H. Maezawa

Osaka Prefecture University, Sakai, Ōsaka, Japan

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Publications (190)306.24 Total impact

  • Source
    T Shiino · K Todoroki · N D Minh · L Jiang · S Shiba · Y Uzawa · H Maezawa · N Sakai · S Yamamoto
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    ABSTRACT: Superconducting hot electron bolometer (HEB) mixers have matured as the most sensitive heterodyne detectors for astronomy and atmospheric science in the THz region. The HEB mixer fabrication is based on an ultra thin superconducting film such as Nb, NbN, and NbTiN. In general, the critical temperature (T c) of such thin films is much lower than those of the corresponding bulk materials. In order to improve T c of the thin films, we have employed an AlN film as a buffer layer between a substrate and NbN/NbTiN films. The AlN film is deposited on the quartz or glass substrate in a mixture of Ar and N 2 gas by DC reactive magnetron sputtering. We optimize the Ar and N 2 flow rates to ensure that the X-ray diffraction from the 002 surface of Wurtzite type AlN is dominant. We measure the T c values of the NbN and NbTiN films with the AlN buffer layer (20 nm) deposited on quartz and glass substrates respectively. For the 8 nm NbTiN film on the grass substrate, T c is increased from 8.4 K to 11.0 K by insertion of the AlN buffer layer. For the 10 nm and 6 nm NbN films on the quartz substrate, the T c is increased from 6.9 K to 11.4 K and 6.1 K to 9.8 K respectively. The improvement in Tc would originate from better epitaxial growth of the NbN and NbTiN films on the AlN buffer layer than on the bare substrate. The HEB mixer fabrication using the NbN and NbTiN films with the AlN buffer layer is ongoing.
    Full-text · Article · Dec 2023
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    ABSTRACT: We have observed the four hyperfine components of the 18 cm OH transition toward the translucent cloud eastward of Heiles Cloud 2 (HCL2E), the cold dark cloud L134N, and the photodissociation region of the ρ-Ophiuchi molecular cloud with the Effelsberg 100 m telescope. We have found intensity anomalies among the hyperfine components in all three regions. In particular, an absorption feature of the 1612 MHz satellite line against the cosmic microwave background has been detected toward HCL2E and two positions of the ρ-Ophiuchi molecular cloud. On the basis of statistical equilibrium calculations, we find that the hyperfine anomalies originate from the non-LTE population of the hyperfine levels, and can be used to determine the kinetic temperature of the gas over a wide range of H2 densities (102-107 cm-3). Toward the center of HCL2E, the gas kinetic temperature is determined to be 53 ± 1 K, and it increases toward the cloud peripheries (∼60 K). The ortho-to-para ratio of H2 is determined to be 3.5 ± 0.9 from the averaged spectrum for the eight positions. In L134N, a similar increase of the temperature is also seen toward the periphery. In the ρ-Ophiuchi molecular cloud, the gas kinetic temperature decreases as a function of the distance from the exciting star HD 147889. These results demonstrate a new aspect of the OH 18 cm line that can be used as a good thermometer of molecular cloud envelopes. The OH 18 cm line can be used to trace a new class of warm molecular gas surrounding a molecular cloud, which is not well traced by the emission of CO and its isotopologues. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Dec 2015 · The Astrophysical Journal
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    ABSTRACT: We have mapped the Orion-A giant molecular cloud in the CO (J = 4–3) line with the Tsukuba 30 cm submillimeter telescope. The map covered a 7.125 deg2 area with a 9′ resolution, including main components of the cloud such as the Orion Nebula, OMC-2/3, and L1641-N. The most intense emission was detected toward the Orion KL region. The integrated intensity ratio between CO (J = 4–3) and CO (J = 1–0) was derived using data from the Columbia–Universidad de Chile CO survey, which was carried out with a comparable angular resolution. The ratio was r4−3/1−0 ∼ 0.2 in the southern region of the cloud and 0.4–0.8 at star forming regions. We found a trend that the ratio shows higher values at the edges of the cloud. In particular, the ratio at the northeastern edge of the cloud at (l, b) ≈ (208$_{.}^{\circ}$375, −19$_{.}^{\circ}$0) shows the highest value of 1.1. The physical condition of the molecular gas in the cloud was estimated by non-LTE calculation. The result indicates that the kinetic temperature has a gradient from north (Tkin = 80 K) to south (20 K). The estimation shows that the gas associated with the edge of the cloud is warm (Tkin ∼ 60 K), dense ($n_{\mathrm{H_2}}\sim 10^{4}\:$cm−3), and optically thin, which may be explained by heating and sweeping of interstellar materials from OB clusters.
    Preview · Article · Nov 2015 · Publications- Astronomical Society of Japan
  • N Yamaguchi · S Morita · C F Dong · M Goto · H Maezawa · H Miyauchi
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    ABSTRACT: The absolute calibration factor of extreme ultraviolet spectroscopic instrument which has recently been determined from absolute radiation profile measurement of bremsstrahlung continuum has been investigated by comparing the calculated diffraction efficiency of grating. An overall tendency of the wavelength dependence of the calibration factor from 40 Å to 500 Å can be reproduced by that of the grating efficiency, especially the agreement between the measured calibration factor and the calculated grating efficiency has been found to be fairly good for the wavelength range 200 Å-500 Å.
    No preview · Article · Jun 2015 · The Review of scientific instruments
