The Arches cluster

The Arches cluster (Figer et al. 1999b, 2002) is the youngest and densest cluster at the GC, containing thousands of stars, including at least 160 O stars and around 10 WNLs, namely WN stars still showing H at the surface (Chiosi & Maeder 1986). The cluster is very young (<2.5 Myr), and the only emission-line stars present are WNLs and OIf+ stars having infrared spectra dominated by H, He i, He ii, and N iii lines. Some have weak C iii/iv lines. The cluster satisfies all requirements for studying the high-mass IMF slope and estimating an upper mass cutoff: individual members can be resolved, there is a large amount of mass in stars, and it is young enough that its most massive members are not pre-supernovae and old enough for its stars to have emerged from their natal coccoons.

Figure 13.3. Observed spectra (solid) and model fits (dashed) for the three WNL and two OfI+ Arches stars.

Figure 13.3. Observed spectra (solid) and model fits (dashed) for the three WNL and two OfI+ Arches stars.

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