With the many ambitious proposals afoot for new generations of very large telescopes, along with spectrographs of unprecedented resolution, there arises the real possibility that the time evolution of the cosmological redshift may, in the not too distant future, prove to be a useful tool rather than merely a theoretical curiosity. Here I contrast this approach with the standard cosmological procedure based on the luminosity (or any other well-defined) distance. I then show that such observations would not only provide a direct measure of all the associated cosmological parameters of the LCDM model, but would also provide wide-ranging internal consistency checks. Further, in a more general context, I show that without introducing further time derivatives of the redshift one could in fact map out the dark energy equation of state should the LCDM model fail. A consideration of brane-world scenarios and interacting dark energy models serves to emphasize the fact that the usefulness of such observations would not be restricted to high redshifts.

We present the first far ultraviolet (FUV) spectra of the four known Balmer-dominated supernova remnants (SNRs) in the Large Magellanic Cloud, acquired with the Far Ultraviolet Spectroscopic Explorer. The remnants DEM L 71 (0505-67.9), 0509-67.5, 0519-69.0 and 0548-70.4 are all in the non-radiative stages of evolution and exhibit expansion speeds ranging from ~ 500 km/s to ~ 5000 km/s. We have detected broad emission lines of Ly beta, Ly gamma, C III and O VI in DEM L 71 (V(FWHM) ~ 1000 km/s) and have detected broad Ly beta and O VI emission in 0519-69.0, (V(FWHM) ~ 3000 km/s). In addition, broad Ly beta emission (V(FWHM) ~ 3700 km/s) has been observed in 0509-67.5, the first detection of broad line emission from this SNR. No emission was detected in our FUSE spectrum of 0548-70.4, allowing us to place only upper limits on the FUV line fluxes. The spectra of these SNRs are unaffected by postshock cooling, and provide valuable probes of collisionless heating efficiency in high Mach number shocks. We have used the Ly beta / O VI flux ratio and relative widths of the broad Ly beta and O VI lines to estimate the degree of electron-proton and proton-oxygen ion equilibration in DEM L 71, 0509-67.5, and 0519-69.0. Although our equilibration estimates are subject to considerable uncertainty due to the faintness of the FUV lines and contributions from bulk Doppler broadening, our results are consistent with a declining efficiency of electron- proton and proton-oxygen ion equilibration with increasing shock speed. From our shock velocity estimates we obtain ages of 295-585 years for 0509-67.5 and 520-900 years for 0519-69.0, respectively, in good agreement with the ages obtained from SN light echo studies.

We present the discovery of 2MASS J11263991-5003550 identified as part of an ongoing survey to discover ultra-cool dwarfs in the Southern Galactic Plane, using data from the 2MASS and SuperCOSMOS Sky Surveys. Strong FeH and H2O absorption features in the near-infrared JH-band spectrum reveal characteristics seen in both mid-L, and L-T transition type dwarfs. We suggest these may be attributable to holes in the condensate cloud layers in the atmosphere of a single sub-stellar object, but cannot at present completely rule out the role of binarity as the possible cause. We also identify this object as a blue L dwarf, and explore the similar observable characteristics of these objects with those of the L-T transition. From this comparison we suggest that the temperature (and thus spectral type) at which the condensate cloud later begins to break-up/rain out, may be highly sensitive to small variations in metallicity. However, the JH-band spectrum of this object does not resemble that of the known L sub-dwarfs, and therefore extreme metal deficiency may not in fact be responsible for the discordant features. We estimate a spectral type of L9+/-1, and measure a large proper-motion of \mu_(tot)=1.65"+/-0.03" per year. Also, a spectrophotometric distance of 8.2pc is estimated, possibly making this object the nearest easily observable single L-T transition object in the southern hemisphere.

We consider here the collective accretion of gas by globular clusters and dwarf galaxies moving through the interstellar medium. In the limit of high velocity and/or sound speed of the ISM, the collective potential of the cluster is insufficient to accrete significant amounts of gas, and stars within the systems accrete gas individually. We show, however, that when the sound speed or the relative velocity of the ambient medium is less than the central velocity dispersion of the cluster, it is accreted into the collective potential of the cluster prior to being accreted onto the individual stars within the cluster. The collective rate is strongly enhanced relative to the individual rates. This effect may potentially modify the white dwarf cooling sequence in globular clusters with low-inclination and low-eccentricity Galactic orbits, and lead to the rejuvenation of some marginally surviving cores of globular clusters and nucleated dwarf galaxies near the Galactic center. Such effects will only occur rarely, but may explain the existence of clusters of young, massive stars near the Galactic center.

Suggestions have been made that the microwave background observed by COBE and WMAP and dubbed Cosmic Microwave Background (CMB) may have an origin within our own Galaxy or Earth. To consider the signal that may be correlated with Earth, a correlate-by-eye exercise was attempted by overlaying the CMB map from Wilkinson Microwave Anisotropy Probe on a topographical map of Earth. Remarkably, several hot spots in the CMB map are found to be well aligned with either large cities on Earth or regions of high altitude. To further study the correlations between Earth and CMB, we performed a complicated cross-correlation analysis in the multipole space. The overall correlations are detected at more than 5 sigma confidence level. These results can be naively interpreted to suggest that large angular scale fluctuations in CMB are generated on Earth by a process that traces the altitude relative to a mean radius. Simply extending our analysis, we suggest that cross-correlations between CMB and any other map of a Solar system body, image of a person, or an image of an animal will be detected at some statistical significance. It is unclear how Occam’s razor can be applied in such a situation to identify which sources are responsible for CMB fluctuations.

Previous work has related the Galactic Bar to structure in the local stellar velocity distribution. Here we show that the Bar also influences the spatial gradients of the velocity vector via the Oort constants. By numerical integration of test-particles we simulate measurements of the Oort C value in a gravitational potential including the Galactic Bar. We account for the observed trend that C is increasingly negative for stars with higher velocity dispersion. By comparing measurements of C with our simulations we improve on previous models of the Bar, estimating that the Bar pattern speed is Omega_b/Omega_0=1.87\pm0.04, where Omega_0 is the local circular frequency, and the Bar angle lies within 20<phi_0<45 deg. We find that the Galactic Bar affects measurements of the Oort constants A and B less than ~2 km/s/kpc for the hot stars.

We present spectroscopic and photometric analysis for eight field galaxies in the direction of the galaxy cluster LCDCS-S001. The spectra were obtained with the GMOS instrument in the Gemini South Observatory. The objects were selected in an i’ band image and the multi-object spectroscopic observations were centered at 7500 A. For the galaxies ID 440 and ID 461 we have determined redshifts of z=0.7464 and z=0.7465, respectively. For the other six galaxies we have confirmed the redshift calculated by Rembold & Pastoriza (2006). The redshifts of the field galaxies are in the range of 0.2201 < z < 0.7784. We determined the blue and visual luminosities and they are brighter than M_B=-18.64. The galaxies ID 180, ID 266, ID 461 follow the Faber-Jackson relation of the Coma and Virgo early-type galaxies, and therefore do not present a brightening of the B luminosity as observed in galaxies at higher redshifts. The stellar velocity dispersion was measured for five galaxies and estimated to be in the range of 200 < sigma < 346 km/s. Lick indices were measured and used to determine the stellar population properties of galaxies ID 120 and ID 146, by means of spectral synthesis. The first galaxy, ID 120, presents in its spectrum absorption and emission lines, and we have found that the main contribution in the flux at lambda 5870 A is of a 0.1 Gyr stellar population of solar metallicity. For ID 146, the dominant flux contribution at lambda 4200 A, is provided by a stellar population of 10 Gyr of subsolar metallicity. From stellar population synthesis we estimated reddening values of E(B-V)=0.90 and E(B-V)=0.82 for ID 120 and ID 146, respectively. According to classical diagnostic diagrams the emission lines present in the spectrum of ID 120 indicate that it is a starburst galaxy.

We investigate strong gravitational lensing in the concordance $\Lambda$CDM cosmology by carrying out ray-tracing along past light cones through the Millennium Simulation, the largest simulation of cosmic structure formation ever carried out. We extend previous ray-tracing methods in order to take full advantage of the large volume and the excellent spatial and mass resolution of the simulation. As a function of source redshift we evaluate the probability that an image will be highly magnified, will be highly elongated or will be one of a set of multiple images. We show that such strong lensing events can almost always be traced to a single dominant lensing object and we study the mass and redshift distribution of these primary lenses. We fit analytic models to the simulated dark halos in order to study how our optical depth measurements are affected by the limited resolution of the simulation and of the lensing planes that we construct from it. We conclude that such effects lead us to underestimate total strong-lensing cross sections by about 15 percent. This is smaller than the effects expected from our neglect of the baryonic components of galaxies. Finally we investigate whether strong lensing is enhanced by material in front of or behind the primary lens. Although strong lensing lines-of-sight are indeed biased towards higher than average mean densities, this additional matter typically contributes only a few percent of the total surface density.

The first short Chandra and XMM-Newton observations of the young and energetic pulsar J1357-6429 provided strong indications of a tail-like pulsar-wind nebula associated with this object, as well as pulsations of its X-ray flux with a pulsed fraction above 50% and a thermal component dominating at lower photon energies (below 2 keV). The elongated nebula is very compact in size and may be interpreted as evidence for a pulsar jet. The thermal radiation is most plausibly emitted from the entire neutron star surface of a 10 km radius and a 1.0+/-0.1 K temperature, covered with a magnetized hydrogen atmosphere. At higher energies the pulsar’s emission is of a nonthermal (magnetospheric) origin, with a power-law spectrum of a photon index of 1.1-1.3. This makes the X-ray properties of PSR J1357-6429 very similar to those of the youngest pulsars J1119-6127 and Vela with a detected thermal radiation.

There is growing consensus that feedback from AGN is the main mechanism responsible for stopping cooling flows in clusters of galaxies. AGN are known to inflate buoyant bubbles that supply mechanical power to the intracluster gas (ICM). High Reynolds number hydrodynamical simulations show that such bubbles get entirely disrupted within 100 Myr, as they rise in cluster atmospheres, which is contrary to observations. This artificial mixing has consequences for models trying to quantify the amount of heating and star formation in cool core clusters of galaxies. It has been suggested that magnetic fields can stabilize bubbles against disruption. We perform MHD simulations of fossil bubbles in the presence of tangled magnetic fields using the high order PENCIL code. We focus on the physically-motivated case where thermal pressure dominates over magnetic pressure and consider randomly oriented fields with and without maximum helicity and a case where large scale external fields drape the bubble.We find that helicity has some stabilizing effect. However, unless the coherence length of magnetic fields exceeds the bubble size, the bubbles are quickly shredded. As observations of Hydra A suggest that lengthscale of magnetic fields may be smaller then typical bubble size, this may suggest that other mechanisms, such as viscosity, may be responsible for stabilizing the bubbles. However, since Faraday rotation observations of radio lobes do not constrain large scale ICM fields well if they are aligned with the bubble surface, the draping case may be a viable alternative solution to the problem. A generic feature found in our simulations is the formation of magnetic wakes where fields are ordered and amplified. We suggest that this effect could prevent evaporation by thermal conduction of cold Halpha filaments observed in the Perseus cluster.

