Far UV spectroscopy of the circumstellar environment of the Herbig Be stars HD 259431 and HD 250550

We present an analysis of FUSE spectra of HD 259431 and HD 250550, two young Herbig Be stars. Numerous absorption lines of H 2 are seen in the spectrum of each star, revealing large amounts of this gas on the lines of sight. In addition, absorption lines from atomic species in different ionization and excitation states are also identified. We demonstrate that all these species probe the close circumstellar environment around the stars, with two or even three temperature components in HD 259431, as revealed by molecular gas analysis. Although favouring the flared disk scenario, our results do not rule out the possibility that we actually detect CS envelopes/halos around these stars.