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Detection of HCN Direct l-Type Transitions Probing Hot Molecular Gas in the Proto-Planetary Nebula CRL 618

S. Thorwirth·F. Wyrowski·P. Schilke·K. M. Menten·S. Bruenken·H. S. P. Mueller·G. Winnewisser
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Abstract

We report the detection of direct l-type transitions towards the proto-planetary nebula CRL 618 during a study of vibrationally excited carbon chains. The J=8,10,11,12,13,14 DJ=0 transitions of HCN in its first excited bending mode v2=1 were detected in absorption against the continuum of the central HII region making use of the Effelsberg 100m telescope and the Very Large Array. Additionally, the J=9 direct l-type transition was detected in emission presumably indicating a weak maser. All lines are blueshifted with respect to the systemic velocity of CRL 618 indicating that the lines originate from a hot, expanding circumstellar envelope. The HCN column density along the line of sight in front of the continuum is 2E18 cm^-2.

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S. Thorwirth, F. Wyrowski, P. Schilke, K. M. Menten, S. Bruenken, H. S. P. Mueller, G. Winnewisser. 2002-11-27. Detection of HCN Direct l-Type Transitions Probing Hot Molecular Gas in the Proto-Planetary Nebula CRL 618. https://doi.org/10.1086/367629

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