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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 of Gl 229 B, the first discovered T-type (T7.0p) 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). Finally, we validated current molecular line lists by leveraging the obtained high-precision, high-resolution 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.

Modeling based on differentiable programming holds great promise for astronomy, as it can employ techniques such as Hamiltonian Monte Carlo, gradient-based optimization, and other machine learning techniques. This new programming paradigm has motivated us to develop the first auto-differentiable spectrum model of exoplanets and brown dwarfs, ExoJAX (Kawahara et al. 2022). ExoJAX is designed to directly calculate cross-sections as functions of temperature and pressure, rather than interpolating tabulated data, to minimize errors in high-dispersion spectra modeling. However, its application was primarily proof-of-concept and limited to narrowband high-dispersion emission spectroscopy. In this paper, we have enhanced the differentiable opacity calculation using a new fast and memory-efficient algorithm, and have developed differentiable radiative transfer schemes, including emission, transmission, and reflection spectroscopy. These enhancements significantly expand the range of applications, as demonstrated through actual atmospheric retrievals: high-dispersion emission spectra of the brown dwarf GL229 B, medium-dispersion transmission spectra of the hot Saturn WASP-39 b from JWST, and high-dispersion reflection spectra of Jupiter. We obtained a C/O ratio for GL229 B consistent with its host star, constrained WASP-39 b's radial velocity from molecular fine structures at original resolution ($R \sim 3,000$), and estimated Jupiter's metallicity consistent with previous studies.

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.

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 $\mu$as) astrometry in the Near-Infrared (NIR) Hw-band (1.0-1.6 $\mu$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.

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.

We report a one-second-cadence wide-field survey for M-dwarf flares using the Tomo-e Gozen camera mounted on the Kiso Schmidt telescope. We detect 22 flares from M3-M5 dwarfs with rise times and amplitudes ranging from $5\, \mathrm{sec} \lesssim t_\mathrm{rise} \lesssim 100\,\mathrm{sec}$ and $0.5 \lesssim \Delta F/F_{\star} \lesssim 20$, respectively. The flare light curves mostly show steeper rises and shallower decays than those obtained from the Kepler one-minute cadence data and tend to have flat peak structures. Assuming a blackbody spectrum with temperatures of $9,000-15,000\,\mathrm{K}$, the peak luminosities and bolometric energies are estimated to be $10^{29}\,\mathrm{erg\,sec^{-1}} \lesssim L_\mathrm{peak} \lesssim 10^{31}\,\mathrm{erg\,sec^{-1}}$ and $10^{31}\,\mathrm{erg} \lesssim E_{\rm bol} \lesssim 10^{34}\,\mathrm{erg}$, which constitutes the bright end of fast optical flares for M dwarfs. We confirm that more than 90\% of the host stars of the detected flares are magnetically active based on their H$\alpha$ emission line intensities obtained by LAMOST. The estimated occurrence rate of the detected flares is $\sim 0.7$ per day per an active star, indicating they are common in magnetically active M dwarfs. We argue that the flare light curves can be explained by the chromospheric compression model; the rise time is broadly consistent with the Alfvén transit time of a magnetic loop with a length scale of $l_\mathrm{loop} \sim 10^4\,\mathrm{km}$ and a field strength of $1,000\,\mathrm{G}$, while the decay time is likely determined by the radiative cooling of the compressed chromosphere down to near the photosphere with a temperature of $\gtrsim 10,000\,\mathrm{K}$. These flares from M dwarfs could be a major contamination source for a future search of fast optical transients of unknown types.

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.

The time series of light reflected from exoplanets by future direct imaging can provide spatial information with respect to the planetary surface. We apply sparse modeling to the retrieval method that disentangles the spatial and spectral information from multi-band reflected light curves termed as spin-orbit unmixing. We use the $\ell_1$-norm and the Total Squared Variation norm as regularization terms for the surface distribution. Applying our technique to a toy model of cloudless Earth, we show that our method can infer sparse and continuous surface distributions and also unmixed spectra without prior knowledge of the planet surface. We also apply the technique to the real Earth data as observed by DSCOVR/EPIC. We determined the representative components that can be interpreted as cloud and ocean. Additionally, we found two components that resembled the distribution of land. One of the components captures the Sahara Desert, and the other roughly corresponds to vegetation although their spectra are still contaminated by clouds. Sparse modeling significantly improves the geographic retrieval, in particular, of cloud and leads to higher resolutions for other components when compared with spin-orbit unmixing using Tikhonov regularization.

Direct images of protoplanets embedded in disks around infant stars provide the key to understanding the formation of gas giant planets like Jupiter. Using the Subaru Telescope and Hubble Space Telescope, we find evidence for a jovian protoplanet around AB Aurigae orbiting at a wide projected separation (93 au), likely responsible for multiple planet-induced features in the disk. Its emission is reproducible as reprocessed radiation from an embedded protoplanet. We also identify two structures located at 430-580 au that are candidate sites of planet formation. These data reveal planet formation in the embedded phase and a protoplanet discovery at wide, > 50 au separations characteristic of most imaged exoplanets. With at least one clump-like protoplanet and multiple spiral arms, the AB Aur system may also provide the evidence for a long-considered alternative to the canonical model for Jupiter's formation: disk (gravitational) instability.

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.

To directly detect exoplanets and protoplanetary disks, the development of high accuracy wavefront sensing and control (WFS&C) technologies is essential, especially for ground-based Extremely Large Telescopes (ELTs). The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a high-contrast imaging platform to discover and characterize exoplanets and protoplanetary disks. It also serves as a testbed to validate and deploy new concepts or algorithms for high-contrast imaging approaches for ELTs, using the latest hardware and software technologies on an 8-meter class telescope. SCExAO is a multi-band instrument, using light from 600 to 2500 nm, and delivering a high Strehl ratio (>80% in median seeing in H-band) downstream of a low-order correction provided by the facility AO188. Science observations are performed with coronagraphs, an integral field spectrograph, or single aperture interferometers. The SCExAO project continuously reaches out to the community for development and upgrades. Existing operating testbeds such as the SCExAO are also unique opportunities to test and deploy the new technologies for future ELTs. We present and show a live demonstration of the SCExAO capabilities (Real-time predictive AO control, Focal plane WFS&C, etc) as a host testbed for the remote collaborators to test and deploy the new WFS&C concepts or algorithms. We also present several high-contrast imaging technologies that are under development or that have already been demonstrated on-sky.

