Photoelectric scanner measurements of Balmer emission line profiles for southern Be stars. II. A survey for variations.
Abstract
Between 1974 and 1979, more than 800 Hα, Hβ and Hγ line profiles were measured for 36 bright southern Be and B-type shell stars as well as for three early-type supergiants (β Ori, ζ Pup, and ζ1 Sco) and for four B-type comparison stars having Balmer lines in absorption. For the measurements, a photoelectric spectrum scanner was used giving a nominal spectral resolution of about 2 Å at Hα and of 1 Å for the other lines. The program includes most of the southern Be stars reported to have Balmer line emission strength of at least e2 in the notation of Lesh (1968). An atlas of about 200 Balmer line profiles is presented containing a selection of typical profiles for the program stars. It demonstrates the variety of profiles as well as the presence of short-and long-term variations. For a few stars, the measurements could be supplemented by photographic coudé spectrograms.
The following main results and conclusions drawn from our data are: 1. If the strength of Balmer line emission according to MK classification spectrograms is at least e2 for a Be star, the equivalent widths of its Hα and Hβ emission lines exceed about -30 Å and -2.4 Å respectively. 2. Between 1974 and 1977, Balmer line emission disappeared in the spectrum of μ Cen, but reappeared for α Eri. 3. HR 2790 (= HD 57219) and HR 4618 (= HD 105382) should be deleted from Be star catalogues. 4. Projected stellar rotational velocities are determined for five Be stars for which they were not previously known. HR 5223 (= HD 120991) was detected to be a pole-on star showing the Balmer lines up to H 24 in emission in early-1979. 5. Changes of Hα equivalent width exceeding ten percent were detected with time scales from a few nights (two stars) up to several years (three stars). Only three stars out of 18 for which observations covering three years are available show Balmer line emission with constant equivalent widths and line shapes. V/R variations from night to night are visible in the Balmer emission line profiles of four stars while V/R variations on longer time scales are very common. 6. For Be stars having single Hα emission lines without central reversal, the half-width of the Hα emission line is usually less than the projected rotational velocity of the central star in the Hα emitting envelope. In a few cases, Hα line broadening is variable in time. 7. Strong persistent asymmetry of Hα emission lines probably indicates permanent radial motions in the envelopes of several Be stars. 8. For six Be stars and for the three supergiants included in the survey, faint wings of Hα emission are detected extending to about 20 to 30 Å from the line centres. Possible origins of these extended wings might be electron scattering or a stellar wind.- Publication:
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Astronomy and Astrophysics Supplement Series
- Pub Date:
- March 1981
- Bibcode:
- 1981A&AS...43..427D
- Keywords:
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- B Stars;
- Balmer Series;
- H Lines;
- Stellar Spectra;
- Stellar Spectrophotometry;
- Supergiant Stars;
- Variable Stars;
- Electrophotometers;
- Emission Spectra;
- Optical Scanners;
- Southern Hemisphere;
- Stellar Rotation;
- Stellar Winds;
- Astronomy