Yutaro SEKIMOTO

This paper aims to introduce two types of submillimeter-wave horn antennae designed by the authors and to present numerical findings obtained by an evaluative testing system that has also been developed by the authors. Submillimeter-wave components are widely used in radio-astronomical observation systems. There is a need to minimize (1) the various losses possibly incurred in the wave-receiving unit, and (2) the quantity of the unwanted electromagnetic waves mixing in. It is a well-known fact that a corrugated horn antenna possesses very low levels of cross-polarized field intensity, loss, and side lobes. It is for this reason that the authors have chosen to use corrugated horn antennae as two types of such antennae - one designed for use in the range of 280 GHz to 360 GHz frequencies and tested at 280 GHz, 332 GHz, and 360 GHz, and the other designed for use in the range of 385 GHz to 500 GHz frequencies and tested at 385 GHz, 442.5 GHz, and 500 GHz. The measurements of the antenna beam patterns have been found to largely correspond to those of the numerical analyses; it may be concluded that the antennae are functionally as efficient as they were designed and the testing system doubtless serves the desired purpose.

We present the results of experimental radioastronomical observations of an interstellar molecular spectral line with an SIS (superconductor-insulator-superconductor) receiver pumped by a photonic local oscillator (LO). A millimeter-wave LO signal was generated by feeding an optical comb signal into a W-band (75-110 GHz) photomixer using a uni-traveling-carrier photodiode (UTC-PD). A CS J = 2-1 line at 98 GHz was observed toward a high-mass star-forming region W 51 (H2O). We compared the obtained spectra with those obtained with a conventional Gunn oscillator as an LO. As a result, the line parameters, such as the width, intensity, and frequency, were consistent with each other. The results presented here show that the photonic LO is a very promising source for heterodyne receivers in millimeter- and submillimeter-wave astronomy.

Noise at millimeter wavelengths from a photonic local oscillator (LO) is compared with that from a Gunn oscillator using a low-noise superconductor-insulator-superconductor (SIS) receiver. No significant additional noise is added to the receiver by the photonic LO in the frequency range of 96-110 GHz. [DOI: 10.1143/JJAP.42.L704].

We developed a cryogenic system, which houses 3 cartridge-type superconductor-insulator-superconductor receivers for millimeter and submillimeter wavelengths. Since it was designed as a prototype receiver of the Atacama Large Millimeter/submillimeter Array (ALMA), high stability, accurate alignment, and easy handling were required. To meet these requirements, the cryogenic system included the following technologies: 1) a thermal link without screws for receiver cartridges; 2) a central support structure to reduce vacuum and gravitational deformation; 3) bellows structures to reduce mechanical vibration of the cryocooler; and 4) a 3-stage Gifford McMahon (GM) cryocooler with an He pot (temperature stabilizer) to reduce the thermal ripple. The cryostat and receiver cartridges are composed of three stages. The temperatures on the 4 K, 12 K, and 100 K stages of the cartridge are 3.5 K, 13.4 K, and 78.3 K, respectively. The thermal conductances of the thermal links showed high performances of 1.7 W K-1 at the 4 K stage, 5.6 W K-1 at the 12 K stage, and 3.3 W K-1 at the 100 K stage. The mechanical vibration on the 4 K stage of the cartridge was reduced to one-tenth, as small as approximate to 2 mum peak-to-peak, compared to that on the 4 K coldhead of the cryocooler, approximate to 20 mum peak-to-peak. The temperature ripple on the cartridge was reduced to as small as 2 mK peak-to-peak, which corresponds to one-seventh of the ripple on the 4 K coldhead with an He pot.

We have developed a waveguide-mounted photomixer in the 75-115 GHz band with a uni-traveling carrier photodiode which is optically-pumped by two 1.55-μm lasers. We have successfully demonstrated to produce an output power of〜2 mW at 100 GHz with an input laser power of〜100 mW. An SIS (Superconductor-Insulator-Superconductor) mixer has been pumped by the photomixer as a local oscillator (LO). It is found that in this configuration the photomixer can provide a sufficient LO power required for optimum operation of the SIS mixer in the frequency band from 85 to 110 GHz. We have carried out similar experiment using a Gunn-diode LO source and carefully compared the receiver noise temperature of the SIS mixer with those pumped by the photomixer. It is found that the receiver noise temperatures of the SIS mixer pumped by the photomixer is as low as those pumped by the Gunn oscillator.

