The SOUL view of IRAS 20126+4104. Kinematics and variability of the H2 jet from a massive protostar
Sanna, A.; Leurini, S.; Esposito, S.; Mazzoni, T.; Puglisi, A.; Caratti o Garatti, A.; Beltrán, M. T.; Cesaroni, R.; Moscadelli, L.; Rothberg, B.; Agapito, G.; Miller, D.; Pinna, E.; Rossi, F.; Taylor, G.; Massi, F.; Power, J.; Briguglio, R.; Sridharan, T. K.; Veillet, C.; Ghose, E.; Plantet, C.; Christou, J.
Italy, Ireland, United States
Abstract
Context. We exploit the increased sensitivity of the recently installed adaptive optics SOUL at the LBT to obtain new high-spatial-resolution near-infrared images of the massive young stellar object IRAS20126+4104 and its outflow.
Aims: We aim to derive the jet proper motions and kinematics, as well as to study its photometric variability by combining the novel performances of SOUL together with previous near-infrared images.
Methods: We used both broad-band (Ks, K') and narrow-band (Brγ, H2) observations from a number of near-infrared cameras (UKIRT/UFTI, SUBARU/CIAO, TNG/NICS, LBT/PISCES, and LBT/LUCI1) to derive maps of the continuum and the H2 emission in the 2.12 µm line. Three sets of images, obtained with adaptive optics (AO) systems (CIAO, in 2003; FLAO, in 2012; SOUL, in 2020), allowed us to derive the proper motions of a large number of H2 knots along the jet. Photometry from all images was used to study the jet variability.
Results: We derived knot proper motions in the range of 1.7-20.3 mas yr−1 (i.e. 13-158 km s−1 at 1.64 kpc), implying an average outflow tangential velocity of ~80 km s−1. The derived knot dynamical age spans a ~200-4000 yr interval. A ring-like H2 feature near the protostar location exhibits peculiar kinematics and may represent the outcome of a wide-angle wind impinging on the outflow cavity. Both H2 geometry and velocities agree with those inferred from proper motions of the H2O masers, located at a smaller distance from the protostar. Although the total H2 line emission from the knots does not exhibit time variations at a ⪞0.3 mag level, we have found a clear continuum flux variation (radiation scattered by the dust in the cavity opened by the jet) which is anti-correlated between the blue-shifted and red-shifted lobes and may be periodic (with a period of ~12-18 yr). We suggest that the continuum variability might be related to inner-disc oscillations which have also caused the jet precession.
Conclusions: Our analysis shows that multi-epoch high-spatial-resolution imaging in the near-infrared is a powerful tool to unveil the physical properties of highly embedded massive protostars.