Formation Of Bow Shock Research Articles

3D Smoothed Particle Hydrodynamics Models of Betelgeuse’s Bow Shock

Betelgeuse, the bright red supergiant (RSG) in Orion, is a runaway star. Its supersonic motion through the interstellar medium has resulted in the formation of a bow shock, a cometary structure pointing in the direction of motion. We present the first 3D hydrodynamic simulations of the formation and evolution of Betelgeuse's bow shock. We show that the bow shock morphology depends substantially on the growth timescale for Rayleigh-Taylor versus Kelvin-Helmholtz instabilities. We discuss our models in light of the recent Herschel, GALEX and VLA observations. If the mass in the bow shock shell is low (~few x 0.001 Msun), as seems to be implied by the AKARI and Herschel observations, then Betelgeuse's bow shock is very young and is unlikely to have reached a steady state. The circular, smooth bow shock shell is consistent with this conclusion. We further discuss the implications of our results, in particular, the possibility that Betelgeuse may have only recently entered the RSG phase.

Bow Shock Formation in a Complex Plasma

A bow shock is observed in a two-dimensional supersonic flow of charged microparticles in a complex plasma. A thin conducting needle is used to make a potential barrier as an obstacle for the particle flow in the complex plasma. The flow is generated and the flow velocity is controlled by changing a tilt angle of the device under the gravitational force. A void, microparticle-free region, is formed around the potential barrier surrounding the obstacle. The flow is bent around the leading edge of the void and forms an arcuate structure when the flow is supersonic. The structure is characterized by the bow shock as confirmed by a polytropic hydrodynamic theory as well as numerical simulation.

Examination of Bow-Shock Formation in Supersonic Radiatively Cooled Plasma Flows

Radiative high-Z plasma bow shocks driven by a 200-kA current are investigated by using high-resolution dark-field laser Schlieren imaging and a Mach-Zehnder interferometer. Results demonstrate stationary high-density compressible bow shocks and provide data on the plasma Mach number and electron density.

Transit variability in bow shock-hosting planets

We investigate the formation of bow shocks around exoplanets as a result of the interaction of the planet with the coronal material of the host star, focusing on physical causes that can lead to temporal variations in the shock characteristics. We recently suggested that WASP-12b may host a bow shock around its magnetosphere, similarly to the one observed around the Earth. For WASP12b, the shock is detected in the near-UV transit light curve. Observational follow-up suggests that the near-UV light curve presents temporal variations, which may indicate that the stand-off distance between the shock and the planet is varying. This implies that the size of the planet's magnetosphere is adjusting itself in response to variations in the surrounding ambient medium. We investigate possible causes of shock variations for the known eccentric (e>0.3) transiting planets. We show that, because the distance from the star changes along the orbit of an eccentric planet, the shock characteristics are modulated by orbital phase. We predict time offsets between the beginnings of the near-UV and optical light curves that are, in general, less than the transit duration. Variations in shock characteristics caused in eccentric systems can only be probed if the shock is observed at different orbital phases, which is, in general, not the case for transit observations. However, non-thermal radio emission produced by the interaction of the star and planet should be modulated by orbital phase. We also quantify the response of the shock to variations in the coronal material itself due to, e.g., a non-axisymmetric stellar corona, planetary obliquity, intrinsic variations of the stellar magnetic field. Such variations do not depend on the system eccentricity. We conclude that, for systems where a shock is detectable through transit light curve observations, shock variations should be a common occurrence. (Abridged)

Structure of the circumbinary envelope around a young binary system

The structure of a circumstellar envelope around a young binary T Tauri star is considered. The supersonic orbital motion of the system components in the envelope gas leads to the formation of bow shocks around the star. Two- and three-dimensional numerical modeling indicates an important role of these shocks in the formation of the structure of the circumbinary envelope. In particular, for systems with circular orbits, the size of the central region of the envelope that is not filled with matter (the “gap”) is essentially determined by the parameters of the bow shocks. These modeling results are supported by comparisons of the obtained estimates for the gap parameters with observations.

Shock wave standoff distance for a sphere slightly above Mach one

This paper describes a numerical simulation of bow shock formation ahead of a sphere at steady supersonic flow in the Mach number range of 1.025–1.20. Turbulent viscous flow results are presented using the Spalart–Allmaras turbulence model. The purpose of this study is to determine the shock standoff distance for a spherical projectile at slightly supersonic free flight speeds. Results are compared to experimental data, including double exposure holographic interferograms obtained from a 40 mm polycarbonate sphere launched by a light gas gun. The shock standoff distance was determined from the interferograms. The present numerical simulations were found to agree with previously published data, and reached down to M = 1.025—a range where almost no previously published data exists. The computed flow structure and shock wave locations agree well with recently obtained free-flight interferograms.

