The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Maurice A Leutenegger - One of the best experts on this subject based on the ideXlab platform.
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measuring the Shock Heating rate in the winds of o stars using x ray line spectra
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: David H Cohen, Zequn Li, K G Gayley, S P Owocki, Jon O Sundqvist, V Petit, Maurice A LeuteneggerAbstract:We present a new method for using measured X-ray emission line fluxes from O stars to determine the Shock-Heating rate due to instabilities in their radiation-driven winds. The high densities of these winds means that their embedded Shocks quickly cool by local radiative emission, while cooling by expansion should be negligible. Ignoring for simplicity any nonradiative mixing or conductive cooling, the method presented here exploits the idea that the cooling post-Shock plasma systematically passes through the temperature characteristic of distinct emission lines in the X-ray spectrum. In this way, the observed flux distribution among these X-ray lines can be used to construct the cumulative probability distribution of Shock strengths that a typical wind parcel encounters as it advects through the wind. We apply this new method to Chandra grating spectra from five O stars with X-ray emission indicative of embedded wind Shocks in effectively single massive stars. The results for all the stars are quite similar: the average wind mass element passes through roughly one Shock that heats it to at least 10 6 K as it advects through the wind, and the cumulative distribution of Shock strengths is a strongly decreasing function of temperature, consistent with a negative power law of index n ≈ 3, implying a marginal distribution of Shock strengths that scales as T −4 , and with hints of an even steeper decline or cut-off above 10 7 K.
William S Cassata - One of the best experts on this subject based on the ideXlab platform.
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evidence for Shock Heating and constraints on martian surface temperatures revealed by 40ar 39ar thermochronometry of martian meteorites
Geochimica et Cosmochimica Acta, 2010Co-Authors: William S Cassata, David L Shuster, Paul R Renne, Benjamin P WeissAbstract:The thermal histories of Martian meteorite are important for the interpretation of petrologic, geochemical, geochronological, and paleomagnetic constraints that they provide on the evolution of Mars. In this paper, we quantify 40Ar/39Ar ages and Ar diffusion kinetics of Martian meteorites Allan Hills (ALH) 84001, Nakhla, and Miller Range (MIL) 03346. We constrain the thermal history of each meteorite and discuss the resulting implications for their petrology, paleomagnetism, and geochronology. Maskelynite in ALH 84001 yields a 40Ar/39Ar isochron age of 4163 ± 35 Ma, which is indistinguishable from recent Pb-Pb (Bouvier et al., 2009a) and Lu-Hf ages (Lapen et al., 2010). The high precision of this result arises from clear resolution of a reproducible trapped 40Ar/36Ar component in maskelynite in ALH 84001 (40Ar/36Ar = 632 ± 90). The maskelynite 40Ar/39Ar age predates the Late Heavy Bombardment and likely represents the time at which the original natural remanent magnetization (NRM) component observed in ALH 84001 was acquired. Nakhla and MIL 03346 yield 40Ar/39Ar isochron ages of 1332 ± 24 and 1339 ± 8 Ma, respectively, which we interpret to date crystallization. Multi-phase, multi-domain diffusion models constrained by the observed Ar diffusion kinetics and 40Ar/39Ar age spectra suggest that localized regions within both ALH 84001 and Nakhla were intensely heated for brief durations during Shock events at 1158 ± 110 and 913 ± 9 Ma, respectively. These ages may date the marginal melting of pyroxene in each rock, mobilization of carbonates and maskelynite in ALH 84001, and NRM overprints observed in ALH 84001. The inferred peak temperatures of the Shock Heating events (>1400 °C) are sufficient to mobilize Ar, Sr, and Pb in constituent minerals, which may explain some of the dispersion observed in 40Ar/39Ar, Rb–Sr, and U–Th–Pb data toward ages younger than ∼4.1 Ga. The data also place conservative upper bounds on the long-duration residence temperatures of the ALH 84001 and Nakhla protolith to be 22-∞+8 °C and 81-∞+9 °C over the last ∼4.16 Ga and ∼1.35 Ga, respectively. MIL 03346 has apparently not experienced significant Shock-Heating since it crystallized, consistent with the fact that various chronometers yield concordant ages.
