Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars!
Volume 39 number 2 (2011)
- Daniel J. Majaess
- Saint Mary’s University, Department of Astronomy and Physics, Halifax, Nova Scotia, B3H 3C3, Canada; dmajaess@ap.smu.ca and The Abbey Ridge Observatory, Stillwater Lake, Nova Scotia, Canada
- David G. Turner
- Saint Mary’s University, Department of Astronomy and Physics, Halifax, Nova Scotia, B3H 3C3, Canada; dmajaess@ap.smu.ca and The Abbey Ridge Observatory, Stillwater Lake, Nova Scotia, Canada
- David J. Lane
- Saint Mary’s University, Department of Astronomy and Physics, Halifax, Nova Scotia, B3H 3C3, Canada; dmajaess@ap.smu.ca and The Abbey Ridge Observatory, Stillwater Lake, Nova Scotia, Canada
- Tom Krajci
- Astrokolkhoz Telescope Facility, P.O. Box 1351, Cloudcroft, NM 88317
Abstract
This research aims to secure precise distances for cluster d 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 d Scuti stars: Hyades, Pleiades, Praesepe, a Persei, and M67 (d = 47 ± 2, 138 ± 6, 183 ± 8, 171 ± 8, 815 ± 40 pc). That analysis provided constraints on the d 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 MÄ) and ensures precise (<– 5%) ZAMS fits. Pulsation modes inferred for the cluster d 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 d Scuti stars lie on VI Wesenheit loci characterizing n >– 1 pulsators. A distance established to NGC 1817 from d 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 d 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.