THE EVOLUTION OF FAR-INFRARED CO EMISSION FROM PROTOSTARS

Abstract

We investigate the evolution of far-IR CO emission from protostars observed with Herschel /PACS for 50 sources from the combined sample of HOPS and DIGIT Herschel key programs. From the uniformly sampled spectral energy distributions, whose peaks are well sampled, we computed the , , and for these sources to search for correlations between far-IR CO emission and protostellar properties. We find a strong and tight correlation between far-IR CO luminosity ( ) and the bolometric luminosity ( ) of the protostars with . We, however, do not find a strong correlation between and protostellar evolutionary indicators, and . FIR CO emission from protostars traces the currently shocked gas by jets/outflows, and far-IR CO luminosity, , is proportional to the instantaneous mass-loss rate, . The correlation between and , then, is indicative of instantaneous tracking instantaneous . The lack of a correlation between and evolutionary indicators and suggests that and, therefore, do not show any clear evolutionary trend. These results are consistent with mass accretion/ejection in protostars being episodic. Taken together with the previous finding that the time-averaged mass-ejection/accretion rate declines during the protostellar phase, our results suggest that the instantaneous accretion/ejection rate of protostars is highly time variable and episodic, but the amplitude and/or frequency of this variability decreases with time such that the time-averaged accretion/ejection rate declines with system age.