Astronomy and Astrophysics Letters dedicated to ISO

The ISO-SWS spectra of Luminous Blue Variables

H.J.G.L.M. Lamers - P.W. Morris - R.H.M. Voors - J.I. van Gent - L.B.F.M. Waters - Th. de Graauw - R.P. Kudritzki - F. Najarro - A. Salama - A.M. Heras


We present the infrared spectra between 2.4 and 45 microns 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: Teff = 13000 K, R* = 250 Rsolar, and M = 9 x 10-5 Msolar yr-1 for AG Car and Teff = 10000 K, R* = 220 Rsolar, and M = 1.7 x 10-5 Msolar 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 Msolar. 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.

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

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