Search

Spatially resolved L-band spectro-polarimetric observations were carried out toward a protoplanetary disk around the Herbig Fe star HD 142527 using the polarimetry mode of the InfraRed Camera and Spectrometer on the 8.2 m Subaru Telescope. The 2.9–4.1 μm polarimetric spectra of the bright central source and the scattered light at a distance of ${0{^{\prime \prime}_{.}}78}$ from the center toward the PA ∼ 290° were obtained using the AO188 adaptive optics system. The polarization spectra of the central region show no significant evidence of the polarization which is expected with the (non-aligned) hot dust emission near the central star, while the disk scattered light spectra shows linear polarization of $\sim\!\! 10\%$, which is consistent with the nature of scattered light. In addition, the polarization PA of ∼20° is also geometrically consistent with the scattered light from the central region. We also derived the flux density spectra of each region and confirmed the 3 μm water-ice absorption feature in the scattered light spectra, which is consistent with the findings in Honda et al. (2009, ApJ, 690, L110). By comparing the model predictions by Tazaki et al. (2021b, ApJ, 921, 173), we estimated the grain properties of the extracted disk region. Assuming the power-law size distribution of silicate and ice, the maximum grain size amax of 3 μm and fractional ice abundance relative to Pollack et al. (1994, ApJ, 421, 615) (fice) of ∼0.1 is inferred, which is consistent with the finding by Tazaki et al. ( 2021b, ApJ, 921, 173).

We present a novel mechanism for the outward transport of crystalline dust particles: the outward radial drift of pebbles. The dust ring structure is frequently observed in protoplanetary disks. One of the plausible mechanisms of the formation of dust rings is the accumulation of pebbles around the pressure maximum, which is formed by the mass loss due to magnetically driven disk winds. In evolving protoplanetary disks due to magnetically driven disk winds, dust particles can migrate outwardly from the crystallization front to the pressure maximum by radial drift. We found that the outward radial drift process can transport crystalline dust particles efficiently when the radial drift timescale is shorter than the advection timescale. Our model predicts that the crystallinity of silicate dust particles could be as high as 100% inside the dust ring position., Comment: 15 pages, 14 figures. Accepted for publication in ApJ

We study the $3~\mu$m scattering feature of water ice detected in the outer disk of HD 142527 by performing radiative transfer simulations. We show that an ice mass abundance at the outer disk surface of HD 142527 is much lower than estimated in a previous study. It is even lower than inferred from far-infrared ice observations, implying ice disruption at the disk surface. Next, we demonstrate that a polarization fraction of disk-scattered light varies across the ice-band wavelengths depending on ice grain properties; hence, polarimetric spectra would be another tool for characterizing water-ice properties. Finally, we argue that the observed reddish disk-scattered light is due to grains with a few microns in size. To explain the presence of such grains at the disk surface, we need a mechanism that can efficiently oppose dust settling. If we assume turbulent mixing, our estimate requires $\alpha\gtrsim2\times10^{-3}$, where $\alpha$ is a non-dimensional parameter describing the vertical diffusion coefficient of grains. Future observations probing gas kinematics would be helpful to elucidate vertical grain dynamics in the outer disk of HD 142527., Comment: 21 pages, 14 figures, 1 table; Accepted for publication in ApJ

An internal cold chopper is one of the key elements for the ground-based mid-infrared astronomical instruments of the next generation large telescopes such as TMT, GMT, and ELT. For ground-based mid-infrared observations, time variations of radiation from atmosphere, telescope, and instrument are often many times greater than the radiation from targets. Relatively fast (~5 Hz) beam switching technique (chopping) using the oscillating secondary mirror is often used for 8-m class telescopes to remove these background variations, but this is impractical for the 30-m class telescopes due to their much larger secondary mirror. Instead of it, internal chopping mirror is desired for the next generation groundbased mid-infrared astronomy. However, since the mid-IR instruments are usually cooled as low as ~30 K, such internal chopping mirror should also be cooled to that low temperature and low power dissipation of

The mid/far infrared hosts a wealth of spectral information that allows direct determination of the physical state of matter in a large variety of astronomical objects, unhindered by foreground obscuration. Accessing this domain is essential for astronomers to much better grasp the fundamental physical processes underlying the evolution of many types of celestial objects, ranging from protoplanetary systems in our own milky way to 10-12 billion year old galaxies at the high noon of galaxy formation in our universe. The joint ESA/JAXA SPICA mission will give such access for the astronomical community at large, by providing an observatory with unprecedented mid- to far-infrared imaging, polarimetric and spectroscopic capabilities.

