On the Spectrum of the Herbig Be Star HD 200775

Abstract

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 T_eff = 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 E_B-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.