Time-resolved spectroscopy of the pulsating CV GW Lib

Abstract

We present time-resolved optical spectroscopy of the dwarf nova GW Librae during its rare April 2007 super-outburst and compare these with quiescent epochs. The data provide the first opportunity to track the evolution of the principal spectral features. In the early stages of the outburst, the optically thick disc dominates the optical and the line components show clear orbital radial velocity excursions. In the course of several weeks, optically thin regions become more prominent as strong emission lines replace the broad disc absorption. Post-outburst spectroscopy covering the I-band illustrates the advantages of CaII relative to the commonly used Balmer lines when attempting to constrain binary parameters. Due to the lower ionisation energy combined with smaller thermal and shear broadening of these lines, a sharp emission component is seen to be moving in between the accretion disc peaks in the CaII line. No such component is visible in the Balmer lines. We interpret this as an emission component originating on the hitherto unseen mass donor star. While our conservative dynamical limits place a hard upper limit on the binary mass ratio of q<0.23, we favour a significantly lower value near q~0.06. Pulsation modeling suggests a WD mass ~1 M_sun. This, paired with a low mass donor, near the empirical sequence of an evolved CV close to the period bounce, appears to be consistent with all the observational constraints to date. [abridged]Comment: Accepted for publication in MNRAS. 13 pages with 5 tables and 7 figure

HSTAND OPTICAL DATA REVEAL WHITE DWARF COOLING, SPIN, AND PERIODICITIES IN GW LIBRAE 3-4 YEARS AFTER OUTBURST

“…While only the C i solution (K = 7.6 ± 0.08 km s −1 ) appears viable, the fits to the other two lines have similar shapes as a function of phase. It is apparent that K wd is very small, much smaller than the past estimates from optical emission lines (38 ± 3 km s from Thorstensen et al 2002 and 19.2 ± 5.3 km s −1 from van Spaandonk et al 2010b). Using a narrow Ca ii line on the secondary that appeared near outburst to determine K sec in combination with a superhump period excess to determine the mass ratio q, van Spaandonk et al (2010a) determined K wd of 6.25 ± 0.4 km s −1 .…”

“…A superhump present soon after outburst (Kato et al 2008), used with the orbital period and the empirical relation of Patterson et al (2005), gave a mass ratio M 2 /M 1 = 0.06. A narrow emission component from the irradiated donor star provided a K velocity (82 ± 5 km s −1 ) and systemic velocity (−15 ± 5 km s −1 ) for the system (van Spaandonk et al 2010b). As the white dwarfs in dwarf novae are known to be heated by their outbursts Sion et al 1998;Piro et al 2005;Godon et al 2006), GW Lib presents the unique opportunity to determine the effect of the outburst on the interior of the white dwarf by following the pulsations.…”

Dissecting the donor star in the eclipsing polar HU Aquarii

“…We thus recommend the preferential use of the Ca ii triplet for mass estimates in magnetic and non-magnetic cataclysmic variables (cf. van Spaandonk et al 2010;Beuermann & Reinsch 2008).…”

The transient OT J213806.6+261957 in Pegasus - Possible emitter of gravitational waves

“…The object was classified as a dwarf nova [6], [7]. Spectra secured during the plateau stage [8] were similar to the spectra of GW Lib at the same stage during the 2007 superoutburst [9], [10], as the spectra measured during the decline from the plateau and the fading tail [11]. The observations of J2138+26 during the plateau, the decay from the plateau and the fading towards quiescence showed that the optical thickness of the accretion disk of J2138+26 was progressively decreasing [12], [11], [13].…”