Jet Bow Shock Research Articles

A kinematical study of the launching region of the blueshifted HH 46/47 outflow with SINFONI K-band observations

Studying outflows is important, as they may significantly contribute to angular momentum removal from a star-disc system and thus affect disc evolution and planet formation. To investigate the different outflow components, including the collimated jet, wide-angled molecular outflow, and outflow cavity, of the Class I HH 46/47 outflow system, we focused on their kinematics. We present near-infrared (NIR) K-band integral field observations of the blueshifted HH 46/47 outflow base obtained using VLT/SINFONI with an angular resolution of 0 Our analysis focuses on Fe ii H$_2$ 1–0 S(1), and Br-gamma emission. We employed a wavelength recalibration technique based on OH telluric lines in order to probe the kinematics of the wide-angled flow with an accuracy of sim 1 km s$^ $ - 3 km s$^ We confirmed a velocity gradient of sim 10 km s$^ $ transverse to the outflow direction in the wide-angled H$_2$ outflow cavity. We find that the H$_2$ cavity peaks at radial velocities of sim $-$15 km s$^ $ to $-$30 km s$^ $, and that the atomic jet peaks at $v_ rad $ sim $-$210 km s$^ $. The outflow exhibits a layered structure: The high-velocity Fe ii and Br-gamma jet is surrounded by a wide-angled H$_2$ outflow cavity that is in turn nested within the continuum emission and CO molecular outflow. The continuum emission and H$_2$ outflow cavity are asymmetric with respect to the jet axis. We propose that the origin of the asymmetries and the velocity gradient detected in the wide-angled H$_2$ cavity is due to a wide-angled outflow or successive jet bowshocks expanding into an inhomogeneous ambient medium or the presence of a secondary outflow. We eliminated outflow rotation as an exclusive origin of this velocity gradient due to large specific angular momenta values, $J(r)$ approx 3000 - 4000 km s$^ \,$au, calculated from 1 to 2 along the outflow and the fact that the sense of apparent rotation we detected is opposite to that of the CO envelope emission. The observations reveal the complexities inherent in outflow systems and the risk of attributing transverse velocity gradients solely to rotation.

JWST study of the DG Tau B disk-wind candidate

Context. The origin of outflows and their impact on protoplanetary disk evolution and planet-formation processes are still crucial open questions. DG Tau B is a Class I protostar associated with a structured disk and a rotating conical CO outflow and was recently identified by ALMA as one of the best CO disk wind candidate. It is therefore a perfect target for studying these questions. Aims. We aim to map and study any outflow component intermediate between the axial jet and the CO outflow in order to constrain the origin (irradiated or shocked disk wind or swept-up material) of the redshifted molecular outflows in DG Tau B. Methods. We analyzed observations obtained with James Webb Space Telescope NIRSpec-IFU and NIRCam, supplemented with IFU data from the SINFONI/VLT instrument. We investigated the morphology, kinematics, and excitation conditions of the ro-vibrational H2 emission lines and their relation with the atomic jet and CO outflow. We focus our analysis on the redshifted outflow lobe. Results. We observe a global layered structure of the redshifted outflows in DG Tau B, with the atomic jet inside the H2 cavity, which in turn is nested inside the CO conical outflow. We also find temperature, velocity, and collimation to be increasing towards the axis of the flow. The redshifted H2 emission traces a narrow conical cavity (semi-opening angle of 9.4°) that is wider than the axial jet but nested just inside the CO outflow. Both the jet and the H2 cavity originate from the innermost regions of the disk (r0 < 6 au). The redshifted H2 cavity flows with a constant vertical velocity of Vz = 22.5 ± 0.8 km s−1, twice faster than the conical CO flow. The excitation conditions imply a hot H2 gas (Tex ≃ 2200 K) with an average mass flux of Ṁ(H2) = 3 × 10−11 M⊙ yr−1, which is significantly lower than the jet and CO values. Conclusions. The global layered H2-CO structure in temperature, velocity, and collimation in the DG Tau B redshifted lobe is consistent with a magneto-hydrodynamic disk wind scenario. The hot H2 could trace the inner, dense photodissociation layer in the wind. An H2 launching region at disk radii of 0.2−0.4 au combined with a large ejection efficiency (ξ ≃ 1) would account for the mass flux and kinematics. Alternatively, the near-IR ro-vibrational H2 could be emitted in the interaction layer driven by successive jet bow shocks into an outer disk wind or envelope. Further constraints on both scenarios will be obtained from the analysis of MIRI observations.

