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Astron. Astrophys. 341, 827-841 (1999)

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Luminous pre-main sequence stars in the LMC?

H.J.G.L.M. Lamers 1,2, J.P. Beaulieu 3 and W.J. de Wit 1

1 Astronomical Institute, Princetonplein 5, 3584 CC Utrecht, The Netherlands (e-mail: lamers@astro.uu.nl; wjdewit@astro.uu.nl)
2 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3 Kapteyn Laboratorium, Postbus 800, 9700 AV Groningen, The Nederlands (e-mail: beaulieu@iap.fr)

Received 4 June 1998 / Accepted 16 October 1998

Abstract

We report the serendipitous discovery of seven luminous irregular variables in the LMC by the EROS project. The stars have [FORMULA] to [FORMULA], [FORMULA], and vary by about [FORMULA] on timescales of 10 to 40 days. The variations in [FORMULA] and [FORMULA] are about equal but the stars are slightly bluer when they are fainter. Medium resolution optical spectra show strong [FORMULA] emission, weak [FORMULA] emission and absorption lines of the higher Balmer lines. Absorption lines of He I , C III , O II and Si IV are present in the spectra of some of the stars. The spectral types derived from the presence or absence of the lines are between late-O and late-B. Effective temperatures and luminosities were derived from the energy distributions and independently from the EROS photometry combined with the approximate spectral types. The luminosity, derived from V, [FORMULA], and the distance of the LMC, are in the range of [FORMULA] to [FORMULA] [FORMULA]. The strong [FORMULA] emission, the spectral types, the luminosities and the irregular variations are similar (but not the same) to those of the Galactic pre-main sequence HAeBe stars (i.e. the Herbig Ae/Be stars). However the stars are about a factor 10 more luminous than the luminosity upper limit for Galactic HAeBe stars. This might be due to a shorter accretion timescale ([FORMULA]), or to the smaller dust-to-gas ratio in the LMC.

Key words: stars: variables: general – stars: emission-line, be – stars: pre-main sequence – stars: formation – ISM: reflection nebulae – galaxies: Magellanic Clouds

Send offprint requests to: H.J.G.L.M. Lamers

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© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998
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