Using 1D NLTE radiative hydrodynamics we model the influence of the particle beams on the Halpha line profile treating the beam propagation and the atmosphere evolution self-consistently. We focus on the influence of the non-thermal collisional rates and the return current. Based on our results, we propose a diagnostic method for determination of the particle beam presence in the formation regions of the Halpha line.

We discuss observations of the first galaxies, within cosmic reionization, at centimeter and millimeter wavelengths. We present a summary of current observations of the host galaxies of the most distant QSOs ($z \sim 6$). These observations reveal the gas, dust, and star formation in the host galaxies on kpc-scales. These data imply an enriched ISM in the QSO host galaxies within 1 Gyr of the big bang, and are consistent with models of coeval supermassive black hole and spheroidal galaxy formation in major mergers at high redshift. Current instruments are limited to studying truly pathologic objects at these redshifts, meaning hyper-luminous infrared galaxies ($L_{FIR} \sim 10^{13}$ L$_\odot$). ALMA will provide the one to two orders of magnitude improvement in millimeter astronomy required to study normal star forming galaxies (ie. Ly-$\alpha$ emitters) at $z \sim 6$. ALMA will reveal, at sub-kpc spatial resolution, the thermal gas and dust — the fundamental fuel for star formation — in galaxies into cosmic reionization.

delta Velorum is a nearby (24pc) triple stellar system, containing a close, eclipsing binary (Aa, Ab) discovered in 2000. Multiple systems provide an opportunity to determine the set of fundamental parameters (mass, luminosity, size and chemical composition) of coeval stars. These parameters can be obtained with particular precision in the case of eclipsing binaries; for delta Velorum’s components (Aa, Ab) this potential has however not yet been exploited. We have analyzed interferometric observations of the close binary (Aa, Ab), obtained with the VINCI instrument and two VLTI siderostats. The measurements, which resolve the two components for the first time, are fitted onto the simple model of two uniformly bright, spherical stars. The observations suggest that Aa and Ab have larger diameters than expected if they were on the main sequence, and that they are, thus, in a later evolutionary state.

We have searched for HI 21cm absorption toward the two brightest radio AGN at high redshift, J0924–2201 at $z = 5.20$, and J0913+5919 at $z=5.11$, using the Giant Meter Wave Radio Telescope (GMRT). These data set a 3$\sigma$ upper limit to absorption of $< 30%$ at 40 km s$^{-1}$ resolution for the 30 mJy source J0913+5919, and $< 3%$ for the 0.55 Jy source J0924–2201 at 20 km s$^{-1}$ resolution. For J0924–2201, limits to broader lines at the few percent level are set by residual spectral baseline structure. For J0924–2201 the column density limit per 20 km s $^{-1}$ channel is: N(HI) $< 2.2\times 10^{18} \rm T_s$ cm$^{-2}$ over a velocity range of -700 km s$^{-1}$ to $+1180$ km s$^{-1}$ centered on the galaxy redshift determined through CO emission, assuming a covering factor of one. For J0913+5919 the column density limit per 40 km s$^{-1}$ channel is: N(HI) $< 2.2\times 10^{19} \rm T_s$ cm$^{-2}$ within $\pm 2400$ km s$^{-1}$ of the optical redshift. These data rule out any cool, high column density HI clouds within roughly $\pm 1000$ km s$^{-1}$ of the galaxies, as are often seen in Compact Steep Spectrum radio AGN, or clouds that might correspond to residual gas left over from cosmic reionization.

We discuss differences between massive single star and massive close binary population number synthesis predictions of WR stars. We show that the WC/WN number ratio as function of metallicity depends significantly on whether or not binaries are included. Furthermore, the observed WC(+OB)/WN(+OB) number ratio in the Solar neighborhood seems to indicate that the WR mass loss rates are lower by another factor two compared to recently proposed clumping corrected formalisms. We then demonstrate that the observed lower luminosity distribution of single WN stars can be explained in a satisfactory way by massive single star evolutionary computations where the red supergiant phase is calculated using a stellar wind mass loss rate formalism that is based on recent observations.

We present new results from our ongoing multiplicity study of exoplanet host stars and present a list of 29 confirmed planet host multiple-star systems. Furthermore, we discuss the properties of these stellar systems and compare the properties of exoplanets detected in these systems with those of planets orbiting single stars.

We present a preliminary analysis of the stellar populations in the central parsecs of a sample of 22 Seyfert 2 galaxies, based on a careful separation of nebular emission and stellar light in high-spatial resolution HST-STIS spectra. 10% of the surveyed nuclei display stellar populations of intermediate age, 1-2 Gyr old, whereas the remaining targets appear to be evenly split between objects showing only very old stellar populations and nuclei requiring also an additional blue featureless component, which we characterise by means of very young, few-Myr-old stars. The small fraction of stellar population of intermediate age seems to argue against the presence of such a young component, however, since the short lifetime of O-stars would imply recurrent star-formation episodes and the build-up over the last 1-2 Gyr of a detectable intermediate-age population. Additionally, a correlation between the luminosity of such a blue component and the emission from highly-ionised species, together with the general absence of Wolf-Rayet features, further suggests that the featureless continuum arises from the central engine rather than from star-forming regions. We discuss our results in the framework of the unification paradigm and of models for star formation close to supermassive black holes.

The spatial power spectrum of the HI 21 cm intensity in the Small Magellanic Cloud (Stanimirovic et al 1999) is a power law over scales as large as those of the SMC itself. It was interpreted as due to turbulence by Goldman (2000) and by Stanimirovic & Lazarian (2001). The question is whether the power spectrum is indeed the result of a dynamical turbulence or is merely the result of a structured static density. In the turbulence interpretation of Goldman (2000) the turbulence was generated by the tidal effects of the last close passage of the LMC about 0.2 Gyr ago. The turbulence time-scale was estimated by Goldman to be 0.4 Gyr, so the turbulence has not decayed yet. Staveley-Smith et al (1997) observed in the SMC about five hundreds of HI super shells. Their age is more than an order of magnitude smaller than the turbulence age. Therefore, if the turbulence explanation holds, their observed radial velocities should reflect the turbulence in the gas in which they formed. In the present work we analyze the observed radial velocities of the super shells. We find that the velocities indeed manifest the statistical spatial correlations expected from turbulence. The turbulence spectrum is consistent with that obtained by Goldman(2000).

(Abridged) We present B, R, and I-band selected galaxy catalogues based on the Munich Near-Infrared Cluster Survey (MUNICS) which, together with the K-selected sample, serve as an important probe of galaxy evolution in the redshift range 0 < z < 2. Furthermore, used in comparison they are ideally suited to study selection effects. The construction of the B, R, and I-selected photometric catalogues, containing ~9000, ~9000, and ~6000 galaxies, respectively, is described in detail. The catalogues reach 50% completeness limits for point sources of B ~ 24.5mag, R ~ 23.5mag, and I ~ 22.5mag and cover an area of about 0.3 square degrees. Photometric redshifts are derived for all galaxies with an accuracy of dz/(1+z) ~ 0.057. We investigate the influence of selection band and environment on the specific star formation rate (SSFR). We find that K-band selection indeed comes close to selection in stellar mass, while B-band selection purely selects galaxies in star formation rate. We use a galaxy group catalogue constructed on the K-band selected MUNICS sample to study possible differences of the SSFR between the field and the group environment, finding a marginally lower average SSFR in groups as compared to the field, especially at lower redshifts. The field-galaxy luminosity function in the B and R band as derived from the R-selected sample evolves out to z ~ 2 in the sense that the characteristic luminosity increases but the number density decreases. This effect is smaller at longer rest-frame wavelengths and gets more pronounced at shorter wavelengths. Parametrising the redshift evolution of the Schechter parameters as M*(z) = M*(0) + a ln(1+z) and Phi*(z) = Phi*(0) (1+z)^b we find evolutionary parameters a ~ -2.1 and b ~ -2.5 for the B band, and a ~ -1.4 and b ~ -1.8 for the R band.

Deviations from geodesic motion caused by gravitational radiation have been discussed in the last decades to describe the motion of particles or photons in strong fields around collapsed objects. On cosmological scale this effect, which in the first order is caused by the finite speed of gravitational interaction, is important also in the weak field limit. In this paper the energy loss by transfer to the gravitational potential is determined in a quasi-Newtonian approximation for the examples of a static Einstein universe and for an expanding universe with flat metric. In both cases the resulting red shift is a considerable fraction of the total red shift and requires an adjustment of the age and the matter composition in our models of the universe.

The uncertainty surrounding the nature of the heating mechanism for the dust that emits at mid- to far-IR (MFIR) wavelengths in active galaxies limits our understanding of the links between active galactic nuclei (AGN) and galaxy evolution, as well as our ability to interpret the prodigious infrared and sub-mm emission of some of the most distant galaxies in the Universe. Here we report deep Spitzer observations of a complete sample of powerful, intermediate redshift (0.05 < z < 0.7) radio galaxies and quasars. We show that AGN power, as traced by [OIII]5007 emission, is strongly correlated with both the mid-IR (24 micron) and the far-IR (70 micron) luminosities, however, with increased scatter in the 70 micron correlation. A major cause of this increased scatter is a group of objects that falls above the main correlation and displays evidence for prodigious recent star formation activity at optical wavelengths, along with relatively cool MFIR colours. These results provide evidence that illumination by the AGN is the primary heating mechanism for the dust emitting at both 24 and 70 microns, with starbursts dominating the heating of the cool dust in only 20 — 30% of objects. This implies that powerful AGN are not always accompanied by the type of luminous starbursts that are characteristic of the peak of activity in major gas-rich mergers.

Galaxy clusters are hotter and more X-ray luminous than in quiescence while they undergo major mergers, which also transiently increase their strong-lensing efficiency. We use semi-analytic models for both effects to study how cluster dynamics in different dark-energy models affects the X-ray selected cluster population and its strong-lensing optical depth. We find that mergers increase the number of observable X-ray clusters by factors of a few and considerably broaden their redshift distribution. Strong-lensing optical depths are increased by a very similar amount. Quite independent of cosmology, X-ray bright clusters above a flux limit of $10^{-13.5} \mathrm{erg s^{-1} cm^{-2}}$ produce $\sim60%$ of the strong-lensing optical depth, and only $\sim1%$ above a flux limit of $10^{-11.5} \mathrm{erg s^{-1} cm^{-2}}$ if mergers are taken into account.

We discuss high resolution VLT/UVES observations (FWHM ~ 6 km/s) from October 2002 (day ~5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (1.5-5.0)E3 cm-3 and temperatures of 6.5E3-2.4E4 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [Fe XIV]. From a nebular analysis we find that the density in the low ionization region is 4E6-1E7 cm-3. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [Fe X-XIV], with the latter extending up to ~ -390 km/s in the blue wing for [Fe XIV], while the low ionization lines extend to typically ~ -260 km/s. For H-alpha a faint extension up to ~ -450 km/s can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool down, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are ~ 510 km/s. We expect the maximum width of especially the low ionization lines to increase with time.

