We calculate the X-ray luminosity and light curve for the stellar binary system Car for the entire orbital period of 5.54 yr. By using a new approach we find, as suggested in previous works, that the collision of the winds blown by the two stars can explain the X-ray emission and temporal behavior. Most X-ray emission in the 2-10 keV band results from the shocked secondary stellar wind. The observed rise in X-ray luminosity just before minimum is due to the increase in density and subsequent decrease in radiative cooling time of the shocked fast secondary wind. Absorption, particularly of the soft X-rays from the primary wind, increases as the system approaches periastron and the shocks are produced deep inside the primary wind. However, absorption cannot account for the drastic X-ray minimum. The 70 day minimum is assumed to result from the collapse of the collision region of the two winds onto the secondary star. This process is assumed to shut down the secondary wind, and hence the main X-ray source. We show that this assumption provides a phenomenological description of the X-ray behavior around the minimum.

We conduct numerical simulations of axisymmetrical jets expanding into a spherical asymptotic giant branch (AGB) slow wind. The three-dimensional flow is simulated with an axially symmetric numerical code. We concentrate on jets that are active for a relatively short time. Our results strengthen other studies that show that jets can account for many morphological features observed in planetary nebulae (PNs). Our main results are as follows. (1) With a single jet's launching episode, we can reproduce a lobe structure having a 'front lobe', that is a small bulge on the front of the main lobe, such as that in the PN Mz 3. (2) In some runs, dense clumps are formed along the symmetry axis, such as those observed in the pre-PN M1-92. (3) The mass-loss history of the slow wind has a profound influence on the PN structure. (4) A dense expanding torus (ring; disc) is formed in most of our runs. The torus is formed from the inflated lobes and not from a separate equatorial mass-loss episode. (5) The torus and lobes are formed at the same time and from the same mass-loss rate episode. However, when the slow wind density is steep enough, the ratio of the distance divided by the radial velocity is larger for regions closer to the equatorial plane than for regions closer to the symmetry axis. (6) With the short jet-active phase, a linear relation between distance and expansion velocity is obtained in many cases. (7) Regions at the front of the lobe are moving sufficiently fast to excite some visible emission lines.

We study the similarities of jet-medium interactions in several quite different astrophysical systems using 2D and 3D hydrodynamical numerical simulations, and find many similarities. The systems include cooling flow (CF) clusters of galaxies, core collapse supernovae (CCSNe), planetary nebulae (PNe), and common envelope (CE) evolution. The similarities include hot bubbles inflated by jets in a bipolar structure, vortices on the sides of the jets, vortices inside the inflated bubbles, fragmentation of bubbles to two and more bubbles, and buoyancy of bubbles. The activity in many cases is regulated by a negative feedback mechanism. In CF clusters we find that heating of the intra-cluster medium (ICM) is done by mixing hot shocked jet gas with the ICM, and not by shocks. Our results strengthen the jet feedback mechanism (JFM) as a common process in many astrophysical objects.

We calculate the X‐ray emission from both constant and time‐evolving shocked fast winds blown by the central stars of planetary nebulae (PNe) and compare our calculations with observations. Using spherically symmetric numerical simulations with radiative cooling, we calculate the flow structure and the X‐ray temperature and luminosity of the hot bubble formed by the shocked fast wind. We find that a constant fast wind gives results that are very close to those obtained from the self‐similar solution. We show that in order for a fast shocked wind to explain the observed X‐ray properties of PNe, rapid evolution of the wind is essential. More specifically, the mass‐loss rate of the fast wind should be high early on when the speed is ∼300–700 km s−1, and then it needs to drop drastically by the time the PN age reaches ∼1000 yr. This implies that the central star has a very short pre‐PN (post‐asymptotic giant branch) phase.

We calculate the X-ray emission from the shocked fast wind blown by the central stars of planetary nebulae (PNe) and compare with observations. Using spherically symmetric self-similar solutions, we calculate the flow structure and X-ray temperature for a fast wind slamming into a previously ejected slow wind. We find that the observed X-ray emission of six PNe can be accounted for by shocked wind segments that were expelled during the early-PN phase, if the fast wind speed is moderate, v 2 ∼ 400-600 km s −1 , and the mass-loss rate is a few times 10 −7 M yr −1 . We find, as proposed previously, that the morphology of the X-ray emission is in the form of a narrow ring inner to the optical bright part of the nebula. The bipolar X-ray morphology of several observed PNe, which indicates an important role of jets, rather than a spherical fast wind, cannot be explained by the flow studied here.