149 research outputs found
Measurements of Antenna Surface for a Millimeter-Wave Space Radio Telescope II; Metal Mesh Surface for Large Deployable Reflector
Large deployable antennas with a mesh surface woven by fine metal wires are
an important technology for communications satellites and space radio
telescopes. However, it is difficult to make metal mesh surfaces with
sufficient radio-frequency (RF) performance for frequencies higher than
millimeter waves. In this paper, we present the RF performance of metal mesh
surfaces at 43 GHz. For this purpose, we developed an apparatus to measure the
reflection coefficient, transmission coefficient, and radiative coefficient of
the mesh surface. The reflection coefficient increases as a function of metal
mesh surface tension, whereas the radiative coefficient decreases. The
anisotropic aspects of the reflection coefficient and the radiative coefficient
are also clearly seen. They depend on the front and back sides of the metal
mesh surface and the rotation angle. The transmission coefficient was measured
to be almost constant. The measured radiative coefficients and transmission
coefficients would cause significant degradation of the system noise
temperature. In addition, we carried out an astronomical observation of a
well-known SiO maser source, R Cas, by using a metal mesh mirror on the NRO
45-m radio telescope Coude system. The metal mesh mirror considerably increases
the system noise temperature and slightly decreases the peak antenna
temperature. These results are consistent with laboratory measurements.Comment: 13 pages, 5 figures, accepted for publication in PAS
Millimeter Light Curve with Abrupt Jump in Cyg X-3 2008 April-May Outburst
Cyg X-3 is a well-known microquasar with a bipolar relativistic jet. Its
famous giant radio outbursts have been repeated once every several years.
However, the behavior of the millimeter wave emission has remained unclear
because of limitations of time resolution in previous observations. We report
here millimeter wave observations of Cyg X-3 experiencing giant outbursts with
one of the finest time resolutions. We find a series of short-lived flares with
amplitude of 1-2 Jy in the millimeter light curve of the 2008 April-May
outburst. They have flat spectra around 100 GHz. We also find abrupt and large
amplitude flux density changes with e-folding time of 3.6 minutes or less. The
source size of Cyg X-3 is constrained within 0.4 AU and the brightness
temperature is estimated to be K.Comment: 4 figures, PASJ, in pres
Measurements of Antenna Surface for Millimeter-Wave Space Radio Telescope
In the construction of a space radio telescope, it is essential to use
materials with a low noise factor and high mechanical robustness for the
antenna surface. We present the results of measurements of the reflection
performance of two candidates for antenna surface materials for use in a radio
telescope installed in a new millimeter-wave astronomical satellite, ASTRO-G.
To estimate the amount of degradation caused by fluctuations in the thermal
environment in the projected orbit of the satellite, a thermal cycle test was
carried out for two candidates, namely, copper foil carbon fiber reinforced
plastic (CFRP) and aluminum-coated CFRP. At certain points during the thermal
cycle test, the reflection loss of the surfaces was measured precisely by using
a radiometer in the 41-45 GHz band. In both candidates, cracks appeared on the
surface after the thermal cycle test, where the number density of the cracks
increased as the thermal cycle progressed. The reflection loss also increased
in proportion to the number density of the cracks. Nevertheless, the loss of
the copper foil surface met the requirements of ASTRO-G at the end of the
equivalent life, whereas that of the aluminum-coated surface exceeded the
maximal value in the requirement even before the end of the cycle.Comment: 11 pages, 6 figures, accepted for publication in PAS
Statistical Properties of Molecular Clumps in the Galactic Center 50 km s Molecular Cloud
We present the statistical properties of molecular clumps in the Galactic
center 50 km s molecular cloud (GCM-0.02-0.07) based on observations of
the CS emission line with the Nobeyama Millimeter Array. In the cloud,
37 molecular clumps with local thermal equilibrium (LTE) masses of
were identified by using the {\it clumpfind}
algorithm. The velocity widths of the molecular clumps are about five-fold
those of Galactic disk molecular clouds with the same radius. The
virial-theorem masses are three-fold the LTE masses. The mass and size spectra
can be described by power laws of () and ( pc),
respectively. The statistical properties of the region interacting with the Sgr
A East shell and those of the non-interacting part of the cloud are
significantly different. The interaction probably makes the mass function
steeper, from in the non-interacting part to
in the interacting region. On the other hand, the
interaction presumably truncates the size spectrum on the larger side of pc.Comment: 16 pages, 5 figures, accepted for publication in PAS
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