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We report a sensitive search for the rotational transitions of the carbonchain alcohol HC4OH in the frequency range of 21.2-46.7 GHz in the star-formingregion L1527 and the dark cloud TMC-1. The motivation was laboratory detectionof HC4OH by microwave spectroscopy. Despite achieving rms noise levels ofseveral millikelvin in the antenna temperature using the 45 m telescope atNobeyama Radio Observatory, the detection was not successful, leading to 3sigma upper limits corresponding to the column densities of 2.0 \times 1012 and5.6 \times 1012 cm-2 in L1527 and TMC-1, respectively. These upper limitsindicate that [HC4OH]/[HC5N] ratios are less than 0.3 and 0.1 in L1527 andTMC-1, respectively, where HC5N is an HC4-chain cyanide and HC4OH is ahydroxide. These ratios suggest that the cyano carbon chain molecule dominatesthe hydroxyl carbon chain molecule in L1527 and TMC-1. This is contrary to thecase of saturated compounds in hot cores, e.g., CH3OH and CH3CN, and can be achemical feature of carbon chain molecules in L1527 and TMC-1. In addition, thecolumn densities of the "unsubstituted" carbon chain molecule C4H and thesulfur-bearing molecules SO and HCS+ were determined from detected lines inL1527.

A Search for Interstellar Carbon Chain Alcohol HC4OH in Star-Forming Region L1527 and Dark Cloud TMC-1