研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 准教授
- 学位
- 博士（理学）(1995年3月 東京大学)
- J-GLOBAL ID
- 200901077188018891
- researchmap会員ID
- 1000304542
研究分野
1経歴
9-
1999年11月 - 2006年3月
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2003年 - 2006年
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1999年 - 2003年
学歴
4-
- 1995年
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- 1995年
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- 1989年
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- 1989年
論文
110-
Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave 2022年8月27日
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 71(1) 2019年1月We performed a far-IR imaging survey of the circumstellar dust shells of 144 evolved stars as a mission program of the AKARI infrared astronomical satellite using the Far-Infrared Surveyor (FIS) instrument. With this survey, we deliver far-IR surface brightness distributions of roughly 10' x 40' or 10' x 20' areas of the sky around the target evolved stars in the four FIS bands at 65, 90, 140, and 160 mu m. Our objectives are to characterize the far-IR surface brightness distributions of the cold dust component in the circumstellar dust shells, from which we derive the amount of cold dust grains as low as 20 K and empirically establish the early mass loss history. In this first installment of the series, we introduce the project and its aims, describe the observations, data reduction, and surface brightness correction process, and present the entire data set along with the results of integrated photometry measurements (i.e., the central source and circumstellar dust shell together). We find that: (1) far-IR emission is detected from all but one object at the spatial resolution about 30 ''-50 '' in the corresponding bands; (2) roughly 60%-70% of the target sources show some extension; (3) previously unresolved nearby objects in the far IR are now resolved around 28 target sources; (4) the results of photometry measurements are reasonable with respect to the entries in the AKARI/FIS Bright Source Catalogue, despite the fact that the targets were assumed to be point sources when catalogue flux densities were computed; and (5) an IR two-color diagram would place the target sources in a roughly linear distribution that may correlate with the age of the circumstellar dust shell and can potentially be used to identify which targets are more extended than others.
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Publications of the Astronomical Society of Japan 71(1) 2019年1月1日
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 71(1) 2019年1月 査読有りAKARI/IRC is capable of conducting slit-less spectroscopy in the mid-infrared (5-13 mu m) over a 10' x 10' area with a spectral resolution of 50, which is suitable for serendipitous surveys. The data reduction is, however, rather complicated by the confusion of nearby sources after dispersing the spectra. To achieve efficient and reliable data reduction, we first compiled a point-source list from the reference image in each field of view and checked the overlaps of the spectra using their relative positions and fluxes. Applying this procedure to 886 mid-infrared slit-less spectroscopic data taken in the cryogenic phase, we obtained 862 mid-infrared spectra from 604 individual non-overlapping sources brighter than 1.5 mJy. We find a variety of objects in the spectroscopic catalogue, ranging from stars to galaxies. We also obtained a by-product catalogue of 9 mu m point sources containing 42837 objects brighter than 0.3 mJy. The spectroscopic and point-source catalogues are available online.
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Publications of the Astronomical Society of Australia 2018年8月Measurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the formation and evolution of stars and planetary systems in galaxies over cosmic time. Previous infrared missions revealed a great deal about the obscured Universe, but were hampered by limited sensitivity. <P />...
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Science Advances 3(11) 2017年11月 査読有り
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Publications of The Korean Astronomical Society 32(1) 131-133 2017年3月31日
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 69(1) 2017年2月 査読有りWe present a general surface brightness correction method for compact extended sources imaged in the slow-scan pointed observation mode of the Far-Infrared Surveyor (FIS) aboard the AKARI infrared astronomical satellite. Our method recovers correct surface brightness distribution maps by rescaling archived raw FIS maps using the surfacebrightness-dependent inverse FIS response function. The flux of a target source is then automatically corrected for as the simple sum of surface brightnesses within the adopted contour encircling the perimeter of the target (i.e., contour photometry). This correction method is contrasted with the previous aperture photometry method for point sources, which directly corrects for the target flux with a flux-dependent scaling law. The new surface brightness correction scheme is applicable to objects of any shape from unresolved point sources to resolved extended objects, as long as the target is not deemed diffuse, i.e., the total extent of the target source does not exceed too much more than a single FIS scan width of 10. The new correction method takes advantage of the well-defined shape (i.e., the scale invariance) of the point spread function, which enables us to adopt a power-law FIS response function. We analyze the point source photometric calibrator data using the FIS AKARI Slow-scan Tool and constrain the parameters of the adopted power-law FIS response function. We conclude that the photometric accuracy of the new correction method is better than 10% error based on comparisons with the expected fluxes of the photometric calibrators, and that resulting fluxes without the present correction method can lead to up to 230% overestimates or down to 50% underestimates.
