内山 瑞穂

Abstract Asymptotic giant branch (AGB) stars are one of the main sources of dust in the Universe. They form and supply dust triggered by stellar pulsations, but the details of the mechanism are still unknown. Among all AGB stars, dusty AGB stars are the most important in terms of dust supply because they contain the star with a high mass-loss rate. To investigate the relationship between the pulsation and the dust supply for such dusty AGB stars, long-term mid-infrared monitoring is necessary. In this study, we combine data from a infrared astronomical satellites AKARI and WISE to generate mid-infrared long-term observation data. This collected data enables us to investigate the variability of dusty AGB stars with a variability period of more than several hundred days (>250 d). Furthermore, we determine the mid-infrared variability amplitudes of 169 O-rich AGB stars and 28 OH/IR stars in our Galaxy, as well as data at other wavelengths. This study is the largest study on mid-infrared variability. Additionally, we discover a positive correlation between the variability amplitude A18μm in the 18μm band and the $\mathit {W3}-\mathit {W4}$ infrared color which is the measure of the dust supply. Also, we find that this relationship is independent of the variability period and mode. Finally, we calculate the radiative transfer of circumstellar dust from AGB stars. The result of our calculations showed that $A_{18\mu \rm {m } }$ is strongly affected by the luminosity change ratio of the central star. These experimental results imply that the luminosity change ratio has a strong influence on the dust supply of AGB star.

We present the discovery of the simultaneous flux variation of a massive young stellar object (MYSO) G036.70+00.09 (G036.70) both in the maser emission and mid-infrared (MIR; lambda = 3-5 mu m) bands. Using the ALLWISE and NEOWISE archival databases that cover a long time span of approximately 10 yr with a cadence of 6 months, we confirm that G036.70 indicates a stochastic year-long MIR variability with no signs of a WISE band color change of W1 (3.4 mu m) -W2 (4.6 mu m). Cross-matching the MIR data set with the high-cadence 6.7 GHz class II methanol maser flux using the Hitachi 32 m radio telescope that discovered its periodicity in the methanol maser of 53.0-53.2 days, we also determine the flux correlations between the two bands at two different timescales, year-long and day-long, both of which have never been reported in MYSOs, except when they are in the accretion burst phase. The results of our study support the scenario that a class II methanol maser is pumped up by infrared emission from accreting disks of MYSOs. We also discuss the possible origins of MIR and maser variability. To explain the two observed phenomena, a stochastic year-long MIR variability with no signs of significant color change and maser-MIR variability correlation or a change in mass accretion rate and line-of-sight extinction because of the nonaxisymmetric dust density distribution in a rotating accretion disk are possible origins. Observations through spectroscopic monitoring of accretion-related emission lines are essential for determining the origin of the observed variability in G036.70.

Abstract The formation of massive stars in dense and cold molecular clouds is a fundamental problem in star formation. In this work, we studied three compact massive star-forming regions, M8E, RAFGL 6366S, and IRAS 18317−0513, to investigate the environment of massive star formation, specifically the possibility of a local feedback process. Our new mid-infrared observations using miniTAO/MAX38 at 31 and 37 μm resolved individual objects in each region and allowed us to obtain their individual luminosities and masses. Together with existence/absence of ultra-compact H ii regions, it is suggested that less-massive objects are more evolved than the more-massive objects in two out of the three regions. Because the objects that are more massive evolve faster, those that are less massive form earlier. This formation trend of local mass-sequential star was first suggested in 0.1 pc-scale massive star-forming regions. Therefore, feedback, such as outflows, jets, or radiative heating, from previously formed lower-mass young stellar objects might affect the environment of parental clouds and lead to next-generation massive young stellar objects.

