Journal Article

Post-common envelope binaries from SDSS – XV. Accurate stellar parameters for a cool 0.4 M<sub>⊙</sub> white dwarf and a 0.16 M<sub>⊙</sub> M dwarf in a 3 h eclipsing binary

S. Pyrzas, B. T. Gänsicke, S. Brady, S. G. Parsons, T. R. Marsh, D. Koester, E. Breedt, C. M. Copperwheat, A. Nebot Gómez-Morán, A. Rebassa-Mansergas, M. R. Schreiber and M. Zorotovic

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 419, issue 1, pages 817-826
Published in print January 2012 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19746.x
Post-common envelope binaries from SDSS – XV. Accurate stellar parameters for a cool 0.4 M⊙ white dwarf and a 0.16 M⊙ M dwarf in a 3 h eclipsing binary

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We identify SDSS J121010.1+334722.9 as an eclipsing post-common-envelope binary, with an orbital period of , containing a very cool, low-mass, DAZ white dwarf and a low-mass main-sequence star of spectral type M5. A model atmosphere analysis of the metal absorption lines detected in the blue part of the optical spectrum, along with the Galaxy Evolution Explorer near-ultraviolet flux, yields a white dwarf temperature of  K and a metallicity value of log [Z/H] =−2.0 ± 0.3. The Na i λλ8183.27, 8194.81 absorption doublet is used to measure the radial velocity of the secondary star, , and Fe i absorption lines in the blue part of the spectrum provide the radial velocity of the white dwarf, , yielding a mass ratio of q = 0.379 ± 0.009. Light-curve model fitting, using the Markov chain Monte Carlo method, gives the inclination angle as i = (79°.05–79°.36) ± 0°.15, and the stellar masses as  and . Systematic uncertainties in the absolute calibration of the photometric data influence the determination of the stellar radii. The radius of the white dwarf is found to be  and the volume-averaged radius of the tidally distorted secondary is . The white dwarf in SDSS J121010.1+334722.9 is a very strong He-core candidate.

Keywords: binaries: close; binaries: eclipsing; stars: fundamental parameters; stars: individual: SDSS 121010.1+334722.9; stars: late-type; white dwarfs

Journal Article.  6480 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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