We have developed a low-noise submillimeter-wave SIS receiver (320-360 GHz) for a 10 m submillimeter telescope, which was installed at Nobeyama in 2000 February. This receiver and a millimeter-wave SIS receiver are mounted on the ceiling of the Cassegrain receiver cabin of the 10 m telescope. Two curved mirrors couple a shaped Cassegrain beam from the subreflector to mixer horns. The minimum noise temperature measured in front of the receiver was 52 K in double sideband (DSB) at a local oscillator (LO) frequency of 354 GHz, which corresponds to three-times quantum limits (3hv/kB). This noise temperature contributions are resolved into the optics, mixer, and IF parts. The temperature ripple of a two-stage Gifford-McMahon cryocooler has been reduced to be 2 mK peak-to-peak at the mixer block with a helium pot temperature stabilizer. Mechanical vibration (30 μm peak-to-peak) of the cold head degrades the receiver stability.

We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with the Chandra X-Ray Observatory (CXO). The northern part of OMC-3 is found to be particularly rich in new X-ray features; four hard X-ray sources are located in and along the filament of cloud cores. Two sources coincide positionally with the submillimeter-millimeter dust condensations of MMS 2 and 3 or an outflow radio source VLA 1, which are in a very early phase of star formation. The X-ray spectra of these sources show an absorption column of (1-3) × 1023 H cm-2. Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be ∼1030 ergs s-1 at a distance of 450 pc. From the large absorption, positional coincidence, and moderate luminosity, we infer that the hard X-rays are coming from very young stellar objects embedded in the molecular cloud cores. We found another hard X-ray source near the edge of the dust filament. The extremely high absorption of 3 × 1023 H cm-2 indicates that the source must be surrounded by dense gas, suggesting that it is either a young stellar object in an early accretion phase or a Type II AGN (e.g., a Seyfert 2), although no counterpart is found at any other wavelength. In contrast to the hard X-ray sources, soft X-ray sources are found spread around the dust filaments, most of which are identified with IR sources in the T Tauri phase.

We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with the Chandra X-Ray Observatory (CXO). The northern part of OMC-3 is found to be particularly rich in new X-ray features four hard X-ray sources are located in and along the filament of cloud cores. Two sources coincide positionally with the submillimeter-millimeter dust condensations of MMS 2 and 3 or an outflow radio source VLA 1, which are in a very early phase of star formation. The X-ray spectra of these sources show an absorption column of (1-3) × 1023 H cm-2. Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be ∼1030 ergs s-1 at a distance of 450 pc. From the large absorption, positional coincidence, and moderate luminosity, we infer that the hard X-rays are coming from very young stellar objects embedded in the molecular cloud cores. We found another hard X-ray source near the edge of the dust filament. The extremely high absorption of 3 × 1023 H cm-2 indicates that the source must be surrounded by dense gas, suggesting that it is either a young stellar object in an early accretion phase or a Type II AGN (e.g., a Seyfert 2), although no counterpart is found at any other wavelength. In contrast to the hard X-ray sources, soft X-ray sources are found spread around the dust filaments, most of which are identified with IR sources in the T Tauri phase.

The P-3(2)-P-3(1) fine-structure line of the neutral carbon atom (809 GHz) has been observed toward the Orion Kleinmann-Low (KL) region with the Mount Fuji submillimeter-wave telescope. The 6' x 6' area centered at Orion KL has been mapped with a grid spacing of 1'.5. The intensity distribution of the P-3(2)-P-3(1) line is found to be similar to that of the P-3(1)-P-3(0) line; these lines are rather weak toward Orion KL, while they are both bright at Orion KL's northern and southern positions. The excitation temperature determined from the intensity ratio between the P-3(2)-P-3(1) and P-3(1)-P-3(0) lines ranges from 40 to 110 K. The excitation temperature is not enhanced toward Orion KL, whereas it tends to be high in the vicinity of theta (1) Orionis C. These results indicate that the C I emission arises from a photodissociation surface illuminated by strong UV radiation from theta (1) Ori C. The relative reduction in the C I intensities toward Orion KL is found to originate from a relatively low excitation temperature rather than from the depletion of the C I column density. The origin of the low-excitation temperature of C I toward Orion KL is discussed in terms of a radiative transfer effect.

