Chemical and Physical Picture of IRAS 16293–2422 Source B at a Sub-arcsecond Scale Studied with ALMA

Abstract

We have analyzed the OCS, H 2 CS, CH 3 OH, and HCOOCH 3 data observed toward the low-mass protostar IRAS 16293-2422 Source B at a sub-arcsecond resolution with ALMA. A clear chemical differentiation is seen in their distributions; OCS and H 2 CS are extended with a slight rotation signature, while CH 3 OH and HCOOCH 3 are concentrated near the protostar. Such a chemical change in the vicinity of the protostar is similar to the companion (Source A) case. The extended component is interpreted by the infalling-rotating envelope model with a nearly face-on configuration. The radius of the centrifugal barrier of the infalling-rotating envelope is roughly evaluated to be (30 − 50) au. The observed lines show the inverse P-Cygni profile, indicating the infall motion with in a few 10 au from the protostar. The nearly pole-on geometry of the outflow lobes is inferred from the SiO distribution, and thus, the infalling and outflowing motions should coexist along the line-of-sight to the protostar. This implies thatthe infalling gas is localized near the protostar and the current launching points of the outflow have an offset from the protostar. A possible mechanism for this configuration is discussed.

The ALMA-PILS survey: gas dynamics in IRAS 16293−2422 and the connection between its two protostars

“…The centroid coordinates of the continuum peaks of components A and B, measured using two-dimensional Gaussian fits on the PILS 0.826-0.912 mm continuum image, are listed in Table 1. These positions of the 0.87 mm continuum measured from our PILS data products are consistent with the 1.15-1.30 mm continuum peak locations reported by Oya et al (2018) to within 0.05 , that is, one tenth of the synthesized beam size of either observation. We select spectral signatures of C 17 O, H 13 CN, H 2 CO, H 2 13 CO, C 34 S, SiO, 29 SiO, and C 2 H. The motivation for selecting these tracer transitions is that their emission is spatially extended across the inter-and circumbinary region, the molecules are chemically simple, and are chosen because they probe a range of densities, temperatures (see E up and n crit in Table 2) and physical processes such as shocks.…”

“…B.7) shows the same morphology, again with mixed blue and red velocities. The morphology and kinematics of SiO 8-7 in our map is consistent with that observed in SiO 7-6 by Oya et al (2018), who interpret this structure as a signature of a pole-on pair of outflows.…”

“…The SiO gas surrounding IRAS 16293B at projected radii up to 250 au (J=8-7, Sect. 4.3 of this work; J=7-6, Oya et al 2018) is of mixed blue-and red-shifted velocity up to ±3 km s −1 from the systemic velocity of source B. The presence of SiO in the gas phase is often used as a tracer of outflow shocks (e.g., Flower et al 1996;Caselli et al 1997;Gusdorf et al 2008a,b).…”

“…The presence of SiO in the gas phase is often used as a tracer of outflow shocks (e.g., Flower et al 1996;Caselli et al 1997;Gusdorf et al 2008a,b). While the overlapping blueshifted and redshifted SiO emission is suggestive of a geometry with approaching and receding outflows superposed in projection (Oya et al 2018), the relatively low velocities would not be expected to lead to grain erosion. Correcting the observed velocity for projection effects has a marginal effect, since the V lsr offset is necessarily almost completely parallel with the true velocity vectors in case of a face-on disk launching an outflow along the line of sight.…”

Implications of a Hot Atmosphere/Corino from ALMA Observations toward NGC 1333 IRAS 4A1

“…The geometry of IRAS 4A1 proposed above is close to the picture suggested by Oya et al (2018) of I16293 B. I16293 is another proto-binary where two (sub)millimeter continuum emission cores, I16293 A and B, show hot-corino activities ). Similar to the case of IRAS 4A, the weaker continuum of I16293 (i.e., A core) show richer COM (emission) features compared to that of B core.…”