14 new eclipsing white dwarf plus main-sequence binaries from the SDSS and Catalina surveys

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A central hypothesis in the theory of cataclysmic variable (CV) evolution is the need to explain the observed lack of accreting systems in the 2-3 h orbital period range, known as the period gap. The standard model, disrupted magnetic braking (DMB), reproduces the gap by postulating that CVs transform into inconspicuous detached white dwarf (WD) plus main sequence systems, which no longer resemble CVs. However, observational evidence for this standard model is currently indirect and thus this scenario has attracted some criticism throughout the last decades. Here, we perform a simple but exceptionally strong test of the existence of detached CVs (dCVs). If the theory is correct, dCVs should produce a peak in the orbital period distribution of detached close binaries consisting of a WD and an M4-M6 secondary star. We measured six new periods which brings the sample of such binaries with known periods below 10 h to 52 systems. An increase of systems in the 2-3 h orbital period range is observed. Comparing this result with binary population models, we find that the observed peak cannot be reproduced by post-common envelope binaries (PCEBs) alone and that the existence of dCVs is needed to reproduce the observations. Also, the WD mass distribution in the gap shows evidence of two populations in this period range, i.e. PCEBs and more massive dCVs, which is not observed at longer periods. We therefore conclude that CVs are indeed crossing the gap as detached systems, which provides strong support for the DMB theory.

Section: Systems From the Sdss Pceb Surveymentioning

confidence: 99%

Detached cataclysmic variables are crossing the orbital period gap

Zorotovic¹,

Schreiber²,

Parsons³

et al. 2016

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“…These include for example: constraining current theories of close compact binary evolution (Davis, Kolb & Willems 2010;Zorotovic et al 2010Zorotovic et al , 2011aRebassa-Mansergas et al 2012b); demonstrating in a robust way that the majority of low-mass white dwarfs are formed in binaries (Rebassa-Mansergas et al 2011); constraining the pairing properties of main-sequence stars (Ferrario 2012); providing robust observational evidence for disrupted magnetic braking ; constraining the rotationage-activity relation of low-mass main-sequence stars (RebassaMansergas, Schreiber & Gänsicke 2013a); studying the statistical properties of the PCEB population using Monte Carlo techniques (Toonen & Nelemans 2013;Camacho et al 2014;Zorotovic et al 2014); analysing why the average mass of white dwarfs in cataclysmic variables is significantly larger than the average mass of single white dwarfs (Zorotovic, Schreiber & Gänsicke 2011b;Nelemans et al 2016;Schreiber, Zorotovic & Wijnen 2016); testing hierarchical probabilistic models used to infer properties of unseen companions to low-mass white dwarfs (Andrews, Price-Whelan & Agüeros 2014); detecting new gravitational wave verification sources (Kilic et al 2014); analysing the interior structural effects of common envelope evolution on low-mass pulsating white dwarfs (Hermes et al 2015). In addition, many eclipsing SDSS PCEBs have been identified (Nebot Gómez-Morán et al 2009;Pyrzas et al 2009Pyrzas et al , 2012Parsons et al 2013Parsons et al , 2015 which are being used to test theoretical mass-radius relations of both white dwarfs and lowmass main-sequence stars (Parsons et al 2012b,a), as well as the existence of circumbinary planets (Zorotovic & Schreiber 2013;Marsh et al 2014;Parsons et al 2014).…”

Section: The Sdss Wdms Binary Cataloguementioning

confidence: 99%

“…We followed the same approach detailed in Parsons et al (2013) and Parsons et al (2015) whereby we selected all WDMS binaries with magnitudes of r < 19 and re-reduced the raw CSS data ourselves to more easily identify very deeply eclipsing systems and remove any contaminated exposures. Out of the 1177 and 91 WDMS binaries and candidates identified here, only 314 were bright enough and with sufficient coverage to search for eclipses, i.e.…”

Section: E C L I P S I N G W D M S B I Na R I E Smentioning

confidence: 99%

The SDSS spectroscopic catalogue of white dwarf-main-sequence binaries: new identifications from DR 9–12

