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Publications (159)
In single-lined spectroscopic binaries (SB1s) where flux variations due to tidal deformation of the primary star (ellipsoidal variations, EVs) are detected, the binary mass can be determined by combining EVs with the primary's radial velocity (RV) variations from orbital motion and information about the primary's radius. This method has been used f...
Sub-Neptunes with radii of 2–3 R ⊕ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI...
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric composition and c...
Exoplanets in their infancy are ideal targets to probe the formation and evolution history of planetary systems, including the planet migration and atmospheric evolution and dissipation. In this paper, we present spectroscopic observations and analyses of two planetary transits of K2-33b, which is known to be one of the youngest transiting planets...
Context . Previous high-angular-resolution 225 GHz (~1.3 mm) continuum observations of the transitional disk DM Tau have resolved an outer ring at 20–120 au radii that is weakly azimuthally asymmetric.
Aims . We aim to examine dust growth and filtration in the outer ring of DM Tau.
Methods . We performed ~0″.06 (~8.7 au) resolution Karl G. Jansky V...
Individual vibrational band spectroscopy presents an opportunity to examine exoplanet atmospheres in detail, by distinguishing where the vibrational state populations of molecules differ from the current assumption of a Boltzmann distribution. Here, retrieving vibrational bands of OH in exoplanet atmospheres is explored using the hot Jupiter WASP-3...
We report on the determination of the mass of TOI-519 b, a transiting substellar object around a mid-M dwarf. We carried out radial velocity measurements using Subaru/InfraRed Doppler (IRD), revealing that TOI-519 b is a planet with a mass of $0.463^{+0.082}_{-0.088}\, M_{\rm Jup}$. We also found that the host star is metal rich ([Fe/H] = 0.27 ± 0....
Individual vibrational band spectroscopy presents an opportunity to examine exoplanet atmospheres in detail by distinguishing where the vibrational state populations of molecules differ from the current assumption of a Boltzmann distribution. Here, retrieving vibrational bands of OH in exoplanet atmospheres is explored using the hot Jupiter WASP-33...
We report the mass determination of TOI-519 b, a transiting substellar object around a mid-M dwarf. We carried out radial velocity measurements using Subaru / InfraRed Doppler (IRD), revealing that TOI-519 b is a planet with a mass of $0.463^{+0.082}_{-0.088}~M_{\rm Jup}$. We also find that the host star is metal rich ($\rm [Fe/H] = 0.27 \pm 0.09$...
Direct imaging of gas giant exoplanets provides information on their atmospheres and the architectures of planetary systems. However, few planets have been detected in blind surveys with direct imaging. Using astrometry from the Gaia and Hipparcos spacecraft, we identified dynamical evidence for a gas giant planet around the nearby star HIP 99770....
The Subaru telescope is currently performing a strategic program (SSP) using the high-precision near-infrared (NIR) spectrometer IRD to search for exoplanets around nearby mid/late M dwarfs via radial velocity (RV) monitoring. As part of the observing strategy for the exoplanet survey, signatures of massive companions such as RV trends are used to...
We report on the discovery of an Earth-sized transiting planet ( R p = 1.015 ± 0.051 R ⊕ ) in a P = 4.02 day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light-curve data obtained by the K2 mission, and it is here shown to exist in the most recent data from TESS. Combining th...
The Subaru telescope is currently performing a strategic program (SSP) using the high-precision near-infrared (NIR) spectrometer IRD to search for exoplanets around nearby mid/late-M~dwarfs via radial velocity (RV) monitoring. As part of the observing strategy for the exoplanet survey, signatures of massive companions such as RV trends are used to...
In this study, we reported the results of high-resolution (${0{^{\prime \prime}_{.}}14}$) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 225 GHz dust continuum and CO molecular emission lines from the transitional disk around SY Cha. Our high-resolution observations clearly revealed the inner cavity and the central point so...
In this study, we reported the results of high-resolution (0.14 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 225 GHz dust continuum and CO molecular emission lines from the transitional disk around SY Cha. Our high-resolution observations clearly revealed the inner cavity and the central point source for the first...
