Spectroscopy of luminous blue stars in M31 and M33

Roberta M. Humphreys, Philip Massey, Wendy L. Freedman

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


We have obtained spectra for classification of 42 candidate supergiants and 12 probable OB stars in M31 and eight early-type stars in M33. Twenty-six of those in M31 and six in M33 are confirmed as apparent single members with spectral types ranging from O8 to F8. We derive their interstellar extinction and luminosities from published photographic and CCD photometry for all of the confirmed members. Our preliminary and still incomplete HR diagram for M31 shows an apparent lack of the most massive stars; stars with initial masses > 60μ⊙. We discuss the effects of incompleteness and observational selection on the interpretation of this HR diagram. There appears to be a real lack of the visually brightest evolved blue and red supergiants in M31. This may indicate that the global starformation rate for massive stars (40-60μ⊙) is lower in M31 than in nearby late-type galaxies but we do not know what other physical factors may be operating. Because the unevolved massive star population will be under-represented in a sample selected by visual brightness they will be rare on our preliminary HR diagram. Our results for the OB stars, selected both by blue color and visual brightness, do not yet allow us to determine the actual upper mass limit in M31 and their relative numbers with respect to other massive stars.

Original languageEnglish (US)
Pages (from-to)84-96
Number of pages13
JournalAstronomical Journal
Issue number1
StatePublished - Jan 1990


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