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Register a new userThe nature of a primary jet within a circumbinary disc outflow in a young stellar system
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Most stars form in binaries, and both stars may grow by accreting material from a circumbinary disc onto their personal discs. We suspect that in many cases a wide molecular wind will envelope a collimated atomic jet emanating from close to an orbiting young star. This so-called Circumbinary Scenario is explored here in order to find common identifiable properties. The dynamical set up is studied with three dimensional simulations with chemistry and cooling included. We extract the properties on scales of order 100,AU and compare to the Co-Orbital Scenario in which the wind and jet sources are in orbit. We find that the rapid orbital motion generates a wide ionised sheath around the jet core with a large opening angle at the base. This is independent of the presence of the surrounding molecular outflow. However, the atomic jet is recollimated beyond ~ 55 AU when the molecular outflow restricts the motion of the ambient medium which, in turn, confines the jet. These physical properties are relayed to the optical H-alpha imaging, providing a means of distinguishing between models. The high excitation sheath and recollimation region can be explored on these scales through the next generation of instruments. However, in general, the amount and location of the ionised material, whether in the knots or the sheath, will depend on several parameters including the orbital period, axis alignment and pulse amplitude.
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We present a 3D hydrodynamics study of gravitational instabilities (GIs) in a 0.14 M$_{odot}$ circumbinary protoplanetary disc orbiting a 1 M$_{odot}$ star and a 0.02 M$_{odot}$ brown dwarf companion. We examine the thermodynamical state of the disc and determine the strengths of GI-induced density waves, nonaxisymmetric density structures, mass inflow and outflow, and gravitational torques. Results are compared with a parallel simulation of a protoplanetary disc without the brown dwarf binary companion. Simulations are performed using CHYMERA, a radiative 3D hydrodynamics code. The onset of GIs in the circumbinary disc is much more violent due to the stimulation of a strong one-armed density wave by the brown dwarf. Despite this early difference, detailed analyses show that both discs relax to a very similar quasi-steady phase by 2,500 years after the beginning of the simulations. Similarities include the thermodynamics of the quasi-steady phase, the final surface density distribution, radial mass influx, and nonaxisymmetric power and torques for spiral arm multiplicities of two or more. Effects of binarity in the disc are evident in gravitational torque profiles, temperature profiles in the inner discs, and radial mass transport. After 3,800 years, the semimajor axis of the binary decreases by about one percentage and the eccentricity roughly doubles. The mass transport in the outer circumbinary disc associated with the one-armed wave may influence planet formation.
We report the detection of a wide young hierarchical triple system where the primary has a candidate debris disc. The primary, TYC 5241-986-1 A, is a known Tycho star which we classify as a late-K star with emission in the X-ray, near and far-UV and Halpha suggestive of youth. Its proper motion, photometric distance (65-105 pc) and radial velocity lead us to associate the system with the broadly defined Local Association of young stars but not specifically with any young moving group. The presence of weak lithium absorption and X-ray and calcium H and K emission support an age in the 20 to ~125 Myr range. The secondary is a pair of M4.5+-0.5 dwarfs with near and far UV and Halpha emission separated by approximately 1 arcsec (~65-105 AU projected separation) which lie 145 arcsec (9200-15200 AU) from the primary. The primary has a WISE 22 micron excess and follow-up Herschel observations also detect an excess at 70 micron. The excess emissions are indicative of a 100-175 K debris disc. We also explore the possibility that this excess could be due to a coincident background galaxy and conclude that this is unlikely. Debris discs are extremely rare around stars older than 15 Myr, hence if the excess is caused by a disc this is an extremely novel system.
The formation of high-mass stars is usually accompanied by powerful protostellar outflows. Such high-mass outflows are not simply scaled-u
We present the results of multi-epoch very long baseline interferometry (VLBI) water (H2O) maser observations carried out with the VLBI Exploration of Radio Astrometry (VERA) toward the Cepheus A HW3d object. We measured for the first time relative proper motions of the H2O maser features, whose spatio-kinematics traces a compact bipolar outflow. This outflow looks highly collimated and expanding through ~ 280 AU (400 mas) at a mean velocity of ~ 21 km/s (~ 6 mas/yr) without taking into account the turbulent central maser cluster. The opening angle of the outflow is estimated to be ~ 30{circ}. The dynamical time-scale of the outflow is estimated to be ~ 100 years. Our results provide strong support that HW3d harbors an internal massive young star, and the observed outflow could be tracing a very early phase of star formation. We also have analyzed Very Large Array (VLA) archive data of 1.3 cm continuum emission obtained in 1995 and 2006 toward Cepheus A. The comparative result of the HW3d continuum emission suggests the possibility of the existence of distinct young stellar objects (YSOs) in HW3d and/or strong variability in one of their radio continuum emission components.
We report the results of VERA multi-epoch VLBI 22 GHz water maser observations of S255IR-SMA1, a massive young stellar object located in the S255 star forming region. By annual parallax the source distance was measured as D = 1.78 +-0.12 kpc and the source systemic motion was (u alpha cos d, u d) = (-0.13 +- 0.20, -0.06 +- 0.27) mas yr-1. Masers appear to trace a U-shaped bow shock whose morphology and proper motions are well reproduced by a jet-driven outflow model with a jet radius of about 6 AU. The maser data, in the context of other works in the literature, reveal ejections from S255IR-SMA1 to be episodic, operating on timescales of ~1000 years.
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