arXiv subjects

Aoi Takahashi

Publications and source records attributed to Aoi Takahashi.

14 recordsLinked to original sources

arXiv2026

Japan's Possible Contributions for Coronagraph of the Habitable Worlds Observatory (HWO)

In this paper, we describe Japan's possible contributions for coronagraph of the Habitable Worlds Observatory (HWO) based on our independent study. We are considering to contribute to the HOW coronagraph by science and hardware, based on Japan's experience for the SPICA coronagraph instrument, contributions to the Nancy Grace Roman Space Telescope, and SCExAO for the Subaru telescope. Currently, hardware contributions of various scales, from large-scale to small components, are considered. As an example of the large-scale hardware case, the optical and mechanical layout of the entire infrared coronagraph is presented. Several individual high-contrast technologies are also briefly introduced, for which research is ongoing in Japan. In discussions, it is pointed out that both the inner working angle (IWA) and sensitivity are particularly critical for the NIR coronagraph. In this situation, dedicated observations of a small number of targets close to the solar system can be one of key science program in this situation, and designing consolidating science objectives, requirements, observation targets, and survey plans is important. It is essential to push the development of advanced coronagraphs that provide small IWAs. On the other hand, it is also necessary to prepare solutions that adopt more robust coronagraphs in parallel. How to coexist visible and NIR coronagraphs within constraints of volume, mass, budget etc. is an important issue. The international sharing for the coronagraph development should be carefully decided by international agreement. Although all of our studies may not be realized in contributions to the first generation of HWO instruments, we are considering Japan's multigenerational participation in the HWO to maximize outcomes of the HWO.

astro-ph.IM↗

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.

astro-ph.EP↗

arXiv2025

The Cosmic Infrared Background Experiment-2: An Intensity Mapping Optimized Sounding-rocket Payload to Understand the Near-IR Extragalactic Background Light

The background light produced by emission from all sources over cosmic history is a powerful diagnostic of structure formation and evolution. At near-infrared wavelengths, this extragalactic background light (EBL) is comprised of emission from galaxies stretching all the way back to the first-light objects present during the Epoch of Reionization. The Cosmic Infrared Background Experiment 2 (CIBER-2) is a sounding-rocket experiment designed to measure both the absolute photometric brightness of the EBL over 0.5 - 2.0 microns and perform an intensity mapping measurement of EBL spatial fluctuations in six broad bands over the same wavelength range. CIBER-2 comprises a 28.5 cm, 80K telescope that images several square degrees to three separate cameras. Each camera is equipped with an HAWAII-2RG detector covered by an assembly that combines two broadband filters and a linear-variable filter, which perform the intensity mapping and absolute photometric measurements, respectively. CIBER-2 has flown three times: an engineering flight in 2021; a terminated launch in 2023; and a successful science flight in 2024. In this paper, we review the science case for the experiment; describe the factors motivating the instrument design; review the optical, mechanical, and electronic implementation of the instrument; present preflight laboratory characterization measurements; and finally assess the instrument's performance in flight.

astro-ph.IM↗

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.

astro-ph.EP↗

arXiv2025

Measurement of Methane Line Broadening in Hot Hydrogen/Helium Atmospheres at $λ$ = 1.60-1.63 μm for Substellar Object Spectroscopy