Comparative Study of Global MHD Simulations of the Terrestrial Magnetosphere With Different Numerical Schemes

We compare recent global MHD simulation models of the terrestrial magnetosphere based on different numerical schemes. The schemes include the finite-difference method based on the modified leapfrog (MLF) scheme, and the semi-Lagrangian scheme based on the constrained interpolation profile (CIP) algorithm. With the two models, we examined the simulation under a northward interplanetary magnetic field (IMF) condition. As a result, we found out that the two simulation models give consistent results on the magnetopause locations at the subsolar point and the terminator, and the overall structures of the cusp in the meridian plane. However, discrepancies are also found in the location and jump conditions of the bow shock. The MLF model showed higher thermal pressure value and weaker magnetic field strength in the downstream than those in the CIP model. The difference in the jump condition across the shock is also reflected in the difference in the length of the magnetotail in the two models. The magnetotail is shorter in the CIP model than that in the MLF model. We conclude that further comparative studies with finite-volume methods are necessary to verify the solution of the bow shock formation and the location of the last closed field line under northward IMF conditions.

Bow shocks in ablated plasma streams for nested wire array z-pinches: A laboratory astrophysics testbed for radiatively cooled shocks

Astrophysical observations have demonstrated many examples of bow shocks, for example, the head of protostellar jets or supernova remnants passing through the interstellar medium or between discrete clumps in jets. For such systems where supersonic and super-Alfvénic flows and radiative cooling are all important, carefully scaled laboratory experiments can add insight into the physical processes involved. The early stage of a wire array z-pinch implosion consists of the steady ablation of material from fine metallic wires. Ablated material is accelerated toward the array axis by the J×B force. This flow is highly supersonic (M>5) and becomes super-Alfvénic (MA>2). Radiative cooling is significant in this flow and can be controlled by varying the material in the ablated plasma. The introduction of wires as obstructions in this steady flow leads to the formation of bow shocks, which can be used as a laboratory testbed for astrophysical bow shocks. The magnetic field associated with this obstruction wire can be controlled by varying the current through it. Differences in the shock for different cooling rates and different magnetic fields associated with the obstruction will be discussed, along with comparisons of dimensionless parameters in the experiments to astrophysical systems.

Non-thermal emission from microquasar/ISM interaction

The high kinetic energy outflowing in the jets of microquasars is delivered to the surrounding interstellar medium. This energy input can cause the formation of bow shocks and cocoons that may be detectable from radio to gamma-ray energies. Evidences or hints of emission from jet/medium interactions have been reported for some sources, but little has been done regarding the theoretical modeling of the resulting non-thermal emission. We have developed an analytical model based on those successfully applied to extragalactic sources or the interaction of AGN jets with their surroundings. Focusing on the adiabatic phase of the growing structures, we give estimations of the expected luminosities through synchrotron, relativistic Bremsstrahlung and inverse Compton processes. We conclude that the interaction structures may be detectable at radio wavelengths, while extreme values for the jet kinetic power, the source age and the medium density are required to make the emission at high and very high energies detectable.

An evolutionary model for pulsar-driven supernova remnants

We present a model of a pulsar wind nebula evolving inside its associated supernova remnant. The model uses a hydrodynamics code to simulate the evolution of this system when the pulsar has a high velocity. The simulation distinguishes four different stages of pulsar wind nebula evolution: the supersonic expansion stage, the reverse shock interaction stage, the subsonic expansion stage and ultimately the bow shock stage. The simulation bears out that, due to the high velocity of the pulsar, the position of the pulsar is off-centered with respect to its pulsar wind nebula, after the passage of the reverse shock. Subsequently the pulsar wind nebula expands subsonically untill the event of the bow shock formation, when the motion of the pulsar becomes supersonic. The bow shock formation event occurs at roughly half the crossing time, when the pulsar is positioned at 0.677 times the radius of the supernova remnant blastwave, in complete agreement with analytical predictions. The crossing time is defined by the age of the supernova remnant, when the pulsar overtakes the blastwave bounding the supernova remnant. The results of the model are applied to three supernova remnants: N157B, G327.1-1.1 and W44. We argue that the head of the pulsar wind nebula, containing the active pulsar, inside the first two systems are not bounded by a bow shock. However, in the case of W44 we argue for a scenario in which the pulsar wind nebula is bounded by a bow shock, due to the supersonic motion of the pulsar.

