Beta Cassiopeiae is a fast rotating early-F subgiant that exhibits smallamplitude pulsations in optical light and radial velocity of the delta Scuti class, and is a bright far-ultraviolet emission-line source having surface fluxes in excess of thirty times those of the quiet Sun. It is plausible that the fast rotation of a Cas, and the recent development of a shallow convection zone as the star has evolved into the blue edge of the Hertzsprung gap, have conspired to produce substantial amounts of surface magnetic activity by means of the dynamo mechanism. The strong chromospheric and higher temperature emissions might then arise from processes analogous to those operating in magnetic "active regions" on the Sun. However, it certainly also is possible that the strong ultraviolet emissions are a byproduct of the delta Sct phenomenon, itself, as in fact has been suggested recently in the case of the Cepheids, which are similar in temperature but more luminous than the delta Scuti stars. Accordingly, I feel that beta Cas is a worthwhile subject for a detailed study with IUE in order to investigate the properties of its chromospheric and higher -temperature emission lines: High-dispersion, far-ultraviolet measurements of beta Cas would extend previous studies of F-M dwarfs, giants, and supergiants into the earliest spectral types where solar-like chromospheric phenomena have been identified; and IUE is sufficiently sensitive to test the hypothesis of pulsationinduced chromospheric heating, through monitoring of the lowdispersion SWP spectrum of beta Cas over several of the 2^h.4 cycles for evidence of periodic behavior in the far-ultraviolet emissions.
- Pub Date:
- July 1984