A5004874578- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Galaxies: Formation, Evolution, Phenomena
- Astrophysical Phenomena and Observations
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Geophysics and Gravity Measurements
- Scientific Research and Discoveries
- Cosmology and Gravitation Theories
- Astronomical and nuclear sciences
- Advanced Statistical Methods and Models
- Dark Matter and Cosmic Phenomena
- High-pressure geophysics and materials
- Facial Nerve Paralysis Treatment and Research
- Particle Accelerators and Free-Electron Lasers
- Systemic Lupus Erythematosus Research
- Dermatological and COVID-19 studies
- RNA and protein synthesis mechanisms
- Face and Expression Recognition
- Astrophysics and Cosmic Phenomena
- Bayesian Methods and Mixture Models
- Metabolism and Genetic Disorders
The Institute of Statistical Mathematics
2020-2024
National Astronomical Observatory of Japan
2020-2024
Nagoya City University
2024
University of Michigan
2017-2023
Carnegie Mellon University
2019-2021
University of Cambridge
2015-2016
The University of Tokyo
2010-2014
Institute of Astronomy
2011
Tokyo University of Science
2010
Higashi Osaka City General Hospital
2003
The rotation curve of the Milky Way is commonly used to estimate local dark matter density $\rho_{{\rm DM},\odot}$. However, estimates are subject choice distribution baryons needed in this type studies. In work we explore several Galactic mass models that differ and matter, order determine For purpose analyze precise circular velocity measurement up $\sim 25$ kpc from centre obtained Gaia DR2 [1]. We find estimated value DM},\odot}$ stays robust reasonable changes spherical halo. show...
We present kinematics of 35 highly r-process-enhanced ([Eu/Fe] >= +0.7) metal-poor (-3.8 < [Fe/H] -1.4) field stars. calculate six-dimensional positions and velocities, evaluate energies integrals motion, compute orbits for each these stars using parallaxes proper motions from the second Gaia data release published radial velocities. All have halo kinematics. Most (66%) remain in inner regions (< 13 kpc), many (51%) that pass within 2.6 kpc Galactic center. Several (20%) extend beyond 20...
Abstract We present a nearly complete rapid neutron-capture process ( r -process) chemical inventory of the metal-poor ([Fe/H] = −1.46 ± 0.10) -process-enhanced ([Eu/Fe] +1.32 0.08) halo star HD 222925. This abundance set is most for any object beyond solar system, with total 63 metals detected and seven upper limits. It comprises 42 elements from 31 ≤ Z 90, including rarely in stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, Au. derive these abundances an analysis 404...
We report the discovery of a candidate binary system consisting black hole (BH) and red giant branch star from Gaia DR3. This is discovered 64108 solutions for which both astrometric spectroscopic data are available. For this system, consistent with each other, making confident BH binary. The primary (visible) in DR3 5870569352746779008, whose mass quite uncertain. Fortunately, albeit uncertainty primary's mass, we can estimate secondary (dark) object to be $>5.68$ $M_\odot$ probability $99$...
Abstract The Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, Aerospace Agency. JASMINE has two main goals. One Galactic archaeology with Center survey, which aims to reveal Milky Way’s central core structure formation history from Gaia-level (∼25 ${\mu} $as) astrometry in near-infrared (NIR) Hw band (1.0–1.6 $m). other an exoplanet discover transiting Earth-like exoplanets...
Abstract We present high-resolution Magellan/MIKE spectroscopy of 42 red giant stars in seven stellar streams confirmed by the Southern Stellar Stream Spectroscopic Survey ( S 5 ): ATLAS, Aliqa Uma, Chenab, Elqui, Indus, Jhelum, and Phoenix. Abundances 30 elements have been derived from over 10,000 individual line measurements or upper limits using photometric parameters a standard LTE analysis. This is currently most extensive set element abundances for streams. Three (ATLAS, Phoenix) are...
