The outer atmospheres of the coolest M giants - Ultraviolet spectra of Rho Persei, 2 Centauri, G Herculis, Theta Apodis, and R Lyrae

Details The outer atmospheres of the coolest M giants - Ultraviolet spectra of Rho Persei, 2 Centauri, G Herculis, Theta Apodis, and R Lyrae The outer atmospheres of the coolest M giants - Ultraviolet spectra of Rho Persei, 2 Centauri, G Herculis, Theta Apodis, and R Lyrae

Feb 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988apj...325..355e&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 325, Feb. 1, 1988, p. 355-371.

Astronomy and Astrophysics

Astrophysics

25

Giant Stars, Late Stars, M Stars, Stellar Atmospheres, Ultraviolet Spectra, Chromosphere, Iue, Magnesium, Radial Velocity, Resonance Lines, Spectral Line Width

Scientific paper

High-dispersion IUE spectra of five M giants (spectral type M4 - M7) are discussed. Most of the emission lines and stronger absorption lines are identified for ρ Per in the wavelength range λλ2320 - 3030. The chromospheric spectra of ρ Per, R Lyr, 2 Cen, and g Her are remarkably similar, both among themselves and with respect to stars of earlier spectral type. Analysis of the emission lines leads to the picture of a turbulent, possibly inhomogeneous, chromosphere. Relative strengths and actual widths of the Fe II and Mg II lines are roughly the same in all these stars and indicate large optical depth in the chromosphere. Electron temperatures have been derived from collisionally excited lines of Fe II. Values could be as low as 6000K but are more likely near 10,000K. The analysis suggests that photoionization by Lyman lines is the chief source of ionization in chromospheres of cool giants. The velocities and shapes of chromospheric lines require both neutral and ionized species to be mixed together in the same part of the chromosphere and not to be primarily stratified with height.

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