Rebassa‐Mansergas

Ren

Parsons

et al. 2016

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We present an updated version of the spectroscopic catalogue of white dwarf-main-sequence (WDMS) binaries from the Sloan Digital Sky Survey (SDSS). We identify 938 WDMS binaries within the data releases (DR) 9-12 of SDSS plus 40 objects from DR 1-8 that we missed in our previous works, 646 of which are new. The total number of spectroscopic SDSS WDMS binaries increases to 3294. This is by far the largest and most homogeneous sample of compact binaries currently available. We use a decomposition/fitting routine to derive the stellar parameters of all systems identified here (white dwarf effective temperatures, surface gravities and masses, and secondary star spectral types). The analysis of the corresponding stellar parameter distributions shows that the SDSS WDMS binary population is seriously affected by selection effects. We also measure the Na I λλ 8183.27, 8194.81 absorption doublet and H α emission radial velocities (RV) from all SDSS WDMS binary spectra identified in this work. 98 objects are found to display RV variations, 62 of which are new. The RV data are sufficient enough to estimate the orbital periods of three close binaries.Key words: binaries: close -binaries: spectroscopic -stars: low-mass -white dwarfs. I N T RO D U C T I O NA large fraction of main-sequence stars are found in binary systems (Duquennoy & Mayor 1991;Raghavan et al. 2010;Yuan et al. 2015b). It is expected that ∼25 per cent of all main-sequence binaries are close enough to begin mass transfer interactions when the more massive star becomes a red giant or an asymptotic giant star (Willems & Kolb 2004). This has been observationally verified e.g. by Farihi, Hoard & Wachter (2010) and by Nebot . Because the mass transfer rate generally exceeds the Eddington limit, the secondary star is not able to accrete the transferred material and the system evolves through a common envelope phase. That is, the core of the giant and the main-sequence companion orbit within a common envelope formed by the outer layers of the giant star. Drag forces between the two stars and the envelope lead to the shrinkage of the orbit and therefore to the release E-mail: alberto.rebassa@upc.edu of orbital energy. The orbital energy is deposited into the envelope and is eventually used to eject it (Webbink 2008). The outcome of common envelope evolution is hence a close binary formed by the core of the giant star (which later becomes a white dwarf) and a main-sequence companion, i.e. a close white dwarf-main-sequence (WDMS) binary. These are commonly referred to as post-common envelope binaries (PCEBs). The remaining ∼75 per cent of mainsequence binaries are wide enough to avoid mass transfer interactions. In these cases the more massive stars evolve like single stars until they eventually become white dwarfs. The orbital separations of such WDMS binaries are similar to those of the main-sequence binaries from which they descend.During the last years we have mined the Sloan Digital Sky Survey (SDSS; York et al. 2000) spectroscopic data base to build up th...

“…In recent years the number of such systems known has ⋆ steven.parsons@uv.cl dramatically increased, thanks mainly to the Sloan Digital Sky Survey (SDSS, York et al 2000;Adelman-McCarthy et al 2008;Abazajian et al 2009), which has lead to the discovery of more than 2000 white dwarf plus main-sequence systems (Rebassa-Mansergas et al 2013a), from which more than 200 close, post common-envelope binaries (PCEBs) have been identified (Nebot Gómez-Morán et al 2011;Parsons et al 2013bParsons et al , 2015. Among this sample are 71 eclipsing binaries (see the appendix of Parsons et al 2015 for a recent census).…”

Section: Introductionmentioning

confidence: 99%

“…Among this sample are 71 eclipsing binaries (see the appendix of Parsons et al 2015 for a recent census). These are extremely useful systems for high precision stellar parameter studies, since the small size of the white dwarf leads to very sharp eclipse profiles, allowing radius measurements to a precision of better than two per cent (e.g.…”

Section: Introductionmentioning

confidence: 99%

The crowded magnetosphere of the post-common-envelope binary QS Virginis

Parsons

Hill

Marsh

et al. 2016

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We present high speed photometry and high resolution spectroscopy of the eclipsing post common envelope binary QS Virginis (QS Vir). Our UVES spectra span multiple orbits over more than a year and reveal the presence of several large prominences passing in front of both the M star and its white dwarf companion, allowing us to triangulate their positions. Despite showing small variations on a timescale of days, they persist for more than a year and may last decades. One large prominence extends almost three stellar radii from the M star. Roche tomography reveals that the M star is heavily spotted and that these spots are longlived and in relatively fixed locations, preferentially found on the hemisphere facing the white dwarf. We also determine precise binary and physical parameters for the system. We find that the 14, 220 ± 350 K white dwarf is relatively massive, 0.782 ± 0.013M ⊙ , and has a radius of 0.01068 ± 0.00007R ⊙ , consistent with evolutionary models. The tidally distorted M star has a mass of 0.382 ± 0.006M ⊙ and a radius of 0.381 ± 0.003R ⊙ , also consistent with evolutionary models. We find that the magnesium absorption line from the white dwarf is broader than expected. This could be due to rotation (implying a spin period of only ∼700 seconds), or due to a weak (∼100kG) magnetic field, we favour the latter interpretation. Since the M star's radius is still within its Roche lobe and there is no evidence that its over-inflated we conclude that QS Vir is most likely a pre-cataclysmic binary just about to become semi-detached.