Open clusters with Hipparcos I. Mean astrometric parameters

TL;DR

This paper uses Hipparcos data to determine precise astrometric parameters for nearby and some distant open clusters, aiding calibration and kinematic studies with minimal systematic errors.

Contribution

It provides new, highly accurate mean parallaxes and proper motions for 18 open clusters within 500 pc, including careful bias analysis and additional data for more distant clusters.

Findings

Precise parallaxes with 0.2-0.5 mas accuracy for nearby clusters.

Proper motions measured with 0.1-0.5 mas/yr precision.

No significant systematic errors found in mean cluster parallaxes.

Abstract

New memberships, mean parallaxes and proper motions of all 9 open clusters closer than 300 pc (except the Hyades) and 9 rich clusters between 300 and 500 pc have been computed using Hipparcos data. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to 0.5 mas/yr for proper motions, are of great interest for calibrating photometric parallaxes as well as for kinematical studies. Careful investigations of possible biases have been performed and no evidence of significant systematic errors on the mean cluster parallaxes has been found. The distances and proper motions of 32 more distant clusters, which may be used statistically, are also indicated.