Searching for tidal tails around ω Centauri using RR Lyrae stars

¹ Institut Utinam, CNRS UMR 6213, Université de Franche-Comté, OSU THETA de Franche-Comté-Bourgogne, 25010 Besançon, France
e-mail: jfernandez@obs-besancon.fr
² Centro de Investigaciones de Astronomía, AP 264, 5101-A Mérida, Venezuela
³ Postgrado en Física Fundamental, Universidad de Los Andes, 5101 Mérida, Venezuela
⁴ Cerro Tololo Interamerican Observatory, Casilla 603 La Serena, Chile
⁵ Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apdo. Postal 877, 22860 Ensenada, Baja California, Mexico
⁶ Department of Astronomy, Yale University, PO Box 20811, New Haven, CT 06520-8101, USA
⁷ Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apdo. Postal 70264, Mexico D.F., 04510, Mexico

Received: 1 September 2014
Accepted: 7 November 2014

Abstract

We present a survey of RR Lyrae stars in an area of 50 deg² around the globular cluster ω Centauri, aimed at detecting debris material from the alleged progenitor galaxy of the cluster. We detected 48 RR Lyrae stars, only 11 of which have been previously reported. Ten of the eleven previously known stars were found inside the tidal radius of the cluster. The rest were located outside the tidal radius up to distances of ~6 degrees from the center of the cluster. Several of these stars are located at distances similar to that of ω Centauri. We investigate the probability that they may have been stripped off the cluster. To do this, we studied their properties (mean periods) by calculating the expected halo and thick-disk population of RR Lyrae stars in this part of the sky, analyzing the radial velocity of a sub-sample of the RR Lyrae stars, and finally, studying the probable orbits of this sub-sample around the Galaxy. The results of these investigations do not support the scenario that there is significant tidal debris around ω Centauri, which confirms previous studies on the region. It is puzzling that tidal debris has been found elsewhere but not near the cluster itself.