Long-term Spot Stability in the Post-common-envelope Binary QS Vir

Abstract

We observed the post-common-envelope eclipsing binary with a white dwarf component, QS Vir, using the 1.88 m telescope of Kotammia Observatory in Egypt. The new observations were analyzed together with all multicolor light curves available online (sampling a period of 25 years), using a full-feature binary system modeling software based on Roche geometry. This is the first time complete photometric modeling was done with most of these data. QS Vir is a detached system, with the red dwarf component underfilling its Roche lobe by a small margin. All light curves feature out-of-eclipse variability that is associated with ellipsoidal variation, mutual irradiation and irregularities in surface brightness of the tidally distorted and magnetically active red dwarf. We tested models with one, two and three dark spots and found that one spot is sufficient to account for the light curve asymmetry in all datasets, although this does not rule out the presence of multiple spots. We also found that a single spotted model cannot fit light curves observed simultaneously in different filters. Instead, each filter requires a different spot configuration. To thoroughly explore the parameter space of spot locations, we devised a grid-search procedure and used it to find consistent solutions. Based on this, we conclude that the dark spot responsible for light curve distortions has been stable for the past 15 years, after a major migration that happened between 1993 and 2002, possibly due to a flip-flop event.

Discovery of a pre-cataclysmic binary with unusual chromaticity of the eclipsed white dwarf by the GPX survey

“…In the case of an eclipsing WDMS system, the depths of the eclipse observed in different bands vary and they are determined by the ratio of temperatures of the components. For a typical system, which consists of a late red dwarf and a WD, observed eclipse depths increase from IR to UV (Maxted et al 2004;Law et al 2012;Parsons et al 2013b;Latković et al 2019). However, in the case of GPX-TF16E-48, multi-colour photometric follow-up observations revealed that depths of eclipses show an unusual colour dependence with an excess in red filters (see Fig.…”

“…Also, if only ellipsoidal variability was present, its depth around the orbital phase 0.0 would be smaller than that at the phase 0.5. These features indicate the presence of spot(s) on the surface of the MS star (Tappert et al 2007;Parsons et al 2016;Latković et al 2019).…”

“…The temperature factor is the ratio of the spot temperature to the temperature of the underlying unspotted surface (for more details of spot modelling see Wilson et al 2017). As a rule, when fitting spot models, a fixed temperature factor is used (Wilson et al 2017;Latković et al 2019). Similarly to these papers, we fixed the temperature factor at 0.85 and 0.9.…”

On the possibilities of classical nova identifications among historical Far Eastern guest star observations

“…The hibernation scenario would require the existence of a large number of detached red dwarf/white dwarf binaries with a configuration close to Roche lobe filling of the secondary star. Up to now, there is only one such case observed, QS Vir (Latkovic et al, ), but according to the Gaia Collaboration et al (), this star is the second closest known CV‐like object (distance d = 50 pc), apart from WZ Sge ( d = 45 pc). Henry et al () analyzed the completeness of stars or stellar systems containing white dwarfs or red dwarfs in the solar neighborhood and concluded that a more or less complete census of such objects (70–90%) is only achieved for distances d = 10 pc, while for larger distances, many of those targets have escaped detection (implying that we presently know only ∼30% for d = 25 pc; ∼15% for d = 50 pc, which is the distance of the nearest CVs; and only ∼2% for d = 100 pc).…”