The P-3(2)-P-3(1) fine-structure line of the neutral carbon atom (809 GHz) has been observed toward the Orion Kleinmann-Low (KL) region with the Mount Fuji submillimeter-wave telescope. The 6' x 6' area centered at Orion KL has been mapped with a grid spacing of 1'.5. The intensity distribution of the P-3(2)-P-3(1) line is found to be similar to that of the P-3(1)-P-3(0) line; these lines are rather weak toward Orion KL, while they are both bright at Orion KL's northern and southern positions. The excitation temperature determined from the intensity ratio between the P-3(2)-P-3(1) and P-3(1)-P-3(0) lines ranges from 40 to 110 K. The excitation temperature is not enhanced toward Orion KL, whereas it tends to be high in the vicinity of theta (1) Orionis C. These results indicate that the C I emission arises from a photodissociation surface illuminated by strong UV radiation from theta (1) Ori C. The relative reduction in the C I intensities toward Orion KL is found to originate from a relatively low excitation temperature rather than from the depletion of the C I column density. The origin of the low-excitation temperature of C I toward Orion KL is discussed in terms of a radiative transfer effect.

We report on submillimeter-wave and millimeter-wave observations toward supernova remnants (SNRs) by using the James Clerk Maxwell Telescope, the Mt. Fuji submillimeter-wave telescope, and the Nobeyama 45-m radio telescope. For the supernova remnant W28, which is an EGRET gamma-ray source, we have convincingly detected the broad CO, HCO+, HCN, and SiO emission lines from the shock-accelerated gas due to the SNR-cloud interaction. The previously-reported 1720-MHz OH maser spot is found to be located at the shock front. By using the Mt. Fuji submillimeter-wave telescope, we observed the 492-GHz CI (neutral atomic carbon), 345-GHz CO (3-2) and 330-GHz (CO)-C-13 (3-2) emission toward SNRs, W44 and W51B/C. We found that the CI/CO and CI/(CO)-C-13 intensity ratio tends to be high in the SNR-cloud interaction region in W51B/C SNR. This fact might suggest the CI relative abundance is enhanced by the interaction, not only in the SNR IC 443, but also in W51B/C SNR.

We have observed the OMC-2/3 region in the H13CO+(1-0), HCO+(1-0), and CO(1-0) lines by using the Nobeyama 45 m radio telescope. We have identified 18 dense cores in H13CO+ and eight molecular outflows in CO and HCO+ in OMC-2/3. Four of these outflows are newly found. The line widths of the H13CO+ cores in OMC-2/3 are twice as large as those in dark clouds, and the momentum fluxes (Ṗflow = Pflow/τD = Ṁflow Vflow) of the outflows in OMC-2/3 are approximately 2 orders of magnitude larger than those of outflows in dark clouds. We found that the mass-loss rate of the outflow is proportional to the third power of the core velocity dispersion, which suggests that the outflow mass-loss rate is proportional to the mass infall rate onto the protostar. From a comparison between the properties of cores associated with protostars and those without protostars, we suggest that the dissipation of turbulence initiates star formation.

We report on detection with the ASCA satellite of hard X-rays from far infrared (FIR) star clusters in the giant molecular cloud (GMC) cores of the NGC 6334 star-forming region. Five FIR cores are visible in the hard X-ray band (E > 2 keV), while in the soft X-ray band (E <2 keV) the emission is absorbed, except for one core. The observed spectra can be fitted with thermal emission from a hot plasma, whose temperature of <similar to> 9 keV is significantly higher than those reported of low-mass Class I pre-main-sequence stars (PMSs) (similar to 3 keV) in nearby dark clouds and those of OB-type main-sequence stars (similar to 1 keV). The X-ray luminosity of each core is typically 10(33) erg s(-1) or 10(3) times that of typical low-mass PMSs. The observed hard X-rays may be emitted from young massive stars and loss-mass/intermediate-mass PMSs in the FIR cores. The observed hard X-ray flux can ionize the inner part (tau similar to 0.3 pc) of the GMC cores at a rate comparable to that by cosmic-ray particles. If the L-X/M ratio of similar to 10(-5)L./M. observed in NGC 6334 is typical among GMCs, the X-ray flux from all GMCs in the Galaxy (similar to 10(9) M.) can account for about 20% of the diffuse galactic ridge hard X-ray emission.

We have developed a 1.2m submillimeter-wave telescope at the summit of Mt. Fuji to survey emission lines of the neutral carbon atom(492GHz)toward the Milky Way. A superconductor-insulator-superconductor(SIS) mixer receiver on the Nasmyth focus is used to observe the 800 / 500 / 350GHz bands, simultaneously. The receiver noise temperature is 100K at 350GHz, 120K at 500GHz, and 600k at 800GHz.