第4回「あかり」国際会議 (2017年10月17-20日. 東京大学), 文京区, 東京, The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, Japan, A thermal imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the mid-IR adaptive optics (AO) system (MIRAO), the instrument will afford 15 times higher sensitivity and 4 times better spatial resolution (0.07 arcsec) with a greatly improved and stable Strehl ratio at 10 micrometers compared to the images delivered by the fast guiding systems of 8m-class telescopes. Through exploiting the large collecting area of the TMT, a high-dispersion spectroscopy mode unrivaled by other ground- and space-based facilities is planned. Such capabilities offer the possibility for breakthrough science, as well as workhorse observing modes of imaging and low/moderate spectral resolution., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: AA1730026006, レポート番号: JAXA-SP-17-009E

Observationally measuring the location of the H2O snowline is crucial for understanding the planetesimal and planet formation processes, and the origin of water on Earth. The velocity profiles of emission lines from protoplanetary disks are usually affected by Doppler shift due to Keplerian rotation and thermal broadening. Therefore, the velocity profiles are sensitive to the radial distribution of the line-emitting regions. In our work (Notsu et al. 2016, 2017), we found candidate water lines to locate the position of the H2O snowline through future high-dispersion spectroscopic observations. First, we calculated the chemical composition of the disks around a T Tauri star and a Herbig Ae star using chemical kinetics. We confirmed that the abundance of H2O gas is high not only in the hot midplane region inside the H2O snowline but also in the hot surface layer and the photodesorption region of the outer disk. The position of the H2O snowline in the Herbig Ae disk exists at a larger radius from the central star than that in the T Tauri disk. Second, we calculated the H2O line profiles and identified that H2O emission lines with small Einstein A coefficients (∼10−6 − 10−3 s−1) and relatively high upper state energies (∼ 1000K) are dominated by emission from the hot midplane region inside the H2O snowline, and therefore their profiles potentially contain information which can be used to locate the position of the H2O snowline. The wavelengths of the H2O lines which are the best candidates to locate the position of the H2O snowline range from mid-infrared to sub-millimeter, and the total line fluxes tend to increase with decreasing wavelengths. We investigated the possibility of future observations using the ALMA and mid-infrared high-dispersion spectrographs (e.g., SPICA/SMI-HRS). Since the fluxes of those identified lines from a Herbig Ae disk are stronger than those of a T Tauri disk, the possibility of a successful detection is expected to increase for a Herbig Ae disk.

Observationally locating the position of the H2O snowline in protoplanetary disks is crucial for understanding planetesimal and planet formation processes, and the origin of water on the Earth. In our studies, we conducted calculations of chemical reactions and water line profiles in protoplanetary disks, and identified that ortho/para-H216O, H218O lines with small Einstein A coefficients and relatively high upper state energies are dominated by emission from the hot midplane region inside the H2O snowline. Therefore, through analyzing their line profiles the position of the H2O snowline can be located. Moreover, because the number density of the H218O is much smaller than that of H216O, the H218O lines can trace deeper into the disk and thus they are potentially better probes of the exact position of the H2O snowline in disk midplane.

Comet 21P/Giacobini-Zinner (hereafter, comet 21P/G-Z) is a Jupiter-family comet and a parent comet of the October Draconids meteor shower. If meteoroids originating from a Jupiter-family comet contain complex organic molecules, such as amino acids, they are essential pieces of the puzzle regarding the origin of life on Earth. We observed comet 21P/G-Z in the mid-infrared wavelength region using the Cooled Mid-infrared Camera and Spectrometer (COMICS) on the 8.2 m Subaru Telescope on UT 2005 July 5. Here, we report the unidentified infrared (UIR) emission features of comet 21P/G-Z, which are likely due to complex organic molecules (both aliphatic and aromatic hydrocarbons), and the thermal emission from amorphous/crystalline silicates and amorphous carbon grains in its mid-infrared low-resolution spectrum. The UIR features at ~8.2 micron, ~8.5 micron, and ~11.2 micron found in the spectrum of comet 21P/G-Z could be attributed to polycyclic aromatic hydrocarbons (or hydrogenated amorphous carbons) contaminated by N- or O-atoms, although part of the feature at ~11.2 micron comes from crystalline olivine. The other feature at ~9.2 micron might originate from aliphatic hydrocarbons. Comet 21P/G-Z is enriched in complex organic molecules. Considering that the derived mass fraction of crystalline silicates in comet 21P/G-Z is typical of comets, we propose that the comet originated from a circumplanetary disk of giant planets (similar to Jupiter and Saturn) where was warmer than the typical comet-forming region (5-30 au from the Sun) and was suitable for the formation of complex organic molecules. Comets from circumplanetary disks might be enriched in complex organic molecules, such as comet 21P/G-Z, and may have provided pre-biotic molecules to ancient Earth by direct impact or meteor showers., 26 pages, 6 figures, 3 tables, accepted for publication in Icarus