We present an auto-differentiable spectral modeling of exoplanets and brown dwarfs. This model enables a fully Bayesian inference of the high--dispersion data to fit the ab initio line-by-line spectral computation to the observed spectrum by combining it with the Hamiltonian Monte Carlo in recent probabilistic programming languages. An open source code, exojax, developed in this study, was written in Python using the GPU/TPU compatible package for automatic differentiation and accelerated linear algebra, JAX (Bradbury et al. 2018). We validated the model by comparing it with existing opacity calculators and a radiative transfer code and found reasonable agreements of the output. As a demonstration, we analyzed the high-dispersion spectrum of a nearby brown dwarf, Luhman 16 A and found that a model including water, carbon monoxide, and $\mathrm{H_2/He}$ collision induced absorption was well fitted to the observed spectrum ($R=10^5$ and 2.28-2.30 $\mu$m). As a result, we found that $T_0=1295_{-32}^{+35}$ K at 1 bar and C/O $=0.62 \pm 0.03$, which is slightly higher than the solar value. This work demonstrates the potential of full Bayesian analysis of brown dwarfs and exoplanets as observed by high-dispersion spectrographs and also directly-imaged exoplanets as observed by high-dispersion coronagraphy.

We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the day-side of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2-m Subaru telescope. The telluric and stellar lines are removed using a de-trending algorithm, SysRem. The residuals are then cross-correlated with OH and H$_{2}$O planetary spectrum templates produced using several different line-lists. We check and confirm the accuracy of OH line-lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at $K_\mathrm{p}$ of 230.9$^{+6.9}_{-7.4}$ km s$^{-1}$ and $v_{\mathrm{sys}}$ of $-$0.3$^{+5.3}_{-5.6}$ km s$^{-1}$ with S/N of 5.4 and significance of 5.5$\sigma$. Additionally, we marginally detect H$_{2}$O emission in the H-band with S/N of 4.0 and significance of 5.2$\sigma$ using the POKAZATEL line-list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line-lists. Nonetheless, this marginal detection is consistent with the prediction that H$_{2}$O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the day-side atmosphere of ultra-hot Jupiters and should be considered when studying their atmosphere.

Recent progress in high-dispersion spectroscopy has revealed the presence of vaporized heavy metals and ions in the atmosphere of hot Jupiters whose dayside temperature is larger than 2000 K, categorized as ultra hot Jupiters (UHJs). Using the archival data of high resolution transmission spectroscopy obtained with the Subaru telescope, we searched for neutral metals in HD149026b, a hot Jupiter cooler than UHJs. By removing stellar and telluric absorption and using a cross-correlation technique, we report tentative detection of neutral titanium with 4.4 sigma and a marginal signal of neutral iron with 2.8 sigma in the atmosphere. This is the first detection of neutral titanium in an exoplanetary atmosphere. In this temperature range, titanium tends to form titanium oxide (TiO). The fact that we did not detect any signal from TiO suggests that the C/O ratio in the atmosphere is higher than the solar value. The detection of metals in the atmosphere of hot Jupiters cooler than UHJs will be useful for understanding the atmospheric structure and formation history of hot Jupiters.

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.

Photometric variability of a directly imaged exo-Earth conveys spatial information on its surface and can be used to retrieve a two-dimensional geography and axial tilt of the planet (spin-orbit tomography). In this study, we relax the assumption of the static geography and present a computationally tractable framework for dynamic spin-orbit tomography applicable to the time-varying geography. First, a Bayesian framework of static spin-orbit tomography is revisited using analytic expressions of the Bayesian inverse problem with a Gaussian prior. We then extend this analytic framework to a time-varying one through a Gaussian process in time domain, and present analytic expressions that enable efficient sampling from a full joint posterior distribution of geography, axial tilt, spin rotation period, and hyperparameters in the Gaussian-process priors. Consequently, it only takes 0.3 s for a laptop computer to sample one posterior dynamic map conditioned on the other parameters with 3,072 pixels and 1,024 time grids, for a total of $\sim 3 \times 10^6$ parameters. We applied our dynamic mapping method on a toy model and found that the time-varying geography was accurately retrieved along with the axial-tilt and spin rotation period. In addition, we demonstrated the use of dynamic spin-orbit tomography with a real multi-color light curve of the Earth as observed by the Deep Space Climate Observatory. We found that the resultant snapshots from the dominant component of a principle component analysis roughly captured the large-scale, seasonal variations of the clear-sky and cloudy areas on the Earth.

We analyze the high-resolution emission spectrum of WASP-33b taken using the High Dispersion Spectrograph (R\,$\approx$\u2009165,000) on the 8.2-m Subaru telescope. The data cover $\lambda$\,$\approx$\,$6170$-$8817$\u2009Å, 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-$\sigma$ located at $K_{\mathrm{p}}$ of 226.0\,$^{+2.1}_{-2.3}$\u2009km\u2009s$^{-1}$and $v_{\mathrm{sys}}$ of -3.2\,$^{+2.1}_{-1.8}$\u2009km\u2009s$^{-1}$ -- 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.

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.

Photometric variation of a directly imaged planet contains information on both the geography and spectra of the planetary surface. We propose a novel technique that disentangles the spatial and spectral information from the multi-band reflected light curve. This will enable us to compose a two-dimensional map of the surface composition of a planet with no prior assumption on the individual spectra, except for the number of independent surface components. We solve the unified inverse problem of the spin-orbit tomography and spectral unmixing by generalizing the non-negative matrix factorization (NMF) using a simplex volume minimization method. We evaluated our method on a toy cloudless Earth and observed that the new method could accurately retrieve the geography and unmix spectral components. Furthermore, our method is also applied to the real-color variability of the Earth as observed by Deep Space Climate Observatory (DSCOVR). The retrieved map explicitly depicts the actual geography of the Earth and unmixed spectra capture features of the ocean, continents, and clouds. It should be noted that, the two unmixed spectra consisting of the reproduced continents resemble those of soil and vegetation.

