Detection of a Dense SiO Jet in the Evolved Protostellar Phase

Jets and outflows trace the accretion history of protostars. High-velocity molecular jets have been observed from several protostars in the early Class 0 phase of star formation, detected with the high-density tracer SiO. Until now, no clear jet has been detected with SiO emission from isolated evolved Class I protostellar systems. We report a prominent dense SiO jet from a Class I source G205S3 (HOPS 315: T_bol ∼ 180 K, spectral index ∼ 0.417), with a moderately high mass-loss rate (∼ 0.59 × 10^-6 M_⊙ yr^-1) estimated from CO emission. Together, these features suggest that G205S3 is still in a high accretion phase, similar to that expected of Class 0 objects. We compare G205S3 to a representative Class 0 system G206W2 (HOPS 399) and literature Class 0/I sources to explore the possible explanations behind the SiO emission seen at the later phase. We estimate a high inclination angle (∼ 40^∘) for G205S3 from CO emission, which may expose the infrared emission from the central core and mislead the spectral classification. However, the compact 1.3 mm continuum, C^18O emission, location in the bolometric luminosity to sub-millimeter fluxes diagram, outflow force (∼ 3.26 × 10^-5 M_⊙km s^-1/yr) are also analogous to that of Class I systems. We thus consider G205S3 to be at the very early phase of Class I, and in the late phase of “high-accretion". The episodic ejection could be due to the presence of an unknown binary, a planetary companion, or dense clumps, where the required mass for such high accretion could be supplied by a massive circumbinary disk.