<jats:title>Abstract</jats:title> <jats:p>We followed up the massive young stellar object S255-NIRS3 (= S255-IRS1b) during its recent accretion outburst event in the $K_{\rm s}$ band with Kanata/HONIR for four years after its burst and obtained a long-term light curve. This is the most complete near-infrared light curve of the S255-NIRS3 burst event that has ever been presented. The light curve showed a steep increase reaching a peak flux that was 3.4 mag brighter than the quiescent phase and then a relatively moderate year-scale fading until the last observation, similar to that of the accretion burst events such as EXors found in lower-mass young stellar objects. The behavior of the $K_{\rm s}$-band light curve is similar to that observed in 6.7 GHz class II methanol maser emission, with a sudden increase followed by moderate year-scale fading. However, the maser emission peaks appear 30–50 d earlier than that of the $K_{\rm s}$ band emission. The similarities confirmed that the origins of the maser emission and the $K_{\rm s}$-band continuum emission are common, as previously shown from other infrared and radio observations by Stecklum et al. (2016, Astronomer’s Telegram, 8732), Caratti o Garatti et al. (2017b, Nature Phys., 13, 276), and Moscadelli et al. (2017, A&amp;A, 600, L8). However, the differences in energy transfer paths, such as the exciting/emitting/scattering structures, may cause the delay in the flux-peak dates.</jats:p>

'Field Stacker' is a unique system mounted on MIMIZUKU, a mid-infrared instrument for the TAO 6.5-m telescope. This system obtains a pair of distant targets simultaneously and aims at performing relative photometry with an accuracy of a few percent. A key to achieve the accurate relative photometry is precise flat fielding. We have developed a new method for the flat fielding using time variation of the sky background. We analyzed the data obtained in an engineering observation at the Subaru in 2018. The error of the flat fielding and the total error propagated from the flat fielding are estimated to be 0.2-0.3% and 0.5%, respectively.

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

The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is a mid-infrared camera and spectrograph developed as a first-generation instrument on the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU covers a wide wavelength range from 2 to 38 pm and has a unique optical device called Field Stacker which realizes accurate calibration of variable atmospheric transmittance with a few percent accuracy. By utilizing these capabilities, MIMIZUKU realizes mid-infrared long-term monitoring, which has not been challenged well.MIMIZUKU has three optical channels, called NIR, MIR-S, and MIR-L, to realize the wide wavelength coverage. The MIR-S channel, which covers 6.8-26 pm, has been completed by now. We are planning to perform engineering observations with this channel at the Subaru telescope before the completion of the TAO 6.5-m telescope. In this paper, we report the results of the laboratory tests to evaluate the optical and detector performances of the MIR-S channel. As a result, we confirmed a pixel scale of 0.12 arcsec/pix and a vignetting free field of view of 2.10 x1.18. The instrument throughputs for imaging modes are measured to be 20-30%. Those for N- and Q-band spectroscopy modes are 17 and 5%, respectively. As for the detector performance, we derived the quantum efficiency to be 40-50% in the mid-infrared wavelength region and measured the readout noise to be 3000-6000 electrons, which are larger than the spec value. It was found that this large readout noise degrades the sensitivity of MIMIZUKU by a factor of two.

We detected flaring flux variability that regularly occurred with a period of 23.9 d on a 6.7 GHz methanol maser emission at V-lsr = 25.30 km s(-1) in G 014.23-00.50 through highly frequent monitoring using the Hitachi 32m radio telescope. Analyzing data from 2013 January 5 to 2016 January 21, the periodic variability has persisted in at least 47 cycles, corresponding to similar to 1100 d. The period of 23.9 d is the shortest one observed in masers around high-mass young stellar objects so far. The flaring component normally falls below the detection limit (3 sigma) of similar to 0.9 Jy. In the flaring periods, the component rises above the detection limit with a ratio of the peak flux density more than 180 in comparison with the quiescent phase, showing intermittent periodic variability. The timescale of the flux rise was typically two days or shorter, and both symmetric and asymmetric profiles of flux variability were observed through intraday monitoring. These characteristics might be explained by a change in the flux of seed photons in a colliding-wind binary (CWB) system, or a variation of the dust temperature by the extra heating source of a shock formed by a CWB system within a gap region in a circumbinary disk, in which the orbital semi-major axes of the binary are 0.26-0.34 au.

