Comparative chemistry of diffuse clouds. V. Ammonia and formaldehydeReport as inadecuate




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1 NRAO - National Radio Astronomy Observatory 2 IRAM - Institut de RadioAstronomie Millimétrique 3 LERMA - Laboratoire d-Etude du Rayonnement et de la Matière en Astrophysique

Abstract : Using the VLA and NRAO 140- telescopes we observed the ?1.3 cm 1, 1 and 2, 2 lines of NH3 in absorption and emission toward the compact extragalactic continuum sources NRAO150 B0355+508 and 3C 111 B0415+379. These sources are occulted by some seven local diffuse and translucent clouds showing molecular absorption in OH, CO, HCO+ and C2H: for the four features having NH3 absorption, we find rotational excitation temperatures 18-24 K, suggesting kinetic temperatures of at least 25-30 K. The abundance ratio NNH 3-NHCO^+ is comparable to values quoted for the cyanopolyyne peak in TMC-1 i.e., 2.5 in three of four cases where NH3 was seen. For clouds with higher column density NHCO^+ ? 1012~~cm-2, the NH3 column density NNH 3 is well correlated only with NCS < NNH 3-NCS> ? 1.0 and NH2CO < NNH 3-NH2CO> ? 0.4. NH2CO is well correlated with NNH 3 and NCS ? 2.3 and the H2CO abundance relative to other species is like TMC-1, with ? 2.3.

Keywords : ISM: molecules





Author: H. S. Liszt - R. Lucas - J. Pety -

Source: https://hal.archives-ouvertes.fr/



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