The Experts below are selected from a list of 207 Experts worldwide ranked by ideXlab platform
Colin Norman - One of the best experts on this subject based on the ideXlab platform.
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Numerical Models of the Multiphase Interstellar Matter with Stellar Energy Feedback on a Galactic Scale
The Astrophysical Journal, 2001Co-Authors: Keiichi Wada, Colin NormanAbstract:High-resolution two-dimensional hydrodynamic simulations for the Interstellar Matter (ISM) in a galactic disk are enhanced to include explicitly star formation and the feedback effects from supernovae and stellar winds. A globally stable multiphase ISM is formed, in which filamentary and clumpy structure is a characteristic feature. We find a new component of 106-108 K gas that is a direct consequence of the energy input from the feedback. The total supernovae rate in the system varies by an order of magnitude over a timescale of 106 yr. The evolution of the supernovae rate exhibits chaotic behavior because the star formation is triggered by supernovae explosions in the inhomogeneous Interstellar medium. We also find that, in spite of its very complicated spatial structure, the multiphase ISM exhibits a one-point probability density function (pdf) that is a perfect lognormal distribution over four decades in density, 102-106 M☉ pc-2. The lognormal pdf is very robust even in regions with frequent bursts of supernovae. Low-density regions or cavities (
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numerical models of the multiphase Interstellar Matter with stellar energy feedback on a galactic scale
The Astrophysical Journal, 2001Co-Authors: Keiichi Wada, Colin NormanAbstract:High-resolution two-dimensional hydrodynamic simulations for the Interstellar Matter (ISM) in a galactic disk are enhanced to include explicitly star formation and the feedback effects from supernovae and stellar winds. A globally stable multiphase ISM is formed, in which filamentary and clumpy structure is a characteristic feature. We find a new component of 106-108 K gas that is a direct consequence of the energy input from the feedback. The total supernovae rate in the system varies by an order of magnitude over a timescale of 106 yr. The evolution of the supernovae rate exhibits chaotic behavior because the star formation is triggered by supernovae explosions in the inhomogeneous Interstellar medium. We also find that, in spite of its very complicated spatial structure, the multiphase ISM exhibits a one-point probability density function (pdf) that is a perfect lognormal distribution over four decades in density, 102-106 M☉ pc-2. The lognormal pdf is very robust even in regions with frequent bursts of supernovae. Low-density regions or cavities (<10 M☉ pc-2), on the other hand, exhibit the normal Gaussian distribution. These characteristic pdf's are achieved over a local dynamical scale. The energy spectra are E(k) ∝ k-3 without feedback and E(k) ∝ k-2 including stellar energy feedback.
Priscilla C. Frisch - One of the best experts on this subject based on the ideXlab platform.
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Interstellar Neutral Helium in the Heliosphere from IBEX Observations. VI. The He + Density and the Ionization State in the Very Local Interstellar Matter
The Astrophysical Journal, 2019Co-Authors: Maciej Bzowski, Priscilla C. Frisch, A Czechowski, S A Fuselier, A Galli, J Grygorczuk, J Heerikhuisen, M A Kubiak, H Kucharek, D J MccomasAbstract:Interstellar neutral gas atoms penetrate the heliopause and reach 1 au, where they are detected by Interstellar Boundary Explorer (IBEX). The flow of neutral Interstellar helium through the perturbed Interstellar plasma in the outer heliosheath (OHS) results in the creation of a secondary population of Interstellar He atoms, the so-called Warm Breeze, due to charge exchange with perturbed ions. The secondary population brings the imprint of the OHS conditions to the IBEX-Lo instrument. Based on a global simulation of the heliosphere with measurementbased parameters and detailed kinetic simulation of the filtration of He in the OHS, we find the number density of the Interstellar He+ population to be (8.98±0.12)×10−3 cm−3. With this, we obtain the absolute density of Interstellar H+ as 5.4×10−2 cm−3 and that of electrons as 6.3×10−2 cm−3, with ionization degrees of 0.26 for H and 0.37 for He. The results agree with estimates of the parameters of the Very Local Interstellar Matter obtained from fitting the observed spectra of diffuse Interstellar EUV and the soft X-ray background.
