ULTRACAM observations of SDSS J170213.26 + 322954.1 ��� an eclipsing cataclysmic variable in the period gap

Abstract

We present high‐speed, three‐colour photometry of the eclipsing cataclysmic variable (CV) Sloan Digital Sky Survey J170213.26 + 322954.1 (hereafter SDSS J1702 + 3229). This system has an orbital period of 2.4 h, placing it within the ‘period gap’ for CVs. We determine the system parameters via a parametrized model of the eclipse fitted to the observed light curve by χ2 minimization. We obtain a mass ratio of q= 0.215 ± 0.015 and an orbital inclination . The primary mass is Mw= 0.94 ± 0.01 M⊙. The secondary mass and radius are found to be Mr= 0.20 ± 0.01 M⊙ and Rr= 0.243 ± 0.013 R⊙, respectively. We find a distance to the system of 440 ± 30 pc, and an effective temperature for the secondary star of 3800 ± 100 K (corresponding to a spectral type of M0 ± 0.5 V). Both the distance and effective temperature are consistent with previous values derived via spectroscopy of the red star. The secondary star is significantly less massive than expected for the orbital period, and significantly warmer than expected for its mass. This can be explained if the secondary star is significantly evolved: the mass and effective temperature are consistent with a secondary star that began mass transfer with a greatly reduced central hydrogen fraction. The nature of the secondary star in SDSS J1702 + 3229 supports predictions that CVs with evolved secondary stars might be found accreting within the period gap.

White dwarf masses in cataclysmic variables

“…The first is apparently the case for two famous long orbital period CVs, AE Aqr and V1309 Ori. The latter has become the standard explanation for some CVs below the period gap with very early spectral types (Thorstensen et al 2002;Littlefair et al 2006;Thorstensen 2013). Recently, such a system has been found well inside the period gap (RebassaMansergas et al 2014), in agreement with the predictions of Kolb & Baraffe (1999) that CVs with evolved donors should enter the period gap at shorter orbital periods or not at all.…”

“…As a consequence, CVs with evolved donors pass the period gap as accreting systems with a bloated donor star that is significantly hotter than a typical CV donor at the same period. Such systems have indeed been found (Thorstensen et al 2002;Littlefair et al 2006;Thorstensen 2013;Rebassa-Mansergas et al 2014). Thus, if many of them are produced in our simulations, then the predicted orbital period distribution could be significantly affected.…”

Orbital periods of cataclysmic variables identified by the SDSS – III. Time-series photometry obtained during the 2004/5 International Time Project on La Palma

“…The newly identified CVs have been followed up by a number of groups (e.g. Wolfe et al 2003; Pretorius et al 2004; Woudt & Warner 2004; Peters & Thorstensen 2005; Roelofs et al 2005; Tramposch et al 2005; Gänsicke et al 2006; Littlefair et al 2006a,b; Southworth et al 2006, 2007a,b). Our group has been awarded the International Time 2004/2005 on La Palma for the study of SDSS CVs, and we report in this paper photometric time‐series obtained for 15 systems.…”

NSV 13983: a new dwarf nova in the period gap

“…• (Littlefair et al 2006). The derived spectroscopic period places NSV 13983 in the upper third of the period gap (Fig.…”