The candidates of long-periodic variable sources in 6.7 GHz methanol masers associated with four high-mass star-forming regions

Results of the long-term monitoring observations of the 6.7 GHz Class II methanol masers associated with the four high-mass star-forming regions by Hitachi 32-m radio telescope are presented. We detected periodic flux variability in G06.795-0.257, G10.472+0.027, G12.209-0.102, and G13.657-0.599 with the periods of 968, 1624, 1272, and 1266 d, respectively, although the detected period is tentative due to the short monitoring term relative to the estimated period. The facts that the flux variation patterns show the symmetric sine curves and that the luminosities of the central protostar and periods of maser flux variation are consistent with the expected period-luminosity (PL) relation suggest that the mechanisms of maser flux variability of G10.472+0.027 and G12.209-0.102 can be explained by protostellar pulsation instability. From the PL relation, central stars of these two sources are expected to be very high-mass protostars with a mass of 40 M and to have the mass accretion rate of 2*10-2 M yr-1. On the other hand, G06.795-0.257 and G13.657-0.599 have the intermittent variation patterns and have luminosities that are an order of magnitude smaller than those expected from PL relation, suggesting variation mechanisms of these sources originated from binary system. Since almost all the maser features vary with the same period regardless of its geometry, periodic accretion model may be appropriate mechanisms for flux variability in G06.795-0.257 and G13.657-0.599.Comment: arXiv admin note: text overlap with arXiv:2301.0143

A New 100-GHz Band Front-End System with a Waveguide-Type Dual-Polarization Sideband-Separating SIS Receiver for the NRO 45-m Radio Telescope

We developed a waveguide-type dual-polarization sideband-separating SIS receiver system of the 100-GHz band for the 45-m radio telescope at the Nobeyama Radio Observatory, Japan. This receiver is composed of an ortho-mode transducer and two sideband-separating SIS mixers, which are both based on the waveguide technique. The receiver has four intermediate frequency bands of 4.0--8.0 GHz. Over the radio frequency range of 80--120 GHz, the single-sideband receiver noise temperatures are 50--100 K and the image rejection ratios are greater than 10 dB. We developed new matching optics for the telescope beam as well as new IF chains for the four IF signals. The new receiver system was installed in the telescope, and we successfully observed the 12CO, 13CO and C18O emission lines simultaneously toward the Sagittarius B2 region to confirm the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, became approximately half of that of the previous receiver system. The Image Rejection Ratios (IRRs) of the two 2SB mixers were calculated from the 12CO and HCO+ spectra from the W51 giant molecular cloud, resulting in > 20 dB for one polarization and > 12 dB for the other polarization.Comment: 10 pages, 13 figures, Accepted for publication in PASJ, version with high resolution figures is available via http://www.nro.nao.ac.jp/library/report/list.htm