Recent high-dispersion spectroscopy from ground-based telescopes and high-precision spectroscopy from space observatories have enabled atmospheric observations of substellar objects, such as brown dwarfs and hot gaseous exoplanets, with sufficient precision to make ambient gas differences in molecular line broadening a significant factor. In this paper, we experimentally measured the pressure broadening of methane in a high-temperature hydrogen-helium background atmosphere in the H band, which had not been previously measured. The experiment used glass cells, inserted in a tube furnace, filled with methane in a hydrogen-helium background atmosphere or pure methane gas. Spectra were obtained at four temperatures ranging from room temperature to 1000 K, in the wavelength range 1.60-1.63 $μ$m, using a tunable laser, yielding eight high-resolution spectra in total. A full Bayesian analysis was performed on the obtained spectra, using the differentiable spectral model ExoJAX and the Hamiltonian Monte Carlo for inferring a large number of parameters, allowing us to infer the H2/He pressure broadening for 22 transitions mainly in the R-branch of the 2$ν_3$ band. As a result, we found a temperature exponent of approximately 0.27 and a reference width at 296 K of around 0.040 for $ J_{lower} $ = 13-20. This temperature dependency is much milder than that provided by the molecular database ExoMol, yielding a line width approximately 5-45% smaller than ExoMol at 296 K, but similar at 1000 K. Our results suggest the need for further accumulation of experimental data for spectral analysis of substellar objects with hydrogen-helium atmospheres.

astro-ph.EP↗

arXiv2024

JASMINE: Near-Infrared Astrometry and Time Series Photometry Science

Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency. JASMINE has two main science goals. One is the Galactic archaeology with Galactic Center Survey, which aims to reveal the Milky Way's central core structure and formation history from Gaia-level (~25 $μ$as) astrometry in the Near-Infrared (NIR) Hw-band (1.0-1.6 $μ$m). The other is the Exoplanet Survey, which aims to discover transiting Earth-like exoplanets in the habitable zone from NIR time-series photometry of M dwarfs when the Galactic center is not accessible. We introduce the mission, review many science objectives, and present the instrument concept. JASMINE will be the first dedicated NIR astrometry space mission and provide precise astrometric information of the stars in the Galactic center, taking advantage of the significantly lower extinction in the NIR. The precise astrometry is obtained by taking many short-exposure images. Hence, the JASMINE Galactic center survey data will be valuable for studies of exoplanet transits, asteroseismology, variable stars and microlensing studies, including discovery of (intermediate mass) black holes. We highlight a swath of such potential science, and also describe synergies with other missions.

astro-ph.IM↗

arXiv2023

An Earth-sized Planet around an M5 Dwarf Star at 22 pc

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 curves with the data secured by our follow-up observations including high-resolution imaging and near infrared spectroscopy with IRD, we rule out false positive scenarios, finding a low false positive probability of $2\times 10^{-4}$. Based on IRD's radial velocities of K2-415, which were sparsely taken over three years, we obtain the planet mass of $3.0\pm 2.7\,M_\oplus$ ($M_p<7.5\,M_\oplus$ at $95\,\%$ confidence) for K2-415b. Being one of the lowest mass stars ($\approx 0.16\,M_\odot$) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy.

astro-ph.EP↗

arXiv2022

A Super-Earth Orbiting Near the Inner Edge of the Habitable Zone around the M4.5-dwarf Ross 508

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 minimum mass $m \sin i = 4.00^{+0.53}_{-0.55}\ M_{\oplus}$. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators or MEarth photometry. The planet, Ross 508 b, has a semimajor-axis of $0.05366^{+0.00056}_{-0.00049}$ au. This gives an orbit-averaged insolation of $\approx$1.4 times the Earth's value, placing Ross 508 b near the inner edge of its star's habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role to find a low-mass planet around cool M dwarfs like Ross 508.

