Free access article

A&A 435, 261-273 (2005)
DOI: 10.1051/0004-6361:20042239

Doppler imaging of Speedy Mic using the VLT

Fast spot evolution on a young K-dwarf star

U. Wolter¹, J. H. M. M. Schmitt¹ and F. van Wyk<sup>2

1</sup>  Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: uwolter@hs.uni-hamburg.de, jschmitt@hs.uni-hamburg.de
²  South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
    e-mail: fvw@saao.ac.za

(Received 22 October 2004 / Accepted 15 December 2004 )

Abstract
We study the short-term evolution of starspots on the ultrafast-rotating star HD 197890 ("Speedy Mic" = BO Mic, K 0-2 V, P_rot=0.380 d) based on two Doppler images taken about 13 stellar rotations apart. Each image is based on spectra densely sampling a single stellar rotation. The images were reconstructed by our Doppler imaging code CLDI (Clean-like Doppler imaging) from line profiles extracted by spectrum deconvolution. Our Doppler images constructed from two independent wavelength ranges agree well on scales down to 10° on the stellar surface. In conjunction with nearly parallel V-band photometry our observations reveal a significant evolution of the spot pattern during as little as two stellar rotations. We suggest that such a fast spot evolution demands care when constructing Doppler images of highly active stars based on spectral time series extending over several stellar rotations. The fast intrinsic spot evolution on BO Mic impedes the determination of a surface differential rotation; in agreement with earlier results by other authors we determine an upper limit of .

Key words: stars: activity -- starspots -- stars: late-type -- stars: imaging -- stars: individual: BO Mic

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© ESO 2005

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