Related papers: Multimodal Distributions along the Horizontal Bran…
Stars with very large mass loss on the red-giant branch can undergo the helium flash while descending the white-dwarf cooling curve. Under these conditions the flash convection zone will mix the hydrogen envelope with the hot helium-…
We have constructed color-magnitude diagrams (CMDs) for ten globular clusters in the halo of the nearby spiral galaxy M33 based on Hubble Space Telescope Wide-Field Planetary Camera 2 observations in the F555W (~V) and F814W (~I) filters.…
We present spectroscopic analyses of 17 faint blue stars in the globular cluster NGC 6752. Effective temperatures, surface gravities, and helium abundances are determined and compared to theoretical predictions. All stars are helium…
We have carried out a search for above-horizontal-branch (AHB) stars--objects lying above the horizontal branch (HB) and blueward of the asymptotic giant branch (AGB) in the color-magnitude diagram--in 97 Galactic and seven Magellanic Cloud…
The connection between mass loss on the red giant branch (RGB) and horizontal branch (HB) morphology in globular clusters (GCs) has long been acknowledged but the mechanisms governing mass loss remains poorly understood from a theoretical…
Six decades and counting, the formation of hot ~20,000-30,000 K Extreme Horizontal Branch (EHB) stars in Galactic Globular Clusters remains one of the most elusive quests in stellar evolutionary theory. Here we report on two discoveries…
We present evidence that some of the compact, luminous, young star clusters recently discovered through images taken with the Hubble Space Telescope (HST) have masses comparable to those of old Galactic globular clusters. The "super star…
(Abridged) The color and luminosity distribution of horizontal branch (HB) stars in globular clusters are sensitive probes of their original helium abundances. However, recent analyses based on visual and near-ultraviolet (UV) CMDs have…
Shells in Elliptical Galaxies are faint, sharp-edged features, believed to provide evidence of a recent ($\sim 0.5 - 2 \times 10^9$ years ago) merger event. We analyse the Globular Cluster (GC) systems of six shell elliptical galaxies, to…
We leverage new high-quality data from Hubble Space Telescope program GO-14164 to explore the variation in horizontal branch morphology among globular clusters in the Large Magellanic Cloud (LMC). Our new observations lead to photometry…
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…
A catalog including a set of the most recent Color Magnitude Diagrams (CMDs) is presented for a sample of 61 Galactic Globular Clusters (GGCs). We used this data-base to perform an homogeneous systematic analysis of the evolved sequences…
Recent Hubble Space Telescope (HST) observations by Rich et al. (1997) have shown that the metal-rich globular clusters (GCs) NGC 6388 and NGC 6441 exhibit a pronounced 2nd parameter effect. Ordinarily metal-rich GCs have only a red…
In this study, we identified and characterized the hot and luminous UV-bright stars in the globular cluster NGC 2808. We combined data from the Ultra Violet Imaging Telescope (UVIT) on-board the Indian space satellite, AstroSat, with the…
I review aspects of the evolution of horizontal branch (HB) stars. I start by discussing current topics in the study of HB stellar evolution, including a brief review of the main determinants of the structure of low-mass core helium burning…
Globular clusters are ideal laboratories to study the evolution of low-mass stars. In this work we concentrate on three types of hot stars observed in globular clusters: horizontal branch stars, UV bright stars, and white dwarfs. After…
Context: Mass loss from red giants in old globular clusters affects the horizontal branch (HB) morphology and post-HB stellar evolution including the production of ultraviolet-bright stars, dredge up of nucleosynthesis products and…
Using the surface brightness fluctuations in HST WFPC-2 images, we determine that M87, NGC 4486B, and NGC 4478 are all at a distance of ~16 Mpc, while NGC 4476 lies in the background at ~21 Mpc. We also examine the globular clusters of M87…
V-band luminosity functions have been obtained for the upper main-sequence, sub-giant branch and red giant branch of 18 galactic globular clusters from HST data. A comparison with four sets of theoretical models has been performed. In…
NGC 6397 is the second closest globular star cluster to the Sun. Using 5 days of time on the Hubble Space Telescope, we have constructed the deepest ever color-magnitude diagram for this cluster. We see a clear truncation in each of its two…