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A. Lecavelier des Etangs, A. Vidal-Madjar, R. Ferlet (IAP), A. Roberge, P.D. Feldman (JHU), M. Deleuil, J.-C. Bouret (LAM), M. André, W.P. Blair, H.W. Moos (JHU), FUSE Science Team
We present the first far UV spectrum of Beta Pictoris obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Although the stellar continuum drops below detectability for wavelengths shorter than 1100~Å, the C{\sc iii} line at 977~Å\ and the O{\sc vi} doublet at 1032 and 1037~Å\ are clearly detected in emission. These emissions are believed to have a stellar origin. Because we did not detect H2 absorption in our spectrum, the coincidence of O{\sc vi} and H2 transitions allows us to set a very low upper limit on the H2 column density toward \beta~Pic. This is surprising, as Beta Pic has one of the largest circumstellar disks seen around a main-sequence star. From the comparison with HST observations, we obtain a CO/H2 ratio above the typical interstellar value of 10-4; this seems to confirm the circumstellar origin of the observed CO. Species observed in the \beta~Pic circumstellar gas at the stellar radial velocity, like Fe{\sc ii} and Ca{\sc ii}, feel strong radiation pressure from the star and should be ejected from the system. Lagrange et al. (1998) suggested that these species could be slowed down by a thick, colliding torus of massive gas; our non-detection of H2 toward Beta Pic leaves this dynamical problem unresolved.
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U.S. participants has been provided by NASA contract NAS5-32985.
The author(s) of this abstract have provided an email address for comments about the abstract: lecaveli@iap.fr