Context. We present a detailed spectroscopic analysis of the stars with helium-dominated spectra in the ESO Supernova Ia Progenitor Survey (SPY). Aims. Atmospheric parameters, masses, and abundances of trace hydrogen are determined and discussed in the context of spectral evolution of white dwarfs. Methods. The spectra are compared with theoretical model atmospheres using a χ 2 fitting technique, leading to determinations of effective temperature, surface gravity, and hydrogen abundance. Results. Our final sample contains 71 objects, of which 6 are new detections and 14 are reclassified from DB to DBA because of the presence of H lines. One is a cool DO with weak He ii lines, 2 are composite DB+dM. 55% of the DB sample show hydrogen and are thus DBA, a significantly higher fraction than found before. Conclusions. The large incidence of DBA, and the derived total hydrogen masses are compatible with the scenario that DBs "reappear" around 30 000 K from the DB gap by mixing and diluting a thin hydrogen layer of the order of 10 −15 M . This hydrogen mass is then during the evolution continuously increased by interstellar accretion. There are indications that the accretion rate increases smoothly with age or decreasing temperature, a trend which continuous even below the current low temperature limit (Dufour 2006). A remaining mystery is the low accretion rate of H compared to that of Ca observed in the DBZA, but a stellar wind extending down to the lowest temperatures with decreasing strength might be part of the solution.

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).

Abstract. We search for faint Ca II lines in the spectra of about 800 apparently single white dwarfs observed at high resolution for the SPY (ESO Supernova Progenitor Survey) survey. Photospheric Ca is detected in 24 DAZ; in 25 mostly hot objects the observed lines must be interstellar. We also rediscover 9 strong H and K lines in helium-dominated atmospheres and discover for the first time faint lines in 8 DB. Most of these also show faint hydrogen lines and are thus classified DBAZ. The distribution of metal abundances is discussed and compared with the predictions of the accretion/diffusion scenario. We argue that the observations are easier to understand in a scenario of continuous ongoing accretion with rates varying with the conditions of the ambient medium, rather than with the strongly idealized "two phase accretion/diffusion scenario" of Dupuis et al. (1992Dupuis et al. ( , 1993a.

Context. The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was R = 12.0, which represents the most luminous quasar state thus far observed (M B ∼ −31.4). Aims. In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT). Methods. Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005. Results. The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004−2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June−July 2005. The high-frequency (37−43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm the brightening of the radio core and show an increasing polarization. An exceptionally bright X-ray state was detected in May 2005, corresponding to the rising mm flux and suggesting an inverse-Compton nature of the hard X-ray spectrum. Conclusions. A further multifrequency monitoring effort is needed to follow the next phases of this unprecedented event.

Abstract. 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.

Abstract. 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 Ia Progenitor) survey show strong Balmer and Ca II 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.

We report the detection of non-radial g-mode oscillations in seven relatively bright (14.4 < B < 16.5) DA white dwarf stars from time-series photometry collected at the Nordic Optical Telescope (NOT) at Roque de Los Muchachos Observatory, Spain. The candidate variable stars were selected from preparatory photometric observations of objects from the Hamburg Quasar Survey (HQS) and from spectroscopy of stars from the Villanova (WD) catalogue. The selection of ZZ Ceti candidate stars from photometric data proved nearly as successful as the more common spectroscopic selection method. The effective temperatures that we derive from both methods are consistent with a pure ZZ Ceti instability strip.

Abstract. We have discovered periodic light variations (P = 0.1718023 d) in the sdB star HS 2333+3927 in the BVR bands with amplitudes of 0.21, 0.28 and 0.33 mag, respectively. Sinusoidal radial velocity variations at the same period were detected with a semi-amplitude of K 1 = 89.6 km s −1 , indicating that it is binary system and that the light variations are caused by the reflection effect with no eclipses. A mass function of f (m) = 0.0128 M has been determined. The analysis of the light curve did not yield a unique solution, mainly because the albedo of the secondary is poorly constrained. Two solutions of equal quality with a high (A 2 = 1.0) and a low (A 2 = 0.39) albedo were considered further. Variability of the Balmer line profiles, most notably for Hα, was discovered, probably also caused by the reflection effect. A spectroscopic analysis results in T eff = 36 500 K, log g = 5.70, and log (n He /n H ) = −2.15. These characteristics are typical for sdB stars. Mass-radius relations are derived from the results of the analysis of light and radial-velocity curves. Comparison with the observed mass-radius relation of the sdB star and with that of lower main sequence stars for the companion allows us to discard the high albedo solution, because the resulting mass of the primary and the radius of the secondary would be unreasonably low. From a discussion of evolutionary models we constrain the plausible mass of the sdB to the range between 0.29 M and 0.47 M . Accordingly, the mass of the secondary is between 0.24 M and 0.32 M , indicating a spectral type of M3 to M4. HS 2333+3927 is only the sixth sdB+dM system discovered so far. An improved measurement of the gravity and the projected rotational velocity of the sdB star is required to further constrain the masses and to identify the evolutionary state of the sdB star uniquely.