We present oxygen abundances of dwarfs in the young open cluster IC 4665 deduced from the OI $\lambda$7774 triplet lines and of dwarfs in the open cluster Pleiades derived from the [OI] $\lambda$6300 forbidden line. Stellar parameters and oxygen abundances were derived using the spectroscopic synthesis tool SME (Spectroscopy Made Easy). We find a dramatic increase in the upper boundary of the OI triplet abundances with decreasing temperature in the dwarfs of IC 4665, consistent with the trend found by Schuler et al. in the open clusters Pleiades and M 34, and to a less extent in the cool dwarfs of Hyades (Schuler et al. 2006a) and UMa (King & Schuler 2005). By contrast, oxygen abundances derived from the [OI] $\lambda$6300 forbidden line for stars in Pleiades and Hyades (Schuler et al. 2006b) are constant within the errors. Possible mechanisms that may lead a varying oxygen triplet line abundance are examined, including systematic errors in the stellar parameter determinations, the NLTE effects, surface activities and granulation. The age-related effects stellar surface activities (especially the chromospheric activities) are suggested by our analysis to blame for the large spreads of oxygen triplet line abundances.

At the end of July 2006, the blazar PKS 2155-304 (z=0.116) underwent a strong outburst observed at TeV energies by HESS (up to 17 Crab flux level at E > 200 GeV). The Swift satellite followed the evolution of the source for about one month. The data analysis – reported in another paper – has shown that, despite the violent activity at TeV energies, the synchrotron energy distribution increased in normalization, but only with a small shift in frequency. In the present work, we fit the broad-band spectrum with a log-parabolic model, to search for indications of intrinsic curvature, which in turn is usually interpreted as a signature of energy-dependent acceleration mechanisms of electrons.

Comets are classified from their orbital characteristics into two separate classes: nearly-isotropic, mainly long-period comets and ecliptic, short-period comets. Members from the former class are coming from the Oort cloud. Those of the latter class were first believed to have migrated from the Kuiper belt where they could have been accreted in situ, but recent orbital evolution simulations showed that they rather come from the trans-Neptunian scattered disc. These two reservoirs are not where the comets formed: they were expelled from the inner Solar System following interaction with the giant planets. If comets formed at different places in the Solar System, one would expect they show different chemical and physical properties. In the present paper, I review which differences are effectively observed: chemical and isotopic compositions, spin temperatures, dust particle properties, nucleus properties… and investigate whether these differences are correlated with the different dynamical classes. The difficulty of such a study is that long-period, nearly-isotropic comets from the Oort cloud are better known, from Earth-based observations, than the weak nearly-isotropic, short-period comets. On the other hand, only the latter are easily accessed by space missions.

A good candidate for a polar-ring galaxy has been detected in the Hubble Ultra Deep Field (HUDF). The galaxy HUDF 1619 (V~25 mag, z~1) is the most distant object of this type known to date. A large-scale structure crosses the highly warped disk of the main galaxy seen almost edge-on at an angle of about 70 grad. The luminosity of this structure (the possible polar ring) reaches \~1/3 of the luminosity of the central galaxy. A strong absorption lane is seen in the region where this structure is projected onto the disk of the central object. There are two galaxies of comparable luminosity adjacent to HUDF 1619 (in projection). One of them may be the donor galaxy in the interaction which gave rise to the ring structure.

It is now well accepted that both Dark Matter and Dark Energy are required in any successful cosmological model. Although there is ample evidence that both Dark components are necessary, the conventional theories make no prediction for the contributions from each of them. Moreover, there is usually no intrinsic relationship between the two components, and no understanding of the nature of the mysteries of the Dark Sector. Here we suggest that if the Dark Side is so seductive then we should not be restricted to just 2 components. We further suggest that the most natural model has 5 distinct forms of Dark Energy in addition to the usual Dark Matter, each contributing precisely equally to the cosmic energy density budget.

The magnetic fields and energy flows in an astronomical jet described by our earlier model are calculated in detail. Though the field distribution varies with the external pressure function p(z), it depends only weakly on the other boundary conditions. Individual fieldlines were plotted; the lines become nearly vertical at the bottom and are twisted at the top. An animation of a fieldline’s motion was made, which shows the line being wound up by the accretion disc’s differential rotation and rising as a result of this. The distribution of Poynting flux within the jet indicates that much of the energy flows up the jet from the inside of the accretion disc but a substantial fraction flows back down to the outside.

A near-Milne Universe produces a very red spectrum of vacuum quantum fluctuations, but has the potential to produce near-scale invariant {\it thermal} fluctuations. This happens if the energy and entropy are mildly sub-extensive, for example if there is a Casimir contribution. Therefore, one does not need to invoke corrections to Einstein gravity (as in loop quantum cosmology) for a thermal scenario to be viable. Neither do we need the energy to scale like the area, as in scenarios where the thermal fluctuations are subject to a phase transition in the early Universe. Some odd features of this model are pointed out: whether they are fatal or merely unusual should be the subject of future investigations.

Current observational bounds on dark energy depend on assumptions about the curvature of the universe. We present a simple and efficient method for incorporating constraints from CMB anisotropy data, and use it to derive constraints on cosmic curvature and dark energy density as a free function of cosmic time using current data. We show that there are two CMB shift parameters, R=sqrt{\Omega_m H_0^2} r(z_{CMB}) (scaled distance to recombination) and l_a=\pi r(z_{CMB})/r_s(z_{CMB})(angular scale of the sound horizon at recombination), with measured values that are nearly uncorrelated with each other. Allowing nonzero cosmic curvature, the three-year WMAP data give R =1.71 +/- 0.03, l_a =302.5 +/- 1.2, and \Omega_b h^2 = 0.02173 +/- 0.00082, independent of the dark energy model. The corresponding bounds for a flat universe are R =1.70 +/- 0.03, l_a =302.2 +/- 1.2, and \Omega_b h^2 = 0.022 +/- 0.00082. We give the covariance matrix of (R, l_a, \Omega_b h^2) from the three-year WMAP data. We find that (R, l_a, \Omega_b h^2) provide an efficient and intuitive summary of CMB data as far as dark energy constraints are concerned. Using current CMB, SN Ia, and BAO data, we find that dark energy density is consistent with a constant in cosmic time, with marginal deviations from a cosmological constant that may reflect current systematic uncertainties or true evolution in dark energy. A flat universe is allowed by current data: \Omega_k=-0.006_{-0.012}^{+0.013}_{-0.025}^{+0.025} for w_X(z)=const., and \Omega_k=-0.002_{-0.018}^{+0.018}_{-0.032}^{+0.041} for w_X(z)=w_0+w_a(1-a)(68% and 95% C.L.). The bounds on cosmic curvature are less stringent if dark energy density is allowed to be a free function of cosmic time, and are also dependent on the assumption about the early time property of dark energy.

(Abridged) Tests that have been proposed to differentiate among dark energy (DE) models are based on observations of galaxies at high redshift (z>0), to be obtained in the future. We suggest here a new test that is valid at z\simeq 0. It is based on existing observational data, numerical simulations, and three well known analytic models that evaluate the bias parameter b, the ratio of galaxy to dark matter (DM) fluctuations. These analytic models are based on the physical processes involved in the formation of stars and in the formation and merging of galaxies. The value of b(z) obtained in each model is a function of the DM growth factor D(z), which, in turn, is a function of the DE. We show that the equations for b in all three analytic models can be reduced to the form of a known constant plus the term E[D(z=0)/D(z)]^{\alpha}, where \alpha=1 or 2 and E is a free parameter. Using the value of b obtained by the 2dFGRS consortium for the \LambdaCDM model, to normalize E, we find that all three analytic models predict b^2(0)=1\pm 0.1 for all DE models. Numerical simulations that evaluated b^2(0) for the \LambdaCDM and CDM (\Lambda=0) models also obtained b^2(0)=1\pm 0.1. Since this value of b^2(0) is indicated by numerical simulations as well as by all three popular analytic models, which are normalized by the 2dFGRS consortium result for the \LambdaCDM model, we suggest the condition that b^2(0)=1\pm 0.1 at z=0 as a new test for the viability of dark energy models. Thus, for a given observed galaxy fluctuation spectrum such as that of the 2dFGRS consortium, if the DM fluctuations are greater or less than the galaxy fluctuations by more than 10%, the DE model can be discarded.

I discuss the prospects for detecting the dark matter via the proper motion of sub-solar mass dark matter halos in the vicinity of the solar neighbourhood. Microhalos that survive tidal disruption could exhibit proper motion of order few arcminutes per year. For dark matter particles that couple to photons, such as the lightest supersymmetric or Kaluza-Klein particles, microhalos could be detected via their Gamma-ray photon emission from annihilations. A detection of proper motion of a microhalo in the Gamma-ray part of the spectrum contains not only information about the particle physics properties of the dark matter particle, but also provides an insight into hierarchical structure formation at very early times.

We present an independent estimate of the interstellar extinction law for the Spitzer IRAC bands as well as a first attempt at extending the law to the 24micron MIPS band. The source data for these measurements are observations of five nearby star-forming regions: the Orion A cloud, NGC 2068/71, NGC 2024/23, Serpens and Ophiuchus. Color excess ratios E(H-Ks)/E(Ks-[lambda]) were measured for stars without infrared excess dust emission from circumstellar disks/envelopes. For four of these five regions, the extinction laws are similar at all wavelengths and differ systematically from a previous determination of the extinction law, which was dominated by the diffuse ISM, derived for the IRAC bands. This difference could be due to the difference in the dust properties of the dense molecular clouds observed here and those of the diffuse ISM. The extinction law at longer wavelengths toward the Ophiuchus region lies between that to the other four regions studied here and that for the ISM. In addition, we extended our extinction law determination to 24micron for Serpens and NGC 2068/71 using Spitzer MIPS data. We compare these results against several ISO extinction law determinations, although in each case there are assumptions which make absolute comparison uncertain. However, our work confirms a relatively flatter extinction curve from 4 – 8micron than the previously assumed standard, as noted by all of these recent studies. The extinction law at 24micron is consistent with previous measurements and models, although there are relatively large uncertainties.

We study the flavor evolution of a dense gas initially consisting of pure mono-energetic $\nu_e$ and $\bar\nu_e$. Using adiabatic invariants and the special symmetry in such a system we are able to calculate the flavor evolution of the neutrino gas for the cases with slowly decreasing neutrino number densities. These calculations give new insights into the results of recent large-scale numerical simulations of neutrino flavor transformation in supernovae. For example, our calculations reveal the existence of what we term the “collective precession mode”. Our analyses suggest that neutrinos which travel on intersecting trajectories subject to destructive quantum interference nevertheless can be in this mode. This mode can result in sharp transitions in the final energy-dependent neutrino survival probabilities across all trajectories, a feature seen in the numerical simulations. Moreover, this transition is qualitatively different for the normal and inverted neutrino mass hierarchies. Exploiting this difference, the neutrino signals from a future galactic supernova can potentially be used to determine the actual neutrino mass hierarchy.

It is argued that holographic bounds on the information content of spacetime might be directly measurable. A new uncertainty principle is conjectured to arise from quantum indeterminacy of nearly flat spacetime: Angular orientations of null trajectories of spatial length L are uncertain, with standard deviation in each transverse direction \Delta \theta> \sqrt{l_P/L}, where l_p denotes the Planck length. It is shown that this angular uncertainty corresponds to the information loss and nonlocality that occur if 3+1-D spacetime has a holographic dual description in terms of Planck-scale waves on a 2+1D screen with encoding close to the Planck diffraction limit, and agrees with covariant holographic entropy bounds on total number of degrees of freedom. The spectrum and spatial structure of predicted quantum-gravitational “holographic noise” are estimated to be directly measurable over a broad range of frequencies using interferometers with current technology.

