A Model for the Infrared Continuum and Ammonia Absorption Line Spectrum of IRC +10 216.

Details A Model for the Infrared Continuum and Ammonia Absorption Line Spectrum of IRC +10 216. A Model for the Infrared Continuum and Ammonia Absorption Line Spectrum of IRC +10 216.

Mar 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982phdt........42c&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF TORONTO (CANADA), 1982.Source: Dissertation Abstracts International, Volume: 43-12, Section: B, pa

Physics

Scientific paper

I have modelled the infrared continuum and NH(,3) absorption line spectrum of the luminous infrared source IRC +10 216. The model consists of a cool central star surrounded by an extensive, spherically symmetric circumstellar envelope. The model is used to investigate the structure, physical conditions and kinematics of the circumstellar envelope surrounding the central star. The infrared brightness distribution of IRC +10 216 has been studied by a number of investigators using both lunar occultation and interferometric techniques, and the resulting eclipse light curves and fringe visibilities are available in the literature. Comparison of these observations with the model predictions demonstrates that the infrared brightness distribution of IRC +10 216 is well explained by a 1/r('2) density distribution for the dust in the envelope. This is the distribution expected for uniform outflow velocity. The mass-loss rate for the model is approximately 10('-4) M(,(CIRCLE))/yr. Several absorption lines in the (nu)(,2) vibrational band of NH(,3) have recently been observed in IRC +10 216 at high velocity resolution ((DBLTURN)0.2 km/sec). These lines cover a wide range of excitation and thus provide a sensitive probe of the physical conditions within the circumstellar envelope. A detailed non-LTE model for the excitation of 123 rotational levels of NH(,3) has been calculated. The model is based on earlier work for plane -parallel geometry but incorporates several modifications which make it more suitable of the geometry of IRC +10 216. The results indicate that it is pumping by infrared photons from the inner regions of the envelope which is largely responsible for the excitation of NH(,3). The excitation model is then used to calculate the radial distribution of NH(,3) for each of the 123 rotational levels. These results are incorporated into the infrared continuum model to obtain synthetic line profiles. The calculated profiles agree very well with the observations, thus confirming that the excitation of NH(,3) is radiatively controlled and providing further support for the continuum model.

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