Kepler showed a paucity of planets with radii of 1.5 – 2 R⊕ around solar mass stars but this radius-gap has not been well studied for low-mass star planets. Energy-driven escape models like photoevaporation and core-powered mass-loss predict opposing transition regimes between rocky and non-rocky planets when compared to models depicting planets fo...
\textit{Kepler} showed a paucity of planets with radii of 1.5 - 2 $\mathrm R_{\oplus}$ around solar mass stars but this radius-gap has not been well studied for low-mass star planets. Energy-driven escape models like photoevaporation and core-powered mass-loss predict opposing transition regimes between rocky and non-rocky planets when compared to...
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), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light curve data by the K2 mission, and is here shown to exist in the most recent data from TESS. Combining the light...
We detect a superjovian extrasolar planet around the dusty A star HIP 99770 using precision astrometry from the Gaia and Hipparcos satellites and direct imaging using the Subaru Coronagraphic Extreme Adaptive Optics Project. HIP 99770 b is the first exoplanet ever discovered jointly through direct imaging and astrometry and the first discovery leve...
We report a search for excess absorption in the 1083.2 nm line of ortho (triplet) helium during transits of TOI-1807b and TOI-2076b, 1.25 and 2.5-R⊕ planets on 0.55- and 10.4-day orbits around nearby ∼200 Myr-old K dwarf stars. We limit the equivalent width of any transit-associated absorption to <4 and <8 mÅ, respectively. We limit the escape of s...
We report a search for excess absorption in the 1083.2 nm line of ortho (triplet) helium during transits of TOI-1807b and TOI-2076b, 1.25 and 2.5R$_{\rm Earth}$ planets on 0.55- and 10.4-day orbits around nearby $\sim$200~Myr-old K dwarf stars. We limit the equivalent width of any transit-associated absorption to $<$4 and $<$8 mA, respectively. We...
We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gai...
We report the near-infrared radial velocity (RV) discovery of a super-Earth planet on a 10.77 d orbit around the M4.5 dwarf Ross 508 (Jmag = 9.1). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of $3.92^{+0.60}_{-0.58}\:\mbox{m}\:{\mbox{s}^{-1}}$, corresponding to a planet with a minimum...
Direct images of protoplanets embedded in disks around infant stars provide the key to understanding the formation of gas giant planets such as Jupiter. Using the Subaru Telescope and the Hubble Space Telescope, we find evidence for a Jovian protoplanet around AB Aurigae orbiting at a wide projected separation (~93 au), probably responsible for mul...
We present the discovery and validation of a temperate sub-Neptune around the nearby mid-M dwarf TIC 470381900 (TOI-1696), with a radius of 3.09 ± 0.11 R ⊕ and an orbital period of 2.5 days, using a combination of Transiting Exoplanets Survey Satellite (TESS) and follow-up observations using ground-based telescopes. Joint analysis of multiband phot...
We report the near-infrared radial-velocity (RV) discovery of a super-Earth planet on a 10.77-day orbit around the M4.5 dwarf Ross 508 ($J_\mathrm{mag}=9.1$). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of $3.92^{+0.60}_{-0.58}$ ${\rm m\,s}^{-1}$, corresponding to a planet with a minim...
We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gai...
Direct images of protoplanets embedded in disks around infant stars provide the key to understanding the formation of gas giant planets like Jupiter. Using the Subaru Telescope and Hubble Space Telescope, we find evidence for a jovian protoplanet around AB Aurigae orbiting at a wide projected separation (93 au), likely responsible for multiple plan...
We present the discovery and validation of a temperate sub-Neptune around the nearby mid-M dwarf TIC 470381900 (TOI-1696), with a radius of $3.09 \pm 0.11 \,R_\oplus$ and an orbital period of $2.5 \,\rm{days}$, using a combination of TESS and follow-up observations using ground-based telescopes. Joint analysis of multi-band photometry from TESS, Mu...
Detailed chemical analyses of M dwarfs are scarce but necessary to constrain the formation environment and internal structure of planets being found around them. We present elemental abundances of 13 M dwarfs (2900 < T eff < 3500 K) observed in the Subaru/IRD planet search project. They are mid- to late-M dwarfs whose abundance of individual elemen...
