The polarized spectrum of stellar radiation encodes valuable information on the conditions of stellar atmospheres and the magnetic fields that permeate them. In this paper, we give explicit expressions to estimate the magnetic field vector and its associated error from the observed Stokes parameters. We study the solar case where specific

Low Luminosity Quasi Stellar Objects comprise key objects in the context of galaxy evolution scenarios. They may represent the transition population between luminous QSOs and less luminous local galaxies and Seyferts. By analyzing the ionizing source within a galaxy, we distinguish different excitation mechanisms in a nearby sample of low

We report evidence for a striking difference between S0 galaxies in the local field and the Virgo Cluster. While field S0 galaxies have disks whose surface-brightness profiles are roughly equally divided between the three main types (Types I, II, and III: single-exponential, truncated, and antitruncated), Virgo S0s appear to be entirely lacking in

We present optical monitoring of the black hole candidate XTE J1752-223 during its 2009-10 outburst and decay to quiescence. The optical light curve can be described by an exponential decay followed by a plateau, then a more rapid fade towards quiescence. The plateau appears to be due to an extra component of optical emission that brightens and

High-precision multi-band Hubble Space Telescope (HST) photometry reveals that the main sequence of the globular cluster NGC 6397 splits into two components, containing ~30% and ~70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (1) a primordial population that has a composition

The MARVELS (Multi-object APO Radial Velocity Large-area Survey) project will monitor the radial velocities of 3300 stars. As a result, the project is likely to find rare objects, such as brown dwarf (BD) companions in the so-called brown dwarf desert. Two BD candidates in the desert have already been uncovered by the survey. Until recently