PLANCK COLD CLUMPS in the λ ORIONIS COMPLEX. I. DISCOVERY of AN EXTREMELY YOUNG CLASS 0 PROTOSTELLAR OBJECT and A PROTO-BROWN DWARF CANDIDATE in the BRIGHT-RIMMED CLUMP PGCC G192.32-11.88

We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the λ Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound bright-rimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity (∼0.8 L⊙) and accretion rate (6.3 × 10-7 M⊙ yr-1) when compared with other young Class 0 sources (e.g., PACS Bright Red Sources) in the Orion complex. It has slightly larger internal luminosity (0.21 ± 0.01 L⊙) and outflow velocity (∼14 km s-1) than the predictions of first hydrostatic cores (FHSCs). G192N might be among the youngest Class 0 sources, which are slightly more evolved than an FHSC. Considering its low internal luminosity (0.08 ± 0.01 L⊙) and accretion rate (2.8 × 10-8 M⊙ yr-1), G192S is an ideal proto-brown dwarf candidate. The star formation efficiency (∼0.3%-0.4%) and core formation efficiency (∼1%) in PGCC G192.32-11.88 are significantly smaller than in other giant molecular clouds or filaments, indicating that the star formation therein is greatly suppressed owing to stellar feedback.