We develop a new retrieval scheme for obtaining two-dimensional surface maps of exoplanets from scattered light curves. In our scheme, the combination of the L1-norm and Total Squared Variation, which is one of the techniques used in sparse modeling, is adopted to find the optimal map. We apply the new method to simulated scattered light curves of the Earth, and find that the new method provides a better spatial resolution of the reconstructed map than those using Tikhonov regularization. We also apply the new method to observed scattered light curves of the Earth obtained during the two-year DSCOVR/EPIC observations presented by Fan et al. (2019). The method with Tikhonov regularization enables us to resolve North America, Africa, Eurasia, and Antarctica. In addition to that, the sparse modeling identifies South America and Australia, although it fails to find the Antarctica maybe due to low observational weights on the poles. Besides, the proposed method is capable of retrieving maps from noise injected light curves of a hypothetical Earth-like exoplanet at 5 pc with noise level expected from coronagraphic images from a 8-m telescope. We find that the sparse modeling resolves Australia, Afro-Eurasia, North America, and South America using 2-year observation with a time interval of one month. Our study shows that the combination of sparse modeling and multi-epoch observation with 1 day or 5 days per month can be used to identify main features of an Earth analog in future direct imaging missions such as the Large UV/Optical/IR Surveyor (LUVOIR).

We analyse the transmission spectra of KELT-20b/MASCARA-2b to search for possible thermal inversion agents. The data consist of three transits obtained using HARPSN and one using CARMENES. We removed stellar and telluric lines before cross-correlating the residuals with spectroscopic templates produced using a 1D plane-parallel model assuming an isothermal atmosphere and chemical equilibrium at solar metallicity. Using a likelihood-mapping method, we detect Fe\,\sc i at $>$ 13-$\sigma$, Ca\,\sc ii H$\&$K at $>$ 6-$\sigma$ and confirm the previous detections of Fe\,\sc ii, Ca\,\sc ii IRT and Na\,\sc i D. The detected signal of Fe\,\sc i is shifted by -3.4$\pm$0.4 km s$^{-1}$ from the planetary rest frame, which indicates a strong day-night wind. Our likelihood-mapping technique also reveals that the absorption features of the detected species extend to different altitudes in the planet's atmosphere. Assuming that the line lists are accurate, we do not detect other potential thermal inversion agents (NaH, MgH, AlO, SH, CaO, VO, FeH and TiO) suggesting that non-chemical equilibrium mechanisms (e.g. a cold-trap) might have removed Ti- and V-bearing species from the upper atmosphere. Our results, therefore, shows that KELT-20b/MASCARA-2b cannot possess an inversion layer caused by a TiO/VO-related mechanism. The presence of an inversion layer would therefore likely be caused by metal atoms such as Fe\,\sc i and Fe\,\sc ii. Finally, we report a double-peak structure in the Fe\,\sc i signal in all of our data-sets that could be a signature of atmospheric dynamics. However, further investigation is needed to robustly determine the origin of the signal.

In Kawahara et al. (2018) and Masuda et al. (2019), we reported the discovery of four self-lensing binaries consisting of F/G-type stars and (most likely) white dwarfs whose masses range from 0.2 to 0.6 solar masses. Here we present their updated system parameters based on new radial velocity data from the Tillinghast Reflector Echelle Spectrograph at the Fred Lawrence Whipple Observatory, and the Gaia parallaxes and spectroscopic parameters of the primary stars. We also briefly discuss the astrophysical implications of these findings.

Previous analyses of Doppler and Kepler data have found that Sun-like stars hosting "cold Jupiters" (giant planets with $a\gtrsim 1\,\mathrm{AU}$) almost always host "inner super-Earths" (1-$4\,R_\oplus$, $a\lesssim1\,\mathrm{AU}$). Here, we attempt to determine the degree of alignment between the orbital planes of the cold Jupiters and the inner super-Earths. The key observational input is the fraction of Kepler stars with transiting super-Earths that also have transiting cold Jupiters. This fraction depends on both the probability for cold Jupiters to occur in such systems, and on the mutual orbital inclinations. Since the probability of occurrence has already been measured in Doppler surveys, we can use the data to constrain the dispersion of the mutual inclination distribution. We find $\sigma=11.8^{+12.7}_{-5.5}\,\mathrm{deg}$ (68% confidence) and $\sigma>3.5\,\mathrm{deg}$ (95% confidence), where $\sigma$ is the scale parameter of the Rayleigh distribution. This suggests that planetary orbits in systems with cold Jupiters tend to be coplanar - although not quite as coplanar as those in the Solar System, which have a mean inclination from the invariable plane of $1.8\,\mathrm{deg}$. We also find evidence that cold Jupiters have lower mutual inclinations relative to inner systems with higher transit multiplicity. This suggests a link between the dynamical excitation in the inner and outer systems. For example, perturbations from misaligned cold Jupiters may dynamically heat or destabilize systems of inner super-Earths.

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.

We present a comprehensive catalog of cool (period $P\gtrsim 2\,\mathrm{yr}$) transiting planet candidates in the four-year light curves from the prime \kepler mission. Most of the candidates show only one or two transits and have largely been missed in the original Kepler Object of Interest catalog. Our catalog is based on all known such candidates in the literature as well as new candidates from the search in this paper, and provides a resource to explore the planet population near the snow line of Sun-like stars. We homogeneously performed pixel-level vetting, stellar characterization with GAIA parallax and archival/Subaru spectroscopy, and light-curve modeling to derive planet parameters and to eliminate stellar binaries. The resulting clean sample consists of 67 planet candidates whose radii are typically constrained to 5\%, in which 23 are newly reported. The number of Jupiter-sized candidates (29 with $r>8\,R_\oplus$) in the sample is consistent with the Doppler occurrence. The smaller candidates are more prevalent (23 with $4<r/R_\oplus<8$, 15 with $r/R_\oplus<4$) and suggest that long-period Neptune-sized planets are at least as common as the Jupiter-sized ones, although our sample is yet to be corrected for detection completeness. If the sample is assumed to be complete, these numbers imply the occurrence rate of $0.39\pm0.07$ planets with $4<r/R_\oplus<14$ and $2<P/\mathrm{yr}<20$ per FGK dwarf. The stars hosting candidates with $r>4\,R_\oplus$ have systematically higher [Fe/H] than the Kepler field stars, providing evidence that giant planet--metallicity correlation extends to $P>2\,\mathrm{yr}$.

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.

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).

