Molecular outflows from FU Orionis stars

We have detected molecular outflows toward six out of eight FU Orionis stars that we observed in the J = 3-2 line of CO. Notably, FU Orionis itself does not show an outflow. Four of the souces were mapped, and two show evidence for multiple outflows. In both Z CMa and RNO 1b, nearby infrared sources may also be driving the outflows. Mass-loss rates derived from the usual assumptions of momentum conservation range from 3 x 10<SUP>-8</SUP> solar masses/yr to 2 x 10<SUP>-6</SUP> solar masses/yr without corrections for optical depth in the CO lines. Corrections for optical depth raise these estimates by a factor of 5 on average. If the outflows are driven by repeated outbursts with peak mass-loss rates of 10<SUP>-5</SUP> solar masses/yr, a duty cycle of 10<SUP>-3</SUP> to 10<SUP>-1</SUP> would be implied, consistent with other recent evidence.

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