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S. Brittain, J. Najita (NOAO)
Fundamental ro-vibrational CO emission has proven to be a powerful probe of the physical conditions of the inner disk of low and high-mass stars. Measurement of the CO profile yields the spatial distribution of gas in the disk. This information may be used to signify gaps carved out of the inner disk. It also provides a measure of the inner radius of the gas disk. This truncation radius may be used to infer the strength of a stellar magnetic field. This is particularly apropos to HAe stars since their magnetic field strength is so difficult to measure directly.
We have observed 14 HAeBe stars and detected the v=1-0 P30 CO line from 9 of the 14 sources. Our results indicate that CO can be excited thermally or by UV fluorescence. The latter case, which is rare, is indicative of a remarkably clear inner disk. Of all the sources observed only one source, HD 141569, reveals evidence of UV fluoresced CO. Stars with optically thick inner disks (E(K-L)>0.5) generally reveal thermally excited CO emission, whereas stars with optically thin inner disks do not.
Naively one might infer that the connection between the presence of thermally excited CO emission and E(K-L) implies CO emission simply traces the presence of dust. However, in the case of T Tauri stars, the correlation between stellar accretion rate and K-L excess also applies to CO emission. Thus this correlation is suggestive of a connection between accretion heating and CO excitation. An improved understanding of the excitation of the gas will help us to understand how to use these tracers to constrain the gas content of inner disks.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.