New evidence supporting membership for TW nor in Lyngå 6 and the centaurus spiral arm

The putative association between the 10.^d 8 classical Cepheid TW Nor and the open cluster Lyngå 6 has generated considerable debate in the literature.NewJHK _sphotometry in tandem with existing radial velocities for Lyngå 6 stars implies cluster membership for TWNor and establishes the variable as a high-weight calibrator for classical Cepheid relations. Fundamental mean parameters determined forLyngå 6 are: d = 1.91±0.10 kpc,E(JH) = 0.38±0.02, and log τ= 7.9 ± 0.1. The Benedict et al./Turner Galactic VIc Wesenheit function was revised using TW Nor's new parameters:W_{V I,0} = (3.37±0.08) log P ₀2.48±0.08. TW Nor/Lyngå 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).