SDSS J123813.73 – 033933.0: A Cataclysmic Variable Evolved Beyond the Period Minimum

Abstract

We present infrared JHK photometry of the cataclysmic variable SDSS J123813.73-033933.0 and analyze it along with optical spectroscopy, demonstrating that the binary system is most probably comprised of a massive white dwarf with T eff = 12000 ± 1000 K and a brown dwarf of spectral type L4. The inferred system parameters suggest that this system may have evolved beyond the orbital period minimum and is a bounce-back system. SDSS J123813.73-033933.0 stands out among CVs by exhibiting the cyclical variability that Zharikov et al. (2006) called brightenings. These are not related to specific orbital phases of the binary system and are fainter than dwarf novae outbursts, that usually occur on longer timescales. This phenomenon has not been observed extensively and, thus, is poorly understood. The new time-resolved, multi-longitude photometric observations of SDSS J123813.73-033933.0 allowed us to observe two consecutive brightenings and to determine their recurrence time. The period analysis of all observed brightenings during 2007 suggests a typical timescale that is close to a period of ∼ 9.3 hours. However, the brightenings modulation is not strictly periodic, possibly maintaining coherence only on timescales of several weeks. The characteristic variability with double orbital frequency that clearly shows up during brightenings is also analyzed.The Doppler mapping of the system shows the permanent presence of a spiral arm pattern in the accretion disk. A simple model is presented to demonstrate that spiral arms in the velocity map appear at the location and phase corresponding to the 2:1 resonance radius and constitute themselves as a double-humped light curves. The longterm and short-term variability of this CV is discussed together with the spiral arm structure of an accretion disk in the context of observational effects taking place in bounce-back systems.

The accretion disk in the post period-minimum cataclysmic variable SDSS J080434.20 + 510349.2

“…The inner parts of the disk should be optically thin in the continuum or be totally void. A synthetic Doppler map constructed using this model of the accretion disk can also reproduce the observed maps, as was recently shown in Aviles et al (2010, Fig. 4).…”

“…The spectrum undergoes some changes throughout the outburst cycle. The flux-calibrated spectra of SDSS0804, which cover a period of more than two years prior to the 2006 superoutburst until one year after the 2010 superoutburst, are shown in the upper panel of Fig We fit the spectral energy distribution (SED) of SDSS0804 in quiescence with the model described in detail by Aviles et al (2010) using a combination of the SDSS spectrum obtained in 2004 with the IR data of Kato et al (2009). Following Aviles et al (2010), we assumed that the total flux, F * (λ), is the sum of the radiation from a hydrogen WD (DA type) F WD (T eff , λ), an accretion disk with F AD ∼ λ Γ , and a red/brown dwarf with F BD (λ):…”

“…SDSS J103533.03+055158.4 (hereafter SDSS1035) Photometry and reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A77 was proposed by Littlefair et al (2008) as a solid example of a bounce-back system based upon the system parameters found using a parametrized model of an eclipse observed in its light curve. Aviles et al (2010) included SDSS J123813.73-033933.0 (hereafter SDSS1238) in the list of bounce-back CVs using a direct IR broad band photometry of the secondary and modeling the spectral energy distribution of the system. The subject of this paper is SDSS J080434.20+510349.2 (hereafter SDSS0804), which has a very peculiar light curve (Szkody et al 2006).…”

The remarkable outburst of the highly-evolved post period-minimum dwarf nova SSS J122221.7−311525

“…in V406 Vir Aviles et al 2010). This longer-term variability produces in the power spectrum an excess of power at low frequencies of 2-3 cycle d −1 (Fig.…”

Short Orbital Period Cataclysmic Variables

“…Direct (spectral) evidence for brown-dwarf secondaries exists only for very few CVs (SDSS J143317.78+101123.3 and WZ Sge [39,40]), whereas the recognition of other candidates is based on radial velocity studies and analysis of the spectral energy distribution. Using such indirect methods, solid evidence for very low mass donor stars was found for GD 552 [41], EZ Lyn [42], V406 Vir [43], SSS J122221.7−311525 [37].…”