Journal
ASTROPHYSICAL JOURNAL
Volume 586, Issue 1, Pages 344-355Publisher
UNIV CHICAGO PRESS
DOI: 10.1086/367637
Keywords
circumstellar matter; line : profiles; radio lines : stars; stars : AGB and post-AGB; stars : individual (CRL 618); stars : mass loss
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We used the Effelsberg 100 m and IRAM 30 m telescopes to observe vibrationally excited cyanoacetylene (HC3N) in several rotational transitions toward the proto-planetary nebula CRL 618. Lines from nine different vibrationally excited states, with energies ranging up to 1600 K above ground, were detected. The lines show P Cygni profiles indicating that the HC3N emission originates from an expanding and accelerating molecular envelope. The HC3N rotational temperature varies with velocity, peaks at 520 K, 3 km s(-1) blueshifted from the systemic velocity, and decreases with higher blueshift of the gas. The column density of the absorbing HC3N is (3-6) x 10(17) cm(-2). We modeled spectra based on spherical models of the expanding envelope that provided an excellent fit to the observations and discuss the implications of the models. Additionally, lines from C-13 substituted cyanoacetylene were observed. They can be used to constrain the C-12/C-13 ratio in this source to 10 +/- 2.
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