Related papers: Modeling He-rich subdwarfs through the Hot-Flasher…
Hot subdwarf stars represent a late and peculiar stage in the evolution of low-mass stars, because they are likely formed by close binary interactions. Here we performed a radial velocity (RV) variability study of a sample of 646 hot…
Hot subdwarf stars with masses above $0.8 M_\odot$ ascend the helium giant branch after the end of core helium burning, before entering the white dwarf cooling track or exploding as type Ib/c supernovae. Such massive helium stars are…
The core helium-flash in low-mass stars with extreme mass loss occurs after the tip of the RGB, when the H-rich envelope is very thin. The low efficiency of the H-shell source enables the He-flash driven convective zone to penetrate H-rich…
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-…
Ultracool subdwarfs are low luminosity, late-type M and L dwarfs that exhibit spectroscopic indications of subsolar metallicity and halo kinematics. Their recent discovery and ongoing investigation have led to new insights into the role of…
Hot subluminous stars (sdO/B) are evolved low mass stars originating from red giants that lost their envelope almost entirely. The multitude of observed phenomena imply that several pathways may form hot subdwarfs, most involving close…
The discovery of extremely zirconium- and lead-rich surfaces amongst a small subgroup of hot subdwarfs has provoked questions pertaining to chemical peculiarity in hot star atmospheres and about their evolutionary origin. With only three…
Hot subdwarfs with close low-mass M-type or brown dwarf companions usually show the reflection effect and often also eclipses. Through inspecting the light variations, we estimate the fractions of reflection effect systems detected in…
Two of the possibilities for the formation of low-mass ($M_{\star}\lesssim 0.5\,M_{\odot}$) hydrogen-deficient white dwarfs are the occurrence of a very-late thermal pulse after the asymptotic giant-branch phase or a late helium-flash onset…
Helium-rich subdwarfs are a rare subclass of hot subdwarf stars which constitute a small and inhomogeneous group showing varying degrees of helium enrichment. Only one star, LS IV $^\circ$14 116 has been found to show multiperiodic…
We investigate the final fate of metal deficient (MD) H burning Red Giants under various assumptions about the amount of mass loss. Adopting a metallicity Z= 10^(-8), we follow the evolution of 0.8 Mo models from the Main Sequence phase…
Hot subdwarf (SD) stars are the stripped cores of red giant stars in transition to the white dwarf sequence. The B-type subdwarfs (sdB) are powered by helium fusion in the core, more evolved ones (sdO) by shell burning. Low mass SDs may…
Research into hot subdwarf stars is progressing rapidly. We present recent important discoveries. First we review the knowledge about magnetic fields in hot subdwarfs and highlight the first detection of a highly-magnetic, helium-rich sdO…
In the past few years, astronomers have uncovered several very low-temperature, metal-poor stars with halo or thick disk kinematics and peculiar spectral and photometric properties, so-called ultracool subdwarfs. These include the first…
Two alternative scenarios concerning the origin and evolution of extremely metal-poor halo stars are investigated. The first one assumes that the stars have been completely metal-free initially and produced observed carbon and nitrogen…
We present evolutionary synthesis models of starbursts on top of old stellar populations to investigate in detailed time evolution the relation between Ha luminosity and star formation rate (SFR). The models show that several effects have…
We show that the winds identified with high-redshift low-mass galaxies may strongly affect the formation of stars in more massive galaxies that form later. With 3D realizations of a simple linear growth model we track gas shocking, metal…
We present FUSE spectra of three He-rich sdB stars. Two of these stars, PG1544+488 and JL87, reveal extremely strong C III lines, suggesting that they have mixed triple-alpha carbon from the deep interior out to their surfaces. Using TLUSTY…
Neutron stars and stellar-mass black holes are the remnants of massive stars, which ended their lives in supernova explosions. These exotic objects can only be studied in relatively rare cases. If they are interacting with close companions…
It has been shown that proton ingestion episodes can happen in the formation of hot-subdwarf stars, and that neutron-capture processes are possible in those cases. Moreover, some helium-rich hot subdwarfs display extraordinarily high…