Dynamical masses of a nova-like variable on the edge of the period gap. Issue 1 (1st July 2015)

• Record Type: Journal Article
• Authors: Rodríguez-Gil, P.; Shahbaz, T.; Marsh, T. R.; Gänsicke, B. T.; Steeghs, D.; Long, K. S.; Martínez-Pais, I. G.; Armas Padilla, M.; Schwarz, R.; Schreiber, M. R.; Torres, M. A. P.; Koester, D.; Dhillon, V. S.; Castellano, J.; Rodríguez, D.
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 452:Issue 1(2015)
• Page Start: 146
• Page End: 157
• Publication Date: 2015-07-01
• Subjects: binaries: close -- stars: fundamental parameters -- stars: individual: HS 0220+0603 -- novae, cataclysmic variables; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stv1244
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract : We present the first dynamical determination of the binary parameters of an eclipsing SW Sextantis star in the 3–4 h orbital period range during a low state. We obtained time-resolved optical spectroscopy and photometry of HS 0220+0603 during its 2004–2005 low-brightness state, as revealed in the combined Small & Moderate Aperture Research Telescope System, IAC80 and M1 Group long-term optical light curve. The optical spectra taken during primary eclipse reveal a secondary star spectral type of M5.5 ± 0.5 as derived from molecular band-head indices. The spectra also provide the first detection of a DAB white dwarf in a cataclysmic variable. By modelling its optical spectrum we estimate a white dwarf temperature of 30 000 ± 5000 K. By combining the results of modelling the white dwarf eclipse from ULTRACAM light curves with those obtained by simultaneously fitting the emission- and absorption-line radial velocity curves and I -band ellipsoidal light curves, we measure the stellar masses to be M 1 = 0.87 ± 0.09 M⊙ and M 2 = 0.47 ± 0.05 M⊙ for the white dwarf and the M dwarf, respectively, and an inclination of the orbital plane of i ≈ 79°. A radius of 0.0103 ± 0.0007 R⊙ is obtained for the white dwarf. The secondary star in HS 0220+0603 is likely too cool and undersized for its mass.