Exotic fluoride molecules in IRC +10216: Confirmation of AlF and searches for MgF and CaF

L. M. Ziurys, A. J. Apponi, T. G. Phillips

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119 Scopus citations


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 Submillimeter 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 θs ∼ 5″-10″ 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) × 1015 cm-2, which indicates a fractional abundance of at least ∼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 < (1-4) × 1014 cm-2. 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.

Original languageEnglish (US)
Pages (from-to)729-732
Number of pages4
JournalAstrophysical Journal
Issue number2
StatePublished - Oct 1 1994


  • Circumstellar matter
  • Line: identification
  • Radio lines: stars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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