Global survey of star clusters in the Milky Way

Abstract

Context. Although they are the main constituents of the Galactic disk population, for half of the open clusters in the Milky Way reported in the literature nothing is known except the raw position and an approximate size. Aims. The main goal of this study is to determine a full set of uniform spatial, structural, kinematic, and astrophysical parameters for as many known open clusters as possible. Methods. On the basis of stellar data from PPMXL and 2MASS, we used a dedicated data-processing pipeline to determine kinematic and photometric membership probabilities for stars in a cluster region. Results. For an input list of 3784 targets from the literature, we confirm that 3006 are real objects, the vast majority of them are open clusters, but associations and globular clusters are also present. For each confirmed object we determined the exact position of the cluster centre, the apparent size, proper motion, distance, colour excess, and age. For about 1500 clusters, these basic astrophysical parameters have been determined for the first time. For the bulk of the clusters we also derived the tidal radius. We estimated additionally average radial velocities for more than 30% of the confirmed clusters. The present sample (called MWSC) reaches both the central parts of the Milky Way and its outer regions. It is almost complete up to 1.8 kpc from the Sun and also covers neighbouring spiral arms. However, for a small subset of the oldest open clusters (log t 9) we found some evidence of incompleteness within about 1 kpc from the Sun.

Rotationally modulated variability and pulsations of the He-rich star CPD −62°2124 with an extraordinarily strong magnetic field

“…There seems to be a good agreement (especially of the UCAC5 values) with the mean IC 2944 proper motion of (−6.2±0.9, −1.2±0.9) mas/yr from Kharchenko et al (2005) and (−7.0±0.9, −1.1±0.9) mas/yr from Kharchenko et al (2013). However, there is a second cluster, vdBergh-Hagen 121, with an only slightly different proper motion of (−5.1±0.5, +1.1±0.6) mas/yr and (−5.9±0.8, +0.5±0.8) mas/yr listed in the latter two catalogues, respectively.…”

“…However, they gave an angular distance to the cluster centre of 19.4 ′ . This is larger than the cluster radius of 14.4 ′ , determined in the cluster survey of Kharchenko et al (2005), based on Hipparcos and Tycho-2 (ESA 1997; Høg et al 2000) proper motions and optical photometry, and of 12 ′ in the more recent survey of Kharchenko et al (2013), based on proper motions from the PPMXL catalogue (Röser, Demleitner & Schilbach 2010) and near-infrared photometry from the Two Micron All Sky Survey (2MASS; Skrutskie et al 2006). The most accurate new proper motion measurements of CPD −62 • 2124 involving Gaia DR1 data (Gaia Collaboration et al 2016a,b;Lindegren et al 2016) in the Hot Stuff for One Year (HSOY; Altmann et al 2017) and UCAC5 (Zacharias, Finch & Frouard 2017) catalogues yield (µ α cos δ, µ δ ) of (−7.7±1.1, +2.0±1.1) mas/yr and (−7.3±1.0, +0.2±1.0) mas/yr, respectively.…”

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

“…Afterwards, Kharchenko et al (2013) recalculated a cluster radius of 31.2 arcmin. We spanned a wide range of Rs values but it has been not possible to find out a clear maximum for ηmax.…”

“…Kharchenko et al 2012;Dias et al 2014;Krone-Martins & Moitinho 2014;Sarro et al 2014;Perren et al 2015;Sampedro et al 2017). The catalogue by Kharchenko et al (2013), mainly based on the PPMXL catalogue (Roeser et al 2010), provides basic astrophysical data for a large set of clusters derived in a uniform and homogeneous way. There is however a need for some caution in this kind of massive data processing because slight variations in the developed strategies can lead to significant biases in the inferred cluster parameters.…”

“…Usually, a King-like function (or any other analytical function) is fitted to the density profile and the cluster radius is extracted from this fit. Systematic determinations of cluster sizes based on this strategy have been performed by Kharchenko et al (2005aKharchenko et al ( , 2012Kharchenko et al ( , 2013 and Piskunov et al (2007Piskunov et al ( , 2008 and compiled in their final catalogue of cluster parameters (Kharchenko et al 2013). However, Kharchenko et al (2005a) pointed out that their published radii are ∼ 1.5 − 2.5 times larger than the corresponding values compiled by Dias et al (2002).…”