Nine new open clusters within 500 pc from the Sun
Abstract
Aims: One of the results of the Milky Way Star Clusters (MWSC) survey 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.
Methods: We derived proper motions from a combination of Tycho-2 with URAT1, and obtained a mean precision of about 1.4 mas/yr per co-ordinate for 1.3 million stars north of -20° declination. We cut the sky into narrow proper motion slices and searched for spatial over-densities of stars in each slice. We then examined stars from over-densities in optical and near-infrared colour-magnitude diagrams to determine if they are compatible with isochrones of a cluster. We estimated the field star contamination using our data and the Besançon Galactic model.
Results: We detected nine 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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 2016
- DOI:
- 10.1051/0004-6361/201629158
- Bibcode:
- 2016A&A...595A..22R
- Keywords:
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- open clusters and associations: general;
- catalogs;
- surveys;
- proper motions