In this paper, we analyse the upper limit fluxes of sub-millimeter ortho-H$_{2}$$^{16}$O 321 GHz, para-H$_{2}$$^{18}$O 322 GHz, and HDO 335 GHz lines from the protoplanetary disk around the Herbig Ae star HD 163296, using the Atacama Large Millimeter/Submillimeter Array (ALMA). These water lines are considered to be the best candidate sub-millimeter lines to locate the position of the H$_{2}$O snowline, on the basis of our previous model calculations. We compare the upper limit fluxes with the values calculated by our models with dust emission included, and we constrain the line emitting region and the dust opacity from the observations. We conclude that, if the outer edge of the region with high water vapor abundance and if the position of the water snowline are beyond 8 au also, the mm dust opacity will have a value larger than 2.0 cm$^{2}$ g$^{-1}$. In addition, the position of the water snowline will be inside 20 au, if the mm dust opacity is 2.0 cm$^{2}$ g$^{-1}$. Future observations of the dust continuum emission at higher angular resolution and sub-millimeter water lines with longer observation time are required to clarify the detailed structures and the position of the H$_{2}$O snowline in the disk midplane., 17 pages, 8 figures, and 3 tables are contained in this paper. It was accepted for publication in The Astrophysical Journal (ApJ) on February 26th, 2019

With the imminent launch of the JWST, the field of thermal-infrared (TIR) astronomy will enjoy a revolution. It is easy to imagine that all areas of infrared (IR) astronomy will be greatly advanced, but perhaps impossible to conceive of the new vistas that will be opened. To allow both follow-up JWST observations and a continuance of work started on the ground-based 8m’s, we continue to plan the science cases and instrument design for a TIR imager and spectrometer for early operation on the TMT. We present the current status of our science cases and the instrumentation plans, harnessing expertise across the TMT partnership. This instrument will be proposed by the MICHI team as a second-generation instrument in any upcoming calls for proposals., Ground-based and Airborne Instrumentation for Astronomy VII, June 10-15, 2018, Austin, USA, Series: Proceedings of SPIE; no. 10702

A thermal-infrared polarimetric capability of the Infrared Camera and Spectrograph (IRCS) for the Subaru Telescope is described. A new half-wave retarder for the thermal-infrared band in 2–5 µm is introduced into the Waveplate Unit of the Nasmyth platform on the infrared side of the telescope to realize imaging- and low resolution spectro-polarimetry in that wavelength region. Through day-time calibrations using a wire-grid polarizer, the peak efficiency of the polarization is found to be 90-98% consistently in both imaging- and spectro- polarimetry in the thermal-infrared bands. In 2016 May and 2017 June, two engineering observing runs have been carried out to verify the on-sky performance.

Transitional disks around the Herbig Ae/Be stars are fascinating targets in the contexts of disk evolution and also planet formation. Oph IRS 48 is one of such Herbig Ae stars, which shows an inner dust cavity and azimuthally lopsided large dust distribution. We present new images of Oph IRS 48 at eight mid-infrared (MIR) wavelengths from 8.59 to 24.6\,$\mu {\rm m}$ taken with the COMICS mounted on the 8.2\,m Subaru Telescope. The N-band (7 to 13\,$\mu {\rm m}$) images show that the flux distribution is centrally peaked with a slight spatial extent, while the Q-band (17 to 25\,$\mu {\rm m}$) images show asymmetric double peaks (east and west). Using 18.8 and 24.6\,$\mu$m images, we derived the dust temperature at both east and west peaks to be 135$\pm$22 K. Thus, the asymmetry may not be attributed to a difference in the temperature. % thus other reason is necessary to explain the asymmetry of east and west peaks in Q-band. Comparing our results with previous modeling works, we conclude that the inner disk is aligned to the outer disk. A shadow casted by the optically thick inner disk has a great influence on the morphology of MIR thermal emission from the outer disk., Comment: 13 pages, 6 figures, accepted in PASJ

In this paper, we extend the results presented in our former papers on using ortho-H216O line profiles to constrain the location of the H2O snowline in T Tauri and Herbig Ae disks, to include submillimeter para-H216O and ortho- and para-H218O lines. Since the number densities of the ortho- and para-H218O molecules are about 560 times smaller than their 16O analogs, they trace deeper into the disk than the ortho-H216O lines (down to z = 0, i.e., the midplane). Thus these H218O lines are potentially better probes of the position of the H2O snowline at the disk midplane, depending on the dust optical depth. The values of the Einstein A coefficients of submillimeter candidate water lines tend to be lower (typically

