EUVE Spectra of Alpha Aurigae (Capella) at Different Phases

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Session 5 -- Chromospheres/Coronae/Active Binaries
Display presentation, Monday, 30, 1994, 9:20-6:30

[5.08] EUVE Spectra of Alpha Aurigae (Capella) at Different Phases

A. K. Dupree (CfA), N. S. Brickhouse (CfA), G. A. Doschek (NRL), G.~J.~Hanson (CfA), and J. C. Raymond (CfA)

Extreme ultraviolet spectra ($\lambda$70 -- $\lambda$740) of the bright spectroscopic binary system, Capella (Alpha Aurigae; G5 III+G0 III) were obtained at three different orbital phases ($\phi$ = 0.84, 0.45, and 0.97) using the spectrometers on the Extreme Ultraviolet Explorer satellite (EUVE ) in December 1992, December 1993, and February 1994. All of the spectra show rich emission dominated by iron emission lines: Fe IX, Fe XV -- XXIV. The emission measure for the system generally maintains a continuous distribution of plasma temperatures between $10^5$ and $10^{7.8} \ K$, with a clear minimum near $10^6\ K$ and a local maximum at $6 \times 10^6\ K$; these features were established from the first spectrum (cf. Dupree et al. , 1993, ApJ, 418, L41). However the relative fluxes of ion species have varied significantly from the December 1992 observations, indicating a modification of the apparent structure of the atmosphere of the Capella system when viewed at different orbital phases. Emission measure distributions, spectral syntheses, and density diagnostics will be presented for the the observations. These spectra were obtained through the Guest Observer Program for the EUVE satellite; this research is supported in part by NASA Grant NAG5-2330 to the Smithsonian Institution.

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