Astronomical observations have shown that the expansion of the universe is at present accelerating, in a way consistent with the presence of a positive cosmological constant. This is a major puzzle, because we do not understand: why the cosmological constant is so small; why, being so small, it is not exactly zero; and why it has precisely the value it must have to make the expansion start accelerating just at the epoch when we are observing the universe. We present a new model of cosmology, which we call the stryngbohtyk model, that solves all these problems and predicts exactly the value that the cosmological constant must have. The predicted value agrees with the observed one within the measurement error. We show that in the stryngbohtyk model, the fact the cosmological constant starts being important at the present epoch is not a coincidence at all, but a necessity implied by our origin in a planet orbiting a star that formed when the age of the universe was of the same order as the lifetime of the star.

We investigate the physical conditions for the growth of intermediate mass seed black holes assumed to have formed from remnants of the first generation of massive stars. We follow the collapse of high-sigma halos with Tvir > 1e4 K using cosmological, smooth-particle hydrodynamic (SPH) simulations in the standard LCDM model. During collapse of the parent halo the seed holes are incorporated through mergers into larger systems and accrete mass from the surrounding gas. We include a self-consistent treatment of star formation, black hole accretion and associated feedback processes. Even under optimistic assumptions for the seed black hole mass and for efficient merger rates, we find that seed holes in halos M<1e10 Msun never reach the conditions for critical Eddington growth. Most of the black hole growth in this regime is determined by the initial mass and the merger rates. Critical accretion rates are reached, albeit only after a significant delay, at the time of collapse z~7) for 3-4 sigma halos of M~1e11 Msun. Our results imply M_BH = 5e6 Msun (M_halo/1e11 Msun)^0.78 at the time of collapse. The required conditions of Eddington growth to explain the build-up of supermassive black holes (~1e9 Msun), as implied by Sloan quasars at z>6, are therefore hard to meet in such a scenario. Without a ‘jump-start’ these conditions may be only achieved in extremely rare halos with M_halo > 1e13 Msun that collapsed before z~6. The sub-Eddington regime in which black holes holes accrete at early time implies a small contribution to the reionization by miniquasar but still sufficient to cause appreciable heating of the IGM at z<15-18.

We summarize our model for long-duration gamma ray bursts (GRBs) that fits the redshift (z) distributions measured with Swift and missions before Swift, and the pre-Swift GRB jet opening-angle distribution inferred from achromatic breaks in the optical light curves. We find that the comoving rate density of GRB sources exhibits positive evolution to $z \gtrsim 3$ — 5, whereas the star formation rate inferred from measurements of the blue and UV luminosity density peaks at $z\sim 1$ — 3. The mean intrinsic beaming factor of GRBs is found to be $\approx 34$ — 42, and we predict that the mean GRB optical jet opening half-angle measured with Swift is $\approx 10^\circ$. We estimate the number of GRBs per year that GLAST is expected to observe based on ratios of BATSE and EGRET GRB fluences.

Using a reionization model simultaneously accounting for a number of experimental data sets, we investigate the nature and properties of reionization sources. Such model predicts that hydrogen reionization starts at z \approx 15, is initially driven by metal-free (PopIII) stars, and is 90% complete by z \approx 8. We find that a fraction f_\gamma >80% of the ionizing power at z > 7 comes from haloes of mass M<10^9 M_sun predominantly harbouring PopIII stars; a turnover to a PopII-dominated phase occurs shortly after, with this population, residing in M>10^9 M_sun haloes, yielding f_\gamma \approx 60% at z=6. Using Lyman-break broadband dropout techniques, J-band detection of sources contributing to 50% (90%) of the ionizing power at z \sim 7.5 requires to reach a magnitude J_{110,AB} = 31.2 (31.7), where about 15 (30) (PopIII) sources/arcmin^2 are predicted. We conclude that z>7 sources tentatively identified in broadband surveys are relatively massive (M \approx 10^9 M_sun) and rare objects which are only marginally (\approx 1%) adding to the reionization photon budget.

The Coma cluster is the richest and most compact of the nearby clusters, yet there is growing evidence that its formation is still on-going. With a new multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru telescope and FOCAS, we have detected and measured the line-of-sight velocities of 37 intracluster planetary nebulae associated with the diffuse stellar population of stars in the Coma cluster core, at 100 Mpc distance. We detect clear velocity substructures within a 6 arcmin diameter field. A substructure is present at ~5000 km/s, probably from in-fall of a galaxy group, while the main intracluster stellar component is centered around ~6500 km/s, ~700 km/s offset from the nearby cD galaxy NGC 4874. The kinematics and morphology of the intracluster stars show that the cluster core is in a highly dynamically evolving state. In combination with galaxy redshift and X-ray data this argues strongly that the cluster is currently in the midst of a subcluster merger, where the NGC 4874 subcluster core may still be self-bound, while the NGC 4889 subcluster core has probably dissolved. The NGC 4889 subcluster is likely to have fallen into Coma from the eastern A2199 filament, in a direction nearly in the plane of the sky, meeting the NGC 4874 subcluster arriving from the west. The two inner subcluster cores are presently beyond their first and second close passage, during which the elongated distribution of diffuse light has been created. We predict the kinematic signature expected in this scenario, and argue that the extended western X-ray arc recently discovered traces the arc shock generated by the collision between the two subcluster gas halos. Any preexisting cooling core region would have been heated by the subcluster collision.

We present a catalog of 110 variable stars within ~1′ of Sgr A* based on image subtraction of near-infrared (H and K) photometry. Our images were obtained over 133 nights from 2000–2002 in H-band and over 134 nights from 2001–2002 in K-band; the typical FWHM is 1.4”. We match the catalog to other near-infrared, X-ray, and radio (i.e., maser) data, and we discuss some of the more interesting objects. The catalog includes 14 periodic sources, several known long-period variables and three new LPV candidates. We associate IRS 10* with OH, SiO, and H2O masers and a bright X-ray point source; this analysis suggests IRS 10* is an AGB star with an accreting companion. Among the approximately 90 newly discovered sources are a probable cataclysmic variable, a potential edge-on contact 84 day period eclipsing binary, and a possible 41 day period pulsating variable.

A simple algorithm is employed to deproject the two dimensional images of a pilot sample of 12 high-quality images of edge-on disk galaxies and to study their intrinsic 3 dimensional stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dustlane. This could be explained by the widespread presence of a thick disk component in these galaxies. In addition, the 3 dimensional view allows the study of the vertical distribution of the outer disk, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated disks. This could be regarded as a weakening of the "truncation" with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies.

Accurate photometry with HST/ACS shows that the main sequence of the globular cluster NGC 2808 splits into three separate branches. The three MS branches may be associated with complexities of the cluster’s horizontal branch and of its abundance distribution. We attribute the MS branches to successive rounds of star formation, with different helium abundances; we discuss possible sources of helium enrichment. Some other massive globulars also appear to have complex populations; we compare them with NGC 2808.

We use nearby K dwarf stars to measure the helium-to-metal enrichment ratio, a diagnostic of the chemical history of the Solar Neighbourhood. Our sample of K dwarfs has homogeneously determined effective temperatures, bolometric luminosities and metallicities, allowing us to fit each star to the appropriate stellar isochrone and determine its helium content indirectly. We use a newly computed set of Padova isochrones which cover a wide range of helium and metal content. Our theoretical isochrones have been checked against a congruous set of main sequence binaries with accurately measured masses, to discuss and validate their range of applicability. We find that the stellar masses deduced from the isochrones are usually in excellent agreement with empirical measurements. Good agreement is also found with empirical mass-luminosity relations. Despite fitting the masses of the stars very well, we find that anomalously low helium content (lower than primordial helium) is required to fit the luminosities and temperatures of the metal poor K dwarfs, while more conventional values of the helium content are derived for the stars around solar metallicity. We have investigated the effect of diffusion in stellar models and LTE assumption in deriving metallicities. Neither of these is able to resolve the low helium problem alone and only marginally if the cumulated effects are included, unless we assume a mixing-length which is strongly decreasing with metallicity. Further work in stellar models is urgently needed. The helium-to-metal enrichment ratio is found to be Delta Y / Delta Z = 2.1 +/- 0.9 around and above solar metallicity, consistent with previous studies, whereas open problems still remain at the lowest metallicities. Finally, we determine the helium content for a set of planetary host stars.

We present results on the X-ray and optical/UV emission from the type IIP SN 2006bp and the interaction of the SN shock with its environment, obtained with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on-board the Swift observatory. SN 2006bp is detected in X-rays at a 4.5 sigma level of significance in the merged XRT data from days 1 to 12 after the explosion. If the X-ray luminosity of (1.8+/-0.4)E39 ergs/s is caused by interaction of the SN shock with circumstellar material (CSM), deposited by a stellar wind from the progenitor’s companion star, a mass-loss rate of ~E-05 M_sun/yr is inferred. The mass-loss rate is consistent with the non-detection in the radio with the VLA on days 2, 9, and 11 after the explosion and characteristic of a red supergiant progenitor with a mass around 12-15 M_sun prior to the explosion. In combination with a follow-up XMM-Newton observation obtained on day 21 after the explosion, an X-ray rate of decline with index 1.2+/-0.6 is inferred. Since no other SN has been detected in X-rays prior to the optical peak and since type IIP SNe have an extended ‘plateau’ phase in the optical, we discuss the scenario that the X-rays might be due to inverse Compton scattering of photospheric optical photons off relativistic electrons produced in circumstellar shocks. However, due to the high required value of the Lorentz factor (~10-100) we conclude that Inverse Compton scattering is an unlikely explanation for the observed X-ray emission. The fast evolution of the optical/ultraviolet spectral energy distribution and the spectral changes observed with Swift reveal the onset of metal line-blanketing and cooling of the expanding photosphere during the first few weeks after the outburst.

Motivated by recent models involving off-centre ignition of type Ia supernova explosions, we undertake three-dimensional time-dependent radiation transport simulations to investigate the range of bolometric light curve properties that could be observed from supernovae in which there is a lop-sided distribution of the products from nuclear burning. We consider both a grid of artificial toy models which illustrate the conceivable range of effects and a recent three-dimensional hydrodynamical explosion model. We find that observationally significant viewing angle effects are likely to arise in such supernovae and that these may have important ramifications for the interpretation of the observed diversity of type Ia supernova and the systematic uncertainties which relate to their use as standard candles in contemporary cosmology.

We investigated the low state of the polar VV Pup by collecting high S/N time series spectra. We monitored VV Pup with VLT+FORS1 and analyzed the evolution of its spectroscopic features across two orbits. We report the first detection of photospheric Zeeman lines in VV Puppis. We argue that the photospheric field structure is inconsistent with the assumption that the accretion shocks are located close to the foot points of a closed field line in a dipolar field distribution. A more complex field structure and coupling process is implied making VV Puppis similar to other well studied AM Herculis type systems.

