A high-velocity bulge RR Lyrae variable on a halo-like orbit

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). ISSN 2041-8205

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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.

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Journal Article
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Astrophysical Journal Letters
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This is an author-created, un-copyedited version of an article accepted for publication/published in Astrophysical Journal Letters. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.1088/2041-8205/808/1/L12
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30 Nov 2016 14:34
Last Modified:
27 Sep 2023 00:14