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ALMA and VLA observations of the outflows in IRAS 16293-2422

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 نشر من قبل Laurent Loinard
 تاريخ النشر 2012
  مجال البحث فيزياء
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 تأليف Laurent Loinard




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We present ALMA and VLA observations of the molecular and ionized gas at 0.1-0.3 arcsec resolution in the Class 0 protostellar system IRAS 16293-2422. These data clarify the origins of the protostellar outflows from the deeply embedded sources in this complex region. Source A2 is confirmed to be at the origin of the well known large scale north-east--south-west flow. The most recent VLA observations reveal a new ejection from that protostar, demonstrating that it drives an episodic jet. The central compact part of the other known large scale flow in the system, oriented roughly east-west, is well delineated by the CO(6-5) emission imaged with ALMA and is confirmed to be driven from within component A. Finally, a one-sided blueshifted bubble-like outflow structure is detected here for the first time from source B to the north-west of the system. Its very short dynamical timescale (~ 200 yr), low velocity, and moderate collimation support the idea that source B is the youngest object in the system, and possibly one of the youngest protostars known.



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Context. The Class 0 protostellar binary IRAS 16293-2422 is an interesting target for (sub)millimeter observations due to, both, the rich chemistry toward the two main components of the binary and its complex morphology. Its proximity to Earth allows the study of its physical and chemical structure on solar system scales using high angular resolution observations. Such data reveal a complex morphology that cannot be accounted for in traditional, spherical 1D models of the envelope. Aims. The purpose of this paper is to study the environment of the two components of the binary through 3D radiative transfer modeling and to compare with data from the Atacama Large Millimeter/submillimeter Array. Such comparisons can be used to constrain the protoplanetary disk structures, the luminosities of the two components of the binary and the chemistry of simple species. Methods. We present 13CO, C17O and C18O J=3-2 observations from the ALMA Protostellar Interferometric Line Survey (PILS), together with a qualitative study of the dust and gas density distribution of IRAS 16293-2422. A 3D dust and gas model including disks and a dust filament between the two protostars is constructed which qualitatively reproduces the dust continuum and gas line emission. Results and conclusions. Radiative transfer modeling of source A and B, with the density solution of an infalling, rotating collapse or a protoplanetary disk model, can match the constraints for the disk-like emission around source A and B from the observed dust continuum and CO isotopologue gas emission. If a protoplanetary disk model is used around source B, it has to have an unusually high scale-height in order to reach the dust continuum peak emission value, while fulfilling the other observational constraints. Our 3D model requires source A to be much more luminous than source B; LA ~ 18 $L_odot$ and LB ~ 3 $L_odot$.
We have analyzed rotational spectral line emission of OCS, CH3OH, HCOOCH3, and H2CS observed toward the low-mass Class 0 protostellar source IRAS 16293-2422 Source A at a sub-arcsecond resolution (~0.6 x 0.5) with ALMA. Significant chemical different iation is found at a 50 AU scale. The OCS line is found to well trace the infalling-rotating envelope in this source. On the other hand, the CH3OH and HCOOCH3 distributions are found to be concentrated around the inner part of the infalling-rotating envelope. With a simple ballistic model of the infalling-rotating envelope, the radius of the centrifugal barrier (a half of the centrifugal radius) and the protostellar mass are evaluated from the OCS data to be from 40 to 60 AU and from 0.5 to 1.0 Msun, respectively, assuming the inclination angle of the envelope/disk structure to be 60 degrees (90 degrees for the edge-on configuration). Although the protostellar mass is correlated with the inclination angle, the radius of the centrifugal barrier is not. This is the first indication of the centrifugal barrier of the infalling-rotating envelope in a hot corino source. CH3OH and HCOOCH3 may be liberated from ice mantles due to weak accretion shocks around the centrifugal barrier, and/or due to protostellar heating. The H2CS emission seems to come from the disk component inside the centrifugal barrier in addition to the envelope component. The centrifugal barrier plays a central role not only in the formation of a rotationally-supported disk but also in the chemical evolution from the envelope to the protoplanetary disk.
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