The Experts below are selected from a list of 28140 Experts worldwide ranked by ideXlab platform
Georges Meynet - One of the best experts on this subject based on the ideXlab platform.
-
Cosmic ray neon wolf rayet stars and the superbubble origin of Galactic Cosmic Rays
The Astrophysical Journal, 2005Co-Authors: Marcel Arnould, J S George, Stephane Goriely, Georges MeynetAbstract:We report the abundances of neon isotopes in the Galactic Cosmic Rays (GCRs) using data from the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE). These abundances have been measured for seven energy intervals over the energy range of 84 ≤ E/M ≤ 273 MeV nucleon^(-1). We have derived the ^(22)Ne/^(20)Ne ratio at the Cosmic-ray source using the measured ^(21)Ne, ^(19)F, and ^(17)O abundances as "tracers" of secondary production of the neon isotopes. Using this approach, the ^(22)Ne/^(20)Ne abundance ratio that we obtain for the Cosmic-ray source is 0.387 ± 0.007(statistical) ± 0.022(systematic). This corresponds to an enhancement by a factor of 5.3 ± 0.3 over the ^(22)Ne/^(20)Ne ratio in the solar wind. This Cosmic-ray source ^(22)Ne/^(20)Ne ratio is also significantly larger than that found in anomalous Cosmic Rays, solar energetic particles, most meteoritic samples of matter, and interplanetary dust particles. We compare our ACE CRIS data for neon and refractory isotope ratios, and data from other experiments, with recent results from two-component Wolf-Rayet (W-R) models. The three largest deviations of GCR isotope ratios from solar system ratios predicted by these models, ^(12)C/^(16)O, ^(22)Ne/^(20)Ne, and ^(58)Fe/^(56)Fe, are indeed present in the GCRs. In fact, all of the isotope ratios that we have measured are consistent with a GCR source consisting of about 80% material with solar system composition and about 20% W-R material. Since W-R stars are evolutionary products of OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of these data with W-R models suggests that superbubbles are the likely source of at least a substantial fraction of GCRs.
-
Cosmic ray neon wolf rayet stars and the superbubble origin of Galactic Cosmic Rays
arXiv: Astrophysics, 2005Co-Authors: W R Binns, A C Cummings, M H Israel, R A Leske, R A Mewaldt, M E Wiedenbeck, Marcel Arnould, J S George, Stephane Goriely, Georges MeynetAbstract:The abundances of neon isotopes in the Galactic Cosmic Rays (GCRs) are reported using data from the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE). We compare our ACE-CRIS data for neon and refractory isotope ratios, and data from other experiments, with recent results from two-component Wolf-Rayet (WR) models. The three largest deviations of GCR isotope ratios from solar-system ratios predicted by these models are indeed present in the GCRs. Since WR stars are evolutionary products of OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of these data with WR models suggests that superbubbles are the likely source of at least a substantial fraction of GCRs.
E Amato - One of the best experts on this subject based on the ideXlab platform.
-
impact of transport modelling on the 60 fe abundance inside Galactic Cosmic ray sources
Physical Review D, 2020Co-Authors: G Morlino, E AmatoAbstract:The ACE-CRIS collaboration has recently released the measurement of radioactive $^{60}$Fe nuclei abundance in Galactic Cosmic Rays, in the energy range $\sim 195-500$ MeV per nucleon. We model Cosmic Ray propagation and derive from this measurement the $^{60}$Fe/$^{56}$Fe ratio that is expected in the sources of Galactic Cosmic Rays. We describe Cosmic Ray origin and transport within the framework of the disk/halo diffusion model, namely a scenario in which the matter and the Cosmic Ray sources in our Galaxy are confined to a thin disk, while Cosmic Ray propagation occurs in a much larger halo with negligible matter density. We solve the Cosmic Ray transport equation accounting for spallation reactions, decay and ionization losses as well as advection. We find that the $^{60}$Fe/$^{56}$Fe ratio at the source must be very close to the value detected in the local Cosmic Ray spectrum at Earth, due to the fact that spallation reactions are more effective for $^{56}$Fe than for $^{60}$Fe. Such a result could help identify the sources of Galactic Cosmic Rays.
A C Cummings - One of the best experts on this subject based on the ideXlab platform.
