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C. Martin, J.-C. Bouret, M. Deleuil (LAM), T. Simon (IfA, U. of Hawaii), C. Catala (Observatoire de Meudon), A. Roberge (DTM)
We present FUSE observations of the Herbig Ae/Be star HD 250550, a well known analog to the prototype of the whole class, AB Aurigae. Previous optical and UV (IUE) observations showed that HD 250550 possesses a strong stellar wind and a dense chromosphere. Quite unexpectedly, the FUSE spectra of HD 250550 show only a faint emission feature at 977 Å, and emission from O VI resonance lines is barely visible, contrary to what was observed for AB Aurigae by FUSE.
Several absorption features from molecular hydrogen are observed and show that H2 is thermalized up to J=3 and its radial velocity is identical to that of the surrounding molecular cloud's velocity. Similar velocities are measured on absorption features arising from excited levels of atomic species like N I, Cl I and Cl II, P II, Fe II and Fe III. This strongly favours a circumstellar origin for these gazeous components.
Besides, the spectra also contains several other absorption features of interstellar origin (Ar I, Fe II, ...) as demonsrated by the lower radial velocities and excitation temperatures.
Our results reveal a complex circumstellar environment with unxepected characteritics, and suggest that quite a large part of the original molecular cloud that collapsed to form the star is still present, though its spatial distribution is still unknown.
Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.