Tomoo Nagahama

A Spatially Complete 13CO J = 1-0 Survey of the Orion A Cloud

We present the results of new 13CO J = 1–0 observations of the Orion A molecular cloud made with two 4 m telescopes at Nagoya University. The area observed, corresponding to l ~ 208°–215° and b ~ -205 to -180, covers the full extent of this giant molecular cloud at a 20 grid spacing with a 27 beam. The present observations provide the first complete coverage of the cloud in 13CO with a reasonably high angular resolution relative to the clouds size. In addition, the high velocity resolution of 0.1 km s-1 allowed us to resolve velocity components of the 13CO emission. The molecular distribution is highly elongated along the Galactic plane and is filamentary, as is consistent with previous molecular maps. The total molecular mass of the cloud is estimated to be ~5.4 × 104 M⊙. By using the velocity channel maps every 0.5 km s-1, 39 individual filamentary components have been identified, and their basic physical quantities have been estimated. They typically are 4.8 pc in length, 1.4 pc in width, and 660 M⊙ in mass. We also find that these filamentary components are nearly in virial equilibrium.

Ground-based millimeter-wave observations of ozone in the upper stratosphere and mesosphere over Tsukuba

We present ground-based millimeter-wave observations of the upper stratospheric and mesospheric ozone, conducted at the National Institute for Environmental Studies (NIES) in Tsukuba, Japan (36°N, 140°E). The measurements were started in October 1995. The millimeter-wave radiometer used for the present study is equipped with the superconductor-insulator-superconductor (SIS) mixer receiver and the acousto-optical spectrometer (AOS). Vertical profiles of ozone mixing ratio from 20 to 80 km were retrieved from the observed ozone spectra for 23 months from October 1996 to August 1998 by using the weighted-damped least squares algorithm adopted for differential emission. Vertical resolution is estimated to be 14 km from the averaging kernels. The total random error on the retrieval is estimated to range from 3 to 13% in summer, and from 2 to 9% in winter, respectively, between 38 and 76 km in altitude. The ozone number density at 38 km with the radiometer which was convolved with the vertical resolution of the lidar agrees well with that of the lidar within a systematic difference of 1%, indicating that the millimeter-wave data at 38 km are validated by the lidar measurements. Annual and semi-annual variations are clearly seen at 50 and 76 km, respectively, in the time series of the ozone mixing ratio observed during 23 months. The annual variation at 50 km is consistent with that in the climatological models. The semi-annual variation at 76 km observed in this work is similar to that of the Solar Mesospheric Explorer (SME) data, except that the ozone mixing ratio in spring measured with SME is about 1.7 times larger than that in autumn while those with the radiometer are almost same.

Variations of nitric oxide in the mesosphere and lower thermosphere over Antarctica associated with a magnetic storm in April 2012

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 time frame 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 Polar-orbiting Operational Environmental Satellite (POES)/The Meteorological Operational (METOP). We found a rapid response (within 1 h) 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.

4 CO OUTFLOWS AND DENSE GAS IN THE DARK CLOUD COMPLEX NEAR IC5146

We report an outflow survey carried out in the dark cloud complex near IC5146 open cluster using the 12 CO(J=1-0) emission line. The observations were carried out with a 15 element imaging array at the FCRAO (QUARRY). An area of about 130 square arcmin was searched for outflows, corresponding to 17% of the extent of the 13 CO cloud and 40% of that of the C 18 O cloud. Four regions exhibiting high velocity CO wings were newly found, and each of them is associated with IRAS point sources. C 18 O(J=1-0) observations were also made with the Nagoya 4 m radio telescope toward the most massive member of the molecular cloud complex, in which the four outflows are located

Millimeter-Wave Radiometer for the Measurement of Stratospheric ClO Using a Superconductive (SIS) Receiver Installed in the Southern Hemisphere