We present an X-ray spectral analysis of the nearby double radio relic merging cluster Abell 3376 ($z$ = 0.046), observed with the $Suzaku$ XIS instrument. These deep ($\sim$360 ks) observations cover the entire double relic region in the outskirts of the cluster. These diffuse radio structures are amongst the largest and arc-shaped relics observed in combination with large-scale X-ray shocks in a merging cluster. We confirm the presence of a stronger shock (${\cal M}_{\rm{W}}$ = 2.8 $\pm~0.4$) in the western direction at $r\sim26$', derived from a temperature and surface brightness discontinuity across the radio relic. In the East, we detect a weaker shock (${\cal M}_{\rm{E}}$ = 1.5 $\pm~0.1$) at $r\sim8$', possibly associated to the 'notch' of eastern relic, and a cold front at $r\sim3$'. Based on the shock speed calculated from the Mach numbers, we estimate that the dynamical age of the shock front is $\sim$0.6 Gyr after core passage, indicating that Abell 3376 is still an evolving merging cluster and that the merger is taking place close to the plane of the sky. These results are consistent with simulations and optical and weak lensing studies from the literature.

We report the discovery of three edge-on binaries with white dwarf companions that gravitationally magnify (instead of eclipsing) the light of their stellar primaries, as revealed by a systematic search for pulses with long periods in the Kepler photometry. We jointly model the self-lensing light curves and radial-velocity orbits to derive the white dwarf masses, all of which are close to 0.6 Solar masses. The orbital periods are long, ranging from 419 to 728 days, and the eccentricities are low, all less than 0.2. These characteristics are reminiscent of the orbits found for many blue stragglers in open clusters and the field, for which stable mass transfer due to Roche-lobe overflow from an evolving primary (now a white dwarf) has been proposed as the formation mechanism. Because the actual masses for our three white dwarf companions have been accurately determined, these self-lensing systems would provide excellent tests for models of interacting binaries.

A suite of science instruments is critical to any high contrast imaging facility, as it defines the science capabilities and observing modes available. SCExAO uses a modular approach which allows for state-of-the-art visitor modules to be tested within an observatory environment on an 8-m class telescope. This allows for rapid prototyping of new and innovative imaging techniques that otherwise take much longer in traditional instrument design. With the aim of maturing science modules for an advanced high contrast imager on an giant segmented mirror telescopes (GSMTs) that will be capable of imaging terrestrial planets, we offer an overview and status update on the various science modules currently under test within the SCExAO instrument.

Spectroscopic observations are extremely important for determining the composition, structure, and surface gravity of exoplanetary atmospheres. High resolution spectroscopy of the planet itself has only been demonstrated a handful of times. By using advanced high contrast imagers, it is possible to conduct high resolution spectroscopy on imageable exoplanets, after the star light is first suppressed with an advanced coronagraph. Because the planet is spatially separated in the focal plane, a single mode fiber could be used to collect the light from the planet alone, reducing the photon noise by orders of magnitude. In addition, speckle control applied to the location where an exoplanet is known to exist, can be used to preferentially reject the stellar flux from the fiber further. In this paper we will present the plans for conducting high resolution spectroscopic studies of this nature with the combination of SCExAO and IRD in the H-band on the Subaru Telescope. This technique will be critical to the characterization of terrestrial planets on ELTs and future space missions.

We promote the precise gamma-ray observation project Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE), which uses balloon-borne emulsion gamma-ray telescopes. The emulsion telescope realizes observations with high angular resolution, polarization sensitivity, and large aperture area in the 0.01--100 GeV energy region. Herein, we report the data analysis of emulsion tracks and the first demonstration of gamma-ray imaging via an emulsion telescope by using the flight data from the balloon experiment performed in 2015 (GRAINE 2015). The emulsion films were scanned by the latest read-out system for a total area of 41 m$^2$ in three months, and then the gamma-ray event selection was automatically processed. Millions of electron-pair events are accumulated in the balloon-borne emulsion telescope. The emulsion telescope detected signals from a calibration source (gamma rays from the interaction of cosmic rays with an aluminum plate) with a high significance during the balloon observation and created a gamma-ray image consistent with the source size and the expected angular resolution in the energy range of 100--300 MeV. The flight performance obtained in the GRAINE 2015 experiment proves that balloon-borne emulsion telescope experiments with larger area are feasible while maintaining expected imaging performance.

We report high-resolution spectroscopic detection of TiO molecular signature in the day-side spectra of WASP-33 b, the second hottest known hot Jupiter. We used High-Dispersion Spectrograph (HDS; R $\sim$ 165,000) in the wavelength range of 0.62 -- 0.88 $\mu$m with the Subaru telescope to obtain the day-side spectra of WASP-33 b. We suppress and correct the systematic effects of the instrument, the telluric and stellar lines by using SYSREM algorithm after the selection of good orders based on Barnard star and other M-type stars. We detect a 4.8-$\sigma$ signal at an orbital velocity of $K_{p}$= +237.5 $^{+13.0}_{-5.0}$ km s$^{-1}$ and systemic velocity $V_{sys}$= -1.5 $^{+4.0} _{-10.5}$ km s$^{-1}$, which agree with the derived values from the previous analysis of primary transit. Our detection with the temperature inversion model implies the existence of stratosphere in its atmosphere, however, we were unable to constrain the volume-mixing ratio of the detected TiO. We also measure the stellar radial velocity and use it to obtain a more stringent constraint on the orbital velocity, $K_{p} = 239.0^{+2.0}_{-1.0}$ km s$^{-1}$. Our results demonstrate that high-dispersion spectroscopy is a powerful tool to characterize the atmosphere of an exoplanet, even in the optical wavelength range, and show a promising potential in using and developing similar techniques with high-dispersion spectrograph on current 10m-class and future extremely large telescopes.