Simultaneous-color Wide-field Infrared Multi-object Spectrograph, SWIMS, is one of the first generation instruments for University of Tokyo Atacama Observatory 6.5m Telescope where almost continuous atmospheric window from 0.9 to 2.5 mu m appears, thanks to the high altitude and dry climate of the site. To utilize this excellent condition, SWIMS is capable of simultaneous two-color imaging with a field of view of 9' : 6 in diameter and lambda/Delta lambda similar to 1000 multi-object spectroscopy at 0.9-2.5 mu m in a single exposure, utilizing a dichroic mirror inserted in the collimated beam. Here, we overview the instrument, report results of its full-assembly tests in the laboratory and present the future plan.

MIMIZUKU is a mid-infrared imager and spectrograph being developed for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope (PI: Y. Yoshii). To fully utilize a high atmospheric transmission of the Chajnantor site, MIMIZUKU covers a wide wavelength range from 2 to 38 mu m with three array detectors: a HAWAII-1RG HgCdTe 1024 x 1024 array with a 5 mu m cutoff manufactured by Teledyne, an Aquarius Si: As IBC 1024 x 1024 array by Raytheon, and a MF-128 Si: Sb BIB 128 x 128 array by DRS. We have newly developed an array controller system to operate these multiple arrays. A sampling rate higher than 0.5 MHz is required to prevent from saturation of their wells in broad-band imaging observations with MIMIZUKU due to high thermal background flux. Such high speed signals are dulled when passing through lines from the arrays to readout circuits. To overcome this problem, we have developed high-speed cryogenic buffer pre-amplifier circuits with commercial GaAs MESFETs, instead of Si JFETs, which are generally used in buffer amplifiers at cryogenic temperatures. The cryogenic buffer circuits are installed on an outer wall of the optical bench of MIMIZUKU at 20 K. We have measured readout noises of the array controller system including the cryogenic buffers in a test cryostat and room temperature circuits and confirmed that input referred noises of the system are lower than the specification value of the readout noise of the Aquarius array.

We introduce a new method named as "weighted average method" to reduce atmospheric noise on the images in ground-based mid-infrared observations. The main idea of this method is to find a sky frame corresponded to an object frame by superposition of several sky frames, instead of the conventional chop-and-nod observation technique. This is very useful not only for improving the observing efficiency but also for taking images of extended objects larger than the chopping throw. This method is also valid for reducing data taken by the chopping with insufficient frequency. In this paper we will report the details of the weighted average method and demonstrate its performance against practical observing data.

We have initiated single-dish monitoring observations of ~400 methanol maser sources at 6.7 GHz using the Hitachi 32-m radio telescope from December 2012 to systematically research periodic flux variations, which are observed in some methanol maser sources associated with high-mass (proto-)stars. In our monitoring, we have made daily monitoring, so that each source has been observed every nine days with an integration time of 5 min (typical detection sensitivities of 0.9 Jy). The monitoring observations help us statistically understand periodic flux variations with a period longer than 50 days. As an initial result, we present a new detection of periodic flux variations in the 6.7 GHz methanol maser source G036.70+00.09. The period of the flux variations is ~53 days (~0.019 cycles), and seems to be stable over 9 cycles, at least until the middle of August 2014....