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METEORITICS & PLANETARY SCIENCE 51 A616-A616 2016年8月
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Journal of Physics: Conference Series 728 072010 2016年7月
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Revised calibration for near- and mid-infrared images from ∼4000 pointed observations with AKARI/IRCPublications of the Astronomical Society of Japan 68(2) 19-19 2016年4月1日
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Monthly Notices of the Royal Astronomical Society 453(1) 879-892 2015年10月11日
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ASTROPHYSICAL JOURNAL 793(1) 2014年9月 査読有りThe detection of the CO2 absorption band at 4.2 mu(m) in brown dwarf spectra by AKARI has made it possible to discuss CO2 molecular abundance in brown dwarf atmospheres. In our previous studies, we found an excess in the 4.2 mu m CO2 absorption band of three brown dwarf spectra, and suggested that these deviations were caused by high C and O elemental abundances in their atmospheres. To validate this hypothesis, we have constructed a set of models of brown dwarf atmospheres with various elemental abundance patterns, and we investigate the variations of the molecular composition and the thermal structure, and how they affect the near-infrared spectra between 1.0 and 5.0 mu m. The 4.2 mu m CO2 absorption band in some late-L and T dwarfs taken by AKARI is stronger or weaker than predicted by corresponding models with solar abundance. By comparing the CO2 band in the model spectra to the observed near-infrared spectra, we confirm possible elemental abundance variations among brown dwarfs. We find that the band strength is especially sensitive to O abundance, but C is also needed to reproduce the entire near-infrared spectra. This result indicates that both the C and O abundances should increase and decrease simultaneously for brown dwarfs. We find that a weaker CO2 absorption band in a spectrum can also be explained by a model with lower "C and O" abundances.
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Proceedings of The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013) 2014年6月
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Monthly Notices of the Royal Astronomical Society 440(4) 3675-3684 2014年6月1日
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Astrophysical Journal 767(1) 2013年4月10日 査読有りWe derive the radii of 16 brown dwarfs observed by AKARI using their parallaxes and the ratios of observed to model fluxes. We find that the brown dwarf radius ranges between 0.64-1.13 RJ with an average radius of 0.83 RJ . We find a trend in the relation between radii and T eff the radius is at a minimum at T eff ∼ 1600 K, which corresponds to the spectral types of mid- to late-L. The result is interpreted by a combination of radius-mass and radius-age relations that are theoretically expected for brown dwarfs older than 108 yr. © 2013. The American Astronomical Society. All rights reserved..
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ASTROPHYSICAL JOURNAL 760(2) 2012年12月 査読有りWe investigate variations in the strengths of three molecular bands, CH4 at 3.3 mu m, CO at 4.6 mu m, and CO2 at 4.2 mu m, in 16 brown dwarf spectra obtained by AKARI. Spectral features are examined along the sequence of source classes from L1 to T8. We find that the CH4 3.3 mu m band is present in the spectra of brown dwarfs later than L5, and the CO 4.6 mu m band appears in all spectral types. The CO2 absorption band at 4.2 mu m is detected in late-L and T-type dwarfs. To better understand brown dwarf atmospheres, we analyze the observed spectra using the Unified Cloudy Model. The physical parameters of the AKARI sample, i.e., atmospheric effective temperature T-eff, surface gravity log g, and critical temperature T-cr, are derived. We also model IRTF/SpeX and UKIRT/CGS4 spectra in addition to the AKARI data in order to derive the most probable physical parameters. Correlations between the spectral type and the modeled parameters are examined. We confirm that the spectral-type sequence of late-L dwarfs is not related to T-eff, but instead originates as a result of the effect of dust.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 64(6) 2012年12月 査読有りWe present the characterization and calibration of the slow-scan observation mode of the Infrared Camera (IRC) aboard AKARI. The IRC Slow-scan observations were operated at the S9W (9 mu m) and Ll8W (18 mu m) bands. We developed a toolkit for data reduction of the IRC Slow-scan observations. We introduced a "self-pointing reconstruction" method to improve the positional accuracy to as good as 1 ''. The sizes of the point spread functions were derived to be similar to 6 '' at the S9W band and similar to 7 '' at the Ll8W bands in full width at half maximum. Flux calibrations were achieved with observations of 3 and 4 infrared standard stars at the S9W and Ll8W bands, respectively. The flux uncertainties are estimated to be better than 20% from comparisons with the AKARI IRC PSC and the WISE preliminary catalog.
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Publications of The Korean Astronomical Society 27(4) 259 2012年9月 査読有り
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ASTROPHYSICAL JOURNAL LETTERS 751(1) 2012年5月 査読有りWe present the discovery of a source with broadband infrared photometric characteristics similar to Sakurai's object. WISE J180956.27-330500.2 (hereafter J1810-3305) shows very red WISE colors, but a very blue 2MASS [K] versus WISE [W1 (3.4 mu m)] color. It was not visible during the IRAS era, but now has a 12 mu m flux well above the IRAS point-source catalog detection limit. There are also indications of variability in historical optical photographic plates as well as in multi-epoch AKARI mid-infrared measurements. The broadband infrared spectral energy distribution (SED) shape, post-IRAS brightening, and multiwavelength variability are all characteristics also shared by Sakurai's object-a post-asymptotic giant branch (post-AGB) star which underwent a late thermal pulse and recently ejected massive envelopes of dust that are currently expanding and cooling. Optical progenitor colors suggest that J1810-3305 may have been of late spectral class. Its dramatic infrared brightening and the detection of a late-type optical counterpart are consistent with a scenario in which we have caught an extremely massive dust ejection event (in 1998 or shortly before) during the thermal pulse of an AGB star, thus providing a unique opportunity to observe stellar evolution in this phase. J1810-3305 is the only source in the entire WISE preliminary data release with similar infrared SED and variability, emphasizing the rarity of such sources. Confirmation of its nature is of great importance.