We present the results of Suzaku and Chandra observations of the galaxy cluster RXC J1053.7+5453 ($z=0.0704$), which contains a radio relic. The radio relic is located at the distance of $\sim 540$ kpc from the X-ray peak toward the west. We measured the temperature of this cluster for the first time. The resultant temperature in the center is $ \sim 1.3$ keV, which is lower than the value expected from the X-ray luminosity - temperature and the velocity dispersion - temperature relation. Though we did not find a significant temperature jump at the outer edge of the relic, our results suggest that the temperature decreases outward across the relic. Assuming the existence of the shock at the relic, its Mach number becomes $M \simeq 1.4 $. A possible spatial variation of Mach number along the relic is suggested. Additionally, a sharp surface brightness edge is found at the distance of $\sim 160$ kpc from the X-ray peak toward the west in the Chandra image. We performed X-ray spectral and surface brightness analyses around the edge with Suzaku and Chandra data, respectively. The obtained surface brightness and temperature profiles suggest that this edge is not a shock but likely a cold front. Alternatively, it cannot be ruled out that thermal pressure is really discontinuous across the edge. In this case, if the pressure across the surface brightness edge is in equilibrium, other forms of pressure sources, such as cosmic-rays, are necessary. We searched for the non-thermal inverse Compton component in the relic region. Assuming the photon index $ \Gamma = 2.0$, the resultant upper limit of the flux is $1.9 \times 10^{-14} {\rm erg \ s^{-1} \ cm^{-2}}$ for $4.50 \times 10^{-3} {\rm \ deg^{2}}$ area in the 0.3-10 keV band, which implies that the lower limit of magnetic field strength becomes $ 0.7 {\rm \ \mu G}$.

Multicore fibers are gaining growing attention in astronomy. The two main attributes which make them attractive for astronomy are that they reduce the distance between cores and hence have a superior fill factor to other approaches and they offer the possibility to transport light in many channels with the overhead of only having to handle a single fiber. These properties are being exploited to realize miniature integral field units that can transport light from different regions in a focal plane to a spectrograph for example. Here we offer an overview of several applications where multicore fibers are now being considered and applied to astronomical observations to enhance scientific yield.

Detection of a planetary ring of exoplanets remains as one of the most attractive but challenging goals in the field. We present a methodology of a systematic search for exoplanetary rings via transit photometry of long-period planets. The methodology relies on a precise integration scheme we develop to compute a transit light curve of a ringed planet. We apply the methodology to 89 long-period planet candidates from the Kepler data so as to estimate, and/or set upper limits on, the parameters of possible rings. While a majority of our samples do not have a sufficiently good signal-to-noise ratio for meaningful constraints on ring parameters, we find that six systems with a higher signal-to-noise ratio are inconsistent with the presence of a ring larger than 1.5 times the planetary radius assuming a grazing orbit and a tilted ring. Furthermore, we identify five preliminary candidate systems whose light curves exhibit ring-like features. After removing four false positives due to the contamination from nearby stars, we identify KIC 10403228 as a reasonable candidate for a ringed planet. A systematic parameter fit of its light curve with a ringed planet model indicates two possible solutions corresponding to a Saturn-like planet with a tilted ring. There also remain other two possible scenarios accounting for the data; a circumstellar disk and a hierarchical triple. Due to large uncertain factors, we cannot choose one specific model among the three.

We present the results of deep 140 ks Suzaku X-ray observations of the north-east (NE) radio relic of the merging galaxy cluster Abell2255. The temperature structure of Abell2255 is measured out to 0.9 times the virial radius (1.9 Mpc) in the NE direction for the first time. The Suzaku temperature map of the central region suggests a complex temperature distribution, which agrees with previous work. Additionally, on a larger-scale, we confirm that the temperature drops from 6 keV around the cluster center to 3 keV at the outskirts, with two discontinuities at \it r$\sim$5\arcmin~(450 kpc) and $\sim$12\arcmin~(1100 kpc) from the cluster center. Their locations coincide with surface brightness discontinuities marginally detected in the XMM-Newton image, which indicates the presence of shock structures. From the temperature drop, we estimate the Mach numbers to be ${\cal M}_{\rm inner}\sim$1.2 and, ${\cal M}_{\rm outer}\sim$1.4. The first structure is most likely related to the large cluster core region ($\sim$350--430 kpc), and its Mach number is consistent with the XMM-Newton observation (${\cal M}\sim$1.24: Sakelliou & Ponman 2006). Our detection of the second temperature jump, based on the Suzaku key project observation, shows the presence of a shock structure across the NE radio relic. This indicates a connection between the shock structure and the relativistic electrons that generate radio emission. Across the NE radio relic, however, we find a significantly lower temperature ratio ($T_1/T_2\sim1.44\pm0.16$ corresponds to~${\cal M}_{\rm X-ray}\sim1.4$) than the value expected from radio wavelengths, based on the standard diffusive shock acceleration mechanism ($T_1/T_2>$ 3.2 or ${\cal M}_{\rm Radio}>$ 2.8).

We consider the time-frequency analysis of a scattered light curve of a directly imaged exoplanet. We show that the geometric effect due to planetary obliquity and orbital inclination induce the frequency modulation of the apparent diurnal periodicity. We construct a model of the frequency modulation and compare it with the instantaneous frequency extracted from the pseudo-Wigner distribution of simulated light curves of a cloudless Earth. The model provides good agreement with the simulated modulation factor, even for the light curve with Gaussian noise comparable to the signal. Notably, the shape of the instantaneous frequency is sensitive to the difference between the prograde, retrograde, and pole-on spin rotations. While our technique requires the albedo map to be static, it does not need to solve the albedo map of the planet. The time-frequency analysis is complementary to other methods which utilize the amplitude modulation. This paper demonstrates the importance of the frequency domain of the photometric variability for the characterization of directly imaged exoplanets in future research.

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.

We present the results of Suzaku observations of the galaxy cluster 1RXS J0603.3+4214 with "toothbrush" radio relic. Although a shock with Mach number $M \simeq 4$ is expected at the outer edge of the relic from the radio observation, our temperature measurements of the intracluster medium indicate a weaker temperature difference than what is expected. The Mach number estimated from the temperature difference at the outer edge of the relic is $M \simeq 1.5$, which is significantly lower than the value estimated from the radio data even considering both statistical and systematic errors. This suggests that a diffusive shock acceleration theory in the linear test particle regime, which is commonly used to link the radio spectral index to the Mach number, is invalid for this relic. We also measured the temperature difference across the western part of the relic, where a shock with $M \simeq 1.6$ is suggested from the X-ray surface brightness analysis of the XMM-Newton data, and obtained consistent results in an independent way. We searched for the non-thermal inverse Compton component in the relic region and the resultant upper limit on the flux is $2.4 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the 0.3-10 keV band. The lower limit of the magnetic field strength becomes 1.6 $\mu$G, which means that magnetic energy density could be more than a few $\% $ of the thermal energy.