astro-ph.EP↗

arXiv2021

Polarization spectrum of near infrared zodiacal light observed with CIBER

We report the first measurement of the zodiacal light (ZL) polarization spectrum in the near-infrared between 0.8 and 1.8 $μ$m. Using the low-resolution spectrometer (LRS) on board the Cosmic Infrared Background Experiment (CIBER), calibrated for absolute spectrophotometry and spectropolarimetry, we acquire long-slit polarization spectral images of the total diffuse sky brightness towards five fields. To extract the ZL spectrum, we subtract contribution of other diffuse radiation, such as the diffuse galactic light (DGL), the integrated star light (ISL), and the extragalactic background light (EBL). The measured ZL polarization spectrum shows little wavelength dependence in the near-infrared and the degree of polarization clearly varies as a function of the ecliptic coordinates and solar elongation. Among the observed fields, the North Ecliptic Pole shows the maximum degree of polarization of $\sim$ 20$\%$, which is consistent with an earlier observation from the Diffuse Infrared Background Experiment (DIRBE) aboard on the Cosmic Background Explorer (COBE). The measured degree of polarization and its solar elongation dependence are reproduced by the empirical scattering model in the visible band and also by the Mie scattering model for large absorptive particles, while the Rayleigh scattering model is ruled out. All of our results suggest that the interplanetary dust is dominated by large particles.

astro-ph.EP↗

arXiv2021

An Extensive Study on Smell-Aware Bug Localization

Bug localization is an important aspect of software maintenance because it can locate modules that should be changed to fix a specific bug. Our previous study showed that the accuracy of the information retrieval (IR)-based bug localization technique improved when used in combination with code smell information. Although this technique showed promise, the study showed limited usefulness because of the small number of: 1) projects in the dataset, 2) types of smell information, and 3) baseline bug localization techniques used for assessment. This paper presents an extension of our previous experiments on Bench4BL, the largest bug localization benchmark dataset available for bug localization. In addition, we generalized the smell-aware bug localization technique to allow different configurations of smell information, which were combined with various bug localization techniques. Our results confirmed that our technique can improve the performance of IR-based bug localization techniques for the class level even when large datasets are processed. Furthermore, because of the optimized configuration of the smell information, our technique can enhance the performance of most state-of-the-art bug localization techniques.

cs.SE↗

arXiv2020

The isotropic interplanetary dust cloud and near-infrared extragalactic background light observed with COBE/DIRBE

We report observation of isotropic interplanetary dust (IPD) by analyzing the infrared (IR) maps of Diffuse Infrared Background Experiment (DIRBE) onboard the Cosmic Background Explorer (COBE) spacecraft. To search for the isotropic IPD, we perform new analysis in terms of solar elongation angle ($ε$), because we expect zodiacal light (ZL) intensity from the isotropic IPD to decrease as a function of $ε$. We use the DIRBE weekly-averaged maps covering $64^\circ \lesssim ε\lesssim 124^\circ$ and inspect the $ε$-dependence of residual intensity after subtracting conventional ZL components. We find the $ε$-dependence of the residuals, indicating the presence of the isotropic IPD. However, the mid-IR $ε$-dependence is different from that of the isotropic IPD model at $ε\gtrsim 90^\circ$, where the residual intensity increases as a function of $ε$. To explain the observed $ε$-dependence, we assume a spheroidal IPD cloud showing higher density further away from the sun. We estimate intensity of the near-IR extragalactic background light (EBL) by subtracting the spheroidal component, assuming the spectral energy distribution from the residual brightness at $12\,{\rm μm}$. The EBL intensity is derived as $45_{-8}^{+11}$, $21_{-4}^{+3}$, and $15\pm3\,{\rm nWm^{-2}sr^{-1}}$ at $1.25$, $2.2$, and $3.5\,{\rm μm}$, respectively. The EBL is still a few times larger than integrated light of normal galaxies, suggesting existence of unaccounted extragalactic sources.

