Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars
Daniel J. Majaess, David G. Turner, David J. Lane
Received December 14, 2010; revised February 23, 2011; accepted February 23, 2011
This research aims to secure precise distances for cluster delta Scuti stars in order to investigate their properties via a VI Wesenheit framework. Deep JHKs color-color and zero-age main sequence (ZAMS) relations derived from ~– 700 unreddened stars featuring 2MASS photometry and precise Hipparcos parallaxes (d <~ 25 pc) are applied to establish distances to several benchmark open clusters that host delta Scuti stars: Hyades, Pleiades, Praesepe, alpha Persei, 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 (WVI,0), evolutionary status, and pulsation modes (order, n). The reliability of JHKs established cluster parameters is demonstrated via a comparison with van Leeuwen (2009a) revised Hipparcos results. Distances for seven of nine nearby (d <– 250 pc) clusters agree, and the discrepant cases (Pleiades and Blanco 1) are unrelated to (insignificant) Te – (J–Ks) variations with cluster age or iron abundance. JHKs photometry is tabulated for ~– 3 × 103 probable cluster members on the basis of proper motions (NOMAD). The deep JHKs photometry extends into the low mass regime (~– 0.4 Msolar) and ensures precise (<– 5%) ZAMS fits. Pulsation modes inferred for the cluster delta Scuti stars from VI Wesenheit and independent analyses are comparable (± n), and the methods are consistent in identifying higher order pulsators. Most small-amplitude cluster delta Scuti stars lie on VI Wesenheit loci characterizing n >– 1 pulsators. A distance established to NGC 1817 from delta Scuti stars (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 Scuti stars as viable distance indicators to intermediate-age open clusters, yet a VI Wesenheit approach is a pertinent means for studying d Scuti stars in harmony with other methods.