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Proceedings of the International Astronomical Union 7(S283) 462 2011年7月
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC 123(905) 852-864 2011年7月The AKARI All-Sky Catalogues are an important infrared astronomical database for next-generation astronomy that take over the IRAS catalog. We have developed an online service, AKARI Catalogue Archive Server (AKARI-CAS), for astronomers. The service includes useful and attractive search tools and visual tools. One of the new features of AKARI-CAS is cached SIMBAD/NED entries, which can match AKARI catalogs with other catalogs stored in SIMBAD or NED. To allow advanced queries to the databases, direct input of SQL is also supported. In those queries, fast dynamic cross-identification between registered catalogs is a remarkable feature. In addition, multiwavelength quick-look images are displayed in the visualization tools, which will increase the value of the service. In the construction of our service, we considered a wide variety of astronomers' requirements. As a result of our discussion, we concluded that supporting users' SQL submissions is the best solution for the requirements. Therefore, we implemented an RDBMS layer so that it covered important facilities, including the whole processing of tables. We found that PostgreSQL is the best open-source RDBMS products for such purpose, and we wrote codes for both simple and advanced searches into the SQL stored functions. To implement such stored functions for fast radial search and cross-identification with minimum cost, we applied a simple technique that is not based on HTM or HEALPix. In contrast, the online application layer became compact and was written in simple procedural PHP codes. In total, our system realizes cost-effective maintenance and enhancements.
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ASTRONOMY & ASTROPHYSICS 528 2011年4月 査読有りContext. Low-to intermediate-mass stars lose a significant fraction of their mass while they are on the asymptotic giant branch (AGB). This mass loss is considered to determine the final stages of their evolution. The material ejected from the stellar photosphere forms a circumstellar envelope in its surroundings. Layers of circumstellar envelope constitute the footprint of mass-loss history. Aims. Our aim is to probe the mass-loss history in the carbon star U Hya in the last similar to 10(4) years by investigating the distribution of dust in the circumstellar envelope with high spatial resolution. Methods. We observed U Hya in the far-infrared (FIR) at 65, 90, 140, and 160 mu m simultaneously, using the slow scan observing mode of the far-infrared surveyor (FIS) aboard the infrared astronomical satellite AKARI. It produced a map of similar to 10' x 40' in size in each band. Results. The FIS maps reveal remarkably circular, ring-like emission structure almost centered on the star, showing the presence of a detached, spherical dust shell. A hollow dust shell model gives the inner radius R-in of 101-107 '' [(2.5-2.6) x 1017 cm], thickness that covers a half of the total dust mass Delta R-hm of 16-23 '' [(3.8-5.6) x 10(16) cm], which gives Delta R-hm/R-in similar to 0.2, and the power-law index of the dust opacity distribution of 1.10-1.15. The dust mass in the shell is well-constrained to be (0.9-1.4) x 10(-4) (kappa(100)/25)(-1) M-circle dot, where kappa(100) is the dust absorptivity at 100 mu m in units of cm(2) g(-1). The dust mass-loss rate at R-in is found to be (1.89.6) x 10(-8)(kappa(100)/25)(-1)(v(e)/15) M-circle dot yr(-1), which shows that the total mass-loss rate in the shell is at least an order of magnitude higher than the current rate, where v(e) is the outflow velocity at R-in in units of km s(-1). An extension of FIR emission along PA similar to -70 degrees is found out to similar to 5' from the star, which is probably a ram-stripping wake by the ISM wind. We also find excess FIR emission that might indicate the earliest departure from spherical symmetry in the AGB mass loss inside the shell. Conclusions. The dust shell of U Hya is a hollow sphere and has an effective width that is narrower than the spatial resolution of the FIS. It could be formed as either a direct consequence of a thermal pulse, a result of two-wind interaction induced by a thermal pulse, a termination shock, or any combination of these processes.
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WHY GALAXIES CARE ABOUT AGB STARS II: SHINING EXAMPLES AND COMMON INHABITANTS 445 627-+ 2011年 査読有りWe have observed the carbon-rich AGB star U Hya in the far-infrared (FIR) at 65, 90, 140, and 160 mu m simultaneously, using the slow-scan observing mode of the Far-Infrared Surveyor (FIS) aboard the Japanese infrared astronomical satellite AKARI. Our aim is to probe the mass-loss history of U Hya in the last similar to 10(4) years by investigating the distribution of cold dust in the extended circumstellar envelope using FIR maps at high spatial resolution. The observed hollow shell and model calculations suggest that the shell was formed as a direct consequence of a thermal pulse, two-wind interactions, a termination shock, or some combination of these processes.
