is problem-independent, and only requires an arbitrary three-dimensional density structure, dust properties, the position and properties of the illuminating sources, and parameters controlling the running and output of the code. HYPERION is parallelized, and is shown to scale well to thousands of processes. Two common benchmark models for protoplanetary disks were computed, and the results are found to be in excellent agreement with those from other codes. Finally, to demonstrate the capabilities of the code, dust temperatures, SEDs, and synthetic multi-wavelength images were computed for a dynamical simulation of a low-mass star formation region. HYPERION is being actively developed to include new features, and is publicly available (http://www.hyperion-rt.org).

New instrumentation is providing new insights into intermediate mass pulsating Cepheids, particularly about their formation and history. Three approaches are discussed, using space (Hubble and Chandra) and ground-based studies (radial velocities). First, we are conducting a survey of Cepheids with the Hubble Space Telescope Wide Field Camera 3 (WFC3) to identify possible resolved companions (for example Eta Aql) and thus provide constraints on star formation. Followup X-ray observations (Chandra and XMM-Newton) can confirm whether possible low mass companions are young enough to be physical companions of Cepheids. In a related study of intermediate mass stars, Chandra X-ray observations of late B stars in Tr 16 have been used to determine the fraction which have X-ray active low mass companions. Finally, the Tennessee State Automatic Spectroscopic Telescope AST and the Moscow University group have obtained velocities of a number of Cepheids. As an example, the orbit of V350 Sgr has been redetermined, providing a new level of accuracy to the orbital velocity amplitude, which is needed for mass determination.

The stability of mass transfer is important in the formation of contact binaries from detached binaries when the primaries of the initially detached binaries fill their Roche lobes. Using Eggleton’s stellar evolution code, we investigate the formation and the short-period limit of contact binaries by considering the effect of the instability of mass transfer. It is found that with decreasing initial primary mass from 0.89M$_{\rm \odot}$ to 0.63M$_{\rm \odot}$, the range of the initial mass ratio decreases for detached binaries that experience stable mass transfer and evolve into contact. If the initial primary mass is less than 0.63M$_{\rm \odot}$, detached binaries would experience dynamically unstable mass transfer when the primaries of detached binaries fill their Roche lobes. These systems would evolve into a common envelope situation and probably then to a complete merger of two components on a quite short timescale. This results in a low mass limit at about 0.63M$_{\rm \odot}$ for the primary mass of contact binaries, which might be a main reason why the period distribution of contact binaries has a short limit of about 0.22 days. By comparing the theoretical period distribution of contact binaries with the observational data, it is found that the observed contact binaries are above the low mass limit for the primary mass of contact binaries and no observed contact binaries are below this limit. This suggests that the short-period limit of contact binaries can be explained by the instability of the mass transfer that occurs when the primaries of the initially detached binaries fill their Roche lobes.

We present the initial-final mass relation derived from 10 white dwarfs in wide binaries that consist of a main sequence star and a white dwarf. The temperature and gravity of each white dwarf was measured by fitting theoretical model atmospheres to the observed spectrum using a $\chi^{2}$ fitting algorithm. The cooling time and mass was obtained using theoretical cooling tracks. The total age of each binary was estimated from the chromospheric activity of its main sequence component to an uncertainty of about 0.17 dex in log \textit{t} The difference between the total age and white dwarf cooling time is taken as the main sequence lifetime of each white dwarf. The initial mass of each white dwarf was then determined using stellar evolution tracks with a corresponding metallicity derived from spectra of their main sequence companions, thus yielding the initial-final mass relation. Most of the initial masses of the white dwarf components are between 1 – 2 M$_{\odot}$. Our results suggest a correlation between the metallicity of a white dwarf’s progenitor and the amount of post-main-sequence mass loss it experiences – at least among progenitors with masses in the range of 1 – 2 M$_{\odot}$. A comparison of our observations to theoretical models suggests that low mass stars preferentially lose mass on the red giant branch.

