Proposal type : Open Time

Scientific category : Stellar_Physics

Title :
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THE MOLECULAR CONTENT OF IRC+10216 BETWEEN 2.38 AND 196.7 MICRONS A SPECTROSCOPIC STUDY OF THE C-RICH STAR IRC+10216

PI : J. CERNICHARO
Instituto de Estructura de la Materia
Dpto. Física Molecular
Serrano 123
28006 Madrid
e-mail : cerni@astro.iem.csic.es
Tel: 91-5901611
Fax: 91-5855184

Keywords :
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abundances
circumstellar envelopes
dust properties
line formation

Abstract :
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IRC+10216 is the nearest and brightest C-rich star. It has a rich chemistry characterized by a variety of processes (thermoequilibrium reactions, radical- radical reactions, ion-molecule reactions and possibly grain surface reactions) and a large variety of molecular species. It is the only C-rich envelope where metal-bearing molecules have been found (NaCl, AlF, AlCl, KCl, MgNC, NaCN) and where the long carbon chain radicals have been detected (C5H, C6H).
We propose to perform a full spectral survey of this object between 2.38 and 196.7 um using the SWS and LWS instruments. The SWS full resolution grating sweep between 2.38 and 45 um will allow to search for the presence of nearly all likely molecular species by covering their stretching and/or bending vibrational bands. It will also allow to determine their abundances. Many new molecules will probably be detected, and our knowledge of the envelope molecular composition greatly improved. The spectral resolution provided by the SWS full resolution grating observations, R~1500-2000, will permit to resolve the rotational structure of the molecular bands arising from molecules with rotational constants larger than 0.15 cm-1 -- i.e. from practically all diatomic and triatomic species and from some four-atomic molecular species.
In order to derive the physical conditions of the gas, we would also like to observe some ro-vibrational lines of known molecular species with the SWS FP instrument. Finally, we would like to perform a fast LWS FP scan of IRC+10216 between 43 and 196.7 um. The signal to noise ratio will be large enough to detect strong absorption or emission lines of heavy molecules or fine structure atomic lines. Key molecules like C3, C4, C5, C6, C4H, C5H, C6H, C4H2, C6H2, ..., have their low lying bending levels in the LWS frequency coverage. The spectral scan will allow to identify these species, precise their spectral constants and study their role in the growth of carbon chains molecules.

Publications :

The ISO/LWS far infrared spectrum of IRC+10216; Cernicharo et al., A.A. 315, L201

"Discovery of far-IR pure rotational transitions CH+ in NGC 7027". Cernicharo et al. (1997). Accepted for the Astrophysical Journal Letters. [Full text].
(The data presented in this paper correspond to GT LWS observations ofM. Barlow.)

Significant Results :

Figure 1 : Continuum subtracted LWS grating spectrum of IRC+10216 from 75 to 197 $\mu$m (thick line). An offset has been introduced to the continuum to show simultaneously the computed emission of the CO v=~0,~1, $^{13}$CO v=~0, HCN and H$^{13}$CN v=~0, and HCN $\nu_2$~=~1,~2 $\nu_{1,3}$=~1 (thin line). See text for the adopte d model parameters. The rotational transitions of CO, HCN, and HCN $\nu_2$=1,2 and $\nu_{1,3}$=1 are indicated by arrows at the top and bottom of each panel. The weak lines in the model correspond to H$^{13}$CN, $^{13}$CO and to the stretching modes of HCN.

Updated: May 23, 1997.