Variable stars of small amplitude. I. Supergiants and OB stars.
Abstract
Summary. We discuss the variability in light of various kinds of stars, by means of 5000 measurements of colour-indices made for 660 stars. These stars have been observed in the Geneva Observatory photometric system; they have not been measured for this purpose and they belong to various programs. The Am stars are found to be non-variable in agreement with Breger's results (1970). The Ap stars are variable in agreement with Preston's results (1971). All the red giants of type KS III and later may be suspected of variability. In this paper, we essentially discuss the case of supergiants and OB stars. For the supergiants of type B3-G8, it is found that: 1) All the Ia supergiants are variable in light with an amplitude in colour index of about 0mO.2 -0 W04; for the Ib supergiants, a large fraction, if not all, also show variability. 2) An amplitude-luminosity relation exists in the sense that we have the largest amplitudes for the brightest stars. 3) Some arguments are given which suggest that, besides the mass loss, at least a part of these variations may be due to an oscillatory mechanism. For the OB stars, it is found that:1) A large fraction of OB stars show photometric variations. 2) A very striking concentration of stars with large dispersion of their colour indices (amplitude 0 04 appears for very high Teff and luminosity. 3) These stars occur in an area of the HR diagram, where there exist much theoretical and UV or visible spectroscopic evidence of mass loss. Key words: variable stars - supergiants - OB stars - multicolour photometry
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 1972
- Bibcode:
- 1972A&A....20..437M