Angular momentum evolution in low-mass stars is determined by initial conditions during star formation, stellar structure evolution, and the behaviour of stellar magnetic fields. Here we show that the empirical picture of angular momentum evolution arises naturally if rotation is related to magnetic field strength instead of to magnetic flux, and formulate a corrected braking law based on this. Angular momentum evolution then becomes a strong function of stellar radius, explaining the main trends observed in open clusters and field stars at a few Gyr: the steep transition in rotation at the boundary to full convection arises primarily from the large change in radius across this boundary, and does not require changes in dynamo mode or field topology. Additionally, the data suggest transient core-envelope decoupling among solar-type stars, and field saturation at longer periods in very low-mass stars. For solar-type stars, our model is also in good agreement with the empirical Skumanich law. Finally, in further support of the theory, we show that the predicted age at which low-mass stars spin down from the saturated to unsaturated field regimes in our model corresponds remarkably well to the observed lifetime of magnetic activity in these stars.

Phase-resolved spectroscopy of the newly discovered X-ray transient MAXI J0556-332 has revealed the presence of narrow emission lines in the Bowen region that most likely arise on the surface of the mass donor star in this low mass X-ray binary. A period search of the radial velocities of these lines provides two candidate orbital periods (16.43+/-0.12 and 9.754+/-0.048 hrs), which differ from any potential X-ray periods reported. Assuming that MAXI J0556-332 is a relatively high inclination system that harbors a precessing accretion disk in order to explain its X-ray properties, it is only possible to obtain a consistent set of system parameters for the longer period. These assumptions imply a mass ratio of q~0.45, a radial velocity semi-amplitude of the secondary of K_2~190 km/s and a compact object mass of the order of the canonical neutron star mass, making a black hole nature for MAXI J0556-332 unlikely. We also report the presence of strong N III emission lines in the spectrum, thereby inferring a high N/O abundance. Finally we note that the strength of all emission lines shows a continuing decay over the ~1 month of our observations.

We have obtained an XMM-Newton observation and a broad-band spectrum from the ultraviolet to the near infrared with X-Shooter for one of the nearest M9 dwarfs, DENIS-P J1048-3956 (4pc). We integrate these data by a compilation of activity parameters for ultracool dwarfs from the literature with the aim to advance our understanding of these objects by comparing them to early-M type dwarf stars and the Sun. Our deep XMM-Newton observation has led to the first X-ray detection of DENIS-P J1048-3956 (log Lx = 25.1) as well as the first measurement of its V band brightness (V = 17.35mag). Flux-flux relations between X-ray and chromospheric activity indicators are here for the first time extended into the regime of the ultracool dwarfs. The approximate agreement of DENIS-P J1048-3956 and other ultracool dwarfs with flux-flux relations for early-M dwarfs suggests that the same heating mechanisms work in the atmospheres of ultracool dwarfs, albeit weaker as judged from their lower fluxes. The observed Balmer decrements of DENIS-P J1048-3956 are compatible with optically thick plasma in LTE at low, nearly photospheric temperature or optically thin LTE plasma at 20000K. Describing the decrements with CaseB recombination requires different emitting regions for Halpha and the higher Balmer lines. The high observed Halpha/Hbeta flux ratio is also poorly fitted by the optically thin models. We derive a similarly high value for the Halpha/Hbeta ratio of vB10 and LHS2065 and conclude that this may be a characteristic of ultracool dwarfs. We add DENIS-P J1048-3956 to the list of ultracool dwarfs detected in both the radio and the X-ray band. The Benz-Guedel relation between radio and X-ray luminosity of late-type stars is well-known to be violated by ultracool dwarfs. We speculate on the presence of two types of ultracool dwarfs with distinct radio and X-ray behavior.

The cold dark matter halo mass function is much steeper than the galaxy stellar mass function on galactic and subgalactic scales. This difference is usually reconciled by assuming that the galaxy formation efficiency drops sharply with decreasing halo mass, so that galaxy formation is effectively suppressed below a threshold mass, M_th ~ 10^10 M_sun . A halo mass threshold implies that, at any given radius, the dark mass enclosed by a galaxy must exceed a certain minimum. We use rotation curves of dwarf galaxies compiled from the literature to explore whether their enclosed mass is consistent with this constraint. We find that almost one half of the dwarfs in our sample with stellar mass between 10^6-10^7 Msun violate this restriction: either they live in halos with masses substantially below the threshold or there is a mechanism capable of reducing the dark mass enclosed by some of the faintest dwarfs. Neither possibility is easily accommodated within the standard LCDM scenario. Extending galaxy formation to halos well below 10^10 M_sun would lead to severe disagreement with the low mass end of the galaxy stellar mass function; at the same time, the extremely low stellar mass of the systems involved make it unlikely that baryonic effects may be responsible for reducing their dark matter content. Resolving this challenge seems to require new insights into dwarf galaxy formation, or else a radical revision of the prevailing paradigm.