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Astronomy and Astrophysics 514(1) 2010年5月3日Context. The AKARI, a Japanese infrared space mission, has performed an All-Sky Survey in six infrared-bands from 9 to 180 μm with higher spatial resolutions and better sensitivities than IRAS. Aims. We investigate the mid-infrared (9 and 18 μm) point source catalog (PSC) obtained with the infrared camera (IRC) onboard AKARI, in order to understand the infrared nature of the known objects and to identify previously unknown objects. Methods. Color-color diagrams and a color-magnitude diagram were plotted with the AKARI-IRC PSC and other available all-sky survey catalogs. We combined the Hipparcos astrometric catalog and the 2MASS all-sky survey catalog with the AKARI-IRC PSC. We furthermore searched literature and SIMBAD astronomical database for object types, spectral types, and luminosity classes. We identified the locations of representative stars and objects on the color-magnitude and color-color diagram schemes. The properties of unclassified sources can be inferred from their locations on these diagrams. Results. We found that the (B-V) vs. (V-S9W) color-color diagram is useful for identifying the stars with infrared excess emerged from circumstellar envelopes or disks. Be stars with infrared excess are separated well from other types of stars in this diagram. Whereas (J-L18W) vs. (S9W-L18W) diagram is a powerful tool for classifying several object types. Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars form distinct sequences in this color-color diagram. Young stellar objects (YSOs), pre-main sequence (PMS) stars, post-AGB stars, and planetary nebulae (PNe) have the largest mid-infrared color excess and can be identified in the infrared catalog. Finally, we plot the L18W vs. (S9W-L18W) color-magnitude diagram, using the AKARI data together with Hipparcos parallaxes. This diagram can be used to identify low-mass YSOs and AGB stars. We found that this diagram is comparable to the [24] vs. ([8.0]-[24]) diagram of Large Magellanic Cloud sources using the Spitzer Space Telescope data. Our understanding of Galactic objects will be used to interpret color-magnitude diagram of stellar populations in the nearby galaxies that Spitzer Space Telescope observed. Conclusions. Our study of the AKARI color-color and color-magnitude diagrams will be used to explore properties of unknown objects in the future. In addition, our analysis highlights a future key project to understand stellar evolution with a circumstellar envelope, once the forthcoming astronometrical data with GAIA are available. © ESO, 2010.
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ASTRONOMY & ASTROPHYSICS 514 2010年5月 査読有りContext. AKARI is the first Japanese astronomical satellite dedicated to infrared astronomy. One of the main purposes of AKARI is the all-sky survey performed with six infrared bands between 9 mu m and 200 mu m during the period from 2006 May 6 to 2007 August 28. In this paper, we present the mid-infrared part (9 mu m and 18 mu m bands) of the survey carried out with one of the on-board instruments, the infrared camera (IRC). Aims. We present unprecedented observational results of the 9 mu m and 18 mu m AKARI all-sky survey and detail the operation and data processing leading to the point source detection and measurements. Methods. The raw data are processed to produce small images for every scan, and the point sources candidates are derived above the 5 sigma noise level per single scan. The celestial coordinates and fluxes of the events are determined statistically and the reliability of their detections is secured through multiple detections of the same source within milli-seconds, hours, and months from each other. Results. The sky coverage is more than 90% for both bands. A total of 877 091 sources (851 189 for 9 mu m, 195 893 for 18 mu m) are confirmed and included in the current release of the point source catalog. The detection limit for point sources is 50 mJy and 90 mJy for the 9 mu m and 18 mu m bands, respectively. The position accuracy is estimated to be better than 2 ''. Uncertainties in the in-flight absolute flux calibration are estimated to be 3% for the 9 mu m band and 4% for the 18 mu m band. The coordinates and fluxes of detected sources in this survey are also compared with those of the IRAS survey and are found to be statistically consistent.
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Publications of the Astronomical Society of Japan 62(2) 273-286 2010年4月We carried out near- to mid-infrared imaging and spectroscopic observations of patchy areas in the Small Magellanic Cloud using the Infrared Camera aboard AKARI. Two lOOarcmin2 areas were imaged in 3.2, 4.1, 7, 11, 15, and 24 μm, and also spectroscopically observed in the wavelength range continuously from 2.5 to 13.4μm. The spectral resolving power, λ/△λ, values were about 20, 50, and 50 at 3.5, 6.6, and 10.6 μm, respectively. Other than the two 100 arcmin2 areas, some patchy areas were imaged and/or spectroscopically observed as well. In this paper, we overview the observations and present a list of near- to mid-infrared photometric results, which lists ̃ 12000 near-infrared and ̃ 1800 mid-infrared bright point sources detected in the observed areas. The 10 σ limits are 16.50, 16.12, 13.28, 11.26, 9.62, and 8.76 in Vega magnitudes at 3.2, 4.1, 7, 11, 15, and 24 μm bands, respectively. © 2010. Astronomical Society of Japan.
