Physics
Scientific paper
Jul 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984iue..prop.1755a&link_type=abstract
IUE Proposal ID #RSGTA
Physics
Scientific paper
We propose to study, at high dispersion, the behavior of the ultraviolet emission line spectrum of the RS CVn-type binary Sigma Geminorum (KI III + ?) as an optically identified starspot group rotates over the limb of the K giant and onto the visible hemisphere. The scientific goal is to distinguish between the two most promising hypotheses to explain the significant changes that were observed in a pair of IUE SWP echelle images of Sigma Gem taken over consecutive days in May 1982: (1) a flare which occurred near the receding limb of the giant (or near disk center but accompanied by significant downflows of 10^5 K material); or (2) the rotation off of the visible hemisphere of a small-scale, but bright, active region associated with a previously identified optical starspot group. We feel that the behavior of similar systems, like II Peg, favors the second hypothesis. If so, a mechanism must operate in the cool, fast rotating giants to produce a significant spatial concentration of the decaying magnetic fields that are thought to be responsible for the enormously enhanced far-ultraviolet emissions of the RS CVn-type binaries. We believe that it is essential to understand why the "activity" on the cool giants can become so concentrated and intense. An important way to explore in detail the physical association of high excitation active regions with photospheric starspot groups is to use the technique of "Doppler, Imaging", developed by Vogt and collaborators to study the changing profiles of absorption features in the spectra of fast rotating late-type stars. We have applied the emission-line analog of the approach previously to the shortperiod RS CVn system, HR 1099, and propose to continue our work in the 7th-year of IUE with a study of Sigma Gem. In addition, we intend to search for the occurrence of flare activity in Si IV and C IV by monitoring the farultraviolet spectrum of a Gem at low dispersion. As a novel twist to the program, we intend to arrange simultaneous coverage with the Very Large Array to explore the association of the microwave corona of a Gem with the farultraviolet emission regions and optical starspots. [Note: this program could be easily integrated into an ITF recalibration effort for the LWP, LWR and SWP cameras: The optimum observing window is in late February or early March, before Spring shadow season.]
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