Spatial and Kinematical Study of the Oosterhoff Dichotomy in the Galactic Bulge
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Date
2020
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Abstract
We present results of spatial and kinematical studies on the Oosterhoff dichotomy in the Galactic bulge based on data from the fourth data release of the Optical Gravitational Lensing Experiment (OGLE). The Oosterhoff groups I and II were separated by conventional augmenting techniques as well as by using a dimensionality reduction machine learning algorithm accompanied by a clustering algorithm. We find, as also seen in globular clusters, that the Oosterhoff II RR Lyrae stars are on the average cooler, more metal-poor, and more massive than RR Lyrae variables associated with the Oosterhoff I group. In addition, neither group seems to be spatially associated with the Galactic bar. For a fraction of our sample, we were able to obtain a 6D kinematical solution, and for these stars, the two Oosterhoff groups do not show a systematic difference in their space velocity distribution. Based on their orbits we estimate that 8 % of the bulge RR Lyrae stars are halo interlopers, and the majority of the studied stars are well confined within the Galactic bulge....