Hajime Kawahara, Teruyuki Hirano
Sep 19, 2014·astro-ph.EP·PDF Future radial velocity, astrometric, and direct-imaging surveys will find nearby Earth-sized planets within the habitable zone in the near future. How can we search for water and oxygen in those nontransiting planets? We show that a combination of high-dispersion spectroscopic and coronagraphic techniques is a promising technique to detect molecular lines imprinted in the scattered light of Earth-like planets (ELPs). In this method, the planetary signals are spectroscopically separated from telluric absorption by using the Doppler shift. Assuming a long observing campaign (a 10-day exposure) using a high-dispersion spectrometer (R=50,000) with speckle suppression on a 30-m telescope, we simulate the spectra from ELPs around M dwarfs (whose stellar effective temperature is 2750-3750 K) at 5 pc. Performing a cross-correlation analysis with the spectral template of the molecular lines, we find that raw contrasts of $10^{-4}$ and $10^{-5}$ (using Y, J, and H bands) are required to detect water vapor at the 3 $σ$ and 16 $σ$ levels, respectively, for $T_\star$=3000 K. The raw contrast of $10^{-5}$ is required for a 6 $σ$ detection of the oxygen 1.27 $μ$m band. We also examine possible systematics, incomplete speckle subtraction, and the correction for telluric lines. When those are not perfect, a telluric water signal appears in the cross-correlation function. However, we find the planetary signal is separated from that resulting from the velocity difference. We also find that the intrinsic water lines in the Phoenix spectra are too weak to affect the results for water detection. We conclude that a combination of high-dispersion spectroscopy and high-contrast instruments can be a powerful means to characterize ELPs in the extremely large telescope era.
Erik D. Reese, Hajime Kawahara, Tetsu Kitayama, Naomi Ota, Shin Sasaki, Yasushi Suto
Jun 23, 2010·astro-ph.CO·PDF We perform a uniform, systematic analysis of a sample of 38 X-ray galaxy clusters with three different Chandra calibrations. The temperatures change systematically between calibrations. Cluster temperatures change on average by roughly ~6% for the smallest changes and roughly ~13% for the more extreme changes between calibrations. We explore the effects of the changing cluster spectral properties on Sunyaev-Zel'dovich effect (SZE) and X-ray determinations of the Hubble constant. The Hubble parameter changes by +10% and -13% between the current calibration and two previous Chandra calibrations, indicating that changes in the cluster temperature basically explain the entire change in H_0. Although this work focuses on the difference in spectral properties and resultant Hubble parameters between the calibrations, it is intriguing to note that the newer calibrations favor a lower value of the Hubble constant, H_0 ~ 60 km s-1 Mpc-1, typical of results from SZE/X-ray distances. Both galaxy clusters themselves and the details of the instruments must be known precisely to enable reliable precision cosmology with clusters, which will be feasible with combined efforts from ongoing observations and planned missions and observatories covering a wide range of wavelengths.
Stevanus K. Nugroho, Neale P. Gibson, Ernst J. W. de Mooij, Miranda K. Herman, Chris A. Watson, Hajime Kawahara, Stephanie Merrit
Jul 10, 2020·astro-ph.EP·PDF We analyze the high-resolution emission spectrum of WASP-33b taken using the High Dispersion Spectrograph (R\,$\approx$\,165,000) on the 8.2-m Subaru telescope. The data cover $λ$\,$\approx$\,$6170$-$8817$\,Å, divided over 30 spectral orders. The telluric and stellar lines are removed using a de-trending algorithm, {\sc SysRem}, before cross-correlating with planetary spectral templates. We calculate the templates assuming a 1-D plane-parallel hydrostatic atmosphere including continuum opacity of bound-free H$^{-}$ and Rayleigh scattering by H$_{2}$ with a range of constant abundances of Fe\,{\sc i}. Using a likelihood-mapping analysis, we detect an Fe\,{\sc i} emission signature at 6.4-$σ$ located at $K_{\mathrm{p}}$ of 226.0\,$^{+2.1}_{-2.3}$\,km\,s$^{-1}$and $v_{\mathrm{sys}}$ of -3.2\,$^{+2.1}_{-1.8}$\,km\,s$^{-1}$ -- consistent with the planet's expected velocity in the literature. We also confirm the existence of a thermal inversion in the day-side of the planet which is very likely to be caused by the presence of Fe\,{\sc i} and previously-detected TiO in the atmosphere. This makes WASP-33b one of the prime targets to study the relative contributions of both species to the energy budget of an ultra-hot Jupiter.
