SIMBAD references

Observations and stellar evolution computations have been dedicated to the search for ¹⁴C in the archetype of AGB stars, IRC+10216/CW Leo. Contrary to Wright's (1994ApJ...436L.157W) tentative detection, we see no trace of ¹⁴CO in this star down to a 3σ limit R=¹³CO/¹⁴CO≥1400. The new limit is consistent with our stellar evolution computations, which indicate that R should be > 4000. Comparison of the C, N, O, Mg, Si, and S isotopic ratios observed in this source with the calculated ones reinforces our earlier conclusion that CW Leo had a main sequence mass 3M_☉<M_ZAMS<5M_☉ (see Guelin et al. 1995). While searching for the ¹⁴CO 2-1 line, we detected the (1ν₃) 9₃₆-8₃₅ line of vibrationally excited SiC₂. The latter line pertains to the first vibrational level of the ν₃ bending state and its upper level has an energy of 290K, lower than the temperature of the dust forming shell. The line has a pyramidal shape and shows acceleration steps, which we interpreted in terms of dust formation.