Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...251..564b&link_type=abstract
Astrophysical Journal, Part 2, vol. 251, Dec. 15, 1981, p. 564-570.
Astronomy and Astrophysics
Astrophysics
3
Giant Stars, Late Stars, M Stars, Radial Velocity, Stellar Envelopes, Stellar Spectra, Velocity Distribution, Emission Spectra, Photosphere, Spectral Line Width, Spectrograms, Stellar Models
Scientific paper
The M2.5 II-III star, β Pegasi, has been found to have exceptionally strong Fe II emission lines' in the 3100 Å region and exceptionally strong circumstellar absorption at Ca II H and K. Nine spectrograms at 6.7 Å (0.13 Å spectral resolution) were obtained over a 4 yr interval with the 2.24 m telescope at Mauna Kea in the 3100-4000 A region to determine radial velocities and line profile shapes to analyze the velocity field and extent of the shell. The Fe II emission is blue-shifed and asymmetric in the sense to indicate outfiowing material. A specific model of an extended moving envelope following the method of Kunasz and Hummer produces emission-line profiles which match the observed Fe II A3228 feature when the material in a 2R* shell expands from 0 to 25 km s-1 and has a characteristic turbulent velocity of 10 km 1 Inferences from the Ca II circumstellar absorption feature show it is formed over a velocity gradient of 0 to 25 km s-1 also; the turbulence beyond ∼2R* averages < 4 km s-1. The giant β Peg, with expansion beginning in the innermost shell, shows more uniform motions in its envelope than do the supergiants α Ori and α Sco.
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