Content: We present the results from $Suzaku$ observations of the merging cluster of galaxies CIZA J2242.8+5301 at $z$=0.192. Aims. To study the physics of gas heating and particle acceleration in cluster mergers, we investigated the X-ray emission from CIZA J2242.8+5301, which hosts two giant radio relics in the northern/southern part of the cluster. Methods. We analyzed data from three-pointed Suzaku observations of CIZA J2242.8+5301 to derive the temperature distribution in four different directions. Results: The Intra-Cluster Medium (ICM) temperature shows a remarkable drop from 8.5$_{-0.6}^{+0.8}$ keV to 2.7$_{-0.4}^{+0.7}$ keV across the northern radio relic. The temperature drop is consistent with a Mach number ${\cal M}_n=2.7^{+0.7}_{-0.4}$ and a shock velocity $v_{shock:n}=2300_{-400}^{+700}\rm\,km\,s^{-1}$. We also confirm the temperature drop across the southern radio relic. However, the ICM temperature beyond this relic is much higher than beyond the northern one, which gives a Mach number ${\cal M}_s=1.7^{+0.4}_{-0.3}$ and shock velocity $v_{shock:s}=2040_{-410}^{+550}\rm \,km\,s^{-1}$. These results agree with other systems showing a relationship between the radio relics and shock fronts which are induced by merging activity. We compare the X-ray derived Mach numbers with the radio derived Mach numbers from the radio spectral index under the assumption of diffusive shock acceleration in the linear test particle regime. For the northern radio relic, the Mach numbers derived from X-ray and radio observations agree with each other. Based on the shock velocities, we estimate that CIZA J2242.8+5301 is observed approximately 0.6 Gyr after core passage. The magnetic field pressure at the northern relic is estimated to be 9% of the thermal pressure.

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.

We present the thermal evolution and emergent spectra of solidifying terrestrial planets along with the formation of steam atmospheres. The lifetime of a magma ocean and its spectra through a steam atmosphere depends on the orbital distance of the planet from the host star. For a type-I planet, which is formed beyond a certain critical distance from the host star, the thermal emission declines on a timescale shorter than approximately $10^6$ years. Therefore, young stars should be targets when searching for molten planets in this orbital region. In contrast, a type-II planet, which is formed inside the critical distance, will emit significant thermal radiation from near-infrared atmospheric windows during the entire lifetime of the magma ocean. The Ks and L bands will be favorable for future direct imaging because the planet-to-star contrasts of these bands are higher than approximately 10$^{-7}$-10$^{-8}$. Our model predicts that, in the type-II orbital region, molten planets would be present over the main sequence of the G-type host star if the initial bulk content of water exceeds approximately 1 wt%. In visible atmospheric windows, the contrasts of the thermal emission drop below $10^{-10}$ in less than $10^5$ years, whereas those of the reflected light remain $10^{-10}$ for both types of planets. Since the contrast level is comparable to those of reflected light from Earth-sized planets in the habitable zone, the visible reflected light from molten planets also provides a promising target for direct imaging with future ground- and space-based telescopes.

Motivated by recent detection of transiting high-density super-Earths, we explore the detectability of hot rocky super-Earths orbiting very close to their host stars. In the environment hot enough for their rocky surfaces to be molten, they would have the atmosphere composed of gas species from the magma oceans. In this study, we investigate the radiative properties of the atmosphere that is in the gas/melt equilibrium with the underlying magma ocean. Our equilibrium calculations yield Na, K, Fe, Si, SiO, O, and O$_2$ as the major atmospheric species. We compile the radiative-absorption line data of those species available in literature, and calculate their absorption opacities in the wavelength region of 0.1--100~$\mathrm{\mu m}$. Using them, we integrate the thermal structure of the atmosphere. Then, we find that thermal inversion occurs in the atmosphere because of the UV absorption by SiO. In addition, we calculate the ratio of the planetary to stellar emission fluxes during secondary eclipse, and find prominent emission features induced by SiO at 4~$\mathrm{\mu m}$ detectable by Spitzer, and those at 10 and 100~$\mathrm{\mu m}$ detectable by near-future space telescopes.

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 $\sigma$ and 16 $\sigma$ levels, respectively, for $T_\star$=3000 K. The raw contrast of $10^{-5}$ is required for a 6 $\sigma$ detection of the oxygen 1.27 $\mu$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.

We propose the application of coronagraphic techniques to the spectroscopic direct detection of exoplanets via the Doppler shift of planetary molecular lines. Even for an unresolved close-in planetary system, we show that the combination of a visible nuller and an extreme adaptive optics system can reduce the photon noise of a main star and increase the total signal-to-noise ratio (S/N) of the molecular absorption of the exoplanetary atmosphere: it works as a spectroscopic coronagraph. Assuming a 30 m telescope, we demonstrate the benefit of these high-contrast instruments for nearby close-in planets that mimic 55 Cnc b ($0.6 \lambda/D$ of the angular separation in the K band). We find that the tip-tilt error is the most crucial factor; however, low-order speckles also contribute to the noise. Assuming relatively conservative estimates for future wavefront control techniques, the spectroscopic coronagraph can increase the contrast to $ \sim 50-130 $ times and enable us to obtain $\sim 3-6 $ times larger S/N for warm Jupiters and Neptunes at 10 pc those without it. If the tip-tilt error can be reduced to $\lesssim 0.3$ mas (rms), it gains $\sim 10-30$ times larger S/N and enables us to detect warm super-Earths with an extremely large telescope. This paper demonstrates the concept of spectroscopic coronagraphy for future spectroscopic direct detection. Further studies of the selection of coronagraphs and tip-tilt sensors will extend the range of application of the spectroscopic direct detection beyond the photon collecting area limit.

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.

