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Astron. Astrophys. 357, 608-620 (2000)


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Doppler imaging of stellar surface structure

XIII. The flaring RS CVn-binary HD 291095 = V1355 Orionis

K.G. Strassmeier *

Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria (strassmeier@astro.univie.ac.at)

Received 19 January 2000 / Accepted 9 March 2000

Abstract

We present the first Doppler images of the newly discovered RS CVn binary HD 291095. The star is a synchronuously rotating subgiant in a 4-day spectroscopic binary with an unseen companion and is particularly interesting because it is one of the few evolved stars that show large flares. Three consecutive years of moderate-resolution KPNO spectra and continuous VI and by photometry with our APTs reveal a large, cool, and long-living asymmetric polar spot. Its temperature is approximately 1100 K below the average photospheric temperature. Several low latitude and even equatorial spots were evident at the same time. We interpret this latitudinal spot bimodality to be due to a combination of poleward meridional circulation and more frequent magnetic reconnections near the pole than near the equator.

During the 1998 Doppler-imaging observations, a strong flare in H[FORMULA] was detected which coincided with a meridian passage of the most asymmetric part of the polar spot. We estimate a total flare energy of 5[FORMULA]1034 erg typical for flares on very active RS CVn systems. No photospheric heating is evident in our surface maps from optically thin spectral lines of various temperature sensitivities.

Key words: stars: activity – stars: imaging – stars: individual: HD 291095 – stars: late-type – stars: starspots

* Visiting Astronomer, Kitt Peak National 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: June 5, 2000

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