Spectroscopic and Photometric Observations of M Supergiants in Carina.
Abstract
Thirty southern-hemisphere M supergiants mostly in Carina have been studied spectroscopically in the blue and near4nfrared and photometrically from 0.4 to 18 . The uncertainties in the determinations of interstellar extinction are discussed, and the spatial distribution of the M supergiants in the Carina arm is shown. The presence of the I1- excess attributed to silicate dust is a common feature. Stars of the same spectral type and luminosity class are remarkably homogeneous in their long-wave behavior. The silicate feature becomes more prominent in the more luminous stars and in stars of later spectral type. Four composite systems show little long-wave excess. The two VV Cephei objects have excesses probably produced by gas emission, and the other two have little or no excess-supporting the suggestion that the presence of the early star prohibits the formation of a dust envelope. Three stars- VY CMa, VX Sgr, and HD 97671-appear to be extreme examples of stars with large excesses over the entire long-wave region. It is suggested that these objects are surrounded by large amounts of particulate material over a great range of distances from the stars. The term "dust thermosphere" is used to describe this material which absorbs much of the stellar energy and reradiates it at long wavelengths. The objects with dust thermospheres are shown to be very luminous with most of their energy in the 2-20- region. The absolute bolometric magnitudes inferred are: VY CMa, = -9.5; VX Sgr, Mb,,I = -8.1; and HD 97671, = -6.8.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1972
- DOI:
- 10.1086/151329
- Bibcode:
- 1972ApJ...172...75H