Proper motions of the optically visible open clusters based on the UCAC4 catalog

Abstract

We present a catalog of mean proper motions and membership probabilities of individual stars for optically visible open clusters, which have been determined using data from the UCAC4 catalog in a homogeneous way. The mean proper motion of the cluster and the membership probabilities of the stars in the region of each cluster were determined by applying the statistical method in a modified fashion. In this study, we applied a global optimization procedure to fit the observed distribution of proper motions with two overlapping normal bivariate frequency functions, which also take the individual proper motion errors into account. For 724 clusters, this is the first determination of proper motion, and for the whole sample, we present results with a much larger number of identified astrometric member stars. Furthermore, it was possible to estimate the mean radial velocity of 364 clusters (102 unpublished so far) with the stellar membership using published radial velocity catalogs. These results provide an increase of 30% and 19% in the sample of open clusters with a determined mean absolute proper motion and mean radial velocity, respectively.

A method for determining the radius of an open cluster from stellar proper motions

“…Kurtenkov et al (2016) used both kinematic and photometric criteria to select the most reliable members and recalculated proper motions for a sample of 15 open clusters. For some of the clusters their results differ significantly from the ones given by Dias et al (2014), and they suggested that the difference could be linked to a field star contamination effect. In the case of NGC 1647, Kurtenkov et al (2016) calculated a proper motion (µα cos δ, µ δ ) = (−1.13, −1.27) mas yr −1 whereas Dias et al (2014) obtained (µα cos δ, µ δ ) = (−0.74, −0.57) mas yr −1 .…”

“…For some of the clusters their results differ significantly from the ones given by Dias et al (2014), and they suggested that the difference could be linked to a field star contamination effect. In the case of NGC 1647, Kurtenkov et al (2016) calculated a proper motion (µα cos δ, µ δ ) = (−1.13, −1.27) mas yr −1 whereas Dias et al (2014) obtained (µα cos δ, µ δ ) = (−0.74, −0.57) mas yr −1 . Our cluster proper motion centroid (µα cos δ, µ δ ) = (−0.85, −1.11) mas yr −1 is in between both values but slightly closer to the Kurtenkov et al (2016) result (|∆µ| = 0.32 mas yr −1 ).…”

“…There should be other additional members beyond the overdensity area where the cluster star density is around or below the local field star density. However, it is interesting to note that the number of overdensity stars is considerably smaller than the 459 very probable members (membership probabilities ≥ 90%) according to Dias et al (2014) (black points in Fig. 12) or than the 618 1-σ members found by K13.…”

“…The latest version (3.5 of 2016 February) of D02 contains updated information on 2167 optically visible open clusters and candidates. Dias et al (2014) used the UCAC4 catalogue (Zacharias et al 2013) to determine in a homogeneous way kinematic memberships and mean proper motions for most of these clusters. However, the apparent radii of many of the clusters in D02 were compiled from older references (e.g.…”

“…A precise knowledge of cluster properties such as distance, age, metallicity or reddening is necessary in order to be able to draw reliable conclusions. Large open cluster catalogues, like that published by Dias et al (2002Dias et al ( , 2014, compile all the available information required to make studies on, for instance, the rotation of the spiral patterns (Dias & Lépine 2005) or the Galactic star formation history (de la Fuente Marcos & de la Fuente Marcos 2004). However, this kind of data collections has the disadvantage of being highly heterogeneous.…”