Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidates LBVs, B[e] Supergiants, and the Warm Hypergiants; How to Tell Them Apart

Roberta M. Humphreys (1), Michael S. Gordon (1), John C. Martin (2), Kerstin Weis (3),
and David Hahn(1)

1. University of Minnesota, 2. University of Illinois Springfield, 3. Astronomical Institute, Ruhr-Universitaet Bochum, Germany

In this series of papers we have presented the results of a spectroscopic survey of
luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission line spectra, including LBVs and candidate LBVs, Fe II emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines to help distinguish these stars in future work: 1. The B[e] supergiants have emission lines of [O I] and [Fe II] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their SEDs.2 Confirmed LBVs it do not have the [O I] emission lines in their spectra. Some LBVs have [Fe II] emission lines, but not all. Their SEDs shows free-free emission in the near infrared but no evidence for warm dust.Their most important and defining characteristic is the S Dor-type variability. 3. The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [Fe II] and [O I] emission in their spectra like the sgB[e] stars, but are distinguished by their A and F-type spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.

Reference: To appear in the Astrophysical Journal
Status: Manuscript has been accepted