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Astron. Astrophys. 359, 1139-1146 (2000)

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5. Conclusions

Thanks to a favorable geometry and to the near-absence of foreground extinction and of confusion with other features, N 66 offers one of the best examples of a photodissociation region. We have presented maps in various interesting lines ([O III ] [FORMULA]5007, H2 v=(1-0) S(1), CO(2-1)), of aromatic mid-infrared bands (AIBs) and of continuum at various infrared wavelengths. There is, as predicted by PDR models, a very clear correlation between H2, the AIBs and CO. We suggest that most of the CO has been photodissociated and that there remains only small molecular clumps with a small area coverage. The CO line emission is thus weaker than in less extreme regions of the SMC because the higher temperature does not compensate for the smaller surface filling factor. We discovered embedded stars (or small unresolved star clusters) in several molecular peaks, which indicate that another stellar generation is starting in this very active region. There are at least three different stellar generations in N 66 within only some [FORMULA] 106 years, the maximum age of the O3 stars. The first generation cannot have started before that time since no Wolf-Rayet star has yet appeared, except for the isolated WR erupting binary HD 5980 whose age is unknown (see Niemela et al. 1999) and the current one, as indicated by the IR embedded sources discovered in our broad band IR survey of the region.

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© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000