Variable Stars in the Inner Region of NGC 6388

Pritzl, B. J.; Stetson, P. B.; Smith, H. A.; Catelan, Marcio; Layden, A. C.; Kinemuchi, K.; Rich, R. M.; Sweigart, A. V.

Variable Stars in the Inner Region of NGC 6388

Date

2005

Authors

Abstract

The metal-rich globular clusters NGC 6388 and NGC 6441 ([Fe/H] ∼-0.6) have unusual sloping blue horizontal branches that extend from a prominent red clump through the RR Lyrae instability strip to a well-populated blue tail. The RR Lyrae variables found from ground-based studies in these clusters have unusually long periods for their metallicities and may represent a new Oosterhoff group. As part of a Hubble Space Telescope Snapshot program we have obtained ACS images of the inner, compact region of NGC 6388 and use archival WFPC2 images to search for additional variable stars. Here we present the results of this variable star search. The properties of the newly discovered RR Lyrae variables will be used to further define the nature of these unusual globular clusters. We gratefully acknowledge financial support through the HST grant GO-09821.09-A.