Dust grains of crystalline silicate, which are rarely presented in interstellar space, were found in cometary nuclei. These crystalline silicates are thought to have formed by annealing of amorphous silicate grains or direct condensation of gaseous materials near the Sun in the solar nebula, and incorporated into cometary nuclei in the cold comet-forming region after radial transportation of grains in the solar nebula. Abundances of the crystalline silicate dust grains were therefore expected to be smaller farther from the Sun. We aim to better understand the formation mechanism of minerals incorporated into comet 17P/Holmes based on its mineral abundances. To derive the mineral composition of comet 17P/Holmes, we applied a thermal emission model for cometary dust grains to mid-infrared spectra of comet 17P/Holmes taken with the Cooled Mid-Infrared Camera and Spectrograph (COMICS) mounted on the Subaru Telescope a few days later the great outburst in October 2007. The resulting mass fraction of crystalline silicate, f_ cry, and an olivine-to-pyroxene abundance ratio, f_OP, are f_cry = 0.31 +/- 0.03 and f_OP = 1.20 +0.16/-0.12, respectively. Based on a simple consideration of the mixing of dust grains originating in both the interstellar medium and solar nebula, the minerals of 17P/Holmes formed by non-equilibrium condensation. This result is consistent with theoretical and experimental predictions for vaporization and condensation of olivine in the solar nebula., Comment: Accepted to AJ (on 2018 Aug 23)

Observationally measuring the location of the H$_{2}$O snowline is crucial for understanding the planetesimal and planet formation processes, and the origin of water on Earth. In disks around Herbig Ae stars ($T_{\mathrm{*}}\sim$ 10,000K, $M_{\mathrm{*}}\gtrsim$ 2.5$M_{\bigodot}$), the position of the H$_{2}$O snowline is further from the central star compared with that around cooler, and less massive T Tauri stars. Thus, the H$_{2}$O emission line fluxes from the region within the H$_{2}$O snowline are expected to be stronger. In this paper, we calculate the chemical composition of a Herbig Ae disk using chemical kinetics. Next, we calculate the H$_{2}$O emission line profiles, and investigate the properties of candidate water lines across a wide range of wavelengths (from mid-infrared to sub-millimeter) that can locate the position of the H$_{2}$O snowline. Those line identified have small Einstein $A$ coefficients ($\sim 10^{-6} -10^{-3}$ s$^{-1}$) and relatively high upper state energies ($\sim$ 1000K). The total fluxes tend to increase with decreasing wavelengths. We investigate the possibility of future observations (e.g., ALMA, SPICA/SMI-HRS) to locate the position of the H$_{2}$O snowline. Since the fluxes of those identified lines from Herbig Ae disks are stronger than those from T Tauri disks, the possibility of a successful detection is expected to increase for a Herbig Ae disk., Comment: 39 pages, 14 figures, and 2 tables are contained in this paper. It was received by The Astrophysical Journal (ApJ) on October 27th, 2016, and was accepted on January 13th, 2017. arXiv admin note: text overlap with arXiv:1606.05828

A cold chopper is a key device for next generation mid-infrared instruments such as TMT/MICHI. It should achieve fast and accurate position switching with a large chopping throw at cryogenic temperature. To satisfy the requirements, voice coil motors using superconducting MgB2 wire have been developed. We have made a first prototype of the VCM and carried out its performance measurements such as a transition temperature, transfer functions, and power dissipation in the laboratory. The results are almost consistent with the expectations and the calculations, but some show significant inconsistency. We have also made a next prototype which is small to fit the size of the MICHI chopper. This will be installed to a developing mid-infrared instrument MIMIZUKU and used for actual observations.

We have carried out a trial production of the large-format (n=11) image slicer unit for a possible future mid-infrared instrument on the TMT aiming to verify its technical feasibility. The key elements in our trial production are the monolithic large-format slice mirrors and the monolithic large-format pupil mirrors. The results of our trial production of those key elements based on the ultra high-precision cutting techniques and the assembly of the large-format image slicer unit are presented in this paper.