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Evidence for Shock Heating and constraints on Martian surface temperatures revealed by 40Ar/39Ar thermochronometry of Martian meteorites
Geochimica et Cosmochimica Acta, 2010Co-Authors: William S Cassata, David L Shuster, Paul R Renne, Benjamin P WeissAbstract:The thermal histories of Martian meteorite are important for the interpretation of petrologic, geochemical, geochronological, and paleomagnetic constraints that they provide on the evolution of Mars. In this paper, we quantify 40Ar/39Ar ages and Ar diffusion kinetics of Martian meteorites Allan Hills (ALH) 84001, Nakhla, and Miller Range (MIL) 03346. We constrain the thermal history of each meteorite and discuss the resulting implications for their petrology, paleomagnetism, and geochronology. Maskelynite in ALH 84001 yields a 40Ar/39Ar isochron age of 4163 ± 35 Ma, which is indistinguishable from recent Pb-Pb (Bouvier et al., 2009a) and Lu-Hf ages (Lapen et al., 2010). The high precision of this result arises from clear resolution of a reproducible trapped 40Ar/36Ar component in maskelynite in ALH 84001 (40Ar/36Ar = 632 ± 90). The maskelynite 40Ar/39Ar age predates the Late Heavy Bombardment and likely represents the time at which the original natural remanent magnetization (NRM) component observed in ALH 84001 was acquired. Nakhla and MIL 03346 yield 40Ar/39Ar isochron ages of 1332 ± 24 and 1339 ± 8 Ma, respectively, which we interpret to date crystallization. Multi-phase, multi-domain diffusion models constrained by the observed Ar diffusion kinetics and 40Ar/39Ar age spectra suggest that localized regions within both ALH 84001 and Nakhla were intensely heated for brief durations during Shock events at 1158 ± 110 and 913 ± 9 Ma, respectively. These ages may date the marginal melting of pyroxene in each rock, mobilization of carbonates and maskelynite in ALH 84001, and NRM overprints observed in ALH 84001. The inferred peak temperatures of the Shock Heating events (>1400 °C) are sufficient to mobilize Ar, Sr, and Pb in constituent minerals, which may explain some of the dispersion observed in 40Ar/39Ar, Rb–Sr, and U–Th–Pb data toward ages younger than ∼4.1 Ga. The data also place conservative upper bounds on the long-duration residence temperatures of the ALH 84001 and Nakhla protolith to be 22-∞+8 °C and 81-∞+9 °C over the last ∼4.16 Ga and ∼1.35 Ga, respectively. MIL 03346 has apparently not experienced significant Shock-Heating since it crystallized, consistent with the fact that various chronometers yield concordant ages.
Benjamin P Weiss - One of the best experts on this subject based on the ideXlab platform.
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evidence for Shock Heating and constraints on martian surface temperatures revealed by 40ar 39ar thermochronometry of martian meteorites
Geochimica et Cosmochimica Acta, 2010Co-Authors: William S Cassata, David L Shuster, Paul R Renne, Benjamin P WeissAbstract:The thermal histories of Martian meteorite are important for the interpretation of petrologic, geochemical, geochronological, and paleomagnetic constraints that they provide on the evolution of Mars. In this paper, we quantify 40Ar/39Ar ages and Ar diffusion kinetics of Martian meteorites Allan Hills (ALH) 84001, Nakhla, and Miller Range (MIL) 03346. We constrain the thermal history of each meteorite and discuss the resulting implications for their petrology, paleomagnetism, and geochronology. Maskelynite in ALH 84001 yields a 40Ar/39Ar isochron age of 4163 ± 35 Ma, which is indistinguishable from recent Pb-Pb (Bouvier et al., 2009a) and Lu-Hf ages (Lapen et al., 2010). The high precision of this result arises from clear resolution of a reproducible trapped 40Ar/36Ar component in maskelynite in ALH 84001 (40Ar/36Ar = 632 ± 90). The maskelynite 40Ar/39Ar age predates the Late Heavy Bombardment and likely represents the