In the slow-roll inflationary scenario, the amplitude of the curvature perturbations approaches a constant value soon after the modes leave the Hubble radius. However, relatively recently, it was shown that the amplitude of the curvature perturbations induced by the canonical scalar field can grow at super-Hubble scales if there is either a transition to fast roll inflation or if inflation is interrupted for some period of time. In this work, we extend the earlier analysis to the case of a non-canonical scalar field described by the Dirac-Born-Infeld action. With the help of a specific example, we show that the amplitude of the tachyonic perturbations can be enhanced or suppressed at super-Hubble scales if there is a transition from slow roll to fast roll inflation. We also illustrate as to how the growth of the entropy perturbations during the fast roll regime proves to be responsible for the change in the amplitude of the curvature perturbations at super-Hubble scales. Furthermore, following the earlier analysis for the canonical scalar field, we show that the power spectrum evaluated in the long wavelength approximation matches the exact power spectrum obtained numerically very well. Finally, we briefly comment on an application of this phenomenon.

We trace the star formation regions in the SMC and study their properties. The size and spatial distribution of these regions is found to support the hierarchical scenario of star formation, whereas, the evaluation of their intensity, contributes to the understanding of the various stages of star formation. Their connection to the LMC-SMC close encounter, about $(0.9-2) \times 10^{8}$ years ago, is investigated as well. The SMC, being almost edge-on, does not easily reveal these areas, as is the case with the LMC. However, a study through multi-wavelength images such as optical, IR and radio has been proved very useful. A selection of areas, with enhanced 60 and 100-$\mu$m infrared flux and emission in all IRAS bands, identifies the star forming regions. All of the identified regions are dominated by early-type stars and considering their overall size (increasing order) a total of 24 aggregates, 23 complexes, and 3 super-complexes were found. We present their coordinates, dimensions, and IR fluxes. Moreover, we correlate their positions with known associations, SNRs, and \hii regions and discuss their activity.

Despite the many studies on stellar nucleosynthesis published so far, the scenario for the production of Cu in stars remains elusive. In particular, it is still debated whether copper originates mostly in massive stars or type Ia supernovae. To answer this question, we compute self-consistent chemical evolution models taking into account the results of updated stellar nucleosynthesis. By contrasting copper evolution in Omega Cen and the Milky Way, we end up with a picture where massive stars are the major responsible for the production of Cu in Omega Cen as well as the Galactic disc.

Regenerated high-energy emissions from gamma-ray bursts (GRBs) are studied in detail. If the intrinsic primary spectrum extends to the TeV range, these very high-energy photons are absorbed by the cosmic infrared background (CIB). Created high-energy electron-positron pairs up-scatter mainly cosmic microwave background (CMB) photons, and secondary photons are generated in the GeV-TeV range. These secondary delayed photons may be observed in the near future, which are useful for a consistency check of the intrinsic primary spectrum. In this paper, we focus on effects of the CIB on delayed secondary emissions. In particular, we show that not only up-scattered CMB photons but also up-scattered CIB ones are important, especially for low redshift bursts. They also give us additional information on the CIB, whose photon density is not definitely determined so far.

We present a detailed analysis of a large spectroscopic and photometric sample of DZ white dwarfs based on our latest model atmosphere calculations. We revise the atmospheric parameters of the trigonometric parallax sample of Bergeron, Leggett, & Ruiz (12 stars) and analyze 147 new DZ white dwarfs discovered in the Sloan Digital Sky Survey. The inclusion of metals and hydrogen in our model atmosphere calculations leads to different atmospheric parameters than those derived from pure helium models. Calcium abundances are found in the range from log (Ca/He) = -12 to -8. We also find that fits of the coolest objects show peculiarities, suggesting that our physical models may not correctly describe the conditions of high atmospheric pressure encountered in the coolest DZ stars. We find that the mean mass of the 11 DZ stars with trigonometric parallaxes, <M> = 0.63 Mo, is significantly lower than that obtained from pure helium models, <M> = 0.78 Mo, and in much better agreement with the mean mass of other types of white dwarfs. We determine hydrogen abundances for 27% of the DZ stars in our sample, while only upper limits are obtained for objects with low signal-to-noise ratio spectroscopic data. We confirm with a high level of confidence that the accretion rate of hydrogen is at least two orders of magnitude smaller than that of metals (and up to five in some cases) to be compatible with the observations. We find a correlation between the hydrogen abundance and the effective temperature, suggesting for the first time empirical evidence of a lower temperature boundary for the hydrogen screening mechanism. Finally, we speculate on the possibility that the DZA white dwarfs could be the result of the convective mixing of thin hydrogen-rich atmospheres with the underlying helium convection zone.

The existence of a population of wandering Intermediate Mass Black Holes (IMBHs) is a generic prediction of scenarios that seek to explain the formation of Supermassive Black Holes in terms of growth from massive seeds. The growth of IMBHs may lead to the formation of DM overdensities called "mini-spikes", recently proposed as ideal targets for indirect DM searches. Current ground-based gamma-ray experiments, however, cannot search for these objects due to their limited field of view, and it might be challenging to discriminate mini-spikes in the Milky Way from the many astrophysical sources that GLAST is expected to observe. We show here that gamma-ray experiments can effectively search for IMBHs in the nearby Andromeda galaxy (also known as M31), where mini-spikes would appear as a distribution of point-sources, isotropically distributed in a \thickapprox 3^{\circ} circle around the galactic center. For a neutralino-like DM candidate with a mass m_{\chi}=150 GeV, up to 20 sources would be detected with GLAST (at 5\sigma, in 2 months). With Air Cherenkov Telescopes such as MAGIC and VERITAS, up to 10 sources might be detected, provided that the mass of neutralino is in the TeV range or above.

With the development of new instrumentation providing measurements of solar photospheric vector magnetic fields, we need to develop our understanding of the effects of current density on coronal magnetic field configurations. The object is to understand the diverse and complex nature of coronal magnetic fields in active regions using a nonlinear force-free model. From the observed photospheric magnetic field we derive the photospheric current density for two active regions: one is a decaying active region with strong currents (AR8151), and the other is a newly emerged active region with weak currents (AR8210). We compare the three-dimensional structure of the magnetic fields for both active region when they are assumed to be either potential or nonlinear force-free. The latter is computed using a Grad-Rubin vector-potential-like numerical scheme. A quantitative comparison is performed in terms of the geometry, the connectivity of field lines, the magnetic energy and the magnetic helicity content. For the old decaying active region the connectivity and geometry of the nonlinear force-free model include strong twist and strong shear and are very different from the potential model. The twisted flux bundles store magnetic energy and magnetic helicity high in the corona (about 50 Mm). The newly emerged active region has a complex topology and the departure from a potential field is small, but the excess magnetic energy is stored in the low corona and is enough to trigger powerful flares.

We explore the possibility that large-scale convection be inhibited over some regions of giant planet interiors, as a consequence of a gradient of composition inherited either from their formation history or from particular events like giant impacts or core erosion during their evolution. Under appropriate circumstances, the redistribution of the gradient of molecular weight can lead to double diffusive layered or overstable convection. This leads to much less efficient heat transport and compositional mixing than large-scale adiabatic convection. We show that this process can explain the abnormally large radius of the transit planet HD209458b and similar objects, and may be at play in some giant planets, with short-period planets offering the most favorable conditions. Observational signatures of this transport mechanism are a large radius and a reduced heat flux output compared with uniformly mixed objects. If our suggestion is correct, it bears major consequences on our understanding of giant planet formation, structure and evolution, including possibly our own jovian planets.

The frequency of planets in binaries is an important issue in the field of extrasolar planet studies, because of its relevance in estimating of the global planet population of our Galaxy and the clues it can give to our understanding of planet formation and evolution. However, only preliminary estimates are available in the literature. We analyze and compare the frequency of planets in multiple systems to the frequency of planets orbiting single stars. We also try to highlight possible connections between the frequency of planets and the orbital parameters of the binaries (such as the periastron and mass ratio.) A literature search was performed for binaries and multiple systems among the stars of the sample with uniform planet detectability defined by Fischer & Valenti (2005), and 202 of the 850 stars of the sample turned out to be binaries, allowing a statistical comparison of the frequency of planets in binaries and single stars and a study of the run of the planet frequency as a function of the binary separation. We found that the global frequency of planets in the binaries of the sample is not statistically different from that of planets in single stars. Even conservatively taking the probable incompleteness of binary detection in our sample into account, we estimate that the frequency of planets in binaries can be no more than a factor of three lower than that of planets in single stars. There is no significant dependence of planet frequency on the binary separation, except for a lower value of frequency for close binaries. However, this is probably not as low as required to explain the presence of planets in close binaries only as the result of modifications of the binary orbit after the planet formation.

In this article we present the O-C diagram of the hot subdwarf B pulsating star HS2201+2610 after seven years of observations. A secular increase of the main pulsation period, Pdot=(1.3+-0.1)x10**(-12), is inferred from the data. Moreover, a further sinusoidal pattern suggests the presence of a low-mass companion (Msini=~3.5 Mjup), orbiting the hot star at a distance of about 1.7 AU with a period near 1140 days.

We present images of quasi-simultaneous VLBI observations of the GHz-Peaked-Spectrum radio source OQ 208 with the Very Long Baseline Array at 1.4, 1.7, 2.3, 5.0, 8.4, 15.4 GHz and the European VLBI Network at 6.7 GHz. The low frequency (1.4, 1.7 and 2.3 GHz) observations reveal a weak and extended steep-spectrum component at about 30 mas away in the position angle of $- 110^\circ$ which may be a remnant emission. The radio structure of OQ 208 consists of two mini-lobes at 5.0, 6.7, 8.4 and 15.4 GHz. Our spectral analysis further confirms that the southwest lobe undergoes free-free absorption and finds that the free-free absorption is stronger in the inner region. By fitting the 8.4 GHz images from 1994 to 2005, we obtain a separation speed of 0.031 $\pm$ 0.006 mas yr$^{-1}$ between the two mini-lobes. This indicates a jet proper motion of 0.105 $\pm$ 0.020 $c$ and a kinematic age of 219 $\pm$ 42 yr for the radio source.

The various requirements on a consistent varying speed of light (`VSL’) theory are surveyed, giving a short check-list of issues that should be satisfactorily handled by such theories.

We present the preliminary results of a Chandra X-ray study of N132D, a young shell-like supernova remnant (SNR) in the Large Magellanic Cloud. The equivalent width maps of emissions from O, Ne, Mg, Si, and S are provided. Spatially resolved spectral analysis for the small-scale regions were tentatively performed. The X-ray spectra of the interior can be described with a single-thermal model. The faint interior regions have lower density and higher temperature (above 1keV) than those of bright interior regions. The X-ray spectra along the shell can be phenomenally fitted with either a double-vpshock model or a vpshock + powerlaw model. If the non-thermal component is true, N132D would be listed as another X-ray synchrotron SNR.

Using Chandra X-ray, Spitzer mid-IR, and 1.5 GHz radio data, we examine the spatial structure of SNR 3C391. The X-ray surface brightness is generally anti-correlative with the IR and radio brightness. The multiband data clearly exhibit a heart-shaped morphology and show the multi-shell structure of the remnant. A thin brace-like shell on the south detected at 24 um is projected outside the radio border and confines the southern faint X-ray emission. The leading 24 um knot on the SE boundary appears to be partly surrounded by soft X-ray emitting gas. The mid-IR emission is dominated by the contribution of the shocked dust grains, which may have been partly destroyed by sputtering.