Kento Masuda, Hajime Kawahara, David W. Latham, Allyson Bieryla, Masanobu Kunitomo, Morgan MacLeod, Wako Aoki
Jul 17, 2019·astro-ph.SR·PDF We report the discovery of the fifth self-lensing binary in which a low-mass white dwarf (WD) gravitationally magnifies its 15th magnitude G-star companion, KIC 8145411, during eclipses. The system was identified from a pair of such self-lensing events in the Kepler photometry, and was followed up with the Tillinghast Reflector Echelle Spectrograph (TRES) on the 1.5m telescope at the Fred Lawrence Whipple Observatory and the High-Dispersion Spectrograph (HDS) on the Subaru 8.2m telescope. A joint analysis of the TRES radial velocities, the HDS spectrum, and the Kepler photometry of the primary star determines the WD mass $0.20\pm0.01\,M_\odot$, orbital semi-major axis $1.28\pm0.03\,\mathrm{au}$, and orbital eccentricity $0.14\pm0.02$. Because such extremely low-mass WDs cannot be formed in isolation within the age of the Galaxy, their formation is believed to involve binary interactions that truncated evolution of the WD progenitor. However, the observed orbit of the KIC 8145411 system is at least ten times wider than required for this scenario to work. The presence of this system in the Kepler sample, along with its similarities to field blue straggler binaries presumably containing WDs, may suggest that some 10% of post-AGB binaries with Sun-like primaries contain such anomalous WDs.
Everett Schlawin, Teruyuki Hirano, Hajime Kawahara, Johanna Teske, Elizabeth M. Green, Benjamin V. Rackham, Jonathan Fraine, Rafia Bushra
Oct 23, 2018·astro-ph.EP·PDF KIC 12557548 b is first of a growing class of intriguing disintegrating planet candidates, which lose mass in the form of a metal rich vapor that condenses into dust particles. Here, we follow up two perplexing observations of the system: 1) the transits appeared shallower than average in 2013 and 2014 and 2) the parameters derived from a high resolution spectrum of the star differed from other results using photometry and low resolution spectroscopy. We observe 5 transits of the system with the 61-inch Kuiper telescope in 2016 and show that they are consistent with photometry from the Kepler spacecraft in 2009-2013, suggesting that the dusty tail has returned to normal length and mass. We also evaluate high resolution archival spectra from the Subaru HDS spectrograph and find them to be consistent with a main-sequence Teff=4440 +/- 70 K star in agreement with the photometry and low resolution spectroscopy. This disfavors the hypothesis that planet disintegration affected the analysis of prior high resolution spectra of this star. We apply Principal Component Analysis to the Kepler long cadence data to understand the modes of disintegration. There is a tentative 491 day periodicity of the second principal component, which corresponds to possible long-term evolution of the dust grain sizes, though the mechanism on such long timescales remains unclear.
