Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...384..613j&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 384, Jan. 10, 1992, p. 613-623.
Astronomy and Astrophysics
Astrophysics
16
Atomic Excitations, Cool Stars, Late Stars, Metallicity, Radiative Transfer, Stellar Spectra, Electron Transitions, Emission Spectra, Iron, Iue, Line Spectra, Ultraviolet Spectra
Scientific paper
Excitation mechanisms are discussed for the 'resonance' transitions (between the 3d(6)4s, 3d7, and 3d(6)4p configurations) of Fe II observed in emission in the near-UV spectra of cool stars. The analysis is based upon: (1) emission measure analysis of previously measured lines in IUE spectra of cool giants; (2) discussion of the behavior of Fe II lines observed above the solar limb from Skylab spectra; (3) approximate radiative-transfer calculations in a 59 level Fe-II model atom using mean escape probabilities and a parameterization of optical radiation fields; and (4) accurate radiative transfer calculations in a smaller atomic model. The solar spectra show unambiguous evidence that electron collisions are responsible for most of the Fe-II emission observed above the white-light limb. The terms leading to UV multiplets 3-6, 34-36, and 61-64 are excited by electron excitation of metastable quartet terms below about 4 eV, followed by photoexcitation in lines at optical wavelengths by photospheric radiation. A 'cool-star' diagnostic diagram is constructed showing the regimes in which electron collisions and continuum photoexcitation are important in the chromospheres of cool stars.
Feldman Uri
Jordan Cathy
Judge Philip G.
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