Sub-arcsecond [Fe ii] spectro-imaging of the DG Tauri jet

Abstract

Context. The origin of protostellar jets as well as their impact on the regulation of angular momentum and the inner disk physics are still crucial open questions in star formation. Aims. We aim to test the different proposed ejection processes in T Tauri stars through high-angular resolution observations of forbidden-line emission from the inner DG Tauri microjet. Methods. We present spectro-imaging observations of the DG Tauri jet obtained with SINFONI/VLT in the lines of [Fe ii]λ1.64 μm, 1.53 μm with 0. 15 angular resolution and R = 3000 spectral resolution. We analyze the morphology and kinematics, derive electronic densities and mass-flux rates and discuss the implications for proposed jet launching models. Results. (1) We observe an onion-like velocity structure in [Fe ii] in the blueshifted jet, similar to that observed in optical lines. Highvelocity (HV) gas at -200 km s −1 is collimated inside a half-opening angle of 4 • and medium-velocity (MV) gas at -100 km s −1 in a cone with an half-opening angle 14.• (2) Two new axial jet knots are detected in the blue jet, as well as a more distant bubble with corresponding counter-bubble. The periodic knot ejection timescale is revised downward to 2.5 yrs. (3) The redshifted jet is detected only beyond 0. 7 from the star, yielding revised constraints on the disk surface density. (4) From comparison to [O i] data we infer iron depletion of a factor 3 at high velocities and a factor 10 at speeds below -100 km s −1 . (5) The mass-fluxes in each of the medium and high-velocity components of the blueshifted lobe are 1.6 ± 0.8 × 10 −8 M yr −1 , representing 0.02−0.2 of the disk accretion rate. Conclusions. The medium-velocity conical [Fe ii] flow in the DG Tau jet is too fast and too narrow to trace photo-evaporated matter from the disk atmosphere. Both its kinematics and collimation cannot be reproduced by the X-wind, nor can the "conical magnetospheric wind". The level of Fe gas phase depletion in the DG Tau medium-velocity component also rules out a stellar wind and a cocoon ejected sideways from the high-velocity beam. A quasi-steady centrifugal MHD disk wind ejected over 0.25−1.5 AU and/or episodic magnetic tower cavities launched from the disk appear as the most plausible origins for the [Fe ii] medium velocity component in the DG Tau jet. The same disk wind model can also account for the properties of the high-velocity [Fe ii] flow, although alternative origins in magnetospheric and/or stellar winds cannot be excluded for this component.

Hubble Space Telescope scale 3D simulations of MHD disc winds: a rotating two-component jet structure

“…However, this only extends out a few AU from the rotation axis, then the Kep- Red is OP, green is µ = −0.12, blue is BP, and purple is PP. In the mass flux figure, we also overplot the observed mass flux in DG tau from Agra-Amboage et al (2011) for the high (HVB) and medium velocity (MVB) blueshifted intervals. The µ = −0.12 jet has the highest mass flux, but because the OP jet is faster, the two have similar momentum and the OP jet has the higher jet power.…”

“…The mass flux in the PP jet is lower than the mass flux in the BP jet throughout. The observed mass flux in the DG tau jet (taken from Agra-Amboage et al 2011) is also shown in Fig. 15.…”

Origin of the wide-angle hot H2in DG Tauri

“…Our toy models favor a slightly larger spatial scale along the jet axis R max 60 AU, givingṀ w ∼ 10 −9 M yr −1 . With an estimated accretion rate ofṀ acc = (3 ± 2) × 10 −7 M yr −1 over the period (Agra-Amboage et al 2011, the ejectionaccretion ratio in the blue lobe of the molecular wind would thus be 0.003-0.014. This would be consistent with the lever arm parameter λ = 13 of the MHD disc wind solution if the external launch radius, r e , and internal launch radius, r i , for the molecular streamlines are in a ratio r e /r i 1.15-2 (see, e.g., Eq.…”

Numerical simulations of stellar jets and comparison between synthetic and observed maps: clues to the launch mechanism

“…Tails are meant to represent the wind lifted from the disk. Coaxial low velocity, wider winds seen in [H 2] lines are observed in many stellar outflows in the IR spectral range (see, e.g., Takami et al 2004;Agra-Amboage et al 2011). As an example, Takami et al (2004) reports a molecular outflow from DG-Tau thermalized at 2000 K that extends up to ∼50 AU from the jet axis in the transverse direction.…”

“…Finally, in both cases the interpretation of the jet spectra is made difficult by projection effects along the line of A&A 567, A13 (2014) sight. Nevertheless, valuable observational studies at high resolution and in different wavelengths have successfully investigated the properties of the jets in the acceleration region immediately downstream from the collimation zone, between ∼10 and 100 AU from the star, and have provided important constraints to the launch process (e.g., Bacciotti et al 2000;Woitas et al 2002;Melnikov et al 2009;Coffey et al 2008;Takami et al 2004;Pyo et al 2003Pyo et al , 2006Hartigan & Morse 2007;Agra-Amboage et al 2011). The only way to connect the observed region to the launch zone, however, is to create a logical link via numerical studies.…”