Observation of C8H- toward IRC +10216

Abstract

Five rotational lines of the C8H- ion were observed in the circumstellar envelope of IRC +10216 with the Nobeyama 45 m telescope. An improved value of the column density of the C8H- radical yielded a [C8H-]Z[C8H] ratio of 37% -nearly 4 times larger than the [C6H-V[C6H] ratio (8.6%) and nearly 1500 times the [C4H-V[C4H] ratio (0.024%), which may indicate more efficient formation of longer carbon chain anions. The excitation temperature of C8H- (16 ± 2K) derived here is somewhat lower than that of the two smaller anions C 6H- (32 K) and C4H- (23 K) in IRC +10216. © 2007. Astronomical Society of Japan.