Insights into internal effects of common-envelope evolution using the extended Kepler mission

Abstract

We present an analysis of the binary and physical parameters of a unique pulsating white dwarf with a main-sequence companion, SDSS J1136+0409, observed for more than 77 d during the first pointing of the extended Kepler mission: K2 Campaign 1. Using new groundbased spectroscopy, we show that this post-common-envelope binary has an orbital period of 6.89760103(60) h, which is also seen in the photometry as a result of Doppler beaming and ellipsoidal variations of the secondary. We spectroscopically refine the temperature of the white dwarf to 12 330 ± 260 K and its mass to 0.601 ± 0.036 M . We detect seven independent pulsation modes in the K2 light curve. A preliminary asteroseismic solution is in reasonable agreement with the spectroscopic atmospheric parameters. Three of the pulsation modes are clearly rotationally split multiplets, which we use to demonstrate that the white dwarf is not synchronously rotating with the orbital period but has a rotation period of 2.49 ± 0.53 h. This is faster than any known isolated white dwarf, but slower than almost all white dwarfs measured in non-magnetic cataclysmic variables, the likely future state of this binary.

White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Line Widths: Kepler Observations of 27 Pulsating DA White Dwarfs through K2 Campaign 8

“…For example, we observed multiple DAVs with hotter effective temperatures and shorter-period pulsations that were completely coherent, within the uncertainties, over several months of Kepler observations (Greiss et al 2014;Hermes et al 2015a).…”

“…We computed a significance threshold for all DAVs from a shuffled simulation of the data, as described in Hermes et al (2015a). In summary, we keep the time sampling of our observed light curves but randomly shuffle the flux values to create 10,000 synthetic light curves, noting the highest peak in the Fourier transform for each synthetic dataset.…”

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

“…The only other reliable white dwarf hydrogen envelope mass measurement in a PCEB system is for the pulsating white dwarf in SDSS J1136+0409, which was found to have an envelope mass of MH/MWD = 10 −4.9 (Hermes et al 2015), implying that there could be a substantial spread in the hydrogen envelope masses of white dwarfs in PCEBs, possibly as a result of the common envelope phase itself. The temperature and surface gravity of the white dwarf in QS Vir place it close to the blue edge of the DA white dwarf instability strip.…”

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

“…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).…”