Hubble Space Telescope imaging of the WR 38/WR 38a cluster

Abstract

We are conducting a high angular resolution imaging survey of Galactic Wolf-Rayet stars using the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope (HST). We have found a small stellar cluster associated with the faint, close pair WR 38 and WR 38a. We present astrometric measurements and photometry in the wideband F336W (U), F439W (5), and F555W (V) filter system for the cluster and nearby stars. We combine our photometry with Johnson and IR magnitudes and compare the observations with calibrated model results for reddened stars to adjust the HST zero points and to identify five probable main-sequence members of the cluster. A least-squares fit of the colors and magnitudes of this set yields a cluster reddening of E(B - V) = 1.63 ±0.05 mag and a distance of 10 -4 +12 kpc for an assumed ratio of total to selective extinction of R = 3.1. We discuss the relationship of this cluster to other objects along the line of sight. If situated at a distance of ≈8 kpc, then the cluster would reside in a dense region of the Carina spiral arm, close to a giant molecular cloud and the starburst cluster NGC 3603.