We have developed a 1.2 m submillimeter-wave telescope at the summit of Mt. Fuji to survey emission lines of the neutral carbon atom (CI) toward the Milky Way. A superconductor-insulator-superconductor mixer receiver on the Nasmyth focus is used to observe the 492 GHz band in SSB and the 345 GHz band in DSB simultaneously. The receiver noise temperature is 300 K in SSB and 200 K in DSB for 492 and 345 GHz, respectively. The intermediate frequency frequency is 1.8-2.5 GHz. An acousto-optical spectrometer which has the total bandwidth of 0.9 GHz and 1024 channel outputs has also been developed. The telescope was installed at the summit of Mt. Fuji (alt. 3725 m) in July 1998. It has been remotely operated via a satellite communication system from Tokyo or Nobeyama. Atmospheric opacity at Mt. Fuji was 0.4-1.0 at 492 GHz during 30% of the time and 0.07-0.5 at 345 GHz during 60% of the time from November 1998 to February 1999. The system noise temperature was 1000-3000 K in SSB at 492 GHz and 500-2000 K in DSB at 345 GHz. We observed the CI (3P1-3P0: 492 GHz) and CO (J = 3 - 2: 345 GHz) emission lines from nearby molecular clouds with the beam size of 2′.2 and 3′.1, respectively. We describe the telescope system and report the performance obtained in the 1998 winter. © 2000 American Institute of Physics. [S0034-6748(00)04907-8].

© 2000 Astronomical Society of Japan. Provided by the NASA Astrophysics Data System. We report on detection with the ASCA satellite of hard X-rays from far infrared (FIR) star clusters in the giant molecular cloud (GMC) cores of the NGC 6334 star-forming region. Five FIR cores are visible in the hard X-ray band (E > 2 keV), while in the soft X-ray band (E < 2 keV) the emission is absorbed, except for one core. The observed spectra can be fitted with thermal emission from a hot plasma, whose temperature of ∼ 9 keV is significantly higher than those reported of low-mass Class I pre-main-sequence stars (PMSs) (∼ 3 keV) in nearby dark clouds and those of OB-type main-sequence stars (∼ 1 keV). The X-ray luminosity of each core is typically 1033 erg s-1 or 103 times that of typical low-mass PMSs. The observed hard X-rays may be emitted from young massive stars and loss-mass/intermediate-mass PMSs in the FIR cores. The observed hard X-ray flux can ionize the inner part (r ∼ 0.3 pc) of the GMC cores at a rate comparable to that by cosmic-ray particles. If the LX/M ratio of ∼ 10-5 L⊙/M⊙ observed in NGC 6334 is typical among GMCs, the X-ray flux from all GMCs in the Galaxy (∼ 109L⊙) can account for about 20% of the diffuse galactic ridge hard X-ray emission.

Large-scale mapping observations of the 3P1-3P0 fine-structure transition of atomic carbon (C I, 492 GHz) and the J = 3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mount Fuji submillimeter-wave telescope. The observations cover 9 deg2 and include the Orion Nebula M42 and the L1641 dark cloud complex. The C I emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO (J = 1-0). The CO (J = 3-2) emission shows a more featureless and extended distribution than C I. The C I/CO (J = 3-2) integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the C I/13CO (J = 1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the C I and 13CO (J = 1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models.

A distribution of the neutral carbon atom (C I) in Heiles cloud 2 (HCL2) has been investigated with the Mount Fuji submillimeter-wave telescope. A region of 1.2 deg(2) covering a whole region of HCL2 has been mapped with the P-3(1)-P-3(0) fine-structure line (492 GHz) of C I. The global extent of the C I emission is similar to that of (CO)-C-13, extending from southeast to northwest. However, the C I intensity is found to be rather weak in dense cores traced by the J = 1-0 line of (CO)-O-18. On the other hand, strong C I emission is observed in a south part of HCL2 in which the (CO)-O-18 intensity is fairly weak. The C I/CO abundance ratio is greater than 0.8 for the C I peak, whereas it is 0.1 for the dense cores such as the cyanopolyyne peak. The C I-rich cloud found in the south part may be in the early evolutionary stage of dense core formation where C I has not yet been converted completely into CO. This result implies that formation of dense cores is taking place from north to south in HCL2.

We report on mapping observations of the CO J = 3-2 and CO J = 1-0 lines toward supernova remnant (SNR) W28, which is supposed to be an EGRET γ-ray source. A broad CO line emission (maximum linewidth reaches 70 km s-1), which suggests an interaction between the molecular cloud and W28 SNR, was detected. Moreover, the distribution of the unshocked and shocked gas is clearly resolved. The distribution of the shocked gas is similar to that of the radio-continuum emission, and tends to be stronger along the radio-continuum ridge. The unshocked gas is displaced by 0.4-1.0 pc outward with respect to the shocked gas. The spatial relationship between shocked and unshocked gas has been clarified for the first time for the SNR-cloud interaction. All of the known OH maser spots are located along the filament of the shocked gas. These facts convincingly indicate that W28 SNR interacts with the molecular cloud.

