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T. P. Snow, E. J. Baker, B. L. Rachford, S. M. Doyle (CASA, University of Colorado)
The negative ion H- is widely understood to be important in many astrophysical environments, including the atmospheres of late-type stars like the Sun. However, the ion has never been detected spectroscopically outside of the laboratory. A search for the far ultraviolet auto-ionizing transitions of H- in interstellar and circumstellar matter seems to be the best hope for directly detecting this ion. We undertook a highly sensitive search using data from the FUSE far-UV instrument. We concentrated on two types of sightlines; planetary nebulae, where model calculations suggest a significant abundance of H-, and translucent clouds, where H- might form on dust grains as an intermediate step during molecular hydrogen formation. Our upper limit column density of H- is 3*1014 cm-2. This limit is too high to be useful in the case of circumstellar shells of planetary nebulae, but it is close to predicted column densities for translucent clouds if indeed H- is part of the H2 formation process, and could constrain or even eliminate this model.
This work was funded through NASA contract NAS5-32985. The research made use of the MAST FUSE archive.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.