arXiv subjects

Tomoyuki Kudo

Publications and source records attributed to Tomoyuki Kudo.

At least 19 recordsLinked to original sources

arXiv2026

Near-infrared spectra of chemically peculiar stars and applications to kilonova spectra

Kilonova spectra provide information on rapid neutron-capture nucleosynthesis in neutron star mergers. However, it remains challenging to identify individual elements in kilonova spectra, primarily due to incomplete atomic data for heavy elements at near-infrared wavelengths. Recent work demonstrated that spectra of chemically peculiar stars offer excellent laboratory for studying kilonova spectra. In this paper, to expand our understanding of strong transitions of heavy elements at near-infrared wavelengths, we present high-resolution near-infrared spectra of 14 chemically peculiar stars covering a range of effective temperatures, surface gravities, and abundance patterns, obtained with Subaru/IRD. The Sr II, Ce III, and Gd III lines, previously suggested to be among the strongest transitions, are detected in the spectra of most of our targets, confirming their intrinsic importance. In addition, Eu II and Nd III lines are detected in several stars. By comparing observed equivalent widths and abundance ratios, we show that under a highly heavy-element-enriched abundance pattern, Eu II and Nd III lines may contribute to kilonova spectral features comparably to Sr II. Importantly, we find no unidentified lines systematically stronger than these transitions despite the larger stellar sample. These results further support the primary importance of the Sr II and Ce III transitions and provide new insights into the potential contribution of Eu II and Nd III.

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arXiv2026

A Search for helium in the atmospheres of three sub-Neptunes and a super-Earth around M-dwarfs

Thousands of sub-Neptunes have been discovered mainly through space-based surveys such as Kepler and TESS. Their bulk compositions and internal structures are thought to reflect their formation and evolutionary pathways, and atmospheric observations provide constraints on these processes. The near-infrared helium triplet is a potential tracer of extended, escaping H/He atmospheres. Recent models that include geometric effects suggest that planets orbiting nearby late M dwarfs may offer favorable conditions for detecting this signal. Nevertheless, helium has been reported for only three planets around M dwarfs to date. We conducted high-resolution transmission spectroscopy of three sub-Neptunes (TOI-2136b, TOI-654b, and LP 791-18c) and a super-Earth (TOI-1634b) orbiting M dwarfs with the InfraRed Doppler (IRD) spectrograph on the Subaru Telescope. We find no statistically significant helium absorption in any target; accordingly, we derive 95% confidence upper limits on the helium line depth of 1.36%, 0.60%, 2.07%, and 3.00%, and on the equivalent width of 7.3, 2.1, 7.4, and 9.1 mÅ, for TOI-2136b, TOI-1634b, TOI-654b, and LP 791-18c, respectively. We further explored constraints on the upper-atmospheric temperature and mass-loss rate by comparing these results with isothermal Parker-wind models. While we have compared with self-consistent ATES models of primordial H/He atmospheres spanning a range of assumed X-ray luminosities, changes in the assumed XUV flux do not appear to account for the non-detections. The results suggest that these planets have metal-enriched H/He primary atmospheres or non-primordial atmospheres, such as water-rich envelopes. Future observations of other absorption lines, such as Lyman-$α$, H-$α$, and H$_2$O, may provide further constraints on these atmospheres.

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arXiv2026

Updating the SCExAO/CHARIS polarimetric calibration following the Nasmyth beam-switcher upgrade

Subaru/SCExAO/CHARIS enables near-infrared integral field spectropolarimetry. Quantitative polarimetry is useful for a variety of science cases, particularly measurements related to dust grain properties in circumstellar disks. This capability requires correcting for polarization effects from the optical path via a Mueller matrix model. We present an updated model accounting for the recently installed SCExAO near-infrared wavefront sensor YJH50 dichroic beamsplitter and the major Subaru Nasmyth beam-switcher upgrade. Using internal light source measurements from before and after the beam switcher installation, we find an elliptical retarder model for the image derotator improves polarimetric accuracy over the previous linear retarder model. We additionally find the YJH50 dichroic produces faint polarization effects that we cannot characterize with our Mueller matrix modeling capabilities, and that the Nasmyth beam-switcher has minimal polarization effects other than inducing a sign flip in Q and V polarized light. Using unpolarized standard star calibration measurements, we fit the diattenuation of Subaru's tertiary mirror as a function of wavelength and find that the diattenuation has increased since the previous CHARIS calibration. We calculate that the polarimetric accuracy of the model in the degree of linear polarization ranges from 0.02% to 0.12% for a 1% polarized target. This model update will soon be incorporated into CHARIS's data processing pipeline, and should be used for any polarimetric data taken after the Nasmyth beam-switcher update in October 2025. Additionally, we provide the code for this calibration as part of an open-source Python package for polarimetric calibration called pyPolCal, enabling straightforward re-calibration of the system after any future changes, e.g. the recent recoating of M3.

