Orbital periods of cataclysmic variables identified by the SDSS

Abstract

We present VLT spectroscopy and NTT photometry of the faint cataclysmic binary SDSS J003941.06+005427.5. This object shows triple-peaked Hα emission with all three peaks variable in both strength and velocity. We measure an orbital period of 91.395 ± 0.093 min from the velocity variations of the wings of the Hα emission line. Using the GALEX and SDSS photometry of this object, we determine a white dwarf temperature of 15 000 K and a very late ( > ∼ L2) spectral type for the companion star. These measurements, plus the relatively long orbital period, suggest that SDSS J003941.06+005427.5 may be a post-bounce cataclysmic variable. Doppler maps of the Hα and He I 6678 Å emission features show an accretion disc with a non-uniform brightness and departures from Keplerian flow. The third emission peak is detected only in Hα and at a relatively low velocity amplitude of 202 ± 3 km s −1 . We are unable to explain this emission as arising from either the white dwarf, the secondary star, or the accretion disc. We tentatively attribute this mysterious central peak to a coronal loop anchored at the secondary star. If confirmed, this would be the first example of a slingshot prominence in a CV with a low mass-transfer rate and/or a fully convective secondary star.

CSS100603:112253−111037: a helium-rich dwarf nova with a 65 min orbital period

“…For completeness, we note that the Hα emission line in the CV SDSSJ003941.06+005427.5 is triple-peaked(Southworth et al 2010), but unlike the central spike observed in AM CVn stars, it has a large radial velocity amplitude (202 km s −1 ), which does not match the expected velocities of the white dwarf, the secondary star, or the accretion disc bright-spot Southworth et al (2010). suggest that it may originate from a coronal loop on a magnetically active secondary star, similar to those that have been observed in outburst spectra of IP Peg and SS Cyg(Steeghs et al 1996).…”

High-speed photometry of the eclipsing cataclysmic variable 1RXS J180834.7+101041

“…Yakin et al also find that J1808+1010 has an asymmetric brightness distribution in its accretion disc (see ref. 20 for an extreme example of this phenomenon). From their observations and from some simple relations Yakin et al infer the masses of the two stars to be 0.8 ± 0.22 and 0.14 ± 0.02 M ⊙ for the white dwarf and secondary component, respectively.…”

The fainter the better: Cataclysmic variable stars from the Sloan Digital Sky Survey

“…We obtained 29 spectra of SDSS J0039 over two nights in 2007 August using VLT/FORS2, finding an orbital period of 91.395 ± 0.093 min. The spectra of this system show a remarkable and unique triple emission peak at Hα (Southworth et al, 2008c). We have used the technique of Doppler tomography (Marsh & Horne 1988) to generate velocity maps of the emission.…”