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

¹ Moscow MV Lomonosov State University, Sternberg Astronomical Institute, 119991 Moscow, Russia
e-mail: kts@sai.msu.ru
² Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Science, 1784 Sofia, Bulgaria
e-mail: dinko@astro.bas.bg
³ Shumen university, 9700 Shumen, Bulgaria
e-mail: d.kyurkchieva@shu-bg.net

Received: 19 September 2012
Accepted: 22 January 2013

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 rate Ṁ = 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.