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arXiv2026

Revealing α-Element's Past with Subaru/IRD: Oxygen Abundance of 35 Very Metal-Poor Stars from Near-IR OH lines

Oxygen abundances in very and extremely metal-poor (V/EMP) stars provide critical constraints on early massive stars' nucleosynthesis. An Oxygen abundance analysis is presented for 35 V/EMP stars (-4.0<[Fe/H]< -1.5) using near-infrared H-band OH vibro-rotational lines from high-resolution Subaru/IRD spectra. To examine the reliability of these NIR OH lines, the results are compared with the abundances obtained from the 3D/NLTE-insensitive forbidden [OI] 6300Å line using archival high-resolution optical spectra. After homogeneously rederiving stellar parameters and 1D/NLTE Fe abundances using Gaia photo-astrometry and literature optical Fe equivalent width data, oxygen abundance from OH and [OI] lines is determined through 1D/LTE spectral synthesis. A sensitivity analysis confirms that near-IR OH lines are highly sensitive to the adopted temperature compared to the forbidden line. A temperature-dependent discrepancy between the tracers is identified: in cool red giants (Teff <4600 K), OH-based abundances are systematically lower than [OI]-based abundance by 0.05 to 0.25 dex, while warmer red giants show higher OH-based abundances as expected from 3D effects. Despite this systematic offset, the numerous measurable NIR OH lines yield significantly smaller random abundance errors than that of the single, weak [OI] line. Leveraging this statistical precision, an empirical calibration as a function of Teff, log g, [Fe/H], and [C/Fe] is derived to align the 1D/LTE OH abundances onto the [OI] scale. Applying this correction substantially reduces the scatter and temperature dependence in the [O/Fe] versus [Fe/H] plane and flattens the trend, bringing the results into fairly good agreement with Galactic chemical evolution models.

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arXiv2026

The mass of TOI-1883 b: A low density super-Neptune in the ridge regime transiting an early-M dwarf

Recent large-scale transit surveys conducted by space telescopes such as Kepler and TESS have revealed a vast number of exoplanets, uncovering the diversity of their population. One of the remarkable findings is the presence of a deficiency region in the period-radius distribution of short-period (< 10 days) Neptune-sized planets (4-8 Earth radii). This region is classified into the Neptune desert (< 3.2 days), the ridge (3.2-5.7 days), and the savanna (> 5.7 days) based on orbital period, each likely reflecting distinct evolutionary pathways. In this study, we used the InfraRed Doppler (IRD) instrument on the Subaru Telescope to determine the mass of the super-Neptune TOI-1883 b, which resides in the ridge region (P ~ 4.51 days) orbiting an M dwarf. We measured a planetary mass of Mp = 13.7 +6.8/-6.5 Earth masses and a mean density of 0.4 +0.3/-0.2 g cm^-3, with 3-sigma upper limits of 34.1 Earth masses, and 5-sigma upper limits of 47.7 Earth masses. These results suggest that TOI-1883 b is likely a low density super-Neptune. We also find that the boundary of the Neptune desert defined by planets orbiting FGK-type stars exhibits a similar distribution for planets around M-type stars. According to the population-based argument of Bourrier et al. (2025), this suggests that TOI-1883 b may have undergone disk-driven migration to reach its current orbit and experienced early atmospheric photoevaporation driven by strong stellar XUV irradiation. The derived planetary mass is comparable to or exceeds the conventional critical core mass. We suggest that the high metallicity of the host star ([Fe/H] = 0.32 +/- 0.18) may have suppressed the onset of runaway gas accretion. Furthermore, TOI-1883 b has a high Transmission Spectroscopy Metric (TSM > 140), making it an excellent target for future atmospheric characterization via transmission spectroscopy.

