A sensitive search for methanol line emission toward evolved stars
  We present a sensitive search for methanol line emission in evolved stars at 1 cm, aiming to detect, for the first time, methanol masers in this type of objects. Our sample comprised post-AGB stars and young planetary nebulae (PNe), whose mass-loss processes and circumstellar structures resemble those of young stellar objects (YSOs), where methanol masers are detected. Class I masers were searched for in 73 objects, whereas Class II ones were searched in 16. No detection was obtained. The non-detection of Class I methanol masers indicated that methanol production in dust grains and/or the enhancement of its gas-phase abundance in the shocked regions of evolved objects are not as efficient as in YSOs. We suggest that relatively more evolved PNe might have a better probability of harboring Class II masers. 
J. F. Gomez (1), L. Uscanga (2), O. Suarez (3), J. R. Rizzo (4), I. de   Gregorio-Monsalvo (5) ((1) IAA-CSIC, Spain, (2) NOA...
astro-ph.GA astro-ph.SR