The High Chromospheres of the Late a Stars, ALTAIR and Alpha Cephei

Details The High Chromospheres of the Late a Stars, ALTAIR and Alpha Cephei The High Chromospheres of the Late a Stars, ALTAIR and Alpha Cephei

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6446s&link_type=abstract

HST Proposal ID #6446

Computer Science

Hst Proposal Id #6446 Cool Stars

Scientific paper

Along the lower half of the main sequence, Altair and AlphaCephei are the hottest stars known to have chromospheres. Wepropose to use the Goddard High Resolution Spectrograph, inmedium resolution mode, to record the strengths and profilesof their Si IV chromospheric emission lines at 1394Angstromand 1403Angstrom. These features have not been observedbefore in the spectrum of any late A star, and may be thehighest temperature chromospheric lines (T_e ~ 50000 K) thatcan be detected in a normal A star spectrum. We will usethese spectra, along with GHRS Ly-alpha spectra from ourCycle 5 GO program and C II spectra from our Cycle 2 program,to model the chromospheric structure of both stars, using aNLTE model atmosphere computer code. Our models for Altair andAlpha Cephei will be the first to take advantage of high S/Nspectra available from HST for a broad range of chromospherictemperatures. These calculations should help to improve ourunderstanding of the chromospheric and coronal heatingprocesses in stars with very shallow convection zones.

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