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arXiv2026

Time-variable Scattered Light in Herbig Disks Observed with Subaru/SCExAO

Using the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument, we present near-infrared K-band polarimetric imaging of nine Herbig stars selected from a volume-limited sample within 200 pc. We detect the disks around MWC 480, HD 163296, and HD 143006 for the first time with SCExAO, and compare these observations with previous VLT/SPHERE datasets to identify surface-brightness variability. In MWC 480, we resolve two azimuthal brightness dips near the disk minor axis and find evidence that one of them shifted between 2021 and 2022. In HD 163296, we identify an apparent linear azimuthal motion of a localized peak in polarized intensity along the outer ring over a 15-month baseline. The rapid motion of these features relative to the local Keplerian velocity suggests that the observed variability is driven by changing illumination rather than physical material motion. Due to uncertainties in the underlying scattering background, however, we cannot determine the precise physical origin of the variability. No significant disk variability is detected in HD 143006 over a 10-month baseline. We also report the first detection of a protoplanetary disk using the fast-PDI mode on SCExAO, illustrating both the promise and current limitations of this observing mode. Finally, we report non-detections toward HD 144432, HD 56895, PDS 76, HIP 80425, HD 148352, and HIP 81474. All non-detections with Meeus classifications belong to Group II systems and are likely self-shadowed. For these six systems, we measure the system-integrated polarization fraction and angle of linear polarization, providing quantitative constraints on their unresolved circumstellar environments.

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arXiv2025

Dynamical Analysis of the HD 169142 Planet-Forming Disk: Twelve Years of High-Contrast Polarimetry

We present a dynamical analysis of the HD 169142 planet-forming disk based on high-contrast polarimetric imaging over a twelve-year observational period, offering insights into its disk evolution and planet-disk interactions. This study explores the evolution of scattered-light features and their relationship with millimeter continuum emission. Archival visible-to-near-infrared scattered-light observations from NACO, SPHERE, and GPI combined with new observations from SCExAO reveal persistent non-axisymmetric structures in both the inner and outer rings of the disk. Through Keplerian image transformations and phase cross-correlation techniques, we show that the azimuthal brightness variations in the inner ring follow the local Keplerian velocity, suggesting these are intrinsic disk features rather than planet-induced spirals or shadows. The motion of the outer ring is weakly detected, requiring a longer observational baseline for further confirmation. Comparing scattered-light features with ALMA 1.3 mm-continuum data, we find that the scattered light traces the edges of dust structures in the inner ring, indicating complex interactions and a leaky dust trap around the water-ice snowline. These findings highlight the capability of long-term monitoring of circumstellar disks to distinguish planetary influences from Keplerian disk dynamics.

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arXiv2025

Direct Imaging Explorations for Companions from the Subaru/IRD Strategic Program II; Discovery of a Brown-dwarf Companion around a Nearby mid-M~dwarf LSPM~J1446+4633

We report the discovery of a new directly-imaged brown dwarf companion with Keck/NIRC2+pyWFS around a nearby mid-type M~dwarf LSPM~J1446+4633 (hereafter J1446). The $L'$-band contrast ($4.5\times10^{-3}$) is consistent with a $\sim20-60\ M_{\rm Jup}$ object at 1--10~Gyr and our two-epoch NIRC2 data suggest a $\sim30\%$ ($\sim3.1σ)$ variability in its $L'$-band flux. We incorporated Gaia DR3 non-single-star catalog into the orbital fitting by combining the Subaru/IRD RV monitoring results, NIRC2 direct imaging results, and Gaia proper motion acceleration. As a result, we derive ${59.8}_{-1.4}^{+1.5}\ M_{\rm Jup}$ and $\approx4.3~{\rm au}$ for the dynamical mass and the semi-major axis of the companion J1446B, respectively. J1446B is one of the intriguing late-T~dwarfs showing variability at $L'$-band for future atmospheric studies with the constrained dynamical mass. Because the J1446 system is accessible with various observation techniques such as astrometry, direct imaging, and high-resolution spectroscopy including radial velocity measurement, it has a potential as a great benchmark system to improve our understanding for cool dwarfs.