Julien Lozi, Olivier Guyon, Nemanja Jovanovic, Sean Goebel, Prashant Pathak, Nour Skaf, Ananya Sahoo, Barnaby Norris, Frantz Martinache, Mamadou N'Diaye, Ben Mazin, Alex B. Walter, Peter Tuthill, Tomoyuki Kudo, Hajime Kawahara, Takayuki Kotani, Michael Ireland, Nick Cvetojevic, Elsa Huby, Sylvestre Lacour, Sebastien Vievard, Tyler D. Groff, Jeffrey K. Chilcote, Jeremy Kasdin, Justin Knight, Frans Snik, David Doelman, Yosuke Minowa, Christophe Clergeon, Naruhisa Takato, Motohide Tamura, Thayne Currie, Hideki Takami, Masa Hayashi
Sep 21, 2018·astro-ph.IM·PDF The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is an extremely modular high-contrast instrument installed on the Subaru telescope in Hawaii. SCExAO has a dual purpose. Its position in the northern hemisphere on a 8-meter telescope makes it a prime instrument for the detection and characterization of exoplanets and stellar environments over a large portion of the sky. In addition, SCExAO's unique design makes it the ideal instrument to test innovative technologies and algorithms quickly in a laboratory setup and subsequently deploy them on-sky. SCExAO benefits from a first stage of wavefront correction with the facility adaptive optics AO188, and splits the 600-2400 nm spectrum towards a variety of modules, in visible and near infrared, optimized for a large range of science cases. The integral field spectrograph CHARIS, with its J, H or K-band high-resolution mode or its broadband low-resolution mode, makes SCExAO a prime instrument for exoplanet detection and characterization. Here we report on the recent developments and scientific results of the SCExAO instrument. Recent upgrades were performed on a number of modules, like the visible polarimetric module VAMPIRES, the high-performance infrared coronagraphs, various wavefront control algorithms, as well as the real-time controller of AO188. The newest addition is the 20k-pixel Microwave Kinetic Inductance Detector (MKIDS) Exoplanet Camera (MEC) that will allow for previously unexplored science and technology developments. MEC, coupled with novel photon-counting speckle control, brings SCExAO closer to the final design of future high-contrast instruments optimized for Giant Segmented Mirror Telescopes (GSMTs).
Ikuyuki Mitsuishi, Hajime Kawahara, Norio Sekiya, Shin Sasaki, Thierry Sousbie, Noriko Y. Yamasaki
Nov 20, 2013·astro-ph.CO·PDF We performed five pointing observations with Suzaku to search for hot gases associated with the junctions of galaxy filaments where no significant diffuse X-ray sources were detected so far. We discovered X-ray sources successfully in all five regions and analyzed two bright sources in each field. Spectral analysis indicates that three sources originate from X-ray diffuse halos associated with optically bright galaxies or groups of galaxies with kT~0.6-0.8 keV. Other three sources are possibly group- and cluster-scale X-ray halos with temperatures of ~1 keV and ~4 keV, respectively while the others are compact object origins such as AGNs. All the three observed intracluster media within the junctions of the galaxy filaments previously found are involved in ongoing mergers. Thus, we demonstrate that deep X-ray observations at the filament junctions identified by galaxy surveys are a powerful mean to explore growing halos in a hierarchical structure undetected so far.
Yuka Fujii, Hajime Kawahara
Apr 16, 2012·astro-ph.EP·PDF Aiming at obtaining detailed information of surface environment of Earth analogs, Kawahara & Fujii (2011) proposed an inversion technique of annual scattered light curves named the spin-orbit tomography (SOT), which enables one to sketch a two-dimensional albedo map from annual variation of the disk-integrated scattered light, and demonstrated the method with a planet in a face-on orbit. We extend it to be applicable to general geometric configurations, including low-obliquity planets like the Earth in inclined orbits. We simulate light curves of the Earth in an inclined orbit in three photometric bands (0.4-0.5um, 0.6-0.7um, and 0.8-0.9um) and show that the distribution of clouds, snow, and continents is retrieved with the aid of the SOT. We also demonstrate the SOT by applying it to an upright Earth, a tidally locked Earth, and Earth analogs with ancient continental configurations. The inversion is model independent in the sense that we do not assume specific albedo models when mapping the surface, and hence applicable in principle to any kind of inhomogeneity. This method can potentially serve as a unique tool to investigate the exohabitats/exoclimes of Earth analogs.