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ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XIX 434 429-+ 2010年 査読有りWe are developing the AKARI reduction tools for the IRC slow-scan. To create an image, we need position information provided from the satellite telemetry. However, the typical accuracy of the position is as large as similar to 10 ''. Here, we developed a software called self-pointing reconstruction, which is the most important part of the tools. Using this method, the position accuracy reaches as good as similar to 1 ''.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(4) 737-750 2009年8月We present the characterization and calibration of the Slow-Scan observation mode of the Far-Infrared Surveyor (FIS) onboard the AKARI satellite. The FIS, one of the two focal-plane instruments on AKARI, has four photometric bands between 50-180 mu m with two types of Ge:Ga array detectors. In addition to the All-Sky Survey, FIS has also taken detailed far-infrared images of selected targets by using the Slow-Scan mode. The sensitivity of the Slow-Scan mode is one to two orders of magnitude better than that of the All-Sky Survey, because the exposure time on a targeted source is much longer. The point spread functions (PSFs) were obtained by observing several bright point-like objects, such as asteroids, stars, and galaxies. The derived full widths at the half maximum (FWHMs) are similar to 30 '' for the two shorter wavelength bands and similar to 40 '' for the two longer wavelength bands, being consistent with those expected by optical simulation, although a certain amount of excess is seen in the tails of the PSFs. A flux calibration was performed by observations of well-established photometric calibration standards (asteroids and stars) over a wide range of fluxes. After establishing the method of aperture photometry, the photometric accuracy for point-sources is better than +/- 15% in all of the bands, expect for the longest wavelength.
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Experimental Astronomy 23(1) 2009年3月The Space Infrared telescope for Cosmology and Astrophysics (SPICA) is planned to be the next space astronomy mission observing in the infrared. The mission is planned to be launched in 2017 and will feature a 3.5 m telescope cooled to <5 K through the use of mechanical coolers. These coolers will also cool the focal plane instruments thus avoiding the use of consumables and giving the mission a long lifetime. SPICA’s large, cold aperture will provide a two order of magnitude sensitivity advantage over current far infrared facilities (>30 microns wavelength). We describe the scientific advances that will be made possible by this large increase in sensitivity and give details of the mission, spacecraft and focal plane conceptual design....
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 459-+ 2009年 査読有りEstablishing a physical association of cooler, evolved stars with hotter, upper main sequence, luminous blue variables and Wolf-Rayet stars, can help provide constraints on high-mass loss cases of stellar evolution, as well as clarify the formation history of the stellar OB association. We are examining AKARI survey data in search of extended circumstellar material of RSGs and evidence for interaction of said material with ambient ISM connected with the high mass stars. In this initial report, we confirm several cases where IRAS indicated that an extended circumstellar shell was present, and identify candidates where interaction with the ISM appears to be underway.
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 117-+ 2009年 査読有りRecent far-infrared mapping of mass-losing stars by the AKARI Infrared Astronomy Satellite and Spitzer Space Telescope have suggested that far-infrared bow shock structures are probably ubiquitous around these mass-losing stars, especially when these stars have high proper motion. Higher spatial resolution data of such far-infrared bow shocks now allow detailed fitting to yield the orientation of the bow shock cone with respect to the heliocentric space motion vector of the central star, using the analytical solution for these bow shocks under the assumption of momentum conservation across a physically thin interface between the stellar winds and interstellar medium (ISM). This fitting analysis of the observed bow shock structure would enable determination of the ambient ISM flow vector, founding a new technique to probe the 3-D ISM dynamics that are local to these interacting systems. In this review, we will demonstrate this new technique for three particular cases, Betelgeuse, R. Hydrae, and R Cassiopeiae.
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 463-+ 2009年 査読有りWe report here on the discovery of an extended far-infrared shell around the AGB star, R Cassiopeia, made by AKARI and Spitzer. The extended, cold circumstellar shell of R Cas spans nearly 3' and is probably shaped by interaction with the interstellar medium. This report is one of several studies of well-resolved mass loss histories of AGB stars under AKARI and Spitzer observing programs labeled "Excavating Mass Loss History in Extended Dust Shells of Evolved Stars (MLHES)."
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 447-+ 2009年 査読有りWe report far-IR observations with AKARI to search for intracluster dust (ICD, hereafter) from globular clusters. We observed 12 clusters and detected both diffuse and point-like sources through our Mission Program (MP) survey. However, it is found that most of them are not associated with clusters, leaving one possible candidate of ICD cloud (Matsunaga et al. 2008). We also searched the beta-1 Bright Source Catalogue of the AKARI All-Sky Survey for ICD but no likely candidate was found. This paucity suggests that the dust disappears within a lifetime shorter than 5-50 Myr depending on the dust temperature.
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EXOPLANETS AND DISKS: THEIR FORMATION AND DIVERSITY 1158 127-+ 2009年AKARI All-sky Survey observations were carried out in the mid- to far-infrared spectral region with six photometric bands during the cryogenic mission phase of AKARI from May 8, 2006 to August 26, 2007. This paper reports the mid-infrared part of the AKARI all-sky survey. It was carried out with two mid-infrared broad bands centered at 9 and 18 gm. More than 90 percent of entire sky was observed by both bands during this period. The 5 sigma sensitivities for point sources are about 50 and 120 mJy, respectively. The spatial resolution is better than 10 '' at both bands. The AKARI mid-infrared survey achieved a deeper sensitivity and a finer spatial resolution than the previous IRAS survey. the AKARI mid-infrared survey has the sensitivity to detect a debris disk of beta Pic at a distance of 100 pc and several new debris disk candidates have already been discovered at 18 mu m in a preliminary study, separately discussed by Fujiwara et al. (in this volume). More debris disk candidates are expected to be found in further investigations, which will make a significant impact on the statistical study of debris disks.
