Related papers: On the most metal-poor PN and its binary central s…
We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars with [Fe/H] < -2.5, of which 86 are extremely metal poor,…
We present the discovery of twelve metal-poor and distant pre-main sequence (PMS) candidates in the dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM)~968 kpc away, at a present-day metallicity of [Fe/H] around $-$0.9. These candidates have…
Cool white dwarf stars are usually found to have an outer atmosphere that is practically pure in hydrogen or helium. However, a small fraction have traces of heavy elements that must originate from the accretion of extrinsic material, most…
We report the discovery of a binary millisecond pulsar (namely PSR J1641+3627F or M13F) in the globular cluster M13 (NGC 6205) and timing solutions of M13A to F using observations made with the Five-hundred-metre Aperture Spherical radio…
Context. The first generation of stars formed in the Galaxy left behind the chemical signatures of their nucleosynthesis in the interstellar medium, visible today in the atmospheres of low-mass stars formed afterwards. Sampling the…
The results of optical spectroscopy of two HII regions in UGCA 292 (CVn I dwA) are presented. UGCA 292 is a nearby (D=3.1 Mpc) gas-rich dwarf irregular galaxy (M_H/L_B ~ 6.9) which was first discovered in a blind HI survey. The derived…
We report the results of a coherent study of three chemically anomalous metal-poor ([Fe/H] ~ -2) stars. These objects exhibit unusually low abundances of Mg, Si, Ca (alpha-elements) and Sr, Y, and Ba (neutron-capture elements). Our analyses…
The recycled pulsar PSR J2222-0137 is one of the closest known neutron stars, with a parallax distance of $267_{-0.9}^{+1.2}\,$pc and an edge-on orbit. We measure the Shapiro delay in the system through pulsar timing with the Green Bank…
Helium-burning hot subdwarf stars of spectral types O and B (sdO/B) are thought to be produced through various types of binary interaction. The helium-rich hot subdwarf star EC22536-5304 was recently found to be extremely enriched in lead.…
Our ongoing spectroscopic survey of faint planetary-nebula nuclei (PNNi) has revealed 30 new hydrogen-deficient central stars. The majority of them (21) belong to the PG1159 spectral class (having He-C-O-dominated atmospheres). They…
We present low-resolution spectroscopy of newly-discovered candidate companions to three stars in the Solar Neighbourhood. All three companions are M dwarfs, with spectral types ranging from M4 to M9.5. In two cases, G85-55`B' (M6) and…
We present radial velocity observations of four extremely low-mass (0.2 Msol) white dwarfs. All four stars show peak-to-peak radial velocity variations of 540 - 710 km/s with 1.0 - 5.9 hr periods. The optical photometry rules out…
We report the discovery of one extremely metal-poor (EMP; [Fe/H]<-3) and one ultra metal-poor (UMP; [Fe/H]<-4) star selected from the SDSS/SEGUE survey. These stars were identified as EMP candidates based on their medium-resolution…
We report the discovery of the carbon-rich ultra metal-poor unevolved star J0815+4729. This dwarf star was selected from SDSS/BOSS as a metal-poor candidate and follow-up spectroscopic observations at medium-resolution were obtained with…
Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift…
We report the discovery of a detached double white dwarf binary with an orbital period of $\approx20.6\,\rm minutes$, PTF J053332.05+020911.6. The visible object in this binary, PTF J0533+0209B, is a $\approx 0.17\,M_\odot$ mass white dwarf…
We study the impact of binary interaction processes on the evolution of low- and intermediate-mass stars using long-term monitoring of their radial velocity. Here we report on our results on the central stars of two planetary nebulae (PNe):…
Binaries harbouring millisecond pulsars enable a unique path to determine neutron star masses: radio pulsations reveal the motion of the neutron star, while that of the companion can be characterised through studies in the optical range.…
We find that low-degree low-order g-modes become unstable in metal-poor low-mass stars due to the $\varepsilon$-mechanism of the pp-chain. Since the outer convection zone of these stars is limited only to the very outer layers, the…
Close binaries consisting of a main sequence star and a white dwarf are considered as candidates for Type~Ia supernova progenitors. We present selfconsistent calculations of the time dependence of the structure of the main sequence star,…