Mitsunori Araki, Shuro Takano, Hiromichi Yamabe, Naohiro Koshikawa, Koichi Tsukiyama, Aya Nakane, Toshiaki Okabayashi, Arisa Kunimatsu, Nobuhiko Kuze
We report a sensitive search for the rotational transitions of the carbon
chain alcohol HC4OH in the frequency range of 21.2-46.7 GHz in the star-forming
region L1527 and the dark cloud TMC-1. The motivation was laboratory detection
of HC4OH by microwave spectroscopy. Despite achieving rms noise levels of
several millikelvin in the antenna temperature using the 45 m telescope at
Nobeyama Radio Observatory, the detection was not successful, leading to 3
sigma upper limits corresponding to the column densities of 2.0 \times 1012 and
5.6 \times 1012 cm-2 in L1527 and TMC-1, respectively. These upper limits
indicate that [HC4OH]/[HC5N] ratios are less than 0.3 and 0.1 in L1527 and
TMC-1, respectively, where HC5N is an HC4-chain cyanide and HC4OH is a
hydroxide. These ratios suggest that the cyano carbon chain molecule dominates
the hydroxyl carbon chain molecule in L1527 and TMC-1. This is contrary to the
case of saturated compounds in hot cores, e.g., CH3OH and CH3CN, and can be a
chemical feature of carbon chain molecules in L1527 and TMC-1. In addition, the
column densities of the "unsubstituted" carbon chain molecule C4H and the
sulfur-bearing molecules SO and HCS+ were determined from detected lines in
L1527.
View original:
http://arxiv.org/abs/1110.4453
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