We investigate the calibration and uncertainties of black hole mass estimates based on the single-epoch (SE) method, using homogeneous and high-quality multi-epoch spectra obtained by the Lick Active Galactic Nucleus (AGN) Monitoring Project for 9 local Seyfert 1 galaxies with black hole masses < 10^8 M_sun. By decomposing the spectra into their AGN and stellar components, we study the variability of the single-epoch Hbeta line width (full width at half-maximum intensity, FWHM_Hbeta; or dispersion, sigma_Hbeta) and of the AGN continuum luminosity at 5100A (L_5100). From the distribution of the "virial products" (~ FWHM_Hbeta^2 L_5100^0.5 or sigma_Hbeta^2 L_5100^0.5) measured from SE spectra, we estimate the uncertainty due to the combined variability as ~ 0.05 dex (12%). This is subdominant with respect to the total uncertainty in SE mass estimates, which is dominated by uncertainties in the size-luminosity relation and virial coefficient, and is estimated to be ~ 0.46 dex (factor of ~ 3). By comparing the Hbeta line profile of the SE, mean, and root-mean-square (rms) spectra, we find that the Hbeta line is broader in the mean (and SE) spectra than in the rms spectra by ~ 0.1 dex (25%) for our sample with FWHM_Hbeta < 3000 km/s. This result is at variance with larger mass black holes where the difference is typically found to be much less than 0.1 dex. To correct for this systematic difference of the Hbeta line profile, we introduce a line-width dependent virial factor, resulting in a recalibration of SE black hole mass estimators for low-mass AGNs.

Extremely low mass (ELM) white dwarfs (WDs) with masses <0.25 Msun are rare objects that result from compact binary evolution. Here, we present a targeted spectroscopic survey of ELM WD candidates selected by color. The survey is 71% complete and has uncovered 18 new ELM WDs. Of the 7 ELM WDs with follow-up observations, 6 are short-period binaries and 4 have merger times less than 5 Gyr. The most intriguing object, J1741+6526, likely has either a pulsar companion or a massive WD companion making the system a possible supernova Type Ia or .Ia progenitor. The overall ELM Survey has now identified 19 double degenerate binaries with <10 Gyr merger times. The significant absence of short orbital period ELM WDs at cool temperatures suggests that common envelope evolution creates ELM WDs directly in short period systems. At least one-third of the merging systems are halo objects, thus ELM WD binaries continue to form and merge in both the disk and the halo.

We briefly review the main physical and structural properties of Very Low-Mass stars. The most important improvements in the physical inputs required for the stellar models computations are also discussed. We show some comparisons with observational measurements concerning both the Color-Magnitude diagrams, mass-luminosity relations and mass-radius one, in order to disclose the level of agreement between the present theoretical framework and observations.

Astronomers are good at sharing data, but poorer at sharing knowledge. Almost all astronomical data ends up in open archives, and access to these is being simplified by the development of the global Virtual Observatory (VO). This is a great advance, but the fundamental problem remains that these archives contain only basic observational data, whereas all the astrophysical interpretation of that data — which source is a quasar, which a low-mass star, and which an image artefact — is contained in journal papers, with very little linkage back from the literature to the original data archives. It is therefore currently impossible for an astronomer to pose a query like “give me all sources in this data archive that have been identified as quasars” and this limits the effective exploitation of these archives, as the user of an archive has no direct means of taking advantage of the knowledge derived by its previous users. The AstroDAbis service aims to address this, in a prototype service enabling astronomers to record annotations and cross-identifications in the AstroDAbis service, annotating objects in other catalogues. We have deployed two interfaces to the annotations, namely one astronomy-specific one using the TAP protocol}, and a second exploiting generic Linked Open Data (LOD) and RDF techniques.