We made near infrared multicolor imaging observations of a disk around Herbig Be star HD100546 using Gemini/NICI. K (2.2\,$\mu$m), H$_2$O ice (3.06\,$\mu$m), and L'(3.8\,$\mu$m) disk images were obtained and we found the 3.1\,$\mu$m absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on \cite{Oka2012} including water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by the both disk models with/without photodesorption effect within the measurement accuracy, but slightly favors the model with photodesorption effects, implying that the UV photons play an important role on the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement on the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models., Comment: accepted in ApJ

We present a study of the radial distribution of dust species in young brown dwarf disks. Our work is based on a compositional analysis of the 10 and 20 micron silicate emission features for brown dwarfs in the Taurus-Auriga star-forming region. A fundamental finding of our work is that brown dwarfs exhibit stronger signs of dust processing in the cold component of the disk, compared to the higher mass T Tauri stars in Taurus. For nearly all of our targets, we find a flat disk structure, which is consistent with the stronger signs of dust processing observed in these disks. For the case of one brown dwarf, 2M04230607, we find the forsterite mass fraction to be a factor of ~3 higher in the outer disk compared to the inner disk region. Simple large-scale radial mixing cannot account for this gradient in the dust chemical composition, and some local crystalline formation mechanism may be effective in this disk. The relatively high abundance of crystalline silicates in the outer cold regions of brown dwarf disks provides an interesting analogy to comets. In this context, we have discussed the applicability of the various mechanisms that have been proposed for comets on the formation and the outward transport of high-temperature material. We also present Chandra X-ray observations for two Taurus brown dwarfs, 2M04414825 and CFHT-BD-Tau 9. We find 2M04414825, which has a ~12% crystalline mass fraction, to be more than an order of magnitude brighter in X-ray than CFHT-BD-Tau 9, which has a ~35% crystalline mass fraction. Combining with previous X-ray data, we find the inner disk crystalline mass fractions to be anti-correlated with the X-ray strength.

We present mid-infrared narrow-band images of the Orion BN/KL region, and N-band low-resolution spectra of IRc2 and the nearby radio source "I." The distributions of the silicate absorption strength and the color temperature have been revealed with a sub-arcsecond resolution. The detailed structure of the 7.8 micron/12.4 micron color temperature distribution was resolved in the vicinity of IRc2. A mid-infrared counterpart to source I has been detected as a large color temperature peak. The color temperature distribution shows an increasing gradient from IRc2 toward source I, and no dominant temperature peak is seen at IRc2. The spectral energy distribution of IRc2 could be fitted by a two-temperature component model, and the "warmer component" of the infrared emission from IRc2 could be reproduced by scattering of radiation from source I. IRc2 itself is not self-luminous, but is illuminated and heated by an embedded luminous young stellar object located at source I., 20 pages, 11 figures. Minor corrections had been done in the ver.2. Accepted for publication in PASJ

著者人数: 42名, Accepted: 2011-03-08, 資料番号: SA1003241000

We investigate gravitational lensing effects of an extrasolar planet transiting its host star. We focus on the `rising spikes' of the light curve just before and after the transit, which is a peculiar feature of the gravitational lensing, and find that it could be a novel observable for determining physical parameters. Detectability of such an effect is also discussed.

Based on optical and infrared observations, we study the albedo and the temperature of the dust grains associated with the spectacular 2007 outburst of Jupiter-family comet 17P/Holmes. We found that the albedo at the solar phase angle ~16° was 0.03-0.12. While the color temperature around 3-4 μm was 360 ± 40 K, the color temperature at 12.4 μm and 24.5 μm was ~200 K, which is consistent with that of a blackbody. We studied the equilibrium temperature of the dust grains at 2.44 AU and found that the big discrepancy in the temperature was caused by the heterogeneity in particle size, that is, hotter components consist of submicron absorbing grains whereas colder components consist of large (1 μm) grains. The contemporaneous optical and mid-infrared observations suggest that the albedo and the temperature could decrease within ~ 3 days after the outburst and stabilized at typical values of the other comets. We estimated the total mass injected into the coma by the outburst on the basis of the derived albedo and the optical magnitude for the entire dust cloud, and found that at least 4 × 1010 kg (equivalent to a few meter surface layer) was removed by the initial outburst event. The derived mass suggests that the outburst is explainable by neither the exogenetic asteroidal impact nor water ice sublimation driven by solar irradiation, but by an endogenic energy source. We conclude that the outburst was triggered by the energy sources several meters or more below the nuclear surface.

