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S. Brittain, T. Rettig (University of Notre Dame)
We present the discovery of CO and H3+ infrared emission from the inner preplanetary disk of an Herbig AeBe star. Detection of upper level transitions of CO indicates excitation by ultraviolet radiation from the central star. An analysis of the CO emission provides a rotational temperature of 190±30 K. The temperature, narrow line width and spatial profiles constrain the location of the gas to a stellar distance of 7-50 AU. The most likely source of this CO emission is from the star/disk interface where radiation clearing of the gas and dust and/or grain sublimation from the inner gap region continues. The two ortho-lines of H3+ represent the first detection of H3+ emission outside the Solar System. The only prior detection of H3+ emission outside of the laboratory has been from the atmospheres of Jupiter, Saturn and Uranus. The differing Doppler velocities and rotational temperatures of CO and H3+ suggest they are produced from different sources in the inner disk. The discovery and production of H3+ emission is difficult to explain as a result of infalling planetesimals or material in the star/disk interface. To generate further discussion, we speculate that the H3+ emission may originate from the extended atmosphere of a gas giant protoplanet prior to hydrodynamic collapse. The data were obtained from observations using CSHELL at IRTF.
Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract from the National Aeronautics and Space Administration.