Nine new open clusters within 500 pc from the Sun

TL;DR

This study used proper motion data and spatial over-density analysis to discover nine previously unknown open clusters within 500 parsecs of the Sun, addressing previous detection limitations.

Contribution

The paper introduces a novel method combining proper motion slices and color-magnitude diagrams to identify faint, low surface brightness open clusters near the Sun.

Findings

Discovered 9 new open clusters within 500 pc of the Sun.

Clusters have ages between 70 Myr and 1 Gyr.

Distances range from 200 to 500 pc.

Abstract

One of the results of the Milky Way Star Clusters (MWSC) survey by Kharchenko et al. (2013) was the detection of a slight under-density of old (ca. 1 Gyr) clusters within the nearest kilo-parsec from the Sun. This under-density may be due to an ineffectiveness in the detection of larger structures with lower surface brightness. We report on our attempts to reveal such clusters. We derived proper motions from a combination of Tycho-2 with URAT1, and obtained a mean precision of about 1.4 mas/y per co-ordinate for 1.3 million stars north of -20 degree declination. We cut the sky into narrow proper motion slices and searched for spatial over-densities of stars in each slice. In optical and near-infrared colour-magnitude diagrams stars from over-densities were than examined to determine if they are compatible with isochrones of a cluster. We estimated the field star contamination using our data and the Besancon Galactic model.We detected 9 hitherto unknown open clusters in the vicinity of the Sun with ages between 70 Myr and 1 Gyr, and distances between 200 and 500 pc.