Kai Ikuta
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View article: TOI-1743 b, TOI-5799 b, TOI-5799 c, and TOI-6223 b: TESS discovery and validation of four super-Earth to Neptune-sized planets around M dwarfs
TOI-1743 b, TOI-5799 b, TOI-5799 c, and TOI-6223 b: TESS discovery and validation of four super-Earth to Neptune-sized planets around M dwarfs Open
We present the discovery by the TESS mission of one transiting Neptune-sized planet, TOI-6223 b, and two transiting super-Earths, TOI-1743 b and TOI-5799 b. We validate these planets using a statistical validation method, multi-color light…
View article: Multiband, Multiepoch Photometry of the Spot-crossing System TOI-3884: Refined System Geometry and Spot Properties
Multiband, Multiepoch Photometry of the Spot-crossing System TOI-3884: Refined System Geometry and Spot Properties Open
Spot-crossing transits offer a unique opportunity to probe spot properties such as temperature, size, and surface distribution. TOI-3884 is a rare system in which spot-crossing features are persistently observed during every transit. This …
View article: The mass of TOI-654 b: A short-period sub-Neptune transiting a mid-M dwarf
The mass of TOI-654 b: A short-period sub-Neptune transiting a mid-M dwarf Open
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-u…
View article: The mass of TOI-654 b: A short-period sub-Neptune transiting a mid-M dwarf
The mass of TOI-654 b: A short-period sub-Neptune transiting a mid-M dwarf Open
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-u…
View article: Time evolution of white-light flare accompanied by probable postflare loops on M-type dwarf EV Lacertae
Time evolution of white-light flare accompanied by probable postflare loops on M-type dwarf EV Lacertae Open
White-light flares are explosive phenomena accompanied by brightening of continuum from near-ultraviolet to optical, which occur on the Sun and stars. In order to investigate the mechanism of white-light flares, we carried out simultaneous…
View article: TOI-1846 b: a super-Earth in the radius valley orbiting a nearby M dwarf
TOI-1846 b: a super-Earth in the radius valley orbiting a nearby M dwarf Open
We present the discovery and validation of a super-Earth planet orbiting the M dwarf star TOI-1846 (TIC 198385543). The host star ($K_{\rm mag} = 9.6$) is located 47 pc away and has a radius of $R_\star = 0.41 \pm 0.01$$\rm \, R_\odot$, a …
View article: High-time-cadence Spectroscopy and Photometry of Stellar Flares on M-dwarf YZ Canis Minoris with Seimei Telescope and TESS. II. Statistical Properties of Blue/Red Asymmetries in the H<i>α</i> Line
High-time-cadence Spectroscopy and Photometry of Stellar Flares on M-dwarf YZ Canis Minoris with Seimei Telescope and TESS. II. Statistical Properties of Blue/Red Asymmetries in the H<i>α</i> Line Open
M-dwarfs frequently produce flares, and their associated coronal mass ejections (CMEs) may threaten the habitability of close-in exoplanets. M-dwarf flares sometimes show prominence eruption signatures, observed as blue/red asymmetries in …
View article: The eccentricity distribution of warm sub-Saturns in <i>TESS</i>
The eccentricity distribution of warm sub-Saturns in <i>TESS</i> Open
We present the eccentricity distribution of warm sub-Saturns (4–8 $R_{\rm{\oplus }}$, 8–200 d periods) as derived from an analysis of transit light curves from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission. We use the ‘photoe…
View article: The Eccentricity Distribution of Warm Sub-Saturns in TESS
The Eccentricity Distribution of Warm Sub-Saturns in TESS Open
We present the eccentricity distribution of warm sub-Saturns (4-8 Re, 8-200 day periods) as derived from an analysis of transit light curves from NASA's Transiting Exoplanet Survey Satellite (TESS) mission. We use the "photoeccentric" effe…
View article: Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System
Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System Open
TOI-1266 is a benchmark system of two temperate ( ), and combine the TTVs with archival radial velocity measurements to improve our knowledge of the planetary masses and radii. We find that, consistent with previous studies, TOI-12…