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Interstellar neutral helium in the heliosphere from IBEX observations. VI. The He$^+$ density and the ionization state in the Very Local Interstellar Matter
arXiv: Solar and Stellar Astrophysics, 2019Co-Authors: Maciej Bzowski, Priscilla C. Frisch, A Czechowski, S A Fuselier, A Galli, J Grygorczuk, J Heerikhuisen, M A Kubiak, H Kucharek, D J MccomasAbstract:Interstellar neutral gas atoms penetrate the heliopause and reach 1~au, where they are detected by IBEX. The flow of neutral Interstellar helium through the perturbed Interstellar plasma in the outer heliosheath (OHS) results in creation of the secondary population of Interstellar He atoms, the so-called Warm Breeze, due to charge exchange with perturbed ions. The secondary population brings the imprint of the OHS conditions to the IBEX-Lo instrument. Based on a global simulation of the heliosphere with measurement-based parameters and detailed kinetic simulation of the filtration of He in the OHS, we find the number density of Interstellar He$^+$ population at $(8.98\pm 0.12)\times 10^{-3}$~cm$^{-3}$. With this, we obtain the absolute density of Interstellar H$^+$ $5.4\times 10^{-2}$~cm$^{-3}$ and electrons $6.3\times 10^{-2}$~cm$^{-3}$, and ionization degrees of H 0.26 and He 0.37. The results agree with estimates of the Very Local Interstellar Matter parameters obtained from fitting the observed spectra of diffuse Interstellar EUV and soft X-Ray background.
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The Local Bubble and Interstellar Material Near the Sun
Space Science Reviews, 2007Co-Authors: Priscilla C. FrischAbstract:The properties of Interstellar Matter at the Sun are regulated by our location with respect to a void in the local Matter distribution, known as the Local Bubble. The Local Bubble (LB) is bounded by associations of massive stars and fossil supernovae that have disrupted dense Interstellar Matter (ISM), driving low density intermediate velocity ISM into the void. The Sun appears to be located in one of these flows of low density material. This nearby Interstellar Matter, dubbed the Local Fluff, has a bulk velocity of ∼19 km s−1 in the local standard of rest. The flow is coming from the direction of the gas and dust ring formed where the Loop I supernova remnant merges into the LB. Optical polarization data suggest that the local Interstellar magnetic field lines are draped over the heliosphere. A longstanding discrepancy between the high thermal pressure of plasma filling the LB and low thermal pressures in the embedded Local Fluff cloudlets is partially mitigated when the ram pressure component parallel to the cloudlet flow direction is included.
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why study Interstellar Matter very close to the sun
Advances in Space Research, 2004Co-Authors: Priscilla C. FrischAbstract:Abstract Interstellar Matter (ISM) sets the boundary conditions of the heliosphere and dominates the interplanetary medium. The heliosphere configuration has varied over recent history, as the Sun emerged from the Local Bubble and entered a turbulent outflow of cloudlets originating from the Scorpius-Centaurus Association direction. Several indicators suggest that the local Interstellar magnetic field is weak and parallel to the galactic plane. Observations of the interaction products of the ISM with the heliosphere, such as pickup ions and anomalous cosmic rays, when combined with data on the ISM towards nearby stars, provide unique constraints on the composition and physical properties of nearby gas. These data suggest abundances in nearby ISM are subsolar, and that gas and dust are not well mixed at the solar location.
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local Interstellar Matter the apex cloud
The Astrophysical Journal, 2003Co-Authors: Priscilla C. FrischAbstract:Several nearby individual low column density Interstellar cloudlets have been identified previously on the basis of kinematical features evident in high-resolution Ca+ observations near the Sun. One of these cloudlets, the "Apex Cloud" (AC), is within 5 pc of the Sun in the solar apex direction. The question of which Interstellar cloud will constitute the next Galactic environment of the Sun can, in principle, be determined from cloudlet velocities. The Interstellar absorption lines toward α Cen (the nearest star) are consistent within measurement uncertainties with the projected "G" cloud (GC) and AC velocities, and also with the velocity of the cloud inside of the solar system (the local Interstellar cloud [LIC]), provided a small velocity gradient is present in the LIC. The high GC column density toward α Oph compared to α Aql suggests that α Aql may be embedded in the GC so that the AC would be closer to the Sun than the GC. This scenario favors the AC as the next cloud to be encountered by the Sun, and the AC would have a supersonic velocity with respect to the LIC. The weak feature at the AC velocity toward 36 Oph suggests that the AC cloud is either patchy or does not extend to this direction. Alternatively, if the GC is the cloud that is foreground to α Cen, the similar values for N(H0) in the GC components toward α Cen and 36 Oph indicate this cloud is entirely contained within the nearest ~1.3 pc, and the Ca+ GC data toward α Oph would then imply a cloud volume density of ~5 cm-3, with dramatic consequences for the heliosphere in the near future.
