Astrophys. J., 857, 132-132 (2018/April-3)
The Magellanic Bridge cluster NGC 796: deep optical AO imaging reveals the stellar content and initial mass function of a massive open cluster.
KALARI V.M., CARRARO G., EVANS C.J. and RUBIO M.
Abstract (from CDS):
NGC 796 is a massive young cluster located 59 kpc from us in the diffuse intergalactic medium of the 1/5-1/10 Z☉ Magellanic Bridge, allowing us to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, and providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics griHα imaging of NGC 796 (at 0.''5, which is ∼0.14 pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore whether star formation and stellar evolution vary as a function of metallicity by comparing the properties of NGC 796 to higher-metallicity clusters. We find an age of 20–5+12 Myr from isochronal fitting of the cluster main sequence in the color-magnitude diagram. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope α = 1.99 ± 0.2, hinting at a metallicity and/or environmental dependence of the IMF, which may lead to a top-heavy IMF in the early universe. Study of the Hα emission-line stars reveals that classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990 ± 200 M☉, and a core radius of 1.4 ± 0.3 pc, which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.
© 2018. The American Astronomical Society. All rights reserved.
galaxies: star clusters: individual: NGC 796 - Hertzsprung-Russell and C-M diagrams - Magellanic Clouds - stars: emission-line, Be - stars: formation - stars: luminosity function, mass function
VizieR on-line data:
<Available at CDS (J/ApJ/857/132): table2.dat>
Table 2: [KCE2018] NNN (Nos 1-577).
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