Yui Kasagi, Hajime Kawahara, Ziying Gu, Teruyuki Hirano, Takayuki Kotani, Masayuki Kuzuhara, Kento Masuda
Jan 19, 2026·astro-ph.IM·PDF PyIRD is a Python-based pipeline for reducing spectroscopic data obtained with IRD (InfraRed Doppler; Kotani et al. (2018)) and REACH (Rigorous Exoplanetary Atmosphere Characterization with High dispersion coronagraphy; Kotani et al. (2020)) on the Subaru Telescope. It is designed to process raw images into one-dimensional spectra in a semi-automatic manner. Unlike traditional methods, it does not rely on IRAF (Tody, 1986; 1993), a software used for astronomical data reduction. This approach simplifies the workflow while maintaining efficiency and accuracy. Additionally, the pipeline includes an updated method for removing readout noise patterns from raw images, enabling efficient extraction of spectra even for faint targets such as brown dwarfs. The code is open source and available at https://github.com/prvjapan/pyird .
Tomoyuki Tajiri, Hajime Kawahara, Masataka Aizawa, Michiko S. Fujii, Kohei Hattori, Yui Kasagi, Takayuki Kotani, Kento Masuda, Munetake Momose, Takayuki Muto, Ryou Ohsawa, Satoshi Takita
Sep 27, 2020·astro-ph.EP·PDF We present a comprehensive catalog of the dippers---young stellar objects that exhibit episodic dimming---derived from the one year's worth of data of Transiting Exoplanet Survey Satellite ($ TESS$) full-frame images. In the survey, we found 35 dippers using the convolutional neural network, most of them newly discovered. Although these dippers are widely distributed over the first half-hemisphere that $TESS$ surveyed, we identified the majority's membership with the nearest association Scorpius--Centaurus, Velorum OB2, and nearby Orion molecular cloud complex. However, several dippers are likely to be located in the field. We also found three old dippers whose age exceeds ten million year, which is considered as the disk dissipation time. The color-color diagram indicates that these old dippers are likely to have an extreme debris disk. In particular, we found a runaway old dipper having a large three-dimensional velocity of $72 \mathrm{km\ s}^{-1}$. The dippers in the field, which were probably escaping from their birth molecular clouds or were born outside the current area of star forming regions, are more common than previously considered.
Yuta Nakagawa, Takanori Kodama, Masaki Ishiwatari, Hajime Kawahara, Yasushi Suto, Yoshiyuki O. Takahashi, George L. Hashimoto, Kiyoshi Kuramoto, Kensuke Nakajima, Shin-ichi Takehiro, Yoshi-Yuki Hayashi
Jun 19, 2020·astro-ph.EP·PDF Direct-imaging techniques of exoplanets have made significant progress recently, and will eventually enable to monitor photometric and spectroscopic signals of earth-like habitable planets in the future. The presence of clouds, however, would remain as one of the most uncertain components in deciphering such direct-imaged signals of planets. We attempt to examine how the planetary obliquity produce different cloud patterns by performing a series of GCM (General Circulation Model) simulation runs using a set of parameters relevant for our Earth. Then we use the simulated photometric lightcurves to compute their frequency modulation due to the planetary spin-orbit coupling over an entire orbital period, and attempt to see to what extent one can estimate the obliquity of an Earth-twin. We find that it is possible to estimate the obliquity of an Earth-twin within the uncertainty of several degrees with a dedicated 4 m space telescope at 10 pc away from the system if the stellar flux is completely blocked. While our conclusion is based on several idealized assumptions, a frequency modulation of a directly-imaged earth-like planet offers a unique methodology to determine its obliquity.
