Binary system and jet precession and expansion in G35.20–0.74N

Abstract

Context. Atacama Large Millimeter/submillimeter Array (ALMA) observations of the high-mass star-forming region G35.20−0.74N have revealed the presence of a Keplerian disk in core B rotating about a massive object of 18 M⊙, as computed from the velocity field. The luminosity of such a massive star would be comparable to (or higher than) the luminosity of the whole star-forming region. To solve this problem it has been proposed that core B could harbor a binary system. This could also explain the possible precession of the radio jet associated with this core, which has been suggested by its S-shaped morphology. Aims. We establish the origin of the free-free emission from core B and investigate the existence of a binary system at the center of this massive core and the possible precession of the radio jet. Methods. We carried out VLA continuum observations of G35.20−0.74N at 2 cm in the B configuration and at 1.3 cm and 7 mm in the A and B configurations. The bandwidth at 7 mm covers the CH3OH maser line at 44.069 GHz. Continuum images at 6 and 3.6 cm in the A configuration were obtained from the VLA archive. We also carried out VERA observations of the H2O maser line at 22.235 GHz.Results. The observations have revealed the presence of a binary system of UC/HC Hii regions at the geometrical center of the radio jet in G35.20−0.74N. This binary system, which is associated with a Keplerian rotating disk, consists of two B-type stars of 11 and 6 M⊙. The S-shaped morphology of the radio jet has been successfully explained as being due to precession produced by the binary system. The analysis of the precession of the radio jet has allowed us to better interpret the IR emission in the region, which would be not tracing a wide-angle cavity open by a single outflow with a position angle of ∼55 • , but two different flows: a precessing one in the NE-SW direction associated with the radio jet, and a second one in an almost E-W direction. Comparison of the radio jet images obtained at different epochs suggests that the jet is expanding at a maximum speed on the plane of the sky of 300 km s −1 . The proper motions of the H2O maser spots measured in the region also indicate expansion in a direction similar to that of the radio jet. Conclusions. We have revealed a binary system of high-mass young stellar objects embedded in the rotating disk in G35.20−0.74N. The presence of a massive binary system is in agreement with the theoretical predictions of high-mass star formation, according to which the gravitational instabilities during the collapse would produce the fragmentation of the disk and the formation of such a system. For the first time, we have detected a high-mass young star associated with an UC/HC Hii region and at the same time powering a radio jet.

Measuring the ionisation fraction in a jet from a massive protostar

“…This emission covers the same velocity range of the [Fe II] emission, consistent with proper motions given by ref. 22 . Emission from [Fe II] and Br γ is, thus, indicative of shocked material 3,27 .…”

“…G35.20-0.74N (hereafter G35.2N) is a main formation site of B-type stars, has a bolometric luminosity of 3 × 10 4 L ⊙ and hosts two main cores, core A and core B. Both cores display discs in Keplerian rotation 21,22 . Core B is a binary system which consists of two B-type protostars with masses of 11 and 6 M ⊙ 22 , sources 8a and 8b, respectively.…”

“…Both cores display discs in Keplerian rotation 21,22 . Core B is a binary system which consists of two B-type protostars with masses of 11 and 6 M ⊙ 22 , sources 8a and 8b, respectively. The rotation axis of the disc, i.e., the jet axis, of source 8a has an inclination angle of i ~19 ± 1° with respect to the plane of the sky 23 .…”

Impact of Low-Energy Cosmic Rays on Star Formation

“…Recent observations have shown the presence of an unexpected extremely high ionisation rate in protostellar environments (e.g., 4 × 10 −14 s −1 in OMC 2 FIR-4, see Ceccarelli et al 2014;Fontani et al 2017;Favre et al 2018) as well as the detection of synchrotron emission (the fingerprint of the presence of relativistic electrons) in the shocks at the position of the knots that develop along protostellar jets (e.g. Beltrán et al, 2016;Rodríguez-Kamenetzky et al, 2017;Osorio et al, 2017;Sanna et al, 2019). Both signatures cannot be explained by interstellar CRs since their flux is strongly attenuated at the high densities typical of protostellar environments.…”

The ALMA early science view of FUor/EXor objects – IV. Misaligned outflows in the complex star-forming environment of V1647 Ori and McNeil's Nebula

“…While some asymmetric jets, like those detected from Herbig-Haro objects, appear to be shaped by their local star-forming environment Bally & Reipurth (2001), others systems exhibit clear evidence that the jet-launching region (i.e., the region perpendicular to the plane of the disc) has precessed over time resulting in outflows with asymmetric and misaligned features (Shepherd et al 2000;Su et al 2007;Cunningham et al 2009;Beltrán et al 2016). While the amount of precession over the lifetime of the outflow varies from case to case, it appears that jet precession of more than a few degrees may be rare (Frank et al 2014).…”