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Astron. Astrophys. 321, L21-L24 (1997)


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Letter to the Editor

A two-component infrared nebula around HR Car *

R.H.M. Voors 1, 2, L.B.F.M. Waters 3, 4, N.R. Trams 5 and H.U. Käufl 6

1 Astronomical Institute, University of Utrecht, Princetonplein 5, 3508 TA Utrecht, The Netherlands
2 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3 Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
4 SRON Laboratory for Space Reserach, PO Box 800, 9700 AV Groningen, The Netherlands
5 ISO Science Operations Center, Astrophysics Division of ESA, PO Box 50727, E-28080 Villafranca, Madrid, Spain
6 European Southern Observatory, D-8046 Garching bei München, Germany

Received 21 January 1996 / Accepted 4 February 1997

Abstract

We present mid-infrared imaging of the LBV HR Car and its surrounding nebula. The 10 [FORMULA] m broad-band N image reveals a geometry which is not point symmetric with respect to the central star on an arcsecond scale. The 12.8 [FORMULA] m narrow-band [Ne II ] image shows a clumpy structure which does not follow the N-band distribution. In addition, we detect a faint and probably clumpy outer nebula about [FORMULA] across.

The morphology of the infrared nebula and in particular its asymmetry is not at all in agreement with the large-scale structures as seen in optical images. Three different episodes of shell ejection can now be distinguished for HR Car: the arc-like structures seen in the optical, about [FORMULA] across, the faint IR nebula seen in the N-band, about [FORMULA] across, and the small, irregular nebula less than [FORMULA] across. The main conclusion we draw from this is that the geometry of mass-ejections in HR Car is highly time-dependent and that multiple shell ejections can occur in LBVs.

The distance of the small IR nebula from the central star can be well explained by a dust shell that is composed of silicates and is in radiative equilibrium with the central star.

Key words: HR Car – Circumstellar matter – Infrared: stars – Mass-loss

* based on observations obtained at ESO, La Silla, Chile

Send offprint requests to: R.H.M. Voors

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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