B. Voss

High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey III. DA white dwarfs

Context. The ESO Supernova Ia Progenitor Survey (SPY) took high-resolution spectra of more than 1000 white dwarfs and pre-white dwarfs. About two thirds of the stars observed are hydrogen-dominated DA white dwarfs. Here we present a catalog and detailed spectroscopic analysis of the DA stars in the SPY. Aims. Atmospheric parameters effective temperature and surface gravity are determined for normal DAs. Double-degenerate binaries, DAs with magnetic fields or dM companions, are classified and discussed. Methods. The spectra are compared with theoretical model atmospheres using a χ 2 fitting technique. Results. Our final sample contains 615 DAs, which show only hydrogen features in their spectra, although some are double-degenerate binaries. 187 are new detections or classifications. We also find 10 magnetic DAs (4 new) and 46 DA+dM pairs (10 new).

Binaries discovered by the SPY project. IV. Five single-lined DA double white dwarfs

We present results from our ongoing follow-up observations of double white dwarf binaries detected in the ESO SN Ia Progenitor SurveY (SPY). We discuss our observing strategy and data analysis and present the orbital solutions of five close double white dwarf binaries: HE0320−1917, HE1511−0448, WD0326−273, WD1013−010 and WD1210+140. Their periods range from 0.44 to 3.22 days. In none of these systems we find any spectral lines originating from the companion. This rules out main sequence companions and indicates that the companion white dwarfs are significantly older and cooler than the bright component. Infrared photometry suggests the presence of a cool, helium-rich white dwarf companion in the binary WD 0326−273. We briefly discuss the consequences of our findings for our understanding of the formation and evolution of double white dwarfs.

HS 0146+1847 : a DAZB white dwarf of very unusual composition

HS 0146+1847, originally identified as a white dwarf candidate in proper motion surveys, was rediscovered as a candidate in the Hamburg Quasar Survey. Spectra obtained for the SPY (ESO Supernova la Progenitor) survey show strong Balmer and Call lines, suggesting a classification as DAZ white dwarf. Contrary to the objects known so far in this class, HS 0146+1847 has a helium-rich atmosphere at T eff = 11 500 K. This is confirmed by very weak He lines, changing the classification to DAZB. Mg and Fe lines are also detected. We discuss the physics of Balmer line broadening by neutral helium, present a spectral analysis and note some implications for the accretion/diffusion scenario of heavy elements in cool white dwarfs.

HS 2333+3927: A new sdB+dM binary with a large reflection effect

We report the discovery of a binary, HS 2233 + 3927, consisting of an sdB star with a faint companion. From its lightcurve the orbital period of 14,844 s, the mass ratio, the inclination, and other system parameters are derived. The companion does not contribute to the optical light of the system except through a strong reflection effect. The semi-amplitude of the radial velocity curve K1= 89.6 km/s−1 and a mass function of f(m) = 0.013 M⊙ are determined. A preliminary spectroscopic analysis of the blue spectra using NLTE model atmospheres results in Teff= 36 500 K, log g= 5.70, and log(nHe/nH) =−2.15. These parameters are typical for sdB stars, the companion is probably an M dwarf.

Two new ZZ Ceti pulsators from the HS and HE surveys

We report the detection of nonradial g-mode oscillations in the DA white dwarfs HS 1039+4112 (B=15.9) and HE 1429 0343 (B=15.8) from time-series photometry made at the Loiano 1.5 m telescope. The two stars were previously selected as probable pulsators based on two-color photometry and spectral analysis respectively. Following our temperature and surface gravity determinations, HS 1039+4112 (Teff=11200 K, log g=8.2) is located near the red edge of the ZZ Ceti instability strip, whereas HE 1429 0343 (Teff=11400 K, log g=7.8) falls in the middle of the strip. Both stars show a multi- mode behavior with the main periods at about 850 and 970 s respectively, and relatively large amplitudes (�7% and�2.5%).