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Astron. Astrophys. 339, 773-781 (1998)


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The cluster pair SL 538 / NGC 2006 (SL 537) *

Andrea Dieball 1 and Eva K. Grebel 2, 3

1 Sternwarte der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany (e-mail: adieball@astro.uni-bonn.de)
2 Astronomisches Institut der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
3 UCO / Lick Observatory, University of California, Santa Cruz, CA 95064, USA

Received 13 February 1998 / Accepted 8 July 1998

Abstract

We studied in detail the binary cluster candidates SL 538 and NGC 2006 in the Large Magellanic Cloud (LMC). This cluster pair is located in the northwestern part of the large OB association LH 77 in supergiant shell LMC 4. A third star cluster, KMHK 1019, is located within [FORMULA] from the cluster pair. Our study is the first age determination of SL 538 and NGC 2006 that is based on CMDs. We derived an age of [FORMULA] Myr for SL 538, [FORMULA] Myr for NGC 2006, and 16 Myr for KMHK 1019. Thus the three clusters are (nearly) coeval. We identified Be star candidates and find the same ratio N(Be)/N(B) for the components of the binary cluster (12%) while the amount of Be stars detected in KMHK 1019 (5%) and in the surrounding field (2%) is considerably lower. Since Be stars are usually rapid rotators this may indicate intrinsically higher rotational velocities in the components of the cluster pair. Also the IMF derived from the CMDs shows the same slope for both SL 538 and NGC 2006 and is consistent with a Salpeter IMF. An estimation of the cluster masses based on the IMF slopes showed that both clusters have similar total masses. These findings support joint, near-simultaneous formation of the cluster pair in the same giant molecular cloud.

Key words: Hertzsprung-Russel (HR) and C-M diagrams – stars: emission line, Be – stars: luminosity function, mass function – galaxies: star clusters: individual: NGC 2006 – galaxies: star clusters: individual: SL 538 – Magellanic Clouds

* Based on observations taken at the European Southern Observatory, La Silla, Chile, during time allocated by the MPIA, Heidelberg.

Send offprint requests to: A. Dieball, (adieball@astro.uni-bonn.de)

© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998

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