We have developed a transportable 492 GHz tipping radiometer to measure the atmospheric opacity at potential sites for future ground-based astronomical observations in the submillimeter-wave band. With this radiometer, we measured the atmospheric opacity at two sites in northern Chile, Pampa la Bola (elevation 4800 m) and Rio Frio (elevation 4100 m), each for a few days. The 492 GHz opacity mostly ranged from 0.5 to 1.5 during the measurements. The 220 GHz opacity was also measured at the same time. The 492 GHz opacity correlates well with the 220 GHz opacity, the ratio between the 492 and 220 GHz opacities being 21.2±0.4. This result supports the standard atmospheric model, and can be used to evaluate the observable fraction of time for submillimeter-wave observations on the basis of the long-term 220 GHz opacity data.

We have studied Cen A (NGC 5128) in the X-ray band (3-20 keV) and soft γ-ray band (40-600 keV) with the Large Area Counter (LAC) of the Ginga sattellite (1989 March and 1990 February) and with a balloon-borne low background detector (Welcome-1, 1991 November), respectively. The observed continuous spectra show a power-law shape (Γ ∼ 1.8) with relatively heavy absorption (NH ∼ 1.5 × 1023H cm-2) at the low-energy end and a possible break at ∼ 180 keV. We analyzed the total spectra as the sum of the direct power-law flux from the central engine, the Compton-scattered flux from a cold cloud near to the engine, and the iron fluorescence-line flux. By assuming that the geometry around the central engine remained unchanged during the two-year period, we studied two possible cold cloud geometries by comparing Monte-Carlo simulations with our observations: the first is the Compton-reflection model in which the cloud forms a slab covering 2π sr behind the central engine, the second is a case where the central source is totally surrounded by a cold cloud. We found that the latter geometry reproduces our data well; the observed power-law spectrum is then identified as direct flux from the central engine which undergoes a break at ∼ 180 keV.

We have developed the azimuth control system utilizing a reaction wheel and a torsion relief motor for the hard X-ray/γ-ray detector Welcome-1 (mk2). In this paper, we describe the hardware characteristics and the performance obtained from the ground test and the flight data.

A high precision clock has been developed for a balloon-borne experiment. In order to study a compact object such as a pulsar, we need the time information as well as the energy and the direction. The clock provides the precise time during the experiment with reference to UTC. It consists of a crystal oscillator on board and a rubidium oscillator backed up by GPS (Global Positioning System) receiver for the calibration on the ground. We have carried out balloon-borne hard X/γ ray observations in Barsil, 1991,with utilizing this clock. By the calibration, the clock operated with the stability of &acd;10^<-12> and the accuracy of 2μsec through the observation. It makes it possible to study an astronomical object by some kinds of detectors at the same time.

資料番号: SA0167043000

We have developed a new kind of phoswich counters that will be capable of detecting low flux hard X-rays/gamma-rays from astronomical objects. The new phoswich counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a rectangular well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). Here, the well-shaped shielding part acts as an active collimator as well as an active shield. We have built a detector system consisting of 64 such phoswich counters: newly developed scintillator (GSO) is used for the detection part and CsI(Tl) is used for the shielding part. The total geometrical area of the 64 detection parts is about 740cm2 and its 3σ sensitivity is expected to reach below 10-5cm-2s-1keV-1 up to 700keV. With several improvements such detectors will be able to detect hard X-rays/gamma-rays at a flux level around 10-6cm-2s-1keV-1 upto 2 MeV. © 1992.

We developed a new kind of star sensor system for a balloon borne experiment. A MCP (micro channel plate) coupled to a CCD camera images the sky. Its field of view is 9.1×6.3 degrees and identifies stars of magnitude &acd;8.1. The star image on the CCD camera is digitalized (512×512 pixels) by the image processing board on VME bus. The microprocessor selects the bright points and then transmits brightness and position of each point to the ground through PCM telemetry (max 2kB/s). On the ground station, the star image is reconstructed every three seconds by using a 32bit workstation. In 1989 we used this star sensor system for the experiment Welcome, to observe hard X/γ rays from astronomical objects. From the reconstructed star image the direction of payload was determined within ±0.02 degree. The attitude of the payload was controlled by yorimodoshi method. And the combination with the new star sensor system enabled us to track the astronomical source with a stability better than ±0.5 degree.