View article: High-Time-Cadence Spectroscopy and Photometry of Stellar Flares on M-dwarf YZ Canis Minoris with Seimei Telescope and TESS. II. Statistical Properties of Blue/Red Asymmetries in the H$α$ Line
High-Time-Cadence Spectroscopy and Photometry of Stellar Flares on M-dwarf YZ Canis Minoris with Seimei Telescope and TESS. II. Statistical Properties of Blue/Red Asymmetries in the H$α$ Line Open
M-dwarfs frequently produce flares, and their associated coronal mass ejections (CMEs) may threaten the habitability of close-in exoplanets. M-dwarf flares sometimes show prominence eruption signatures, observed as blue/red asymmetries in …
View article: TOI-2015 b: A sub-Neptune in strong gravitational interaction with an outer non-transiting planet
TOI-2015 b: A sub-Neptune in strong gravitational interaction with an outer non-transiting planet Open
TOI-2015 is a known exoplanetary system around an M4 dwarf star, consisting of a transiting sub-Neptune planet in a 3.35-day orbital period, TOI-2015 b, accompanied by a non-transiting companion, TOI-2015 c. High-precision radial-velocity …
View article: TOI-2015b: a sub-Neptune in strong gravitational interaction with an outer non-transiting planet
TOI-2015b: a sub-Neptune in strong gravitational interaction with an outer non-transiting planet Open
TOI-2015 is a known exoplanetary system around an M4 dwarf star, consisting of a transiting sub-Neptune planet in a 3.35-day orbital period, TOI-2015b, accompanied by a non-transiting companion, TOI-2015c. High-precision RV measurements we…
View article: TOI-5108 b and TOI 5786 b: Two transiting sub-Saturns detected and characterized with TESS, MaHPS, and SOPHIE
TOI-5108 b and TOI 5786 b: Two transiting sub-Saturns detected and characterized with TESS, MaHPS, and SOPHIE Open
We report the discovery and characterization of two sub-Saturns from the Transiting Exoplanet Survey Satellite ( TESS ) using high- resolution spectroscopic observations from the MaHPS spectrograph at the Wendelstein Observatory and the SO…
View article: Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. II. Understanding Prominence Eruption through Data-driven Modeling and Observed Magnetic Environment
Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. II. Understanding Prominence Eruption through Data-driven Modeling and Observed Magnetic Environment Open
EK Draconis, a nearby young solar-type star (G1.5V, 50–120 Myr), is known as one of the best proxies for inferring the environmental conditions of the young Sun. The star frequently produces superflares, and Paper I presented the first evi…
View article: Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. II. Understanding Prominence Eruption through Data-Driven Modeling and Observed Magnetic Environment
Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. II. Understanding Prominence Eruption through Data-Driven Modeling and Observed Magnetic Environment Open
EK Draconis, a nearby young solar-type star (G1.5V, 50-120 Myr), is known as one of the best proxies for inferring the environmental conditions of the young Sun. The star frequently produces superflares and Paper I presented the first evid…
View article: Sun-as-a-star Analysis of the X1.6 Flare on 2023 August 5: Dynamics of Postflare Loops in Spatially Integrated Observational Data
Sun-as-a-star Analysis of the X1.6 Flare on 2023 August 5: Dynamics of Postflare Loops in Spatially Integrated Observational Data Open
Postflare loops are loop-like plasmas observed during the decay phase of solar flares, and they are expected to exist for stellar flares. However, it is unclear how postflare loops are observed in stellar flares’ cases. To clarify behavior…
View article: Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System
Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System Open
TOI-1266 is a benchmark system of two temperate ($<$ 450 K) sub-Neptune-sized planets orbiting a nearby M dwarf exhibiting a rare inverted architecture with a larger interior planet. In this study, we characterize transit timing variations…