astro-ph.GA↗

arXiv2019

Mid-infrared spectroscopy of zodiacal emission with AKARI/IRC

Interplanetary dust (IPD) is thought to be recently supplied from asteroids and comets. Grain properties of the IPD can give us the information about the environment in the proto-solar system, and can be traced from the shapes of silicate features around 10 $μ$m seen in the zodiacal emission spectra. We analyzed mid-IR slit-spectroscopic data of the zodiacal emission in various sky directions obtained with the Infrared Camera on board AKARI satellite. After we subtracted the contamination due to instrumental artifacts, we have successfully obtained high S/N spectra and have determined detailed shapes of excess emission features in the 9 -- 12 $μ$m range in all the sky directions. According to a comparison between the feature shapes averaged over all directions and the absorption coefficients of candidate minerals, the IPD was found to typically include small silicate crystals, especially enstatite grains. We also found the variations in the feature shapes and the related grain properties among the different sky directions. From investigations of the correlation between feature shapes and the brightness contributions from dust bands, the IPD in dust bands seems to have the size frequency distribution biased toward large grains and show the indication of hydrated minerals. The spectra at higher ecliptic latitude showed a stronger excess, which indicates an increase in the fraction of small grains included in the line of sight at higher ecliptic latitudes. If we focus on the dependence of detailed feature shapes on ecliptic latitudes, the IPD at higher latitudes was found to have a lower olivine/pyroxene ratio for small amorphous grains. The variation of the mineral composition of the IPD in different sky directions may imply different properties of the IPD from different types of parent bodies, because the spatial distribution of the IPD depends on the type of the parent body.

astro-ph.EP↗

arXiv2017

Laboratory demonstration of a cryogenic deformable mirror for wavefront correction of space-borne infrared telescopes

This paper demonstrates a cryogenic deformable mirror (DM) with 1,020 actuators based on micro-electrical mechanical systems (MEMS) technology. Cryogenic space-borne infrared telescopes can experience a wavefront error due to a figure error of their mirror surface, which makes the imaging performance worse. For on-orbit wavefront correction as one solution, we developed a MEMS-processed electro-static DM with a special surrounding structure for use under the cryogenic temperature. We conducted a laboratory demonstration of its operation in three cooling cycles between 5 K and 295 K. Using a laser interferometer, we detected the deformation corresponding to the applied voltages under the cryogenic temperature for the first time. The relationship between voltages and displacements was qualitatively expressed by the quadratic function, which is assumed based on the principle of electro-static DMs. We also found that it had a high operating repeatability of a few nm RMS and no significant hysteresis. Using the measured values of repeatability, we simulated the improvement of PSF by wavefront correction with our DM. These results show that our developed DM is effective in improving imaging performance and PSF contrast of space-borne infrared telescopes.

astro-ph.IM↗

arXiv2016

Experimental demonstration of binary shaped pupil mask coronagraphs for telescopes with obscured pupils

We present the fabrication and experimental demonstration of three free-standing binary shaped pupil mask coronagraphs, which are applicable for telescopes with partially obscured pupils. Three masks, designed to be complementary (labeled Mask-A, Mask-B, and Mask-C), were formed in 5 micron thick nickel. The design of Mask-A is based on a one-dimensional barcode mask. The design principle of Mask-B is similar, but has a smaller inner working angle and a lower contrast than Mask-A. Mask-C is based on a concentric ring mask and provides the widest dark region and a symmetric point spread function. Mask-A and Mask-C were both designed to produce a flexibly tailored dark region (i.e., non-uniform contrast). The contrast was evaluated using a light source comprising a broadband super-luminescent light-emitting diode with a center wavelength of 650 nm, and the measurements were carried out in a large vacuum chamber. Active wavefront control was not applied in this work. The coronagraphic images obtained by experiment were mostly consistent with the designs. The contrast of Mask-A within the ranges 3.3 - 8 lambda/D and 8 - 12 lambda/D was ~10^{-4} - 10^{-7} and ~10^{-7}, respectively, where lambda is the wavelength and D is the pupil diameter. The contrast close to the center of Mask-B was ~10^{-4} and that of Mask-C over an extended field of view (5 - 25 lambda/D) was ~10^{-5} - 10^{-6}. The effect of tilting the masks was investigated, and found to be irrelevant at the ~10^{-7} contrast level. Therefore the masks can be tilted to avoid ghosting. These high-contrast free-standing masks have the potential to enable coronagraphic imaging over a wide wavelength range using both ground-based and space-borne general-purpose telescopes with pupil structures not specifically designed for coronagraphy.

astro-ph.IM↗