Paper detail

Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars

This research aims to secure precise distances for cluster delta Scutis in order to investigate their properties via a VI Wesenheit framework. Deep JHKs colour-colour and ZAMS relations derived from ~700 unreddened stars featuring 2MASS photometry and precise HIP parallaxes (d<~25 pc) are applied to establish distances to several benchmark open clusters that host delta Scutis: Hyades, Pleiades, Praesepe, alpha Per, and M67 (d=47+-2,138+-6,183+-8,171+-8,815+-40 pc). That analysis provided constraints on the delta Sct sample's absolute Wesenheit magnitudes (W_VI,0), evolutionary status, and pulsation modes (order, n). The reliability of JHKs established cluster parameters is demonstrated via a comparison with van Leeuwen 2009 revised HIP results. Distances for 7 of 9 nearby (d<250 pc) clusters agree, and the discrepant cases (Pleiades & Blanco 1) are unrelated to (insignificant) Te/J-Ks variations with cluster age or [Fe/H]. JHKs photometry is tabulated for ~3x10^3 probable cluster members on the basis of proper motions (NOMAD). The deep JHKs photometry extends into the low mass regime (~0.4 Msun) and ensures precise (<5%) ZAMS fits. Pulsation modes inferred for the cluster delta Scutis from VI Wesenheit and independent analyses are comparable (+-n), and the methods are consistent in identifying higher order pulsators. Most small-amplitude cluster delta Scutis lie on VI Wesenheit loci characterizing n>~1 pulsators. A distance established to NGC 1817 from delta Scutis (d~1.7 kpc) via a universal VI Wesenheit template agrees with estimates in the literature, assuming the variables delineate the n>~1 boundary. Small statistics in tandem with other factors presently encumber the use of mmag delta Scutis as viable distance indicators to intermediate-age open clusters, yet a VI Wesenheit approach is a pertinent means for studying delta Scutis in harmony with other methods.