Fig 18
Pulsed jet model i with radiative cooling at day 74: Grey scale plots of the logarithm of density in g cm −3 (top), of the velocity components parallel (middle) and perpendicular (bottom) to the jet axis in km s −1
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We performed hydrodynamical simulations with and without radiative cooling of jet models with parameters representative for the symbiotic system MWC 560. For symbiotic systems we have to perform jet simulations of a pulsed underdense jet in a high density ambient medium. We present the jet structure resulting from our simulations and calculate emis...
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In this paper we present a full general relativistic one-dimensional hydro-code which incorporates a modern high-resolution shock-capturing algorithm, with an approximate Riemann solver, for the correct modelling of formation and propagation of strong shocks. The efficiency of this code in treating strong shocks is demonstrated by some numerical ex...
Cornell University Library Publications (e-print)
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In this paper we analyse the jet like features observed in some symbiotic systems, we present the objects in which such features were detected. One of this objects is R Aqr. In this object high collimated outflows emerging from the central region has been observed since the 1970s. We present the possible explanation for this outflows and analyse some new kinematic data of this object comparing them with previous observations.
R Aquarii is a symbiotic system consisting of a Mira variable and a white dwarf companion. Its jet-like structures have been observed in the X-rays through the radio and extend up to 2500 AU from the central object. We report Far Ultraviolet Spectroscopic Explorer observations of O VI emission from these stellar jets that reveal signature line profiles of bow shocks. We have calculated bow shock models for a fully radiative shock, fully non-radiative shock, and a new hybrid set of models. We found that fully non-radiative shocks do not produce good fits to the data. While a fully radiative bow shock model cannot be excluded, the high densities required led us to develop hybrid bow shock models in which the shock is non-radiative near the apex of the bow shock, but becomes radiative at some distance from the apex. The model that best fits the data is the hybrid bow shock with a shock speed of approximately 235-285 km s–1 and an inclination angle of ~ +10° and +35° with the plane of the sky for the northeast and the southwest jets, respectively. A turbulent velocity of about 60 km s–1 was required to obtain good fits. Surprisingly, both of the opposing jets have similar model parameters in spite of their very different O VI flux and distance from the central object. This analysis confirms the ejecta bow shock scenario as opposed to the cloudlet bow shock, constraining the mechanism of jet production to characteristics of the central object. The striking similarities in the physical parameters of the jets indicate a common origin and support the precessing accretion disk scenario for the white dwarf in the R Aqr system. For both jets we find pre-shock densities in the range of 103-104 cm–3 at positions of the brightest X-ray emission from the jets, which are also the positions of the apparent outer terminal points of the jets, providing strong support for the theory that the emission and shock structures we are seeing are produced when the jet material interacts with an external nebular wall.
