天体物理学
Ground-based & HST images of the nearby galaxy SBS 1543+593 (z=0.009) show it to be a Low Surface Brightness (LSB) galaxy with a central surface brightness of mu_B(0)=23.2 mag/arcsec-2 and scale length 0.9 h-1 kpc, values typical for the…
We present disk wind model calculations for the broad emission lines seen in the ultraviolet spectra of the X-ray binary Hercules X-1. Recent HST/STIS observations of these lines suggest that they are kinematically linked to the orbital…
We discuss how several of the questions that remain unclear on the physics of Active Galactic Nuclei may find elements of answers when using in the coming years the extraordinary set of instruments that will be flying simultaneously to…
We have studied the FR I radio galaxy NGC 6251 and its environment at several wavelengths and scale lengths. On the large scale, we have probed the gravity field by measuring the velocity dispersion of the cluster members associated with…
Galaxy disk formation must incorporate the multiphase nature of the interstellar medium. The resulting two-phase structure is generated and maintained by gravitational instability and supernova energy input, which yield a source of…
We investigate the development of bipolar outflows during the early post-AGB evolution. A sample of ten OH/IR stars is observed at high angular resolution, including bipolar nebulae (OH231.8+4.2), bright post-AGB stars (HD 101584) and…
Two continuum subtracted H-alpha HST frames of M101 are used to determine the positions, angular sizes and absolute fluxes of 237 HII regions using a semi-automated technique. From these we have constructed the luminosity and diameter…
Sharp dips observed in the pulse profiles of three X-ray pulsars (GX 1+4, RX J0812.4-3114 and A 0535+26) have previously been suggested to arise from partial eclipses of the emission region by the accretion column occurring once each…
We present the results of a series of imaging and spectroscopic observations aimed at identifying and studying the galaxy responsible for the z = 3.38639 damped lya system in the z = 3.61 QSO Q0201+1120. We find that the DLA is part of a…
In contrast to the situation with the geodynamo, no breakthrough has been made in the solar dynamo problem for decades. Since the appearance of mean-field electrodynamics in the 1960's, the only really significant advance was in the field…
We reveal the role of clustering of sub-clumps, which is expected in the cold dark matter (CDM) universe, in forming a bright elliptical galaxy (BEG) from a low-spin seed galaxy. This can be done by comparing the evolution of a low-spin…
We report the results of spatially resolved X-ray spectroscopy of 8 different ASCA pointings distributed symmetrically around the center of the Perseus cluster. The outer region of the intracluster gas is roughly isothermal, with…
The Narrow Line Seyfert 1 galaxy Mrk 766 has been observed by BeppoSAX on May 1997. The source was fairly variable, both in flux and spectrum, during the observation. The variability is the largest around 2 keV, possibly due to variations…
Extremely Red Objects (EROs) offer a window to the universe at z~1 analogous to that provided by the Lyman Break galaxies at z=3. Passive evolution and hierarchical galaxy formation models make very distinct predictions for the K (2.2um)…
I present the results of a multiyear survey of very low mass stars and brown dwarfs, at high spectral resolution. The spectra were gathered with the HIRES echelle at the Keck Observatory. Some of these objects are stellar and others are…
We examine the polarization signal of the cosmic microwave background radiation associated with distant clusters. The polarization is induced by the Thomson scattering of microwave photons with ionized gas of clusters and contains…
We study correlations between the burst properties and the position in the color-color diagram of the low mass X-ray binary 4U 1728-34 using 21 bursts found in two data sets obtained with the Rossi X-ray Timing Explorer. Using spectral fits…
We present a geometrical canonical description for superconducting membranes. We consider a general action which includes a general class of superconducting extended objects (strings and domain walls). The description is inspired in the ADM…
We present the results of a redshift survey of galaxies in the A3528 complex, a chain of interacting clusters in the core of the Shapley Concentration. This complex is characterized in the X-ray band by two pairs of roughly similar…
For many years, astronomers interested in white dwarf stars have promised that the study of these relatively simple compact objects would ultimately lead to useful information about the physics under extreme conditions of temperature and…