Research Subjects: Submillimeter-wave and Terahertz Astronomy, Chemical Evolution of Interstellar Molecular Clouds, Star and Planet Formation, Development of Terahertz Detectors
Members: Satoshi Yamamoto and Nami Sakai
Molecular clouds are birthplaces of new stars and planetary systems, which are being studied extensively as an important target of astronomy and astrophysics. Although the main constituent of molecular clouds is a hydrogen molecule, various atoms and molecules also exist as minor components. The chemical composition of these minor species reflects formation and evolution of molecular clouds as well as star formation processes. It therefore tells us how a particular star has been formed. We are studying star formation processes from such a unique viewpoint.
Since the temperature of molecular cloud is as low as 10 K, only way to observe its physical structure and chemical composition is to observe the radio wave emitted from atoms and molecules. In particular, there exist a number of atomic and molecular lines in the millimeter to terahertz region, and we are observing them with various radio telescopes such as Nobeyama 45 m telescope and IRAM 30 m telescope.
We have recently established a new chemistry occurring in the vicinity of a newly born star, which is called Warm Carbon Chain Chemistry (WCCC). We have found high abundances of various carbon-chain molecules in a lukewarm region near the protostar in L1527. This is very surprising, because carbon-chain molecules are known to exist in the early stages of cold starless cores. In WCCC, carbon-chain molecules are produced by gas phase reactions of CH4 which is evaporated from ice mantles. Existence of WCCC clearly indicates a chemical variety of low-mass star forming regions, which would probably reflect a variety of star formation.
In parallel to such observational studies, we are developing a hot electron bolometer mixer (HEB mixer) for the future terahertz astronomy. We are fabricating the diffusion cooled HEB mixer using Nb and the phonon cooling HEB mixer using NbTiN in our laboratory. Our NbTiN mixer shows the noise temperature of 500 K at 800 GHz, which is well comparable to the results reported by other groups. We are also studying bath-temperature dependence of the noise temperature in order to explore the mixing mechanism of the HEB mixer.
 Sakai, N., Sakai, T., Hirota, T., and Yamamoto, S., Abundant Carbon-Chain Molecules toward the Low-Mass Protostar IRAS04368+2557 in L1527, ApJ, 672, 371 (2008)
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