Related papers: Hot subdwarfs in the Galactic Bulge
We present a summary of our recent work on the vertical distribution of the resolved stellar populations in six low mass, edge-on, spiral galaxies observed with the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS). In each…
The majority of the inhomogeneities in the chemical composition of Globular Cluster (GC) stars appear due to primordial enrichment by hot-CNO cycled material processed in stars belonging to a first stellar generation. Either massive AGB…
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…
Hot subluminous stars can be roughly divided into B- and O-types. Unlike the latter many sdBs are found in close binaries, indicating that binary evolution plays a vital role. Recent NLTE spectral analyses revealed that an evolutionary link…
We predict mass-loss rates for the late evolutionary phases of low-mass stars, with special emphasis on the consequences for the morphology of the Horizontal Branch (HB). We show that the computed rates, as predicted by the most plausible…
Binary evolution is investigated as the source for the extreme horizontal branch (EHB) stars in the old and metal rich open cluster NGC~6791. Employing an updated version of our binary stellar evolution code we demonstrate that EHB stars…
The young stars near the supermassive black hole at the galactic center follow orbits that are nearly random in orientation and that have an approximately thermal distribution of eccentricities, N(e) ~ e. We show that both of these…
Using detailed spectral energy distribution fits we present evidence that submillimeter- and radio-bright gamma-ray burst host galaxies are hotter counterparts to submillimeter galaxies. This hypothesis makes them of special interest since…
The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars,…
From the main sequence to their late evolutionary stages, massive stars spend most of their life as hot stars. Due to their high effective temperatures, the maximum of their emitted flux falls into the ultraviolet (UV) regime. Consequently,…
A subgroup of dwarf galaxies have characteristics of a possible evolutionary transition between star-forming systems and dwarf ellipticals. These systems host significant starbursts in combination with smooth, elliptical outer envelopes and…
We present a 1620 A image of the nearby globular cluster NGC 6752 obtained with the Ultraviolet Imaging Telescope (UIT) during the Astro-2 mission of the Space Shuttle Endeavour in 1995 March. An ultraviolet-visible color-magnitude diagram…
In recent years several hypervelocity stars (HVSs) have been observed in the halo of our Galaxy. Such stars are thought to be ejected through dynamical interactions near the massive black hole (MBH) in the Galactic center. Three scenarios…
We present far-ultraviolet (far-UV) images of the rich galaxy cluster ZwCl1358.1+6245, taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope (HST). When combined with archival HST observations, our data…
We have studied ultraviolet (UV) bright sources in the Galactic globular cluster (GGC) NGC 4590 using Ultraviolet Imaging Telescope (UVIT) on-board the \mbox{{\em AstroSat}} satellite. Using UV-optical color-magnitude diagrams (CMDs), we…
Atmospheric parameters (effective temperature Teff, surface gravity log g), masses and helium abundances are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC 6752. For 19 stars we derive magnesium and iron…
The presence of a substantial number of hot stars in the extremely metal-rich} open cluster NGC6791 has been a mystery. If these hot stars are in their core helium burning phase, they are significantly bluer (hotter) than predicted by…
In this paper we compare the properties of three sub-systems of Galactic globular clusters, which are defined according to metallicity and HB morphology. We focus on cluster luminosities, structures, surface brightnesses (SB) and…
Globular clusters offer ideal laboratories to test the predictions of stellar evolution. When doing so with spectroscopic analyses during the 1990s, however, the parameters we derived for hot horizontal branch stars deviated systematically…
We briefly review the recent results on hot horizontal-branch stars in globular clusters. Since the first Ivanfest, in 1992, there have been a number of new observational lines of evidence which have allowed significant progress in our…