SDSS J0926 3624: The shortest period eclipsing binary star - Astrophysics > Solar and Stellar AstrophysicsReport as inadecuate

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Abstract: With orbital periods of the order of tens of minutes or less, the AM CanumVenaticorum stars are ultracompact, hydrogen deficient binaries with theshortest periods of any binary subclass, and are expected to be among thestrongest gravitational wave sources in the sky. To date, the only knowneclipsing source of this type is the P = 28 min binary SDSS J0926+3624. Wepresent multiband, high time resolution light curves of this system, collectedwith WHT-ULTRACAM in 2006 and 2009. We supplement these data with additionalobservations made with LT-RISE, XMM Newton and the Catalina Real-Time TransientSurvey. From light curve models we determine the mass ratio to be q = M2 - M1 =0.041 +- 0.002 and the inclination to be 82.6 +- 0.3 deg. We calculate themass of the primary white dwarf to be 0.85 +- 0.04 solar masses and the donorto be 0.035 +- 0.003 solar masses, implying a partially degenerate state forthis component. We observe superhump variations that are characteristic of anelliptical, precessing accretion disc. Our determination of the superhumpperiod excess is in agreement with the established relationship between thisparameter and the mass ratio, and is the most precise calibration of thisrelationship at low q. We also observe a quasi-periodic oscillation in the 2006data, and we examine the outbursting behaviour of the system over a 4.5 yearperiod.

Author: C.M. Copperwheat, T.R. Marsh, S.P. Littlefair, V.S. Dhillon, G. Ramsay, A.J. Drake, B.T. Gaensicke, P.J. Groot, P. Hakala, D. Koe



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