In this paper we present simulated solar coronal X-ray observations to verify the sensitivity of a new hypothetical instrument design. These simulations are folded through this X-ray spectrometer having a moderate size circular field of view of 1.6 degrees. This SCXM (Solar Coronal X-ray Mapper) is designed to compose of a single pixel silicon PIN detector equipped with a single reflection double frustum X-ray optics. A moderate FoV would enable a morphological study of the expanded X-ray emission from the solar corona during a high activity of the Sun. The main scientific task of SCXM would be the mapping of the coronal X-ray emission, i.e. to resolve the radial distribution of the X-ray surface brightness around the Sun. These kind of off-limb observations would help to interpret the coronal plasma diagnostics as a function of the elongation angle. Direct solar full disc observations could be also performed with SCXM. In this work we have applied real solar coronal X-ray data obtained by the SMART-1 XSM (X-ray Solar Monitor) to simulate on-solar observations at different flux levels to derive full disc sensitivity and performance of SCXM. A challenging attempt for SCXM would also be to distinguish the X-ray spectrum of the decaying axions around the Sun. These axions are assumed to be created as side products of fusion reactions in the core of the Sun. These axions are predicted to be gravitationally trapped to orbit the Sun forming a halo-like X-ray emitting object. No signature of an axion X-ray emission around the Sun has been observed to this day. This simple X-ray spectrometer with an optical concentrator would be an inexpensive instrument with low mass and telemetry budgets compared with more accurate X-ray instruments of imaging capability. Hence SCXM would be an advanced choice as an auxiliary instrument for solar coronal X-ray observations.

In this paper we present simulated solar coronal X-ray observations to verify the sensitivity of a new hypothetical instrument design. These simulations are folded through this X-ray spectrometer having a moderate size circular field of view of 1.6 degrees. This SCXM (Solar Coronal X-ray Mapper) is designed to compose of a single pixel silicon PIN detector equipped with a single reflection double frustum X-ray optics. A moderate FoV would enable a morphological study of the expanded X-ray emission from the solar corona during a high activity of the Sun. The main scientific task of SCXM would be the mapping of the coronal X-ray emission, i.e. to resolve the radial distribution of the X-ray surface brightness around the Sun. These kind of off-limb observations would help to interpret the coronal plasma diagnostics as a function of the elongation angle. Direct solar full disc observations could be also performed with SCXM. In this work we have applied real solar coronal X-ray data obtained by the SMART-1 XSM (X-ray Solar Monitor) to simulate on-solar observations at different flux levels to derive full disc sensitivity and performance of SCXM. A challenging attempt for SCXM would also be to distinguish the X-ray spectrum of the decaying axions around the Sun. These axions are assumed to be created as side products of fusion reactions in the core of the Sun. These axions are predicted to be gravitationally trapped to orbit the Sun forming a halo-like X-ray emitting object. No signature of an axion X-ray emission around the Sun has been observed to this day. This simple X-ray spectrometer with an optical concentrator would be an inexpensive instrument with low mass and telemetry budgets compared with more accurate X-ray instruments of imaging capability. Hence SCXM would be an advanced choice as an auxiliary instrument for solar coronal X-ray observations.

As part of the WISH (Water In Star-forming regions with Herschel) key project, we report on the observations of several ortho- and para-H2O lines performed with the HIFI instrument towards two bright shock spots (R4 and B2) along the outflow driven by the L1448 low-mass proto-stellar system, located in the Perseus cloud. These data are used to identify the physical conditions giving rise to the H2O emission and infer any dependence with velocity. These observations provide evidence that the observed water lines probe a warm (T_kin~400-600 K) and very dense (n 10^6 – 10^7 cm^-3) gas, not traced by other molecules, such as low-J CO and SiO, but rather traced by mid-IR H2 emission. In particular, H2O shows strong differences with SiO in the excitation conditions and in the line profiles in the two observed shocked positions, pointing to chemical variations across the various velocity regimes and chemical evolution in the different shock spots. Physical and kinematical differences can be seen at the two shocked positions. At the R4 position, two velocity components with different excitation can be distinguished, with the component at higher velocity (R4-HV) being less extended and less dense than the low velocity component (R4-LV). H2O column densities of about 2 10^13 and 4 10^14 cm^-2 have been derived for the R4-LV and the R4-HV components, respectively. The conditions inferred for the B2 position are similar to those of the R4-HV component, with H2O column density in the range 10^14 – 5 10^14 cm^-2, corresponding to H2O/H2 abundances in the range 0.5 – 1 10^-5. The observed line ratios and the derived physical conditions seem to be more consistent with excitation in a low velocity J-type shock with large compression rather than in a stationary C-shock, although none of these stationary models seems able to reproduce all the characteristics of the observed emission.

