Pyrzas, S., Gaensicke, B. T., Marsh, T. R., Aungwerojwit, A., Rebassa-Mansergas, A., Rodriguez-Gil, P., Southworth, J., Schreiber, Matthias R., Gomez-Moran, A. Nebot and Koester, Detlev (2009) Post-common-envelope binaries from SDSS - V. Four eclipsing white dwarf main-sequence binaries. Monthly Notices of the Royal Astronomical Society, Vol.394 (No.2). pp. 978-994. doi:10.1111/j.1365-2966.2008.14378.x ISSN 0035-8711.

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Abstract

We identify SDSS 011009.09+132616.1, SDSS 030308.35+005444.1, SDSS 143547.87+373338.5 and SDSS 154846.00+405728.8 as four eclipsing white dwarf plus main-sequence (WDMS) binaries from the Sloan Digital Sky Survey ( SDSS), and report on follow-up observations of these systems. SDSS 0110+1326, SDSS 1435+3733 and SDSS 1548+4057 contain DA white dwarfs, while SDSS 0303+0054 contains a cool DC white dwarf. Orbital periods and ephemerides have been established from multiseason photometry. SDSS 1435+3733, with P-orb = 3 h has the shortest orbital period of all known eclipsing WDMS binaries. As for the other systems, SDSS 0110+1326 has P-orb = 8 h, SDSS 0303+0054 has P-orb = 3.2 h and SDSS 1548+4057 has P-orb = 4.4 h. Time-resolved spectroscopic observations have been obtained and the Ha and Ca II lambda lambda 8498.02, 8542.09, 8662.14 triplet emission lines, as well as the Na I lambda lambda 8183.27, 8194.81 absorption doublet were used to measure the radial velocities of the secondary stars in all four systems. A spectral decomposition/ fitting technique was then employed to isolate the contribution of each of the components to the total spectrum, and to determine the white dwarf effective temperatures and surface gravities, as well as the spectral types of the companion stars. We used a light-curve modelling code for close binary systems to fit the eclipse profiles and the ellipsoidal modulation/reflection effect in the light curves, to further constrain the masses and radii of the components in all systems. All three DA white dwarfs have masses of M-WD similar to 0.4-0.6M(circle dot), in line with the expectations from close binary evolution. The DC white dwarf in SDSS 0303+0054 has a mass of M-WD greater than or similar to 0.85M(circle dot), making it unusually massive for a post-common-envelope system. The companion stars in all four systems are M dwarfs of spectral type M4 and later. Our new additions raise the number of known eclipsing WDMS binaries to 14, and we find that the average white dwarf mass in this sample is < MWD > =0.57 +/- 0.16M(circle dot), only slightly lower than the average mass of single white dwarfs. The majority of all eclipsing WDMS binaries contain low-mass (<0.6M(circle dot)) secondary stars, and will eventually provide valuable observational input for the calibration of the mass-radius relations of low-mass main-sequence stars and of white dwarfs.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Double stars, Eclipsing binaries, Cool stars, White dwarf stars
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Wiley
ISSN:	0035-8711
Official Date:	1 April 2009
Dates:	Date Event 1 April 2009 Published
Volume:	Vol.394
Number:	No.2
Number of Pages:	17
Page Range:	pp. 978-994
DOI:	10.1111/j.1365-2966.2008.14378.x
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	Fondo Nacional de Desarrollo Científico y Tecnológico (Chile) (FONDECYT), Universidad de Valparaíso, Centro de Astrofísica y Tecnologias Afines (CATA)
Grant number:	1061199 (FONDECYT), 35 (UV), PFB 06/09 (CATA)

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