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Period study of the contact system VW Cep
New photoelectric U,B and V observations of the eclipsing contact systemVW Cep were taken in 1998-2000 and 23 new minima times were determined.The (O-C) diagram constructed using photographic and photoelectricminima times can be explained by the light-time effect caused by thepresence of a third and fourth body in the system and the long-termperiod decrease interpreted by the mass transfer from the more to theless massive component or/and the magnetic-braking process. The suddenperiod increase detected in 1999 is probably a consequence of theepisodic mass transfer from the less to the more massive component.Enhanced surface activity causes short-term apparent variations of theorbital period. The differences of times of the subsequent primary andsecondary minima show two significant periodicities P_1 = 2.94 +/- 0.07years and P_2 = 2.36 +/- 0.05 years. The latter periodicity is probablythe beat period of the orbital and rotational period at the latitudes ofmost frequent occurrence of the spots.
| Doppler Imaging of VW Cephei: Distribution and Evolution of Starspots on a Contact Binary
We present maximum entropy Doppler images of the contact binary VWCephei, produced from seven data sets of simultaneous spectroscopic andphotometric data at epochs from 1991 March to 1993 May. The geometricand orbital parameters of the contact binary were fitted, along withthird-light characteristics, at the same time as spots, using both thespectroscopic and photometric data to constrain the models. The Dopplerimages indicated the presence of large polar spots on both components.The polar spot on the primary was about 50 deg in diameter and slightlyoff-center, similar to polar spots on other unevolved systems, while thepolar spot on the secondary was 30 deg in diameter. A number of lowerlatitude features were also present. Spots were found to migrate aroundthe primary component in the same direction as the orbital motion of thesystem. Slow differential rotation of the primary component wasobserved, with spots at higher latitudes moving at higher angular rates.The spot distribution on the secondary appeared to be quite stable, withspots congregating at active longitudes, and with no organized patternof migration. The spot coverage on both components was extremely high,though not unrealistic compared to spot coverages of some RS CVnsystems. Spots covered 66% of the surface area of the primary and 55% ofthe secondary. The spot coverage was much greater than that suggested byasymmetry of the light curves. Our Doppler images were modeled inagreement with the Mullan starspot model. However, they also explainedthe success of the hot secondary model, since the bolometricflux-weighted mean surface temperature of the primary was less than thatof the secondary, owing to the large numbers of nonblack spots. Themodels indicated the presence of a great number of unresolved spots. Wediscuss the implications of this to the field of Doppler imaging andargue in favor of the use of two-temperature photosphere models for theDoppler imaging of all rapidly rotating systems. We detected threeflares at Hα and estimate that one such detectable flare occurs onVW Cep every 35+/-20 hr. We also noted that the distribution ofchromospheric emission at Hα over the primary of VW Cep may varyfrom epoch to epoch.
| Stromgren Four-Colour UVBY Photometry of G5-TYPE Hd-Stars Brighter than MV=8.6
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...89O&db_key=AST
| Photoelectric Observations and Lightcurve Variations of Vw-Cephei
452 photoelectric observations of VW Cep obtained in three succesivenights are reported. The light curve of VW Cep changes from night tonight.
| Photoelectric Light Curves of VW Cephei
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| Lichtelektrische Beobachtungen von VW Cephei. Mit 2 Textabbildungen
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