Mid-infrared 8–25 m imaging and spectroscopic observations of the comet 17P/Holmes in the early phase of its outburst in brightness were performed on 2007 October 25–28 UT using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the 8.2-m Subaru Telescope. We detected an isolated dust cloud that moved toward the south-west direction from the nucleus. The 11.2 m peak of a crystalline silicate feature onto a broad amorphous silicate feature was also detected both in the central condensation of the nucleus and an isolated dust cloud. The color temperature of the isolated dust cloud was estimated to be 200K, which is slightly higher than the black-body temperature. Our analysis of the motion indicates that the isolated cloud moved anti-sunward. We propose several possibilities for the motion of the cloud: fluffy dust particles in the isolated cloud started to depart from the nucleus due to radiation pressure almost as soon as the main outburst occurred, or dust particles moved by some other antisunward forces, such as a rocket effect and photophoresis when the surrounding dust coma became optically thin. The origin and the nature of the isolated dust cloud are discussed in this paper.

We carried out high spatial resolution N-band imaging and spectroscopic observations of the planetary nebula BD +30 3639 with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the Subaru telescope. Mid-infrared images reveal a rectangle shell structure of the nebula extending over 4'', which is supposed to be formed by the superwind from the central star. We have detected [Ne II] 12.8 μm and the unidentified infrared (UIR) bands at 8.6 and 11.2 μm, together with the broad plateau emission in 11-13 μm. In addition, the spectra clearly indicate the presence of silicate absorption around 10 μm for the first time, which increases sharply at the outside of the shell. This can be attributed to silicate grains that were formed in the O-rich phase of the central star, which is now C-rich. The present data indicate that these silicate grains are located in a very thin shell, suggesting that BD +30 3639 underwent a short period (~100 yr) of a high mass-loss rate (~3 × 10−3 M☉ yr−1) at the last epoch of the O-rich phase. N-band spectra show that the distribution of [Ne II] is not clearly different from that of the UIR band and suggest that the UIR band carriers coexist with the ionized gas to some extent. This may be attributed to a slow destruction of the band carriers in the ionized region of the high electron density. The 10 μm continuum and the 11-13 μm plateau emission are dominant in the shell region, while the UIR 11.2 μm band becomes stronger in the outside of the shell, suggesting a change in the dust composition or the dust size distribution between the shell and the outside of the shell region. On the contrary, the peak wavelength of the UIR 11.2 μm band agrees with the class B spectrum, which is often seen in planetary nebulae, and does not change between the shell and the outside of the shell region. These facts suggest that the UIR band carriers are originally formed in the carbon-rich stellar wind and partially destroyed in the shell by shocks. The change of the UIR band spectrum from class B to A, which is generally seen in H II regions, should take place outside of the nebula.

We carried out spectroscopic observations ( R ∼ 250 ) of Oort cloud comet C/2001 Q4 (NEAT) at the post-perihelion ( r h = 1.02 AU , Δ = 0.93 AU , 2004 June 4.2 UT) in mid-infrared 8 – 13 μ m region using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on 8.2 m Subaru Telescope. The silicate feature of comet Q4 shows the crystalline olivine peak at 11.2 μ m along with the broad amorphous silicate features. We present the detailed results of our fitting analysis by using a thermal emission model of cometary coma grains, and compare with other results of C/2001 Q4 (NEAT) at the different heliocentric distance pre-perihelion ( r h = 0.97 AU ), comet C/2002 V1 (NEAT), and comet C/1995 O1 (Hale–Bopp). The mass ratios of crystalline to amorphous silicate in sub- μ m grain size are between 1.9 and 2.5 for these comets. The similarity of coma dust mineralogy among these Oort cloud comets implies that the dust grains in these comets represent the similar physical conditions in the solar nebula and potentially similar regions of icy planetesimal formation.

著者人数：13名, Accepted: 2006-05-15, 資料番号: SA1000388000

Accepted: 2006-04-11, 資料番号: SA1000390000

Faint standard stars in the mid-infrared region (less than a few hundred millijanskys at 9 μm) are required for the on-orbit calibration of the Infrared Camera (IRC) on board ASTRO-F because of its high sensitivity, as well as the small dynamic range. Mid-infrared low-resolution (λ/Δλ ~ 250) spectra of six faint K and M giant stars (70-180 mJy at 9 μm, K1.5-M0 III), which are located in the north ecliptic polar region and are thus suitable for calibrators for the IRC, are obtained by using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope to test the faint-infrared standard-star network recently constructed for space-borne instruments. The spectra are directly calibrated relative to Vega (A0 V). The present results indicate that the spectra of the faint standard K-M0 giant stars show good agreement with those predicted in the standard network within 10% accuracy on average. The overall spectral shapes are also in agreement with the predictions. In particular, the observed SiO absorption feature in the 8 μm region matches well with the prediction for an M0 III star. The present observations directly connect a primary standard calibrator (Vega) to faint K giant calibrators of the network in the 10 μm region and validate several faint (~0.1 Jy) members of the standard-star network for the first time. Absolute calibrations are provided for five of the medium-band filters of the COMICS instrument in the 10 μm window.

