A High-Precision Trigonometric Parallax to an Ancient Metal-Poor Globular Cluster
Abstract
Using the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST), we have obtained a direct trigonometric parallax for the nearest metal-poor globular cluster, NGC 6397. Although trigonometric parallaxes have been previously measured for many nearby open clusters, this is the first parallax for an ancient metal-poor population -- one that is used as a fundamental template in many stellar population studies. This high-precision measurement was enabled by the HST/WFC3 spatial-scanning mode, providing hundreds of astrometric measurements for dozens of stars in the cluster and also for Galactic field stars along the same sightline. We find a parallax of 0.418 +/- 0.013 +/- 0.018 mas (statistical, systematic), corresponding to a true distance modulus of 11.89 +/- 0.07 +/- 0.09 mag (2.39 +/- 0.07 +/- 0.10 kpc). The V luminosity at the stellar main sequence turnoff implies an absolute cluster age of 13.4 +/- 0.7 +/- 1.2 Gyr.
Keywords
Cite
@article{arxiv.1803.02927,
title = {A High-Precision Trigonometric Parallax to an Ancient Metal-Poor Globular Cluster},
author = {T. M. Brown and S. Casertano and J. Strader and A. Riess and D. A. VandenBerg and D. R. Soderblom and J. Kalirai and R. Salinas},
journal= {arXiv preprint arXiv:1803.02927},
year = {2018}
}
Comments
Accepted for publication in The Astrophysical Journal Letters. Version 2 includes minor revisions to proof