Computer Science
Scientific paper
Jul 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984iue..prop.1881s&link_type=abstract
IUE Proposal ID #CCGTS
Computer Science
Scientific paper
59 Vir (GO V) and 31 Com (GO III) are among the youngest G stars for which high dispersion spectra can be obtained with the short-wavelength camera of IUE. Their ages are estimated to be 0.2 Gyr (31 Com is a member of the Coma cluster). 59 Vir was observed at low resolution in a study of the relation between ultraviolet chromospheric activity and age in solar dwarf stars. 31 Com was observed as an example of a young yellow giant making its first crossing of the Hertzsprung Gap. Their spectra show bright chromospheric and transition region emission lines. We request observing time in this proposal to secure doubleshift (up to 16 hours) high dispersion exposures of each star with the SWP camera. These observations will allow us to resolve the profiles of individual chromospheric and transition region emission lines. From radiative transfer calculations, emission measure analyses, and line flux ratios, we will derive temperature, density, and velocity field models in the chromosphere and transition region. We will investigate the energy balance of these atmospheres in order to compare their non-thermal energy requirements with results derived for older solar-type dwarfs and more highly evolved yellow and red giants. With precautions to ensure the fidelity of the wavelength scale, we will also look far differential velocity shifts between TR and chromospheric lines, which may arise from global atmospheric circulation patterns. We have shown in previous work that redshifted TR lines are most clearly seen in giant stars and that the downflows causing the line shifts may affect the energy balance of giant atmospheres. As one of the very few normal G giants whose spectrum can be studied at high dispersion, 31 Com is important to such studies.
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