1996A&A...312..565T

Our previous discovery of the HC₉N molecule in CRL 2688 via the J=43-42 transition has prompted us to search for other transitions. We report here our detection of the HC₉N J=39-38 emission from the CRL 2688 and CRL 618 nebulae, using the 100-m Effelsberg telescope. Toward CRL 2688, the line is double peaked like the stronger J=43-42 one. Toward CRL 618, the line is tentatively detected; and a reversal ammonia line, non-metastable transition (5,4), appears in the spectrum. This absorption line is due to the ammonia emission in the west side of the fast wind which is absorbed by the cooler outer HII region emitting the radio continuum. We define the hot clump region extending from -30 to the systemic velocity -21 km/sand which emits non-metastable and metastable lines. Our previously described envelope model of CRL 2688 was applied to both HC₉N J=39-38 and J=43-42 observed line profiles to derive the HC₉N abundance and other physical parameters of the envelope.