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arXiv2025

The mass of TOI-654 b: A short-period sub-Neptune transiting a mid-M dwarf

Sub-Neptunes are small planets between the size of the Earth and Neptune. The orbital and bulk properties of transiting sub-Neptunes can provide clues for their formation and evolution of small planets. In this paper, we report on follow-up observations of a planetary system around the mid-M dwarf TOI-654, whose transiting sub-Neptune TOI-654 b ($P=1.53$ day) is validated as a suitable target for the atmospheric observation. We measure the planetary mass and stellar properties with the InfraRed Doppler instrument (IRD) mounted on the Subaru telescope and obtain the stellar and planetary properties from additional transit observations by the Transit Exoplanetary Survey Satellite (TESS) and a series of the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT). As a result, the planetary mass of TOI-654 b is determined to be $M_{\rm p} = 8.71 \pm 1.25 M_{\oplus}$, and the radius is updated to be $R_{\rm p} = 2.378 \pm 0.089 R_{\oplus}$. The bulk density suggests that the planet is composed of a rocky and volatile-rich core or a rocky core surrounded by a small amount of H/He envelope.TOI-654 b is one of unique planets located around the radius valley and and also on the outer edge of the Neptune desert. The precise mass determination enables us to constrain the atmospheric properties with future spectroscopic observations especially for the emission by the James Webb Space Telescope and Ariel.

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arXiv2025

Atmospheric retrieval of Subaru/IRD high-resolution spectrum of the archetype T-type brown dwarf Gl 229 B

Brown dwarfs provide a unique opportunity to study atmospheres and their physical and chemical processes with high precision, especially in temperature ranges relevant to exoplanets. In this study, we performed high-resolution ($R \sim 70,000$) spectroscopy using Subaru/IRD ($Y$, $J$, $H$-bands) of the T7.0p-type object Gl 229 B, the first discovered T-type brown dwarf, which orbits an M1V host star at a separation of 33 au. We conducted atmospheric retrieval on the reduced $H$-band spectrum using the high-resolution spectrum model compatible with automatic differentiation and GPU, ExoJAX. In contrast to previous retrieval studies on medium-resolution spectra, we obtained a C/O ratio consistent with that of the host star, aligning with the expected formation process for such a massive brown dwarf. Additionally, based on the strong constraint on temperature from the high-resolution spectrum and previously measured photometric magnitude, our analysis indicates that Gl 229 B is a binary, which was also proposed by Brandt et al. (2021) and recently confirmed by Xuan et al. (2024). Finally, we validated current molecular line lists by leveraging the obtained high-resolution, high signal-to-noise ratio spectrum of this warm ($\sim 900$ K) atmosphere. This study highlights the importance of observing companion brown dwarfs as benchmark objects for establishing characterization techniques for low-mass objects and enhancing our understanding of their atmospheres, given the wealth of available information and the relative ease of observation.

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arXiv2024

Weighing Single-lined Spectroscopic Binaries Using Tidal Effects on Radial Velocities: The Case of V723 Monocerotis

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 for mass estimation in close binaries including X-ray systems, but it has been pointed out that contaminating light from sources other than the primary star could introduce systematic errors in the mass and inclination estimates. Here, we focus on the apparent RV variations caused by asymmetric distortion of the absorption lines of the tidally deformed primary star (tidal RV). Because this signal contains information equivalent to that from photometric EVs, it enables mass estimation of the binary system using only the primary star's absorption lines from high-resolution spectroscopic data, providing a potentially more robust approach against contaminating light. We apply the method to the binary system V723 Monocerotis, where both photometric EV and tidal RV signals are detected, and successfully determine the component masses using only the primary star's RVs and projected rotational velocity, without relying on absolute flux measurements or on stellar evolutionary models. The masses derived from the tidal RV model show a reasonable agreement with those obtained from EVs after carefully modeling the flux contamination from the secondary. This result demonstrates that tidal RVs provide a useful alternative means for mass estimation in SB1s.

