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Exotic fluoride molecules in IRC +10216: Confirmation of AlF and searches for MgF and CaF
Ziurys, L. M.; Apponi, A. J.; Phillips, T. G.
AA(Arizona State University, Tempe, AZ), AB(Arizona State University, Tempe, AZ), AC(Arizona State University, Tempe, AZ)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 433, no. 2, p. 729-732 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Abundance, Aluminum Fluorides, Calcium Fluorides, Magnesium Fluorides, Optical Transition, Radio Astronomy, Radio Spectra, Spectrum Analysis, Stellar Envelopes, Chemical Equilibrium, Hydrogen, Nuclear Fusion, Radio Telescopes
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Three new rotational transitions of aluminum fluoride (AlF) at 0.8 and 1.2 mm have been observed. The J = 10-9, J = 8-7, and J = 7-6 lines of AlF at 230, 263, and 329 GHz, respectively, were seen toward IRC +10216 using the Caltech Submillimter Observatory (CSO). Combined with the earlier data obtained for this species at IRAM at 2 and 3 mm, these measurements confirm the presence of the metal halide in this carbon-rich circumstellar shell. Analysis of the CSO and IRAM data suggests that AlF arises from a source with a diameter of thetas approximately = 5-10 sec and hence is present chiefly in the inner envelope of IRC +10216. In this region, the molecule has a column density of (0.3-1.1) x 1015/sq cm, which indicates a fractional abundance of at least approximately 10-9, relative to H2. Searches for the metal fluoride species CaF and MgF have also been conducted toward IRC +10216, but with negative results. The column density upper limits for MgF and CaF are Ntot less than (1-4) x 1014/sq cm. Relative abundances of these metal fluoride molecules can be understood in terms of chemical thermodynamic equilibrium. The presence of AlF in IRC +10216 also indicates that large quantities of fluorine must be present in the inner stellar envelope, suggesting that this element may be produced not primarily in explosive nucleosynthesis but rather in helium shell flashes, as indicated also by HF spectroscopy of red giant stars.

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