A5014849160- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Scientific Research and Discoveries
- Phase-change materials and chalcogenides
- Dark Matter and Cosmic Phenomena
- Nuclear physics research studies
- Astronomical Observations and Instrumentation
- Neutrino Physics Research
- Semiconductor materials and interfaces
- Astrophysical Phenomena and Observations
- Radiation Detection and Scintillator Technologies
- Nuclear Physics and Applications
- Chalcogenide Semiconductor Thin Films
- Silicon Nanostructures and Photoluminescence
- Force Microscopy Techniques and Applications
- Semiconductor Quantum Structures and Devices
- ZnO doping and properties
- Thin-Film Transistor Technologies
- Space Exploration and Technology
Tohoku University
2020-2024
University of Notre Dame
2020-2024
Joint Institute for Nuclear Astrophysics
2022-2024
RIKEN Center for Computational Science
2018-2022
Kyushu University
1996-2020
The University of Tokyo
2014-2018
National Astronomical Observatory of Japan
2014-2018
Japan Society for the Promotion of Science
2015-2016
Kanazawa Institute of Technology
2016
Campbell Collaboration
2016
Abstract The primordial He abundance Y P is a powerful probe of cosmology. Currently, best determined by observations metal-poor galaxies, while there are only few known local extremely (<0.1 Z ⊙ ) galaxies (EMPGs) having reliable He/H measurements with i λ 10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, values 5 out EMPGs reliably derived Markov chain Monte Carlo algorithm. Adding 3 and 51 moderately...
The dominant site of production $r$-process elements remains unclear despite recent observations a neutron star merger. Observational constraints on the properties sites can be obtained by comparing abundances in different environments. Gaia data releases and large samples from high-resolution optical spectroscopic surveys are enabling us to compare element between stars formed an accreted dwarf galaxy, Gaia-Enceladus, those Milky Way. We aim understand origin Gaia-Enceladus. first construct...
Intermediate-mass black holes (IMBHs) are those between 100 and 10$^5$ solar masses ($M_{\odot}$); their formation process is debated. One possible origin the growth of less massive (BHs) via mergers with stars compact objects within globular clusters (GCs). However, previous simulations have indicated that this only produces IMBHs $<500 M_{\odot}$ because gravitational wave recoil ejects them when they merge other BHs. We perform star-by-star GC formation, finding high-density star in a...
The rapid neutron-capture process (r-process) is a major to synthesize elements heavier than iron, but the astrophysical site(s) of r-process not identified yet. Neutron star mergers (NSMs) are suggested be site from nucleosynthesis studies. Previous chemical evolution studies however require unlikely short merger time NSMs reproduce observed large star-to-star scatters in abundance ratios relative [Eu/Fe], extremely metal-poor stars Milky Way (MW) halo. This problem can solved by...
We construct a sample of 644 carbon-enhanced metal-poor (CEMP) stars with abundance analyses based on moderate- to high-resolution spectroscopic studies. Dynamical parameters for these are estimated, radial velocities, Bayesian parallax-based distance estimates, and proper motions from $Gaia$ EDR3 DR3, supplemented by additional available information where needed. After separating our into the different CEMP morphological groups in Yoon-Beers Diagram absolute carbon vs. metallicity, we used...
Context. The first stars might have been fast rotators. This would important consequences for their radiative, mechanical, and chemical feedback. Aims. We discuss the impact of initial rotation on evolution massive Population III models nitrogen oxygen stellar yields. Methods. explore with masses in range 9 M ⊙ ≤ ini 120 , starting an zero-age main sequence equal to 70% critical one. Results. find that physics considered here, our rapidly rotating do not follow a homogeneous evolution. They...
The $r$-process-enhanced (RPE) stars provide fossil records of the assembly history Milky Way and nucleosynthesis heaviest elements. Observations by $R$-Process Alliance (RPA) others have confirmed that many RPE are associated with chemo-dynamically tagged groups, which likely came from accreted dwarf galaxies (MW). However, we do not know how formed. Here, present result a cosmological zoom-in simulation an MW-like galaxy $r$-process enrichment, performed highest resolution in both time...
