In order that a rotating star be in hydrostatic and radiative equilibrium, the effective temperature of the stellar atmosphere must decrease between the star's poles and its equator. Wavelength differences in this “gravity darkening” have been suggested to account for the observed differences in the rotational broadening of lines in the ultraviolet and visual spectral regions (hutchings, 1976; Sonneborn and Collins, 1977). This paper investigates the problem, using detailed model atmospheres to examine the surface brightness distribution of a rapidly rotating star.

On the basis of high-dispersion spectra (I. Appenzeller, C. Bertout) and other observational material HD 200775 has been reanalyzed using ι Her as a comparison star. By comparing the depths in the wings of Hγ and Hδ and the equivalent widths of HeI-lines with predictions from model atmospheres we find for both stars Teff = 17000 ± 1000 k (in the scale of Kurucz' models, 1979) and log (g cm s−1) = 3.6 ± 0.3 corresponding to a spectral type of B3V. With a colorexcess EB-V = 0.56 and the standard interstellar reddening also the continuum energy distribution of HD 200775 corresponds to the above photospheric parameters if one allows for some circumstellar emission. However, the interstellar absorption features (4430 A and 2200 A) are of unusual weakness. The strength of the Hα emission requires either a nonthermal source of energy or a substantial rate of photo ionization from the level n = 2. We tend to conclude that for this second reason the dilution factor in the HII-region cannot be less than 10−2, a conclusion which is in accord with the finding that the radio emission at λ = 2 cm is less than 0.3 mJ which also indicates a very compact HII-region.

“Herbig-Ae-Be-Stars” are assumed to be pre-main sequence objects of moderate mass with line emitting envelopes of an unknown nature. From our present theoretical knowledge it is not clear whether the physical structure of these envelopes is dominated by mass accretion or mass loss induced by a stellar wind or radiation pressure effects. Radial velocities and remarks on peculiarities are given for the star HD 200 775, which seems to represent a typical Herbig-Ae-Be-star fairly well. A catalogue of about 60 supposed Herbig-Ae-Be-stars is presented and comments, in particular on the brighter members, are invited.

This paper, written in summary of IAU Symposium 98 on the Be Stars, contains an outline of the proceedings, organized according to physical parameters of the stars, the circumstellar environment, models explaining the data, and a summary of the outstanding problems. Suggested future observations and needed theoretical work are described.