Elliptical galaxies are modelled as homeoidally striated Jacobi ellipsoids where the peculiar velocity distribution is anisotropic, or equivalently as their adjoints configurations i.e. classical Jacobi ellipsoids of equal mass and axes, in real or imaginary rotation. Reasons for the coincidence of bifurcation points from axisymmetric to triaxial configurations in both the sequences, contrary to earlier findings, are presented and discussed. The effect of centrifugal support at the ends of the major equatorial axis, is briefly outlined. The existence of a lower limit to the flattening of elliptical galaxies is investigated in dealing with a number of limiting situations. More specifically, (i) elliptical galaxies are considered as isolated systems, and an allowed region within Ellipsoidland, related to the occurrence of bifurcation points from ellipsoidal to pear-shaped configurations, is shown to be consistent with observations; (ii) elliptical galaxies are considered as embedded within dark matter haloes and, under reasonable assumptions, it is shown that tidal effects from hosting haloes have little influence on the above mentioned results; (iii) dark matter haloes and embedded elliptical galaxies, idealized as a single homeoidally striated Jacobi ellipsoid, are considered in connection with the cosmological transition from expansion to relaxation, by generalizing an earlier model, and the existence of a lower limit to the flattening of relaxed (oblate-like) configurations, is established. On the other hand, no lower limit is found to the elongation of relaxed (prolate-like) configurations, and the observed lack of elliptical galaxies more elongated than E7 needs a different physical interpretation, such as the fully investigated bending instabilities.

We have observed oscillations in the nearby G2 subgiant star beta Hyi using high-precision velocity observations obtained over more than a week with the HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb structure, as expected for solar-like oscillations, but with several l=1 modes being strongly affected by avoided crossings. The data, combined with those we obtained five years earlier, allow us to identify 28 oscillation modes. By scaling the large frequency separation from the Sun, we measure the mean density of beta Hyi to an accuracy of 0.6%. The amplitudes of the oscillations are about 2.5 times solar and the mode lifetime is 2.3 d. A detailed comparison of the mixed l=1 modes with theoretical models should allow a precise estimate of the age of the star.

In this short contribution we consider what types of surveys might be optimally pursued with path-finding instruments of 1%, 10% and finally 100% of the projected SKA sensitivity from the perspective of scientific applications that utilize the red-shifted 21 cm emission line. Achieving interesting HI galaxy sample sizes with 1% SKA surveys requires very substantial survey durations, of about 1000 days. Good sampling (log(N)~5) down to below M_HI* can then be achieved out to z=0.2 over 8000 deg^2 of survey area or even to z=0.5 over 800 deg^2. The same surveys will permit the resolved imaging of order 1000 galaxies in each of several red-shift bins as well as detection of faint neutral filaments in the vicinity of galaxies with a column density of about 10^18 cm^-2. Once 10% SKA sensitivities are achieved, then ground-breaking surveys are possible with only 100 day duration. Sample sizes of log(N)~6 extending below M_HI* are possible over 800 deg^2 out to z=0.5 and over 80 deg^2 out to z=1. Such surveys will permit very competitive measurement of acoustic oscillations in the galaxy power spectrum. One can then envision a series of 10% SKA surveys probing different depths. With the 100% SKA sensitivity the capabilities are truly phenomenal. Survey sample sizes in the range log(N)=7-8 are feasible over the red-shift range of 0.2 to about 5. Precise tracking of potential time evolution of dark energy (via the baryonic acoustic oscillation signature) should be possible out to z~3. The local cosmic web will be imaged down to N_HI=10^16 cm^-2. What exactly will be seen at z > 3 ? This will depend crucially on the SKA sensitivity in the critical frequency window of 350 to 200 MHz.

We investigate the plasma dynamics (outflow speed and turbulence) inside polar plumes. We compare line profiles (mainly of \ion{O}{6}) observed by the UVCS instrument on SOHO at the minimum of solar cycle 22-23 with model calculations. We consider Maxwellian velocity distributions with different widths in plume and inter-plume regions. Electron densities are assumed to be enhanced in plumes and to approach inter-plume values with increasing height. Different combinations of the outflow and turbulence velocity in the plume regions are considered. We compute line profiles and total intensities of the \ion{H}{1} Ly$\alpha$ and the \ion{O}{6} doublets. The observed profile shapes and intensities are reproduced best by a small solar wind speed at low altitudes in plumes that increases with height to reach ambient inter-plume values above roughly 3-4 $R_\sun$ combined with a similar variation of the width of the velocity distribution of the scattering atoms/ions. We also find that plumes very close to the pole give narrow profiles at heights above 2.5 $R_\sun$, which are not observed. This suggests a tendency for plumes to be located away from the pole. We find that the inclusion of plumes in the model computations provides an improved correspondence with the observations and confirms previous results showing that published UVCS observations in polar coronal holes can be roughly reproduced without the need for large temperature anisotropy. The latitude distributions of plumes and magnetic flux distributions are studied by analyzing data from different instruments on SOHO and with SOLIS.

We discuss the general framework for a perfect continuum medium in cosmology and show that an interesting generalization of the fluids normally used is for the medium to have rigidity and, hence, be analogous to an elastic solid. Such models can provide perfect, adiabatic fluids which are stable even when the pressure is negative, if the rigidity is sufficiently large, making them natural candidates to describe the dark energy. In fact, if the medium is adiabatic and isotropic, they provide the most general description of linearized perturbations. We derive the equations of motion and wave propagation speeds in the isotropic case. We point out that anisotropic models can also be incorporated within the same formalism and that they are classified by the standard Bravais Lattices. We identify the adiabatic and isocurvature modes allowed in both the scalar and vector sectors and discuss the predictions they make for CMB and matter power spectra. We comment on the relationship between these models and other fluid-based approaches to dark energy, and discuss a possible microphysical manifestation of this class of models as a continuum description of defect-dominated scenarios.

We present a catalog of spectro-photometric redshifts for 1308 galaxies from the GRism ACS Program for Extragalactic Science (GRAPES) observations with the Hubble Space Telescope. These low-resolution spectra between 6000 A and 9500 A are supplemented with U, J, H, and Ks from various facilities, resulting in redshifts computed with ~40 spectral bins per galaxy. For 81 galaxies between 0.5<z<1.5 with spectroscopic redshifts, the standard deviation in the fractional error in (1+z) is 0.046. With this catalog, we compute the B-band luminosity function in this redshift range from 72 galaxies. Owing to the depth of the GRAPES survey, we are able to accurately constrain the faint-end slope by going to M_B~-18 mag at 0.8<z<1.2, nearly two magnitudes fainter than previous studies. The faint-end slope is alpha=-1.32+-0.07. When compared to numerous published values at various redshifts, we find strong evidence for a steepening of the faint-end slope with redshift which is expected in the hierarchical formation scenario of galaxies.

Astrophysical relativistic flow problems require high resolution three-dimensional numerical simulations. In this paper, we describe a new parallel three-dimensional code for simulations of special relativistic hydrodynamics (SRHD) using both spatially and temporally structured adaptive mesh refinement (AMR). We used the method of lines to discretize the SRHD equations spatially and a total variation diminishing (TVD) Runge-Kutta scheme for time integration. For spatial reconstruction, we have implemented piecewise linear method (PLM), piecewise parabolic method (PPM), third order convex essentially non-oscillatory (CENO) and third and fifth order weighted essentially non-oscillatory (WENO) schemes. Flux is computed using either direct flux reconstruction or approximate Riemann solvers including HLL, modified Marquina flux, local Lax-Friedrichs flux formulas and HLLC. The AMR part of the code is built on top of the cosmological Eulerian AMR code {\sl enzo}. We discuss the coupling of the AMR framework with the relativistic solvers. Via various test problems, we emphasize the importance of resolution studies in relativistic flow simulations because extremely high resolution is required especially when shear flows are present in the problem. We also present the results of two 3d simulations of astrophysical jets: AGN jets and GRB jets. Resolution study of those two cases further highlights the need of high resolutions to calculate accurately relativistic flow problems.

We study the importance of baryonic physics on predictions of the matter power spectrum as it is relevant for forthcoming weak lensing surveys. We quantify the impact of baryonic physics using a set of three cosmological numerical simulations. Each simulation has the same initial density field, but models a different set of physical processes. The first simulation evolves the density field using gravity alone, the second includes non-radiative gasdynamics, and the third includes radiative heating and cooling of baryons, star formation, and supernova feedback. We find that baryonic processes alter predictions for the matter power spectrum significantly relative to models that include only gravitational interactions. Our results imply that future weak lensing experiments such as LSST and SNAP will be very sensitive to the poorly-understood physics governing the nonlinear evolution of the baryonic component of the universe. The net effect is significantly larger in the case of the model with cooling and star formation, in which case our results imply that contemporary surveys such as the CFHT Wide survey may also be sensitive to baryonic processes. In particular, this effect could be important for forecasts of the constraining power of future surveys if information from scales larger than l ~ 1000 is included in the analysis. We find that deviations are caused primarily by the rearrangement of matter within individual dark matter halos relative to the gravity-only case, rather than a large-scale rearrangement of matter. Consequently, we propose a simple model, based on the phenomenological halo model of dark matter clustering, for baryonic effects that can be used to aid in the interpretation of forthcoming weak lensing data.

Cosmic reionization progresses as HII regions form around sources of ionizing radiation. Their average size grows continuously until they percolate and complete reionization. We demonstrate how this typical growth can be calculated around the largest, biased sources of UV emission, such as quasars, by further developing an analytical model based on the excursion set formalism. This approach allows us to calculate the sizes and growth of the HII regions created by the progenitors of any dark matter halo of given mass and redshift with a minimum of free parameters. Statistical variations in the size of these pre-existing HII regions are an additional source of uncertainty in the determination of very high redshift quasar properties from their observed HII region sizes. We use this model to demonstrate that the transmission gaps seen in very high redshift quasars can be understood from the radiation of only their progenitors and associated clustered small galaxies. The fit sets a lower limit on the redshift of overlap at z = 5.8 +/- 0.1. This interpretation makes the transmission gaps independent of the age of the quasars observed. If this interpretation were correct it would raise the prospects of using radio interferometers currently under construction to detect the epoch of reionization.

The general relativistic cosmological Friedmann equations which describe how the scale factor of the universe evolves are expanded explicitly to include energy forms not usually seen. The evolution of the universe as predicted by the Friedmann equations when dominated by a single, isotropic, stable, static, perfect-fluid energy form is discussed for different values of its gravitational pressure to density ratio $w$. These energy forms include phantom energy ($w<-1$), cosmological constant ($w=-1$), domain walls ($w = -2/3$), cosmic strings ($w = -1/3$), normal matter ($w = 0$), radiation and relativistic matter ($w = 1/3$), and a previously little-discussed form of energy called "ultralight" ($w>1/3$). A brief history and possible futures of Friedmann universes dominated by a single energy form are discussed.

We describe a statistical reconstruction methodology for the GLAST LAT. The methodology incorporates in detail the statistics of the interactions of photons and charged particles with the tungsten layers in the LAT, and uses the scattering distributions to compute the full probability distribution over the energy and direction of the incident photons. It uses model selection methods to estimate the probabilities of the possible geometrical configurations of the particles produced in the detector, and numerical marginalization over the energy loss and scattering angles at each layer. Preliminary results show that it can improve on the tracker-only energy estimates for muons and electrons incident on the LAT.

