EDP Sciences
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Volume 380, Number 1, December II 2001
Page(s) 168 - 176
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011313

A&A 380, 168-176 (2001)
DOI: 10.1051/0004-6361:20011313

Blue irregular variable stars in the Small Magellanic Cloud from EROS2: Herbig Ae/Be or classical Be stars?

J.-P. Beaulieu1, W. J. de Wit1, 2, 3, H. J. G. L. M. Lamers2, 3, J.-B. Marquette1, C. Coutures4, P. Leisy5, S. Totor1, N. Palanque-Delabrouille4, C. Afonso4, C. Alard1, J. N. Albert6, J. Andersen7, R. Ansari6, É. Aubourg4, P. Bareyre4, F. Bauer4, G. Blanc4, X. Charlot4, F. Couchot6, F. Derue6, R. Ferlet1, P. Fouqué J. F. Glicenstein5, 8, 4, B. Goldman4, D. Graff9, M. Gros4, J. Haissinski6, J. C. Hamilton10, D. Hardin4, J. de Kat4, T. Lasserre4, É. Lesquoy1, 4, C. Loup1, C. Magneville4, B. Mansoux4, É. Maurice11, A. Milsztajn4, M. Moniez6, O. Perdereau6, L. Prévot11, N. Regnault6, J. Rich4, M. Spiro4, A. Vidal-Madjar1, L. Vigroux4 and S. Zylberajch4

1  Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
2  Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 CC, Utrecht, The Netherlands
3  SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands
4  CEA, DSM, DAPNIA, Centre d'Études de Saclay, 91191 Gif-sur-Yvette, Cedex, France
5  ESO La Silla, casilla 19001, Santiago 19, Chile
6  Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS, Université de Paris-Sud, 91405 Orsay Cedex, France
7  Astronomical Observatory, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
8  DESPA, Observatoire de Paris section Meudon, 1 place Jules Janssen, Meudon Cedex 92195, France
9  Departments of Astronomy and Physics, Ohio State University, Columbus, OH 43210, USA
10  Collège de France, 11 place Marcelin-Bertherlot, 75231 Paris Cedex 05, France
11  Observatoire de Marseille, 2 Pl. Le Verrier, 13248 Marseille Cedex 04, France

(Received 2 May 2001 / Accepted 14 September 2001 )

Using data from the EROS2 microlensing survey, we report the discovery of two blue objects with irregular photometric behaviour of $\Delta V \sim 0.1$-0.4mag on time scales of 20 to 200 days. They show a bluer when fainter behaviour. Subsequent spectra taken with the ESO 3.6 m telescope show spectral type B4eIII and B2eIV-V with strong ${\rm H} \alpha$ emission. These objects resemble the Herbig AeBe but also classical Be stars. At this stage, it is not possible to distinguish unambiguously between pre-main sequence and classical Be nature. If we favour the pre-main sequence interpretation, they are more luminous than the luminosity upper limit for Galactic HAeBe stars. The same was found for the HAeBe candidates in the LMC. This might be due to a shorter accretion time scale ( $\tau = M_*/\dot{M}$), or the smaller dust content during the pre-main sequence evolution of SMC and LMC stars. Further studies on a larger scale of the environment and IR properties of the stars are needed.

Key words: stars -- emission line, Be -- stars: pre-main sequence -- stars: variable: general -- gravitational lensing -- galaxies: individual: SMC

Offprint request: J. P. Beaulieu, beaulieu@iap.fr

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© ESO 2001