151 citations · 1.2k across the 43 of their papers we have counts for
43 papers
A differentiable hydrodynamical approach to the Milky Way bar pattern speed with CO longitude--velocity data
Junichi Baba, Kohei Hattori
We present a differentiable hydrodynamical framework for modeling barred gas flow in the Milky Way and constraining broad low-loss regions in bar-pattern-speed parameter space from…
Dynamical clock of the Helmi stream -- Analysis of the clumping of stars in the orbital frequency-space
Kohei Hattori
Reconstructing the assembly history of the Milky Way requires precise constraints on the dynamical age of its merger remnants -- the time elapsed since a progenitor satellite was d…
HR-GO II: chemical abundances of low- retrograde dynamically-tagged-groups: Revealing Thamnos as a very metal-poor substructure
Renjing Xie, Zhen Yuan, Haining Li +12
Milky Way halo substructures identified in dynamical space are known to suffer from contamination from the Milky Way in-situ stars, which makes their accreted origins uncertain. We…
Discovery of WINERED-HVS1: A metal-rich hyper-velocity star candidate ejected from the Galactic center
Kohei Hattori, Daisuke Taniguchi, Takuji Tsujimoto +4
We report the discovery of a metal-rich red giant star, WINERED-HVS1, which is a candidate for a hyper-velocity star (HVS). Its past trajectory suggests that this star may have bee…
JASMINE image simulator for high-precision astrometry and photometry
Takafumi Kamizuka, Hajime Kawahara, Ryou Ohsawa +23
JASMINE is a Japanese planned space mission that aims to reveal the formation history of our Galaxy and discover habitable exoEarths. For these objectives, the JASMINE satellite pe…
Minimum-entropy constraints on galactic potentials
Leandro Beraldo e Silva, Monica Valluri, Eugene Vasiliev +3
A tracer sample in a gravitational potential, starting from a generic initial condition, phase-mixes towards a stationary state. This evolution is accompanied by an entropy increas…
The R-Process Alliance: 2MASS J22132050-5137385, the Star with the Highest-known r-process Enhancement at [Eu/Fe] = +2.45
Ian U. Roederer, Timothy C. Beers, Kohei Hattori +6
We present stellar parameters and chemical abundances of 47 elements detected in the bright (V = 11.63) very metal-poor ([Fe/H] = -2.20 +- 0.12) star 2MASS J22132050-5137385. We ob…
Metallicity and -abundance for 48 million stars in low-extinction regions in the Milky Way
Kohei Hattori
We estimate ([M/H], [/M]) for 48 million giants and dwarfs in low-dust extinction regions from the Gaia DR3 XP spectra by using tree-based machine-learning models trained on APO…
JASMINE: Near-Infrared Astrometry and Time Series Photometry Science
Daisuke Kawata, Hajime Kawahara, Naoteru Gouda +86
Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, the Japan Aero…
Learning from AI: An Interactive Learning Method Using a DNN Model Incorporating Expert Knowledge as a Teacher
Kohei Hattori, Tsubasa Hirakawa, Takayoshi Yamashita +1
Visual explanation is an approach for visualizing the grounds of judgment by deep learning, and it is possible to visually interpret the grounds of a judgment for a certain input b…
Search for a Black Hole Binary in Gaia DR3 Astrometric Binary Stars with Spectroscopic Data
Ataru Tanikawa, Kohei Hattori, Norita Kawanaka +3
We report the discovery of a candidate binary system consisting of a black hole (BH) and a red giant branch star from the Gaia DR3. This binary system is discovered from 64108 bina…
Finding -II sibling stars in the Milky Way with the Greedy Optimistic Clustering algorithm
Kohei Hattori, Akifumi Okuno, Ian U. Roederer
-process enhanced stars with [Eu/Fe] (so-called -II stars) are believed to have formed in an extremely neutron-rich environment in which a rare astrophysical event…
SIRIUS Project. V. Formation of off-center ionized bubbles associated with Orion Nebula Cluster
Michiko S. Fujii, Kohei Hattori, Long Wang +4
Massive stars born in star clusters terminate star cluster formation by ionizing the surrounding gas. This process is considered to be prevalent in young star clusters containing m…
The R-Process Alliance: A Nearly Complete R-Process Abundance Template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925
Ian U. Roederer, James E. Lawler, Elizabeth A. Den Hartog +9
We present a nearly complete rapid neutron-capture process (r-process) chemical inventory of the metal-poor ([Fe/H] = -1.46 +/- 0.10) r-process-enhanced ([Eu/Fe] = +1.32 +/- 0.08)…
A Greedy and Optimistic Approach to Clustering with a Specified Uncertainty of Covariates
Akifumi Okuno, Kohei Hattori
In this study, we examine a clustering problem in which the covariates of each individual element in a dataset are associated with an uncertainty specific to that element. More spe…
Probability of forming gaps in the GD-1 stream by close encounters of globular clusters
Yuka Doke, Kohei Hattori
One of the most intriguing properties of the GD-1 stellar stream is the existence of three gaps. If these gaps were formed by close encounters with dark matter subhalos, the GD-1 s…
High-precision chemical abundances of Galactic building blocks. II. Revisiting the chemical distinctness of the Helmi streams
Tadafumi Matsuno, Emma Dodd, Helmer H. Koppelman +6
Context: The Helmi streams are a kinematic substructure whose progenitor is likely a dwarf galaxy. Although 20 years have passed since their discovery, it is still unclear whether…
Dippers from TESS Full-frame Images. II. Spectroscopic Characterization of Four Young Dippers
Yui Kasagi, Takayuki Kotani, Hajime Kawahara +9
Photometric monitoring by the Transiting Exoplanet Survey Satellite (TESS) has discovered not only periodic signals by transiting exoplanets but also episodic or quasi-periodic dim…
A Very Metal-poor RR Lyrae Star with a Disk Orbit Found in the Solar Neighborhood
Noriyuki Matsunaga, Akinori Itane, Kohei Hattori +28
Metal-deficient stars are important tracers for understanding the early formation of the Galaxy. Recent large-scale surveys with both photometric and spectroscopic data have report…
High-precision chemical abundances of Galactic building blocks. The distinct chemical abundance sequence of Sequoia
Tadafumi Matsuno, Helmer H. Koppelman, Amina Helmi +5
Context: Sequoia is a retrograde kinematic substructure in the nearby Galactic halo, whose properties are a matter of debate. For example, previous studies do not necessarily agree…
Dynamically Tagged Groups of Metal-Poor Stars from the Best \& Brightest Survey
Derek Shank, Timothy C. Beers, Vinicius M. Placco +9
Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for metal-poor stars ([Fe/H] ) compiled from the Best B…
Action-based distribution function modelling for constraining the shape of the Galactic dark matter halo
Kohei Hattori, Monica Valluri, Eugene Vasiliev
We estimate the 3D density profile of the Galactic dark matter (DM) halo within kpc from the Galactic centre by using the astrometric data for halo RR Lyrae stars f…
591 high velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia DR2
Yin-Bi Li, A-Li Luo, You-Jun Lu +14
In this paper, we report 591 high velocity star candidates (HiVelSCs) selected from over 10 million spectra of the data release seven (DR7) of the Large Sky Area Multi-object Fiber…
Dippers from the TESS Full-Frame Images I: The Results of the first 1 year data and Discovery of A Runaway dipper
Tomoyuki Tajiri, Hajime Kawahara, Masataka Aizawa +9
We present a comprehensive catalog of the dippers---young stellar objects that exhibit episodic dimming---derived from the one year's worth of data of Transiting Exoplanet Survey S…