Chromospheric Activity in Old Stars: HD 106516

Details Chromospheric Activity in Old Stars: HD 106516 Chromospheric Activity in Old Stars: HD 106516

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7395p&link_type=abstract

HST Proposal ID #7395

Computer Science

Hst Proposal Id #7395 Cool Stars

Scientific paper

All normal stars cool enough to have convection zones share a common minimum level of chromospheric activity which decreases with advancing spectral type; most show higher emission levels which vary with time. The ubiquity of a minimum ``basal'' level suggests that this component of chromospheric activity is produced by some form of time- and metallicity-independent mechanism, such as acoustic waves arising from convection, while activity above this level most probably originates with magnetic fields generated by a rotationally-driven dynamo. Such a picture implies that even very old cool stars should show a minimum level of such activity, and that ones with rotationally-generated magnetic fields should show a higher level. Our Cycle 5 GHRS snapshot program has confirmed the first prediction: all nine of the old, low-metallicity, Population II field subdwarfs that were observed do indeed show chromospheric Mg II emission. In this STIS GO proposal we are requesting a Mg II observation for the tenth star of that sample, the only one with measurable rotation. Both the profile and the level of Mg II emission should help indicate to what extent rotation affects chromospheric emission in very old solar-type stars. This observation failed in Cycle 5 due to a failed guide star acquisition, and was not repeated in accord with snapshot policy.

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