Saturday, January 24, 2015

Class O Protostar IRAS 16547−4247 has a Compact, hot Protoplanetary Disk

ALMA reveals a candidate hot and compact disc around the O-type protostar IRAS 16547−4247


Zapata et al


We present high angular resolution (∼0.3 arcsec) submillimeter continuum (0.85 mm) and line observations of the O-type protostar IRAS 16547−4247 carried out with the Atacama Large Millimeter/Submillimeter Array (ALMA). In the 0.85 mm continuum band, the observations revealed two compact sources (with a separation of 2 arcsec), one of them associated with IRAS 16547−4247, and the other one to the west. Both sources are well-resolved angularly, revealing a clumpy structure. On the other hand, the line observations revealed a rich variety of molecular species related to both continuum sources. In particular, we found a large number of S-bearing molecules, such as the rare molecule methyl mercaptan (CH3SH). At scales larger than 10 000 au, molecules (e.g. SO2 or OCS) mostly with low-excitation temperatures in the upper states (Ek ≲ 300 K) are present in both millimeter continuum sources, and show a south-east–north-west velocity gradient of 7 km s− 1 over 3 arcsec (165 km s−1 pc−1). We suggest that this gradient probably is produced by the thermal (free–free) jet emerging from this object with a similar orientation at the base. At much smaller scales (about 1000 au), molecules with high-excitation temperatures (Ek ≳ 500 K) are tracing a rotating structure elongated perpendicular to the orientation of the thermal jet, which we interpret as a candidate disc surrounding IRAS 16547−4247. The dynamical mass corresponding to the velocity gradient of the candidate to disc is about 20 M⊙, which is consistent with the bolometric luminosity of IRAS 16547−4247.

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