New Evidence Supporting Membership for TW Nor in Lynga 6 and the Centaurus Spiral Arm

TL;DR

This study confirms TW Nor as a member of Lynga 6, refining its parameters and updating the Galactic Wesenheit function, thereby improving Cepheid-based distance calibrations within the Centaurus spiral arm.

Contribution

It provides new photometric and radial velocity data establishing TW Nor's cluster membership and revises the Galactic Wesenheit function using this data.

Findings

TW Nor is confirmed as a member of Lynga 6.

Lynga 6 is at 1.91 kpc distance with specific reddening and age.

Revised Galactic Wesenheit function incorporating TW Nor's parameters.

Abstract

The putative association between the 10.8 d classical Cepheid TW Nor and the open cluster Lynga 6 has generated considerable debate in the literature. New JHKs photometry in tandem with existing radial velocities for Lynga 6 stars imply cluster membership for TW Nor, and establish 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(t)=7.9+-0.1. The Benedict et al.(2007)/Turner (2010) Galactic VIc Wesenheit function was revised using TW Nor's new parameters: W_VI,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 & VVV CL070).