Accepted: 2004-10-18, 資料番号: SA1003389000

We carried out imaging and long-slit spectroscopic observations of the Red Rectangle in the N -band using the 8.2-m SUBARU telescope. The resulting images reveal a central bright core and an extended nebula. The central core is slightly extended in the N -band. The core radius is estimated to be ~, which corresponds to 60 AU. The core spectrum is well modeled by blackbody emission with a temperature of 358 K. The estimated size and temperature are in good agreement with the predictions of recent dusty torus models. In the north/south nebula, unidentified infrared (UIR) emission features at 8.6 μ m and 11.2 μ m are prominently observed. At radii > they completely dominate the N -band spectra, suggesting that the nebula seen at N -band wavelengths is primarily brightened by the UIR-band emission, not by scattered light. We also detected shifts in the UIR-feature peaks with increasing distance from the center. These may be attributed to isotopic shifts due to the presence of in polycyclic aromatic hydrocarbons (PAH) like particles. In addition to the UIR emission, a broad feature at 11.27 μ m is seen at a distance of 0.3´´ on all sides of the nebula. We attribute this to crystalline silicate olivine grains around the central torus.

著者人数: 14名, Accepted: 2003-10-01, 資料番号: SA1003371000

Accepted: 2003-09-12, 資料番号: SA1004076000

We report the results of mid-infrared (7.8μm–13.2 μm) high-spatial resolution imaging and spectroscopic observations of the Galactic center region with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope. The images clearly show bright infrared sources and small structures in the diffuse emission. The spectra of all the observed positions show the 9.7 μm silicate absorption feature. After corrected for the empirically-derived extinction, the intrinsic spectra of the infrared sources show either strong silicate emission or absorption, while the intrinsic diffuse emission has a power-law type spectrum. This difference indicates a possibility of dust processing due to the interaction between the infrared sources and their surrounding medium or a different origin of the dust grains surrounding the sources from those in the diffuse region.

Accepted: 2002-10-14, 資料番号: SA1003358000

著者人数: 12名, Accepted: 2017-05-24, 資料番号: SA1170040000

We have carried out the trial production of small format (n=5) image slicer aiming to obtain the technical verification of the Integral Field Unit (IFU) that can be equipped to the next generation infrared instruments such as TMT/MICHI and SPICA/SMI. Our goal is to achieve stable pseudo slit image with high efficiency. Here we report the results of the assembly of the image slicer unit and the non-cryogenic evaluation system of the pseudo slit image quality in the infrared.

We report the first independent, second-epoch (re-)detection of a directly-imaged protoplanet candidate. Using $L^\prime$ high-contrast imaging of HD 100546 taken with the Near-Infrared Coronagraph and Imager (NICI) on Gemini South, we recover `HD 100546 b' with a position and brightness consistent with the original VLT/NaCo detection from Quanz et al, although data obtained after 2013 will be required to decisively demonstrate common proper motion. HD 100546 b may be spatially resolved, up to $\approx$ 12-13 AU in diameter, and is embedded in a finger of thermal IR bright, polarized emission extending inwards to at least 0.3". Standard hot-start models imply a mass of $\approx$ 15 $M_{J}$. But if HD 100546 b is newly formed or made visible by a circumplanetary disk, both of which are plausible, its mass is significantly lower (e.g. 1--7 $M_{J}$). Additionally, we discover a thermal IR-bright disk feature, possibly a spiral density wave, at roughly the same angular separation as HD 100546 b but 90 degrees away. Our interpretation of this feature as a spiral arm is not decisive, but modeling analyses using spiral density wave theory implies a wave launching point exterior to $\approx$ 0.45" embedded within the visible disk structure: plausibly evidence for a second, hitherto unseen wide-separation planet. With one confirmed protoplanet candidate and evidence for 1--2 others, HD 100546 is an important evolutionary precursor to intermediate-mass stars with multiple super-jovian planets at moderate/wide separations like HR 8799., Comment: 6 pages, 3 figures, 1 table. Accepted for publication/to be published in ApJ Letters

