Disc-winds originating from the inner parts of accretion discs are considered as the basic component of magnetically collimated outflows. The only available analytical MHD solutions to describe disc-driven jets are those characterized by the symmetry
of radial self-similarity. However, radially self-similar MHD jet models, in general, have three geometrical shortcomings, (i) a singularity at the jet axis, (ii) the necessary assumption of axisymmetry, and (iii) the non-existence of an intrinsic radial scale, i.e. the jets formally extend to radial infinity. Hence, numerical simulations are necessary to extend the analytical solutions towards the axis, by solving the full three-dimensional equations of MHD and impose a termination radius at finite radial distance. We focus here on studying the effects of relaxing the (ii) assumption of axisymmetry, i.e. of performing full 3D numerical simulations of a disc-wind crossing all magnetohydrodynamic critical surfaces. We compare the results of these runs with previous axisymmetric 2.5D simulations. The structure of the flow in all simulations shows strong similarities. The 3D runs reach a steady state and stay close to axisymmetry for most of the physical quantities, except for the poloidal magnetic field and the toroidal velocity which slightly deviate from axisymmetry. The latter quantities show signs of instabilities, which, however, are confined to the region inside the fast magnetosonic separatrix surface. The forces present in the flow, both of collimating and accelerating nature, are in good agreement in both the 2.5D and the 3D runs. We conclude that the analytical solution behaves well also after relaxing the basic assumption of axisymmetry.
Hen 3-1341 is a symbiotic binary system consisting of a white dwarf and a red giant star that is one of about ten symbiotics that show hints of jets. The bipolar jets have been detected through displaced components of emission lines during its outbur
st from 1998 to 2004. These components disappeared when Hen 3-1341 reached quiescence. On February 23, 2012, Hen 3-1341 started a new outburst with the emergence of new bipolar jets on March 3, 2012. We observed Hen 3-1341 during quiescence with XMM-Newton in March 2010 with an effective exposure time of 46.8 ks and with Swift on March 8-11, 2012 as ToO observations with an effective exposure time of 10 ks in order to probe the interaction of the jet with the ambient medium and also the accretion onto the white dwarf. We fitted the XMM-Newton X-ray spectra with XSPEC and examined the X-ray and UV light curves. We report the detection of X-ray emission during quiescence from Hen 3-1341 with XMM-Newton. The spectrum can be fitted with an absorbed one-temperature plasma or an absorbed blackbody. We did not detect Hen 3-1341 during our short Swift exposure. Neither periodic or aperiodic X-ray nor UV variability were found. Our XMM-Newton data suggest that interaction of the residual jet with the interstellar medium might survive for a long time after outbursts and might be responsible for the observed X-ray emission during quiescence. Additional data are strongly needed to confirm these suggestions.
Analytical radially self-similar models are the best available solutions describing disk-winds but need several improvements. In a previous article, we introduced models of jets from truncated disks, i.e. evolved in time numerical simulations based o
n a radially self-similar MHD solution but including the effects of a finite radius of the jet-emitting disk and thus the outflow. In paper I of this series, we compared these models with available observational data varying the jet density and velocity, the mass of the protostar and the radius of the aforementioned truncation. In paper I, we assumed that the jet lies in the plane of the sky. In this paper, we investigate the effect of different inclinations of the jet. In order to compare our models with observed jet widths inferred from recent optical images taken with HST and AO, we create again emission maps in different forbidden lines and from such emission maps, we determine the jet width as the full-width half-maximum of the emission. We can reproduce the jet width of DG Tau and its variations very well and the derived inclination of 40$^circ$ is in excellent agreement with literature values of 32--52$^circ$. In CW Tau we overestimate the inclination in our best-fit model. In the other objects, we cannot find appropriate models which reproduce the variations of the observed jet widths, only the average jet width itself is well modeled as in paper I. We conclude that truncation -- i.e. taking into account the finite radius of the jet launching region -- is necessary to reproduce the observed jet widths and our simulations limit the possible range of truncation radii. The effects of inclination are important for modeling the intrinsic variations seen in observed jet widths. Our models can be used to infer independently the inclinations in the observed sample, however, a parameter study with a finer grid of parameters is needed.
