Probing the Earliest Stage of Protostellar Evolution ― from "pre-Class 0" to "Class 0"
Naomi Hirano1*, Shigehisa Takakuwa2, Kazuya Saigo3
1Institute of Astronomy & Astrophysics, Academia Sinica, Taipei, Taiwan
2Department of Physics and Astronomy, Kagoshima University, Kagoshima, Japan
3Chile Observatory, Nathinal Astronomical Observatory Japan, Mitaka, Tokyo, Japan
* Presenter:Naomi Hirano,
Two extremely young protostars, B1-bN and B1-bS, and a Class 0 protostar, B1-c have been observed with the Atacama Large Millimeter/submillimeter Array at an angular resolution of ~0.2". The high resolution data successfully revealed spatially compact C17O emission localized to B1-bN and B1-bS, toward which C-containing molecules are depleted in the gas phase. The radii of the C17O emitting regions, which correspond to the CO evaporation radii, around B1-bN and B1-bS are ~0.15" (58 AU) and ~0.5" (115 AU), respectively. On the other hand, the C17O is spatially extended more than 1" in the Class 0 protostar, B1-c. These results confirmed that both B1-bN and B1-bS are in the earlier evolutionary stage than Class 0. Toward the continuum peaks of B1-bS and B1-c, the methanol emission lines in the vt=0 and vt=1 states, including the one having the upper energy above 500 K, are detected. The methanol emission originates from the central r < 30--40 AU region in both sources. No methanol emission has been detected toward the continuum source of B1-bN. The C17O and methanol results imply that B1-bS is in the evolutionary stage between B1-bN and B1-c, and is likely to be the earliest phase of hot corino.

Keywords: star formation, ALMA, astrochemistry