AAS 195th Meeting, January 2000
Session 76. Geometrically Variable Stars
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

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[76.04] Capella: Separating the Giants

P.R. Young, A.K. Dupree (Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138), R.L. Gilliland (Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218)

Faint Object Camera (FOC) images from the Hubble Space Telescope are presented showing a clean spatial separation of the two giants in the Capella system (\alpha Aur, HD 34029). These images were taken at elongation (Dec.\ 21, 1997) when the apparent separation of the stars, 55 milliarcseconds, corresponded to ~4 pixels in the FOC image. Careful use of the objective prism mode of the FOC yielded ultraviolet spectra with dispersion perpendicular to the axis of separation of the two stars. The relative flux contributions to prominent UV emission lines such as O\,I \lambda1305, C\,II \lambda1335 and Si\,IV \lambda1397 can then be derived.

This direct measurement of each star's emission can be compared to the total spectrum as obtained by STIS at a similar phase (Sept.\ 12, 1999) where multiple gaussian fitting must be invoked to separate the individual contributions. The relation of these ratios to the known evolutionary states of the two stars, and the consequences for theories of stellar magnetic dynamos are discussed.

This research is supported in part by an STScI Grant to SAO.

The author(s) of this abstract have provided an email address for comments about the abstract: pyoung@cfa.harvard.edu

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