Takuya Takarada
A5025413929- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Adaptive optics and wavefront sensing
- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Geophysics and Gravity Measurements
- Inertial Sensor and Navigation
- Spacecraft Design and Technology
- Seismic Waves and Analysis
- Calibration and Measurement Techniques
- Advanced Fiber Laser Technologies
- Atmospheric Ozone and Climate
- Optical Systems and Laser Technology
- earthquake and tectonic studies
- Planetary Science and Exploration
- Advanced Fiber Optic Sensors
- High-pressure geophysics and materials
- Spectroscopy and Laser Applications
- History and Developments in Astronomy
- Spacecraft and Cryogenic Technologies
Astrobiology Center
2020-2024
National Institutes of Natural Sciences
2021-2024
Saitama University
2020-2024
National Astronomical Observatory of Japan
2020-2024
Tokyo Institute of Technology
2015-2018
Abstract We present the direct-imaging discovery of a substellar companion in orbit around Sun-like star member Hyades open cluster. So far, no other companions have been unambiguously confirmed via direct imaging main-sequence stars Hyades. The HIP 21152 is an accelerating as identified by astrometry from Gaia and Hipparcos satellites. detected companion, B, multiple epochs using high-contrast SCExAO/CHARIS Keck/NIRC2. also obtained stellar radial-velocity data Okayama 188 cm telescope....
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres terrestrial via follow-up spectroscopic observations. However, number such receiving low insolation is still small, limiting our ability understand diversity atmospheric composition and climates temperate planets. We report discovery an planet (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with orbital period ($P_{\rm{orb}}$) 12.76 days. The planet, 12b, was initially...
We present results of radial-velocity follow-up observations for the two Kepler evolved stars Kepler-91 (KOI-2133) and KOI-1894, which had been announced as candidates to host transiting giant planets, with Subaru 8.2m telescope High Dispersion Spectrograph (HDS). By global modeling high-precision data taken Subaru/HDS photometric ones by mission taking account orbital brightness modulations (ellipsoidal variations, reflected/emitted light, etc.) stars, we independently confirmed that hosts...
Abstract We report the near-infrared radial velocity (RV) discovery of a super-Earth planet on 10.77 d orbit around M4.5 dwarf Ross 508 (Jmag = 9.1). Using precision RVs from Subaru Telescope IRD (InfraRed Doppler) instrument, we derive semi-amplitude $3.92^{+0.60}_{-0.58}\:\mbox{m}\:{\mbox{s}^{-1}}$, corresponding to with minimum mass $m \sin i 4.00^{+0.53}_{-0.55}\, M_{\oplus }$. find no evidence significant signals at detected period in spectroscopic stellar activity indicators or MEarth...
Abstract In this study, we revisit 32 planetary systems around evolved stars observed within the framework of Okayama Planet Search Program (OPSP) and its collaborative East Asian Network to search for additional companions investigate properties giant planets in multiple-planet systems. With our latest radial velocities obtained from Astrophysical Observatory, confirm an planet wide orbit 75 Cet system ($P_{\rm {c}} = 2051.62_{-40.47}^{+45.98}\ \rm {d}$, $M_{\rm {c}}\sin...
We report the discovery of two exoplanets around M dwarfs GJ 724 and 3988 using radial velocity (RV) method. obtained a total 153 3.5 m Calar Alto/CARMENES spectra for both targets measured their RVs activity indicators. also added archival ESO/HARPS data infrared RV measurements from Subaru/IRD 3988. searched periodic stable signals to subsequently construct Keplerian models, considering different numbers planets, we selected best models based on Bayesian evidence. Gaussian process (GP)...
We report the detection of planets around two evolved giant stars from radial velocity measurements at Okayama Astrophysical observatory. 24 Boo (G3IV) has a mass $0.99\,M_{\odot}$, radius $10.64\,R_{\odot}$, and metallicity ${\rm [Fe/H]}=-0.77$. The star hosts one planet with minimum $0.91\,M_{\rm Jup}$ an orbital period $30.35{\rm d}$. shortest periods among those ever found by radial-veloocity methods. stellar velocities show additional periodicity $150{\rm d}$, which are probably...
Abstract The Laser Interferometer Gravitational-wave Observatory Scientific Collaboration and Virgo (LVC) sent out 56 gravitational-wave (GW) notices during the third observing run (O3). Japanese for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical near-infrared observations to identify observe an electromagnetic (EM) counterpart. We constructed a web-based system that enabled us obtain share information on candidate host galaxies counterpart, status of our...
We report on the discovery of an Earth-sized transiting planet ($R_p=1.015\pm0.051\,R_\oplus$) in a $P=4.02$ day orbit around K2-415 (EPIC 211414619), M5V star at 22 pc. The candidate was first identified by analyzing light curve data K2 mission, and is here shown to exist most recent from TESS. Combining curves with secured our follow-up observations including high-resolution imaging near infrared spectroscopy IRD, we rule out false positive scenarios, finding low probability $2\times...