Jet-related Excitation of the [C ii] Emission in the Active Galaxy NGC 4258 with SOFIA

Abstract We detect widespread [C ii] 157.7 μm emission from the inner 5 kpc of the active galaxy NGC 4258 with the SOFIA integral field spectrometer FIFI-LS. The emission is found to be associated with warm H2, distributed along and beyond the end of the southern jet, in a zone known to contain shock-excited optical filaments. It is also associated with soft X-ray hotspots, which are the counterparts of the “anomalous radio arms” of NGC 4258, and a 1 kpc long filament on the minor axis of the galaxy that contains young star clusters. Palomar CWI Hα integral field spectroscopy shows that the filament exhibits non-circular motions within NGC 4258. Many of the [C ii] profiles are very broad, with the greatest line width, 455 km s−1, observed at the position of the southern jet bow-shock. Abnormally high ratios of L([C ii])/L(FIR) and L([C ii])/L(PAH 7.7 μm) are found along and beyond the southern jet and in the X-ray hotspots. These are the same regions that exhibit unusually large intrinsic [C ii] line widths. This suggests that the [C ii] traces warm molecular gas in shocks and turbulence associated with the jet. We estimate that as much as 40% (3.8 × 1039 erg s−1) of the total [C ii] luminosity from the inner 5 kpc of NGC 4258 arises in shocks and turbulence (<1% bolometric luminosity from the active nucleus), the rest being consistent with [C ii] excitation associated with star formation. We propose that the highly inclined jet is colliding with, and being deflected around, dense irregularities in a thick disk, leading to significant energy dissipation over a wide area of the galaxy.

Interaction between a pulsating jet and a surrounding disk wind

Context. The molecular richness of fast protostellar jets within 20–100 au of their source, despite strong ultraviolet irradiation, remains a challenge for the models investigated so far. Aim.We aim to investigate the effect of interaction between a time-variable jet and a surrounding steady disk wind, to assess the possibility of jet chemical enrichement by the wind, and the characteristic signatures of such a configuration. Methods. We have constructed an analytic model of a jet bow shock driven into a surrounding slower disk wind in the thin shell approximation. The refilling of the post bow shock cavity from below by the disk wind is also studied. An extension of the model to the case of two or more successive internal working surfaces (IWS) is made. We then compared this analytic model with numerical simulations with and without a surrounding disk wind. Results. We find that at early times (of order the variability period), jet bow shocks travel in refilled pristine disk wind material, before interacting with the cocoon of older bow shocks. This opens the possibility of bow shock chemical enrichment (if the disk wind is molecular and dusty) and of probing the unperturbed disk wind structure near the jet base. Several distinctive signatures of the presence of a surrounding disk wind are identified, in the bow shock morphology and kinematics. Numerical simulations validate our analytical approach and further show that at large scale, the passage of many jet IWS inside a disk wind produces a stationary V-shaped cavity, closing down onto the axis at a finite distance from the source.

CSO CO (2–1) and Spitzer IRAC observations of a bipolar outflow in high-mass star-forming region IRAS 22506+5944

We present Caltech Submillimeter Observatory CO (2–1) and Spitzer IRAC observations toward IRAS 22506+5944, which is a 104 L⊙ massive star-forming region. The CO (2–1) maps show an east-west bipolar molecular outflow originating from the 3 mm dust continuum peak. The Spitzer IRAC color-composite image reveals a pair of bow-shaped tips which are prominent in excess 4.5μm emission and are located at the leading fronts of the bipolar outflow, providing compelling evidence for the existence of bow-shocks as the driving agents of the molecular outflow. By comparing our CO (2–1) observations with previously published CO (1–0) data, we find that the CO (2–1)/(1–0) line ratio increases from low (∼5 kms−1) to moderate (∼8–12 kms−1) velocities, and then decreases at higher velocities. This is qualitatively consistent with the scenario that the molecular outflow is driven by multiple bow-shocks. We also revisit the position-velocity diagram of the CO (1–0) data, and find two spur structures along the outflow axis, which are further evidence for the presence of multiple jet bowshocks. Finally, power-law fittings to the mass spectrum of the outflow gives power law indexes more consistent with the jet bow-shock model than the wide-angle wind model.

