1. Introduction and scientific goals of this series
One of the most challenging observational goals of today's stellar activity research is to obtain two-dimensional images of inhomogeneous stellar surfaces. Spots cooler than the undisturbed photosphere of a late-type star are a manifestation of surface magnetic fields and a time-dependent study of their latitudinal and longitudinal behavior might provide a link to the stellar dynamo. Our long-term objective is thus to provide conclusive observational constraints for a generalized theory of stellar magnetism as repeatedly suggested, e.g., by Moss et al. (1991) and Landstreet (1992). The near-term goal, however, is to enlarge the available sample of stars with a Doppler map and to investigate the spot morphology as a function of stellar rotation, stellar mass, and evolutionary status. The tenth star to be investigated in this series of papers is the well-known FK Comae star HD 199178 = V1794 Cyg.
HD 199178 (V=7:m 2, G5III-IV, =3.3 days) belongs to the FK Comae group of rapidly rotating single giants. These stars are located in the Hertzsprung gap of the H-R diagram and have in common strong magnetic activity from the radio to the X-ray wavelengths (e.g., Bopp & Stencel 1981, Bopp et al. 1983, Huenemoerder 1986, Schachter et al. 1996). Because of their rapid rotation, it has been argued that FK Comae-type stars did not evolve from the main sequence as single stars but have evolved from short-period binaries (Bopp & Rucinski 1981, Webbink 1976). Fekel & Balachandran (1993) suggested another scenario in which high angular momentum material is being dredged up to the surface from a rapidly rotating core of a single star. The situation is not settled yet, we are not even sure whether stars like HD 199178 are special objects or just in a rarely observed evolutionary state. Clearly, more detailed observations of these stars are needed to understand FK Comae-type stars.
In this paper we present five new Doppler images of HD 199178 obtained between 1988 and 1997. Sect. 2 describes the photometric and spectroscopic observations. Because the present paper is already the tenth in a series of papers on Doppler imaging of late-type stars, we rediscuss in Sect. 3 some details of our (evolving) mapping technique. In Sect. 4 we obtain the stellar parameters of HD 199178 and in Sect. 5 we present the Doppler maps. Finally, in Sect. 6 we summarize our conclusions.
© European Southern Observatory (ESO) 1999
Online publication: June 18, 1999