Might stable energy species "lighter" than radiation, with $w > 1/3$, exist? A dimensional expansion of the cosmological Friedmann Equation of energy has a clear place for them. Such energies would affect the universe much differently than dark energies, and so are here dubbed "ultralight." As the universe expands, ultralight dilutes even faster than light. Although any specie of energy can be mimicked by a properly evolving scalar field, ultralight energy species are hypothesized here to be stable and not related to dynamics of a scalar field. Ultralight is not considered a candidate to make a significant contribution to the energy budget of the universe today, although ultralight might have affected the universe in the distant past. In particular, the $w=2/3$ ultralight energy specie appears to have relatively mundane physical attributes. A discussion of properties and falsifiable attributes of ultralight is given. The duration of primordial nucleosynthesis is extrapolated to limit the present density of $w=2/3$ ultralight to below one part in 100 billion of the critical density.

We report spatially resolved, spectrally dispersed N-band observations of the B[e] star Hen 3-1191 with the MIDI instrument of the Very Large Telescope Interferometer. The object is resolved with a 40 m baseline and has an equivalent uniform disc diameter ranging from 24 mas at 8 microns to 36 mas at 13 microns. The MIDI spectrum and visibilities show a curvature which can arise from a weak silicate feature in which the object appears ~ 15% larger than in the continuum, but this could result from a change in the object’s geometry within the band. We then model Hen’s 3-1191 spectral energy distribution (.4-60 microns) and N-band visibilities. Because of the unknown nature for the object, we use a wide variety of models for objects with IR excesses. We find the observations to be consistent with a disc featuring an unusually high mass accretion and a large central gap almost void of matter, an excretion disc, and a binary made of two IR sources. We are unable to find a circumstellar shell model consistent with the data. At last, we review the different hypotheses concerning the physical nature of the star and conclude that it is neither a Be supergiant nor a symbiotic star. However, we could not discriminate between the scenario of a young stellar object featuring an unusually strong FU Orionis-like outburst of mass accretion (4 to 250 x 10^-4 solar mass per year) and that of a protoplanetary nebula with an equatorial mass excretion rate (>~ 4 x 10^-5 solar mass per year). In both cases, taking the additional presence of an envelope or wind into account would result in lower mass flows.

We present new sensitive, high angular resolution 1.3, 2, and 6 cm observations of the continuum emission from the peculiar emission-line star MWC 349A, made with the Very Large Array. This radio emission is believed to originate in an ionized flow produced by the photoevaporation of a disk that surrounds the star. We determine for the first time the proper motion of this source, which is consistent with that expected for the location of the source in the galaxy. Our analysis of the images, that include the new observations as well as archive data covering a time interval of more than 20 years, indicates that the appearance of MWC 349A has been systematically changing over time. The well-defined “hourglass” shape that characterized the 2 and 1.3 cm appearance of the source in the early 1980’s has disappeared to be replaced by a more “square” shape. We discuss if these changes can be accounted for by precession of the MWC 349A disk or by intrinsic changes in the parameters of the disk, but could not reach a satisfactory explanation.

In recent years increasing evidence has emerged for a thermal component in the gamma- and X-ray spectrum of the prompt emission phase in gamma-ray bursts. The temperature and flux of the thermal component show a characteristic break in the temporal behavior after a few seconds. We show here, that measurements of the temperature and flux of the thermal component at early times (before the break) allow the determination of the values of two of the least restricted fireball model parameters: the size at the base of the flow and the outflow bulk Lorentz factor. Relying on the thermal emission component only, this measurement is insensitive to the inherent uncertainties of previous estimates of the bulk motion Lorentz factor. We give specific examples of the use of this method: for GRB970828 at redshift z=0.9578, we show that the physical size at the base of the flow is r_0 = (2.9+-1.8)*10^8 Y_0^{-3/2} cm and the Lorentz factor of the flow is Gamma = (305\+-28) Y_0^{1/4}, and for GRB990510 at z=1.619, r_0=(1.7+-1.7)*10^8 Y_0^{-3/2} cm and Gamma=(384+-71) Y_0^{1/4}, where Y = 1 Y_0 is the ratio between the total fireball energy and the energy emitted in gamma- rays.

We measure variations in orientation of fourteen dynamic fibrils as a function of time in a small isolated plage and nearby network using a 10-min time sequence of H-alpha filtergrams obtained by the Dutch Open Telescope. We found motions with average angular velocities of the order of 1 deg/min suggesting systematic turning from one limit position to another, particularly apparent in the case of fibrils with lifetimes of a few minutes. Shorter fibrils tend to turn faster than longer ones, which we interpret as due to vortex flows in the underlying granulation that twist magnetic fields.

Vortices have been postulated at a range of size scales in the universe including at the stellar size-scale. Whilst hydrodynamically simulating the wind from an asymptotic giant branch (AGB) star moving through and sweeping up its surrounding interstellar medium (ISM), we have found vortices on the size scale of 10^-1 pc to 10^1 pc in the wake of the star. These vortices appear to be the result of instabilities at the head of the bow shock formed upstream of the AGB star. The instabilities peel off downstream and form vortices in the tail of AGB material behind the bow shock, mixing with the surrounding ISM. We suggest such structures are visible in the planetary nebula Sh 2-188.

Our knowledge of the phenomenology of accretion onto black holes has increased considerably thanks to ten years of observations with the RXTE satellite. However, only recently it has been possible to derive a scheme for the outburst evolution of transient systems on the basis of their spectral and timing properties, reaching a comprehensive definition of source states. These states are in turn linked to the ejection of relativistic jets as observed in the radio band. Here I concentrate on some specific aspects of this classification, concentrating on the properties of the aperiodic variability and on their link with jet ejection.

The aim of these lectures is to introduce some basic problems arising in gravitation and modern cosmology. All along the discussion the guiding theme is provided by the phenomenological and theoretical properties of the Cosmic Microwave Background (CMB). These lectures have been prepared for a regular Phd course of the University of Milan-Bicocca.

We study star formation in a sample of 1204 galaxies in minor (| \Delta m_z | \geq 2) pairs and compact groups, drawn from the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). We analyze an analogous sample of 2409 galaxies in major (| \Delta m_z | < 2$) pairs and compact groups to ensure that our selection reproduces previous results, and we use a “field” sample of 65,570 galaxies for comparison. Our major and minor pairs samples include only galaxies in spectroscopically confirmed pairs, where the recessional velocity separation $\Delta V < 500$ km/s and the projected spatial separation $\Delta D < 50$ kpc/h. The relative magnitude (a proxy for the mass ratio) of the pair is an important parameter in the effectiveness of the tidally triggered star formation in minor interactions. As expected, the secondary galaxies in minor pairs show evidence for tidally triggered star formation, whereas the primary galaxies in the minor pairs do not. The galaxy color is also an important parameter in the effectiveness of triggered star formation in the major galaxy pairs. In the major pairs sample, there is a correlation between the specific H$\alpha$ star formation rate (SSFR) and $\Delta D$ in the blue primary and blue secondary galaxies; for the red primary and red secondary galaxies, there is none. Galaxies in pairs have a higher mean SSFR at every absolute magnitude compared to matched sets of field galaxies, and the relative increase in mean SSFR becomes larger with decreasing intrinsic luminosity. We also detect a significantly increased AGN fraction in the pair galaxies compared to matched sets of field galaxies.

In this work, we want to find out if the IMF can be determined from colour images, integrated colours, or mass-to-light ratios, especially at high redshift, where galaxies cannot be resolved into individual stars, which would enable us to investigate dependencies of the IMF on cosmological epoch. We use chemo-dynamical models to investigate the influence of the Initial Mass Function (IMF) on the evolution of a Milky Way-type disk galaxy, in particular of its colours. We find that the effect of the IMF on the internal gas absorption is larger than its effect on the light from the stellar content. However, the two effects work in the opposite sense: An IMF with more high mass stars leads to brighter and bluer star-light, but also to more interstellar dust and thus to more absorption, causing a kind of "IMF degeneracy". The most likely wavelength region in which to detect IMF effects is the infrared (i. e., JHK). We also provide photometric absorption and inclination corrections in the SDSS ugriz and the HST WFPC2 and NICMOS systems.

We present a new multi-wavelength study of supernova remnant (SNR) B0513-692 in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed, essentially unresolved, but unrelated radio source at its north-western edge, J051324-691049. This is identified as a likely compact HII region based on related optical imaging and spectroscopy. We use the Australia Telescope Compact Array (ATCA) at 4790 and 8640 MHz to determine the large scale morphology, spectral index and polarization characteristics of B0513-692 for the first time. We detect a strongly polarized region (49%) in the remnant’s southern edge. Interestingly we also detect a small (~40 arcsec) moderately bright, but distinct optical, circular shell in our Halpha imagery which is adjacent to the compact HII region and just within the borders of the NE edge of B0513-692. We suggest this is a separate new SNR candidate based on its apparently distinct character in terms of optical morphology in 3 imaged emission lines and indicative SNR optical spectroscopy (including enhanced optical [SII] emission relative to Halpha).

Most Type I X-ray bursts from accreting neutron stars have a lightcurve with a single peak, but there is a rare population of faint bursts that are double or even triple peaked. Suggested mechanisms include polar ignition with equatorial stalling, or multi-step energy release; the latter being caused by hydrodynamic instabilities or waiting points in the nuclear reaction sequence. We present an analysis of the accretion rate dependence of the multi-peak bursts, and discuss the consequences for the various models. The observations pose particular challenges for the polar ignition mechanism given current models of ignition latitude dependence.

The discovery of the short-period giant exoplanet population, the so-called hot Jupiter population, and their link to brown dwarfs and low-mass stars challenges the conventional view of planet formation and evolution. We took advantage of the multi-fiber facilities GIRAFFE and FLAMES-UVES (VLT) to perform the first large radial velocity survey using a multi-fiber spectrograph, aiming at detecting planetary and brown dwarfs candidates and binaries. We observed during 5 consecutive half-nights 816 stars selected within one of the exoplanet field of the space mission CoRoT. We computed the radial velocities of these stars and shown that a systematic error of 30 m s$^{-1}$ has been reached over 5 consecutive nights. Over the whole sample the Doppler measurements allowed us to identify a sample of 50 binaries, 9 active or blended binary stars, 5 unsolved cases and 14 exoplanets and brown dwarf candidates. Further higher precision Doppler measurements are now necessary to confirm and better characterize these candidates. This study demonstrates the efficiency of such a multi-fiber approach for large radial velocity surveys in search for exoplanets as well as the follow-up of transiting exoplanet candidates of existing and future programs like the CoRoT space mission.

A review is presented of some of the ingredients, assumptions and techniques that are used in the computation of the structure and evolution of low-mass stars. Emphasis is placed on several ingredients which are still subject to considerable uncertainty. An overview of the evolution of low-mass stars is also presented, from the cloud collapse phase all the way to the white dwarf cooling curve.

