Oral Presentation
ALMA survey of the Orion dense cores: Discovery of the prestellar core on the verge of star formation
Presenter: Naomi Hirano (ASIAA)
The ALMA survey toward 72 dense cores in Orion molecular cloud complex has revealed the internal structure of the starless core G208.68-19.02-N2 (G208-N2), The 1.3 mm continuum emission from G208-N2 is brightest among 26 starless cores in our sample. The high resolution (~0.35" = 150 au) 1.3 mm continuum image shows an elongated structure with ~10" (4200 au) long surrounded by a triangle-shaped envelope. The H2 volume density of this elongated structure is 2.5 x 10^7 cm-^3, which is a factor of ten larger than that of the well-studied starless core L1544. At the eastern tip of the elongated structure, there is compact condensation with a radius of ~200 au and a mass of ~0.1 M_sun. The H2 volume density of this condensation, 2 x 10^8 cm^-3, is a factor of ten higher than its surroundings. There is no signature of outflow in the CO and H2CO images, implying that the protostar has not yet been formed in this condensation. The absence of molecular line emission such as C18O and N2D+ toward this condensation also support that the dense gas in this condensation is still cold, where both CO and N2 deplete onto dust grain. The observational results support that the compact condensation discovered in G208-N2 is in the evolutionary stage on the verge of star formation.
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