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Astron. Astrophys. 315, L225-L228 (1996)

The ISO-SWS spectra of Luminous Blue Variables*

H.J.G.L.M. Lamers1,2, P.W. Morris3,2, R.H.M. Voors1,2, J.I. van Gent1,2, L.B.F.M. Waters4,5, Th. de Graauw5, R.P. Kudritzki6,7, F. Najarro6, A. Salama3, and A.M. Heras3

1 Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 CC Utrecht, The Netherlands
2 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3 ISO Science Operations Centre, Astrophysics Division of ESA, PO Box 50727, E-28080 Villafranca, Madrid, Spain
4 Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
5 SRON Laboratory for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
6 Institut for Astronomie und Astrophysik der Universität München, Scheinerstrasse 1, D-81679 München, Germany
7 Max Planck Institut für Astrophysik, Karl-Schwarzschild-Str.1, D-85740 Garching bei München, Germany

Received 23 July 1996 / Accepted 19 August 1996

Abstract. We present the infrared spectra between 2.4 and 45 img1.gifm of two Luminous Blue Variables (AG Car, HR Car ) observed with the Short Wavelength Spectrometer of ISO. The spectra consist of two parts: (1) the tail of the photospheric energy distribution with the free-free excess from the lower layers of the stellar wind, (2) emission from circumstellar dust. The free-free emission can be explained by models with the following parameters: img2.gif = 13000 K, img3.gif =250 img4.gif , and img5.gif img6.gif yr-1 for AG Car and img2.gif = 10000 K, img3.gif =220 img4.gif , and img8.gif img6.gif yr-1 for HR Car. The mass loss rate has an uncertainty of a factor 1.5 within the context of our models. We also derive the properties of the dust by modelling the energy distribution with optically thin dust models. The difference in the flux measured through two different apertures gives information on the projected distribution of the dust. The distribution of the dust around AG Car corresponds with that of the gaseous nebula and has a dust mass of 0.03 img6.gif . The dust around HR Car extends to a much larger distance than the gaseous nebula and cannot be modelled with a single spherically symmetric shell.

Key words: infrared radiation - stars: circumstellar matter - stars: variable - stars: mass loss - stars: supergiant - stars: individual: AG Car - stars: individual: HR Car

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

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