Abstract Photometric stellar surveys now cover a large fraction of the sky, probe to fainter magnitudes than large-scale spectroscopic surveys, and are relatively free from target selection biases often associated with such studies. Photometric-metallicity estimates that include narrow/medium-band filters can achieve comparable accuracy precision existing low-resolution as Sloan Digital Sky Survey/SEGUE LAMOST. Here we report on an effort identify likely members Galactic disk system among...
Most stars are formed as star clusters in galaxies, which then disperse into galactic disks. Upcoming exascale supercomputational facilities will enable performing simulations of galaxies and their formation by resolving individual (star-by-star simulations). This substantially advance our understanding cluster formation, assembly histories galaxies. In previous galaxy simulations, a simple stellar population approximation was used. It is, however, difficult to improve the mass resolution...
Recent progress of nucleosynthesis work as well the discovery a kilonova associated with gravitational-wave source GW170817 indicates that neutron star mergers (NSM) can be site r-process. Several studies galactic chemical evolution, however, have pointed out inconsistencies between this idea and observed stellar abundance signatures in Milky Way: (a) presence Eu at low (halo) metallicity (b) descending trend Eu/Fe high (disc) metallicity. In study, we explore evolution Way's halo, disc...
Abstract We present the demography of dynamics and gas mass fraction 33 extremely metal-poor galaxies (EMPGs) with metallicities 0.015–0.195 Z ⊙ low stellar masses 10 4 –10 8 M in local universe. conduct deep optical integral field spectroscopy (IFS) for low-mass EMPGs medium-high resolution ( R = 7500) grism m Subaru FOCAS IFU instrument by EMPRESS 3D survey, investigate H α emission EMPGs. Exploiting high enough galaxies, we derive lines fitting three-dimensional disk models. obtain an...
Abstract Metal-poor stars enriched by a single supernova (mono-enriched stars) are direct proof (and provide valuable probes) of nucleosynthesis. Photometric and spectroscopic observations have shown that metal-poor wide variety chemical compositions; the star’s composition reflects nucleosynthesis process(es) occurred before formation. While identification mono-enriched enables us to study ejecta properties supernova, fraction among remains unknown. Here we identify in dwarf galaxy...
The origin of fluorine is still a debated question. Asymptotic giant branch stars synthesise this element and likely contribute significantly to its synthesis in the present-day Universe. However, it not clear whether other sources contribute, especially early We discuss variations surface abundances coming from our massive star models compare them with available observations. compute contribution single producing $ $F over metallicities covering whole cosmic history ( i.e. zero up...
The abundance of elements synthesized by the rapid neutron-capture process (r-process elements) extremely metal-poor (EMP) stars in Local Group galaxies gives us clues to clarify early evolutionary history Milky Way halo. dwarf would have similarly evolved with building blocks However, how chemo-dynamical evolution affects r-process is not yet clear. In this paper, we perform a series simulations using galaxy models various dynamical times and total mass, which determine star-formation...
One of the computational challenges cluster formation simulations is resolving individual stars and simulating massive clusters with masses more than $10^4 M_{\odot}$ without gravitational softening. Combining direct $N$-body code smoothed-particle hydrodynamics (SPH) code, we have developed a new \textsc{ASURA+BRIDGE}, in which can integrate stellar particles We add feedback model for \HII regions into this thermal momentum given within Str{\"o}mgren radius. perform $N$-body/SPH star...
Abstract Metal mixing plays a critical role in the enrichment of metals galaxies. The abundance elements such as Mg, Fe, and Ba metal-poor stars helps us understand metal However, efficiency galaxies is not yet understood. Here we report series N -body/smoothed particle hydrodynamics simulations dwarf with different efficiencies using turbulence-induced model. We show that apparently occurs from Mg abundances. find scaling factor for diffusion larger than 0.01 necessary to reproduce measured...
