Computer Science
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992hst..prop.3737s&link_type=abstract
HST Proposal ID #3737
Computer Science
Hst Proposal Id #3737
Scientific paper
IUE observations of main sequence stars have established that late A and early F type stars with 0.23 < B - V <= 0.42 exhibit chromospheric emission as in- tense as that of much cooler and much more deeply convective dwarf stars like the Sun. It is suspected that the source of chromospheric heating in the hot- ter stars is the shock dissipation of acoustic waves, not the MHD waves impli- cated in solar activity. If this is so, then, on the basis of theoretical estimates of the acoustic flux produced by stellar convection, this UV chromo- spheric emission should reach maximum brightness at B - V = 0.29, near spectral type F0 V, and should decline by an order of magnitude among the middle and early A stars at B - V = 0.14. Our program with HST is designed to look for this predicted weakening of UV chromospheric emission in a group of A stars with 0.11 <= B - V <= 0.23 as a test of the acoustic heating idea. For this purpose, we are proposing to measure the strength of the chromospheric emis- sion in the resonance lines of C II near 1335 A. The spectral resolution and quality of GHRS spectra needed for such a study far exceed the capabilities of IUE, and so it only with HST that such a test of competing models of chromospheric excitation can be conducted.
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