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Starspot evolution, differential rotation, and magnetic cycles in the chromospherically active binaries lambda andromedae, sigma Geminorum, II Pegasi, and V711 Tauri
We have analyzed 15-19 yr of photoelectric photometry, obtained manuallyand with automated telescopes, of the chromospherically active binarieslambda And, sigma Gem, II Peg, and V711 Tau. These observations let usidentify individual dark starspots on the stellar surfaces from periodicdimming of the starlight, follow the evolution of these spots, andsearch for long-term cyclic changes in the properties of these starspotsthat might reveal magnetic cycles analogous to the Sun's 11 yr sunspotcycle. We developed a computer code to fit a simple two-spot model toour observed light curves that allows us to extract the most easilydeterminable and most reliable spot parameters from the light curves,i.e., spot longitudes and radii. We then used these measured propertiesto identify individual spots and to chart their life histories byconstructing migration and amplitude curves. We identified and followed11 spots in lambda And, 16 in sigma Gem, 12 in II Peg, and 15 in V711Tau. Lifetimes of individual spots ranged from a few months to longerthan 6 yr. Differential rotation coefficients, estimated from theobserved range of spot rotation periods for each star and defined byequation (2), were 0.04 for lambda And, 0.038 for sigma Gem, 0.005 forII Peg, and 0.006 for V711 Tau, versus 0.19 for the Sun. We searched forcyclic changes in mean brightness, B-V color index, and spot rotationperiod as evidence for long-term cycles. Of these, long-term variabilityin mean brightness appears to offer the best evidence for such cycles inthese four stars. Cycles of 11.1 yr for lambda And, 8.5 yr for sigmaGem, 11 yr for II Peg, and 16 yr V711 Tau are implied by these meanbrightness changes. Cyclic changes in spot rotation period were found inlambda And and possibly II Peg. Errors in B-V were too large for anylong-term changes to be detectable.
| The 72nd Name-List of Variable Stars
Not Available
| The active dynamo stars: RS CVn, BY Dra, FK Com, Algol, W UMa, and T Tau
Not Available
| Two New Spotted Variables-HD 191262 and HD 191011
Abstract image available at:http://adsabs.harvard.edu/abs/1992AJ....104.1936H
| Photometry of 50 suspected variable stars
Fifty stars have been chosen as suspected variable stars and analyzedfor variability. A large portion of this sample are stars that areeither proved active chromosphere stars or are candidates for suchactivity. The photometric data base consists of differential Vmeasurements of the Vanderbilt 16 inch (41 cm) automatic photoelectrictelescope and 25 observers at 26 observatories worldwide. Publishedphotometric data have also been utilized, with proper adjustments madeto ensure that all magnitudes are differential. Searches for photometricperiod, amplitudes, and times of minimum light showed 68 percent of thesample to be photometrically variable with periods found for 34. Twostars were deemed norvariable for the period of observation. Conclusivestatements could not be made concerning the photometric variability ofthe 14 remaining stars.
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