The optical gravitational lensing experiment. Variable stars in globular clusters^*

II. Fields 5139D-F in ω Centauri

¹ Warsaw University Observatory, Al. Ujazdowskie  4, 00-478 Warsaw, Poland
² Carnegie Observatories, Las Campanas Observatory, Casilla 601, La Serena, Chile e-mail: wojtek@roses.ctio.noao.edu
³ Department of Astronomy, University of Michigan, 821 Dennison Bldg., Ann Arbor, MI 48109-1090, U.S.A.
⁴ Princeton University Observatory, Peyton Hall, Princeton NJ 08544, U.S.A.

Send offprint request to: J. Kaluzny

Received: 11 April 1996
Accepted: 23 July 1996

Abstract

Three fields located close to the center of the globular cluster ω Cen were surveyed in a search for variable stars. We present V-band light curves for 32 periodic variables. This sample includes 10 SX Phe stars, 19 eclipsing binaries, and three likely spotted variables (FK Com or RS CVn type stars). Only 5 of these variables were previously known (including two objects reported in Paper I). All SX Phe stars and 8 eclipsing binaries from our sample belong to blue stragglers. Five binaries occupy positions on the upper main-sequence of the cluster and another four are located at the base of the subgiant branch. Of particular interest is detection of a detached binary system with a period day. Further study of this star can provide direct information about properties of turnoff stars in ω Cen. All SX Phe stars and most of eclipsing binaries discovered in our survey are likely cluster members. We present V vs. color-magnitude diagrams for the monitored fields. A populous group of likely hot subdwarfs as well as numerous candidates for blue stragglers can be noted in these diagrams. Our data indicate that ω Cen possesses the largest number of blue stragglers among all galactic globulars.