A5087752717- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Spectroscopy and Laser Applications
- Atmospheric Ozone and Climate
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Atmospheric and Environmental Gas Dynamics
- Planetary Science and Exploration
- Solar and Space Plasma Dynamics
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- Hydrocarbon exploration and reservoir analysis
- Atmospheric aerosols and clouds
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- Particle Detector Development and Performance
- Space Exploration and Technology
- Gamma-ray bursts and supernovae
National Astronomical Observatory of Japan
2019-2021
The University of Tokyo
2011-2016
Japan Aerospace Exploration Agency
2012-2014
Institute of Space and Astronautical Science
2011-2014
Nagoya University
2013-2014
Goddard Space Flight Center
2014
Planetary Science Institute
2009
We present new $L^\prime$ (3.8 $μm$) and Br-$α$ (4.05 data reprocessed archival for the young, planet-hosting star HR 8799 obtained with Keck/NIRC2, VLT/NaCo Subaru/IRCS. detect all four planets in each dataset at a moderate to high signal-to-noise (SNR $\gtrsim$ 6-15). fail identify fifth planet, "HR f", $r$ $
We investigate variations in the strengths of three molecular bands, CH4 at 3.3 μm, CO 4.6 and CO2 4.2 16 brown dwarf spectra obtained by AKARI. Spectral features are examined along sequence source classes from L1 to T8. find that μm band is present dwarfs later than L5, appears all spectral types. The absorption detected late-L T-type dwarfs. To better understand atmospheres, we analyze observed using Unified Cloudy Model. physical parameters AKARI sample, i.e., atmospheric effective...
Most exoplanets detected by direct imaging thus far have been characterized relatively hot (≳1000 K) and cloudy atmospheres. A surprising feature in some of their atmospheres has a distinct lack methane, possibly implying non-equilibrium chemistry. Recently, we reported the discovery planetary companion to Sun-like star GJ 504 using Subaru/HiCIAO within Strategic Exploration Exoplanets Disks with Subaru survey. The planet is substantially colder (<600 than previously imaged planets,...
We propose that the 2.7-μm H2O, 3.3-μm CH4 and 4.6-μm CO absorption bands can be good tracers of chromospheric activity in brown dwarfs. In our previous study, we found there are difficulties explaining entire spectra between 1.0 5.0 μm with unified cloudy model (UCM), a dwarf atmosphere model. Based on simple radiative equilibrium, temperature usually decreases monotonically height. However, if has chromosphere, as inferred by some observations, upper is higher. construct takes into account...
Brown dwarf spectra contain a wealth of information about their molecular abundances, temperature structure, and gravity. We present new data driven retrieval approach, previously used in planetary atmosphere studies, to extract the abundances structure from brown spectra. The feasibility approach is first demonstrated on synthetic spectrum. Given typical spectral resolutions, wavelength coverage, noise properties precisions tens percent can be obtained for 10s-100s K profile. technique then...
The detection of the CO_2 absorption band at 4.2 {\mu}m in brown dwarf spectra by AKARI has made it possible to discuss molecular abundance atmospheres. In our previous studies, we found an excess three spectra, and suggested that these deviations were caused high C O elemental abundances their To validate this hypothesis construct a set models atmospheres with various patterns, investigate variations composition, thermal structure effects near-infrared between 1.0 5.0 {\mu}m. some late-L T...
Recent observations with the infrared astronomical satellite AKARI have shown that CO2 bands at 4.2 μm in three brown dwarfs are much stronger than expected from unified cloudy model (UCM) based on recent solar C & O abundances. This result has been a puzzle, but we now find it is simply due to effect of We show these strong can be explained UCMs classical abundances (log AC and log AO), which about 0.2 dex larger compared values. Since other could interpreted fairly well abundances, require...
We derive the radii of 16 brown dwarfs observed by AKARI using their parallaxes and ratios to model fluxes. find that dwarf radius ranges between 0.64–1.13 RJ with an average 0.83 RJ. a trend in relation Teff; is at minimum Teff ∼ 1600 K, which corresponds spectral types mid- late-L. The result interpreted combination radius–mass radius–age relations are theoretically expected for older than 108 yr.
We describe the expected scientific capabilities of CHARIS, a high-contrast integral-field spectrograph (IFS) currently under construction for Subaru telescope. CHARIS is part new generation instruments, enabled by extreme adaptive optics (AO) systems (including SCExAO at Subaru), that promise greatly improved contrasts small angular separation thanks to their ability use spectral information distinguish planets from quasistatic speckles in stellar point-spread function (PSF). similar...
Initial C/O ratios of circumstellar disks have been obtained in solar-type stars by differential photospheric abundance analysis with respect to the Sun. We present M dwarfs absolute derived from CO and H2O spectra K-band. compare distributions using Kolmogorov-Smirnov test. The distribution is consistent low frequency high stars.
We have analyzed 1.74 μ m nightside emission of Venus recorded using Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) onboard European Space Agency's (ESA) Express (Orbit 344, 30–31 March 2007). Attention was paid to how infrared radiance, intense at the center “window”, dims an off‐center wavelength (1.71 m). Cloud models are required simultaneously reproduce intensity ratio intensities ( I 1.71 / ). Our best‐fit model (5 km vertical resolution) has located main cloud opacity in...
Using the data release 1 of Hyper Suprime-Cam Subaru Strategic Program covering about 130 square degrees at high galactic latitudes, we have obtained L dwarf counts based on selection criteria colors, limiting magnitude and PSF morphology using $i$, $z$, $y$ bands. 3665 dwarfs brighter than $z=24$ been detected by these criteria. The surface number differentially in $z$ are compared with predictions an exponential disk model to estimate thin-disk scale height vicinity Sun. In model, first...
We present the latest results from Mission Program NIRLT, NIR spectroscopic observations of brown dwarfs using IRC on board AKARI. The near-infrared spectra in wavelength range between 2.5 and <TEX>$5.0{\mu}m$</TEX> is especially important to study dwarf atmospheres because presence non-blended bands major molecules, including <TEX>$CH_4$</TEX> at <TEX>$3.3{\mu}m$</TEX>, <TEX>$CO_2$</TEX> <TEX>$4.2{\mu}m$</TEX>, CO <TEX>$4.6{\mu}m$</TEX> <TEX>$H_2O$</TEX> around <TEX>$2.7{\mu}m$</TEX>. Our...
We present the latest results from Mission Program NIRLT (PI: I.Yamamura), near-infrared spectroscopy of brown dwarfs using AKARI/IRC grism mode with spectral resolution ~ 120. The spectra in wavelength range between 2.5 and <TEX>$5.0{\mu}m$</TEX> are especially important to study dwarf atmospheres because presence major molecular bands, including <TEX>$CH_4$</TEX> at <TEX>$3.3{\mu}m$</TEX>, <TEX>$CO_2$</TEX> <TEX>$4.2{\mu}m$</TEX>, CO <TEX>$4.6{\mu}m$</TEX>, <TEX>$H_2O$</TEX> around...
In this study, we demonstrate the dependence of atmospheric dust size on near-infrared spectra ten L dwarfs, and constrain sizes grains in each dwarf atmosphere. previous studies, by comparing observed modeled spectra, it was suggested that deviations their spectral shapes from theoretical prediction are general characteristics. Here, focus brown atmospheres to understand spectra. We confirm changing changes temperature-pressure structure atmosphere, with shape spectrum accordingly. At...