Anchoring the Universal Distance Scale via a Wesenheit Template

Details Anchoring the Universal Distance Scale via a Wesenheit Template Anchoring the Universal Distance Scale via a Wesenheit Template

2010-07-14

arxiv.org/abs/1007.2300v2

Astronomy and Astrophysics

Astrophysics

Galaxy Astrophysics

Accepted for Publication (JAAVSO)

Scientific paper

A VI Wesenheit diagram featuring SX Phoenicis, delta Scuti, RR Lyrae, type II and classical Cepheid variables is calibrated by means of geometric-based distances inferred from HST, Hipparcos, and VLBA observations (n=30). The distance to a target population follows from the offset between the observed Wesenheit magnitudes and the calibrated template. The method is evaluated by ascertaining the distance moduli for the LMC (mu_0=18.43+-0.03 se) and the globular clusters omega Cen, M54, M13, M3, and M15. The results agree with estimates cited in the literature, although a nearer distance to M13 is favoured (pending confirmation of the data's photometric zero-point) and observations of variables near the core of M15 suffer from photometric contamination. The calibrated LMC data is subsequently added to the Wesenheit template since that galaxy exhibits precise OGLE photometry for innumerable variables of differing classes, that includes recent observations for delta Scuti variables indicating the stars follow a steeper VI Wesenheit function than classical Cepheids pulsating in the fundamental mode. VI photometry for the calibrators is tabulated to facilitate further research, and includes new observations acquired via the AAVSO's robotic telescope network (e.g., VY Pyx: =7.25 and -=0.67). The approach outlined here supersedes the lead author's prior first-order effort to unify variables of the instability strip in order to establish reliable distances.