G Gloeckler - One of the best experts on this subject based on the ideXlab platform.
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investigation of the composition of solar and Interstellar Matter using solar wind and pickup ion measurements with swics and swims on the ace spacecraft
Space Science Reviews, 1998Co-Authors: G Gloeckler, J Cain, F M Ipavich, E O Tums, Peter D Bedini, L A Fisk, T H Zurbuchen, P Bochsler, J FischerAbstract:The Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ions Mass Spectrometer (SWIMS) on ACE are instruments optimized for measurements of the chemical and isotopic composition of solar and Interstellar Matter. SWICS determines uniquely the chemical and ionic-charge composition of the solar wind, the thermal and mean speeds of all major solar wind ions from H through Fe at all solar wind speeds above 300 km s−1 (protons) and 170 km s−1 (Fe+16), and resolves H and He isotopes of both solar and Interstellar sources. SWICS will measure the distribution functions of both the Interstellar cloud and dust cloud pickup ions up to energies of 100 keV e−1. SWIMS will measure the chemical, isotopic and charge state composition of the solar wind for every element between He and Ni. Each of the two instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made with SWICS and SWIMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of Matter entering the magnetosphere. In addition, SWICS and SWIMS 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; (vii) the physics of the pickup process of Interstellar He in the solar wind; and (viii) the spatial distribution and characteristics of sources of neutral Matter in the inner heliosphere.
Kathrin Altwegg - One of the best experts on this subject based on the ideXlab platform.
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Sample return of Interstellar Matter (SARIM)
Experimental Astronomy, 2009Co-Authors: Ralf Srama, Thomas Stephan, Eberhard Grün, Norbert Pailer, Anton Kearsley, Amara Graps, Rene Laufer, Pascale Ehrenfreund, Nicolas Altobelli, Kathrin AltweggAbstract:The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We propose a new mission concept, SARIM, that collects Interstellar and interplanetary dust particles and returns them to Earth. SARIM is optimised for the collection and discrimination of Interstellar dust grains. Improved active dust collectors on-board allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important constraints for subsequent laboratory analysis. The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and inside the solar-wind charging environment. SARIM is three-axes stabilised and collects Interstellar grains between July and October when the relative encounter speeds with Interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection period several hundred Interstellar and several thousand interplanetary grains will be collected by a total sensitive area of 1 m^2. At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule. SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of Interstellar samples by latest laboratory technologies.
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sample return of Interstellar Matter sarim
Experimental Astronomy, 2009Co-Authors: Ralf Srama, Thomas Stephan, Eberhard Grün, Norbert Pailer, Anton Kearsley, Amara Graps, Rene Laufer, Pascale Ehrenfreund, Nicolas Altobelli, Kathrin AltweggAbstract:The scientific community has expressed strong interest to re-fly Stardust- like missions with improved instrumentation. We propose a new mission concept, SARIM, that collects Interstellar and interplanetary dust particles and returns them to Earth. SARIM is optimised for the collection and discrimination of Interstellar dust
J Fischer - One of the best experts on this subject based on the ideXlab platform.
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investigation of the composition of solar and Interstellar Matter using solar wind and pickup ion measurements with swics and swims on the ace spacecraft
Space Science Reviews, 1998Co-Authors: G Gloeckler, J Cain, F M Ipavich, E O Tums, Peter D Bedini, L A Fisk, T H Zurbuchen, P Bochsler, J FischerAbstract:The Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ions Mass Spectrometer (SWIMS) on ACE are instruments optimized for measurements of the chemical and isotopic composition of solar and Interstellar Matter. SWICS determines uniquely the chemical and ionic-charge composition of the solar wind, the thermal and mean speeds of all major solar wind ions from H through Fe at all solar wind speeds above 300 km s−1 (protons) and 170 km s−1 (Fe+16), and resolves H and He isotopes of both solar and Interstellar sources. SWICS will measure the distribution functions of both the Interstellar cloud and dust cloud pickup ions up to energies of 100 keV e−1. SWIMS will measure the chemical, isotopic and charge state composition of the solar wind for every element between He and Ni. Each of the two instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made with SWICS and SWIMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of Matter entering the magnetosphere. In addition, SWICS and SWIMS 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; (vii) the physics of the pickup process of Interstellar He in the solar wind; and (viii) the spatial distribution and characteristics of sources of neutral Matter in the inner heliosphere.
