Detection of C 3 in Diffuse Interstellar Clouds

Abstract

The smallest polyatomic carbon chain, C 3 , has been identified in interstellar clouds ( A v ~ 1 mag) toward ζ Ophiuchi, 20 Aquilae, and ζ Persei by detection of the origin band in its A 1 Π u - X 1 Σ ##IMG## [http://ej.iop.org/images/0004-637X/553/1/267/img1.gif] {img1.gif} electronic transition, near 4052 Å. Individual rotational lines were resolved up to J = 30, allowing the rotational-level column densities and temperature distributions to be determined. The inferred limits for the total column densities (~1-2 × 10 12 cm -2 ) offer a strong incentive to laboratory and astrophysical searches for the longer carbon chains. Concurrent searches for C ##IMG## [http://ej.iop.org/images/0004-637X/553/1/267/img2.gif] {img2.gif} , C ##IMG## [http://ej.iop.org/images/0004-637X/553/1/267/img3.gif] {img3.gif} , and C ##IMG## [http://ej.iop.org/images/0004-637X/553/1/267/img4.gif] {img4.gif} were negative, but provide sensitive estimates for their maximum column densities.