time at which the original natural remanent magnetization (NRM) component observed in ALH 84001 was acquired. Nakhla and MIL 03346 yield 40Ar/39Ar isochron ages of 1332 ± 24 and 1339 ± 8 Ma, respectively, which we interpret to date crystallization. Multi-phase, multi-domain diffusion models constrained by the observed Ar diffusion kinetics and 40Ar/39Ar age spectra suggest that localized regions within both ALH 84001 and Nakhla were intensely heated for brief durations during Shock events at 1158 ± 110 and 913 ± 9 Ma, respectively. These ages may date the marginal melting of pyroxene in each rock, mobilization of carbonates and maskelynite in ALH 84001, and NRM overprints observed in ALH 84001. The inferred peak temperatures of the Shock Heating events (>1400 °C) are sufficient to mobilize Ar, Sr, and Pb in constituent minerals, which may explain some of the dispersion observed in 40Ar/39Ar, Rb–Sr, and U–Th–Pb data toward ages younger than ∼4.1 Ga. The data also place conservative upper bounds on the long-duration residence temperatures of the ALH 84001 and Nakhla protolith to be 22-∞+8 °C and 81-∞+9 °C over the last ∼4.16 Ga and ∼1.35 Ga, respectively. MIL 03346 has apparently not experienced significant Shock-Heating since it crystallized, consistent with the fact that various chronometers yield concordant ages.
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Evidence for Shock Heating and constraints on Martian surface temperatures revealed by 40Ar/39Ar thermochronometry of Martian meteorites
Geochimica et Cosmochimica Acta, 2010Co-Authors: William S Cassata, David L Shuster, Paul R Renne, Benjamin P WeissAbstract:The thermal histories of Martian meteorite are important for the interpretation of petrologic, geochemical, geochronological, and paleomagnetic constraints that they provide on the evolution of Mars. In this paper, we quantify 40Ar/39Ar ages and Ar diffusion kinetics of Martian meteorites Allan Hills (ALH) 84001, Nakhla, and Miller Range (MIL) 03346. We constrain the thermal history of each meteorite and discuss the resulting implications for their petrology, paleomagnetism, and geochronology. Maskelynite in ALH 84001 yields a 40Ar/39Ar isochron age of 4163 ± 35 Ma, which is indistinguishable from recent Pb-Pb (Bouvier et al., 2009a) and Lu-Hf ages (Lapen et al., 2010). The high precision of this result arises from clear resolution of a reproducible trapped 40Ar/36Ar component in maskelynite in ALH 84001 (40Ar/36Ar = 632 ± 90). The maskelynite 40Ar/39Ar age predates the Late Heavy Bombardment and likely represents the time at which the original natural remanent magnetization (NRM) component observed in ALH 84001 was acquired. Nakhla and MIL 03346 yield 40Ar/39Ar isochron ages of 1332 ± 24 and 1339 ± 8 Ma, respectively, which we interpret to date crystallization. Multi-phase, multi-domain diffusion models constrained by the observed Ar diffusion kinetics and 40Ar/39Ar age spectra suggest that localized regions within both ALH 84001 and Nakhla were intensely heated for brief durations during Shock events at 1158 ± 110 and 913 ± 9 Ma, respectively. These ages may date the marginal melting of pyroxene in each rock, mobilization of carbonates and maskelynite in ALH 84001, and NRM overprints observed in ALH 84001. The inferred peak temperatures of the Shock Heating events (>1400 °C) are sufficient to mobilize Ar, Sr, and Pb in constituent minerals, which may explain some of the dispersion observed in 40Ar/39Ar, Rb–Sr, and U–Th–Pb data toward ages younger than ∼4.1 Ga. The data also place conservative upper bounds on the long-duration residence temperatures of the ALH 84001 and Nakhla protolith to be 22-∞+8 °C and 81-∞+9 °C over the last ∼4.16 Ga and ∼1.35 Ga, respectively. MIL 03346 has apparently not experienced significant Shock-Heating since it crystallized, consistent with the fact that various chronometers yield concordant ages.
