The expanding chromospheres of A stars

Details The expanding chromospheres of A stars The expanding chromospheres of A stars

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.6083s&link_type=abstract

HST Proposal ID #6083

Physics

Hst Proposal Id #6083 Cool Stars

Scientific paper

Our Cycle 2 GHRS spectra of the C II {1334.5 Angstrom, 1335.7 Angstrom} lines of the bright A7 V star Altair reveal that the chromospheric emission of this star is blueshifted by 60 kms or more with respect to its photospheric spectrum, making it the first normal main sequence A star known to have an expanding chromosphere, that is to say, a warm wind. To confirm this result, we now propose to obtain high quality GHRS spectra at Ly-alpha 1215 Angstrom for this star and for a representative sample of stars with mid- to late-A spectral types. Ly-alpha should be the strongest emission line in the UV spectrum of any A star with a chromosphere. We will look for asymmetries in the line profile due to mass loss and will model the Ly-alpha spectra using a NLTE moving atmosphere code in order to estimate the wind velocity and mass loss rate.

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