We have developed a near-infrared camera called ANIR (Atacama Near-InfraRed camera) for the University of Tokyo Atacama Observatory 1.0m telescope (miniTAO) installed at the summit of Cerro Chajnantor (5640 m above sea level) in northern Chile. The camera provides a field of view of 5'.1 $\times$ 5'.1 with a spatial resolution of 0".298 /pixel in the wavelength range of 0.95 to 2.4 $\mu$m. Taking advantage of the dry site, the camera is capable of hydrogen Paschen-$\alpha$ (Pa$\alpha$, $\lambda=$1.8751 $\mu$m in air) narrow-band imaging observations, at which wavelength ground-based observations have been quite difficult due to deep atmospheric absorption mainly from water vapor. We have been successfully obtaining Pa$\alpha$ images of Galactic objects and nearby galaxies since the first-light observation in 2009 with ANIR. The throughputs at the narrow-band filters ($N1875$, $N191$) including the atmospheric absorption show larger dispersion (~10%) than those at broad-band filters (a few %), indicating that they are affected by temporal fluctuations in Precipitable Water Vapor (PWV) above the site. We evaluate the PWV content via the atmospheric transmittance at the narrow-band filters, and derive that the median and the dispersion of the distribution of the PWV are 0.40+/-0.30 mm for $N1875$ and 0.37+/-0.21 mm for $N191$, which are remarkably smaller (49+/-38% for $N1875$ and 59+/-26% for $N191$) than radiometry measurements at the base of Cerro Chajnantor (5100 m alt.). The decrease in PWV can be explained by the altitude of the site when we assume that the vertical distribution of the water vapor is approximated at an exponential profile with scale heights within 0.3-1.9 km (previously observed values at night). We thus conclude that miniTAO/ANIR at the summit of Cerro Chajnantor indeed provides us an excellent capability for a "ground-based" Pa$\alpha$ observation.

Luminous infrared galaxies (LIRGs) are enshrouded by a large amount of dust,<br /> produced by their active star formation, and it is difficult to measure their<br /> activity in the optical wavelength. We have carried out Pa$\alpha$ narrow-band<br /> imaging observations of 38 nearby star-forming galaxies including 33 LIRGs<br /> listed in $IRAS$ RBGS catalog with the Atacama Near InfraRed camera (ANIR) on<br /> the University of Tokyo Atacama Observatory (TAO) 1.0 m telescope (miniTAO).<br /> Star formation rates (SFRs) estimated from the Pa$\alpha$ fluxes, corrected for<br /> dust extinction using the Balmer Decrement Method (typically $A_V$ $\sim$ 4.3<br /> mag), show a good correlation with those from the bolometric infrared<br /> luminosity of $IRAS$ data within a scatter of 0.27 dex. This suggests that the<br /> correction of dust extinction for Pa$\alpha$ flux is sufficient in our sample.<br /> We measure the physical sizes and the surface density of infrared luminosities<br /> ($\Sigma_{L(\mathrm{IR})}$) and $SFR$ ($\Sigma_{SFR}$) of star-forming region<br /> for individual galaxies, and find that most of the galaxies follow a sequence<br /> of local ultra luminous or luminous infrared galaxies (U/LIRGs) on the<br /> $L(\mathrm{IR})$-$\Sigma_{L(\mathrm{IR})}$ and $SFR$-$\Sigma_{SFR}$ plane. We<br /> confirm that a transition of the sequence from normal galaxies to U/LIRGs is<br /> seen at $L(\mathrm{IR})=8\times10^{10}$ $L_{\odot}$. Also, we find that there<br /> is a large scatter in physical size, different from those of normal galaxies or<br /> ULIRGs. Considering the fact that most of U/LIRGs are merging or interacting<br /> galaxies, this scatter may be caused by strong external factors or differences<br /> of their merging stage.

We report the latest volcanic activity on Io based on our ground-based observations made in 2011 and 2012 using just a 1-m telescope, at 8.9 mu m where Io's thermal radiation dominates solar reflected light seen at shorter wavelengths. A particular result from these observations is that the power we detected from a bright hotspot at the longitude of 282 +/- 18 degrees, perhaps Daedalus Patera, was similar to 10(13) (W) which is comparable to that of Loki Patera, the most powerful volcanic hotspot on Io. We conclude this hotspot is one of the most powerful volcanic hotspots on Io, but its activation is not as frequent as Loki Patera. (c) 2014 Published by Elsevier Inc.

