2001/11/07 by Aki Roberge, A. Roberge, P. D. Feldman +9 · 2 citations
Chemistry · Physics and Astronomy · #Astrophysics and Star Formation Studies #Molecular Spectroscopy and Structure #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/338877
published as Roberge, A. et al. 2002, ApJ, 568, 343 · 11 pages, 4 color figures, LaTex2e, accepted for publication in ApJ
arxiv created 2001/11/07 · openalex publication_date 2002/03/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We present the first observations of the circumstellar (CS) disk system 51 Ophiuchi with the Far Ultraviolet Spectroscopic Explorer ( FUSE ). We detect several absorption lines arising from the unusual metastable atomic species N I ( 2 D ), N I ( 2 P ), and S II ( 2 D ). These levels lie 1.8-3.6 eV above the ground level and have radiative decay lifetimes of 2 days or less, indicating that the lines arise from warm CS gas. The high S/N FUSE spectra, obtained 6 days apart, also show time-variable absorption features arising from N I, N II, O I ( 1 D ), and Fe III, which are redshifted with respect to the stellar velocity. The resolved redshifted absorption extends over many tens of km s -1 (40 for N I, 100 for N II, 65 for O I ( 1 D ), and 84 for Fe III). We calculate column densities for all the variable infalling CS gasses, using the apparent optical depth method. The Fe III and N II infalling gasses must be produced through collisional ionization, and the ionization fraction of nitrogen suggests a gas temperature between 20,000 and 34,000 K. The infalling gas shows a peculiar, nonsolar composition, with nitrogen and iron more abundant than carbon. We also set upper limits on the line-of-sight column densities of H 2 and CO. These observations strengthen the connection between 51 Oph and the older debris-disk system β Pictoris and indicate that there may be infalling planetesimals in the 51 Oph system.