The SW Sextantis-type star 2MASS J01074282+4845188: an unusual bright accretion disk with non-steady emission and a hot white dwarf

Abstract

Context. Cataclysmic variables (CVs) present a short evolutional stage of binary systems. The nova-like stars are rare objects, especially those with eclipses (only several tens). But precisely these allow to determine the global parameters of their configurations and to learn more about the late stage of stellar evolution. Aims. The light curve solution allows one to determine the global parameters of the newly discovered nova-like eclipsing star 2MASS J01074282+4845188 and to estimate the contribution of the different light sources. Methods. We present new photometric and spectral observations of 2MASS J01074282+4845188. To obtain a light curve solution we used a model of a nova-like star whose emission sources are a white dwarf surrounded by an accretion disk, a secondary star filling its Roche lobe, a hot spot and a hot line. The obtained global parameters are compared with those of the eclipsing nova-like UX UMa. Results. 2MASS J01074282+4845188 shows the deepest permanent eclipse among the known nova-like stars. It is reproduced by covering the very bright accretion disk by the secondary component. The luminosity of the disk is much bigger than that of the rest light sources. The determined high temperature of the disk is typical for that observed during the outbursts of CVs. The primary of 2MASS J01074282+4845188 is one of the hottest white dwarfs in CVs. The temperature of 5090 K of its secondary is also quite high and more appropriate for a long-period SW Sex star. It might be explained by the intense heating from the hot white dwarf and the hot accretion disk of the target. Conclusions. The high mass accretion rateṀ = 8 × 10 −9 M yr −1 , the broad and single-peaked Hα emission profile, and the presence of an S-wave are sure signs for the SW Sex classification of 2MASS J01074282+4845188. The obtained flat temperature distribution along the disk radius as well as the deviation of the energy distribution from the black-body law are evidence of the non-steady emission of the disk. It can be attributed to the low viscosity of the disk matter due to its unusual high temperature. The close values of the disk temperature and the parameter α g of 2MASS J01074282+4845188 and those of the cataclysmic stars at eruptions might be considered as an additional argument for the permanent active state of nova-like stars.

2MASS J22560844+5954299: the newly discovered cataclysmic star with the deepest eclipse

“…For comparison, Rutten et al (1992) studied accretion disks of six nova-like CVs (RW Tri, UX UMa, SW Sex, LX Ser, V1315 Aql, V363 Aur) and found that the temperatures of their disks close to the white dwarf are 10000-30000 K, and the temperatures of the hot spots are higher than the disk by a few thousand K. SW Sex and V1315 Aql, which are SW Sexsubtypes, exhibit a flatter temperature distribution of their disks than that of the steady-state disk (Groot et al 2001). This result, together with our conclusions for the two SW Sex stars, 2MASS J01074282+4845188 (Khruzina et al 2013) and J2256, imply that the non-steady-state temperature distributions of the accretion disks is an additional characteristic of the SW Sexphenomenon.…”

“…The shapes of the J2256 light curves are typical of nova-like CVs. Particularly, 2MASS J01074282 + 4845188, observed by us with the same equipment, has a similar light curve (Khruzina et al 2013). That is why we used the model applied successfully for other cataclysmic variables to determine the system parameters of J2256.…”

“…The deepest eclipses belong to the SW Sex stars. Only nine SW Sex stars in the list of Rodriguez-Gil et al (2007) have eclipse depths more than 2.0 mag (Khruzina et al 2013). Two SW Sex stars, DW UMa (Stanishev et al 2004) and V1315 Aql (Papadaki et al 2009), normally have eclipse depths less than 2.0 mag, but on rare occasions and only within two to three days do they show deeper eclipses of 3.2−3.4 mag.…”

“…To estimate the errors of the adjusted parameters, we used the procedure described in Khruzina et al (2013). The very small errors of the Rozhen photometric data of J2256 meant that the residuals of all obtained solutions were bigger than the critical value χ 2 α,N .…”

On the Sw Sex-Type Eclipsing Cataclysmic Variable Sdss0756+0858

“…It has a 3.29 hr orbital period, placing it in the middle of the SW Sex stars' period distribution, next to DW UMa, a classic representative of the class with which it shares many common features, as outlined by Araujo-Betancor et al (2003); Dhillon et al (2013). Two other similar systems, 2MASS J01074282+4845188 and HBHA 4705-03, have recently been discovered (Khruzina et al 2013;Yakin et al 2013, although the latter is not recognized as an SW Sex star), and are not yet included in the big-list of SW Sex objects compiled by Hoard. 4 But the number of CVs in the ∼3-4 hr orbital range bearing characteristics of SW Sex stars grows, and curiously, the fraction of eclipsing systems among SW Sex-type grows too, although we are far from understanding the phenomenon itself.…”