Physical parameter eclipse mapping of the quiescent disc in V2051 Ophiuchi

Abstract

We analyse simultaneous UBVR quiescent light curves of the cataclysmic variable V2051 Oph using the Physical Parameter Eclipse Mapping (PPEM) method in order to map the gas temperature and surface density of the disc for the first time. The disc appears optically thick in the central regions, and gradually becomes optically thin towards the disc edge or shows a more and more dominating temperature inversion in the disc chromosphere. The gas temperatures in the disc range from about 13 500 K near the white dwarf to about 6000 K at the disc edge. The intermediate part of the disc has temperatures of 9000 to 6500 K. The quiescent disc (chromosphere) shows a prominent bright region with temperatures of 10 500 K around the impact region of the stream from the secondary with an extension towards smaller azimuths. The disc has a size of 0.53±0.03Rℒ1 and a mass accretion rate ℳ˙=1015 to 1017 g s−1. The light curves must include an uneclipsed component, a hot chromosphere and/or a disc wind. The PPEM method allows us to determine a new distance of 146±20 pc, compatible with previous rough estimates. For the white dwarf we then reconstruct a temperature of 19 600 K, if the lower hemisphere of the white dwarf is occulted by the disc. We suggest that the accretion disc is a sandwich of a cool, optically thick central disc with hot chromospheric layers on both sides, as was suggested for HT Cas. This chromosphere is the origin of the emission lines. We find that although V2051 Oph is very similar to the SU UMa‐type dwarf novae HT Cas, OY Car and Z Cha, there must be a substantial difference in order to explain its unique light curve. The reason for the difference could be a higher mass transfer rate caused by the more massive secondary, and/or a small but significant magnetic field of the white dwarf, just strong enough to disrupt the innermost disc.

Infrared photometry of the dwarf nova V2051 Ophiuchi – II. The quiescent accretion disc and its spiral arms

“…Our results suggest that either an extended hot and tenuous chromosphere veils the emission from an underlying, colder accretion disc up to R ∼ 0.3 R L1 , or that the inner disc itself has evaporated into a hot and tenuous corona -although such quiescent accretion disc corona are expected to be much hotter than the ∼ 10 4 K inferred from our study (e.g., Meyer, Liu & Meyer-Hofmeister 2000;Hellier 2001;Barbera, Orlando & Peres 2017). These results are in good agreement with and underscore the previous findings of Vrielmann, Stiening & Offutt (2002) and Saito & Baptista (2006) -which suggested that the quiescent accretion disc of V2051 Oph is a sandwich of a cool, optically thick underlying disc with hot chromospheric layers on both sides -, and of Berriman, Kenyon & Bailey (1986), which found that most of the V2051 Oph disc would consist of hot and optically thin gas for binary distances above 100 pc (as confirmed by Paper I and the results of Sect. 3.1).…”

Spiral structures and temperature distribution in the quiescent accretion disc of the cataclysmic binary V2051 Ophiuchi

“…Warner & Odonoghue (1987) have found ∼ 1777 km/s, which means ∼ 4.4R wd , and Watts et al (1986) derived ∼ 2000 km/s which gives ∼ 3.6R wd . However, Steeghs et al (2001) found much broader line wings but, as mentioned by Vrielmann, Stiening & Offutt (2002), their lines could be enhanced by the disc wind because during the observations V2051 Oph was declining from outburst. The fact that the accretion disc is truncated before it reaches the surface of the white dwarf agrees with the suggestion of Warner & Odonoghue (1987) that V2051 Oph may be an intermediate polar.…”

“…As the original method involves the brightness temperature derived from a single hydrogen emission line, it needs knowledge of the system-observer distance, which could be difficult to obtain with proper accuracy. Based on this method, Vrielmann, Horne & Hessman (1999); Vrielmann, Stiening & Offutt (2002) developed the physical parameter eclipse mapping (PPEM) approach and decoupled the temperature and surface density of V2051 Oph. Our approach to revealing the temperature distribution fromDoppler tomography is, to our knowledge, the first attempt of this kind.…”

V2051 Ophiuchi after superoutburst: out-of-plane material and the superhump light source

“…Compared to other SU UMa systems, V2051 Oph displays a variety of eclipse morphologies and shows humps at various phases and irregular occurrences (Warner & Cropper 1983;Warner & O'Donoghue 1987;Vrielmann et al 2002). This behaviour was the cornerstone of the polar scenario, especially since no superoutbursts had been observed up to that point.…”