Thierry Sousbie, Christophe Pichon, Hajime Kawahara
Sep 21, 2010·astro-ph.CO·PDF The recently introduced discrete persistent structure extractor (DisPerSE, Soubie 2010, paper I) is implemented on realistic 3D cosmological simulations and observed redshift catalogues (SDSS); it is found that DisPerSE traces equally well the observed filaments, walls, and voids in both cases. In either setting, filaments are shown to connect onto halos, outskirt walls, which circumvent voids. Indeed this algorithm operates directly on the particles without assuming anything about the distribution, and yields a natural (topologically motivated) self-consistent criterion for selecting the significance level of the identified structures. It is shown that this extraction is possible even for very sparsely sampled point processes, as a function of the persistence ratio. Hence astrophysicists should be in a position to trace and measure precisely the filaments, walls and voids from such samples and assess the confidence of the post-processed sets as a function of this threshold, which can be expressed relative to the expected amplitude of shot noise. In a cosmic framework, this criterion is comparable to friend of friend for the identifications of peaks, while it also identifies the connected filaments and walls, and quantitatively recovers the full set of topological invariants (Betti numbers) {\sl directly from the particles} as a function of the persistence threshold. This criterion is found to be sufficient even if one particle out of two is noise, when the persistence ratio is set to 3-sigma or more. The algorithm is also implemented on the SDSS catalogue and used to locat interesting configurations of the filamentary structure. In this context we carried the identification of an ``optically faint'' cluster at the intersection of filaments through the recent observation of its X-ray counterpart by SUZAKU. The corresponding filament catalogue will be made available online.
Yui Kasagi, Takayuki Kotani, Hajime Kawahara, Tomoyuki Tajiri, Takayuki Muto, Masataka Aizawa, Michiko S. Fujii, Kohei Hattori, Kento Masuda, Munetake Momose, Ryou Ohsawa, Satoshi Takita
Jan 24, 2022·astro-ph.EP·PDF Photometric monitoring by the Transiting Exoplanet Survey Satellite (TESS) has discovered not only periodic signals by transiting exoplanets but also episodic or quasi-periodic dimming around young stellar objects. The mechanisms of the dimming of these objects, so-called "dippers", are thought to be related to the property of the accretion or the structure of protoplanetary disks especially in regions close to the host star. Recently, we have created the catalog of dippers from the one year of TESS Full Frame Image (FFI) data. In this paper, we report spectral features of four newly found dippers in that catalog and show that they potentially shed light on the dimming mechanisms. We found that all of the targets exhibit the H alpha emission line, which is an indicator of an ongoing accretion. Based on its line profiles and/or their variability, we characterized the properties of the disks of each source, which can support the dimming mechanisms due to a dusty disk wind or an accretion warp. Also, we found an interesting dipper (TIC 317873721), "close-in binary dipper," showing the complex variability of the line profile and the large radial velocity variation. Since the dimming intervals are similar to the orbital period of the binary, we suggest that the dips are caused by dust in the warp of accretion from a circumbinary disk onto stars. Such a close-in ($<$ 0.1 au) binary dipper is rarely reported so far, further investigation will reveal the new aspect of the disk evolution and planetary formation.
Hiroki Harakawa, Takuya Takarada, Yui Kasagi, Teruyuki Hirano, Takayuki Kotani, Masayuki Kuzuhara, Masashi Omiya, Hajime Kawahara, Akihiko Fukui, Yasunori Hori, Hiroyuki Tako Ishikawa, Masahiro Ogihara, John Livingston, Timothy D. Brandt, Thayne Currie, Wako Aoki, Charles A. Beichman, Thomas Henning, Klaus Hodapp, Masato Ishizuka, Hideyuki Izumiura, Shane Jacobson, Markus Janson, Eiji Kambe, Takanori Kodama, Eiichiro Kokubo, Mihoko Konishi, Vigneshwaran Krishnamurthy, Tomoyuki Kudo, Takashi Kurokawa, Nobuhiko Kusakabe, Jungmi Kwon, Yuji Matsumoto, Michael W. McElwain, Koyu Mitsui, Takao Nakagawa, Norio Narita, Jun Nishikawa, Stevanus K. Nugroho, Eugene Serabyn, Takuma Serizawa, Aoi Takahashi, Akitoshi Ueda, Taichi Uyama, Sébastien Vievard, Ji Wang, John Wisniewski, Motohide Tamura, Bun'ei Sato
May 24, 2022·astro-ph.EP·PDF 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.