Context. Ultracompact X-ray binaries (UCXBs) typically consist of a white dwarf donor and a neutron star or black hole accretor. The evolution of UCXBs and very low mass ratio binaries in general is poorly understood. Aims. We investigate the evolution of UCXBs in order to learn for which mass ratios and accretor types these systems can exist, and if they do, what are their orbital and neutron star spin periods, mass transfer rates and evolutionary timescales. Methods. For different assumptions concerning accretion disk behavior we calculate for which system parameters dynamical instability, thermal-viscous disk instability or the propeller effect emerge. Results. At the onset of mass transfer, the survival of the UCXB is determined by how efficiently the accretor can eject matter in the case of a super-Eddington mass transfer rate. At later times, the evolution of systems strongly depends on the binary’s capacity to return angular momentum from the disk to the orbit. We find that this feedback mechanism most likely remains effective. In the case of steady mass transfer, the propeller effect can stop accretion onto recycled neutron stars completely at a sufficiently low mass transfer rate, based on energy considerations. However, mass transfer will likely be non-steady because disk instability allows for accretion of some of the transferred matter. Together, the propeller effect and disk instability cause the low mass ratio UCXBs to be visible a small fraction of the time at most, thereby explaining the lack of observations of such systems. Conclusions. Most likely UCXBs avoid late-time dynamically unstable mass transfer and continue to evolve as the age of the Universe allows. This implies the existence of a large population of low mass ratio binaries with orbital periods ~ 70 – 80 min, unless some other mechanism has destroyed these binaries.

Extrapolation of the astrometric motion of the nearby low-mass star VB 10 indicates that sometime in late December 2011 or early January 2012, the star will approach to within short angular distance of a background point source. Based on astrometric uncertainties, we estimate a 1 in 2 chance that the distance of closest approach rho_{min} will be less than 100 mas, a 1 in 5 chance that rho_{min} < 50 mas, and a 1 in 10 chance that rho_{min} 0.3 AU) orbit, this planet could pass closer to the background source up to several weeks preceding or following the primary event, and produce a secondary event of significantly higher magnification (tens of percent or higher). The secondary events have timescales of several days but detectable, high-magnification peaks lasting only about 5-10 hours. We argue that an intensive, multi-site monitoring campaign using 1-meter class telescopes would be required to detect secondary events due to orbiting planets.

I review the relation between virial mass and concentration for groups and clusters of galaxies as measured in a number of recent works. As previously noted by several authors, low-mass clusters and groups of galaxies display systematically larger concentrations than simple prescriptions based on pure $n$-body simulations would predict. This implies an observed concentration-mass relation with a substantially larger slope/normalization than expected from theoretical investigations. Additionally, this conclusion seems to be quite independent on selection effects, holding for both lensing based and X-ray based cluster samples. I develop a simple structure model containing dark matter, stars, and hot diffuse gas in proportions and with distributions in agreement with the most recent observations. Moreover, I include the contraction effect experienced by dark matter due to the cooling of baryons in the very central part of the structure itself. The resulting modified concentration-mass relation is steeper than the theoretical input one, because star formation is fractionally more efficient in low-mass objects. However, the effect is non-vanishing at all masses, thus resulting also in a larger normalization. Overall the new relation provides a better representation of the observed one for almost all catalogs considered in this work, although the specific details depend quite significantly on the baryon fraction prescription adopted. Specifically, the observed concentration-mass relation seems to favor a scenario where the stellar mass fraction in large clusters of galaxies is substantially lower than several works have found. Finally I use this simple structure model to show how the estimated concentration of cosmic structures is expected to be overestimated as a function of the radial range covered by the analysis. (abridged)

