Cycles in the cataclysmic variable V795 Herculis

Abstract

Aims. We investigate the photometric activity of the cataclysmic variable (CV) V795 Her. We pay attention to the time evolution of the length of its superhump cycle P sh . We investigate how well the superhump profile is reproduced in the individual phases Φ sh of P sh . We also analyze the mutual relation of the intensity of the superhump light and the superimposed rapid intensity variations. Methods. We used the photometric V-band CCD observations obtained between 2008 and 2010. The observing run on a given night consisted of a dense series of V-band images (exp. time of 20 s), which enabled us to investigate the superhump profile and the superimposed rapid changes. Results. We identified several time segments characterized by a relatively stable P sh and mean intensity level. We find that inside such a segment, the smoothed profile of the intensity curve folded with P sh displays the largest scatter of the residuals of the mean profile in Φ sh of the peak intensity and during the decay from this peak. A zone of quiescence occurs at Φ sh ≈ 0.6−0.7. The profile of these residuals can be explained if the strength and luminosity of the spiral arms undergo large variations on a timescale much shorter than the segment's duration, as predicted in a previously developed model, while the conditions for the disk precession remain much more stable. The formation of these arms is considerably faster than their fading. We find that the emission of the superimposed short cycle (∼0.01-0.02 d) in this CV depends on Φ sh . We conclude that it does not come from pulsations of the white dwarf or, generally, from the close vicinity of this accretor. We argue that it is flickering with the site in the disk region that produces the superhump. This flickering is not located in the impact of the stream on the disk. V795 Her is a borderline case in the sense that its disk is close to the switch to the cool state. We explain the suppression of the thermal-viscous instability of the disk in V795 Her as caused by the tidal force that is also the reason for the superhumps. This tidal heating can also help to keep the accretion disks in other permanent superhumpers in the hot state.

Analysis of a Kepler Light Curve of the Novalike Cataclysmic Variable KIC 8751494

“…Since the same superhumps were observed in Williams et al (2010), the positive superhumps seem to have been very stably seen in this object. The object appears to be very similar to V795 Her, another novalike system in the period gap having a similar orbital period (Patterson, Skillman 1994;Papadaki et al 2006;Šimon et al 2012). The superhumps of KIC J1924, however, may be more stable than those in V795 Her (Patterson, Skillman 1994;Papadaki et al 2006).…”

A comparative study of the strength of flickering in cataclysmic variables

“…V795 Her: The superhump properties of V795 Her have been investigated by various authors (e.g. Patterson & Skillman 1994;Papdaki et al 2006;Šimon et al 2012). 37 suitable light curves (spanning 57 cycles) were used here.…”

“…( 2010) estimate the primary star mass and the orbital inclination. V795 Her shows photometric variations with a period somewhat longer than the spectroscopic period (see, e.g., Patterson & Skillman 1994;Papadaki et al 2006;Šimon 2012), establishing the system as a permanent superhumper. Superposed upon the superhumps are rapid flickering variations and occasional QPOs with periods of 10 -20 min (Rosen et al 1995;Patterson & Skillman 1994;Papadaki et al 2006).…”