G. C. Boynton - One of the best experts on this subject based on the ideXlab platform.
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MHD Shock Heating in Solar Corona Holes
2007 IEEE 34th International Conference on Plasma Science (ICOPS), 2007Co-Authors: M. A. Huerta, J. A. Orta, G. C. BoyntonAbstract:Summary form only given. We report on a one dimensional simulation of plane polarized, large amplitude, Alfven waves traveling upwards through a gravitationally stratified solar corona hole. In the low plasma beta region the waves develop into fast magnetic Shocks that reach great heights with little heat dissipation, where they excite large amplitude slow hydrodynamic Shocks that deposit sufficient energy to be a possible important mechanism of Heating the corona. We also report on progress in doing a three dimensional simulation of the same problem using the FCTMHD3D code.
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One dimensional simulations of MHD Shock Heating of a stratified solar coronal hole
2007 16th IEEE International Pulsed Power Conference, 2007Co-Authors: J. A. Orta, M. A. Huerta, G. C. BoyntonAbstract:Our one dimensional numerical simulations describe the evolution of large amplitude Alfvèn waves excited in the lower corona as they travel upwards guided by the open magnetic field lines of a gravitationally stratified solar coronal hole. When the waves reach the region where β ≪ 1 they develop into magnetohydrodynamic (MHD) Shocks. The Shock waves seem to produce sufficient heat fluxes to be important contributors to the Heating of the solar corona.
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magnetohydrodynamic Shock Heating of the solar corona
The Astrophysical Journal, 2003Co-Authors: J. A. Orta, M. A. Huerta, G. C. BoyntonAbstract:Coronal MHD waves excited by perturbations of magnetic field lines propagate upward, carrying with them the energy from the excitation. Under favorable conditions Shocks form, and part of the wave energy is converted to plasma Heating and motion. We use numerical simulations to accurately follow the Shock formation and subsequent energy release. The model includes an adiabatic energy equation for the explicit evaluation of temperature increases and energy fluxes contributed by the Shocks. Transverse, plane-polarized excitations are considered; they can be periodic, as in Alfven wave trains, or pulsed, as might result from nanoflares. The model is tested with a set of validation runs that produce good agreement with theoretical predictions. Our results show that nonlinear waves moving along large magnetic fields with low plasma β, with field amplitudes comparable to the background field, develop Shocks that form important amounts of plasma Heating and that mass outflow may occur. Fast and slow magnetoacoustic Shocks are generated, each one making its own contribution. Most of the Heating takes place in the low corona, but long-range distributed Heating still occurs up to heights of several solar radii. The energy fluxes for the stronger cases are sufficient to compensate for thermal and convective losses, consistent with observations. We conclude that large-amplitude MHD Shocks in low-β regions could be a viable mechanism for coronal Heating and wind acceleration in regions of open magnetic field lines.
Jon O Sundqvist - One of the best experts on this subject based on the ideXlab platform.
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measuring the Shock Heating rate in the winds of o stars using x ray line spectra
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: David H Cohen, Zequn Li, K G Gayley, S P Owocki, Jon O Sundqvist, V Petit, Maurice A LeuteneggerAbstract:We present a new method for using measured X-ray emission line fluxes from O stars to determine the Shock-Heating rate due to instabilities in their radiation-driven winds. The high densities of these winds means that their embedded Shocks quickly cool by local radiative emission, while cooling by expansion should be negligible. Ignoring for simplicity any nonradiative mixing or conductive cooling, the method presented here exploits the idea that the cooling post-Shock plasma systematically passes through the temperature characteristic of distinct emission lines in the X-ray spectrum. In this way, the observed flux distribution among these X-ray lines can be used to construct the cumulative probability distribution of Shock strengths that a typical wind parcel encounters as it advects through the wind. We apply this new method to Chandra grating spectra from five O stars with X-ray emission indicative of embedded wind Shocks in effectively single massive stars. The results for all the stars are quite similar: the average wind mass element passes through roughly one Shock that heats it to at least 10 6 K as it advects through the wind, and the cumulative distribution of Shock strengths is a strongly decreasing function of temperature, consistent with a negative power law of index n ≈ 3, implying a marginal distribution of Shock strengths that scales as T −4 , and with hints of an even steeper decline or cut-off above 10 7 K.
