Shan Zhang,1,2 Gaochao Liu,1,2‹ Yang Huang,3,4‹ Zongfei Lv,5,6 Sarah Ann Bird , 1,2 Bingqiu Chen , 7 Huawei Zhang,8,9 Timothy C. Beers,10 Xinyi Li,7 Haijun Tian11 and Peng Zhang1,2
1College of Science, China Three Gorges University, Yichang 443002, P. R. China 2Center for Astronomy and Space Sciences, China Three Gorges University, Yichang 443002, P. R. China 3School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, P. R. China 4CAS Key Lab of Optical Astronomy, National Astronomical Observatories, University of Chinese Academy of Sciences, Beijing 100101, P. R. China 5Purple Mountain Observatory, University of Chinese Academy of Sciences, Nanjing 210023, P. R. China 6School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei 230026, P. R. China 7South-Western Institute For Astronomy Research, Yunnan University, Kunming 650500, P. R. China 8Department of Astronomy, School of Physics, Peking University, Beijing 100871, P. R. China 9Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, P. R. China 10Department of Physics and Astronomy and JINA Center for the Evolution of the Elements (JINA-CEE), University of Notre Dame, Notre Dame, IN 46556, USA 11School of Sciences, Hangzhou Dianzi University, Hangzhou 310018, P. R. China Accepted 2023 September 3. Received 2023 September 2; in original form 2023 July 6
ABSTRACT
We use 3653 (2661 RRab, 992 RRc) RR Lyrae stars (RRLs) with 7D (3D position, 3D velocity, and metallicity) information selected from Sloan Digital Sky Survey, Large Sky Area Multi-Object Fiber Spectroscopic Telescope, and Gaia EDR3, and divide the sample into two Oosterhoff groups (Oo I and Oo II) according to their amplitude–period behaviour in the Bailey diagram. We present a comparative study of these two groups based on chemistry, kinematics, and dynamics. We fifind that Oo I RRLs are relatively more metal-rich, with predominately radially dominated orbits and large eccentricities, while Oo II RRLs are relatively more metal-poor, and have mildly radially dominated orbits. The Oosterhoff dichotomy of the Milky Way’s halo is more apparent for the inner-halo region than for the outer-halo region. Additionally, we also search for this phenomenon in the haloes of the two largest satellite galaxies, the Large and Small Magellanic clouds, and compare over different bins in metallicity. We fifind that the Oosterhoff dichotomy is not immutable, and varies based on position in the Galaxy and from galaxy to galaxy. We conclude that the Oosterhoff dichotomy is the result of a combination of stellar and galactic evolution, and that it is much more complex than the dichotomy originally identifified in Galactic globular clusters.
Key words: stars: variables: RR Lyrae – Galaxy: evolution – Galaxy: halo – Galaxy: kinematics and dynamics.
