Extremely Strong ^{13}CO J=3-2 Line in the "Water Fountain" IRAS 16342-3814: Evidence for the Hot-Bottom Burning

Abstract: We observed four "water fountain" sources in the CO J=3-2 line emission with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in 2010-2011. The water fountain sources are evolved stars that form high-velocity collimated jets traced by water maser emission. The CO line was detected only from IRAS 16342-3814. The present work confirmed that the ^{12}CO to ^{13}CO line intensity ratio is ~1.5 at the systemic velocity. We discuss the origins of the very low ^{12}CO to ^{13}CO intensity ratio, as possible evidence for the "hot-bottom burning" in an oxygen-rich star, and the CO intensity variation in IRAS 16342-3814.