Violent variation of transit depths and an ingress-egress asymmetry of the transit light curve discovered in KIC 12557548 have been interpreted as evidences of a catastrophic evaporation of atmosphere with dust (M_p gtrsim 1 M_oplus/Gyr) from a close-in small planet. To explore what drives the anomalous atmospheric escape, we perform time-series analysis of the transit depth variation of Kepler archival data for ~ 3.5 yr. We find a ~ 30% periodic variation of the transit depth with P1 = 22.83 pm 0.21 days, which is within the error of the rotation period of the host star estimated using the light curve modulation, Prot = 22.91 pm 0.24 days. We interpret the results as evidence that the atmospheric escape of KIC 12557548b correlates with stellar activity. We consider possible scenarios that account for both the mass loss rate and the correlation with stellar activity. X-ray and ultraviolet (XUV)-driven evaporation is possible if one accepts a relatively high XUV flux and a high efficiency for converting the input energy to the kinetic energy of the atmosphere. Star-planet magnetic interaction is another possible scenario though huge uncertainty remains for the mass loss rate.

We examine the validity of the hydrostatic equilibrium (HSE) assumption for galaxy clusters using one of the highest-resolution cosmological hydrodynamical simulations. We define and evaluate several effective mass terms corresponding to the Euler equations of the gas dynamics, and quantify the degree of the validity of HSE in terms of the mass estimate. We find that the mass estimated under the HSE assumption (the HSE mass) deviates from the true mass by up to ~ 30 %. This level of departure from HSE is consistent with the previous claims, but our physical interpretation is rather different. We demonstrate that the inertial term in the Euler equations makes a negligible contribution to the total mass, and the overall gravity of the cluster is balanced by the thermal gas pressure gradient and the gas acceleration term. Indeed the deviation from the HSE mass is well explained by the acceleration term at almost all radii. We also clarify the confusion of previous work due to the inappropriate application of the Jeans equations in considering the validity of HSE from the gas dynamics extracted from cosmological hydrodynamical simulations.

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-2 keV with high spectral resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.

We consider the effect of planetary spin on the planetary radial velocity (PRV) in dayside spectra of exoplanets. To understand the spin effect qualitatively, we derive an analytic formula of the intensity-weighted radial velocity from planetary surface on the following assumptions: 1) constant and solid rotation without precession, 2) stable and uniform distribution of molecules/atoms, 3) emission models from dayside hemisphere, and 4) a circular orbit. On these assumptions, we find that the curve of the PRV is distorted by the planetary spin and this anomaly is characterized by spin radial velocity at equator and a projected angle on a celestial plane between the spin axis and the axis of orbital motion \lambda_p in a manner analogous to the Rossiter-McLaughlin effect. The latter can constrain the planetary obliquity. Creating mock PRV data with 3 km/s accuracy, we demonstrate how \lambda_p and the spin radial velocity at equator are estimated. We find that the stringent constraint of eccentricity is crucial to detect the spin effect. Though our formula is still qualitative, we conclude that the PRV in the dayside spectra will be a powerful means for constraining the planetary spin.

The oxygen absorption line imprinted in the scattered light from the Earth-like planets has been considered the most promising metabolic biomarker of the exo-life. We examine the feasibility of the detection of the 1.27 micron oxygen band from habitable exoplanets, in particular, around late- type stars observed with a future instrument on a 30 m class ground-based telescope. We analyzed the night airglow around 1.27 micron with IRCS/echelle spectrometer on Subaru and found that the strong telluric emission from atmospheric oxygen molecules declines by an order of magnitude by midnight. By compiling nearby star catalogs combined with the sky background model, we estimate the detectability of the oxygen absorption band from an Earth twin, if it exists, around nearby stars. We find that the most dominant source of photon noise for the oxygen 1.27 micron band detection comes from the night airglow if the contribution of the stellar PSF halo is suppressed enough to detect the planet. We conclude that the future detectors for which the detection contrast is limited by photon noise can detect the oxygen 1.27 micron absorption band of the Earth twins for ~50 candidates of the late type star. This paper demonstrates the importance of deploying small inner working angle efficient coronagraph and extreme adaptive optics on extremely large telescopes, and clearly shows that doing so will enable study of potentially habitable planets.

We report near-infrared measurements of the terminator region transmission spectrum and dayside emission spectrum of the exoplanet WASP-12b obtained using the HST WFC3 instrument. The disk-average dayside brightness temperature averages about 2900 K, peaking to 3200 K around 1.46 microns. We modeled a range of atmospheric cases for both the emission and transmission spectrum and confirm the recent finding by Crossfield et al. (2012b) that there is no evidence for C/O >1 in the atmosphere of WASP-12b. Assuming a physically plausible atmosphere, we find evidence that the presence of a number of molecules is consistent with the data, but the justification for inclusion of these opacity sources based on the Bayesian Information Criterion (BIC) is marginal. We also find the near-infrared primary eclipse light curve is consistent with small amounts of prolate distortion. As part of the calibration effort for these data, we conducted a detailed study of instrument systematics using 65 orbits of WFC3-IR grims observations. The instrument systematics are dominated by detector-related affects, which vary significantly depending on the detector readout mode. The 256x256 subarray observations of WASP 12 produced spectral measurements within 15% of the photon-noise limit using a simple calibration approach. Residual systematics are estimated to be less than 70 parts per million.

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.

We perform a systematic X-ray analysis of six giant radio relics in four clusters of galaxies using the Suzaku satellite. The sample includes CIZA 2242.8-5301, Zwcl 2341.1-0000, the South-East part of Abell 3667 and previously published results of the North-West part of Abell 3667 and Abell 3376. Especially we first observed the narrow (50 kpc) relic of CIZA 2242.8-5301 by Suzaku satellite, which enable us to reduce the projection effect. We report X-ray detections of shocks at the position of the relics in CIZA2242.8-5301 and Abell 3667 SE. At the position of the two relics in ZWCL2341.1-0000, we do not detect shocks. From the spectroscopic temperature profiles across the relic, we find that the temperature profiles exhibit significant jumps across the relics for CIZA 2242.8-5301, Abell 3376, Abell 3667NW, and Abell 3667SE. We estimated the Mach number from the X-ray temperature or pressure profile using the Rankine-Hugoniot jump condition and compared it with the Mach number derived from the radio spectral index. The resulting Mach numbers (M=1.5-3) are almost consistent with each other, while the Mach number of CIZA2242 derived from the X-ray data tends to be lower than that of the radio observation. These results indicate that the giant radio relics in merging clusters are related to the shock structure, as suggested by previous studies of individual clusters.

