Outer bulge rr lyrae stars in the vvv survey

Abstract

The VISTA Variables in the V´ıa L´actea (VVV) is a near-IR time-domain survey of the Galactic bulge and southern plane. One of the main goals of this survey is to reveal the 3D structure of the Milky Way through their variable stars. This primary distance indicator are the RR Lyrae stars due to the high number density present in the bulge area and the tight period–luminosity (P–L) relation that they follow in near-IR bands. Our goal in this project is to characterize the RR Lyrae population in the outer bulge (−10! . ` . 10! and −10! . b . −8!) in terms of their periods, amplitudes, Fourier coefficients, and distances, in order to evaluate the 3D structure of the bulge in this area. The distance distribution of RR Lyrae stars will be compared to the one of red clump stars that is known to trace a x-shaped structure in order to determine if these two di↵erent stellar populations share or not the same Galactic distribution. A search for RR Lyrae stars was performed in more than ⇠ 40 sq deg. In the procedure the "2 value and analysis of variance (AoV) statistic methods were used for determining the variability and periodic features of the light curves, respectively. On the other hand, the red clump stars of the same analyzed region were selected applying cuts in the color-magnitude diagram and restricting the maximum distance to ⇠ 20 kpc to construct a similar catalog in terms of distances and covered area compared to the RR Lyrae stars. As a result of this analysis, we report the detection of more than 880 RR Lyrae ab-type stars in the VVV Survey located in the outskirts of the Galactic bulge. Some of them possibly associated with the Sagittarius Dwarf Spheroidal Galaxy. We calculated colors, reddening, extinction, and distances of the detected RR Lyrae stars in order to determine the outer bulge 3D structure. Our main result is that, at the low galactic latitudes mapped here, the RR Lyrae stars trace a centrally concentrated spheroidal distribution. This is a noticeably di↵erent spatial distribution to the one traced by red clump stars known to follow a bar and x-shape structure.