Global‐scale simulation of foreshock structures at the quasi‐parallel bow shock

A two‐dimensional, global‐scale hybrid simulation is carried out to study the kinetic structure of the quasi‐parallel bow shock. In the simulation the bow shock forms by the interaction of the supersonic solar wind and the geomagnetic field. Strong temporal electromagnetic waves occur in the shock transition and foreshock regions due to backstreaming and reflected ions at the bow shock. This self‐consistent, global‐scale simulation shows the formation of diamagnetic cavities in the foreshock regions of the parallel and quasi‐parallel shocks, where ion beams interact with the incoming solar wind plasma. The cavities are crater‐like and saturate at a width ∼1–2 RE, with a low‐density and low‐magnetic field center bounded by a rim of high density and high magnetic field. The bulk flow speed decreases slightly in the center of the cavity, while the ion temperature often, but not always, increases. The craters convect downstream with the solar wind flow. When the interplanetary magnetic field (IMF) lies nearly parallel to the solar wind flow, the craters develop into elongated phase‐standing spatial structures along the field lines, both upstream and downstream, with alternate increases and decreases in the density and corresponding in‐phase variations in the magnetic field strength. In the general cases with an oblique IMF the foreshock cavities can convect toward the Earth as transient compressional structures and impinge on the magnetopause. The generation and structure of the diamagnetic cavities are compared with those of hot flow anomalies. The simulation results are also compared with satellite observations of the foreshock of quasi‐parallel shocks.

The Dynamics of Wave Clouds Upwind of Coastal Orography

Abstract The Naval Research Laboratory’s Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) is used in conjunction with satellite observations and data from the Coastal Waves 1996 experiment to investigate the dynamics of unusual wave clouds that occur upwind and offshore of orographic features along the California coast. Results indicate that supercritical flow within the marine boundary layer, interacting with blocking coastal orography, is forced to decelerate and an atmospheric bow shock forms. The location and orientation of the COAMPS forecast shock matches well with the leading edge of the wave clouds in satellite imagery, and the modeled jump in boundary layer depth across the shock is in good agreement with the aircraft observations. In the parameter space of Froude number and jump strength that develops within the flow (observed and modeled), the shock manifests itself as an undular bore. On the innermost grid (Δx = ⅓ km), long, lineal variations in the wind, temperature, and moisture...

Magnetosheath conditions and magnetopause structure for high magnetic shear

The supersonic solar wind - Earth's magnetosphere coupling plays the main role in the solar wind energy, momentum and mass input into the magnetosphere. A new dynamic model of the magnetic field in the coupled solar wind — magnetosphere system taking into account bow shock formation is considered. The solution for plasma flow and magnetic field upstream and downstream the bow shock was obtained in kinematic approximation. The magnetic field near the magnetopause was compared with those obtained in terms of subsonic solar wind - magnetosphere interaction. For typical magnetosheath conditions, the former is about twice the latter. The magnetic field near the magnetopause is formed due to mutual diffusion of the magnetospheric and interplanetary magnetic fields. The proposed model allows to determine reconnection efficiency by IMF and solar wind parameters: velocity, density, conductivity. The calculated magnetic field in the magnetosheath is compared with those measured by AMPTEARM satellite for high magnetopause magnetic shear.

Bow shock ‘splitting’ in bi‐ion flows

This paper discusses modifications of a bow shock ahead of an obstacle in the solar wind (SW) which can occur when the flow consists of a proton plasma and a secondary ion populations. The secondary species may be composed of alpha particles, which are a natural part of the ambient SW, or of heavier particles which are picked up by the solar wind in source regions, such as at comets or Mars. By using a 2D collisionsless bi‐ion fluid model which treats protons and heavy ions as distinct and which assumes that the two fluids communicate with each other by means of electromagnetic forces only, it is shown that for high enough value of the heavy ion mass density a ‘splitting’ of the bow shock takes place. Downstream from the proton bow shock, where differential streaming between ion species arises, a second discontinuity is formed which resembles a shock‐like transition for the heavy ion flow. This plasma boundary, called the heavy‐ion discontinuity (HID), causes also a distinct deflection of the proton flow and significant magnetic field variation. The results seem to be of importance for different types of SW obstacles, especially for planetary objects where massloading of the SW plays a dominant role in bow shock formation, as at comets and probably at Mars. It is suggested that the ‘massloading boundary (MLB)' found in the magnetosheath of Mars and the ‘mysterious boundary’ detected in the cometosheath of Halley and Grigg‐Skejllerup are HID's of the described nature.

Three‐dimensional MHD simulations of the interaction between venus and the solar wind

We have developed a three‐dimensional, single‐fluid, MHD code which has successfully simulated the major qualitative features of the Venus‐solar wind interaction. A bow shock forms at a height above the ionosphere close to that deduced from Pioneer Venus Orbiter (PVO) observations. The bow shock shows an asymmetry in the terminator plane qualitatively similar to results obtained from PVO data analyses. The magnetic field drapes over the planet and forms a two‐lobed magnetotail. The magnetic field configuration near the planet is very similar to that recorded by PVO as well. We model the Venus obstacle as a hard, conducting sphere. We simulate the case in which the IMF is tilted with respect to the incoming solar wind velocity at approximately the Parker spiral angle; this is the first simulation of this particular case which includes all spatial regions of the interaction.