Yuka Fujii, Hajime Kawahara, Yasushi Suto, Satoru Fukuda, Teruyuki Nakajima, Timothy A. Livengood, Edwin L. Turner
Feb 17, 2011·astro-ph.EP·PDF As a test-bed for future investigations of directly imaged terrestrial exoplanets, we present the recovery of the surface components of the Earth from multi-band diurnal light curves obtained with the EPOXI spacecraft. We find that the presence and longitudinal distribution of ocean, soil and vegetation are reasonably well reproduced by fitting the observed color variations with a simplified model composed of a priori known albedo spectra of ocean, soil, vegetation, snow and clouds. The effect of atmosphere, including clouds, on light scattered from surface components is modeled using a radiative transfer code. The required noise levels for future observations of exoplanets are also determined. Our model-dependent approach allows us to infer the presence of major elements of the planet (in the case of the Earth, clouds and ocean) with observations having S/N $\gtrsim 10$ in most cases and with high confidence if S/N $\gtrsim 20$. In addition, S/N $\gtrsim 100$ enables us to detect the presence of components other than ocean and clouds in a fairly model-independent way. Degradation of our inversion procedure produced by cloud cover is also quantified. While cloud cover significantly dilutes the magnitude of color variations compared to the cloudless case, the pattern of color changes remains. Therefore, the possibility of investigating surface features through light curve fitting remains even for exoplanets with cloud cover similar to the Earth's.
Takafumi Kamizuka, Hajime Kawahara, Ryou Ohsawa, Hirokazu Kataza, Daisuke Kawata, Yoshiyuki Yamada, Teruyuki Hirano, Kohei Miyakawa, Masataka Aizawa, Masashi Omiya, Taihei Yano, Ryouhei Kano, Takehiko Wada, Wolfgang Löffler, Michael Biermann, Pau Ramos, Naoki Isobe, Fumihiko Usui, Kohei Hattori, Satoshi Yoshioka, Takayuki Tatekawa, Hideyuki Izumiura, Akihiko Fukui, Makoto Miyoshi, Daisuke Tatsumi, Naoteru Gouda
JASMINE is a Japanese planned space mission that aims to reveal the formation history of our Galaxy and discover habitable exoEarths. For these objectives, the JASMINE satellite performs high-precision astrometric observations of the Galactic bulge and high-precision transit monitoring of M-dwarfs in the near-infrared (1.0-1.6 microns in wavelength). For feasibility studies, we develop an image simulation software named JASMINE-imagesim, which produces realistic observation images. This software takes into account various factors such as the optical point spread function (PSF), telescope jitter caused by the satellite's attitude control error (ACE), detector flat patterns, exposure timing differences between detector pixels, and various noise factors. As an example, we report a simulation for the feasibility study of astrometric observations using JASMINE-imagesim. The simulation confirms that the required position measurement accuracy of 4 mas for a single exposure of 12.5-mag objects is achievable if the telescope pointing jitter uniformly dilutes the PSF across all stars in the field of view. On the other hand, the simulation also demonstrates that the combination of realistic pointing jitter and exposure timing differences in the detector can significantly degrade accuracy and prevent achieving the requirement. This means that certain countermeasures against this issue must be developed. This result implies that this kind of simulation is important for mission planning and advanced developments to realize more realistic simulations help us to identify critical issues and also devise effective solutions.
Yoh Takei, Eugenio Ursino, Enzo Branchini, Takaya Ohashi, Hajime Kawahara, Kazuhisa Mitsuda, Luigi Piro, Alessandra Corsi, Lorenzo Amati, Jan-Willem den Herder, Massimiliano Galeazzi, Jelle Kaastra, Lauro Moscardini, Fabrizio Nicastro, Frits Paerels, Mauro Roncarelli, Matteo Viel
We assess the possibility to detect the warm-hot intergalactic medium (WHIM) in emission and to characterize its physical conditions and spatial distribution through spatially resolved X-ray spectroscopy, in the framework of the recently proposed DIOS, EDGE, Xenia, and ORIGIN missions, all of which are equipped with microcalorimeter-based detectors. For this purpose we analyze a large set of mock emission spectra, extracted from a cosmological hydrodynamical simulation. These mock X-ray spectra are searched for emission features showing both the OVII K alpha triplet and OVIII Ly alpha line, which constitute a typical signature of the warm hot gas. Our analysis shows that 1 Ms long exposures and energy resolution of 2.5 eV will allow us to detect about 400 such features per deg^2 with a significance >5 sigma and reveals that these emission systems are typically associated with density ~100 above the mean. The temperature can be estimated from the line ratio with a precision of ~20%. The combined effect of contamination from other lines, variation in the level of the continuum, and degradation of the energy resolution reduces these estimates. Yet, with an energy resolution of 7 eV and all these effects taken into account, one still expects about 160 detections per deg^2. These line systems are sufficient to trace the spatial distribution of the line-emitting gas, which constitute an additional information, independent from line statistics, to constrain the poorly known cosmic chemical enrichment history and the stellar feedback processes.