Numerical Simulation of Star Formation by the Bow Shock of the Centaurus A Jet

Abstract Recent Hubble Space Telescope (HST) observations of the extragalactic radio source Centaurus A (Cen A) display a young stellar population around the southwest tip of the inner filament 8.5 kpc from the galactic center of Cen A, with ages in the range 1–3 Myr. Crockett et al. have argued that the transverse bow shock of the Cen A jet triggered this star formation as it impacted dense molecular cores of clouds in the filament. To test this hypothesis, we perform three-dimensional numerical simulations of star formation induced by the jet bow shock in the inner filament of Cen A, using a positivity-preserving, weighted, essentially non-oscillatory method to solve the equations of gas dynamics with radiative cooling. We find that star clusters form inside a bow-shocked molecular cloud when the maximum initial density of the cloud is ≥ 40 H2 molecules cm−3. In a typical molecular cloud of mass 10 6 M ⊙ and diameter 200 pc, approximately 20 star clusters of mass 10 4 M ⊙ are formed, matching the HST images.

ALMA CYCLE 1 OBSERVATIONS OF THE HH46/47 MOLECULAR OUTFLOW: STRUCTURE, ENTRAINMENT, AND CORE IMPACT

ABSTRACT We present Atacama Large Millimeter/sub-millimeter Array Cycle 1 observations of the HH 46/47 molecular outflow using combined 12 m array and Atacama Compact Array observations. The improved angular resolution and sensitivity of our multi-line maps reveal structures that help us study the entrainment process in much more detail and allow us to obtain more precise estimates of outflow properties than in previous observations. We use (1–0) and (1–0) emission to correct for the (1–0) optical depth to accurately estimate the outflow mass, momentum, and kinetic energy. This correction increases the estimates of the mass, momentum, and kinetic energy by factors of about 9, 5, and 2, respectively, with respect to estimates assuming optically thin emission. The new and data also allow us to trace denser and slower outflow material than that traced by the maps, and they reveal an outflow cavity wall at very low velocities (as low as 0.2 with respect to the core’s central velocity). Adding the slower material traced only by and , there is another factor of three increase in the mass estimate and 50% increase in the momentum estimate. The estimated outflow properties indicate that the outflow is capable of dispersing the parent core within the typical lifetime of the embedded phase of a low-mass protostar and that it is responsible for a core-to-star efficiency of 1/4 to 1/3. We find that the outflow cavity wall is composed of multiple shells associated with a series of jet bow-shock events. Within about 3000 au of the protostar the and emission trace a circumstellar envelope with both rotation and infall motions, which we compare with a simple analytic model. The CS (2–1) emission reveals tentative evidence of a slowly moving rotating outflow, which we suggest is entrained not only poloidally but also toroidally by a disk wind that is launched from relatively large radii from the source.

Characteristics of Cascaded Fuel Injectors Within an Accelerating Scramjet Combustor

Performances of cascaded hydrogen injectors within an accelerating scramjet combustor were characterized via a three-dimensional numerical study. Two streamwise-aligned jets are employed, with the upstream injector half the diameter of the rear jet. Each are inclined at 45 deg to the freestream and achieve a jet-to-freestream momentum ratio of unity. Performance was evaluated over a range of freestream Mach numbers, modeling combustor entrance conditions on an accelerating access-to-space scramjet trajectory. Distance between injectors was varied to estimate the optimum jet-to-jet spacing to achieve robust performance across the Mach number range. It is shown that the downstream injector benefits jointly from shielding effects induced by the smaller upstream injector, as well as its increased diameter. Injector spacings greater than two total jet diameters displayed improved absolute jet penetration, spanwise spread, and entrainment rates over an equivalent single injector across all Mach numbers. Jet bow shock pressure recovery was improved at spacings above . Unique optimal injector spacings existed for each performance metric, at each freestream Mach number examined. Although no universal optimum spacing was determined, spacings between 4 and provided substantial performance enhancements over single injectors, throughout the accelerating scramjet flight conditions.