Silicon and Strontium are key elements to explore the nucleosynthesis and chemical evolution of the Galaxy by measurements of very metal-poor stars. There are, however, only a few useful spectral lines of these elements in the optical range that are measurable for such low-metallicity stars. Here we report on abundances of these two elements determ...
Detailed chemical analyses of M dwarfs are scarce but necessary to constrain the formation environment and internal structure of planets being found around them. We present elemental abundances of 13 M dwarfs (2900 < Teff < 3500 K) observed in the Subaru/IRD planet search project. They are mid-to-late M dwarfs whose abundance of individual elements...
We report the non-detection of excess absorption in the 1083.2 nm line of neutral triplet helium during a transit of K2-136c, a 2.9 R ⊕ planet on a 17.3 days orbit around a K-type dwarf in the 650 Myr old Hyades cluster. We limit the equivalent width of any transit-associated absorption in the He i line to <25 mÅ at 99% confidence.
We present observations of two bright M dwarfs (TOI-1634 and TOI-1685: J = 9.5–9.6) hosting ultra-short-period (USP) planets identified by the TESS mission. The two stars are similar in temperature, mass, and radius (T_(eff) ≈ 3500 K, M⋆ ≈ 0.45–0.46 M_⊙, and R⋆ ≈ 0.45–0.46 R_⊙), and the planets are both super-Earth size (1.25 R_⊕ < R_p < 2.0 R_⊕)....
We obtained high-resolution spectra of the ultracool M-dwarf TRAPPIST-1 during the transit of its planet "b"using two high-dispersion near-infrared spectrographs, the Infrared Doppler (IRD) instrument on the Subaru 8.2m telescope, and the Habitable Zone Planet Finder (HPF) instrument on the 10 m Hobby-Eberly Telescope. These spectroscopic observati...
SCExAO at the Subaru telescope is a visible and near-infrared high-contrast imaging instrument employing extreme adaptive optics and coronagraphy. The instrument feeds the near-infrared light (JHK) to the integral-field spectrograph CHARIS. The spectropolarimetric capability of CHARIS is enabled by a Wollaston prism and is unique among high-contras...
SCExAO at the Subaru telescope is a visible and near-infrared high-contrast imaging instrument employing extreme adaptive optics and coronagraphy. The instrument feeds the near-infrared light (JHK) to the integralfield spectrograph CHARIS. The spectropolarimetric capability of CHARIS is enabled by a Wollaston prism and is unique among high-contrast...
We obtained high-resolution spectra of the ultra-cool M-dwarf TRAPPIST-1 during the transit of its planet `b' using two high dispersion near-infrared spectrographs, IRD instrument on the Subaru 8.2m telescope and HPF instrument on the 10m Hobby-Eberly Telescope. These spectroscopic observations are complemented by a photometric transit observation...
We present observations of two bright M dwarfs (TOI-1634 and TOI-1685: $J=9.5-9.6$) hosting ultra-short period (USP) planet candidates, identified by the TESS mission. The two stars are similar in temperature, mass, and radius, and the planet candidates are both super-Earth-sized ($1.25\,R_\oplus<R_p<2.0\,R_\oplus$). For both systems, light curves...
We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the day-side of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2-m Subaru telescope. The telluric and stellar lines...
We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the dayside of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2 m Subaru telescope. The telluric and stellar lines...
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) serves both a science instrument in operation, and a prototyping platform for integrating and validating advanced wavefront control techniques. It provides a modular hardware and software environment optimized for flexible prototyping, reducing the time from concept formulation to on-sky ope...
Polarization Differential Imaging (PDI) is one of the most productive modes of current high-contrast imagers. Dozens of new protoplanetary, transition and debris disks were imaged recently for the first time, helping us understand the processes of planet formation, and giving clues on the mass of potential planets inside these disks, even if they c...
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a high-contrast imaging system installed at the 8-m Subaru Telescope on Maunakea, Hawaii. Due to its unique evolving design, SCExAO is both an instrument open for use by the international scientific community, and a testbed validating new technologies, which are critical to fut...
