The Evolution of Far-infrared CO Emission from Protostars

November 2016 • 2016ApJ...831...69M

Authors • Manoj, P. • Green, J. D. • Megeath, S. T. • Evans, N. J., II • Stutz, A. M. • Tobin, J. J. • Watson, D. M. • Fischer, W. J. • Furlan, E. • Henning, T.

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 {L}_{bol}, {T}_{bol}, and {L}_{bol}/{L}_{smm} 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 ({L}_{CO}^{fir}) and the bolometric luminosity ({L}_{bol}) of the protostars with {L}_{CO}^{fir} \propto {L}_{bol} ^0.7. We, however, do not find a strong correlation between {L}_{CO}^{fir} and protostellar evolutionary indicators, {T}_{bol} and {L}_{bol}/{L}_{smm}. FIR CO emission from protostars traces the currently shocked gas by jets/outflows, and far-IR CO luminosity, {L}_{CO}^{fir}, is proportional to the instantaneous mass-loss rate, {\dot{M}}_{out}. The correlation between {L}_{CO}^{fir} and {L}_{bol}, then, is indicative of instantaneous {\dot{M}}_{out} tracking instantaneous {\dot{M}}_{acc}. The lack of a correlation between {L}_{CO}^{fir} and evolutionary indicators {T}_{bol} and {L}_{bol}/{L}_{smm} suggests that {\dot{M}}_{out} and, therefore, {\dot{M}}_{acc} 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.

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• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2016ApJ...831...69M
• PDF https://iopscience.iop.org/article/10.3847/0004-637X/831/1/69/pdf
• DATA http://archives.esac.esa.int/hsa/whsa/?ACTION=PUBLICATION&ID=2016ApJ...831...69M
• DATA https://irsa.ipac.caltech.edu/bibdata/2016/M/2016ApJ...831...69M.html
• ELECTR https://doi.org/10.3847/0004-637X/831/1/69