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    Hiroyuki Maezawa
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    ABSTRACT: Recently, a next-generation heterodyne mixer detector—a hot electron bolometer (HEB) mixer employing a superconducting microbridge—has gradually opened up terahertz-band astronomy. The surrounding state-of-the-art technologies including fabrication processes, 4 K cryostats, cryogenic low-noise amplifiers, local oscillator sources, micromachining techniques, and spectrometers, as well as the HEB mixers, have played a valuable role in the development of super-low-noise heterodyne spectroscopy systems for the terahertz band. The current developmental status of terahertz-band HEB mixer receivers and their applications for spectroscopy and astronomy with ground-based, airborne, and satellite telescopes are presented.
    Preview · Article · Mar 2015 · IEICE Transactions on Electronics
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    ABSTRACT: We have developed waveguide-type low-noise superconducting hot-electron bolometer (HEB) mixers for astronomical observations in the 1.3–1.5 THz region by using a relatively thick NbTiN superconducting film (10.8 nm). We have achieved a receiver noise temperature of 490 K (DSB: double side band) at 1.475 THz. This noise temperature corresponds to seven times the quantum noise. According to gain bandwidth measurements, the contribution of diffusion cooling is found to be responsible for such a good noise performance.
    No preview · Article · Mar 2015 · Japanese Journal of Applied Physics
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    ABSTRACT: We present fully sampled ~3' resolution images of the 12CO(J=2-1), 13CO(J=2-1), and C18O(J=2-1) emission taken with the newly developed 1.85-m mm-submm telescope toward the entire area of the Orion A and B giant molecular clouds. The data were compared with the J=1-0 of the 12CO, 13CO, and C18O data taken with the Nagoya 4-m telescope and the NANTEN telescope at the same angular resolution to derive the spatial distributions of the physical properties of the molecular gas. We explore the large velocity gradient formalism to determine the gas density and temperature by using the line combinations of 12CO(J=2-1), 13CO(J=2-1), and 13CO(J=1-0) assuming uniform velocity gradient and abundance ratio of CO. The derived gas density is in the range of 500 to 5000 cm-3, and the derived gas temperature is mostly in the range of 20 to 50 K along the cloud ridge with a temperature gradient depending on the distance from the star forming region. We found the high-temperature region at the cloud edge facing to the HII region, indicating that the molecular gas is interacting with the stellar wind and radiation from the massive stars. In addition, we compared the derived gas properties with the Young Stellar Objects distribution obtained with the Spitzer telescope to investigate the relationship between the gas properties and the star formation activity therein. We found that the gas density and star formation efficiency are well positively correlated, indicating that stars form effectively in the dense gas region.
    Preview · Article · Dec 2014 · The Astrophysical Journal Supplement Series
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    ABSTRACT: We report temporal variations of the partial column density of nitric oxide (NO) in an altitude range 75–105 km at Syowa Station, Antarctica, from January 2012 to September 2013. We found two patterns of NO temporal variation: (1) a seasonal cycle with a maximum in winter and a minimum in summer, and (2) short-term enhancements on a timeframe of 5–10 days associated with solar activities. In the seasonal cycle, the variation pattern of NO showed good agreement with scotoperiod of solar radiation rather than the downwelling atmospheric transport, suggesting that photodissociation is the main driver of the seasonal variation. To study the short-term enhancements, we compared the NO column density with the proton and electron fluxes obtained by the Polar Orbiting Environmental Satellite/Meteorological Operational (POES/METOP) satellites. There is a weak but significant correlation between the NO and the electron flux, but no correlation between the NO and the proton flux. We also made a detailed comparison of the time series of NO and proton/electron fluxes for 12 selected 25-day timeframes, and found that at least 2 remarkable NO enhancements occurred without any solar proton events (SPEs). During electron precipitation, the NO column density peaked 1–5 days after the commencement of geomagnetic storms, whereas the relationship between NO and the solar proton is not clear because the electron flux also increased at the same time. These results suggest that energetic electron precipitation may be a major cause of NO enhancements above Syowa station in the auroral region, even during SPEs.
    No preview · Article · Sep 2014 · Journal of Geophysical Research: Space Physics
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    ABSTRACT: The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS ($J_N=4_3-3_2$), HC$_3$N ($J=5-4$), N$_2$H$^+$ ($J=1-0$), and SiO ($J=2-1, v=0$) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely-strong CCS emission is detected. The CCS-to-N$_2$H$^+$ abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different $V_{\rm LSR}$. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few $\times \ 10^5$ yr because CCS is abundant only in such a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is $0.4 \times \ 10^5$ yr, is extremely high as about 70 percent in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.
    Preview · Article · Jul 2014 · The Astrophysical Journal Letters

