PI: Daryl Haggard, Northwestern University/CIERA, email@example.com
Address: Physics Department, Dearborn Observatory, 2131 Tech Drive, Evanston, IL 60208, USA
CoI: Aaron Geller, Northwestern University/CIERA
CoI: Adrienne M. Cool, San Francisco State University
Title: X-ray Binary Candidates Along Omega Centauri's Annomolous Subgiant Branch
Abstract: \omega Centauri, the Milky Way's most massive and enigmatic old stellar cluster, offers a treasure trove of astronomical discovery and controversy. Is the cluster a globular or a dwarf galaxy remnant? Does it host a massive central black hole? Does a population of millisecond pulsars lurk just below detection limits? What are the origins and dynamical histories of the cluster's multiple stellar populations? In the midst of these debates, \wcen has recently yielded a new mystery: a population of X-ray sources seemingly coincident with its metal-rich ``anomalous'' red and subgiant branches (RGB/SGB-a). If these X-ray bright sources are cluster members associated with the metal-rich RGB/SGB-a, they would signify an unusual over-density of X-ray sources among this stellar population. Alternatively if these X-ray sources are associated with the dominant RGB/SGB, they might represent the largest population of ``sub-subgiants'' (or ``red-stragglers'') found to date, and provide an unprecedented sample from which to investigate these poorly understood stars, which may be linked to binary interactions or mergers. We propose multi-epoch, multi-slit, medium resolution spectroscopy from Gemini-South's GMOS instrument for seven of these X- ray sources to measure radial velocities (to search for binarity and establish cluster membership) and to make the preliminary metallicity measurements necessary to associate them with one of \wcen's numerous giant branches.
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