Context. The “mass discrepancy” in massive O stars represents a long-standing problem in stellar astrophysics with far-reaching implications for the chemical and dynamical feedback in galaxies. Aims: Our goal is to investigate this mass discrepancy by comparing state-of-the-art model masses with model-independent masses determined from eclipsing

We report on the optical spectroscopy of the eclipsing halo low-mass X-ray binary 2S 0921-630, which reveals the absorption-line radial velocity curve of the K0 III secondary star with a semiamplitude K2=92.89+/-3.84 km s-1, a systemic velocity γ=34.9+/-3.3 km s-1, and an orbital period Porb of 9.0035+/-0.0029 days (1 σ). Given the quality of the

Presently every telescope at McDonald Observatory is utilized for the search for extrasolar planets. Here we give an overview of the precision Doppler surveys currently in progress at the 9.2 m Hobby-Eberly Telscope (HET) and the Harlan J. Smith 2.7 m telescope. Other planet search programs at McDonald Observatory include a transit search at the 0

We present the metallicity distribution function (MDF) for 24,270 G and 16,847 K dwarfs at distances from 0.2 to 2.3 kpc from the Galactic plane, based on spectroscopy from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. This stellar sample is significantly larger in both number and volume than previous spectroscopic

SDSS DR6 includes about 300,000 stellar spectra, and a significant fraction of them belong to members of the halo. We make use of these data to examine closely the shape of the halo metallicity distribution. Does it have a single peak? Is it bimodal? Does it offer any clues on its formation and evolution?

The spectral lines observed in penumbrae are asymmetrical, revealing the existence of spatially unresolved structures. We infer their physical properties by fitting Stokes spectra of Fe I 6301.5 Å and Fe I 6302.5 Å with model atmospheres having two magnetic components interleaved along the line-of-sight (LOS). Combining ten thousand fits, we set up