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

Abstract

This research aims to secure precise distances for cluster δ 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 δ Scuti stars: Hyades, Pleiades, Praesepe, α Persei, and M67 (d = 47 ± 2, 138 ± 6, 183 ± 8, 171 ± 8, 815 ± 40 pc). That analysis provided constraints on the Δ 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 (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 ~3x10^3 probable cluster members on the basis of proper motions (NOMAD). The deep JHKs photometry extends into the low mass regime (~0.4 M_sun) and ensures precise (≤5%) ZAMS fits. Pulsation modes inferred for the cluster δ 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 δ Scuti stars lie on VI Wesenheit loci characterizing n≥1 pulsators. A distance established to NGC 1817 from δ 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 Δ Scuti stars as viable distance indicators to intermediate-age open clusters, yet a VI Wesenheit approach is a pertinent means for studying δ Scuti stars in harmony with other methods.


Publication:
Journal of the American Association of Variable Star Observers (JAAVSO)
Pub Date:
September 2011
DOI:

10.48550/arXiv.1102.1705

arXiv:
arXiv:1102.1705
Bibcode:
2011JAVSO..39..219M
Keywords:
  • Astrophysics - Galaxy Astrophysics;
  • Astrophysics - Solar and Stellar Astrophysics
E-Print:
Accepted for Publication (JAAVSO)
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