SCExAO at the Subaru telescope is a visible and near-infrared high-contrast imaging instrument employing extreme adaptive optics and coronagraphy. The instrument feeds the near-infrared light (JHK) to the integral field spectrograph CHARIS. Recently, a Wollaston prism was added to CHARIS’ optical path, giving CHARIS a spectropolarimetric capability...
SCExAO at the Subaru telescope is a visible and near-infrared high-contrast imaging instrument employing extreme adaptive optics and coronagraphy. The instrument feeds the near-infrared light (JHK) to the integral field spectrograph CHARIS. Recently, a Wollaston prism was added to CHARIS' optical path, giving CHARIS a spectropolarimetric capability...
Precision radial velocity (RV) measurements in the near-infrared are a powerful tool to detect and characterize exoplanets around low-mass stars or young stars with higher magnetic activity. However, the presence of strong telluric absorption lines and emission lines in the near-infrared that significantly vary in time can prevent extraction of RV...
We present current status of Hα high-contrast imaging observations with Subaru/SCExAO+VAMPIRES. Our adaptive optics correction at optical wavelengths in combination with (double) spectral differential imaging (SDI) and angular differential imaging (ADI) was capable of resolving a ring feature around omi Cet and detect the Hα counterpart of jet arou...
We present current status of H$\alpha$ high-contrast imaging observations with Subaru/SCExAO+VAMPIRES. Our adaptive optics correction at optical wavelengths in combination with (double) spectral differential imaging (SDI) and angular differential imaging (ADI) was capable of resolving a ring feature around omi Cet and detect the H$\alpha$ counterpa...
We obtained spectra of the pre-main-sequence star AU Microscopii during a transit of its Neptune-sized planet to investigate its orbit and atmosphere. We used the high-dispersion near-infrared spectrograph InfraRed Doppler (IRD) on the Subaru telescope to detect the Doppler “shadow” from the planet and constrain the projected stellar obliquity. Mod...
We present Subaru/SCExAO+CHARIS broadband ($JHK$-band) integral field spectroscopy of HD 34700 A. CHARIS data recover HD 34700 A's disk ring and confirm multiple spirals discovered in Monnier et al. (2019). We set limits on substellar companions of $\sim12\ M_{\rm Jup}$ at $0\farcs3$ (in the ring gap) and $\sim5\ M_{\rm Jup}$ at $0\farcs75$ (outsid...
We present Subaru/SCExAO+CHARIS broadband (JHK-band) integral field spectroscopy of HD 34700 A. CHARIS data recover HD 34700 A's disk ring and confirm multiple spirals discovered in Monnier et al. (2019). We set limits on substellar companions of ∼12 M_(Jup) at 0.”3 (in the ring gap) and ∼5 M_(Jup) at 0.”75 (outside the ring). The data reveal darke...
Precision radial velocity (RV) measurements in the near infrared are a powerful tool to detect and characterize exoplanets around low-mass stars or young stars with higher magnetic activity. However, the presence of strong telluric absorption lines and emission lines in the near infrared that significantly vary in time can prevent extraction of RV...
We obtained spectra of the pre-main sequence star AU Microscopii during a transit of its Neptune-sized planet to investigate its orbit and atmosphere. We used the high-dispersion near-infrared spectrograph IRD on the Subaru telescope to detect the Doppler "shadow" from the planet and constrain the projected stellar obliquity; we find that the stell...
We present L′-band Keck/NIRC2 imaging and H-band Subaru/AO188+HiCIAO polarimetric observations of CQ Tau disk with a new spiral arm. Apart from the spiral feature our observations could not detect any companion candidates. We traced the spiral feature from the r²-scaled HiCIAO polarimetric intensity image and the fitted result is used for forward m...
In an effort to measure the Rossiter–McLaughlin effect for the TRAPPIST-1 system, we performed high-resolution spectroscopy during transits of planets e, f, and b. The spectra were obtained with the InfraRed Doppler spectrograph on the Subaru 8.2 m telescope, and were supplemented with simultaneous photometry obtained with a 1 m telescope of the La...
