The magnetic field of IRAS 16293-2422 as traced by shock-induced H₂O masers

Abstract

Context. Shock-induced H 2 O masers are important magnetic field tracers of very high density gas. Water masers are found in both high-and low-mass star-forming regions, and are a powerful tool for comparing magnetic field morphologies in both mass regimes. Aims. We present one of the first magnetic field determinations for the low-mass protostellar core IRAS 16293-2422 at volume densities as high as 10 8−10 cm −3 . Our goal is to determine wether the collapsing regime of this source is controlled by magnetic fields or other factors such as turbulence. Methods. We used the Very Large Array (VLA) to carry out spectropolarimetric observations of the 22 GHz Zeeman emission from H 2 O masers. From the Stokes V line profile, we are then able to estimate the magnetic field strength in the dense regions around the protostar. Results. A blend of at least three maser features can be inferred from our relatively high spatial resolution data set (∼0.1 ), which is reproduced as a clear non-Gaussian line profile. The emission is very stable in terms of polarization fraction and position angle across the channels. The maser spots are aligned with some components of the complex outflow configuration of IRAS 16293-2422, and are excited in zones of compressed gas produced by shocks. The post-shock particle density is in the range of 1−3 × 10 9 cm −3 , consistent with typical water-maser pumping densities. Zeeman emission is produced by a very strong line-of-sight magnetic field (B ∼ 113 mG). Conclusions. The magnetic field pressure derived from our data is comparable to the ram pressure of the outflow dynamics. This indicates that the magnetic field is energetically important to the dynamical evolution of IRAS 16293-2422.

Protostars: Forges of cosmic rays?

“…If B = 10 µG in the initial (pre-collapse) volume of radius 0.1 pc and assuming field freezing, the magnetic field strength in the final (postcollapse) volume of radius 100 AU is about 400 mG. This naive estimate is comparable within a factor of 2 with the value found by Alves et al (2012) who estimate B ≈ 200 mG from observations of shock-induced H 2 O masers. This is an averaged quantity, but Imai et al (2007) computed the position of the H 2 O masers, and found the farther one to be at about 110 AU.…”

Warm water deuterium fractionation in IRAS 16293-2422

“…The Gaussian fit to these data peaks closer to v LSR = 3.2 km s −1 , indicative indeed of resolved velocity structure. Outflow emission (cf., Loinard et al 2012 scales (Alves et al 2012), could explain this velocity shift, but it is not possible to deduce its importance from the current data.…”

Linear polarization of submillimetre masers

“…Alves et al 2012;Amiri et al 2012;Leal-Ferreira et al 2012;Vlemmings et al 2011Vlemmings et al , 2006b). Both single-dish and interferometric observations have revealed that silicon monoxide (SiO), water (H 2 O), hydrogen cyanide (HCN), hydroxyl (OH), and methanol (CH 3 OH), among others, can naturally generate polarized maser emission in these enviroments (e.g.…”