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Roche tomography of cataclysmic variables - IV. Star-spots and slingshot prominences on BV Cen
We present Roche tomograms of the G5-G8 IV/V secondary star in thelong-period cataclysmic variable BV Cen reconstructed from MagellanInamori Kyocera Echelle spectrograph echelle data taken on the MagellanClay 6.5-m telescope. The tomograms show the presence of a number oflarge, cool star-spots on BV Cen for the first time. In particular, wefind a large high-latitude spot which is deflected from the rotationalaxis in the same direction as seen on the K3-K5 IV/V secondary star inthe cataclysmic variable AE Aqr. BV Cen also shows a similar relativepaucity of spots at latitudes between 40° and 50° when comparedwith AE Aqr. Furthermore, we find evidence for an increased spotcoverage around longitudes facing the white dwarf which supports modelsinvoking star-spots at the L1 point to explain the low statesobserved in some cataclysmic variables. In total, we estimate that some25 per cent of the Northern hemisphere of BV Cen is spotted.We also find evidence for a faint, narrow, transient emission line withcharacteristics reminiscent of the peculiar low-velocity emissionfeatures observed in some outbursting dwarf novae. We interpret thisfeature as a slingshot prominence from the secondary star and derive amaximum source size of 75000 km and a minimum altitude of 160000 kmabove the orbital plane for the prominence.The entropy landscape technique was applied to determine the systemparameters of BV Cen. We find M1 = 1.18+/-0.280.16Msolar and M2 =1.05 +/-0.230.14Msolar and an orbitalinclination of i = 53° +/- 4° at an optimal systemic velocity ofγ = -22.3 km s-1. Finally, we also report on thepreviously unknown binarity of the G5IV star HD 220492.
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