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Astron. Astrophys. 328, 107-120

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Wolf-Rayet stars and OB assoctations as gamma-ray line sources

E. Parizot1, M. Cassé1,2, and E. Vangioni-Flam2

1Service d'astrophysique, CEA-Saclay, F-91191 Gif-sur-Yvette, France
2Institut d'Astrophysique de Paris, CNRS, 98bis bd Arago, F-75014 Paris, France

Received 18 April 1997 / Accepted 24 July 1997


We calculate the gamma-ray line production induced by energetic particles (EPs) in molecular clouds where massive star formation is taking place, assuming that the EPs originate from the winds of these stars. On the basis of recent Wolf-Rayet (W-R) models of the Geneva group, we analyse in detail the average composition of the winds from OB associations. We consider two initial stellar metallicities (solar and twice solar), and study the metallicity dependence of the gamma-ray line ratios and profiles. In particular, we find that the gamma-ray lines are narrower at twice solar metallicity, which is of interest for the emission from the inner Galaxy. We pay particular attention to the gamma-ray emission detected by COMPTEL in Orion, and show that our mean-wind EP compositions satisfy all the available observational constraints. We predict a flux of 1-$2 10^{-5}
{\rm ph.cm}^{-2}{\rm s}^{-1}$ at $\sim 0.450$ MeV from the Orion complex, due to the de-excitation of the spallation products 7Li and 7Be. Such a flux is below the current OSSE upper limit, but above INTEGRAL's expected sensitivity. We analyse the most relevant present and future observables, such as the broad band ratios (0.2-1 / 1-3 / 3-7 MeV), the 12C and 16O line width and the C$^{\star}$/O$^{\star}$ line ratio, and discuss the differences between our results and those obtained with a WC composition based only on the extreme late phase wind, used up to now.

Key words: gamma rays: theory - nuclear reactions - interstellar medium: clouds: Orion - stars: Wolf-Rayet, mass loss - OB associations

© European Southern Observatory (ESO) 1997

Online publication: October 30, 1997
Last change: March 24, 1998