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Astron. Astrophys. 347, 212-224 (1999)


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Doppler imaging of stellar surface structure

X. The FK Comae-type star HD 199178 = V 1794 Cygni

K.G. Strassmeier  *  1, S. Lupinek 1, R.C. Dempsey[FORMULA]  2 and J.B. Rice 3

1 Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, A-1180 Wien, Austria (strassmeier, lupinek@astro.univie.ac.at)
2 NASA Johnson Space Center, Code DF25, Houston, TX 77598, USA (robert.c.dempsey1@jsc.nasa.gov)
3 Department of Physics, Brandon University, Brandon, Manitoba R7A 6A9, Canada (rice@brandonU.ca)

Received 24 November 1998 / Accepted 19 January 1999

Abstract

Doppler imaging is used to derive the surface temperature distribution of the FK Comae star HD 199178 for five observing epochs between 1988 and 1997. Our maps are mainly based on Ca I 6439-Å line profiles and simultaneous and contemporary BV and VI photometry. All images of HD 199178 are characterized by a large polar spot and several low-latitude spots with an average surface temperature difference, photosphere minus spots, of 710[FORMULA]260(rms) K for the equatorial spots, [FORMULA]1700 K for the polar spot, and 1300[FORMULA]300(rms) K for the polar-spot appendages. The lifetime of some of the low-latitude spots was found to be as short as one month or even less. The lifetime of the polar spot and most of its very cool appendages must exceed the time of our observations, i.e. 9 years or approximately 1000 stellar rotations, and could be as long as 12 years since its discovery by Vogt in 1985. Two consecutive Doppler maps in 1989 show no evidence for differential surface rotation, nor is there substantial evidence for the existence of active longitudes in any of our five images. Instead, we suspect that most of the time variability of the surface features on HD 199178 is short term and possibly chaotic in origin. We conclude that spot lifetimes estimated from the timing of light-curve minima could lead to grossly overestimated lifetimes of individual spots.

With the aid of our optical spectra and the Hipparcos parallax, we redetermine the absolute stellar parameters of HD 199178 and confirm it to be a single G5III-IV star and find 1.65 [FORMULA] and 11 [FORMULA] with [FORMULA] K, [FORMULA], and solar abundances.

Key words: stars: activity – stars: imaging – stars: individual: HD 199178 – stars: late-type – stars: starspots

* Visiting Astronomer, Kitt Peak National Observatory and 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) 1999

Online publication: June 18, 1999

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