Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apjs...74..891r&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 74, Dec. 1990, p. 891-909.
Astronomy and Astrophysics
Astrophysics
51
H Alpha Line, K Stars, Late Stars, M Stars, Main Sequence Stars, Metallicity, Absorption Spectra, Calcium, Chromosphere, Emission Spectra, Stellar Spectra
Scientific paper
Observations of H-alpha and Ca II H and K in the chromospheres of 50 main-sequence K and M stars are reported. The photospheric contribution to the integrated core flux in these lines is found to be more important than previously thought, and earlier estimates of the basal flux of cool dwarf stars are revised. The H-alpha data confirm the presence of both an upper and a lower limit to the H-alpha equivalent width attained at any given spectral type. The maximum H-alpha absorption strength decreases gradually toward cooler stars while the maximum 'saturated' quiescent emission strength increases. The Ca II emission strength is related to the strength of the emission or absorption feature at H-alpha, but there is not a one-to-one correlation. The main results may be explained in terms of photoionization and collisional control of the non-LTE H-alpha source function. Several aspects of the structure and heating of the outer atmospheres of dwarf K and M stars are discussed.
Cram Lawrence E.
Giampapa Mark S.
Robinson Richard D.
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