Development of 45-GHz band receiver

z45 receiver
 According to the recent theoretical works of star formation process, the gravitational collapse of molecular cloud cores is largely influenced by the magnetic field there. However, there are no precise observational measurements of the magnetic field strength in prestellar core regions. We thus plan to directly measure the magnetic field strength by observing the Zeeman splitting of a molecular line, CCS (J_N = 4_3-3_2) which is abundant in the pre-protostellar phase. The CCS molecular line is one of the most suitable probes for the Zeeman splitting, because CCS has a large dipole moment. The 45 m telescope has a good spatial resolution enough to resolve such prestellar cores in nearby star formation regions (the spatial resolution : 0.03 pc in Taurus). The Zeeman splitting frequency is expected to be approximately 60 Hz, and therefore, the Stokes V is quit small, about 0.3 % of I even at the narrow line width of 0.3 km /s.
We are replacing the original 40 GHz band receiver system (H40 and S40) on the 45 m telescope, because the receiver noise temperature (~200 K) is not that low for the current technology and it can detect only one polarization. We then developed a new receiver for dual polarization measurements with a low noise temperature.

Reference
Tokuda, K. et al., "A New 45 GHz Band Receiver with Dual Polarization for NRO 45-m Telescope", ASP Conference Series, Vol. 476, 403, 2013
Nakamura, F. et al., "Cluster Formation Triggered by Filament Collisions in Serpens South", The Astrophysical Journal Letters, 791, 23, 2014
Nakamura, F. et al., "Z45: A New 45-GHz Band Dual-Polarization HEMT Receiver for the NRO 45-m Radio Telescope", Publ. Astron. Soc. Japan, 2015