Abstract We present the discoveries of two giant plants orbiting red-giant-branch star HD 112570 and red-clump 154391, based on radial-velocity (RV) measurements from Xinglong station Okayama Astrophysical Observatory. Spectroscopic asteroseismic analyses suggest that has a mass 1.15 ± 0.12 M ☉ , radius 9.85 0.23 R metallicity [Fe/H] −0.46 0.1, <?CDATA $\mathrm{log}\,g$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mspace...
To understand the evolution of global accretion disk structure in ``rebrightening'' phase MAXI J1820$+$070, we perform a comprehensive analysis its near infrared/optical/UV to X-ray spectral energy distribution (SED) utilizing data obtained by OISTER, Las Cumbres Observatory (LCO), Swift, NICER, and NuSTAR 2019. Optical spectra observed with Seimei telescope 2019 2020 are also analyzed. On basis optical light curves their flux ratios, divide whole into 3 periods, Periods I (flux rise), II...
Abstract We report on a radial-velocity search for short-period planets in the Pleiades open cluster. observed 30 member stars at Okayama Astrophysical Observatory with High Dispersion Echelle Spectrograph. To evaluate and mitigate effects of stellar activity (RV) measurements, we computed four indicators (full width half maximum, Vspan, Wspan, SHα). Among our sample, no planet candidates were detected. Stellar intrinsic RV jitter was estimated to be 52 m s−1, 128 173 s−1 $v$ sin i 10 km 15...
We report the detection of radial velocity variations in nine evolved G- and K-type giant stars. The observations were conducted at Okayama Astrophysical Observatory. Planets or planet candidates can best explain these regular variations. However, a coincidence near 280-day variability among five them prevents us from fully ruling out stellar origins for some variations, since all stars behave similarly properties. In hypotheses to RV planets (including one candidate) may survive close...
We report the results of quasi-simultaneous multiwavelength (near-infrared, optical, UV, and X-ray) observations Galactic X-ray black hole binary MAXI J1820+070 performed in 2019 May 10-13, $\sim 60$ days after onset first rebrightening phase. It showed a much larger optical-to-X-ray luminosity ratio ($\sim 8$) than initial outburst epoch. The primary components spectral energy distribution (SED) can be best interpreted by radiatively inefficient accretion flow (RIAF) spectrum showing peak...
Brown dwarfs provide a unique opportunity to study atmospheres and their physical chemical processes with high precision, especially in temperature ranges relevant exoplanets. In this study, we performed high-resolution ($R \sim 70,000$) spectroscopy using Subaru/IRD of Gl 229 B, the first discovered T-type (T7.0p) brown dwarf, which orbits an M1V host star at separation 33 au. We conducted atmospheric retrieval on reduced $H$-band spectrum model compatible automatic differentiation GPU,...
Abstract We report the detection of a giant planet orbiting G-type star HD 167768 from radial velocity measurements using High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory (OAO). has mass $1.08_{-0.12}^{+0.14}\, M_{\odot }$, radius $9.70_{-0.25}^{+0.25}\, R_{\odot metallicity $[\mbox{Fe}/\mbox{H}]=-0.67_{-0.08}^{+0.09}$, and surface gravity $\log g = 2.50_{-0.06}^{+0.06}$. The is warm Jupiter, having period $20.6532_{-0.0032}^{+0.0032}\:\mbox{d}$, minimum...
Abstract We report the discovery of a triple-giant-planet system around an evolved star HD 184010 (HR 7421, HIP 96016). This is based on observations from Okayama Planet Search Program, precise radial velocity survey, undertaken at Astrophysical Observatory between 2004 April and 2021 June. The K0 type located beginning red giant branch. It has mass $1.35_{-0.21}^{+0.19}\, M_{\odot }$, radius $4.86_{-0.49}^{+0.55} R_{\odot surface gravity log g $3.18_{-0.07}^{+0.08}$. planetary composed...
We report on the discovery of an Earth-sized transiting planet ($R_p=1.015\pm0.051\,R_\oplus$) in a $P=4.02$ day orbit around K2-415 (EPIC 211414619), M5V star at 22 pc. The candidate was first identified by analyzing light curve data K2 mission, and is here shown to exist most recent from TESS. Combining curves with secured our follow-up observations including high-resolution imaging near infrared spectroscopy IRD, we rule out false positive scenarios, finding low probability $2\times...
In this study, we revisit 32 planetary systems around evolved stars observed within the framework of Okayama Planet Search Program and its collaborative EAPS-Net to search for additional companions investigate properties giant planets in multiple-planet systems. With our latest radial velocities obtained from Astrophysical Observatory (OAO), confirm an planet wide orbit 75 Cet system ($P_{\rm{c}} = 2051.62_{-40.47}^{+45.98}\ \rm{d}$, $M_{\rm{c}}\sin i=0.912_{-0.090}^{+0.088}\ M_{\rm{J}}$,...