We develop an inversion technique of annual scattered light curves to sketch a two-dimensional albedo map of exoplanets in face-on orbits. As a test-bed for future observations of extrasolar terrestrial planets, we apply this mapping technique to simulated light curves of a mock Earth-twin at a distance of 10 pc in a face-on circular orbit. A primary feature in recovered albedo maps traces the annual mean distribution of clouds. To extract information of other surface types, we attempt to reduce the cloud signal by taking difference of two bands. We find that the inversion of reflectivity difference between 0.8-0.9 and 0.4-0.5 micron bands roughly recover the continental distribution, except for high latitude regions persistently covered with clouds and snow. The inversion of the reflectivity difference across the red edge (0.8-0.9 and 0.6-0.7 micron) emphasizes the vegetation features near the equator. The planetary obliquity and equinox can be estimated simultaneously with the mapping under the presence of clouds. We conclude that the photometric variability of the scattered light will be a powerful means for exploring the habitat of a second Earth.

ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z=10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z ~ 0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs.

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.

We report on a new merging group of galaxies, Suzaku J1552+2739 at z ~ 0.08 revealed by a SUZAKU observation. The group was found by observing a junction of galaxy filaments optically identified in the Sloan Digital Sky Survey spectroscopic data. Suzaku J1552+2739 exhibits an irregular morphology and presents several peaks in its X-ray image. A bright elliptical galaxy, observable in the central peak, allows the localization of the group at z = 0.083. We found a significant hot spot visible in the X-ray hardness map, close to the second peak. The spectroscopic temperature is T = 1.6+0.4-0.1 keV within R500 = 0.6 Mpc and T = 3 - 5 keV in the hot spot. We interpret those results as Suzaku J1552+2739 being located in the center of a major merging process. The observation of a galaxy group showing multiple X-ray peaks and a hot spot at the same time is rare and we believe in particular that the study of Suzaku J1552+2739 potentially presents a significant interest to better understand the dynamical and thermal evolution of the intragroup and intracluster medium, as well as its relation with surrounding environment.

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.

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.

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.

Scattered lights from terrestrial exoplanets provide valuable information about the planetary surface. Applying the surface reconstruction method proposed by Fujii et al. (2010) to both diurnal and annual variations of the scattered light, we develop a reconstruction method of land distribution with both longitudinal and latitudinal resolutions. We find that one can recover a global map of an idealized Earth-like planet on the following assumptions: 1) cloudless, 2) a face-on circular orbit, 3) known surface types and their reflectance spectra 4) no atmospheric absorption, 5) known rotation rate 6) static map, and 7) no moon. Using the dependence of light curves on the planetary obliquity, we also show that the obliquity can be measured by adopting the chi-square minimization or the extended information criterion. We demonstrate a feasibility of our methodology by applying it to a multi-band photometry of a cloudless model Earth with future space missions such as the occulting ozone observatory (O3). We conclude that future space missions can estimate both the surface distribution and the obliquity at least for cloudless Earth-like planets within 5 pc.

Characterizing the surfaces of rocky exoplanets via the scattered light will be an essential challenge to investigate the existence of life on habitable exoplanets. We present a simple reconstruction method for fractional areas of different surface types from photometric variations, or colors, of a second Earth. We create mock light curves for Earth without clouds using empirical data. Then these light curves are fitted to the isotropic scattering model consisting of 4 surface types: ocean, soil, snow and vegetation. In an idealized situation where the photometric errors are only photon shot noise, we are able to reproduce the fractional areas of those components fairly well. We may be even able to detect a signature of vegetation from the distinct feature of photosynthesis on the Earth, known as the red edge. In our reconstruction method, Rayleigh scattering due to the atmosphere has an important effect, and for terrestrial exoplanets with atmosphere similar to our Earth, it is possible to estimate the presence of oceans and an atmosphere simultaneously.

We derive the axis ratio distribution of X-ray clusters using the XMM-Newton catalogue (Snowden et al. 2008). By fitting the contour lines of the X-ray image by ellipses, we confirm the X-ray distribution is well approximated by the elliptic distribution with a constant axis ratio and direction. We construct a simple model describing the axis ratio of the X-ray gas assuming the hydrostatic equilibrium embedded in the triaxial dark matter halo model proposed by Jing & Suto (2002) and the hydrostatic equilibrium. We find that the observed probability density function of the axis ratio is consistent with this model prediction.

Our previous analysis indicates that small-scale fluctuations in the intracluster medium (ICM) from cosmological hydrodynamic simulations follow the lognormal distribution. In order to test the lognormal nature of the ICM directly against X-ray observations of galaxy clusters, we develop a method of extracting statistical information about the three-dimensional properties of the fluctuations from the two-dimensional X-ray surface brightness. We first create a set of synthetic clusters with lognormal fluctuations. Performing mock observations of these synthetic clusters, we find that the resulting X-ray surface brightness fluctuations also follow the lognormal distribution fairly well. Systematic analysis of the synthetic clusters provides an empirical relation between the density fluctuations and the X-ray surface brightness. We analyze \chandra observations of the galaxy cluster Abell 3667, and find that its X-ray surface brightness fluctuations follow the lognormal distribution. While the lognormal model was originally motivated by cosmological hydrodynamic simulations, this is the first observational confirmation of the lognormal signature in a real cluster. Finally we check the synthetic cluster results against clusters from cosmological hydrodynamic simulations. As a result of the complex structure exhibited by simulated clusters, the empirical relation shows large scatter. Nevertheless we are able to reproduce the true value of the fluctuation amplitude of simulated clusters within a factor of two from their X-ray surface brightness alone. Our current methodology combined with existing observational data is useful in describing and inferring the statistical properties of the three dimensional inhomogeneity in galaxy clusters.

The Hubble constant estimated from the combined analysis of the Sunyaev-Zel'dovich effect and X-ray observations of galaxy clusters is systematically lower than those from other methods by 10-15 percent. We examine the origin of the systematic underestimate using an analytic model of the intracluster medium (ICM), and compare the prediction with idealistic triaxial models and with clusters extracted from cosmological hydrodynamical simulations. We identify three important sources for the systematic errors; density and temperature inhomogeneities in the ICM, departures from isothermality, and asphericity. In particular, the combination of the first two leads to the systematic underestimate of the ICM spectroscopic temperature relative to its emission-weighed one. We find that these three systematics well reproduce both the observed bias and the intrinsic dispersions of the Hubble constant estimated from the Sunyaev-Zel'dovich effect.