FLIERs and other microstructures in planetary nebulae, 2

view Abstract Citations (141) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS FLIERs and Other Microstructures in Planetary Nebulae. II. Balick, Bruce ; Perinotto, M. ; Maccioni, A. ; Terzian, Yervant ; Hajian, A. Abstract We report continued detailed spectroscopic studies of highly articulated structures, called 'microstructures', in NGC 6543, 6826, and 7009. Of particular interest of these planetary nebulae (PNs) are FLIERs (fast, low-ionization emission regions) characterized by the following: ionization: much lower ionization than immediately adjacent gas; size: small size in at least one dimension (approx. = 2 sec, or about 0.01 pc at a distance of 1 kpc); morphology: generally ansae, jets, knots, or strings of knots; distribution: pairs (or sets of pairs) on equal and opposite sides of the central nucleus located near a nebular symmetry axis; velocity: each partner has equal and opposite highly supersonic velocity (approx. +/- 50 km/s); kinematic age: the kinematic age (projected distance/redshift) of some FLIERs is less than that of the rest of the PN; N abundance: apparent enhancement of nitrogen (only) relative to hydrogen by factors of 2-5; kinematic/thermal energy density: much higher kinetic energy per mass than thermal energy; and mass: typically 10-4 to 10-5 solar masses, and yet FLIERs exhibit little difference in density or temperature from their surroundings. These properties and their small kinematic ages lead one to expect that FLIERs are high-density, opaque (i.e., partly neutral), and highly collimated material expelled recently from the nucleus. Their high ram pressure (10 times greater than the thermal pressure of the confining gas) should lead to the formation of bow shocks. Contrary to intuitive expectations, however, most FLIERs show the ionization structure expected of bow shocks. No simple model accounts naturally for the observed properties of FLIERs. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/173932 Bibcode: 1994ApJ...424..800B Keywords: Abundance; Ionization; Kinematics; Line Spectra; Microstructure; Morphology; Nitrogen; Planetary Nebulae; Size (Dimensions); Spatial Distribution; Velocity; Astronomical Spectroscopy; Density (Mass/Volume); Helium; Hydrogen; Imagery; Interstellar Matter; Red Shift; Shock Waves; Sulfur; Astrophysics; ISM: PLANETARY NEBULAE: GENERAL; ISM: STRUCTURE full text sources ADS | data products SIMBAD (5) Related Materials (3) Part 1: 1993ApJ...411..778B Part 3: 1997ApJ...487..304H Part 4: 1998AJ....116..360B

The wind-disk interaction in X-ray burst sources

The interaction between a radiatively driven wind from the surface of a neutron star and an accretion disk surrounding the star is considered. A bow shock forms if the wind is supersonic when it reaches the inner edge of the disk. The resultant heating of the wind material can enhance the X-ray luminosity of the source, but this effect is important only if the wind is very strong. If the terminal velocity of the wind is at least about 0.99c and the integrated kinetic energy flux of the wind is at least about 30 times the Eddington limit, then super-Eddington X-ray luminosities will be generated. The conditions that are required for the formation of such a wind are briefly discussed. Also developed are estimates for the spectral shape, color temperature, and X-ray luminosity resulting from the wind-disk interaction, and it is shown that these results are consistent with the observed properties of type I cosmic X-ray bursts.

The 1979-1980 eclipse of Zeta Aurigae. II - The emission spectrum

UV observations using the IUE are employed to discuss the strength and changes of Zeta Aur between a second contact and mid-eclipse in 1979, the relative visibility of the supergiant's chromosphere as compared with the circumstellar (CS) nebular scattering of the B star photons, and the origin of the high speed CS components observed at all orbital phases. Agreement has been found for a spectoscopic radius of 200 solar radii and a 400 pc distance, and eclipse emission lines were recorded from 1238.9-2802.7 microns. An asymmetry in the Fe III lines at 46 plus or minus 15 km/sec was seen during eclipse and is taken to indicate downflowing material. The high speed wind flowing from the K supergiant is thought to expand homogeneously until encountering the B type main sequence star, where an accretion bow shock forms, and the smaller star's passage near the K star at periastron may cause local surface heating and subsequent high speed flows.

Molecular beam extraction from equilibrium gas flows

Abstract : The report presents a model for the formation of shock beams. Re-expansion downstream of the compression region may be present, but the dominating phenomenon appears to be effusion from a beam source region which itself is moving at the subsonic velocity U2. Also, the proposed shock beam model does not conflict with the results of electron beam studies by McMichael and French since bow shock formation is restricted to denser flows than studied. As far as the use of nozzle beams for diagnostic purposed is concerned, the regions behind or within normal shocks appear to be no longer off-limits for molecular beam sampling, if the observations are related to analyses which incorporate the shock beam model in its proposed or in a modified form. (Author)