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A New Nearby Candidate Star Cluster in Ophiuchus at d~=170 pc
The recent discoveries of nearby star clusters and associations within afew hundred pc of the Sun, as well as the order of magnitude differencein the formation rates of the embedded and open cluster populations,suggests that additional poor stellar groups are likely to be found atsurprisingly close distances to the Sun. Here I describe a new nearbystellar aggregate found by virtue of the parallel proper motions,similar trigonometric parallaxes, and consistent color-magnitudedistribution of its early-type members. The 120 Myr old group lies inOphiuchus at d~=170 pc, with its most massive member being the 4thmagnitude post-main-sequence B8 II-III star μ Oph. The group may haveescaped previous notice due to its nonnegligible extinction(AV~=0.9 mag). If the group was born with a normal initialmass function, and the nine B- and A-type systems represent a completesystem of intermediate-mass stars, then the original population wasprobably of order ~200 systems. The age and space motion of the newcluster are very similar to those of the Pleiades, the α Percluster, and the AB Dor moving group, suggesting that these aggregatesmay have formed in the same star-forming complex some ~108 yrago.
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