THE DISK-OUTFLOW SYSTEM IN THE S255IR AREA OF HIGH-MASS STAR FORMATION

We report the results of our observations of the S255IR area with the SMA at 1.3 mm in the very extended configuration and at 0.8 mm in the compact configuration as well as with the IRAM-30m at 0.8 mm. The best achieved angular resolution is about 0.4 arcsec. The dust continuum emission and several tens of molecular spectral lines are observed. The majority of the lines is detected only towards the S255IR-SMA1 clump, which represents a rotating structure (probably disk) around the young massive star. The achieved angular resolution is still insufficient for conclusions about Keplerian or non-Keplerian character of the rotation. The temperature of the molecular gas reaches 130-180 K. The size of the clump is about 500 AU. The clump is strongly fragmented as follows from the low beam filling factor. The mass of the hot gas is significantly lower than the mass of the central star. A strong DCN emission near the center of the hot core most probably indicates a presence of a relatively cold ($\lesssim 80$ K) and rather massive clump there. High velocity emission is observed in the CO line as well as in lines of high density tracers HCN, HCO+, CS and other molecules. The outflow morphology obtained from combination of the SMA and IRAM-30m data is significantly different from that derived from the SMA data alone. The CO emission detected with the SMA traces only one boundary of the outflow. The outflow is most probably driven by jet bow shocks created by episodic ejections from the center. We detected a dense high velocity clump associated apparently with one of the bow shocks. The outflow strongly affects the chemical composition of the surrounding medium.

The structure of the Cepheus E protostellar outflow: The jet, the bowshock, and the cavity

Context. Protostellar outflows are a crucial ingredient of the star-formation process. However, the physical conditions in the warm outflowing gas are still poorly known.Aims. We present a multi-transition, high spectral resolution CO study of the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow and to constrain the physical conditions of the various components in order to understand the origin of the mass-loss phenomenon.Methods. We have observed the J = 12–11, J = 13–12, and J = 16–15 CO lines at high spectral resolution with SOFIA/GREAT and the J = 5–4, J = 9–8, and J = 14–13 CO lines with HIFI/Herschel towards the position of the terminal bowshock HH377 in the southern outflow lobe. These observations were complemented with maps of CO transitions obtained with the IRAM 30 m telescope (J = 1–0, 2–1), the Plateau de Bure interferometer (J = 2–1), and the James Clerk Maxwell Telescope (J = 3–2, 4–3).Results. We identify three main components in the protostellar outflow: the jet, the cavity, and the bowshock, with a typical size of 1.7″ × 21″, 4.5″, and 22″ × 10″, respectively. In the jet, the emission from the low-J CO lines is dominated by a gas layer at T kin = 80–100 K, column density N (CO) = 9 × 1016 cm-2 , and density n (H2 ) = (0.5−1) × 105 cm-3 ; the emission of the high-J CO lines arises from a warmer (T kin = 400–750 K), denser (n (H2 ) = (0.5−1) × 106 cm-3 ), lower column density (N (CO) = 1.5 × 1016 cm-2 ) gas component. Similarly, in the outflow cavity, two components are detected: the emission of the low-J lines is dominated by a gas layer of column density N (CO) = 7 × 1017 cm-2 at T kin = 55–85 K and density in the range (1−8) × 105 cm-3 ; the emission of the high-J lines is dominated by a hot, denser gas layer with T kin = 500–1500K, n (H2 ) = (1−5) × 106 cm-3 , and N (CO) = 6 × 1016 cm-2 . A temperature gradient as a function of the velocity is found in the high-excitation gas component. In the terminal bowshock HH377, we detect gas of moderate excitation, with a temperature in the range T kin ≈ 400–500 K, density n (H2 ) ≃ (1 −2) × 106 cm-3 and column density N (CO) = 1017 cm-2 . The amounts of momentum carried away in the jet and in the entrained ambient medium are similar. Comparison with time-dependent shock models shows that the hot gas emission in the jet is well accounted for by a magnetized shock with an age of 220–740 yr propagating at 20–30 km s-1 in a medium of density n (H2 ) = (0.5−1) × 105 cm-3 , consistent with that of the bulk material.Conclusions. The Cep E protostellar outflow appears to be a convincing case of jet bowshock driven outflow. Our observations trace the recent impact of the protostellar jet into the ambient cloud, produing a non-stationary magnetized shock, which drives the formation of an outflow cavity.

