Doppler imaging of stellar surface structure - X. The FK Comae-type star HD 199178=V 1794 Cygni

Doppler imaging is used to derive the surface temperature distribution of t he Fit Comae star HD 199178 for five observing epochs between 1988 and 1997 . Our maps are mainly based on Ca I 6439-Angstrom line profiles and simulta neous and contemporary BV and VI photometry. All images of HD 199178 are ch aracterized by a large polar spot and several low-latitude spots with an av erage surface temperature difference, photosphere minus spots, of 710+/-260 (rms) K for the equatorial spots, approximate to 1700 K for the polar spot, and 1300+/-300(rms)K for the polar-spot appendages. The lifetime of some o f 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 ste llar rotations, and could be as long as 12 years since its discovery by Vog t in 1985. Two consecutive Doppler maps in 1989 show no evidence for differ ential surface rotation, nor is there substantial evidence for the existenc e 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 estima ted from the timing of light-curve minima could lead to grossly overestimat ed lifetimes of individual spots. With the aid of our optical spectra and the Hipparcos parallax, we redeterm ine the absolute stellar parameters of HD 199178 and confirm it to be a sin gle G5III-IV star and find 1.65 M. and 11 L. with T-eff approximate to 5450 K, log g = 2.5, and solar abundances.