We report the restraint deformation and the corrosion protection of gold deposited aluminum mirrors for mid-infrared instruments. To evaluate the deformation of the aluminum mirrors by thermal shrinkage, monitoring measurement of the surface of a mirror has been carried out in the cooling cycles from the room temperature to 100 K. The result showed that the effect of the deformation was reduced to one fourth if the mirror was screwed with spring washers. We have explored an effective way to prevent the mirror from being galvanically corroded. A number of samples have been prepared by changing the coating conditions, such as inserting an insulation layer, making a multi-layer and over-coating water blocking layer, or carrying out precision cleaning before coating. Precision cleaning before the deposition and protecting coat with SiO over the gold layer seemed to be effective in blocking corrosion of the aluminum. The SiO over-coated mirror has survived the cooling test for the mid-infrared use and approximately 1 percent decrease in the reflectance has been detected at 6-25 microns compared to gold deposited mirror without coating.

The near-Earth asteroid 308635 (2005 YU55) is a potentially hazardous asteroid which was discovered in 2005 and passed Earth on Nov. 8, 2011 at 0.85 lunar distances. This was the closest known approach by an asteroid of several hundred metres in diameter since 1976 when an object of similar size passed at 0.5 lunar distances. We observed 2005 YU55 from the ground with a recently developed mid-IR camera (miniTAO/MAX38) in N and Q bands and with the Submillimeter Array (SMA) at 1.3 mm. In addition, we obtained space observations with Herschel/PACS at 70, 100, and 160 mu m. Our thermal measurements cover a wide range of wavelengths from 8.9 mu m to 1.3 mm and were taken after opposition at phase angles between -97 degrees and -18 degrees. We performed a radiometric analysis via a thermophysical model and combined our derived properties with results from radar, adaptive optics, lightcurve observations, speckle, and auxiliary thermal data. We find that 308635 (2005 YU55) has an almost spherical shape with an effective diameter of 300 to 312 m and a geometric albedo p(V) of 0.055 to 0.075. Its spin axis is oriented towards celestial directions (lambda(ecl), beta(ecl)) = (60 degrees +/- 30 degrees, -60 degrees +/- 15 degrees), which means it has a retrograde sense of rotation. The analysis of all available data combined revealed a discrepancy with the radar-derived size. Our radiometric analysis of the thermal data together with the problem to find a unique rotation period might be connected to a non-principal axis rotation. A low to intermediate level of surface roughness (rms mean slope in the range 0.1-0.3) is required to explain the available thermal measurements. We found a thermal inertia in the range 350-800 Jm(-2) s(-0.5) K-1, very similar to the rubble-pile asteroid 25 143 Itokawa and indicating a surface with a mixture of low conductivity fine regolith with larger rocks and boulders of high thermal inertia.

TAO (The University of Tokyo Atacama Observatory) is planned to be constructed at the summit of Co. Chajnantor (5640 m altitude) in Chile. MIMIZUKU (Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe) is a mid-infrared imager (Field of View: 1' x 1'- 2' x 2') and spectrometer (∆λ/λ: 60-230) for the 6.5-m TAO telescope, covering the wavelength range of 2-38 μm. The MIMIZUKU has a unique equipment called Field Stacker (FS) which enables the simultaneous observation of target and reference object. The simultaneity is expected to improve photometric accuracy and to realize long-term monitoring observations. The development status of the MIMIZUKU is reported in this paper. The FS and the cryostat of the MIMIZUKU have been fabricated and under testing. The cold optics (550 mm x 750 mm x 2 floors) with 28 mirrors has been constructed. The mirrors were aligned with the positional precision of 0.1 mm and the angular precision of 0.1 deg. The evaluated optical performance is that the diffraction-limited image at λ &lt;8 μm and the enough compact image (r &lt;2 pix=0.22") at 2 λ ~2μm can be obtained. In the cold optics, the drive systems with backlash-less gears are employed and work well even in cryogenic environment. The grisms made with silicon and germanium have been fabricated by ultraprecision cutting. It was found that their surface roughness, grating constant, and blaze angle almost measure up to the designed values. <P />...

