Showing papers on "Stellar-wind bubble published in 1995"
TL;DR: In this paper, a two-dimensional (axisymmetric) time-dependent gas dynamic model for the interaction of the solar wind with the local interstellar medium is presented, which includes the mutual influence of the interstellar and interplanetary plasma (protons and electrons) and the neutral interstellar hydrogen atoms.
Abstract: First results from a two-dimensional (axisymmetric) time-dependent gas dynamic model for the interaction of the solar wind with the local interstellar medium are presented The model includes the mutual influence of the interstellar and interplanetary plasma (protons and electrons) and the neutral interstellar hydrogen atoms Neutrals created by charge exchange with the solar wind are ignored; this allows us to approximate the dynamical evolution of the system with the isotropic fluid equations A supersonic interstellar wind is assumed The global structure of the heliosphere and interaction region is described for both the plasma and neutral gas The self-consistent model is compared to a noninteracting gas dynamic model, and dramatic differences in the size of the heliosphere are found The distribution of neutral hydrogen in the heliosphere is also discussed
253 citations
TL;DR: In this paper, the authors used simple energy budget arguments to show that pickup ion generated wave dissipation may play a significant role in determining the solar wind radial temperature profile in the outer heliosphere.
Abstract: The deposition of energy into the solar wind by the pickup of interstellar neutrals is due to both the creation of hot, nonthermal ions and the associated generation of low frequency magnetohydrodynamic (MHD) waves. Dissipation of some fraction of the free wave energy released by ion pickup and isotropization is possible through nonlinear turbulent processes which may lead to heating of the core thermal solar wind proton distribution. Simple energy budget arguments are utilized to show that pickup ion generated wave dissipation may play a significant role in determining the solar wind radial temperature profile in the outer heliosphere. In particular, depending on the density of interstellar hydrogen in the heliosphere, there will be some radial distance beyond which the thermal solar wind core temperature increases steadily until the termination shock. Existing Pioneer and Voyager temperature profiles are consistent with this interpretation.
107 citations
TL;DR: The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms−1 (protons) to 1280 kms −1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to
Abstract: The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms−1 (protons) to 1280 kms−1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium.
103 citations
TL;DR: In this article, the predicted slowdown of the solar wind with heliospheric distance was investigated using the data from the Voyager 2 and IMP 8 spacecraft and was found to be consistent with a pickup ion density equal to 8% of the total ion density.
Abstract: Voyager 2 and IMP 8 plasma data are used to look for the predicted slowdown of the solar wind with heliospheric distance. Decreases of roughly 7% in the radial velocity and of the same order in the flux are found if the Voyager 2 and IMP 8 velocities are normalized to agree in the inner heliosphere. This decrease is consistent with a pickup ion density equal to 8% of the total ion density, similar to predictions and other determinations of this density. Comparison with published model results allows us to infer an interstellar neutral density of 0.05 cm−3.
95 citations
TL;DR: In this paper, the authors present observations of Abell 30 showing compact, hydrogen-poor knots with wind-blown tails, obtained with the Wide Field Planetary Camera (WFPC2) on board the Hubble Space Telescope.
Abstract: Clumpy, hydrogen-depleted material in the planetary nebula Abell 30 was ejected by its central star ~1000 yr ago. We present observations of Abell 30 showing compact, hydrogen-poor knots with wind-blown tails, obtained with the Wide Field Planetary Camera (WFPC2) on board the Hubble Space Telescope, which offer an unprecedented view of the interaction of a stellar wind with an ambient inhomogeneous medium. We can see how dense clumps of material, left within an expanding bubble blown by a stellar wind, are being photoevaporated by the stellar radiation and then swept back and accelerated by the wind. This accelerated material mixes with the wind, slowing it and increasing its density. The observed extent of this mass loading in Abell 30 supports claims that the mass-loading process is generally important in highly inhomogeneous astrophysical flows. In particular, mass loading of the magnitude observed in Abell 30 may explain the detection of X-ray-emitting gas in planetary nebulae.
47 citations
TL;DR: In this article, the authors review the exciting work on interstellar pickup ions which took place during the last quadrennium, concentrating on the efforts of the U.S. scientists and their collaborators.