  • No preview · Conference Paper · Jun 2014
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    ABSTRACT: We report extreme enhancements of the nitric oxide (NO) column density observed with the ground-based millimeter-wave spectroscopic radiometer installed at Syowa Station, Antarctica, during a large geomagnetic storm in April 2012. From the NO spectrum line shape and NO column density relationship with solar radiation, we concluded that the NO was emitted in the altitude range between 75 km and 100 km. The column density of NO gradually increased during the recovery phase. In addition to variations on a timeframe of several days, we found diurnal variations. The increase of NO was related to precipitated electrons in the energy range of 30–300 keV observed by POES/METOP. We found a rapid response (within one hour) and a one-to-one correspondence between them. For the first time we show that a remarkable increase of the column density of NO is caused by dawn-dusk asymmetry of the plasma sheet electrons.
    No preview · Article · Apr 2014
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    ABSTRACT: We have made new CO observations of two molecular clouds, which we call "jet" and "arc" clouds, toward the stellar cluster Westerlund 2 and the TeV gamma-ray source HESS J1023-575. The jet cloud shows a linear structure from the position of Westerlund 2 on the east. In addition, we have found a new counter jet cloud on the west. The arc cloud shows a crescent shape in the west of HESS J1023-575. A sign of star formation is found at the edge of the jet cloud and gives a constraint on the age of the jet cloud to be ~Myrs. An analysis with the multi CO transitions gives temperature as high as 20 K in a few places of the jet cloud, suggesting that some additional heating may be operating locally. The new TeV gamma-ray images by H.E.S.S. correspond to the jet and arc clouds spatially better than the giant molecular clouds associated with Westerlund 2. We suggest that the jet and arc clouds are not physically linked with Westerlund 2 but are located at a greater distance around 7.5 kpc. A microquasar with long-term activity may be able to offer a possible engine to form the jet and arc clouds and to produce the TeV gamma-rays, although none of the known microquasars have a Myr age or steady TeV gamma-rays. Alternatively, an anisotropic supernova explosion which occurred ~Myr ago may be able to form the jet and arc clouds, whereas the TeV gamma-ray emission requires a microquasar formed after the explosion.
    Full-text · Article · Jan 2014 · The Astrophysical Journal