We report the discovery of 30 stars with extreme space velocities ($>$ 480 km/s) in Gaia-DR2 archive. These are a subset 1743 high-precision parallax, large tangential velocity ($v_{tan}>$ 300 km/s), and measured line-of-sight DR2. By tracing orbits back time, we find at least one them is consistent having been ejected by supermassive black hole Galactic Center. Another star has an orbit that passed near Large Magellanic Cloud (LMC) about 200 Myr ago. Unlike previously discovered blue...
The dynamics of stellar streams in rotating barred potentials is explained for the first time. Naturally, neighbouring stream stars reach pericentre at slightly different times. In presence a bar, these experience bar orientations during pericentric passage and hence each star receives torque from bar. These differing torques reshape angular momentum energy distribution stream, which turn changes growth rate stream. For progenitor orbiting same sense as bar's rotation satisfying resonance...
We search for dynamical substructures in the LAMOST DR3 very metal-poor (VMP) star catalog. After cross-matching with Gaia DR2, there are 3300 VMP stars available high-quality astrometric information that have halo-like kinematics. apply a method based on self-organizing maps to find groups clustered 4D space of orbital energy and angular momentum. identify 57 dynamically tagged groups, which we label DTG-1 DTG-57. Most them belong existing nearby halo, such as $Gaia$ Sausage or Sequoia. The...
Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for ${\sim} 4000$ metal-poor stars ([Fe/H] $\leq -0.8$) compiled from the Best $\&$ Brightest survey. Selected as candidates broadband near- and far-IR photometry, $43\%$ of these had medium-resolution ($1200 \lesssim R 2000$) validation spectra obtained over a seven-year campaign $2014$ to $2020$ with variety telescopes. The remaining were chosen photometric metallicity determinations Huang et al....
Context: Sequoia is a retrograde kinematic substructure in the nearby Galactic halo, whose properties are matter of debate. For example, previous studies do not necessarily agree on chemical abundances stars, which important for understanding its nature. Aim: We characterize sample stars from by determining high-precision abundances. Methods: measured Na, Mg, Si, Ca, Ti, Cr, Mn, Ni, Zn, Y, and Ba differential abundance analysis high signal-to-noise ratio, high-resolution spectra new...
Context: The Helmi streams are a kinematic substructure whose progenitor is likely dwarf galaxy. Although 20 years have passed since their discovery, it still unclear whether members chemically distinguishable from other halo stars in the Milky Way. Aim: We aim to precisely characterize chemical properties of streams. Methods: analyzed high-resolution, high signal-to-noise ratio spectra for 11 stream through line-by-line abundance analysis. compared derived abundances homogenized literature...
Abstract We estimate ([M/H], [ α /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 APOGEE DR17 a metal-poor star sample Li et al. The root mean square error of our estimation is 0.0890 dex [M/H] 0.0436 /M], when we evaluate test data that are not used training models. Because dominated giants, most reliable giants. high-[ /M] stars low-[ selected show different kinematical properties...
In this paper, we report 591 high velocity star candidates (HiVelSCs) selected from over 10 million spectra of the data release seven (DR7) Large Sky Area Multi-object Fiber Spectroscopic Telescope and second Gaia release, with three-dimensional velocities in Galactic rest-frame larger than 445 km/s. We show that at least 43 HiVelSCs are unbound to Galaxy escape probabilities 50%, number decreases eight if possible parallax zero-point error is corrected. Most these metal-poor slightly...
The orbital motions of halo stars in the Milky Way reflect progenitor systems which they formed, making it possible to trace mass-assembly history Galaxy. Direct measurement three-dimensional velocities, based on accurate proper and line-of-sight has revealed that majority inner-halo region move eccentric orbits. However, our understanding distant, in-situ halo-star samples is still limited, due lack for these stars. Here we explore a model-independent analysis velocities spatial...
The velocity anisotropy parameter, beta, is a measure of the kinematic state orbits in stellar halo which holds promise for constraining merger history Milky Way (MW). We determine global trends beta as function radius from three suites simulations, including accretion only and cosmological hydrodynamic simulations. find that both types simulations are consistent predict strong radial (<beta>~0.7) Galactocentric radii greater than 10 kpc. Previous observations MW's claim detection an...