Abstract: Although the far-flung Pioneer and Voyager spacecraft will not leave the heliosphere (the region of particles and fields emitted by the Sun) for at least another few quadrennia, an important component of the surrounding interstellar medium is already under study in the form of interstellar pickup ions. In the last four years, there have been great advances in the study of these particles, primarily motivated by the new observations from instruments on the Ulysses spacecraft. This article will review the exciting work on interstellar pickup ions which took place during the last quadrennium, concentrating on the efforts of the U.S. scientists and their collaborators.
As the Sun moves through interstellar space, the heliospheric magnetic field prevents the ionized portion of the surrounding interstellar gas from entering the solar system, but the population of interstellar neutral atoms flows unimpeded through the essentially collisionless plasma. When these atoms travel close enough to the Sun, solar radiation (in the form of both photons and solar wind particles) acts to ionize them and the new ions must suddenly respond to the electromagnetic fields of the supersonic solar wind. In the reference frame moving with the solar wind, this response consists of an immediate gyration of the new ions about the magnetic field, followed by a rapid isotropization by ambient or self-generated low-frequency fluctuations in the plasma. This isotropization in the solar wind frame means that the ions are now convecting with the solar wind - they have been “picked up”. Since the inflowing interstellar atoms move very slowly with respect to the Sun (20 – 25 km/s), they have supersonic speeds in the solar wind frame, and the isotropization of the ions in this frame results in a distinct energetic population of ions with origins in the interstellar medium.
29 citations
TL;DR: In this article, the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%.
Abstract: Advances in instrumentation have resulted in the determination of the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%. Comparisons with solar energetic particle (SEP) abundances and galactic cosmic ray abundances have revealed many similarities, especially when compared with solar photospheric abundances. It is now well established that fractionation in the corona results in an overabundance (with respect to the photosphere) of elements with first ionization potentials less than 10 eV. These observations have in turn led to the development of fractionation models that are reasonably successful in reproducing the first ionization (FIP) effect. Under some circumstances it has been possible to relate solar wind observations to particular source regions in the corona. The magnetic topologies of the source regions appear to have a strong influence on the fractionation of elements. Comparisons with spectroscopic data are particularly useful in classifying the different topologies. Ions produced from interstellar neutral atoms are also found in the solar wind. These ions are picked up by the solar wind after ionization by solar radiation or charge exchange and can be identified by their velocity in the solar wind. The pick-up ions provide most of the pressure in the interplanetary medium at large distances. Interstellar abundances can be derived from the observed fluxes of solar wind pick-up ions.
22 citations
TL;DR: In this article, the wave-induced pick-up ion pressure has been introduced into the equations of motion in an adequate nonpolytropic form to correctly describe the multicomponent plasma dynamics.
Abstract: The solar wind at larger distances is known to be a multicomponent plasma. The different components, solar ions, pick-up ions, and anomalous ions, are without collisional coupling but they are all coupled to the intrinsic wave turbulences by nonlinear wave-particle interactions. Since quite a long time it is not understood why dynamical processes associated with the loading of the primary solar wind by secondary pick-up ions neither lead to a recognizable heating nor to a deceleration of the solar wind at larger distances. While the inefficient heating seems to be explained by the fact that pick-up ions do not assimilate quickly enough to the solar wind distribution function, the unobservable deceleration of the distant solar wind always remained mysterious. Different from all theoretical approaches up to now, here we intend to show that the wave-induced pick-up ion pressure has to be introduced into the equations of motion in an adequate non-polytropic form to correctly describe the multicomponent plasma dynamics. If this is done it becomes clear that the deceleration of the solar wind is considerably reduced or even vanishing.
20 citations
19 citations
01 Jan 1995
TL;DR: In this article, the process of dust formation in the hydrogen-poor environments characteristic of WC winds is reviewed and compared to the chemical pathway to soot particle production in AGB stars.
Abstract: WC-type Wolf-Rayet stars show episodic or persistent infrared emission attributed to amorphous carbon grains forming in their winds. The process of dust formation in the hydrogen-poor environments characteristic of WC winds is reviewed and compared to the chemical pathway to soot particle production in AGB stars. Emphasis is put on the formation of the dust precursors, and the physical conditions necessary to nucleate them in WC winds. In particular, it is concluded that dust formation around WC stars occurs in a dense, largely neutral, circumstellar disk.
