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Session 13 - Stellar Spectra.
Display session, Wednesday, January 07
Exhibit Hall,
We have obtained spectroscopic observations of the Mg II h amp; k emission lines from three carbon stars, using the moderate resolution (R\ge20,000) G270M grating of the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). The emission profiles from all three stars are very broad and heavily mutilated by overlying absorption. The profiles from two of the stars, TX Psc (N0; C6,2) and TW Hor (N0; C7,2), are very similar. However, the profiles from the third star, UU Aur (N3; C5,3) are dramatically different from the other two stars on the blue side, with strong emission persisting out to \approx -200 km/s (cf. to only weak emission out to \approx -100 km/s in TX Psc and TW Hor). If the intrinsic (i.e. chromospheric) width of the emission in the carbon stars is comparable to that in oxygen-rich giants, then the spectra of the first two carbon stars are easily understood in terms of additional overlying absorptions, but the amount of excess emission from the blue side of the UU Aur profiles is difficult to explain. If, on the other hand, the intrinsic width of the Mg II emission in the carbon stars is more comparable to that of the supergiant oxygen-rich stars (e.g. \alpha Ori), then all the carbon stars have tremendous overlying absorption on both the blue and red wings of the profiles and UU Aur is notable only because it has significantly less absorption on the blue-side of the profiles, relative to the other carbon stars. In this paper, we present an analysis of the spectra and our interpretation, based on all the available data, of these fascinating and complex line profiles and their formation.