HD 149427 is a very enigmatic object. It has been classified either as a planetary nebula or as a D-type symbiotic star. Its distance is also highly uncertain. Furthermore, HD 149427 is a potential jet source. We report the non-detection of X-ray emi
ssion from HD 149427 and explore the implications to its nature. We observed the object with XMM-Newton with an effective exposure time of 33.5 ks. The upper limit for the flux of the X-ray emission in the soft band (<2 keV) is 10^-15 erg/s/cm^2, while in the hard band (>2 keV) it is about 10^-14 erg/s/cm^2. We discuss the implication of our results in light of the possible natures of HD 149427 -- being a planetary nebula or a symbiotic star, close or very distant. The derived upper limits on the mass accretion rate of the white dwarf are untypical for symbiotic stars and may favor the picture of HD 149427 being a young PN. HD 149427 might be a symbiotic star in hibernation -- if a symbiotic star at all. We estimate the possible mass-loss rate and kinetic luminosity of the jet and find no contradiction with our upper limit of soft X-ray emission. Therefore the jet may be still present but it was too faint to be detected via soft X-ray emission.
We report the detection of X-ray emission from the symbiotic star V1329 Cyg with XMM-Newton. The spectrum from the EPIC pn, MOS1 and MOS2 instruments consists of a two-temperature plasma with k T = 0.11 keV and k T = 0.93 keV. Unlike the vast majorit
y of symbiotic stars detected in X-rays, the soft component of the spectrum seems to be absorbed only by interstellar material. The shock velocities corresponding to the observed temperatures are about 300 km/s and about 900 km/s. We did not find either periodic or aperiodic X-ray variability, with upper limits on the amplitudes of such variations being 46 % and 16 % (rms), respectively. We also did not find any ultraviolet variability with an rms amplitude of more than approximately 1 %. The derived velocities and the unabsorbed nature of the soft component of the X-ray spectrum suggest that some portion of the high energy emission could originate in shocks within a jet and beyond the symbiotic nebula. The lower velocity is consistent with the expansion velocity of the extended structure present in HST observations. The higher velocity could be associated with an internal shock at the base of the jet or with shocks in the accretion region.
(abridged) Significant progress has been made in the last years in the understanding of the jet formation mechanism through a combination of numerical simulations and analytical MHD models for outflows characterized by the symmetry of self-similarity
. In a previous article we introduced models of truncated jets from disks, i.e. evolved in time numerical simulations based on a radially self-similar MHD solution, but including the effects of a finite radius of the jet-emitting disk and thus the outflow. These models need now to be compared with available observational data. A direct comparison of the results of combined analytical theoretical models and numerical simulations with observations has not been performed as yet. In order to compare our models with observed jet widths inferred from recent optical images taken with HST and AO observations, we use a new set of tools to create emission maps in different forbidden lines, from which we determine the jet width as the FWHM of the emission. It is shown that the untruncated analytical disk outflow solution considered here cannot fit the small jet widths inferred by observations of several jets. Various truncated disk-wind models are examined, whose extracted jet widths range from higher to lower values compared to the observations. Thus we can fit the observed range of jet widths by tuning our models. We conclude that truncation is necessary to reproduce the observed jet widths and our simulations limit the possible range of truncation radii. We infer that the truncation radius, which is the radius on the disk mid-plane where the jet-emitting disk switches to a standard disk, must be between around 0.1 up to about 1 AU in the observed sample for the considered disk-wind solution. One disk-wind simulation with an inner truncation radius at about 0.11 AU also shows potential for reproducing the observations, but a parameter study is needed.
Aims: We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamenta
l questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods: To this end, we observed seven 15 times 15 arcmin^2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results: In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.
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.
(Abridged) Finite radius accretion disks are a strong candidate for launching astrophysical jets from their inner parts and disk-winds are considered as the basic component of such magnetically collimated outflows. The only available analytical MHD s
olutions for describing disk-driven jets are those characterized by the symmetry of radial self-similarity. Radially self-similar MHD models, in general, have two geometrical shortcomings, a singularity at the jet axis and the non-existence of an intrinsic radial scale, i.e. the jets formally extend to radial infinity. Hence, numerical simulations are necessary to extend the analytical solutions towards the axis and impose a physical boundary at finite radial distance. We focus here on studying the effects of imposing an outer radius of the underlying accreting disk (and thus also of the outflow) on the topology, structure and variability of a radially self-similar analytical MHD solution. The initial condition consists of a hybrid of an unchanged and a scaled-down analytical solution, one for the jet and the other for its environment. In all studied cases, we find at the end steady two-component solutions.
