The LMC hosts a rich variety of star clusters seen in close projected
proximity. Ages have been derived for few of them showing differences up to few
million years, hinting at being binary star clusters. However, final
confirmation needs to be done through spectroscopic analysis. Here we focus on
the LMC cluster pair NGC2006-SL538 and aim to determine whether the star
cluster pair is a bound entity (binary star cluster) or a chance alignment.
Using the MIKE echelle spectrograph at LCO we have acquired integrated-light
spectra for each cluster. We have measured radial velocities by two methods: a)
direct line profile measurement yields vr=300.3±5±6 km/s for NGC2006 and
vr=310.2±4±6 km/s for SL538. b) By comparing observed spectra with
synthetic bootstrapped spectra yielding vr=311.0±0.6 km/s for NGC2006 and
vr=309.4±0.5 km/s for SL538. Finally when spectra are directly compared,
we find a Δv=1.08±0.47 km/s. Full-spectrum SED fits reveal that the
stellar population ages lie in the range 13-21 Myr with a metallicity of
Z=0.008. We find indications for differences in the chemical abundance patterns
as revealed by the helium absorption lines between the two clusters. The
dynamical analysis shows that the two clusters are likely to merge within the
next ∼150 Myr. The NGC2006-SL538 cluster pair shows radial velocities,
stellar population and dynamical parameters consistent with a gravitational
bound entity. We conclude that this is a genuine binary cluster pair, and we
propose that their differences in ages and stellar population chemistry is most
likely due to variances in their chemical enrichment history within their
environment. We suggest that their formation may have taken place in a loosely
bound star-formation complex which saw initial fragmentation but then had its
clusters become a gravitationally bound pair by tidal capture.Comment: Accepted for publication in Astronomy & Astrophysics. 15 pages, 10
figures in low resolutio