We use a combination of X-shooter spectroscopy, ULTRACAM high-speed photometry and SOFI near-infrared photometry to measure the masses and radii of both components of the eclipsing post common envelope binaries SDSS J1212-0123 and GK Vir. For both systems we measure the gravitational redshift of the white dwarf and combine it with light curve model fits to determine the inclinations, masses and radii. For SDSS J1212-0123 we find a white dwarf mass and radius of 0.439 +/- 0.002 Msun and 0.0168 +/- 0.0003 Rsun, and a secondary star mass and radius of 0.273 +/- 0.002 Msun and 0.306 +/- 0.007 Rsun. For GK Vir we find a white dwarf mass and radius of 0.564 +/- 0.014 Msun and 0.0170 +/- 0.0004 Rsun, and a secondary star mass and radius of 0.116 +/- 0.003 Msun and 0.155 +/- 0.003 Rsun. The mass and radius of the white dwarf in GK Vir are consistent with evolutionary models for a 50,000K carbon-oxygen core white dwarf. Although the mass and radius of the white dwarf in SDSS J1212-0123 are consistent with carbon-oxygen core models, evolutionary models imply that a white dwarf with such a low mass and in a short period binary must have a helium core. The mass and radius measurements are consistent with helium core models but only if the white dwarf has a very thin hydrogen envelope, which has not been predicted by evolutionary models. The mass and radius of the secondary star in GK Vir are consistent with evolutionary models after correcting for the effects of irradiation by the white dwarf. The secondary star in SDSS J1212-0123 has a radius ~9 per cent larger than predicted.

The stellar luminosity and depth of the convective envelope vary rapidly with mass for G- and K-type main sequence stars. In order to understand how these properties influence the convective turbulence, differential rotation, and meridional circulation, we have carried out 3D dynamical simulations of the interiors of rotating main sequence stars, using the anelastic spherical harmonic (ASH) code. The stars in our simulations have masses of 0.5, 0.7, 0.9, and 1.1 M_sun, corresponding to spectral types K7 through G0, and rotate at the same angular speed as the sun. We identify several trends of convection zone properties with stellar mass, exhibited by the simulations. The convective velocities, temperature contrast between up- and down-flows, and meridional circulation velocities all increase with stellar luminosity. As a consequence of the trend in convective velocity, the Rossby number (at a fixed rotation rate) increases and the convective turnover timescales decrease significantly with increasing stellar mass. The 3 lowest mass cases exhibit solar-like differential rotation, in a sense that they show a maximum rotation at the equator and minimum at higher latitudes, but the 1.1 M_sun case exhibits anti-solar rotation. At low mass, the meridional circulation is multi-cellular and aligned with the rotation axis; as the mass increases, the circulation pattern tends toward a unicellular structure covering each hemisphere in the convection zone.

In the present study, we analyze the radial velocity distribution as a function of different stellar parameters such as stellar age, mass, rotational velocity and distance to the Sun for a sample of 6781 single low–mass field dwarf stars, located in the solar neighborhood. We show that the radial velocity distributions are best fitted by $q$–Gaussians that arise within the Tsallis nonextensive statistics. The obtained distributions cannot be described by the standard Gaussian that emerges within Boltzmann-Gibbs (B–G) statistical mechanics. The results point to the existence of a hierarchical structure in phase space, in contrast to the uniformly occupied phase space of B–G statistical mechanics, driven by the $q$–Central Limit Theorem, consistent with nonextensive statistical mechanics.

In the present study, we analyze the radial velocity distribution as a function of different stellar parameters such as stellar age, mass, rotational velocity and distance to the Sun for a sample of 6781 single low–mass field dwarf stars, located in the solar neighborhood. We show that the radial velocity distributions are best fitted by $q$–Gaussians that arise within the Tsallis nonextensive statistics. The obtained distributions cannot be described by the standard Gaussian that emerges within Boltzmann-Gibbs (B–G) statistical mechanics. The results point to the existence of a hierarchical structure in phase space, in contrast to the uniformly occupied phase space of B–G statistical mechanics, driven by the $q$–Central Limit Theorem, consistent with nonextensive statistical mechanics.

We present high spatial (0.05 over much of the core. The N2H+ column density profile across the major axis of Oph A-N6 is well represented by an isothermal cylinder, with temperature 20 K, peak density 7.1 \times 10^6 cm^{-3}, and N2H+ abundance 2.7 \times 10^{-10}. The mass of Oph A-N6 is estimated to be 0.29 M\odot, compared to a value of 0.18 M\odot from the isothermal cylinder analysis, and 0.63 M\odot for the critical mass for fragmentation of an isothermal cylinder. Compared to isolated low-mass cores, Oph A-N6 shows similar narrow line widths and small velocity variation, with a deuterium fraction similar to “evolved” dense cores. It is significantly smaller than isolated cores, with larger peak column and volume density. The available evidence suggests Oph A-N6 has formed through the fragmentation of the Oph A filament and is the precursor to a low-mass star. The dust continuum emission suggests it may already have begun to form a star.