Kunder, Andrea and Rich, R. M. and Hawkins, K. and Poleski, R. and Storm, J. and Johnson, C. I. and Shen, J and Li, Z.-y. and Cordero, M. J. and Nataf, D. M. and Bono, G. and Walker, A. R. and Koch, Andreas and Propris, R. De and Udalski, A. and Szymanski, M. K. and Soszynski, I. and Pietrzynski, G. and Ulaczyk, K. and Wyrzykowski, L. and Pietrukowicz, P. and Skowron, J. and Kozłowski, S. and Mróz, P. (2015) A high-velocity bulge RR Lyrae variable on a halo-like orbit. Astrophysical Journal Letters, 808 (1): L12. ISSN 2041-8205
Abstract
We report on the RR Lyrae variable star, MACHO 176.18833.411, located toward the Galactic bulge and observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay, which has the unusual radial velocity of −372 ± 8 km s−1 and true space velocity of −482 ± 22 km s−1 relative to the Galactic rest frame. Located less than 1 kpc from the Galactic center and toward a field at (l, b)=(3, −2.5), this pulsating star has properties suggesting it belongs to the bulge RR Lyrae star population, yet a velocity indicating it is abnormal, at least with respect to bulge giants and red clump stars. We show that this star is most likely a halo interloper and therefore suggest that halo contamination is not insignificant when studying metal-poor stars found within the bulge area, even for stars within 1 kpc of the Galactic center. We discuss the possibility that MACHO 176.18833.411 is on the extreme edge of the bulge RR Lyrae radial velocity distribution, and also consider a more exotic scenario in which it is a runaway star moving through the Galaxy.