New Close Binary Systems from the SDSS-I (Data Release Five) and the Search for Magnetic White Dwarfs in Cataclysmic Variable Progenitor Systems

et al. 2009

A&A

We report the discovery of the ninth pre-polar consisting of a late-type ZAMS secondary and a magnetic white dwarf. The white dwarf accretes at an extreme low rate,Ṁ ∼ 10 −14 M yr −1 , from the wind of the companion donor star. The source was found in our systematic search for WD/MS binaries within SDSS/SEGUE. Based on seven Sloan spectra we estimate a binary period of ∼200, 230, or 270 min. The UV to IR spectral energy distribution was decomposed into a dM3-dM4 ZAMS secondary and a cool white dwarf, ∼9000 K, which consistently imply a distance between 360 and 420 pc. The optical spectrum displays one pronounced cyclotron hump, likely originating from a low-temperature plasma, ∼1 keV, in a field of 108 MG. We comment on the evolutionary link between polars and pre-polars.

Section: Discussionmentioning

confidence: 99%

Post common envelope binaries from the SDSS

Schwope¹,

Gómez‐Morán²,

et al. 2009

A&A

“…Important in this respect, SDSS has not only provided a deep sample of CVs, but also the first-ever large homogeneous population of detached white-dwarf/main-sequence (WDMS) binaries (e.g., Silvestri et al 2007;Rebassa-Mansergas et al 2010) of which a considerable fraction, ∼30%, are PCEBs (Rebassa-Mansergas et al 2007, 2010Schreiber et al 2008;Nebot Gómez-Morán et al 2009Pyrzas et al 2009;Schwope et al 2009). Those PCEBs that will evolve into semidetached binaries undergoing stable mass transfer on timescales shorter than the age of the Galaxy are representative of the progenitors of the current-day CV population.…”

Section: Introductionmentioning

confidence: 99%

Post common envelope binaries from SDSS

Zorotovic

Gänsicke

2011

A&A

292

336

Context. We have known for a long time that many of the measured white dwarf (WD) masses in cataclysmic variables (CVs) significantly exceed the mean mass of single WDs. This was thought to be related to observational biases, but recent high-precision measurements of WD masses in a great number of CVs are challenging this interpretation. A crucial question in this context is whether the high WD masses seen among CVs are already imprinted in the mass distribution of their progenitors, i.e. among detached postcommon-envelope binaries (PCEBs) that consist of a WD and a main-sequence star. Aims. We review the measured WD masses of CVs, determine the WD-mass distribution of an extensive sample of PCEBs that are representative for the progenitors of the current CV population (pre-CVs) and compare both distributions. Methods. We calculate the CV formation time of the PCEBs in our sample by determining the post common-envelope (CE) and the main-sequence evolution of the binary systems and define a pre-CV to be a PCEB that evolves into a semi-detached configuration with stable mass transfer within less than the age of the Galaxy. Possible observational biases affecting the WD-mass distribution for the pre-CV and the CV samples are discussed. Results. The mean WD mass among CVs is M wd = 0.83 ± 0.23 M , much larger than that found for pre-CVs, M wd = 0.67 ± 0.21 M . Selection effects cannot explain the high WD masses observed in CVs. We also note that compared to the predictions of binary-population models, the observed fraction of He-core WDs is small both among CVs (≤10%) and pre-CVs (≤17 ± 8%). Conclusions. We suggest two possible explanations for the high WD masses among CVs, both of which imply substantial revisions to the standard model of CV evolution: either most CVs have formed above the orbital-period gap (which requires a high WD mass to initiate stable mass transfer or a previous phase of thermal-timescale mass transfer), or the mass of the WDs in CVs grows through accretion (which strongly disagrees with the predictions of classical nova models). Both options may imply that CVs contribute to the single-degenerate progenitors of type Ia supernovae. The number of He-core WDs in CVs (≤10%) is roughly consistent with the number of He-core WDs in pre-CVs (≤17 ± 8%). This indicates a low value of the CE efficiency.

“…Thanks to its broad ugriz colour space, and massive spectroscopic follow-up, SDSS has identified over 1900 WDMS binaries (Smolčić et al 2004;Silvestri et al 2006Silvestri et al , 2007Schreiber et al 2007;Heller et al 2009;Rebassa-Mansergas et al 2007;Rebassa-Mansergas et al 2010). We have initiated an intensive follow-up study of the SDSS WDMS binaries, with the ultimate aim to substantially improve our understanding of compact binary evolution.…”

Section: Introductionmentioning

confidence: 99%

Post common envelope binaries from SDSS

Gómez‐Morán

Gänsicke

et al. 2011

A&A

130

113

Context. The complexity of the common-envelope phase and of magnetic stellar wind braking currently limits our understanding of close binary evolution. Because of their intrinsically simple structure, observational population studies of white dwarf plus main sequence (WDMS) binaries can potentially test theoretical models and constrain their parameters. Aims. The Sloan Digital Sky Survey (SDSS) has provided a large and homogeneously selected sample of WDMS binaries, which we characterise in terms of orbital and stellar parameters. Methods. We have obtained radial velocity information for 385 WDMS binaries from follow-up spectroscopy and for an additional 861 systems from the SDSS subspectra. Radial velocity variations identify 191 of these WDMS binaries as post common-envelope binaries (PCEBs). Orbital periods of 58 PCEBs were subsequently measured, predominantly from time-resolved spectroscopy, bringing the total number of SDSS PCEBs with orbital parameters to 79. Observational biases inherent to this PCEB sample were evaluated through extensive Monte Carlo simulations. Results. We find that 21-24% of all SDSS WDMS binaries have undergone common-envelope evolution, which is in good agreement with published binary population models and high-resolution HST imaging of WDMS binaries unresolved from the ground. The bias-corrected orbital period distribution of PCEBs ranges from 1.9 h to 4.3 d and approximately follows a normal distribution in log(P orb ), peaking at ∼10.3 h. There is no observational evidence for a significant population of PCEBs with periods in the range of days to weeks. Conclusions. The large and homogeneous sample of SDSS WDMS binaries provides the means to test fundamental predictions of binary population models, hence to observationally constrain the evolution of all close compact binaries.