Physical conditions in the Protoplanetary Nebula CRL 618 derived from observations of vibrationally excited HC 3
نویسندگان
چکیده
We used the Effelsberg 100 m and IRAM 30 m telescopes to observe vibra-tionally excited cyanoacetylene (HC 3 N) in several rotational transitions toward the proto-planetary nebula CRL 618. Lines from 9 different vibrationally excited states with energies ranging up to 1600 K above ground were detected. The lines show P Cygni profiles indicating that the HC 3 N emission originates from an expanding and accelerating molecular envelope. The HC 3 N rotational temperature varies with velocity, peaks at 520 K, 3 km s −1 blue-shifted from the systemic velocity and decreases with higher blueshift of the gas. The column density of the absorbing HC 3 N is 3–6×10 17 cm −2. We modeled spectra based on spherical models of the expanding envelope which provide an excellent fit to the observations, and discuss the implications of the models. Additionally, lines from 13 C substituted cyanoacetylene were observed. They can be used to constrain the 12 C/ 13 C ratio in this source to 10 ± 2. Subject headings: stars: individual(CRL 618) – stars: AGB and post-AGB – radio lines: stars – stars: mass loss circumstellar matter – line: profiles
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