Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991a%26a...250..573c&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 250, no. 2, Oct. 1991, p. 573-579. Research supported by CNR, CNRS, and MURST.
Astronomy and Astrophysics
Astrophysics
11
Chromosphere, Iue, Lyman Alpha Radiation, Stellar Atmospheres, Stellar Rotation, Stellar Spectra, A Stars, Hertzsprung-Russell Diagram, Line Shape, Stellar Structure
Scientific paper
The definition of the spectral type along the main sequence where chromospheres appear is of crucial importance for the study of the stellar structure and the chromospheric heating mechanism. Due to the bright UV continuum and the fast rotation typical of early type stars, the Ly-alpha emission core remains the only good chromospheric indicator in late A-type stars. Altair (A7IV - V) lays just in the spectral type range where the most common chromospheric and transition region indicators are not generally observed. The detection of the Ly-alpha emission core and coronal X-ray emission makes Altair a key star in this respect. Different methods which make it possible to eliminate the geocoronal Ly-alpha emission from high dispersion IUE spectra obtained with the large aperture are examined. Using four long exposure images, a well defined Ly-alpha emission profile of chromospheric origin showing a wide central IS absorption is obtained for Altair.
Catalano Santo
Ferrero Rubens Freire
Gouttebroze Pierre
Marilli Ettore
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