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 9-+ 2009年AKARI is the first Japanese astronomical infrared satellite mission orbiting around the Earth in a sun-synchronous polar orbit at the altitude of 700 km. One of the major observation programs of the AKARI is an all-sky survey in the mid- to far-infrared spectral regions with 6 photometric bands. The mid-infrared part of the AKARI All-Sky Survey was carried out with the Infrared Camera (IRC) at the 9 and 18 mu m bands with the sensitivity of about 50 and 120 mJy (5 sigma per scan), respectively. The spatial resolution is about 9.4 '' at both bands. AKARI mid-infrared (MIR) all-sky survey substantially improves the MIR dataset of the IRAS survey of two decades ago and provides a significant database for studies of various fields of astronomy ranging from star-formation and debris disk systems to cosmology. This paper describes the current status of the data reduction and the characteristics of the AKARI MIR all-sky survey data.
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 143-+ 2009年 査読有りWe report the results of the near-infrared spectroscopic observations of brown dwarfs with the AKARI/IRC. The spectra covering 2.5-5.0 mu m are significantly better quality than any previous observations ever made from the ground. So far spectra of seven objects are available. Their SEDs are consistent in principle with the prediction by the numerical model atmospheres including dust formation (Unified Cloudy Models; UCMs). We confirm the detection of CO absorption band in late-T dwarfs, supporting the idea of non-equilibrium processes contributing on the chemical abundance in these objects. In addition, we detect the CO2 band for the first time in brown dwarfs. The band commonly presents in the T-dwarfs. This could be a hint to understand the chemistry in the brown dwarf atmospheres.
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 127-+ 2009年 査読有りA Far-IR imaging survey of the circumstellar dust shells of 144 evolved stars has been performed as a mission program with the Far-Infrared Surveyor ( FIS) on the infrared astronomical satellite AKARI. The survey has produced simultaneous maps of 10' x 40' areas in the four FIS bands at 65, 90. 140, and 160 mu m for most of the objects. Maps of 10' x 20' area have been taken for the remaining 17 fainter objects. Extended dust shells, most of which show departure from circular symmetry or offset with respect to the star, have been found in both dozen oxygen-rich and dozen carbon-rich evolved objects. In the carbon star U Hya, however, a circular dust shell centered at the star of similar to 1.30 '' (3.2 x 10(17) cm, similar to 0.1pc) in radius is revealed in the four FIS bands, for the first time by direct imaging in the far-infrared. The FIS images of U Hya are analysed by a simple detached dust shell model. The best fit model gives the inner radius of 2.4 x 10(17) cm, thickness of 2.2 x 10(17) cm, indices of power-law dust opacity and dust density distribution of 1.1 and 2.5, respectively. Dust mass of 3 x 10(-4) M-circle dot is obtained for the case of a dust opacity of 25 cm(2) g(-1) at 100 mu m. A thinner shell with a smaller index of the density distribution could also be viable. Possible origin of the dust shell of U Hya is discussed.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 S415-S428 2008年12月 査読有りWe report on observations of 12 globular clusters with the Far-Infrared Surveyor (FIS) aboard the AKARI satellite. Our goal is to search for emission from cold dust within clusters. We detected diffuse emissions toward NGC 6402 and 2808, but the IRAS 100 mu m maps show the presence of strong background radiation. They are likely to have been emitted from the Galactic cirrus. We also detected 28 point-like sources mainly in WIDE-S images (90 mu m). At least several of them are not associated with clusters, but background galaxies identified in external catalogs. We present the spectral energy distributions (SEDs) by combining near-and-mid infrared data obtained with the Infrared Camera (IRC), if possible. Those SEDs suggest that most of the point sources are background galaxies. For most of the other clusters, we have confirmed a lack of intracluster dust. We evaluated the upper limits of the intracluster dust mass to be between 10(-5) and 10(-3) M-circle dot, depending on the dust temperature. The inferred lifetime of the intracluster dust is shorter than 5 Myr (T-d = 70 K) or 50 Myr (35 K). Such a short lifetime indicates some mechanism(s) are at work to remove the intracluster dust. We also discuss its impact on the chemical evolution of globular clusters.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 387(2) 601-615 2008年6月We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-mu m band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS (Infrared Astronomy Satellite) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-mu m flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio (S/N) > 5 for a single detector row is 1.1 +/- 0.1 Jy which corresponds to a point-source detection limit of the survey of similar to 0.4 Jy.Wavelet transform offers a multiscale representation of the Time Series Data (TSD). We calculate the continuous wavelet transform of the TSD and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4 sigma can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non-IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non-IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds.