Abstract Cylindrical molecular filaments are observed to be the main sites of Sunlike star formation, while massive stars form in dense hubs at junction multiple filaments. The role hub–filament configurations has not been discussed yet relation birth environment solar system and infer origin isotopic ratios short-lived radionuclides (SLR, such as 26 Al) calcium–aluminum-rich inclusions (CAIs) meteorites. In this work, we present simple analytical estimates impact stellar feedback on young...
Abstract Elucidating dark matter density profiles in Galactic dwarf satellites is essential to understanding not only the quintessence of matter, but also evolution themselves. In this work, we present current constraints on densities ultrafaint (UFD) and diffuse galaxies. Applying our constructed nonspherical mass models currently available kinematic data 25 UFDs two satellites, find that whereas most galaxies have huge uncertainties inferred profiles, Eridanus II, Segue I, Willman 1 favor...
ABSTRACT We employ a sample of 135 873 RR Lyrae stars (RRLs) with precise photometric-metallicity and distance estimates from the newly calibrated P–ϕ31–R21–[Fe/H] Gaia G band P–R21–[Fe/H] absolute magnitude–metallicity relations Li et al., combined available proper motions EDR3, 6955 systemic radial velocities DR3 other sources, in order to explore chemistry kinematics halo Milky Way (MW). This is ideally suited for characterization inner- outer-halo populations stellar halo, free bias...
Light trans-iron elements such as Sr serve the key to understanding astrophysical sites of heavy elements. Spectroscopic studies metal-poor stars have revealed large star-to-star scatters in ratios [Sr/Ba], which indicates that there are multiple for production Sr. Here we present enrichment history by a series $N$-body/smoothed particle hydrodynamics simulations dwarf galaxy with stellar mass 3 $\times$ 10$^{6}$ $M_{\odot}$. We show binary neutron star mergers (NSMs) and asymptotic giant...
Abstract Star clusters form via clustering star formation inside molecular clouds. In order to understand the dynamical evolution of in their early phase, which they are still embedded surrounding gas, we need accurate integration individual stellar orbits without gravitational softening systems including both gas and stars, as well modeling stars with a realistic mass function. We develop new tree-direct hybrid smoothed particle hydrodynamics/N-body code, ASURA$+$BRIDGE, integrated using...
Abstract The chemical abundances of Milky Way’s (MW's) satellites reflect their star formation histories (SFHs), yet, due to the difficulty determining ages old stars, SFHs most are poorly measured. Ongoing and upcoming surveys will obtain around 10 times more medium-resolution spectra for stars in than currently available. To correctly extract from large samples abundances, relationship between needs be clarified. Here, we perform a high-resolution cosmological zoom-in simulation MW-like...
Abstract The heaviest iron-peak element Zinc (Zn) has been used as an important tracer of cosmic chemical evolution. Spectroscopic observations the metal-poor stars in Local Group galaxies show increasing trend [Zn/Fe] ratios toward lower metallicity. However, enrichment Zn is not well understood due to poor knowledge astrophysical sites Zn, metal mixing galaxies. Here we possible explanations for observed by taking into account electron-capture supernovae (ECSNe) one sources our...
Thin-film transistors were fabricated from polycrystalline silicon films which produced by glow discharge decomposition of silane at 500 °C on thermal oxidized substrates. The dependence the crystalline and electrical properties was observed for thicknesses about to 4500 Å. As film grew thicker, strongly (110) oriented structures became predominant. conductivity changed 4×10−9 10−6 (Ω cm)−1 activation energy 0.57 0.5 eV. field-effect mobility these thin-film also varied with thickness film.
We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities ($0.016-0.098\ Z_{\odot}$) and stellar masses ($10^{4.7}-10^{7.6} M_{\odot}$). Taking deep medium-high resolution ($R\sim7500$) integral-field spectra 8.2-m Subaru, we resolve the small inner velocity gradients dispersions EMPGs H$\alpha$ emission. Carefully masking out sub-structures originated by inflow and/or outflow, fit 3-dimensional disk models to observed flux, velocity, velocity-dispersion...