文章基本信息

标题：The Bulge Radial Velocity Assay for RR Lyrae Stars (BRAVA-RR) DR2: A Bimodal Bulge?
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作者：Andrea Kunder ; Angeles Pérez-Villegas ; R.Michael Rich 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2020
卷号：159
期号：6
页码：3766-3778
DOI：10.3847/1538-3881/ab8d35
语种：English
出版社：American Institute of Physics
摘要：The radial velocities of 2768 fundamental-mode RR Lyrae stars (RRLs) toward the southern Galactic bulge are presented, spanning the southern bulge from −8° < l < + 8° and −3° < b < −6°.Distances derived from the pulsation properties of the RRLs are combined with Gaia proper motions to give constraints on the orbital motions of 1389 RRLs.The majority (~75%) of the bulge RRLs have orbits consistent with these stars being permanently bound to <3.5 kpc from the Galactic Center, similar to the bar.However, unlike the bulge giants, the RRLs exhibit slower rotation and a higher velocity dispersion.The higher velocity dispersion arises almost exclusively from halo interlopers passing through the inner Galaxy.We present 82 stars with space velocities gsim500 km s−1 and find that the majority of these high-velocity stars are halo interlopers; it is unclear if a subsample of these stars with similar space velocities has a common origin.Once the 25% of the sample represented by halo interlopers is cleaned, we can clearly discern two populations of bulge RRLs in the inner Galaxy.The first population of RRLs is not as tightly bound to the Galaxy (but is still confined to the inner ~3.5 kpc) and is both spatially and kinematically consistent with the barred bulge.The second population is more centrally concentrated and does not trace the bar.One possible interpretation is that this population was born prior to bar formation, as their spatial location, kinematics, and pulsation properties suggest, possibly from an accretion event at high redshift.
关键词：Galactic bulge;Stellar populations;Milky Way formation;RR Lyrae variable stars;Stellar kinematics;Galaxy radial velocities;Halo stars