The nearby red giant beta Ceti (HD 4128: K0 III; d= 16 pc) is in the postflash core helium burning phase. It is a member of a class of coronally active ``Clump'' giants that includes the G8 primary of Capella (alpha Aur: G8 III + G1 III) and the Hyad theta (1) Tauri (K0 III). Prior to the first ascent of the giant branch, such stars very likely were hyperactive Hertzsprung-gap giants, like the G0 secondary of Capella and 31 Comae (G0 III). HST/GHRS obtained spectra of beta Ceti on 1994 June 2, in five intervals using both the SSA and LSA. Exposure times ranged from 5.4 minutes (ECH-B/2800 Angstroms) to 43.5 minutes (G160M/1400 Angstroms). Strong emissions of H I, Mg II, Si III, Si IV, C IV, and N V were recorded with high S/N. Fainter lines of N I, C I, Si I, O IV], and O V] also were seen. After correction for systematic effects, we find that emissions which form below about 3*E(4) K are close to the rest frame of the star, but higher excitation species are systematically redshifted (as had been suggested previously on the basis of lower S/N IUE echelle spectra). The redshifts are 10+/-2 km s(-1) at N V/O IV temperatures (2*E(5) K); 16+/-1 at C IV (1*E(5) K); and 7+/-1 at Si IV (6*E(4) K). The strong high-excitation emissions have nearly uniform FWHM's (~ 90 km s(-1) ), but show evidence for ``broad components'' (FWHM ~ 150 km s(-1) ) at the bases of their profiles which are slightly more redshifted than the parent lines. We see no evidence for wind absorptions in the very high S/N (>50:1) profiles of Mg II k or H I Lyalpha , although the former displays a clear chromospheric central reversal outside of the sharp ISM feature. We will compare the HST/GHRS spectra with a 140 ks pointing on beta Ceti by the EUVE, conducted during the six day period beginning 1994 September 30. This work was supported by NASA grants GO-5323.01-93A (HST) and NAG5-2274 (EUVE).
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1994