Fluorescent molecular hydrogen emission from the reflection nebula NGC 2023

Observations of NGC 2023, obtained at 1.4-2.5 microns using the circular variable filter and a Fabry-Perot interferometer on the 3.8-m UKIRT during August 1984 and December 1985, are reported. Maps in the v = (1-0) S1 line of H2, in the J = (1-0) line of (C-12)O, and at 1.65 and 2.2 microns are presented and characterized in detail. UV-pumped H2 fluorescence is found to come from a circumstellar thin shell of radius 0.3 pc, which appears broken, clumpy, and nonspherical due to internal density variations and which lies just outside the nebula of 1-nm-radius grains proposed by Sellgren (1984) on the basis of continuum observations. 30 references.