Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf

Silvotti R, Ostensen RH, Bloemen S, Telting JH, Heber U, Oreiro R, Reed MD, Farris LE, O'Toole SJ, Lanteri L, Degroote P, Hu H, Baran AS, Hermes JJ, Althaus LG, Marsh TR, Charpinet S, Li J, Morris RL, Sanderfer DT (2012)

Publication Type: Journal article

Publication year: 2012

Journal

Monthly Notices of the Royal Astronomical Society Oxford University Press

Book Volume: 424

Pages Range: 1752-1761

Journal Issue: 3

DOI: 10.1111/j.1365-2966.2012.21232.x

Abstract

We have used 605 days of photometric data from the Kepler spacecraft to study KIC 6614501, a close binary system with an orbital period of 0.15749747(25) days (3.779939 h), that consists of a low-mass subdwarf B (sdB) star and a white dwarf (WD). As seen in many other similar systems, the gravitational field of the WD produces an ellipsoidal deformation of the sdB which appears in the light curve as a modulation at two times the orbital frequency. The ellipsoidal deformation of the sdB implies that the system has a maximum inclination of ~40°, with i ≈ 20° being the most likely. The orbital radial velocity (RV) of the sdB star is high enough to produce a Doppler beaming effect with an amplitude of 432 ± 5 ppm, clearly visible in the folded light curve. The photometric amplitude that we obtain, K 1 = 85.8kms -1, is ~12 per cent less than the spectroscopic RV amplitude of 97.2 ± 2.0kms -1. The discrepancy is due to the photometric contamination from a close object at about 5arcsec north-west of KIC 6614501, which is difficult to remove. The atmospheric parameters of the sdB star, T eff = 23700 ± 500K and logg = 5.70 ± 0.10, imply that it is a rare object below the extreme horizontal branch (EHB), similar to HD 188112. The comparison with different evolutionary tracks suggests a mass between ~0.18 and ~0.25 M ⊙, too low to sustain core helium burning. If the mass was close to 0.18-0.19 M ⊙, the star could be already on the final He-core WD cooling track. A higher mass, up to ~0.25M ⊙, would be compatible with a He-core WD progenitor undergoing a cooling phase in a H-shell flash loop. A third possibility, with a mass between ~0.32 and ~0.40 M ⊙, cannot be excluded and would imply that the sdB is a 'normal' (but with an unusually low mass) EHB star burning He in its core. In all these different scenarios, the system is expected to merge in less than 3.1 Gyr due to gravitational wave radiation. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Authors with CRIS profile

Ulrich Heber Naturwissenschaftliche Fakultät

Involved external institutions

Osservatorio Astrofisico di Torino IT Italy (IT) Katholieke Universiteit Leuven (KUL) / Catholic University of Leuven BE Belgium (BE) Roque de los Muchachos Observatory / Observatorio del Roque de los Muchachos (ORM) ES Spain (ES) Institute of Astrophysics of Andalusia / Instituto de Astrofísica de Andalucía (IAA-CSIC) ES Spain (ES) Missouri State University US United States (USA) (US) Australian Astronomical Observatory AU Australia (AU) University of Cambridge GB United Kingdom (GB) University of Texas at Austin US United States (USA) (US) National University of La Plata / Universidad Nacional de La Plata (UNLP) AR Argentina (AR) University of Warwick GB United Kingdom (GB) Université Fédérale de Toulouse Midi-Pyrénées FR France (FR) National Aeronautics and Space Administration (NASA) US United States (USA) (US)

How to cite

APA:

Silvotti, R., Ostensen, R.H., Bloemen, S., Telting, J.H., Heber, U., Oreiro, R.,... Sanderfer, D.T. (2012). Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf. Monthly Notices of the Royal Astronomical Society, 424(3), 1752-1761. https://doi.org/10.1111/j.1365-2966.2012.21232.x

MLA:

Silvotti, Roberto, et al. "Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf." Monthly Notices of the Royal Astronomical Society 424.3 (2012): 1752-1761.

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