Far Ultraviolet Spectroscopic ExplorerObservations of Molecular Hydrogen in Translucent Interstellar Clouds. II. The Line of Sight toward HD 110432

We report the second study from the FUSE survey of molecular hydrogen intranslucent clouds, for the line of sight toward HD 110432. This star liesbeyond the Coalsack dark nebula, and with E(B-V) = 0.40, and A_V = 1.32 thisline of sight bridges the gap between less extinguished diffuse cloud lines ofsight with A_V \sim 1, such as Zeta Oph, and the translucent clouds with A_V\gtrsim 2 such as HD 73882. Through profile fitting and a curve-of-growthanalysis, we have derived rotational populations for H2 for J = 0--7. The lineof sight has a total molecular hydrogen column density, log N(H2) = 20.68 \pm0.05 cm^{-2}, nearly identical to that toward Zeta Oph, but a factor of threeless than HD 73882. The ratio of N(J=1) to N(J=0) yields a kinetic temperatureT_{kin} = 63 \pm 7 K, similar to other lines of sight with A_V \gtrsim 1. Thehigh-J lines show considerable excitation above this temperature. The high-Jexcitation is similar to that toward Zeta Oph, but much smaller than thattoward HD 73882. Chemical modeling indicates that the physical conditions inthe cloud(s) are very similar to those in the cloud(s) toward Zeta Oph. Ananalysis of IUE spectra of the Lyman-alpha line gives log N(H I) = 20.85 \pm0.15 cm^{-2}. Combined with N(H2), we derive a hydrogen molecular fraction,f_{H2} = 0.58 pm 0.12, statistically identical to that found for the lines ofsight toward Zeta Oph and HD 73882. We also report column densities for the HDand CO molecules. From the combined measurements of hydrogen and carbon-containing molecules, the line of sight toward HD 110432 appears quite similarto the diffuse cloud line of sight toward Zeta Oph, and quite dissimilar to thetranslucent cloud line of sight toward HD 73882.Comment: 28 pages, 7 figures, accepted for publication in The Astrophysical Journa