Probable detection of H2D+ in the starless core Barnard 68

Abstract

Context: The presence of H2D+ in dense cloud cores underlies ion-molecule reactions that strongly enhance the deuterium fraction-ation of many molecular species. Aims: We determine the H 2D+ abundance in one starless core, Barnard 68, that has a particularly well established physical, chemical, and dynamical structure. Methods: We observed the ortho-H2D+ ground-state line 110-111, the N2H+ J = 4-3 line, and the H13CO+ 4-3 line with the APEX telescope. Results: We report the probable detection of the o-H2D+ line at an intensity Tmb = 0.22 ± 0.08 K and exclusively thermal line width, and find only upper limits to the N2H+ 4-3 and H13CO+ 4-3 intensities. Conclusions: Within the uncertainties in the chemical reaction rates and the collisional excitation rates, chemical model calculations and excitation simulations reproduce the observed intensities and that of o-H2D+ in particular. © ESO 2006.