A SEARCH FOR INTERSTELLAR CARBON-CHAIN ALCOHOL HC$_{4}$OH IN THE STAR FORMING REGION L1527

Abstract

We have made a sensitive search for the rotational transitions of carbon-chain alcohol HC$_4$OH with the frequency ragne from 21.2 to 46.7 GHz in the star forming region L1527 in Taurus with rich carbon-chain chemistry. The incentive of this observation was a laboratory detection of HC$_4$OH by the microwave spectroscopy. Despite achieving an rms of several mK in antenna temperature by the 45m telescope at Nobeyama Radio Observatory, the searche for HC$_4$OH was negative, leading to a 5 sigma upper limit corresponding to the column density of $4 \times 10^{12}$ cm$^{-2}$ based on the excitation temperature of 12.3 K. The upper limit indicates that the [HC$_4$-OH]/[HC$_4$-CN] ratio is less than 1.0. The ratio suggests that the cyanide species with carbon-chain structure is dominant in comparison with the hydroxyl one in L1527, which can be the opposite case of saturated compounds, $e.g.$ CH$_3$OH and CH$_3$CN, in hot cores and dark clouds.