In section 1. Letters to the Editor
Time-dependent molecular emission in IRC+10216
This paper presents the first results from an almost three-year long monitoring of the molecular emission from the Mira variable star IRC+10216. Several rotational lines from species such as HC3N, HC5N, CCH, C4H, C5H, and CN present evidence of periodical variability, with periods consistent with the stellar IR variability. The different phase lags in the light curves suggest that the variability of the molecular lines results from radiative transfer and pumping effects, and not from chemical changes in the envelope composition.