We present radio observations at frequencies ranging from 240 to 8460 MHz of the radio galaxy 4C29.30 (J0840+2949) using the Giant Metrewave Radio Telescope (GMRT), the Very Large Array (VLA) and the Effelsberg telescope. We report the existence of weak extended emission with an angular size of $\sim$520 arcsec (639 kpc) within which a compact edge-brightened double-lobed source with a size of 29 arcsec (36 kpc) is embedded. We determine the spectrum of the inner double from 240 to 8460 MHz and show that it has a single power-law spectrum with a spectral index of $\sim$0.8. Its spectral age is estimated to be $\lapp$33 Myr. The extended diffuse emission has a steep spectrum with a spectral index of $\sim$1.3 and a break frequency $\lapp$240 MHz. The spectral age is $\gapp$200 Myr, suggesting that the extended diffuse emission is due to an earlier cycle of activity. We reanalyse archival x-ray data from Chandra and suggest that the x-ray emission from the hotspots consists of a mixture of nonthermal and thermal components, the latter being possibly due to gas which is shock heated by the jets from the host galaxy.

According to recent general-relativistic simulations, the coalescence of two spinning black holes (BHs) could lead to recoil speeds of the BH remnant of up to thousands of km/s as a result of the emission of gravitational radiation. Such speeds would enable the merger product to escape its host galaxy. Here we examine the circumstances resulting from a gas-rich galaxy merger under which the ejected BH would carry an accretion disk with it and be observable. As the initial BH binary emits gravitational radiation and its orbit tightens, a hole is opened around it in the disk which delays the consumption of gas prior to the eventual BH ejection. The punctured disk remains bound to the ejected BH within the region where the gas orbital velocity is larger than the ejection speed. For a ~10^7 solar mass BH the ejected disk has a characteristic size of tens of thousands of Schwarzschild radii and an accretion lifetime of ~10^7 years. During that time, the ejected BH could traverse a considerable distance and appear as an off-center quasar with a feedback trail along the path it left behind. A small fraction of all quasars could be associated with an escaping BH.

High frequency acoustic waves have been suggested as a source of mechanical heating in the chromosphere. In this work the radial component of waves in the frequency interval 22mHz to 1mHz are investigated. Observations were performed using 2D spectroscopy in the spectral lines of Fe I 543.45nm and Fe I 543.29nm at the Vacuum Tower Telescope, Tenerife, Spain. Speckle reconstruction has been applied to the observations. We have used Fourier and wavelet techniques to identify oscillatory power. The energy flux is estimated assuming that all observed oscillations are acoustics running waves. We find that the estimated energy flux is not sufficient to cover the chromospheric radiative losses.

SN 1987A in the Large Magellanic Cloud is close enough for a study of the very late time evolution of a supernova and its transition to a supernova remnant. Nearly two decades after explosion we are witnessing the supernova shock wave engaging the inner circumstellar ring, which had been fluorescing since being ionised by the soft X-ray flash from shock breakout. We follow the interaction of the supernova shock with the ring material. The spatially resolved information provides us with insight into the individual shock regions around the ring. Near-infrared integral field spectroscopy observations with SINFONI/VLT of the SN-ring interaction is presented. SINFONI’s adaptive optics supported integral field spectrograph spatially resolves the ring and the data thus we obtain a better spatial understanding of the spectrum in different regions of the object. With a dynamical map of the interacting ring we determine parameters for its geometry. Since most of the IR emission lines originate behind the shock front we obtain an indication of the radial velocity of the shocked material after deconvolving the geometry. The ring geometry is consistent with a circle and we also derive a new, independent measurement of the systemic ring, and presumably also supernova, velocity. We find from the spatial distributions of the flux in the different emission lines the degree of cooling in the shocked material and follows the increases observed in the radio and X-rays. Emission from the ejecta is detected only in the strongest [Fe II] lines.

We consider gamma-ray burst outflows with a substantial neutron component that are either dominated by thermal energy (fireballs) or by magnetic energy. In the latter case, we focus on the recently introduced `AC’ model which relies on magnetic reconnection to accelerate the flow and power the prompt emission. For both the fireball and the AC model, we investigate the dynamical importance of neutrons on the outflow. We study particle creation in inelastic neutron – proton collisions and find that in both models the resulting neutrino emission is too weak to be detectable. The inelastic collisions also produce gamma-rays, which create pairs in interactions with soft photons carried with the flow. In magnetically driven outflows, the energy of these pairs is radiated away as synchrotron emission. The bulk of the emission takes place at a few hundred keV, which makes it difficult to disentangle this signal from the prompt emission. In fireballs, however, pair cascading leads to the emission of gamma-rays with observer energy in the range of 2 – 20 GeV and a fluence well above the GLAST threshold. Therefore this emission can be a useful diagnostic of the nature of the outflow.

We aim to study the structure of the nebula around the post-AGB, binary star 89 Her. The presence of a rotating disk around this star had been proposed but not been yet confirmed by observations. We present high-resolution PdBI maps of CO J=2-1 and 1-0. Properties of the nebula are directly derived from the data and model fitting. We also present N-band interferometric data on the extent of the hot dust emission, obtained with the VLTI. Two nebular components are found: (a) an extended hour-glass-like structure, with expansion velocities of about 7 km/s and a total mass ~ 3 10$^{-3}$ Mo, and (b) an unresolved very compact component, smaller than ~ 0.4" and with a low total velocity dispersion of ~ 5 km/s. We cannot determine the velocity field in the compact component, but we argue that it can hardly be in expansion, since his would require too recent and too sudden an ejection of mass. On the other hand, assuming that this component is a keplerian disk, we derive disk properties that are compatible with expectations for such a structure; in particular, the size of the rotating gas disk should be very similar to the extent of the hot dust component from our VLTI data. Assuming that the equator of the extended nebula coincides with the binary orbital plane, we provide new results on the companion star mass and orbit.

With the ongoing AKARI infrared sky survey, of much greater sensitivity than IRAS, a wealth of post-AGB objects may be discovered. It is thus time to organize our present knowledge of known post-AGB stars in th galaxy with a view to using it to search for new post-AGB objects among AKARI sources. We searched the literature available on the NASA Astrophysics Data System up to 1 October 2006, and defined criteria for classifying sources into three categories: "very likely", "possible" and "disqualified" post-AGB objects. The category of "very likely" post-AGB objects is made up of several classes. We have created an evolutionary, on-line catalogue of Galactic post-AGB objects, to be referred to as "The Torun catalogue of Galactic post-AGB and related objects". The present version of the catalogue contains 326 "very likely", 107 "possible" and 64 "disqualified" objects. For the very likely post-AGB objects, the catalogue gives the available optical and infrared photometry, infrared spectroscopy and spectral types, and links to finding charts and bibliography.

H2 formation in metal-free gas occurs via the intermediate H- or H2+ ions. Destruction of these ions by photodissociation therefore serves to suppress H2 formation. In this paper, I highlight the fact that several processes that occur in ionized primordial gas produce photons energetic enough to photodissociate H- or H2+ and outline how to compute the photodissociation rates produced by a particular distribution of ionized gas. I also show that there are circumstances of interest, such as during the growth of HII regions around the first stars, in which this previously overlooked form of radiative feedback is of considerable importance.

For the Delta Scuti star 44 Tau 13 independent frequencies have been detected in previous studies. This star is unusual among the Delta Scuti stars because of its very low v sin i value of 2 +/- 1 km/s, indicating that it is either an extremely slow rotator or seen pole-on. 44 Tau shows unusually high amplitudes for a typical nonradially pulsating Delta Scuti star and is believed to be a connecting link between the high-amplitude Delta Scuti stars (HADS) and the low-amplitude Delta Scuti stars. We performed an asteroseimic study to find the appropriate theoretical model for this star. The fact that the radial fundamental and first overtone frequencies have been identified allows for reducing the number of possible solutions significantly. Standard post-main sequence models with inefficient convection in the envelope seem to be preferable in comparison with various models on the main sequence. They fit both observed global parameters of 44 Tau and most of identified radial and nonradial frequencies.

The recent revision of the solar chemical composition (Asplund, Grevesse and Sauval 2005)is characterized by about 40 per cent decrease of C, N, O, Ne, Ar abundances and by 20 percent decrease of Fe and some other metal abundances. We tested the effect of these modifications on the instability of Beta Cephei models. For the opacities, the newest OP data from the Opacity Project (Seaton 2005) were used. We show that the Beta Cephei instability domain in the Hertzsprung-Russel diagram, when computed with new data for Z=0.012 (revised solar value), is very similar to the instability domain computed earlier using the OPAL opacities for the older solar composition with Z=0.02. Almost all observed Beta Cephei variables are located within the instability domain. Two effects are responsible for stronger instability when using the new data: (i) Metal opacity bump in the OP case is located slightly deeper in the star than that in the OPAL case, which results in more effective driving; (ii) at a fixed Z value, the new Fe-group abundances are higher than the older ones because the Z value is determined mainly by the abundances of C, N, 0, and Ne.

We estimate the two-point correlation function in redshift space of the recently compiled HIPASS neutral hydrogen (HI) sources catalogue, which if modeled as a power law, $\xi(r)=(r_{0}/r)^{\gamma}$, the best-fitting parameters for the HI selected galaxies are found to be $r_{0}=3.3 \pm 0.3 h^{-1}$ Mpc with $\gamma=1.38 \pm 0.24$. Fixing the slope to its universal value $\gamma=1.8$, we obtain $r_{0}= 3.2\pm 0.2 h^{-1}$ Mpc. Comparing the measured two point correlation function with the predictions of the concordance cosmological model, we find that at the present epoch the HI selected galaxies are anti-biased with respect to the underlying matter fluctuation field with their bias value being $b_{0}\simeq 0.68$. Furthermore, dividing the HI galaxies into two richness subsamples we find that the low mass HI galaxies have a very low present bias factor ($b_{0}\simeq 0.48$), while the high mass HI galaxies trace the underlying matter distribution as the optical galaxies ($b_{0}\simeq 1$). Using our derived present-day HI galaxy bias we estimate their redshift space distortion parameter, and correct accordingly the correlation function for peculiar motions. The resulting real-space correlation length is $r^{\rm re}_{0}=1.8 \pm 0.2 h^{-1}$Mpc and $r^{\rm re}_{0}=3.9 \pm 0.6 h^{-1}$Mpc for the low and high mass HI galaxies, respectively. The low-mass HI galaxies appear to have the lowest correlation length among all extragalactic populations studied to-date. Also, we have correlated the IRAS-PSCz reconstructed density field, smoothed over scales of 5$h^{-1}$ Mpc, with the positions of the HI galaxies, to find that indeed the HI galaxies are typically found in negative overdensity regions ($\delta\rho/\rho_{\rm PSCz} \mincir 0$).

We consider the classical picture of three dimensional motion of charged particles in pulsar magnetosphere. We adopt a perturbative method to solve the equation of motion, and find the trajectory of particles as they move along the rotating dipolar magnetic field lines. Our aim is to study the influence of rotation on the pulsar radio emission by considering the constrained motion of particles along the open dipolar magnetic field lines. We find that the rotation induces a significant curvature into the particle trajectories. Our model predicts the intensity on leading side dominates over that of trailing side. We expect that if there is any curvature induced radio emission from the region close to the magnetic axis then it must be due to the rotation induced curvature. Our model predicts the radius–to–frequency mapping (RFM) in the core emissions.

Some basic properties of the solar convection zone are considered and the use of helioseismology as an observational tool to determine its depth and internal angular velocity is discussed. Aspects of solar magnetism are described and explained in the framework of dynamo theory. The main focus is on mean field theories for the Sun’s magnetic field and its differential rotation.