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arXiv2024

Visible-Light High-Contrast Imaging and Polarimetry with SCExAO/VAMPIRES

We present significant upgrades to the VAMPIRES instrument, a visible-light (600 nm to 800 nm) high-contrast imaging polarimeter integrated within SCExAO on the Subaru telescope. Key enhancements include new qCMOS detectors, coronagraphs, polarization optics, and a multiband imaging mode, improving sensitivity, resolution, and efficiency. These upgrades position VAMPIRES as a powerful tool for studying sub-stellar companions, accreting protoplanets, circumstellar disks, stellar jets, stellar mass-loss shells, and solar system objects. The instrument achieves angular resolutions from 17 mas to 21 mas and Strehl ratios up to 60\%, with 5$σ$ contrast limits of $10^{\text{-}4}$ at 0.1'' to $10^{\text{-}6}$ beyond 0.5''. We demonstrate these capabilities through spectro-polarimetric coronagraphic imaging of the HD 169142 circumstellar disk, ADI+SDI imaging of the sub-stellar companion HD 1160B, narrowband H$α$ imaging of the R Aqr emission nebula, and spectro-polarimetric imaging of Neptune.

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arXiv2024

SCExAO/CHARIS Near-Infrared Scattered-Light Imaging and Integral Field Spectropolarimetry of the AB Aurigae Protoplanetary System

We analyze near-infrared integral field spectropolarimetry of the AB Aurigae protoplanetary disk and protoplanet (AB Aur b), obtained with SCExAO/CHARIS in 22 wavelength channels covering the J, H, and K passbands ($λ_{\rm o}$ = 1.1--2.4 $μm$) over angular separations of $ρ$ $\approx$ 0.13" to 1.1" ($\sim$20--175 au). Our images resolve spiral structures in the disk in each CHARIS channel. At the longest wavelengths, the data may reveal an extension of the western spiral seen in previous polarimetric data at $ρ$ $<$ 0.3" out to larger distances clockwise from the protoplanet AB Aur b, coincident with the ALMA-detected $CO$ gas spiral. While AB Aur b is detectable in complementary total intensity data, it is a non-detection in polarized light at $λ$ $>$ 1.3 $μ$m. While the observed disk color is extremely red across $JHK$, the disk has a blue intrinsic scattering color consistent with small dust grains. The disk's polarization spectrum is redder than AB Aur b's total intensity spectrum. The polarization fraction peaks at $\sim$ 0.6 along the major disk axis. Radiative transfer modeling of the CHARIS data shows that small, porous dust grains with a porosity of $p$ = 0.6--0.8 better reproduce the scattered-light appearance of the disk than more compact spheres ($p$ = 0.3), especially the polarization fraction. This work demonstrates the utility of integral field spectropolarimetry to characterize structures in protoplanetary disks and elucidate the properties of the disks' dust.

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arXiv2024

Transit Spectroscopy of K2-33b with Subaru/IRD: Spin-Orbit Alignment and Tentative Atmospheric Helium

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 (age $\approx 8-11$ Myr) around a pre-main-sequence M-type star. Analysing K2-33's near-infrared spectra obtained by the IRD instrument on Subaru, we investigate the spin-orbit angle and transit-induced excess absorption for K2-33b. We attempt both classical modelling of the Rossiter-McLaughlin (RM) effect and Doppler-shadow analyses for the measurements of the projected stellar obliquity, finding a low angle of $λ=-6_{-58}^{+61}$ deg (for RM analysis) and $λ=-10_{-24}^{+22}$ deg (for Doppler-shadow analysis). In the modelling of the RM effect, we allow the planet-to-star radius ratio to float freely to take into account the possible smaller radius in the near infrared, but the constraint we obtain ($R_p/R_s=0.037_{-0.017}^{+0.013}$) is inconclusive due to the low radial-velocity precision. Comparison spectra of K2-33 of the 1083 nm triplet of metastable ortho-He I obtained in and out of the 2021 transit reveal excess absorption that could be due to an escaping He-rich atmosphere. Under certain conditions on planet mass and stellar XUV emission, the implied escape rate is sufficient to remove an Earth-mass H/He in $\sim$1 Gyr, transforming this object from a Neptune to a super-Earth.

