The abundance distribution of C4H in IRC + 10216

Aditya Dayal, John H Bieging

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

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 ∼10″ and a velocity resolution of ∼1.3 km s-1. 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-1 is ∼0.88 K at a projected radius of 15″. From the brightness temperature profile we infer that the thickness of the shell at half-peak intensity is ∼15″. 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 ×10-6 (with respect to the H2 number density) at a radius of 16″.7 or 2.5 × 1016 cm assuming a distance of 100 pc, a mass-loss rate of 2 × 10-5 M yr-1, and an outflow velocity of 13.8 km s-1. 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.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume407
Issue number1 PART 2
StatePublished - Apr 10 1993

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shell
stars
carbon stars
radii
local thermodynamic equilibrium
brightness temperature
angular resolution
interferometer
temperature profile
temperature profiles
brightness
envelopes
outflow
interferometers
apertures
carbon
synthesis
profiles
prediction
predictions

Keywords

  • Molecular processes
  • Stars: carbon
  • Stars: circumstellar matter
  • Stars: mass loss

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

The abundance distribution of C4H in IRC + 10216. / Dayal, Aditya; Bieging, John H.

In: Astrophysical Journal, Vol. 407, No. 1 PART 2, 10.04.1993.

Research output: Contribution to journalArticle

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abstract = "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 ∼10″ and a velocity resolution of ∼1.3 km s-1. 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-1 is ∼0.88 K at a projected radius of 15″. From the brightness temperature profile we infer that the thickness of the shell at half-peak intensity is ∼15″. 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 ×10-6 (with respect to the H2 number density) at a radius of 16″.7 or 2.5 × 1016 cm assuming a distance of 100 pc, a mass-loss rate of 2 × 10-5 M⊙ yr-1, and an outflow velocity of 13.8 km s-1. 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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T1 - The abundance distribution of C4H in IRC + 10216

AU - Dayal, Aditya

AU - Bieging, John H

PY - 1993/4/10

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N2 - 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 ∼10″ and a velocity resolution of ∼1.3 km s-1. 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-1 is ∼0.88 K at a projected radius of 15″. From the brightness temperature profile we infer that the thickness of the shell at half-peak intensity is ∼15″. 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 ×10-6 (with respect to the H2 number density) at a radius of 16″.7 or 2.5 × 1016 cm assuming a distance of 100 pc, a mass-loss rate of 2 × 10-5 M⊙ yr-1, and an outflow velocity of 13.8 km s-1. 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.

AB - 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 ∼10″ and a velocity resolution of ∼1.3 km s-1. 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-1 is ∼0.88 K at a projected radius of 15″. From the brightness temperature profile we infer that the thickness of the shell at half-peak intensity is ∼15″. 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 ×10-6 (with respect to the H2 number density) at a radius of 16″.7 or 2.5 × 1016 cm assuming a distance of 100 pc, a mass-loss rate of 2 × 10-5 M⊙ yr-1, and an outflow velocity of 13.8 km s-1. 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.

KW - Molecular processes

KW - Stars: carbon

KW - Stars: circumstellar matter

KW - Stars: mass loss

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