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Astron. Astrophys. 328, 107-120 (1997)

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8. Influence of the assumed limit mass [FORMULA]

As discussed in Sect.  2.2, the EPs accelerated within a superbubble energized by strong stellar winds and SN explosions should be made of the wind ejecta of the most massive stars ([FORMULA]) in the OB association responsible for the creation of the superbubble. However, this limit mass is admitedly somewhat arbitrary. To be general, we thus did the same calculations as above with EP compositions which include all the stars with a mass greater than [FORMULA]. This is considered as an extreme case.

As expected from the resulting lower abundances of C and O (see Sect.  2.2), we obtain a (1-3 MeV)/(3-7 MeV) band ratio, R, some 20 to 30 % higher than with [FORMULA] for models C, while R is virtually unchanged for models E. In particular, all the mean-wind and mean-OB compositions still satisfy the Orion constraint [FORMULA], whatever the value of [FORMULA]. The same quantitative changes ([FORMULA] - [FORMULA] for models C; no change for models E) are also obtained for the (0.2-1 MeV)/(3-7 MeV) band ratio.

Concerning the 12 C [FORMULA] /16 O [FORMULA] line ratio, we find a value [FORMULA] lower for model C at solar metallicity, and [FORMULA] lower for model C at twice solar metallicity. This is a consequence of the lower C/O abundance ratio in the EP composition. Finally, we obtain smaller broad-to-narrow line component ratios (i.e. narrower lines), as expected again from the lower abundance of C and O in the EPs, favouring the direct processes. Quantitatively, we find values [FORMULA] smaller for the 12 C line and [FORMULA] smaller for the 16 O line, at either solar and twice solar metallicity.

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© European Southern Observatory (ESO) 1997

Online publication: March 24, 1998