HST and groundbased observations of the 'Hubble-Sandage' variables in M 31 and M 33

Th Szeifert, R. M. Humphreys, K. Davidson, T. J. Jones, O. Stahl, B. Wolf, E. J. Zickgraf

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30 Scopus citations

Abstract

The small group of peculiar stars known as the Hubble-Sandage variables in M 31 and M 33 belong to the class of stars we now call the Luminous Blue Variables - highly unstable, evolved massive stars found in many spiral and irregular galaxies. We have used the Hubble Space Telescope to obtain UV imaging and spectroscopy of several of the LBVs in M 31 and M 33. The UV observations are combined with ground-based spectra and optical and infrared photometry to estimate their apparent temperatures, luminosities, and mass loss rates. We were fortunate to catch Var B in M 33 during an LBV eruption while Var C in M 33 was observed during its decline from its recent maximum. Var B is especially interesting because one of the optical spectra showed emission lines of He I, indicating a temperature of 20 000 K or more while the rest of the lines were typical of an LBV in eruption, at a temperature near 9000 K. With no other indication of a temperature or radial change, we suggest the He I lines were excited by a shock or produced by hot radiation escaping from the polar regions. The UV spectrum of AE And shows an unusually strong emission line of Fe II at 2507 Å similar to η Carinae. The spectra of AE And, AF And, and Var 83 in M 33, all observed at visual minimum, show a veritable forest of Fe II and [Fe II] emission lines. This is in contrast to the quiescent spectra of some LBVs which resemble Of/WN9 stars, such as R 127 and AG Car.

Original languageEnglish (US)
Pages (from-to)131-145
Number of pages15
JournalAstronomy and Astrophysics
Volume314
Issue number3
StatePublished - Oct 1 1996

Keywords

  • Galaxies: individual: M 31, M 33
  • Stars: early type
  • Stars: supergiants
  • Stars: variables: other

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