Related papers: The UV Upturn: From M32 to Distant Clusters
We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet (FUV, ~1500A) and optical (UBVRI) passbands to characterize galaxy morphology as a function of wavelength. This sample, which includes a range of classical Hubble…
Velocity dispersions $\sigma$ and Mg absorption line-strengths Mg$_b$ have been measured for a sample of 16 ellipticals in 3 clusters at a redshift of 0.37. Like local cluster ellipticals, these objects show a correlation between Mg$_b$ and…
The importance of stellar rotation in setting the observed properties of young star clusters has become clearer over the past decade, with rotation being identified as the main cause of the observed extended main sequence turn-off (eMSTO)…
Connecting the observed rest-ultraviolet (UV) luminosities of high-$z$ galaxies to their intrinsic luminosities (and thus star formation rates) requires correcting for the presence of dust. We bypass a common dust-correction approach that…
(Abbreviated) We present an imaging survey of 37 nearby galaxies observed with HST/WFPC2 in the mid-UV F300W filter and in F814W. 11 galaxies were also imaged in F255W. These galaxies were selected to be detectable with WFPC2 in one orbit,…
Correct estimates of stellar extreme ultraviolet (EUV; 100 - 1170 \AA) flux are important for studying the photochemistry and stability of exoplanet atmospheres, as EUV radiation ionizes hydrogen and contributes to the heating, expansion,…
We construct a speculative scenario for rotation-induced extra helium mixing to the envelope of horizontal branch (HB) stars. This scenario differs from previous ones in that the mixing occurs after the star has left the red giant branch…
We have worked out evolutionary synthesis models of the broad-band spectral energy distribution of elliptical galaxies over the whole frequency range from UV to far--IR. Internal extinction and far--IR re--emission by interstellar dust have…
We examine ultraviolet halos around a sample of highly inclined galaxies within 25 Mpc to measure their morphology and luminosity. Despite contamination from galactic light scattered into the wings of the point-spread function, we find that…
We present a progress report on an extensive survey to find and characterize all types of blue horizontal-branch stars in the nuclear bulge of the Galaxy. We have obtained wide, shallow imaging in UBV of ~12 square degrees in the bulge,…
Globular clusters (GCs) are fundamental for understanding the integrated light of old stellar populations and galaxy assembly processes. However, the role of hot, evolved stars, such as horizontal branch (HB), extreme HB, and blue…
We consider the origin of the UV bright phase of metal-rich helium-burning stars, the slow blue phase (SBP), that was predicted by various earlier works. Based on improved physics including OPAL opacities, we confirm the existence of the…
Extended main-sequence stars that are dim in the ultraviolet passbands of Hubble Space Telescope (UV-dim stars) are found in several young and intermediate-age Magellanic Cloud star clusters. The obscuring of the dust in the discs of stars…
Fundamental properties of the extinction curve, like the slope in the rest-frame ultraviolet (UV) and the presence/absence of a broad absorption excess centred at 2175 A (the UV bump), are investigated for a sample of 108 massive,…
I review recent observational progress concerning the evolution of the morphological distribution of galaxies in the rich cluster environment and in the faint field population. By coupling HST imagery with ground-based spectroscopic…
Brightest cluster galaxies (BCGs) are usually quiescent, but many exhibit star formation. Here we exploit the opportunity provided by rest-frame UV imaging of galaxy clusters in the CLASH (Cluster Lensing and Supernovae with Hubble)…
We explore the properties of galaxies on the outskirts of clusters and their dependence on recent dynamical history in order to understand the real impact that the cluster core has on the evolution of galaxies. We analyse the properties of…
We determine the abundance of i'-band drop-outs in the recently-released HST/ACS Hubble Ultra Deep Field (UDF). Since the majority of these sources are likely to be z~6 galaxies whose flux decrement between the F775W i'-band and F850LP…
Systematic studies have revealed hundreds of ultra-compact dwarf galaxies (UCDs) in the nearby Universe. With half-light radii $r_h$ of approximately 10-100 parsecs and stellar masses $M_*$ $\approx$ $10^6-10^8$ solar masses, UCDs are among…
The star formation history derived from ultraviolet and H$\alpha$ data, without correction for dust extinction, on the one hand, and from far infrared and submillimetre data, on the other, is investigated. The latter estimates are found to…