We present a new method of analysis for determining the surface geometry of five protoplanetary disks observed with near-infrared imaging polarimetry using Subaru-HiCIAO. Using as inputs the observed distribution of polarized intensity (PI), disk inclination, assumed properties for dust scattering, and other reasonable approximations, we calculate a differential equation to derive the surface geometry. This equation is numerically integrated along the distance from the star at a given position angle. We show that, using these approximations, the local maxima in the PI distribution of spiral arms (SAO 206462, MWC 758) and rings (2MASS J16042165-2130284, PDS 70) are associated with local concave-up structures on the disk surface. We also show that the observed presence of an inner gap in scattered light still allows the possibility of a disk surface that is parallel to the light path from the star, or a disk that is shadowed by structures in the inner radii. Our analysis for rings does not show the presence of a vertical inner wall as often assumed in studies of disks with an inner gap. Finally, we summarize the implications of spiral and ring structures as potential signatures of ongoing planet formation., Comment: 35 pages, 13 figures, 7 tables, accepted by ApJ

著者人数: 18名, Accepted: 2013-09-13, 資料番号: SA1004666000

Inside the H$_{2}$O snowline of protoplanetary disks, water evaporates from the dust-grain surface into the gas phase, whereas it is frozen out on to the dust in the cold region beyond the snowline. H$_{2}$O ice enhances the solid material in the cold outer part of a disk, which promotes the formation of gas-giant planet cores. We can regard the H$_{2}$O snowline as the surface that divides the regions between rocky and gaseous giant planet formation. Thus observationally measuring the location of the H$_{2}$O snowline is crucial for understanding the planetesimal and planet formation processes, and the origin of water on Earth. In this paper, we find candidate water lines to locate the H$_{2}$O snowline through future high-dispersion spectroscopic observations. First, we calculate the chemical composition of the disk and investigate the abundance distributions of H$_{2}$O gas and ice, and the position of the H$_{2}$O snowline. We confirm that the abundance of H$_{2}$O gas is high not only in the hot midplane region inside the H$_{2}$O snowline but also in the hot surface layer of the outer disk. Second, we calculate the H$_{2}$O line profiles and identify those H$_{2}$O lines which are promising for locating the H$_{2}$O snowline: the identified lines are those which have small Einstein $A$ coefficients and high upper state energies. The wavelengths of the candidate H$_{2}$O lines range from mid-infrared to sub-millimeter, and they overlap with the regions accessible to ALMA and future mid-infrared high dispersion spectrographs (e.g., TMT/MICHI, SPICA)., 33 pages, 9 figures, and 2 tables are contained in this paper. It was received by The Astrophysical Journal (ApJ) on December 30th, 2015, and was accepted on June 16th, 2016

We present high resolution H-band polarized intensity (PI; FWHM = 0."1: 14 AU) and L'-band imaging data (FWHM = 0."11: 15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0."2) up to 210 AU (1."5). In both images, a giant inner gap is clearly resolved for the first time, and the radius of the gap is ~70 AU. Our data show that the geometric center of the disk shifts by ~6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of SED fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit mass of companions at ~30 to ~50MJ within the gap. Taking account of the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap., accepted by APJL

A mid-infrared (MIR) imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the MIR adaptive optics (AO) system (MIRAO), the instrument will afford ~15 times higher sensitivity and ~4 times better spatial resolution (0.07”) at 10μm compared to 8m-class telescopes. Additionally, through exploiting the large collection area of the TMT, the high-dispersion spectroscopy mode will be unrivaled by other ground- and space-based facilities. These combined capabilities offer the possibility for breakthrough science, as well as ‘workhorse’ observing modes of imaging and low/moderate spectral resolution. In this paper we summarize the primary science drivers that are guiding the instrument design.

We present the current status of the development of the SPICA Coronagraph Instrument (SCI). SPICA is a next-generation 3-meter class infrared telescope, which will be launched in 2022. SCI is high-contrast imaging, spectroscopic instrument mainly for direct detection and spectroscopy of extra-solar planets in the near-to-mid infrared wavelengths to characterize their atmospheres, physical parameters and evolutionary scenarios. SCI is now under the international review process. In this paper, we present a science case of SCI. The main targets of SCI, not only for direct imaging but also for spectroscopy, are young to matured giant planets. We will also show that some of known exoplanets by ground-based direct detection are good targets for SCI, and a number of direct detection planets that are suitable for SCI will be significantly increased in the next decade. Second, a general design of SCI and a key technology including a new high-throughput binary mask coronagraph, will be presented. Furthermore, we will show that SCI is potentially capable of achieving 10 -6 contrast by a PSF subtraction method, even with a telescope pointing error. This contrast enhancement will be important to characterize low-mass and cool planets.

Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 microns in their Spectral Energy Distributions (SED), recently measured by the Spitzer Infrared Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter (sub-mm) continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for micron-sized grains, with little discontinuity in the surface density of the micron-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the micron-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust-ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models., 41 pages (single column), 1 table, 10 figures, ApJ accepted