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Proceedings of SPIE - The International Society for Optical Engineering 7010 2008年AKARI is the first Japanese astronomical infrared satellite mission orbiting around the Earth in a sun-synchronous polar orbit at the altitude of 700 km. One of the major observation programs of the AKARI is an all-sky survey in the mid- to far-infrared spectral regions with 6 photometric bands. The mid-infrared part of the AKARI All-Sky Survey was carried out with the Infrared Camera (IRC) at the 9 and 18 μm bands with the sensitivity of about 50 and 120 mJy (5σ per scan), respectively. The spatial resolution is about 9.4" at both bands. AKARI mid-infrared (MIR) all-sky survey substantially improves the MIR dataset of the IRAS survey of two decades ago and provides a significant database for studies of various fields of astronomy ranging from star-formation and debris disk systems to cosmology. This paper describes the current status of the data reduction and the characteristics of the AKARI MIR all-sky survey data.
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SPACE TELESCOPES AND INSTRUMENTATION 2008: OPTICAL, INFRARED, AND MILLIMETER, PTS 1 AND 2 7010 2008年AKARI is the first Japanese astronomical infrared satellite mission orbiting around the Earth in a sun-synchronous polar orbit at the altitude of 700 kin. One of the major observation programs of the AKARI is an all-sky survey in the mid- to far-infrared spectral regions with 6 photometric bands. The mid-infrared part of the AKARI All-Sky Survey was carried out with the Infrared Camera (IRC) at the 9 and 18 mu m bands with the sensitivity of about 50 and 120 mJy (5(5 per scan), respectively. The spatial resolution is about 9.4 '' at both bands. AKARI mid-infrared (MIR) all-sky survey substantially improves the MIR dataset of the IRAS survey of two decades ago and provides a significant database for studies of various fields of astronomy ranging from star-formation and debris disk systems to cosmology. This paper describes the current status of the data reduction and the characteristics of the AKARI MIR all-sky survey data.
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SPACE TELESCOPES AND INSTRUMENTATION 2008: OPTICAL, INFRARED, AND MILLIMETER, PTS 1 AND 2 7010 2008年We have developed an imaging Fourier transform spectrometer (iFTS) for space-based far-infrared astronomical observations. The iFTS employs newly developed photoconductive detector arrays with a capacitive transimpedance amplifier, which makes the iFTS a completely unique instrument. The iFTS was installed as a function of the far-infrared instrument (FIS: Far-Infrared Surveyor) on the Japanese astronomical satellite, AKARI, which was launched on February 21, 2006 (UT) from the Uchinoura Space Center. The iFTS had worked properly in the space environment as well as in laboratory for more than one year before liquid helium ran out on August 26, 2007. The iFTS was operated nearly six hundreds of pointed observations. More than one hundred hours of astronomical observations and almost the same amount of time for calibrations have been carried out in the mission life. Meanwhile. it becomes clear that the detector transient effect is a considerable factor for FTSs with photoconductive detectors. In this paper, the instrumentation of the iFTS and interesting phenomena related to FTSs using photoconductive detectors are described, and the calibration strategy of the iFTS is discussed briefly.
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SPACE TELESCOPES AND INSTRUMENTATION 2008: OPTICAL, INFRARED, AND MILLIMETER, PTS 1 AND 2 7010 2008年We present the in-orbit performance of slow-scan observation of the Far-Infrared Surveyor (FIS) onboard the AKARI satellite. The FIS, one of the two focal-plane instruments of AKARI, has four photometric bands from 50-180 mu m with two kinds of Ge:Ga array detectors. In addition to the All-Sky Survey, the FIS also took images of specific targets by the slow-scan. Because of the longer exposure time on a targeted source, the sensitivity in the slow-scan mode is 1-2 orders of magnitude better than that in the All-Sky Survey mode. In order to evaluate the point spread functions (PSFs), several bright point-like objects such as asteroids, stars, and galaxies were observed. Though significant enhancements are seen at the tails of the PSFs, the derived full width at the half maximum (FWHM) are consistent with those expected from the optical simulation and the laboratory measurements; similar to 40 '' for two shorter wavelength bands and similar to 60 '' for two longer wavelength bands, respectively. The absolute photometric calibration has been performed by observing well established photometric calibration standards (asteroids and stars) in a wide range of fluxes. After the establishment for the method of the aperture photometry, the photometric accuracy for point sources is less than 10% in all bands.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S369-S376 2007年10月AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from mid- to far-infrared. The instruments also have a capability for imaging and spectroscopy in the wavelength range 2-180 mu m in the pointed observation mode, occasionally inserted into a continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90% of the whole sky with a higher spatial resolution and a wider wavelength coverage than that of the previous IRAS all-sky survey. Point-source catalogues of the All-Sky Survey will be released to the astronomical community. Pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.
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2007年8月2日We present the spatially resolved observations of IRAS sources from the Japanese infrared astronomy satellite AKARI All-Sky Survey during the performance verification (PV) phase of the mission. We extracted reliable point sources matched with IRAS point source catalogue. By comparing IRAS and AKARI fluxes, we found that the flux measurements of some IRAS sources could have been over or underestimated and affected by the local background rather than the global background. We also found possible candidates for new AKARI sources and confirmed that AKARI observations resolved IRAS sources into multiple sources. All-Sky Survey observations are expected to verify the accuracies of IRAS flux measurements and to find new extragalactic point sources.