Modeling the X-ray light curves of Cygnus X-3

Context: Physics behind the soft X-ray light curve asymmetries in Cygnus X-3, a well-known microquasar, was studied. AIMS: Observable effects of the jet close to the line-of-sight were investigated and interpreted within the frame of light curve physics. METHODS: The path of a hypothetical imprint of the jet, advected by the WR-wind, was computed and its crossing with the line-of-sight during the binary orbit determined. We explore the possibility that physically this 'imprint' is a formation of dense clumps triggered by jet bow shocks in the wind ("clumpy trail"). Models for X-ray continuum and emission line light curves were constructed using two absorbers: mass columns along the line-of-sight of i) the WR wind and ii) the clumpy trail, as seen from the compact star. These model light curves were compared with the observed ones from the RXTE/ASM (continuum) and Chandra/HETG (emission lines). Results: We show that the shapes of the Cygnus X-3 light curves can be explained by the two absorbers using the inclination and true anomaly angles of the jet as derived in Dubus et al. (2010) from gamma-ray Fermi/LAT observations. The clumpy trail absorber is much larger for the lines than for the continuum. We suggest that the clumpy trail is a mixture of equilibrium and hot (shock heated) clumps. Conclusions: A possible way for studying jets in binary stars when the jet axis and the line-of-sight are close to each other is demonstrated. The X-ray continuum and emission line light curves of Cygnus X-3 can be explained by two absorbers: the WR companion wind plus an absorber lying in the jet path (clumpy trail). We propose that the clumpy trail absorber is due to dense clumps triggered by jet bow shocks.

Characteristics of unsteady type IV shock/shock interaction

Characteristics of the unsteady type IV shock/shock interaction of hypersonic blunt body flows are investigated by solving the Navier–Stokes equations with high-order numerical methods. The intrinsic relations of flow structures to shear, compression, and heating processes are studied and the physical mechanisms of the unsteady flow evolution are revealed. It is found that the instantaneous surface-heating peak is caused by the fluid in the “hot spot” generated by an oscillating and deforming jet bow shock (JBS) just ahead of the body surface. The features of local shock/boundary layer interaction and vortex/boundary layer interaction are clarified. Based on the analysis of flow evolution, it is identified that the upstream-propagating compression waves are associated with the interaction of the JBS and the shear layers formed by a supersonic impinging jet, and then the interaction of the freestream bow shocks and the compression waves results in entropy and vortical waves propagating to the body surface. Further, the feedback mechanism of the inherent unsteadiness of the flow field is revealed to be related to the impinging jet. A feedback model is proposed to reliably predict the dominant frequency of flow evolution. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to this complex flow.

Evidence for episodic warm outflowing CO gas from the intermediate-mass young stellar object IRAS 08470-4321★

We present a R=10,000 M-band spectrum of LLN19 (IRAS 08470-4321), a heavily embedded intermediate-mass young stellar object located in the Vela Molecular Cloud, obtained with VLT-ISAAC. The data were fitted by a 2-slab cold-hot model and a wind model. The spectrum exhibits deep broad ro-vibrational absorption lines of 12CO v=1<-0 and 13CO v=1<-0. A weak CO ice feature at 4.67 micron is also detected. Differences in velocity indicate that the warm gas is distinct from the cold millimeter emitting gas, which may be associated with the absorption by cooler gas (45K). The outflowing warm gas at 300-400K and with a mass-loss rate varying between 0.48E-7 and 4.2E-7 MSun /yr can explain most of the absorption. Several absorption lines were spectrally resolved in subsequent spectra obtained with the VLT-CRIRES instrument. Multiple absorption substructures in the high-resolution (R=100,000) spectra indicate that the mass-loss is episodic with at least two major events that occurred recently (<28 years). The discrete mass-loss events together with the large turbulent width of the gas (dv=10-12 km/s) are consistent with the predictions of the Jet-Bow shock outflow and the wide-angle wind model. The CO gas/solid column density ratio of 20-100 in the line-of-sight confirms that the circumstellar environment of LLN~19 is warm. We also derive a 12C/13C ratio of 67 +/- 3, consistent with previous measurements in local molecular clouds but not with the higher ratios found in the envelope of other young stellar objects.

