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Register a new userBinary outflows from young stars: interaction of co-orbital jet and wind
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Jets from young stellar objects provide insight into the workings of the beating heart at the centre of star forming cores. In some cases, multiple pulsed outflows are detected such as the atomic and molecular jets from a proposed binary system in the T,Tauri star HH30. We investigate here the development and propagation of duelling atomic and molecular outflows stemming from the two stars in co-orbit. We perform a series of numerical experiments with the {small ZEUS-MP} code with enhanced cooling and chemistry modules. The aim of this work is to identify signatures on scales of order 100 AU. The jet sources are off the grid domain and so it is the propagation and interaction from ~ 20AU out to 100,AU simulated here. We find that the molecular flow from the orbiting source significantly disturbs the atomic jet, deflecting and twisting the jet and disrupting the jet knots. Regions of high ionisation are generated as the atomic jet rams through the dense molecular outflow. Synthetic images in atomic and molecular lines are presented which demonstrate identifying signatures. In particular, the structure within the atomic jet is lost and H-alpha may trace the walls of the present CO cavity or where the walls have been recently. These results provide a framework for the interpretation of upcoming high resolution observations.
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Isotopologue line intensity ratios of circumstellar molecules have been widely used to trace the photospheric elemental isotopic ratios of evolved stars. However, depending on the molecular species and the physical conditions of the environment, the circumstellar isotopologue ratio may deviate considerably from the stellar atmospheric value. In this paper, we aim to examine how the CO and HCN abundance ratios vary radially due to chemical reactions in the outflows of AGB stars and the effect of excitation and optical depth on the resulting line intensity ratios. We find that the circumstellar 12CO/13CO can deviate from its atmospheric value by up to 25-94% and 6-60% for C- and O-type CSEs, respectively. We show that variations of the intensity of the ISRF and the gas kinetic temperature can significantly influence the CO isotopologue ratio in the outer CSEs. On the contrary, the H12CN/H13CN ratio is stable for all tested mass-loss rates. The RT modeling shows that the integrated line intensity ratio of CO of different rotational transitions varies significantly for stars with intermediate mass-loss rates due to combined chemical and excitation effects. In contrast, the excitation conditions for the both HCN isotopologues are the same. We demonstrate the importance of using the isotopologue abundance profiles from chemical models as inputs to RT models in the interpretation of isotopologue observations. Previous studies of CO isotopologue ratios are based on multi-transition data for individual sources and it is difficult to estimate the errors in the reported values due to assumptions that are not entirely correct according to this study. If anything, previous studies may have overestimated the circumstellar 12CO/13CO abundance ratio. The use of the HCN as a tracer of C isotope ratios is affected by fewer complicating problems, provided one accounts corrections for high optical depths.
Jets are ubiquitous in the Universe and, as demonstrated in this volume, are seen from a large number of astrophysical objects. For a number of reasons, in particular their proximity and the abundant range of diagnostics to determine their characteristics, jets from young stars and their associated outflows may offer us the best opportunity to discover how jets are generated in general and the nature of the link between outflows and their accretion disks. Recently it has become clear that jets may be fundamental to the star formation process in removing angular momentum from the surrounding protoplanetary disk thereby allowing accretion to proceed. Moreover, with the realisation that planetary formation begins much earlier than previously thought, jets may also help forge planets by determining initial environmental characteristics. This seems to be particularly true within the so-called terrestrial planet forming zone. Here we review observations of jets from young stars which have greatly benefitted from new facilities such as ALMA, space observatories like Spitzer, Herschel and HST, and radio facilities like LOFAR and the VLA. Interferometers such as CHARA and GRAVITY are starting to make inroads into resolving how they are launched, and we can look forward to a bright future in our understanding of this phenomenon when JWST and the SKA come on stream. In addition, we examine the various magnetohydrodynamic models for how jets from young stars are thought to be generated and how observations may help us select between these various options.
We present 3 mm ALMA continuum and line observations at resolutions of 6.5 au and 13 au respectively, toward the Class 0 system IRAS 16293-2422 A. The continuum observations reveal two compact sources towards IRAS 16293-2422 A, coinciding with compact ionized gas emission previously observed at radio wavelengths (A1 and A2), confirming the long-known radio sources as protostellar. The emission towards A2 is resolved and traces a dust disk with a FWHM size of ~12 au, while the emission towards A1 sets a limit to the FWHM size of the dust disk of ~4 au. We also detect spatially resolved molecular kinematic tracers near the protostellar disks. Several lines of the J=5-4 rotational transition of HNCO, NH2CHO and t-HCOOH are detected, with which we derived individual line-of-sight velocities. Using these together with the CS (J=2-1), we fit Keplerian profiles towards the individual compact sources and derive masses of the central protostars. The kinematic analysis indicates that A1 and A2 are a bound binary system. Using this new context for the previous 30 years of VLA observations, we fit orbital parameters to the relative motion between A1 and A2 and find the combined protostellar mass derived from the orbit is consistent with the masses derived from the gas kinematics. Both estimations indicate masses consistently higher (0.5< M1<M2<2 Msun) than previous estimations using lower resolution observations of the gas kinematics. The ALMA high-resolution data provides a unique insight into the gas kinematics and masses of a young deeply embedded bound binary system.
Infrared imaging of the colliding-wind binary Apep has revealed a spectacular dust plume with complicated internal dynamics that challenges standard colliding-wind binary physics. Such challenges can be potentially resolved if a rapidly-rotating Wolf-Rayet star is located at the heart of the system, implicating Apep as a Galactic progenitor system to long-duration gamma-ray bursts. One of the difficulties in interpreting the dynamics of Apep is that the spectral composition of the stars in the system was unclear. Here we present visual to near-infrared spectra that demonstrate that the central component of Apep is composed of two classical Wolf-Rayet stars of carbon- (WC8) and nitrogen-sequence (WN4-6b) subtypes. We argue that such an assignment represents the strongest case of a classical WR+WR binary system in the Milky Way. The terminal line-of-sight wind velocities of the WC8 and WN4-6b stars are measured to be $2100 pm 200$ and $3500 pm 100$ km s$^{-1}$, respectively. If the mass-loss rate of the two stars are typical for their spectral class, the momentum ratio of the colliding winds is expected to be $approx$ 0.4. Since the expansion velocity of the dust plume is significantly smaller than either of the measured terminal velocities, we explore the suggestion that one of the Wolf-Rayet winds is anisotropic. We can recover a shock-compressed wind velocity consistent with the observed dust expansion velocity if the WC8 star produces a significantly slow equatorial wind with a velocity of $approx$530 km s$^{-1}$. Such slow wind speeds can be driven by near-critical rotation of a Wolf-Rayet star.
FUors are young stellar objects experiencing large optical outbursts due to highly enhanced accretion from the circumstellar disk onto the star. FUors are often surrounded by massive envelopes, which play a significant role in the outburst mechanism. Conversely, the subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. Here we present an APEX $^{12}$CO and $^{13}$CO survey of eight southern and equatorial FUors. We measure the mass of the gaseous material surrounding our targets. We locate the source of the CO emission and derive physical parameters for the envelopes and outflows, where detected. Our results support the evolutionary scenario where FUors represent a transition phase from envelope-surrounded protostars to classical T Tauri stars.
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