EMPLOYING A NEW, BVIc PHOTOMETRIC SURVEY OF IC 4665 TO INVESTIGATE THE AGE OF THIS YOUNG OPEN CLUSTER

We present a new, BVIc photometric survey of the young open cluster IC 4665, 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 IC 4665. Namely, using a statistical approach incorporating tau(2) color-magnitude diagram modeling, we measure a pre-main-sequence (PMS) isochrone age and distance of 36 +/- 9 Myr and 360 +/- 12 pc, as well as an 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 similar to 10-20 Myr in age and similar to 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 IC 4665 to the published lithium depletion boundary (LDB) 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 LDB ages. In addition, comparing the overall magnetic activity (X-ray and Ha emission) in IC 4665 with other well-studied open clusters, we find that the observed activity distributions for this young cluster are best characterized by assuming an age of 30-40 Myr, thus in agreement with our PMS and turn-off isochrone ages for IC 4665. Overall, although some age discrepancies do exist, particularly in the ages measured from PMS isochrones, the range of possible IC 4665 ages derived from the various dating techniques employed here is relatively small compared to that found for other well-studied open clusters.