The ACS Survey of Galactic Globular Clusters is a Hubble Space Telescope (HST) Treasury program designed to provide a new large, deep and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for a sample of 64 Galactic globular clusters by comparing the relative position of the clusters'

We analyzed far-UV (FUSE), UV (HST, IUE) and optical spectra of hot massive stars in the Milky Way with non-LTE, line-blanketed models with sphericity and expanding winds. We were able to reconcile previously discrepant diagnostics from Hα to highly ionized transitions (e.g. OVI and NV) with a revised treatement of soft X-rays from shocks and

Close but detached binaries consisting of a white dwarf and a main sequence star are important objects for the understanding of the evolution of compact binaries such as cataclysmic variables (CVs), supersoft X-ray sources, and X-ray binaries. Since they are still detached, no accretion takes place, and both stars can be studied without the strong

The duration of a starburst is a fundamental parameter affecting the evolution of galaxies yet, to date, observational constraints on the durations of starbursts are not well established. We present the recent star formation histories (SFHs) of 18 nearby dwarf galaxies and rigorously quantify the duration of their starburst events using a uniform

We report the discovery of a T8.5 dwarf, which is a companion to the M4 dwarf Wolf 940. At a distance of 12.50+0.75-0.67 pc, the angular separation of 32 arcsec corresponds to a projected separation of 400 au. The M4 primary displays no Hα emission, and we apply the age-activity relations of West et al. to place a lower limit on the age of the

The near-UV NH3360 feature has been measured in a sample of 35 early-type galaxies spanning a wide range of masses and environments. We found that, contrary to what is seen with Mg- and C-sensitive Lick-style indices, NH3360 does not vary significantly with galaxy velocity dispersion. When compared with solar-scaled stellar population models N/Fe