Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...224..527s&link_type=abstract
Astrophysical Journal, Part 1, vol. 224, Sept. 1, 1978, p. 527-534.
Astronomy and Astrophysics
Astronomy
37
B Stars, Early Stars, Infrared Astronomy, Stellar Spectrophotometry, High Temperature Tests, Hydrogen, Stellar Envelopes, Thermodynamic Equilibrium
Scientific paper
Spectrophotometry of the classical Be star Gamma Cas (1-4 microns, with about 2% spectral resolution) is presented. These data, together with existing broad-band observations, are accurately described by simple isothermal LTE models for the IR excess which differ from most previously published work in three ways: (1) hydrogenic bound-free emission is included; (2) the attenuation of the star by the shell is included; and (3) no assumption is made that the shell contribution is negligible in some bandpass. It is demonstrated that the bulk of the IR excess consists of hydrogenic bound-free and free-free emission from a shell of hot ionized hydrogen gas, although a small thermal component cannot be ruled out. The bound-free emission is strong, and the Balmer, Paschen, and Brackett discontinuities are correctly represented by the shell model with physical parameters as follows: a shell temperature of approximately 18,000 K, an optical depth (at 1 micron) of about 0.5, an electron density of approximately 1 trillion per cu cm, and a size of about 2 trillion cm. Phantom shells (i.e., ones which do not alter the observed spectrum of the underlying star) are discussed.
Erickson Edwin F.
Scargle Jeffrey D.
Strecker Donald W.
Witteborn Fred. C.
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