We have been developing high-throughput optical elements with the moth-eye structures for mid-infrared optical systems. The moth-eye structures are optimized for the wavelength of 25-45 μm. It consists of cones with a height of 15-20 μm arranged at an interval of 5 μm. They are formed on silicon substrate by electron-beam lithography and reactive ion etching. As a verification of the usefulness of moth-eye, a double-sided moth-eye silicon plane was fabricated. It shows a transmittance increase of 60% compared with the unprocessed silicon plane. As the first trial of the moth-eye optical element, two silicon lenses with single-sided moth-eye were fabricated. One is a plane-convex lens with the moth-eye on the convex surface. The size of the moth-eye formed region is 30 mm x 30 mm. Its focal length is 186 mm. The other one is a biconvex lens with moth-eye formed region of φ 33 mm and a focal length of 94 mm. Uniform moth-eye pattern was fabricated especially for the second lens sample. Imaging test with the first sample showed that neither image degradation nor focal length variation was induced by the moth-eye fabrication. As a step to grism with moth-eye, a moth-eye grating sample was fabricated. The grating pattern (Grating constant: 124.9 μm, Blaze angle: 4 deg) was successfully fabricated with anisotropic etching. Moth-eye patterns were fabricated on the grating surface. Although the resulted moth-eye was successfully fabricated in the most regions, some non-uniformity was found. It can be attributed to unevenness of resist coating, and improvement of coating method is needed. © 2012 SPIE.

A metal mesh filter is appropriate to a band-pass filter for astronomy in the long mid-infrared between 25 and 40 win, where most of optical materials are opaque. The mesh filter does not require transparent dielectric materials unlike interference filters because the transmission characteristics bare determined by surface plasmon-polariton (SPP) resonances excited on a metal surface with a periodic structure. In this study, we have developed the mesh filters optimized to atmospheric windows at 31.8 and 37.5 mu m accessible from the Chajnantor site of 5,640 m altitude. First, mesh filters made of a gold film of 2 jam thickness have been fabricated. Four identical film-type filters are stacked incoherently to suppress leakages at stop-bands The transmissions of the stacked filters have been measured to be 0.8 at the peaks and below 1 x 10(-3) at the stop-bands at 4 K. The ground-based mid-infrared camera MAX38 has been equipped with the stacked filters and successfully obtained diffraction-limited stellar images at the Chajnantor site. The film-type mesh filter does not have sufficient mechanical strength for a larger aperture and for use in space. We have developed mesh filters with higher strength by applying the membrane technology for X-ray optics. The membrane-type mesh filter is made of SiC and coated with a thin gold layer. The optical performance of the mesh filter is independent of internal materials in principle because the SPP resonances are excited only on the metal surface. The fabricated membrane-type mesh filter has been confirmed to provide comparable optical performance to the film-type mesh filter.

Mid-infrared, 25 - 45 microns, is a very important wavelength region to investigate the physics of lower temperature environments in the universe. There are few transparent materials in the range of mid-infrared except silicon. However, the reflection on a silicon surface reaches 30 % because of its high refractive index (similar to 3.4). To apply silicon to mid-infrared astronomical instruments, we need a way of antireflection and have adopted a moth-eye structure. This structure keeps durable under cryogenic environments, which is advantageous to mid-infrared instruments. We have fabricated three samples of the moth-eye structure on plane silicon surfaces by electron-beam lithograph and reactive ion etching. The structures consist of many cones standing on silicon surfaces. We have substantiated the transmittance of 96 % or higher in the wide range of 20 - 50 microns and higher than 98 % at the maximum. The transmittance of moth-eye surfaces, however, is theoretically expected as 100 %. We have examined the discrepancy between the transmittance of the theory and fabrications with electromagnetic simulations. It has been revealed that shapes of the cones and gaps at the bottom of the cones seriously affect the transmittance. We have estimated a few tolerances for manufacturing the moth-eye structures achieving sufficient transmittance of nearly 100 %.