New Times of Minima of Eclipsing Binary Systems
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CCD Minima for Selected Eclipsing Binaries in 2002
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Starspot distributions on XY UMa during 1997-2000 from eclipse mapping
We present narrow-band red light curves and surface maps of theshort-period RS CVn binary system XY UMa, obtained between 1997 Januaryand 2000 March. The light-curve morphology of this system is known tovary on time-scales of a few days. We have used eclipse-mappingtechniques to map the distribution of cool starspots on the surface ofthe primary star. The resulting maps show the continued evolution ofspot features on time-scales of a few days to a week. By comparison withthe images of Collier Cameron & Hilditch, we also find evidence forlonger term trends, including a decline to an activity minimum during1997 and a rise in activity during 1998-2000. We also find marginalevidence from the O-C ephemeris curves for a periodicity and a peakcorresponding to the time of activity minimum.
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An active binary XY UMa revisited
New extensive multicolour photoelectric photometry, performed since1994, is presented. 17 more-or-less complete light curves were obtainedand analyzed. The Wilson-Devinney code applied to the BVRI light curveswithout the maculation effect together with published spectroscopic massratio and semi-major axis yielded new absolute parameters of theeclipsing pair: m1 = 1.10 Msun, m2 =0.66 Msun, R1 = 1.16 Rsun,R2 = 0.63 Rsun, a = 3.107 Rsun and theorbital inclination i = 80.9degr . The observed orbital period changesare conclusively explained by the mutual action of the third body in thesystem (P3 = 30 years) and the maculation effects.Simultaneous analysis of the period changes and the visual brightnessexcludes the possibility of their explanation by Applegate's mechanism.The differences in the maxima heights caused by the maculation exhibitvariations with the period of 709 +/- 10 days. The distance to thesystem d = 86 +/- 5 pc determined from the absolute dimensions andluminosities of the components is larger than the Hipparcos astrometricvalue d = 66 +/- 6 pc. Tables~4 and~8 are only available in electronicform at http://www.edpsciences.org
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Times of Minimum Light for XY Ursae Majoris
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The RS CVn binary XY UMa as a member of a triple system
New minima of the short period RS CVn binary system XY UMa taken in1997-98 follow the light-time orbit with a 30.5 years period. Aninferior conjunction of the third body with mass 0.23 +/- 0.03Msun occurred in 1979. It is suggested that the light-curvesof XY UMa taken in 1978-79 were affected by the eclipse of the binarysystem by a dusty envelope of the protostellar object responsible alsofor the observed infrared excess. There is no correlation between thelong-term brightness variations of the system and the minima times inthe O-C diagram, so its explanation by the Applegate mechanism proposedrecently by Erdem & Gueduer (\cite{ergu98}) is brought intoquestion.
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The orbital period study and photometric analysis of XY Ursae Majoris
Photoelectric observations of the eclipsing binary XY UMa have beencarried out in B and V colours at the Ege University Observatory.Combining these newly obtained data with the previous ones available inthe literature, the problem pertaining to the orbital period of thesystem has been investigated through a detailed description of the O-Cdiagram. The sinusoidal and secular changes have been found. Suchvariations of the orbital period have been examined in terms of threeplausible mechanisms, namely (i) a light-time effect due to a thirdbody, (ii) the orbital period modulation due to magnetic activity cycleof a component star, and (iii) a mass loss case in which the ejectedmaterial escapes out from the binary system. A combination of a magneticactivity cycle mechanism and a mass loss case is found to reproducesatisfactorily the period changes. Further, the observed photoelectriclight curves of the system have been analyzed with the Wilson-Devinneyapproach. This analysis shows that the asymmetries of the light curvesof XY UMa can be interpreted in terms of cool star-spot covering 7% ofthe stellar photosphere of the primary component of this binary. Thesystem is found to be a beta Lyrae type detached binary. The absoluteelements of the system are also deduced.
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Eclipse mapping of starspots on XY UMa in 1992 and 1995
We present and analyse V-band light curves of the detached eclipsingbinary system XY UMa, obtained in 1992 October, 1995 March and November,and 1996 February. The light-curve morphology of this system is known tovary on time-scales of a few days. We have used eclipse mappingtechniques to search for evidence that cool starspots are the agentsresponsible for the variability of the light curve. We derive a new setof geometric system parameters, which we find to be very similar tothose derived by Hilditch & Bell. The image derived from the 1992light curve shows an amorphous band of unresolved spots with a lowfilling factor, extending over much of the inward-facing hemisphere ofthe primary. This result is consistent with the extent of the dark-zonemodel proposed by Hilditch & Bell in their earlier analysis of thissame light curve. Irregularities in the primary eclipse profile observedin 1995 and early 1996 are consistent with the eclipse of a dark spot orspots on the inner face of the primary. The major spot in this regionappears to be resolved on our 9 deg surface grid, indicating that thespot consists of an unbroken umbral region some 15 deg in radius.
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V-Band Photometry of XY UMa in 1993 and 1995
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Photometric evidence for widespread spot activity on the primary component of the short-period RS CVn binary XY UMa
A survey of published light curves, obtained since 1975, of theeclipsing RS CVn-type binary star XY UMa, coupled with results from arecent high-precision light curve, provides substantial evidence forthe existence of a polar spot on the G2V primary component. Thewell-known and strong variability of the shape of the light curve hasbeen explained by the presence of surface maculation, often at lowlatitudes, which varies on time-scales of ∼1 month, and which maypersist for longer intervals. The 20-year span of published lightcurves, however, shows that the entire system brightness varies by asmuch as 0.5 mag in the V band. No orbital phase is exempt from thislonger-term variation, suggesting that the portion of the dominantprimary component that is always visible - namely the polar region -is at least partly responsible for the long-term variation in systembrightness.It is proposed that the surface of the primary component of XY UMa isvery like that seen in the rapidly rotating single G dwarf star ABDor, and the RS CVn binary DM UMa, namely, dominated by a polar spotbut with a second belt of spot activity at lower latitudes.
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1990 BVR Photometry of XY UMa
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Infrared Photometry of Xy-Ursae
Complete infraredJ andK light curves of the RS CVn system XY UMa havebeen obtained at the beginning of 1989. We point out some interestingmorphological changes observed in these light curves.
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Photoelectric Light Curves and Minimum Times of XY UMa
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1987 Photometry of XY Ursae Majoris
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The short-period eclipsing system XY UMa - 1982 UBV light curves and a flare-like event
Abstract image available at:http://adsabs.harvard.edu/abs/1983AJ.....88..532Z
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The variable light-curve of the eclipsing binary XY UMa
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