GRB Precursors in the Fallback Collapsar Scenario

Precursor emission has been observed in a non-negligible fraction of gamma-ray bursts.The time gap between the precursor and the main burst extends in some case up to hundreds of seconds, such as in GRB041219A, GRB050820A and GRB060124. Both the origin of the precursor and the large value of the time gap are controversial. Here we investigate the maximum possible time gaps arising from the jet propagation inside the progenitor star, in models which assume that the precursor is produced by the jet bow shock or the cocoon breaking out of the progenitor. Due to the pressure drop ahead of the jet head after it reaches the stellar surface, a rarefaction wave propagates back into the jet at the sound speed, which re-accelerates the jet to a relativistic velocity and therefore limits the gap period to within about ten seconds. This scenario therefore cannot explain gaps which are hundreds of seconds long. Instead, we ascribe such long time gaps to the behavior of the central engine, and suggest a fallback collapsar scenario for these bursts. In this scenario, the precursor is produced by a weak jet formed during the initial core collapse, possibly related to MHD processes associated with a short-lived proto-neutron star, while the main burst is produced by a stronger jet fed by fallback accretion onto the black hole resulting from the collapse of the neutron star. We have examined the propagation times of the weak precursor jet through the stellar progenitor. We find that the initial weak jet can break out of the progenitor in a time less than ten seconds (a typical precursor duration) provided that it has a moderately high relativistic Lorentz factor \Gamma>=10 (abridged).

Hydrodynamical Simulations of the Jet in the Symbiotic Star MWC 560. III. Application to X‐Ray Jets in Symbiotic Stars

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.

Anatomy of HH 111 from CO Observations: A Bow‐Shock‐driven Molecular Outflow

We present single-dish and interferometric millimeter line observations of the HH 111 outflow and its driving source. The physical conditions of the core have been determined from the emission of the millimeter line of CO and its isotopomers and CS with the IRAM 30 m telescope, and the CO J = 7 → 6 line with the Caltech Submillimeter Observatory. The emission reveals a small condensation of cold (T = 20-25 K) and dense gas [n(H2) = 3 × 105 cm-3]. The outflow has been mapped with the IRAM Plateau de Bure interferometer (PdBI). The cold gas is distributed in a hollow cylinder surrounding the optical jet. The formation of this cavity and its kinematics are well accounted for in the frame of outflow gas entrainment by jet bow shocks. Evidence of gas acceleration is found along the cavity walls, correlated with the presence of optical bow shocks. The separation of the inner walls reaches 8''-10'', which matches the transverse size of the wings in the bow shock. CSO observations of the J = 7 → 6 line show evidence of a high-velocity and hot gas component (T = 300-1000 K) with a low filling factor. This emission probably arises from shocked gas in the jet. Observations of the 3P2-3P1 [C I] line are consistent with C-type nondissociative shocks. Mapping of the high-velocity molecular bullets B1-B3, located beyond the optical jet, reveals small structures of 3'' × 7'' flattened perpendicular to the flow direction. They are made of cold (T ~ 30 K), moderate density gas [n(H2) = (0.5-1.0) × 104 cm-3], expanding into the low-density surrounding medium. Their properties are consistent with their being shocked gas knots resulting from past time-variable ejections in the jet.

