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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 448057.0, MPI für Astronomie / Publikationen_mpia
The low-mass initial mass function in the 30 Doradus starburst cluster
Authors:Andersen, M.; Zinnecker, H.; Moneti, A.; McCaughrean, M. J.; Brandl, B.; Brandner, W.; Meylan, G.; Hunter, D.
Date of Publication (YYYY-MM-DD):2009
Title of Journal:The Astrophysical Journal
Journal Abbrev.:ApJ
Issue / Number:2
Start Page:1347
End Page:1360
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We present deep Hubble Space Telescope NICMOS 2 F160W band observations of the central 56'' × 57'' (14 pc × 14.25 pc) region around R136 in the starburst cluster 30 Dor (NGC 2070) located in the Large Magellanic Cloud. Our aim is to derive the stellar initial mass function (IMF) down to ~1 M sun in order to test whether the IMF in a massive metal-poor cluster is similar to that observed in nearby young clusters and the field in our Galaxy. We estimate the mean age of the cluster to be 3 Myr by combining our F160W photometry with previously obtained HST WFPC2 optical F555W and F814W band photometry and comparing the stellar locus in the color-magnitude diagram with main sequence and pre-main sequence isochrones. The color-magnitude diagrams show the presence of differential extinction and possibly an age spread of a few megayear. We convert the magnitudes into masses adopting both a single mean age of 3 Myr isochrone and a constant star formation history from 2 to 4 Myr. We derive the IMF after correcting for incompleteness due to crowding. The faintest stars detected have a mass of 0.5 M sun and the data are more than 50% complete outside a radius of 5 pc down to a mass limit of 1.1 M sun for 3 Myr old objects. We find an IMF of \frac{dN}{d\log M }\propto M^{-1.20\pm 0.2} over the mass range 1.1-20 M sun only slightly shallower than a Salpeter IMF. In particular, we find no strong evidence for a flattening of the IMF down to 1.1 M sun at a distance of 5 pc from the center, in contrast to a flattening at 2 M sun at a radius of 2 pc, reported in a previous optical HST study. We examine several possible reasons for the different results including the possible presence of mass segregation and the effects of differential extinction, particularly for the pre-main sequence sources. If the IMF determined here applies to the whole cluster, the cluster would be massive enough to remain bound and evolve into a relatively low-mass globular cluster.
Free Keywords:globular clusters: individual: 30 Doradus; stars: formation; stars: luminosity function; mass function; stars: pre-main sequence
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL: [ID No:1]
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