  • No preview · Article · Oct 2013
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    ABSTRACT: We have developed low-noise waveguide-type superconducting hot electron bolometer (HEB) mixers for astronomical observations in the 0.8-1.0 and 1.3-1.5 THz bands, by using a relatively thick NbTiN superconducting film (10.8 nm). The receiver noise temperature of 350 K (DSB) at 0.81 THz and 490 K at 1.475 THz has been achieved. We have built the 0.8-1.0/1.3-1.5 THz dual band heterodyne receiver using these low noise HEB mixers, and have installed it on the ASTE (Atacama Submillimeter Telescope Experiment) 10 m telescope in Chile in 2011. The 13CO emission (J = 8-7 : 0.8813 THz) has successfully been detected toward the Orion A molecular cloud with our HEB mixer receiver.
    No preview · Article · Oct 2013
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    ABSTRACT: Stars form out of dense cores in turbulent, magnetized molecular clouds. However, the role of magnetic fields in star formation remains poorly understood both theoretically and observationally. This is in part due to the lack of the observational characterization of the magnetic fields that are associated with the dense cores prior to star formation, or pre-protostellar cores. To shed light on the issue of the magnetic field in the gravitational collapse of pre-protostellar cores, we have started a project of the magnetic field measurements toward pre-protostellar cores using the Zeeman splitting of CCS (JN = 43 - 32) line. We are now developing a new 45GHz band, dual polarization, reciever for the Nobeyama 45m telescope. In this contribution, we summarize a current status of our Zeeman project and future plan.
    No preview · Article · Oct 2013
  • H. Inokuma · N. Sakai · H. Maezawa · K. Menten · S. Yamamoto
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    ABSTRACT: We have recently observed four hyperfine components of the ground state Λ-doublet-type transition of OH toward several positions in the Taurus Molecular Cloud with the Effelsberg 100 m radio telescope. We have found that the 1612 MHz line appears in absorption toward the eastern position of HCL2, where the [CI](3P1-3P0) emission shows a local peak. Furthermore, the spectrum observed toward the other positions in HCL2 shows two velocity components. The higher velocity component is seen in absorption, whereas the lower velocity component is seen in emission. In order to understand the above results, we have made statistical equilibrium calculations of the OH molecule. It is found that the 1612 MHz line appears in absorption only when the gas kinetic temperature is higher than 40 K. Thus, intensities of the four hyperfine components of OH can be a good thermometer. The combination of emission and absorption observed in HCL2 would reflect a cloud structure like cold dense cores surrounded by a warm less-dense envelope.
    No preview · Article · Oct 2013
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    ABSTRACT: We are developing a new dual polarization receiver at 45GHz band to be installed on the Nobeyama 45 m radio telescope. The purpose of the receiver is to measure the polarization difference caused by the Zeeman effect in magnetized molecular cores, and then we are focusing on the stability of the polarization observations for the development. The magnetic field is considered to play an important role in a star formation process. However, our understanding of the magnetic field in molecular clouds/cores is still very limited, because the measurement of the magnetic field has been quite difficult as it requires very sensitive, stable receiver system. We then plan to develop a new receiver system for measuring the Zeeman effect, and the details about the project is described by Nakamura et al. in this volume. In this presentation, we focus on the development of the new dual polarization receiver.
    No preview · Article · Oct 2013