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1ST ARENA CONFERENCE ON LARGE ASTRONOMICAL INFRASTRUCTURES AT CONCORDIA, PROSPECTS AND CONSTRAINTS FOR ANTARCTIC OPTICAL/IR ASTRONOMY 25 175-178 2007年 査読有りAntarctica offers probably the best ground-based conditions for observing in the 1-3 mu m region, and may thus be considered as an alternative to Space for this domain. We examine the potential of integral-field spectro-photometry over wide areas of the sky in this wavelength range for the study of carbon stars, that seems promising. On the other hand, the conditions of transparency, background, and their short-time stability from Antarctic sites still need to be evaluated.
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UNSOLVED PROBLEMS IN STELLAR PHYSICS 948 365-+ 2007年 査読有りWith the Japanese IR Astronomy Satellite, AKARI, we have performed a far-IR imaging survey of extended cold dust shells around evolved stars. Our observations yield far-IR surface brightnesses of these shells, from which we can reconstruct the history of mass loss (as a function of time) during the critical epochs of mass loss near the end of the asymptotic giant branch phase. Below, we will present the motivation of the study, review the past studies, introduce the AKARI Astronomy Satellite and present a glimpse of the preliminary results of the MLHES Mission Programme.
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ASTRONOMY & ASTROPHYSICS 447(3) 971-989 2006年3月 査読有りWe present ESO/VLT spectra in the 2.9-4.1 mu m range for a large sample of infrared stars in the Large Magellanic Cloud (LMC), selected on the basis of MSX and 2MASS colours to be extremely dust-enshrouded AGB star candidates. Out of 30 targets, 28 are positively identified as carbon stars, significantly adding to the known population of optically invisible carbon stars in the LMC. We also present spectra for six IR-bright stars in or near three clusters in the LMC, identifying four of them as carbon stars and two as oxygen-rich supergiants. We analyse the molecular bands of C2H2 at 3.1 and 3.8 mu m, HCN at 3.57 mu m, and sharp absorption features in the 3.70-3.78 mu m region that we attribute to C2H2. There is evidence for a generally high abundance of C2H2 in LMC carbon stars, suggestive of high carbon-to-oxygen abundance ratios at the low metallicity in the LMC. The low initial metallicity is also likely to have resulted in less abundant HCN and CS. The sample of IR carbon stars exhibits a range in C2H2:HCN abundance ratio. We do not find strong correlations between the properties of the molecular atmosphere and circumstellar dust envelope, but the observed differences in the strengths and shapes of the absorption bands can be explained by differences in excitation temperature. High mass-loss rates and strong pulsation would then be seen to be associated with a large scale height of the molecular atmosphere.
MISC
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Astrophysical Journal 753(2) 2012年7月10日We combine data from two all-sky surveys in order to study the connection between the infrared and hard X-ray (>10keV) properties for local active galactic nuclei (AGNs). The Swift Burst Alert Telescope all-sky survey provides an unbiased, flux-limited selection of hard X-ray-detected AGNs. Cross-correlating the 22month hard X-ray survey with the AKARI all-sky survey, we studied 158 AGNs detected by the AKARI instruments. We find a strong correlation for most AGNs between the infrared (9, 18, and 90 μm) and hard X-ray (14-195keV) luminosities, and quantify the correlation for various subsamples of AGNs. Partial correlation analysis confirms the intrinsic correlation after removing the redshift contribution. The correlation for radio galaxies has a slope and normalization identical to that for Seyfert 1 galaxies, implying similar hard X-ray/infrared emission processes in both. In contrast, Compton-thick (CT) sources show a large deficit in the hard X-ray band, because high gas column densities diminish even their hard X-ray luminosities. We propose two photometric diagnostics for source classification: one is an X-ray luminosity versus infrared color diagram, in which type 1 radio-loud AGNs are well isolated from the others in the sample. The other uses the X-ray versus infrared color as a useful redshift-independent indicator for identifying CT AGNs. Importantly, CT AGNs and starburst galaxies in composite systems can also be differentiated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new and upcoming surveys such as WISE and NuSTAR. © 2012. The American Astronomical Society. All rights reserved..
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Astrophys J 751(1,Pt.2) L1,1-L1,6 2012年5月20日
書籍等出版物
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宇宙航空研究開発機構特別資料 JAXA-SP-18-006E 2019年2月 Refereed
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宇宙航空研究開発機構特別資料 JAXA-SP-17-009E 2018年3月 Refereed
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宇宙航空研究開発機構特別資料 JAXA-SP-17-010E 2018年3月 Refereed
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Astronomical Society of the Pacific 2009年 (ISBN: 9781583817162)
講演・口頭発表等
2所属学協会
4共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 基盤研究(C) 2018年4月 - 2022年3月
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日本学術振興会 科学研究費助成事業 基盤研究(C) 2010年 - 2012年
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日本学術振興会 科学研究費助成事業 2007年 - 2010年
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日本学術振興会 科学研究費助成事業 2004年 - 2008年
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日本学術振興会 科学研究費助成事業 2003年 - 2006年