Kento Masuda, Sho Uehara, Hajime Kawahara
Many of the Kepler close binaries are suggested to constitute hierarchical triple systems through their eclipse timing variations (ETVs). Eclipses by the third body in those systems, if observed, provide precise constraints on its physical and orbital properties, which are otherwise difficult to obtain. In this Letter, we analyze such a "tertiary event" observed only once in the KIC 6543674 system. The system consists of a short-period ($2.4\,\mathrm{days}$) inner eclipsing binary and a third body on a wide ($1100\,\mathrm{days}$) and eccentric ($e\simeq0.6$) orbit. Analysis of three tertiary eclipses around a single inferior conjunction of the third body yields the mutual inclination between the inner and outer binary planes to be $3.3^\circ\pm0.6^\circ$, indicating an extremely flat geometry. Furthermore, combining the timings and shapes of the tertiary eclipses with the phase curve and ETVs of the inner binary, we determine the mass and radius ratios of all three bodies in the system using the Kepler photometry alone. With the primary mass and temperature from the Kepler Input Catalog, the absolute masses, radii, and effective temperatures of the three stars are obtained as follows: $M_\mathrm{A}=1.2\pm0.3\,M_\odot$, $R_\mathrm{A}=1.8\pm0.1\,R_\odot$, $M_\mathrm{B}=1.1_{-0.2}^{+0.3}\,M_\odot$, $R_\mathrm{B}=1.4\pm0.1\,R_\odot$, $M_\mathrm{C}=0.50_{-0.08}^{+0.07}\,M_\odot$, $R_\mathrm{C}=0.50\pm0.04\,R_\odot$, $T_\mathrm{A} \simeq T_\mathrm{B}\simeq 6100\,\mathrm{K}$, and $T_\mathrm{C}<5000\,\mathrm{K}$. Implication for the formation scenario of close binaries is briefly discussed.
Sho Uehara, Hajime Kawahara, Kento Masuda, Shin'ya Yamada, Masataka Aizawa
Feb 25, 2016·astro-ph.EP·PDF We visually inspected the light curves of 7557 Kepler Objects of Interest (KOIs) to search for single transit events (STEs) possibly due to long-period giant planets. We identified 28 STEs in 24 KOIs, among which 14 events are newly reported in this paper. We estimate the radius and orbital period of the objects causing STEs by fitting the STE light curves simultaneously with the transits of the other planets in the system or with the prior information on the host star density. As a result, we found that STEs in seven of those systems are consistent with Neptune- to Jupiter-sized objects of orbital periods ranging from a few to $\sim$ $20\,\mathrm{yr}$. We also estimate that $\gtrsim20\%$ of the compact multi-transiting systems host cool giant planets with periods $\gtrsim 3\,\mathrm{yr}$ on the basis of their occurrence in the KOIs with multiple candidates, assuming the small mutual inclination between inner and outer planetary orbits.
Yui Kawashima, Hajime Kawahara, Yui Kasagi, Hiroyuki Tako Ishikawa, Kento Masuda, Takayuki Kotani, Tomoyuki Kudo, Teruyuki Hirano, Masayuki Kuzuhara, Stevanus K Nugroho, John Livingston, Hiroki Harakawa, Jun Nishikawa, Masashi Omiya, Takuya Takarada, Motohide Tamura, Akitoshi Ueda
Oct 15, 2024·astro-ph.EP·PDF 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.