Fortnightly fluctuations in the O−C diagram of CS 1246★

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.

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“…This is a light-travel-time effect as the white dwarf moves around its centre of mass (e.g. Barlow et al 2011).…”

Section: Discussionmentioning

confidence: 99%

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

Hermes

Gänsicke

Kim

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…In addition to the detection of planets around pulsars and other pulsating stars, it was the primary diagnostic tool that helped earn Hulse and Taylor the Nobel Prize in Physics for their indirect detection of gravitational wave emission (Taylor et al 1979). The O − C diagram remains a critical tool across time domain astronomy (see, e.g., Oksala et al 2012;Barlow et al 2011;Mullally et al 2008;Hermes et al 2012). For pulsating white dwarf stars and other short-period variables, it is convenient to describe O − C as a time-varying absolute phase.…”

Section: Introduction and Formalismmentioning

confidence: 99%

PERIODIC VARIATIONS IN THEO–CDIAGRAMS OF FIVE PULSATION FREQUENCIES OF THE DB WHITE DWARF EC 20058–5234

Dalessio

Sullivan

Provençal

et al. 2013

ApJ

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Variations in the pulsation arrival time of five independent pulsation frequencies of the DB white dwarf EC 20058−5234 individually imitate the effects of reflex motion induced by a planet or companion but are inconsistent when considered in unison. The pulsation frequencies vary periodically in a 12.9 year cycle and undergo secular changes that are inconsistent with simple neutrino plus photon-cooling models. The magnitude of the periodic and secular variations increases with the period of the pulsations, possibly hinting that the corresponding physical mechanism is located near the surface of the star. The phase of the periodic variations appears coupled to the sign of the secular variations. The standards for pulsation-timing-based detection of planetary companions around pulsating white dwarfs, and possibly other variables such as subdwarf B stars, should be re-evaluated. The physical mechanism responsible for this surprising result may involve a redistribution of angular momentum or a magnetic cycle. Additionally, variations in a supposed combination frequency are shown to match the sum of the variations of the parent frequencies to remarkable precision, an expected but unprecedented confirmation of theoretical predictions.

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“…The secular decrease in the CS 1246 pulsation amplitude which Barlow et al [56] report is understood by them to be a consequence of structural changes as a consequence of stellar evolution.…”

Section: Pulsation Amplitude Changesmentioning

confidence: 92%

Concluding remarks

Lynas-Gray

2013

EPJ Web of Conferences

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Abstract. Precision asteroseismic observations with the Kepler and CoRot satellites enable the internal structure and evolution of pulsating stars to be more exhaustively studied than has hitherto been possible. It is particularly important to study the evolutionary links between white dwarfs and subdwarf-B stars with stars considered to have been their progenitors, those on the Red Giant and Asymptotic Giant Branches. Though observations present challenges for existing stellar evolution and pulsation models, and the data (atomic, molecular and nuclear) on which they are based, excellent prospects for development are identified which will in turn facilitate studies of the Galaxy and extra-solar planets.

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Fortnightly fluctuations in the O−C diagram of CS 1246★

Cited by 19 publications

References 31 publications

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

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

PERIODIC VARIATIONS IN THEO–CDIAGRAMS OF FIVE PULSATION FREQUENCIES OF THE DB WHITE DWARF EC 20058–5234

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