najarro1_7297

Participants:

Lamers, Henny J.G.L.M.
SRON Laboratory for Space Research Utrecht, Sorbonnelaan 2, Utrecht, 3584 CA, The Netherlands
Kudritzki, Rolf P.
Universitaetssternwarte Muenchen, Scheinerstr. 1, 81679, Muenchen, Germany
Najarro, Francisco
Universitaetssternwarte Muenchen, Scheinerstr. 1, 81679, Muenchen, Germany
Waters, Rens B.F.M.
Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, NL-1098 SJ, Amsterdan, The Netherlands

Project:

The winds of early type supergiants: The critical mass loss phase of massive stars (I).

PI :

Lamers, Henny J.G.L.M.
SRON Laboratory for Space Research Utrecht, Sorbonnelaan 2 , Utrecht , 3584 CA, The Netherlands
The Netherlands

Abstract :
We propose to study the winds of massive stars in the high mass-loss phase of their evolution, i.e. in stages from O- to A-supergiants. The intention is to use the unique spectroscopic and photometric capability of ISO to measure accurate strengths and profiles of H and He lines formed in stellar winds, and the IR-continuum which is also formed in the wind. By means of detailed NLTE radiative transfer and line formation techniques it will be possible to determine rates of mass-loss and stratification of wind velocity fields much more precisely than hitherto possible. (The present best estimates of the mass loss rates of A and B-stars have an uncertainty of one order of magnitude!)
The results of this study will have important repercussions for our understanding of massive star evolution. They will also provide a crucial test for the theory of radiation driven winds, which is normally applied to predict stellar wind properties as function of stellar parameters. Last but not least, the results will be used to calibrate the wind momentum-luminosity relation of blue supergiants which has been found very recently and which has great potential for extragalactic distance determinations.

Allocated time and instruments/detectors Summary :

SWS AOT useage:

SWS1 31286 seconds.
SWS2 4022 seconds.
SWS6 16764 seconds.
total SWS usage 52072 seconds

PHT AOT useage:

PHT22 4413 seconds.
PHT40 1656 seconds.
total PHT usage 6069 seconds

Overall total time usage 58141 seconds
So far ca. half of the targets observed.

Significant Results :

The free-free IR excess and the IR emission lines of H and He I of the Luminous Blue Variable PCygni are observed with the ISO-SWS instrument. The observed profiles and the free-free emission are compared with predictions from a non-LTE model atmosphere with a stellar wind. The observations agree very well with a model that has the following properties: Teff = 18100K, R*= 76 Rsun, He/H=0.30 by number, Mdot=3.0e-5 Msun/yr and Vinf=185 km/s. We observed forbidden emission lines of [Fe II], [Fe III], [Ni II], [Ne II], [Ne III] and [Si II]. From the study of the [Ne II] and [Ne III] lines we derived an abundance of Ne/(H+He) = 2.2e-4 which shows that the nebula is not significantly enriched in Ne.

We obtained infrared spectra between 2.4 and 45 microns of three Luminous Blue Variables (PCygni, AG Car, HR Car ) observed with Short Wave Spectrometer of ISO. The spectra consist of two parts: (1) the tail of the photospheric energy distibution with the free-free excess from the lower layers of the stellar wind, (2) emission from circumstellar dust. PCygni does not show dust emission. We derive the mass loss rate and the velocity law in the wind by modelling the free-free emission. The velocity law of the wind of AG Car is much flatter than that of PCygni and HR Car. 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 dust distribution around AG Car corresponds with that of the gasous nebula. We did not find a satisfactory quantitative explanation of the dust emission of HR Car.

Publications :

The ISO-SWS spectra of Luminous Blue Variables, Lamers, H.J.G.L.M., Morris, P.W., Voors, R.H.M., van Gent, J.I., Waters, L.B.F.M., de Graauw, T., Kudritzki, R.P., Najarro, F., Salama, A., Heras, A.M., 1996, A&A, 315, L225

The ISO-SWS spectrum of PCygni, Lamers, H.J.G.L.M., Najarro, F., Kudritzki, R.P., Morris, P.W., Voors, R.H.M., van Gent, J.I., Waters, L.B.F.M., de Graauw, T., Beintema, D., Valentijn, E.A., Hillier, D.J., 1996, A&A, 315, L229

Updated: Feb 7, 1997.