11 citations
TL;DR: A critical review of the interstellar hydrogen in the heliosphere is presented in this article, where the influence of heliospheric interface on neutral flow and the remaining refinements, which could help to better interpret the results of the SWAN experiment on board SOHO are discussed.
Abstract: A critical review of the interstellar hydrogen in the heliosphere will be presented. Recent Sun-interstellar matter interaction model improvements, a non-stationary flow and a flexible latitude dependence, will be discussed. We also consider the influence of heliospheric interface on neutral flow and the remaining refinements, which could help to better interpret the results of the SWAN experiment on board SOHO.
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TL;DR: In this paper, the Orion-Eridanus Bubble was examined with the aid of data from the Leiden/Dwingeloo HI survey, which allowed identification of the HI filaments and arcs delineating the Bubble and derivation of its expansion velocity.
Abstract: Observations of the interstellar medium in the vicinity of the Orion OB1 association show a cavity filled with hot ionized gas, surrounded by an expanding shell of neutral hydrogen (the Orion-Eridanus Bubble). In this paper we examine this cavity and the surrounding bubble with the aid of data from the Leiden/Dwingeloo HI survey. We present neutral-hydrogen maps for the Orion-Eridanus region which allow identification of the HI filaments and arcs delineating the Bubble and derivation of its expansion velocity. The HI data are compared to X-ray, CO and IRAS 100 micron data. Using models of wind blown bubbles that take the density stratification of the Galactic HI layer into account we show that the stellar winds and supernovae from stars in Orion OB1 can account for the size as well as the expansion velocity of the HI shell. However, density inhomogeneities in the ambient interstellar medium cause significant discrepancies between our model and the observed shell.
30 Jun 1995
TL;DR: In this paper, the authors present evidence from interplanetary scintillation measurements of the 'disturbance factor' g that active regions play a role in modulating the solar wind and possibly contribute to the total solar wind mass output.
Abstract: A common descriptive framework for discussing the solar wind structure in the inner heliosphere uses the global magnetic field as a reference: low density, high velocity solar wind emanates from open magnetic fields, with high density, low speed solar wind flowing outward near the current sheet In this picture, active regions, underlying closed magnetic field structures in the streamer belt, leave little or no imprint on the solar wind We present evidence from interplanetary scintillation measurements of the 'disturbance factor' g that active regions play a role in modulating the solar wind and possibly contribute to the solar wind mass output Hence we find that the traditional view of the solar wind, though useful in understanding many features of solar wind structure, is oversimplified and possibly neglects important aspects of solar wind dynamics
TL;DR: For example, observations from the Voyager and Pioneer spacecraft in the distant heliosphere continue to show interesting and unexpected features as discussed by the authors, such as the slowing down of the wind as it propagates into the distant Heliosphere; the reduction in speed is of the order of 30 km/s and is consistent with the change expected from pickup of interstellar neutrals.
30 Jun 1995
TL;DR: In this paper, the authors review the observed properties of the solar wind in the outer heliosphere, including observations from Voyager and the Pioneers, as well as from inner heliospheric probes as appropriate.
Abstract: We review the observed properties of the solar wind in the outer heliosphere, including observations from Voyager and the Pioneers, as well as from inner heliospheric probes as appropriate. These observations are crucial to modeling of the heliosphere and its interactions with the interstellar medium, since the wind ram pressure and its temporal variations are important in understanding the distance to the termination shock and heliopause and how those boundaries might vary in time. We focus on results since Solar Wind 7. Among the issues we will discuss are: (1) the time scales for and statistical properties of variations in the ram pressure in the outer heliosphere, and how those variations might affect the morphology of the heliospheric/interstellar medium interface; (2) the question of possible solar wind slowing in the outer heliosphere due to the pick-up of interstellar ions; (3) the issue of whether there is bulk heating of the solar wind associated either with interstellar ion pick-up or with continued heating due to stream-stream interactions; (4) evidence for latitudinal variations in solar wind properties; and (5) the 1.3 year periodicities apparent in the outer heliosphere, and the close correspondence with similar variations seen with inner heliospheric probes.