Related papers: The Dearth of UV-Bright Stars in M32: Implications…
We present the deepest near-UV image of M32 to date, which for the first time resolves hot HB stars in an elliptical galaxy. Given the near-solar metallicity of M32, much larger than that of globular clusters, the existence of an extended…
The compact elliptical galaxy M32 offers a unique testing ground for theories of stellar evolution. Because of its proximity, solar-blind UV observations can resolve the hot evolved stars in its center. Some of these late evolutionary…
I review the observational constraints on the stars responsible for the upturn in the UV spectra of ellipticals, ranging from galaxies in the local Universe to distant clusters. In nearby galaxies, this UV upturn is produced by a minority…
We have performed a census of the UV-bright population in 78 globular clusters using wide-field UV telescopes. This population includes a variety of phases of post-horizontal branch (HB) evolution, including hot post-asymptotic giant branch…
As part of the Panchromatic Hubble Andromeda Treasury (PHAT) multi-cycle program, we observed a 12' \times 6.5' area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample of \sim4000…
We present new Hubble Space Telescope WFC3/IR medium-band photometry of the compact elliptical galaxy M32, chemically resolving its thermally pulsating asymptotic giant branch stars. We find 2829 M-type stars and 57 C stars. The carbon…
The UV upturn phenomenon observed in elliptical galaxies is attractive for its potential value as an age indicator of old stellar systems. We present our most recent population models for the UV evolution of elliptical galaxies. We confirm…
This series of papers comprises a systematic exploration of the hypothesis that the far ultraviolet radiation from star clusters and elliptical galaxies originates from extremely hot horizontal-branch (HB) stars and their post-HB progeny.…
We present Faint Object Camera (FOC) ultraviolet images of the central 14x14'' of Messier 31 and Messier 32. The hot stellar population detected in the composite UV spectra of these nearby galaxies is partially resolved into individual…
Blue horizontal branch and UV bright stars in several globular clusters are analysed spectroscopically and the results are compared with predictions of stellar evolutionary theory. We find that the distribution of temperatures and surface…
We present photometry for all bright red giant branch (RGB), horizontal branch (HB), and asymptotic giant branch (AGB) stars within 10' of the center of M13. We find support for the idea that the population of HB stars redder than the…
We present models of the late stages of stellar evolution intended to explain the UV upturn phenomenon in elliptical galaxies. Such models are sensitive to values of a number of poorly-constrained physical parameters, including metallicity,…
We present preliminary results from spectral synthesis models of old stellar populations for the spectral range 912-4000 A with ~ 10A resolution, which can be used to investigate the UVX phenomenon and to assess ages and abundances. Model…
The puzzling origin of the ``UV-upturn'' phenomenon, observed in some elliptical galaxies, has recently been settled by identifying hot HB stars as main contributors to galaxy ultraviolet luminosity excess. While a blue HB morphology seems…
Recent observations and theories suggest that extreme horizontal branch (EHB) stars and their progeny should be the cause of the UV excess seen in the spectra of many elliptical galaxies. Since the Galactic Bulge is the closest…
We present UV images of M 31 and M 32, as observed by HST with the refurbished FOC. The galaxies were observed through the F175W and F275W filters, allowing the construction of color magnitude diagrams (CMDs) for the hundreds of detected…
Extremely hot horizontal branch (HB) stars and their progeny are widely considered to be responsible for the "ultraviolet upturn" (or UVX) phenomenon observed in elliptical galaxies and the bulges of spirals. Yet, the precise evolutionary…
The far-ultraviolet is the most rapidly evolving portion of the spectrum in both very young galaxies and very old galaxies. The ``UV upturn'' in the spectra of elliptical galaxies shortward of 2000 Angstroms offers a promising probe of the…
We consider the general theoretical problem of ultraviolet light from old stellar populations (t > 2 Gyr), and the interpretation of galaxy spectra at short wavelengths (lamda < 3200A) The sources believed to be responsible for the observed…
The rest-frame UV contains the most sensitive indicators of age for elliptical galaxies. While the near-UV flux from young ellipticals isolates the main sequence turnoff, the far-UV flux in old ellipticals is dominated by hot horizontal…