Evidence from K2 for Rapid Rotation in the Descendant of an Intermediate-mass Star

Abstract

(2017) Evidence from K2 for rapid rotation in the descendant of an intermediate-mass star. The Astrophysical Journal, 841 (1). L2. Permanent WRAP URL:http://wrap.warwick.ac.uk/89100 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement:Reproduced by permission of the AAS. AbstractUsing patterns in the oscillation frequencies of a white dwarf observed by K2, we have measured the fastest rotation rate (1.13 ± 0.02 hr) of any isolated pulsating white dwarf known to date. Balmer-line fits to follow-up spectroscopy from the SOAR telescope show that the star (SDSSJ0837+1856, EPIC 211914185) is a 13,590 340  K, 0.87±0.03 M e white dwarf. This is the highest mass measured for any pulsating white dwarf with known rotation, suggesting a possible link between high mass and fast rotation. If it is the product of single-star evolution, its progenitor was a roughly 4.0 M e main-sequence B star; we know very little about the angular momentum evolution of such intermediate-mass stars. We explore the possibility that this rapidly rotating white dwarf is the byproduct of a binary merger, which we conclude is unlikely given the pulsation periods observed.

Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems

“…Furthermore, R A will remain well above the stellar surface unless the star is essentially non-magnetic and B * < 1 G, or the accretion rate is extreme at M > 10 16 g s −1 . For typical (single) white dwarfs, rotation periods 2π/Ω * are many hours to days (Hermes et al 2017), and hence the corotation radius R c = (GM * /Ω 2 * ) 1/3 will also be outside the expected radius of the gas disk. The accretion flow should therefore divert onto the stellar magnetosphere near the radius R A (without a propellor), interior to which matter will be placed onto field lines leaving the magnetic polar region at a characteristic latitude θ m ≈ sin −1 ( R * /R A ) ≈ R * /R A .…”

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

“…After the failure of its second reaction wheel, Kepler has entered a new phase of observations, K2, where it observes new fields along the ecliptic every three months (How- References. -Discovery of pulsations announced by (1) Greiss et al (2016); (2) Hermes et al (2011); (3) Greiss et al (2014); (4) Gianninas et al (2006); (5) Castanheira et al (2010); (6) Mukadam et al (2004); (7) Pyrzas et al (2015) -search for DAVs in WD+dM systems; (8) Voss et al (2006); (9) Hermes et al (2017c) ell et al 2014). This has significantly expanded the number of white dwarfs available for extended observations.…”

Destroying Aliases from the Ground and Space: Super-Nyquist ZZ Cetis in K2 Long Cadence Data

“…While these data sets are individually non-ideal for asteroseismic measurements, they complement each other such that we can measure pulsation frequencies to a precision of ∼ 0.01 µHz. We used a similar approach in Hermes et al (2017a) to confirm the super-Nyquist nature of a rotationally split = 1 triplet centered on 109.15103 s in the short-cadence K2 light curve of the ZZ Ceti star EPIC 211914185, but this work is the first example of recovering frequencies beyond 4-5 times the Nyquist.…”

“…Both in its original mission and while observing new fields along the ecliptic as K2, Kepler has targeted known and candidate pulsating white dwarf stars at short cadence, collecting the most extensive coverage of ZZ Ceti variability to date. This has enabled the precise determination of pulsation frequencies for asteroseismic analysis (Greiss et al 2014;Hermes et al 2014Hermes et al , 2015aHermes et al , 2017aBell et al 2015), as well as the discovery of a pulsation-related outburst phenomenon that operates near the cool edge of the ZZ Ceti instability strip (Bell et al 2015(Bell et al , 2016(Bell et al , 2017Hermes et al 2015b). …”