View article: Sun-as-a-star Analysis of the X1.6 Flare on 2023 August 5: Dynamics of Post-flare Loops in Spatially Integrated Observational Data
Sun-as-a-star Analysis of the X1.6 Flare on 2023 August 5: Dynamics of Post-flare Loops in Spatially Integrated Observational Data Open
Post-flare loops are loop-like plasmas observed during the decay phase of solar flares, and they are expected to exist for stellar flares. However, it is unclear how post-flare loops are observed in stellar flares' cases. To clarify behavi…
View article: Low abundances of TiO and VO on the dayside of KELT-9 b: Insights from ground-based photometric observations
Low abundances of TiO and VO on the dayside of KELT-9 b: Insights from ground-based photometric observations Open
We present ground-based photometric observations of secondary eclipses of the hottest known planet KELT-9 b using MuSCAT2 and Sinistro. We detect secondary eclipse signals in i and $z_{\rm s}$ with eclipse depths of $373^{+74}_{-75}$ and $…
View article: Validation of up to seven TESS planet candidates through multi-colour transit photometry using MuSCAT2 data
Validation of up to seven TESS planet candidates through multi-colour transit photometry using MuSCAT2 data Open
The TESS mission searches for transiting exoplanets by monitoring the brightness of hundreds of thousands of stars across the entire sky. M-type planet hosts are ideal targets for this mission due to their smaller size and cooler temperatu…
View article: Low abundances of TiO and VO on the Dayside of KELT-9 b: Insights from Ground-Based Photometric Observations
Low abundances of TiO and VO on the Dayside of KELT-9 b: Insights from Ground-Based Photometric Observations Open
We present ground-based photometric observations of secondary eclipses of the hottest known planet KELT-9b using MuSCAT2 and Sinistro. We detect secondary eclipse signals in $i$ and $z_{\rm s}$ with eclipse depths of $373^{+74}_{-75}$ ppm …
View article: Validation of up to seven TESS planet candidates through multi-colour transit photometry using MuSCAT2 data
Validation of up to seven TESS planet candidates through multi-colour transit photometry using MuSCAT2 data Open
The TESS mission searches for transiting exoplanets by monitoring the brightness of hundreds of thousands of stars across the entire sky. M-type planet hosts are ideal targets for this mission due to their smaller size and cooler temperatu…
View article: TOI-1408: Discovery and Photodynamical Modeling of a Small Inner Companion to a Hot Jupiter Revealed by Transit Timing Variations
TOI-1408: Discovery and Photodynamical Modeling of a Small Inner Companion to a Hot Jupiter Revealed by Transit Timing Variations Open
We report the discovery and characterization of a small planet, TOI-1408 c, on a 2.2 day orbit located interior to a previously known hot Jupiter, TOI-1408 b ( P = 4.42 days, M = 1.86 ± 0.02 M Jup , R = 2.4 ± 0.5 R Jup ) that exhibits graz…
View article: Optical Nonlinearity Mitigation Using Reservoir Computing with Tapped-Delay Lines
Optical Nonlinearity Mitigation Using Reservoir Computing with Tapped-Delay Lines Open
We investigated a nonlinear equalizer based on reservoir computing (RC) with tapped-delay lines for compensating for linear and nonlinear waveform distortion caused by, e.g., chromatic dispersion and self-phase modulation. We evaluated and…
View article: The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M Dwarfs
The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M Dwarfs Open
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 s…
View article: Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy Open
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 i…
View article: Three short-period Earth-sized planets around M dwarfs discovered by TESS: TOI-5720 b, TOI-6008 b, and TOI-6086 b
Three short-period Earth-sized planets around M dwarfs discovered by TESS: TOI-5720 b, TOI-6008 b, and TOI-6086 b Open
One of the main goals of the NASA Transiting Exoplanet Survey Satellite (TESS) mission is the discovery of Earth-like planets around nearby M-dwarf stars. We present the discovery and validation of three new short-period Earth-sized planet…