Employing a New BVIc Photometric Survey of IC 4665 to Investigate the Age of this Young Open Cluster

TL;DR

This study uses a new high-quality BVIc photometric survey of IC 4665 to refine its age and distance, finding a consistent age range of about 30-40 million years across multiple methods.

Contribution

The paper introduces a rigorous photometric standardization and applies multiple age-dating techniques to better constrain IC 4665's properties, highlighting model-dependent uncertainties.

Findings

Age estimates range from 36 to 42 Myr depending on models and colors.

The cluster's age from lithium depletion boundary is 28±5 Myr, close to isochrone ages.

Magnetic activity suggests an age of 30-40 Myr, aligning with isochrone results.

Abstract

We present a new, BVIc photometric survey of the young open cluster IC4665, which improves on previous studies of this young cluster by incorporating a rigorous standardization procedure, thus providing high-fidelity colors and magnitudes for cluster members. We use this new photometric dataset to reevaluate the properties (age and distance) of IC4665. Namely, using a statistical approach incorporating Tau^2 CMD modeling, we measure a pre-main-sequence isochrone age and distance of 36+-9 Myr and 360+-12 pc, as well as a upper-main-sequence turn-off age and distance of 42+-12 Myr and 357+-12 pc. These ages and distances are highly dependent on the isochrone model and color used for the fitting procedure, with a possible range of ~10-20 Myr in age and ~20 pc in distance. This spread in calculated ages and distances seen between colors and models is likely due to limitations in the individual membership catalogs and/or systematic differences in the predicted stellar parameters from the different sets of models. Interestingly, when we compare the isochrone ages for IC4665 to the published lithium depletion boundary age, 28+-5 Myr, we observe that this cluster does not appear to follow the trend of isochrone ages being 1.5 times smaller than lithium depletion boundary ages. In addition, comparing the overall magnetic activity (X-ray and H-alpha emission) in IC4665 with other well studied open clusters, we find the observed activity distributions for this young cluster are best characterized by assuming an age of 30-40 Myr, thus in agreement with our pre-main-sequence and turn-off isochrone ages for IC4665. Overall, although some age discrepancies do exist, particularly in the ages measured from pre-main-sequence isochrones, the range of possible IC4665 ages derived from the various dating techniques employed here is relatively small compared to that found for other well studied open clusters.