Abstract We present a comprehensive catalog of the dippers—young stellar objects that exhibit episodic dimming—derived from one year’s worth data Transiting Exoplanet Survey Satellite (TESS) full-frame images. In survey, we found 35 dippers using convolutional neural network, most them newly discovered. Although these are widely distributed over first half-hemisphere TESS surveyed, identified majority’s membership with nearest association Scorpius–Centaurus, Velorum OB2, and nearby Orion...
We report the discovery of J1521-3538, a bright (V=12.2), very metal-poor ([Fe/H]=-2.8) strongly r-process enhanced field horizontal branch star, based on high-resolution, high signal-to-noise Magellan/MIKE spectrum. J1521-3538 shows largest element over-abundance in any known r-process-enhanced with [Eu/Fe]=+2.2, and its chemical abundances 22 neutron-capture elements closely match scaled solar pattern. is also one few carbon-enhanced stars enhancement (CEMP-r stars), as found after...
One of the most intriguing properties GD-1 stellar stream is existence three gaps. If these gaps were formed by close encounters with dark matter subhalos, opens an exciting window through which we can see size, mass, and velocity distributions subhalos in Milky Way. However, order to use as a probe substructure, need disprove that are not due perturbations from baryonic components Here ran large number test particle simulations investigate probability each known globular clusters (GCs) form...
Abstract R -process enhanced stars with [Eu/Fe] ≥ +0.7 (so-called r -II stars) are believed to have formed in an extremely neutron-rich environment which a rare astrophysical event (e.g., neutron-star merger) occurred. This scenario is supported by the existence of ultra-faint dwarf galaxy, Reticulum II, where most highly elements. In this scenario, some small fraction galaxies around Milky Way were enhanced. When each r-enhanced galaxy accreted Way, it deposited many Galactic halo similar...
Abstract It is unclear whether pregnancy has any influence on chronic hepatitis C virus (HCV) infection. The aim of this study was to investigate the relationship between and parturition with HCV viremia levels natural resolution RNA. Twenty‐two pregnant patients 120 nonpregnant control female patients, both positive for anti‐HCV RNA, were studied. core protein quantified by enzyme immunoassay, RNA detected reverse transcription‐polymerase chain reaction (RT‐PCR). Of group, two females whose...
The origin of the Hercules stream, most prominent velocity substructure in Solar neighbour disc stars, is still under debate. Recent accurate measurements position, velocity, and metallicity provided by Tycho Gaia Astrometric Solution (TGAS) RAdial Velocity Experiments (RAVE) have revealed that stream clearly seen metal-rich region ([Fe/H] ≳ 0), while it not lower ≲ −0.25). By using a large number chemo-dynamical 2D test-particle simulations with rotating bar and/or spiral arms, we find...
We present the first spectroscopic measurements of ATLAS and Aliqa Uma streams from Southern Stellar Stream Spectroscopic Survey ($S^5$), in combination with photometric data Dark Energy astrometric $Gaia$. From coherence members radial velocity proper motion, we find out that these two systems are extremely likely to be one stream discontinuity morphology density on sky (the "kink" feature). refer this entire as ATLAS-Aliqa stream, or AAU stream. perform a comprehensive exploration effect...
We report that LAMOST-HVS1 is a massive hyper-runaway subgiant star with mass of 8.3 and super-solar metallicity, which was ejected from the inner stellar disk Milky Way ∼33 ago intrinsic ejection velocity (corrected for streaming motion disk), based on proper data Gaia Data Release 2 (DR2) high-resolution spectroscopy. The extremely large indicates this not by supernova explosion binary companion. Rather, it probably three- or four-body dynamical interaction more objects in high-density...
Gravitational three-body interaction among binary stars and the supermassive black hole at center of Milky Way occasionally ejects a hypervelocity star (HVS) with velocity . Due to ejection location, such an HVS initially has negligible azimuthal angular momentum Even if halo is mildly triaxial, Lz recently ejected nearby remains negligible, since its flight time from Galactic too short accumulate noticeable torque. However, we make wrong assumption about solar position velocity, would...