Pulsed, supersonic fuel jets—A review of their characteristics and potential for fuel injection

High pressure fuel injection has provided considerable benefits for diesel engines, substantially reducing smoke levels while increasing efficiency. Current maximum pressures provide jets that are at less than the sonic velocity of the compressed air in the cylinders at injection. It has been postulated that a further increase into the supersonic range may benefit the combustion process due to increased aerodynamic atomization and the presence of jet bow shock waves that provide higher temperatures around the fuel. Pulsed, supersonic injection may also be beneficial for scramjet engines. The current program is examining pulsed, supersonic jets from a fundamental viewpoint both experimentally and numerically. Shock wave structures have been viewed for jets ranging from 600 to 2400 m/s, velocity attenuation and penetration distance measured, different nozzle designs examined and autoignition experiments carried out. Inside the nozzle, numerical simulation using the Autodyne code has been used to support an analytic approach while in the spray, the FLUENT code has been used. While benefits have not yet been defined, it appears that some earlier claims regarding autoignition at atmospheric conditions were optimistic but that increased evaporation and mixing are probable. The higher jet velocities are likely to mean that wall interactions are increased and hence matching such injectors to engine size and airflow patterns will be important.

Hydrodynamical simulations of the jet in the symbiotic star MWC 560

We performed hydrodynamical simulations with and without radiative cooling of jet models with parameters representative of 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 emission plots which account for expected radiative processes. In addition, our calculations provide expansion velocities for the jet bow shock, the density and temperature structure in the jet, and the propagation and evolution of the jet pulses. In MWC 560 the jet axis is parallel to the line of sight so that the outflowing jet gas can be seen as blue shifted, variable absorption lines in the continuum of the underlying jet source. Based on our simulations we calculate and discuss synthetic absorption profiles. Based on a detailed comparison between model spectra and observations we discuss our hydrodynamical calculations for a pulsed jet in MWC 560 and suggest improvements for future models.

Parameters for very light jets of cD galaxies

Recent Chandra X-ray observations of jets in central cluster galaxies show interesting features around the symmetry plane. We have carried out simulations involving bipolar jets, removing the artificial boundary condition at the symmetry plane. We use a very low jet density (IGM/jet ≈10 4) and take into account a decreasing density profile. We find that the jet bow shock undergoes two phases: First a nearly spherical one and second the well-known cigar-shaped one. We propose Cygnus A to be in a transition phase, showing clear signs from both phases. Due to inward growing of Kelvin Helmholtz instabilities (KHI) between cocoon and shocked IGM, mass entrainment is observed predominantly in the symmetry plane. We propose this mechanism to produce some of the so far enigmatic X-ray features in the symmetry plane in Cygnus A.

Bow Shocks, Wiggling Jets, and Wide‐Angle Winds: A High‐Resolution Study of the Entrainment Mechanism of the PV Cephei Molecular (CO) Outflow

We present a new set of high-resolution molecular-line maps of the gas immediately surrounding various Herbig-Haro (HH) knots of the giant HH flow HH 315 from the young star PV Cephei. The observations, aimed at studying the entrainment mechanism of the 2.6 pc-long HH 315 flow, include IRAM 30 m maps of the 12CO (2-1), 12CO (1-0), and 13CO (1-0) lines, with beam sizes of 11'', 21'', and 22'', respectively. We compare the morphology and the kinematics of the outflow gas, as well as the temperature and momentum distribution of the molecular outflow, with those predicted by different entrainment models. With our detailed study we are able to conclude that jet bow shock entrainment by an episodic stellar wind, with a time-varying axis, produces most of the high-velocity molecular outflow observed far from the source. In addition, near PV Cep we find evidence for a poorly collimated, wide-angle molecular outflow and a collimated, wiggling jet-like molecular outflow. We propose that the poorly collimated component is entrained by a wide-angle wind and the collimated component is entrained by a variable jet with internal working surfaces. If this picture is true, then a stellar wind model that allows for the coexistence of a wide-angle component and a collimated (jetlike) stellar wind component is needed to explain the observed properties of the PV Cep outflow. The wiggling axis of the redshifted molecular outflow lobe indicates that the outflow ejection axis is changing over time. We find that the timescale of the axis variation shown by the molecular outflow lobe is about a factor of 10 less than that shown by the large-scale optical HH knots.