XHIP-II: Clusters and associations

TL;DR

This study improves candidate lists and distance estimates for 42 clusters and 45 associations from Hipparcos data, resolving the Pleiades distance discrepancy and supporting stellar evolutionary models.

Contribution

It introduces a six-dimensional fitting method to identify cluster members and accurately determine their distances, enhancing previous catalogues and resolving the Pleiades distance controversy.

Findings

Identified candidate members for 42 clusters and 45 associations.

Found agreement between parallax and photometric distances for key clusters.

Determined the Pleiades distance as approximately 126 pc, consistent with stellar models.

Abstract

Context. In the absence of complete kinematic data it has not previously been possible to furnish accurate lists of member stars for all moving groups. There has been an unresolved dispute concerning the apparent inconsistency of the Hipparcos parallax distance to the Pleiades. Aims. To find improved candidate lists for clusters and associations represented among Hipparcos stars, to establish distances, and to cast light on the Pleiades distance anomaly. Methods. We use a six dimensional fitting procedure to identify candidates, and plot CMDs for 20 of the nearest groups. We calculate the mean parallax distance for all groups. Results. We identify lists of candidates and calculated parallax distances for 42 clusters and 45 associations represented within the Hipparcos catalogue. We find agreement between parallax distance and photometric distances for the most important clusters. For single stars in the Pleiades we find mean parallax distance 125.6 \pm 4.2 pc and photometric distance 132 \pm 3 pc calibrated to nearby groups of similar in age and composition. This gives no reason to doubt either the Hipparcos database or stellar evolutionary theory.