Spectrometer Using superconductor MIxer Receiver (SUMIRE) for laboratory submillimeter spectroscopy

Abstract

Recent spectroscopic observations by sensitive radio telescopes require accurate molecular spectral line frequencies to identify molecular species in a forest of lines detected. To measure rest frequencies of molecular spectral lines in the laboratory, an emission-type millimeter and submillimeter-wave spectrometer utilizing state-of-the-art radio-astronomical technologies is developed. The spectrometer is equipped with a 200 cm glass cylinder cell, a two-sideband (2SB) superconductor-insulator-superconductor (SIS) receiver in the 230 GHz band, and wide-band auto-correlation digital spectrometers. By using the four 2.5 GHz digital spectrometers, a total instantaneous bandwidth of the 2SB SIS receiver of 8 GHz can be covered with a frequency resolution of 88.5 kHz. Spectroscopic measurements of CH3CN and HDO are carried out in the 230 GHz band so as to examine the frequency accuracy, stability, sensitivity, as well as the intensity calibration accuracy of our system. As for the result of CH3CN, we confirm that the frequency accuracy for lines detected with sufficient signal-to-noise ratio is better than 1 kHz, when the high-resolution spectrometer having a channel resolution of 17.7 kHz is used. In addition, we demonstrate the capability of this system by spectral scan measurement of CH3OH from 216 GHz to 264 GHz. We assign 242 transitions of CH3OH, 51 transitions of 13CH3OH, and 21 unidentified emission lines for 295 detected lines. Consequently, our spectrometer demonstrates sufficient sensitivity, spectral resolution, and frequency accuracy for in-situ experimental-based rest frequency measurements of spectral lines for various molecular species.

Laboratory Measurement of Millimeter-wave Transitions of 13CH2DOH for Astronomical Use

“…The pressure of the gas for all the measurements are kept within the range of 0.51 ± 0.05 Pa and the cell temperature is kept to be 296 ± 1 K (room temperature). The thermal emission of the sample gas is measured against a background of the blackbody radiation at the liquid nitrogen temperature (77 K) by using the twosideband superconductor heterodyne-mixer receiver (Watanabe et al 2021). The backend is a bank of the eXtended Fast Fourier Transform Spectrometers (XFFTS; Klein et al 2006Klein et al , 2012.…”

“…This will benefit future astronomical studies as it covers nearly the entire receiver band (Band 6) that is most frequently used in the Atacama Large Millimeter/submillimeter Array (ALMA). The emission-type millimeter-and submillimeterwave spectrometer, Spectrometer Using superconductor MIxer REceiver (SUMIRE), used in this study (Watanabe et al 2021) enables us to determine the transition frequencies and the line intensities (Section 2). In this study, effective molecular constants of 13 CH 2 DOH are derived by using the common program distributed by JPL (SPFIT; Pickett 1991).…”

Exploring the 100 au Scale Structure of the Protobinary System NGC 2264 CMM3 with ALMA

“…The frequency resolution is 0.98 MHz. (Top) CH3OH lines observed at the room temperature in the laboratory(Watanabe et al 2021). Molecular lines are rich in CMM3A and deficient in CMM3B as found byWatanabe et al (2017).…”

“…Here, we employ the systemic velocities of 7.4 km s −1 and 7.8 km s −1 for CMM3A and CMM3B, respectively (Watanabe et al 2017). The spectrum of CH 3 OH observed at room temperature in laboratory is also shown for reference (Watanabe et al 2021). Molecular emission lines in this figure mostly come from the torsionally excited CH 3 OH (v A = 1).…”

Exploring the 100 au Scale Structure of the Protobinary System NGC 2264 CMM3 with ALMA

“…Here, we employ the systemic velocities of 7.4 km s −1 and 7.8 km s −1 for CMM3A and CMM3B, respectively (Watanabe et al 2017). The spectrum of CH 3 OH observed at room temperature in a laboratory is also shown for reference (Watanabe et al 2021). Molecular emission lines in this figure mostly come from the torsionally excited CH 3 OH (v t = 1).…”