We report the detection of X-ray emission from the jet-driving symbiotic star MWC 560. We observed MWC 560 with XMM-Newton for 36 ks. We fitted the spectra from the EPIC pn, MOS1 and MOS2 instruments with XSPEC and examined the light curves with the package XRONOS. The spectrum can be fitted with a highly absorbed hard X-ray component from an optically-thin hot plasma, a Gaussian emission line with an energy of 6.1 keV and a less absorbed soft thermal component. The best fit is obtained with a model in which the hot component is produced by optically thin thermal emission from an isobaric cooling flow with a maximum temperature of 61 keV, which might be created inside an optically-thin boundary layer on the surface of the accreting with dwarf. The derived parameters of the hard component detected in MWC 560 are in good agreement with similar objects as CH Cyg, SS7317, RT Cru and T CrB, which all form a new sub-class of symbiotic stars emitting hard X-rays. Our previous numerical simulations of the jet in MWC 560 showed that it should produce detectable soft X-ray emission. We infer a temperature of 0.17 keV for the observed soft component, i.e. less than expected from our models. The total soft X-ray flux (i.e. at < 3 keV) is more than a factor 100 less than predicted for the propagating jet soon after its birth (<0.3 yr), but consistent with the value expected due its decrease with age. The ROSAT upper limit is also consistent with such a decrease. We find aperiodic or quasi-periodic variability on timescales of minutes and hours, but no periodic rapid variability. All results are consistent with an accreting white dwarf powering the X-ray emission and the existence of an optically-thin boundary layer around it. Comment: 8 pages, 5 figure, accepted for publication in A & A
In papers I and II in this series, we presented hydrodynamical simulations of jet models with parameters representative of the symbiotic system MWC 560. These were simulations of a pulsed, initially underdense jet in a high density ambient medium. Since the pulsed emission of the jet creates internal shocks and since the jet velocity is very high, the jet bow shock and the internal shocks are heated to high temperatures and should therefore emit X-ray radiation. In this paper, we investigate in detail the X-ray properties of the jets in our models. We have focused our study on the total X-ray luminosity and its temporal variability, the resulting spectra and the spatial distribution of the emission. Temperature and density maps from our hydrodynamical simulations with radiative cooling presented in the second paper are used together with emissivities calculated with the atomic database ATOMDB. The jets in our models show extended and variable X-ray emission which can be characterized as a sum of hot and warm components with temperatures that are consistent with observations of CH Cyg and R Aqr. The X-ray spectra of our model jets show emission line features which correspond to observed features in the spectra of CH Cyg. The innermost parts of our pulsed jets show iron line emission in the 6.4 - 6.7 keV range which may explain such emission from the central source in R Aqr. We conclude that MWC 560 should be detectable with Chandra or XMM-Newton, and such X-ray observations will provide crucial for understanding jets in symbiotic stars. Comment: 10 pages, 12 figures, accepted for publication in ApJ, uses emulateapj
We compare two scenarios to launch jets -- formation by MHD processes or formation by thermal pressure in the boundary layer (BL) -- with respect to their compatibility with observational data of jets in symbiotic stars, especially in the well studied jet source MWC 560. Finally, we discuss points of further research to be done. Comment: 4 pages, accepted for publication in A & A Letters
(Abridged) In the first paper of this series, we presented hydrodynamical simulations with radiative cooling of jet models with parameters representative of the symbiotic system MWC 560. These were jet simulations of a pulsed, initially underdense jet in a high-density ambient medium. They were stopped when the jet reached a length of 50 AU. There, however, a transition of the initially underdense jet towards an overdense jet should occur, which should result in changed kinematics. Therefore, we describe two hydrodynamical simulations with cooling beyond this density balance, one with the same parameters as model i in Paper I (now called model i'), which was presented there with and without cooling, and the second with higher gas densities in the jet pulses (model iv'). Hydrodynamical simulations, with a further approximated cooling treatment compared to Paper I, were used to be able to enlarge the computational domain. The transition causes changes in the expansion of the cocoon and therefore the morphology of the jet, e.g. a larger radial width of the jet knots. We investigate the radiation properties of the jets, the bremsstrahlung and optical emissivities, integrated emission maps, and synthetic absorption line profiles. The conclusion that the high observed velocities in CH Cygni, R Aquarii, and MWC 560 favor the models with cooling is unchanged by the transition. The observed parallel features in R Aquarii can be produced by the internal knots or by a variable dense radiative shell of shocked ambient medium. The absorption line profiles show that the real parameters in MWC 560 are closer to model iv' than to model i'. Comment: 10 pages, 9 figures, published in A & A; submission of this older paper now possible due to increased size limits
We present two numerical simulations of an accretion flow from a rotating torus onto a compact object with and without a solid surface -- representing a neutron star and a black hole -- and investigate its influence on the process of jet formation. We report the emergence of an additional ejection component, launched by thermal pressure inside a boundary layer (BL) around the neutron star and examine its structure. Finally, we suggest improvements for future models. Comment: 7 pages, 11 figures, accepted for publication in A & A
