INFRARED EMISSIVITY OF HD IN MAGNETOHYDRODYNAMIC SHOCKS

摘要

A discussion of IR line emission of deuterated hydrogen HD that emanates from regions of shocked molecular gas (C type) is presented. Results are given for shock speeds of 15 < u_s < 45 km s~(-1) and preshock densities of 10~4 < n_H < 10~6 cm~(-3), where all available data for HD to date are utilized. We find that a fraction of HD is converted to atomic deuterium in the hot postshocked gas with u_s approx> 30 km s~(-1) when H_2 becomes sufficiently dissociated. However, a part of this atomic deuterium is recovered to HD through chemical reactions with H_2 when the shocked gas cools down again. Measurements of HD line intensities may be used to derive its abundance in the dense interstellar medium (ISM). Having assumed a deuterium abundance of HD/H_2 = 3.0 x 10~(-5) for the ISM we find that line emission of HD may be detectable with currently available IR spectrometers at ground-based telescopes when the preshock densities are n_H approx> 10~5 cm~(-3). ISO may even observe rotational transitions of HD from less dense gas.