On the formation of the hydrogen shell spectrum and the envelopes of some shell stars.
Abstract
The formation of shell absorption lines in the Balmer series of the shell stars is considered. The expression for the line profiles is given by taking into account the existence of a large-scale velocity field due to differential rotation andlor other causes. When no appreciable Balmer progression appears, the problem is simplified and we can specify an envelope by two kinds of parameters: the fractional area p of the stellar disk which is screened by the envelope, and the mean optical thickness r(Hoc) of the envelope in the Hoc line. Applications are made for six shell stars ( Per, 4; Per, Tau, Mon A, Cap, and EW Lac), for each of which the values of p and r(Hoc) are estimated based on the measurements of the radial velocities and central intensities of shell lines. The results show that the envelope can be well specified either by a single set of p and (Hoc) (the single4ayer approximation), or by two sets of them (the double-layer approximation). The equatorial radii, electron densities and masses of the envelopes of these stars are estimated under the assumption of rotational broadening and the equator-on model. The results are also compared with the current models of the circumstellar envelopes of Be stars derived from the infrared and polarization data. Agreement is satisfactory in general. The possible effect of the continuous emission from the envelope is considered in some detail and no appreciable influence on the present analysis is seen. Finally an implication of the last quantum number t of the visible shell lines in the Balmer series is briefly discussed in the Appendix. Key words: Be stars; Extended atmospheres; Shell stars; Spectral line formation.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- 1978
- Bibcode:
- 1978PASJ...30..385K
- Keywords:
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- Be Stars:Circumstellar Envelopes;
- Be Stars:H Alpha