Optical TiO and VO Band Emission in Two Embedded Protostars: IRAS 04369+2539 and IRAS 05451+0037

Archival spectra from the Sloan Digital Sky Survey of two optically faint flat-spectrum protostars, IRAS 04369+2539 and IRAS 05451+0037, show strong emission-line features including—notably—clear and broad emission across several molecular bands of TiO and VO. The molecular emission is indicative of dense, warm circumstellar gas and has been seen previously in only one object: the flat-spectrum protostar IRAS 20496+4354 during a strong optical outburst (PTF 10nvg). The presence of broad molecular emission features in two additional objects having similar mid-infrared properties (but not known to be undergoing outbursts) could provide new insight into phases of rapid accretion/outflow at early stages of the protoplanetary disk. At present, the relevant geometry and the formation or heating mechanisms responsible for the observed TiO/VO cooling emission remain unexplained.