NEW EVIDENCE SUPPORTING MEMBERSHIP FOR TW NOR IN LYNGA 6 AND THE CENTAURUS SPIRAL ARM

The putative association between the 10.(d)8 classical Cepheid TW Nor and the open cluster Lynga 6 has generated considerable debate in the literature. New JHK(s) photometry in tandem with existing radial velocities for Lynga 6 stars implies cluster membership for TW Nor and establishes the variable as a high-weight calibrator for classical Cepheid relations. Fundamental mean parameters determined for Lynga 6 are: d = 1.91 +/- 0.10 kpc, E(J-H) = 0.38 +/- 0.02, and log tau = 7.9 +/- 0.1. The Benedict et al./Turner Galactic V-Ic Wesenheit function was revised using TW Nor's new parameters: W-VI,W-0 = (-3.37 +/- 0.08) log P-0-2.48 +/- 0.08. TW Nor/Lynga 6 lie beyond the Sagittarius-Carina spiral arm and occupy the Centaurus arm, along with innumerable young Cepheids and clusters (e. g., VW Cen and VVV CL070).