15min:

LEWIS M. HOBBS, JULIE A. THORBURN, DONALD G. YORK, TAKESHI OKA, Department of Astronomy and Astrophysics, The University of Chicago, Chicago IL 60637; THEODORE P. SNOW, Center for Astrophysics and Space Astronomy University of Colorado, Boulder, CO 80309-0389; AND JOHN BARENTINE, New Mexico State University, Apache Point Observatory, Sunspot, New Mexico, 88349-0059 .

Using the 3.5 meter telescope at the Apache Point Observatory, we have observed the 0 - 0, 1 - 0, 0 - 1, 1 - 2, and 2 - 1 bands of the A¹ X^{1 +} transition (origin at 4238 Å) of CH⁺ and the 0 - 0 band of the A² X² transition (4307 Å) of CH in emission from HD 44179, the central star of the Red Rectangle. The 0 - 0 band emission of CH⁺ was reported earlier, but all other emission bands are new.

The CH⁺ emission lines are observed up to the Q(7) and the P(6) lines demonstrating population of CH⁺ up to at least J = 6 in the ground state. Since CH⁺ has a large dipole moment (1.656 D, 1.804 D) the spontaneous emission of the J = 6 5 rotational transition at 165.96 cm^-1 is fast (the Einstein coefficient A = 1.81 s^-1, 2.15 s^-1). In order to populate up to the J = 6 level, CH⁺ must be in an environment with a high density on the order of 10⁹ cm^-3. It has to be a cloud of H atoms since H₂ will immediately react with CH⁺ to produce CH₂⁺. Existence of such a high density H I cloud is remarkable.

The observed CH emission, on the other hand, is limited to the R₂(1/2), R₁(3/2) and R₁(5/2) lines all of which can be reached from the lowest two levels in the ground state that are separated by only 17.9 cm^-1 and spontaneous emission between them is slow. This clearly demonstrates that CH⁺ and CH exist in entirely different regions of the cloud surrounding HD 44179. A more detailed analysis will be given.