Fluorescent Clues to the Atmospheric Structure of AGB Stars

Details Fluorescent Clues to the Atmospheric Structure of AGB Stars Fluorescent Clues to the Atmospheric Structure of AGB Stars

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.4513l&link_type=abstract

American Astronomical Society, 185th AAS Meeting, #45.13; Bulletin of the American Astronomical Society, Vol. 26, p.1381

Astronomy and Astrophysics

Astronomy

Scientific paper

Results from coincident observations with IUE and the McMath--Pierce telescope are presented for the asymptotic giant branch (AGB) stars R Leo (M8 IIIe, M) and R Lyr (M5 III, SRb). This survey was made to investigate the differences between the atmospheric structure of Mira--type and semiregular variables through the Fe I (42) lines at 4202 Angstroms and 4308 Angstroms. These lines are fluoresced by the Mg II lines near 2800 Angstroms via an Fe I (UV3) transition. The Fe I (42) lines peak in flux at the same phase ( ~ 0.3) as the Mg II lines, which corresponds to a ~ 0.3 phase lag behind the peak Balmer line flux. NLTE radiative transfer calculations show that this phase lag between the Mg II and the Balmer line peak fluxes results from the existence of a permanent chromosphere in the Mira. The fact that Fe I (42) variability matches the Mg II variability indicates that these fluorescent lines originate from a cooler circumstellar shell and not from the inner--shock region or photosphere. The Fe I (42) lines in the semiregular variable do not vary from changes in the Mg II flux. This suggests that the circumstellar shells surrounding semiregulars are not as optically thick as those around Miras.

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