Z45: A New 45-GHz Band Dual-Polarization HEMT Receiver for the NRO 45-m
  Radio Telescope
  We developed a dual-linear-polarization HEMT (High Electron Mobility
Transistor) amplifier receiver system of the 45-GHz band (hereafter Z45), and
installed it in the Nobeyama 45-m radio telescope. The receiver system is
designed to conduct polarization observations by taking the cross correlation
of two linearly-polarized components, from which we process full-Stokes
spectroscopy. We aim to measure the magnetic field strength through the Zeeman
effect of the emission line of CCS ($J_N=4_3-3_2$) toward pre-protostellar
cores. A linear-polarization receiver system has a smaller contribution of
instrumental polarization components to the Stokes $V$ spectra than that of the
circular polarization system, so that it is easier to obtain the Stokes $V$
spectra. The receiver has an RF frequency of 42 $-$ 46 GHz and an intermediate
frequency (IF) band of 4$-$8 GHz. The typical noise temperature is about 50 K,
and the system noise temperature ranges from 100 K to 150K over the frequency
of 42 $-$ 46 GHz. The receiver system is connected to two spectrometers, SAM45
and PolariS. SAM45 is a highly flexible FX-type digital spectrometer with a
finest frequency resolution of 3.81 kHz. PolariS is a newly-developed digital
spectrometer with a finest frequency resolution of 60 Hz, having a capability
to process the full-Stokes spectroscopy. The Half Power Beam Width (HPBW) of
the beam was measured to be 37$"$ at 43 GHz. The main beam efficiency of the
Gaussian main beam was derived to be 0.72 at 43 GHz. The SiO maser observations
show that the beam pattern is reasonably round at about 10 \% of the peak
intensity and the side-lobe level was less than 3 \% of the peak intensity.
Finally, we present some examples of astronomical observations using Z45.
