SIMBAD references

Abundances for five molecules (C¹⁸O, CS, NH₃, H₂CO, and C₃H₂) and one molecular ion (N₂H⁺) and upper limits for the abundances of one molecule (¹³CO) and one molecular ion (HCO⁺) are derived for gas within the Bok globule Barnard 68 (B68). The abundances were determined using our own BIMA millimeter interferometer data and single-dish data gathered from the literature, in conjunction with a Monte Carlo radiative transfer model. Since B68 is the only starless core to have its density structure strongly constrained via extinction mapping, a major uncertainty has been removed from these determinations. All abundances for B68 are lower than those derived for translucent and cold dense clouds, but perhaps significantly only for N₂H⁺, NH₃, and C₃H₂. Depletion of CS toward the extinction peak of B68 is hinted at by the large offset between the extinction peak and the position of maximum CS line brightness. Abundances derived here for C¹⁸O and N₂H⁺ are consistent with other, recently determined values at positions observed in common.