In an effort to measure the Rossiter-McLaughlin effect for the TRAPPIST-1 system, we performed high-resolution spectroscopy during transits of planets e, f, and b. The spectra were obtained with the InfraRed Doppler spectrograph on the Subaru 8.2-m telescope, and were supplemented with simultaneous photometry obtained with a 1-m telescope of the La...
We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2–1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to ~240...
We present κ Andromeda b's photometry and astrometry taken with Subaru/SCExAO+HiCIAO and Keck/NIRC2, combined with recently published SCExAO/CHARIS low-resolution spectroscopy and published thermal infrared photometry to further constrain the companion's atmospheric properties and orbit. The Y/Y−K colors of κ And b are redder than field dwarfs, con...
The SR 24 multistar system hosts both circumprimary and circumsecondary disks, which are strongly misaligned with each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.″1 resol...
We analyzed the young (2.8-Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and sub-millimeter CO (J=2-1) line emission data from ALMA. Both the near-infrared and sub-millimeter observations reveal several clear structures extending to $\sim$240 AU from the stars. Based on these observat...
The SR24 multi-star system hosts both circumprimary and circumsecondary disks, which are strongly misaligned from each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.''1 reso...
We present $\kappa$ Andromeda b's photometry and astrometry taken with Subaru/SCExAO+HiCIAO and Keck/NIRC2, combined with recently published SCExAO/CHARIS low-resolution spectroscopy and published thermal infrared photometry to further constrain the companion's atmospheric properties and orbit. $\kappa$ And b's Y/Y-K colors are redder than field dw...
We present $L^\prime$-band Keck/NIRC2 imaging and $H$-band Subaru/AO188+HiCIAO polarimetric observations of CQ Tau disk with a new spiral arm. Apart from the spiral feature our observations could not detect any companion candidates. We traced the spiral feature from the $r^2$-scaled HiCIAO polarimetric intensity image and the fitted result is used...
We present an analysis of instrument performance using new observations taken with the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) instrument and the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system. In a correlation analysis of our data sets (which use the broadband mode covering the J band through the K band in...
Two studies utilizing sparse aperture-masking (SAM) interferometry and Hα differential imaging have reported multiple Jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly formed planets ("protoplanets"). We present new near-infrared direct imaging/spectroscopy from the Subaru...
We present an analysis of instrument performance using new observations taken with the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) instrument and the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system. In a correlation analysis of our datasets (which use the broadband mode covering J through K band in a single spec...
Two studies utilizing sparse aperture masking (SAM) interferometry and $H_{\rm \alpha}$ differential imaging have reported multiple jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly-formed planets ("protoplanets"). We present new near-infrared direct imaging/spectroscopy f...
We present H-band polarized scattered light imagery and JHK high-contrast spectroscopy of the protoplanetary disk around HD 163296 observed with the High-Contrast Coronographic Imager for Adaptive Optics (HiCIAO) and Subaru Coronagraphic Extreme Adaptive Optics (SCExAO)/Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) instruments...
We report 0.″14 resolution observations of the dust continuum at band 7, and the CO(3-2) and HCO ⁺ (4-3) line emissions toward the transitional disk around Sz 91 with the Atacama Large Millimeter/submillimeter Array. The dust disk appears to be an axisymmetric ring, peaking at a radius of ∼95 au from a Gaussian fit. The Gaussian fit widths of the d...
We report $0.14"$ resolution observations of the dust continuum at band 7, and the CO(3--2) and HCO$^{+}$(4--3) line emissions toward the transitional disk around Sz 91 with Atacama Large Millimeter/submillimeter Array (ALMA). The dust disk appears to be an axisymmetric ring, peaking a radius of $\sim$95~au from a Gaussian fit. The Gaussian fit wid...
We present SCExAO/CHARIS 1.1--2.4 micron integral field direct spectroscopy of the young HIP 79124 triple system. HIP 79124 is a member of the Scorpius-Centaurus association, consisting of an A0V primary with two low-mass companions at a projected separation of <1 arcsecond. Thanks to the high quality wavefront corrections provided by SCExAO, both...