A POSSIBLE CONNECTION BETWEEN ENHANCED CH+ AND INTENSE FAR-ULTRAVIOLET RADIATION-FIELDS

Evidence favoring a radiative formation mechanism for CH+ is described, based largely on new observations of the star BD + 31-degrees-643 in the young cluster IC 348, a region associated with reflection nebulosity and large grains. The CH+ column density in this line of sight is 8.3 x 10(13) cm-2, larger than can be easily explained by shock formation models, and the velocity displacement between the lines of CH+ and cold-gas species such as CH is inconsistent with the expectations of the shock formation hypothesis. In addition, the two observed lines of CH+ are fitted by a very low velocity dispersion parameter (1.5 km s-1), in contrast with other lines of sight where shock or turbulent formation mechanisms may be more appropriate. Optical scattering data, infrared emission, and radio measurements of molecular emission indicate that the material in the line of sight to BD +31-degrees-643 is subjected to a very intense radiation field. Therefore, it is proposed that a strongly enhanced ultraviolet radiation field in IC 348 may contribute to the formation of CH+ in this line of sight. Possible mechanisms are discussed.