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arXiv2024

Forming localized dust concentrations in a dust ring: DM Tau case study

The previous, high angular resolution 225 GHz ($\sim$1.3 mm) continuum observations on the transitional disk DM Tau have resolved an outer ring at 20-120 au radii that is weakly azimuthally asymmetric. We aimed to examine dust growth and filtration in the outer ring. We performed the $\sim$0$''$.06 ($\sim$8.7 au) resolution Karl G. Jansky Very Large Array (JVLA) 40-48 GHz ($\sim$7 mm; Q band) continuum observations and the complementary observations at lower frequencies. In addition, we analyzed the archival JVLA observations that were taken since 2010. Intriguingly, the Q band image resolved the azimuthally highly asymmetric, knotty dust emission sources close to the inner edge of the outer ring. Fitting the 8-700 GHz spectral energy distribution (SED) with two dust components indicates that the maximum grain size in these knotty dust emission sources is likely $\gtrsim$300 $μ$m while it is $\lesssim$50 $μ$m in the rest of the ring. These results may be explained by trapping of inward migrating grown dust close to the ring inner edge. The exact mechanism for developing the azimuthal asymmetry has not yet been identified, which may be due to planet-disk interaction that might also be responsible for the creation of the dust cavity and pressure bump, or the fluid instabilities and vortex formation due to shear motions. Finally, we remark that the asymmetries in DM Tau are hard to diagnose from the $\gtrsim$225 GHz observations owing to a high optical depth at the ring. In other words, the apparent symmetric or asymmetric morphology of the transitional disks may be related to the optical depths of those disks at the observing frequency.

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arXiv2023

A spectroscopic thermometer: individual vibrational band spectroscopy with the example of OH in the atmosphere of WASP-33b

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-33b as an example. We simulate low-resolution spectroscopic data for observations with the JWST's NIRSpec instrument and use high resolution observational data obtained from the Subaru InfraRed Doppler instrument (IRD). Vibrational band-specific OH cross section sets are constructed and used in retrievals on the (simulated) low and (real) high resolution data. Low resolution observations are simulated for two WASP-33b emission scenarios: under the assumption of local thermal equilibrium (LTE) and a toy non-LTE model for vibrational excitation of selected bands. We show that mixing ratios for individual bands can be retrieved with sufficient precision to allow the vibrational population distributions of the forward models to be reconstructed. A simple fit for the Boltzmann distribution in the LTE case shows that the vibrational temperature is recoverable in this manner. For high resolution, cross-correlation applications, we apply the individual vibrational band analysis to an IRD spectrum of WASP-33b, applying an 'un-peeling' technique. Individual detection significances for the two strongest bands are shown to be in line with Boltzmann distributed vibrational state populations consistent with the effective temperature of the WASP-33b atmosphere reported previously. We show the viability of this approach for analysing the individual vibrational state populations behind observed and simulated spectra including reconstructing state population distributions.

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arXiv2023

The mass determination of TOI-519 b: a close-in giant planet transiting a metal-rich mid-M dwarf

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 ($\rm [Fe/H] = 0.27 \pm 0.09$ dex) and has the lowest effective temperature ($T_{\rm eff}=3322 \pm 49$ K) among all stars hosting known close-in giant planets based on the IRD spectra and mid-resolution infrared spectra obtained with NASA Infrared Telescope Facility / SpeX. The core mass of TOI-519 b inferred from a thermal evolution model ranges from $0$ to $\sim30~M_\oplus$, which can be explained by both the core accretion and disk instability models as the formation origins of this planet. However, TOI-519 is in line with the emerging trend that M dwarfs with close-in giant planets tend to have high metallicity, which may indicate that they formed in the core accretion model. The system is also consistent with the potential trend that close-in giant planets around M dwarfs tend to be less massive than those around FGK dwarfs.

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arXiv2023

Direct Imaging and Astrometric Detection of a Gas Giant Planet Orbiting an Accelerating Star

Direct imaging of gas giant exoplanets provides key information on planetary atmospheres and the architectures of planetary systems. However, few planets have been detected in blind surveys used to achieve imaging detections. Using Gaia and Hipparcos astrometry we identified dynamical evidence for a gas giant planet around the nearby star HIP 99770 and then confirmed this planet by direct imaging with the Subaru Coronagraphic Extreme Adaptive Optics Project. HIP 99770 b orbits 17 astronomical units from its host star, with an insolation comparable to Jupiter's and a dynamical mass of 13.9--16.1 Jupiter masses. Its planet-to-star mass ratio (7--8$\times$10$^{-3}$) is comparable to that other directly-imaged planets. The planet's atmosphere resembles an older, less-cloudy analogue of the atmospheres of previously-imaged exoplanets around HR 8799.

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