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    ABSTRACT: We have developed a new mm-submm telescope with a diameter of 1.85-m installed at the Nobeyama Radio Observatory. The scientific goal is to precisely reveal the physical properties of molecular clouds in the Milky Way Galaxy by obtaining a large-scale distribution of molecular gas, which can also be compared with large-scale observations at various wavelengths. The target frequency is ̃230 GHz; simultaneous observations at the molecular rotational lines of J = 2-1 of three carbon monoxide isotopes (12CO, 13CO, C18O) are achieved with a beam size (HPBW) of 2:07. In order to accomplish the simultaneous observations, we have developed waveguide-type sidebandseparating SIS mixers to obtain spectra separately in the upper and lower side bands. A Fourier digital spectrometer with a 1 GHz bandwidth having 16384 channels is installed, and the bandwidth of the spectrometer is divided into three parts, corresponding to each of the three spectra; the IF system has been designed so as to inject these three lines into the spectrometer. A flexible observation system was created mainly in Python on Linux PCs, enabling effective OTF (On-The-Fly) scans for large-area mapping. The telescope is enclosed in a radome with a membrane covered to prevent any harmful effects of sunlight, strong wind, and precipitation in order to minimize errors in the telescope pointing, and to stabilize the receiver and the IF devices. From 2011 November, we started science operation, resulting in a large-scale survey of the Orion A/B clouds, Cygnus OB7, Galactic Plane, Taurus, and so on. We also updated the receiver system for dual-polarization observations.
    Preview · Article · Aug 2013 · Publications- Astronomical Society of Japan
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    ABSTRACT: We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC3603 in the transitions 12CO(J=2-1, J=1-0) and 13CO(J=2-1, J=1-0). We suggest that two molecular clouds at 13 km s-1 and 28 km s-1 are associated with NGC3603 as evidenced by higher temperatures toward the H II region as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ~20 km s-1. We suggest that the two clouds collided with each other a Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster which is as young as a Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along side Westerlund2 where formation may have been triggered by a cloud-cloud collision.
    Full-text · Article · Jun 2013 · The Astrophysical Journal
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    ABSTRACT: We present an analysis of the interstellar medium (ISM) toward the γ-ray supernova remnant (SNR) W44. We used NANTEN2 12CO(J = 2-1) and 12CO(J = 1-0) data and Arecibo H I data in order to identify the molecular and atomic gas in the SNR. We confirmed that the molecular gas is located in the SNR shell with a primary peak toward the eastern edge of the shell. We newly identified high-excitation molecular gas along the eastern shell of the SNR in addition to the high-excitation broad gas previously observed inside the shell; the line intensity ratio between the 12CO(J = 2-1) and 12CO(J = 1-0) transitions in these regions is greater than ~1.0, suggesting a kinetic temperature of 30 K or higher, which is most likely due to heating by shock interaction. By comparing the ISM with γ-rays, we find that target protons of hadronic origin are dominated by molecular protons of average density around 200 cm–3, where the possible contribution of atomic protons is 10% or less. This average density is consistent with the recent discovery of the low-energy γ-rays suppressed in 50 MeV-10 GeV as observed with AGILE and Fermi. The γ-ray spectrum differs from place to place in the SNR, suggesting that the cosmic-ray (CR) proton spectrum significantly changes within the middle-aged SNR perhaps due to the energy-dependent escape of CR protons from the acceleration site. We finally derive a total CR proton energy of ~1049 erg, consistent with the SN origin of the majority of the CRs in the Galaxy.
    Full-text · Article · Apr 2013 · The Astrophysical Journal

Publication Stats

1k Citations
306.24 Total Impact Points

Institutions

  • 2012-2015
    • Osaka Prefecture University
      • • Department of Physical Science
      • • Graduate School of Science
      Sakai, Ōsaka, Japan
  • 1997-2015
    • High Energy Accelerator Research Organization
      • Photon Factory
      Tsukuba, Ibaraki, Japan
    • Institute Energy Economics Japan
      Edo, Tōkyō, Japan
  • 2005-2011
    • Nagoya University
      • Solar-Terrestrial Environment Laboratory
      Nagoya, Aichi, Japan
  • 2010
    • Raman Research Institute
      Bengalūru, Karnataka, India
  • 2000-2008
    • The University of Tokyo
      • Department of Physics
      Tōkyō, Japan
  • 2003-2004
    • National Astronomical Observatory of Japan
      • Astronomy Data Center
      Edo, Tōkyō, Japan
  • 1992-1996
    • University of Tsukuba
      • Applied Physics
      Tsukuba, Ibaraki, Japan
  • 1966-1992
    • Tokyo Medical and Dental University
      • • Department of Internal Medicine
      • • Department of Medicine
      Edo, Tōkyō, Japan