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

We studied in detail the binary cluster candidates SL 538 and NGC2006 in the Large Magellanic Cloud (LMC). This cluster pair is located in the northwestern part of the large OB association LH77 in supergiant shell LMC4. A third star cluster, KMHK1019, is located within 5 from the cluster pair. Our study is the first age determination of SL 538 and NGC2006 that is based on CMDs. We derived an age of 18 ± 2 Myr for SL 538, 22.5±2.5 Myr for NGC2006, and 16 Myr for KMHK1019. 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 KMHK1019 (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 NGC2006 and is consistent with a Salpeter aIMF. 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.