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Luminous variable stars in M31 and M33
Humphreys, R. M.
Astrophysical Journal, Part 1, vol. 219, Jan. 15, 1978, p. 445-451. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Andromeda Galaxy, Stellar Luminosity, Stellar Spectrophotometry, Supergiant Stars, Ubv Spectra, Variable Stars, Absorption Spectra, Emission Spectra, Hot Stars, Infrared Spectra, Stellar Magnitude
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Spectra and UBVRI photometry of four luminous blue variables in M31 and four luminous blue variables in M33 are presented along with a spectrum of a red supergiant variable in M31 and a 2-micron measurement of one of the blue variables in M31. The spectra were obtained over the wavelength range from about 3000 to 5500 A at a dispersion of 79 A/mm with a resolution of approximately 4 A. The spectra of two blue variables in M31 and one in M33 are found to be characterized by Fe II and forbidden Fe II emission lines, hydrogen and helium emission, a very strong UV continuum, and no evident Balmer discontinuity. Changes in the spectra of two other blue variables in M33 are briefly described, and the spectra of all eight blue variables are shown to be very similar. It is concluded that the eight blue variables in M31 and M33, together with Eta Car in the Milky Way, S Dor in the Large Magellanic Cloud, and related objects in the latter two galaxies, form a recognizable group of very luminous hot stars with very low surface gravities.

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