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Astron. Astrophys. 341, L67-L70 (1999)


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Letter to the Editor

Dust in R71: first detection of crystalline silicates in the LMC *

R.H.M. Voors 1,2, L.B.F.M. Waters 3,4, P.W. Morris 1,3, N.R. Trams 5, A. de Koter 3 and J. Bouwman 3

1 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Astronomical Institute, University of Utrecht, Princetonplein 5, 3508 TA Utrecht, The Netherlands
3 Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
4 SRON Laboratory for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
5 Integral Science Operations, Astrophysics Division of ESA, ESTEC SCI-SAG, P.O. Box 299, 2200 AG Noordwijk, The Netherlands

Received 12 November 1998 / Accepted 27 November 1998

Abstract

We present infrared spectroscopy taken with the Infrared Space Observatory (ISO) of the Luminous Blue Variable (LBV) R71 in the Large Magellanic Cloud (LMC). The spectrum shows clear evidence for the presence of crystalline olivine at 23.5 µm. This is the first detection of circumstellar crystalline silicates outside our galaxy. In addition, we identify emission at 6.2, 7.7 and possibly 8.6 µm from C-rich small grains (PAHs). The presence of C-rich grains is not expected in an environment where C/O is less than 1. We fit the dust spectrum using a radiative transfer model and find a dust mass of 0.02 [FORMULA]. R71 was probably a Red Supergiant when it produced the dust shell and had a time-averaged mass loss rate of the order of [FORMULA] [FORMULA] yr-1 for a gas/dust ratio of 100.

Key words: stars: circumstellar matter – stars: evolution – stars: individual: R71 – stars: mass-loss – infrared: stars

* based on observations obtained with ISO, an ESA project with instruments funded by ESA Member states (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA

Send offprint requests to: L.B.F.M. Waters

© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998

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