WIYN Open Cluster Study. XXVI. Improved kinematic membership and spectroscopy of IC 2391

TL;DR

This study refines the membership list of the young open cluster IC 2391, analyzes its stellar properties, and compares distance measurements, providing insights into stellar evolution and addressing the Hipparcos distance controversy.

Contribution

It provides an expanded, more accurate membership catalog for IC 2391 and compares main-sequence fitting with Hipparcos data, highlighting a notable distance discrepancy.

Findings

66 bona fide cluster members identified

Main sequence fitting distance is 0.19 mag larger than Hipparcos distance

Cluster has a mean [Fe/H] of +0.06 ± 0.06

Abstract

[Abridged] Contex. Young open clusters provide important clues to the interface between the main sequence and pre-main-sequence phases of stellar evolution. The young and nearby open cluster IC 2391 is well-suited to studies of these two evolutionary phases. Aims. We establish a bona fide set of cluster members and then analyze this set in terms of binary frequency, projected rotational velocities, [Fe/H], and lithium abundance. In the wake of the Hipparcos distance controversy for the Pleiades, we compare the main-sequence fitting distance modulus to the Hipparcos mean parallax for IC 2391. Results. The proper-motion survey covers a 6 times larger sky area than the prior targeted searches for cluster members in IC 2391. A total of 66 stars are considered bona fide cluster members down to a mass equivalent to 0.5M_sun. A quarter of them have been newly identified with many in the F2-K5 spectral range, which is crucial for a main-sequence fit. We find a mean [Fe/H] value of +0.06+/-0.06, when a solar abundance of log epsilon (Fe)=7.45 is adopted. The main sequence fitting yields a distance modulus that is 0.19 mag larger than that derived from Hipparcos parallaxes; thus this offset nearly has the size of a similar offset found for the Pleiades. The Li abundance pattern is similar to the earlier findings and is typical for a 40 Myr old open cluster.