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Astron. Astrophys. 354, 537-550 (2000)


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Doppler imaging of stellar surface structure

XII. Rapid spot changes on the RS CVn binary V711 Tauri = HR 1099

K.G. Strassmeier  *  1 and J. Bartus 2,1

1 Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria (strassmeier@astro.univie.ac.at)
2 Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest, Hungary (bartus@konkoly.hu)

Received 15 April 1999 / Accepted 9 December 1999

Abstract

We present a time series of Doppler images of the RS CVn binary V711 Tauri from spectra taken during 57 consecutive nights in November and December 1996. VRI-band APT photometry throughout the entire observing season is used to support the Doppler imaging. A set of altogether 37 overlapping images from the Ca I -6439 line allows us to trace the latitudinal and longitudinal migration of individual starspots and their morphological evolution. We confirm the poleward migration scenario discovered by Vogt & Hatzes (1996) and obtain an average latitudinal migration rate of +0.41[FORMULA]0.23 (rms) o/day. Of the five spots detected, one was migrating clockwise and one counter clockwise with respect to the orbital period. One feature possibly changed its direction of migration. The two dominating polar features remained at their respective longitudes. Therefore, we are unable to fully attribute the poleward migration to differential rotation and suggest that a combination of differential rotation, meridional circulation, and local crosstalk between starspots causes the observed migration pattern. For one low-latitude spot, the latitudinal migration was briefly interrupted and seen to reverse before it resumed its poleward migration. We possibly witnessed the merging of two spots after they got too close to each other. One spot became significantly cooler shortly before it merged with the bigger and already cooler polar spot, suggesting that some flux exchange took place likely due to a partial reconnection of their magnetic field lines. The polar spot appeared in our images as a non-axisymmetric feature barely covering the actual stellar rotation pole and was not a cap-like feature as seen in several previous maps. Relative spot temperatures varied between 400 K for the weakest features and 1100 K for the main polar spot.

Key words: stars: activity – stars: imaging – stars: individual: V711 Tau – stars: late-type – stars: starspots

* Visiting Astronomer, National Solar Observatory, operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation

© European Southern Observatory (ESO) 2000

Online publication: February 9, 2000

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