EXOTIC FLUORIDE MOLECULES IN IRC- CONFIRMATION OF ALF AND SEARCHES FOR MGF AND CAF(10216 )

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 to ward IRC + 10216 using the Caltech Submillimeter Observatory (CSO). Co mbined with the earlier data obtained for this species at IRAM at 2 an d 3 mm, these measurements confirm the presence of the metal halide in this carbon-rich circumstellar shell. Analysis of the CSO and IRAM da ta suggests that AlF arises from a source with a diameter of theta(s) approximately 5''-10'' and hence is present chiefly in the inner envel ope of IRC + 10216. In this region, the molecule has a column density of (0.3-1.1) x 10(15) cm-2, which indicates a fractional abundance of at least approximately 10(-9), relative to H-2. Searches for the metal fluoride species CaF and MgF have also been conducted toward IRC + 10 216, but with negative results. The column density upper limits for Mg F and CaF are N(tot) < (1-4) x 10(14) cm-2. Relative abundances of the se metal fluoride molecules can be understood in terms of chemical the rmodynamic equilibrium. The presence of AlF in IRC + 10216 also indica tes that large quantities of fluorine must be present in the inner ste llar envelope, suggesting that this element may be produced not primar ily in explosive nucleosynthesis but rather in helium shell flashes, a s indicated also by HF spectroscopy of red giant stars.