Astronomy and Astrophysics, volume 391, 547-564 (2002/8-4)
A statistical study of binary and multiple clusters in the LMC.
DIEBALL A., MUELLER H. and GREBEL E.K.
Abstract (from CDS):
Based on the Bica et al. (1999AJ....117..238B
) catalogue, we studied the star cluster system of the LMC and provide a new catalogue of all binary and multiple cluster candidates found. As a selection criterion we used a maximum separation of 1.4' corresponding to 20pc (assuming a distance modulus of 18.5mag). We performed Monte Carlo simulations and produced artificial cluster distributions that we compared with the real one in order to check how many of the found cluster pairs and groups can be expected statistically due to chance superposition on the plane of the sky. We found that, depending on the cluster density, between 56% (bar region) and 12% (outer LMC) of the detected pairs can be explained statistically. We studied in detail the properties of the multiple cluster candidates. The binary cluster candidates seem to show a tendency to form with components of similar size. When possible, we studied the age structure of the cluster groups and found that the multiple clusters are predominantly young with only a few cluster groups older than 300Myr. The spatial distribution of the cluster pairs and groups coincides with the distribution of clusters in general; however, old groups or groups with large internal age differences are mainly located in the densely populated bar region. Thus, they can easily be explained as chance superpositions. Our findings show that a formation scenario through tidal capture is not only unlikely due to the low probability of close encounters of star clusters, and thus the even lower probability of tidal capture, but the few groups with large internal age differences can easily be explained with projection effects. We favour a formation scenario as suggested by Fujimoto & Kumai (1997AJ....113..249F
) in which the components of a binary cluster formed together and thus should be coeval or have small age differences compatible with cluster formation time scales.
(galaxies:) Magellanic Clouds - galaxies: star clusters - catalogs
VizieR on-line data:
<Available at CDS (J/A+A/391/547): clusters.dat refs.dat>
Table 6: [DMG2002] NNN (Nos 1-473).
Multiple clusters have not been integrated into Simbad. The clusters Rob1 and U1 have not been found.
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