The abundance distribution of C4H in IRC + 10216

Details The abundance distribution of C4H in IRC + 10216 The abundance distribution of C4H in IRC + 10216

Apr 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...407l..37d&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 407, no. 1, p. L37-L40.

Astronomy and Astrophysics

Astrophysics

26

Carbon Stars, Photochemical Reactions, Stellar Envelopes, Stellar Models, Stellar Spectra, Concentration (Composition), Emission Spectra, Interferometers, Line Spectra, Spectrum Analysis

Scientific paper

We have observed the N = 9-8 spin doublet emission line of C4H at 85.6 GHz in the carbon star IRC + 10216 with the BIMA millimeter interferometer. The aperture synthesis images have an angular resolution of about 10 arcsec and a velocity resolution of about 1.3 km/s. The data clearly show that C4H is distributed in a shell surrounding the central star, with little emission from the inner envelope. The peak of the average radial brightness profile in a map centered at the systemic velocity and with a width of 10 km/s is about 0.88 K at a projected radius of 15 arcsec. From the brightness temperature profile we infer that the thickness of the shell at half-peak intensity is about 15 arcsec. We derive the abundance of the molecule as a function of distance from the star using an LTE model. The peak abundance is calculated to be 1.8 x 10 exp -6 (with respect to the H2 number density) at a radius of 16.7 arcsec or 2.5 x 10 exp 16 cm assuming a distance of 100 pc, a mass-loss rate of 2 x 10 exp -5 solar mass/yr, and an outflow velocity of 13.8 km/s. We compare our derived C4H distribution with the predictions of a photochemical model and find that the model underestimates the observed abundance of C4H by a factor of 5.

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