A new sensitive radiometer for atmospheric minor constituents has been developed by Nagoya University and the National Institute for Environmental Studies (NIES). The instrument equipped low-noise superconducting (SIS) mixer with a system noise temperature of ≈200K (SSB) at 204GHz. The SIS mixer is operated in a single side band mode with a side band ratio grater than 10dB by adjusting the two tunable backshorts of the mixer. Since any additional SSB filters are not necessary, we can simplify the quasi-optical system and reduce the standing waves which makes difficult to achieve a flat spectral baseline. We installed the observation system at Las Campanas Observatory, Chile in December 1999, and started the test observation from 2000 October. We have detected significant ClO emission at 204.3 GHz with an actual observation time of only 4 hours. This is the first detection of the ClO at 40km altitude from the mid-latitude region of the southern hemisphere. The Nagoya-NIES system has enabled continuous monitoring of ClO in the stratosphere with a time resolution of 4 or 5 hours.

Stability of a Quasi-Optical Superconducting NbTiN Hot-Electron Bolometer Mixer at 1.5 THz Frequency Band

We are developing quasi-optical superconducting hot-electron bolometer (HEB) mixer receivers for astronomical and atmospheric remote sensing applications. The microbridge of the HEB mixer was fabricated at room temperature from a 6.8-nm-thick niobium titanium nitride (NbTiN) film deposited on a 20-nm-thick aluminum nitride (AlN) buffer layer, using a helicon sputtering technique at a slow deposition rate. The mixer was cooled to 4.2 K using a closed-cycled mechanical 4 K pulse-tube cryocooler with a temperature fluctuation of ±1.6 mK. The stability of a large-volume NbTiN HEB mixer was studied at 1.47 THz by changing local oscillator (LO) power with the mixer bias voltage fixed. The intermediate frequency (IF) signal measured at 1.5 GHz had a maximum peak at a certain mixer bias current. The receiver noise temperature was lowest at around the IF maximum peak. It was also found that the IF signal was most stable at around the IF maximum peak under conditions in which the instability of LO pumping level, induced by small mechanical vibrations of the cryostat, remained in the optical system.

Ground‐based observations of nitric oxide in the mesosphere and lower thermosphere over Antarctica in 2012–2013

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 time frame 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 POES/METOP (Polar Orbiting Environmental Satellite/Meteorological Operational) 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 time frames, and found that at least two 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.

Ground-based millimeterwave instrument for measurement of stratospheric ClO using a superconductive (SIS) receiver

Abstract In 1997, Nagoya University and the National Institute for Environmental Studies (NIES) started a joint research project to develop a high-sensitivity ground-based millimeter-wave receiver capable of detecting thermal emission from the rotational lines of chlorine monoxide (ClO) and other constituents in the stratosphere. We have already constructed ozone sensors at 110 GHz employing an SIS receiver. In this project, we shall develop a 200–300 GHz SIS receiver system. The receiver noise temperature at 230 GHz is expected to be better than 50 K in single sideband. In 1999, we will install this instrument at Las Campanas Observatory at an altitude of ∼2400 m (29°S, 71°W) in Chile. This project is a first dedicated effort to measure O 3 , ClO and other constituents in South America where the polar vortex in the Antarctic sometimes tends to move away from the South Pole, and this study should be able to provide valuable information on their behavior, giving us a better understanding of the mechanism of O 3 depletion in the mid-latitude region of southern hemisphere.

Ground-based millimeter-wave observations of ozone in the upper stratosphere and mesosphere at Tsukuba and Nagoya

Abstract We report on ground-based observations of the upper stratospheric and mesospheric ozone by using two millimeter-wave radiometers at the National Institute for Environmental Studies (NIES) in Tsukuba and Nagoya University since October 1995 and January 1992, respectively. The 61,5 to 60,6 transition of ozone at 110.836 GHz was observed, and vertical profiles from 38 to 76 km were retrieved. Comparison with the radiometer and co-located ozone lidar results at 38 km shows reasonable agreement with each other, indicating that the radiometer data are reliable. From 19 months of observations, we have clearly detected seasonal and short-term variations of ozone at various altitudes.

Observation of C18O (J=1−0) emission from Cepheus C☆

C18O (J = 1 − 0) emission from Cepheus C was observed for the first time using the millimetre wave telescope of the Department of Astrophysics, Nagoya University. The integrated intensity map reveals three emission cores. Their parameters are derived.