Associate Professor    Hattori, Kohei

Research Field

• Galactic Dynamics, Galactic Archaeology, Astrometry, Data Science

Degree

• Doctor of Science (Institute of Astronomy, The University of Tokyo)

Summary of Research

The Milky Way is the only galaxy in which we can observe in detail the 3D positions, velocities, and elemental composition of a vast number of stars. Since a star's orbit and elemental composition do not change a lot after its birth, studying old stars (e.g., stars that are 10 billion years old) allows us to estimate the Milky Way's dynamical state and star-formation history 10 billion years ago. Given that the universe is 13.8 billion years old, these ancient stars are truly "living witnesses to history."

I use data from the Gaia space telescope to study the structure and history of the Milky Way from both theoretical and observational perspectives. I am also focused on developing statistical methods and applying machine learning to this research. Additionally, I am involved in the Japanese-led JASMINE space telescope project, working to unravel the mysteries of the Galactic center. I welcome graduate students who are interested in galactic astronomy, the application of data science, and observational data from space telescopes.

Research Achievements or Papers

• Metallicity and alpha-abundance for 48 million stars in low-extinction regions in the Milky Way (Hattori 2025, ApJ, 980, 90) https://ui.adsabs.harvard.edu/abs/2025ApJ...980...90H/abstract
• Finding r-II sibling stars in the Milky Way with the Greedy Optimistic Clustering algorithm (Hattori, Okuno, Roederer 2023, ApJ, 946, 48) https://ui.adsabs.harvard.edu/abs/2023ApJ...946...48H/abstract
• Action-based distribution function modelling for constraining the shape of the Galactic dark matter halo (Hattori, Valluri, Vasiliev 2021, MNRAS, 508, 5468) https://ui.adsabs.harvard.edu/abs/2021MNRAS.508.5468H/abstract
• Old, Metal-Poor Extreme Velocity Stars in the Solar Neighborhood (Hattori et al. 2018a, ApJ, 866, 121) https://ui.adsabs.harvard.edu/abs/2018ApJ...866..121H/abstract
• Shepherding tidal debris with the Galactic bar: the Ophiuchus stream (Hattori, Erkal, Sanders 2016, MNRAS, 460, 497) https://ui.adsabs.harvard.edu/abs/2016MNRAS.460..497H/abstract
• Very Metal-poor Outer-halo Stars with Round Orbits (Hattori et al. 2013 ApJ Letter, 763, 17) https://ui.adsabs.harvard.edu/abs/2013ApJ...763L..17H/abstract

Academic Society

• Astronomical Society of Japan, GOPIRA (Group of Optical and Infrared Astronomers)

Other Activity

• Part-time lecturer (Bunkyo University)
• Outreach activity (Asahi culture center)

Contact us

• kohei.hattori[at]nao.ac.jp
  (In the mailing address, replace [at] with @)
• https://koheihattori.github.io/