-
Galactic Cosmic Rays in the local interstellar medium voyager 1 observations and model results
The Astrophysical Journal, 2016Co-Authors: A C Cummings, W R Webber, E C Stone, B C Heikkila, N Lal, G Johannesson, I V Moskalenko, E Orlando, T A PorterAbstract:Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic Cosmic-ray nuclei down to 3 MeV nuc^(−1) and electrons down to 2.7 MeV. The H and He spectra have the same energy dependence between 3 and 346 MeV nuc^(−1), with a broad maximum in the 10–50 MeV nuc^(−1) range and a H/He ratio of 12.2 ± 0.9. The peak H intensity is ~15 times that observed at 1 AU, and the observed local interstellar gradient of 3–346 MeV H is −0.009 ± 0.055% AU^(−1), consistent with models having no local interstellar gradient. The energy spectrum of electrons (e^− + e^+) with 2.7–74 MeV is consistent with E^(−1.30±0.05) and exceeds the H intensity at energies below ~50 MeV. Propagation model fits to the observed spectra indicate that the energy density of Cosmic-ray nuclei with >3 MeV nuc^(−1) and electrons with >3 MeV is 0.83–1.02 eV cm−3 and the ionization rate of atomic H is in the range of 1.51–1.64 × 10^(−17) s^(−1). This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy Cosmic Rays or the presence of a suprathermal tail on the energy spectrum at much lower energies. The propagation model fits also provide improved estimates of the elemental abundances in the source of Galactic Cosmic Rays.
-
abundance measurements of zn ga ge se from the Cosmic ray isotope spectrometer cris experiment on the advanced composition explorer ace satellite
Bulletin of the American Physical Society, 2009Co-Authors: W R Binns, A C Cummings, M H Israel, R A Leske, R A Mewaldt, G A De Nolfo, T T Von Rosenvinge, E C Stone, M E WiedenbeckAbstract:The Cosmic ray elemental abundances of _(30)Zn, _(31)Ga, _(32)Ge, and _(34)Se provide important tests of the model of the OB-association origin of Galactic Cosmic Rays that has resulted from previous ACE measurements of the neon and iron isotopes and which appears to be confirmed by elemental abundances of Zn, Ga, Ge, and Se measured by the balloon-borne Trans-Iron Galactic Element Recorder (TIGER). These ultra-heavy (Z≥30) nuclei are very rare and require an instrument with a large product of geometrical factor and exposure time. We have measured these abundances using the CRIS instrument, which has a geometrical factor of about 250 cm^2sr, on the NASA-ACE spacecraft. Over the 11+ years since launch in 1997 we have collected ∼400 nuclei with Z≥30 over the energy range of ∼150 to 600 MeV/nucleon. These measured abundances relative to iron are presented and compared with those from the TIGER and HEAO-3 experiments. Our measurements are in reasonable agreement with the TIGER results and are consistent with an OB association origin of Galactic Cosmic Rays.
-
Cosmic ray neon wolf rayet stars and the superbubble origin of Galactic Cosmic Rays
arXiv: Astrophysics, 2005Co-Authors: W R Binns, A C Cummings, M H Israel, R A Leske, R A Mewaldt, M E Wiedenbeck, Marcel Arnould, J S George, Stephane Goriely, Georges MeynetAbstract:The abundances of neon isotopes in the Galactic Cosmic Rays (GCRs) are reported using data from the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE). We compare our ACE-CRIS data for neon and refractory isotope ratios, and data from other experiments, with recent results from two-component Wolf-Rayet (WR) models. The three largest deviations of GCR isotope ratios from solar-system ratios predicted by these models are indeed present in the GCRs. Since WR stars are evolutionary products of OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of these data with WR models suggests that superbubbles are the likely source of at least a substantial fraction of GCRs.
I G Usoskin - One of the best experts on this subject based on the ideXlab platform.
-
solar energetic particles and Galactic Cosmic Rays over millions of years as inferred from data on cosmogenic 26 al in lunar samples
Astronomy and Astrophysics, 2018Co-Authors: Stepan Poluianov, Gennady A Kovaltsov, I G UsoskinAbstract:Aims. Lunar soil and rocks are not protected by a magnetic field or an atmosphere and are continuously irradiated by energetic particles that can produce cosmogenic radioisotopes directly inside rocks at different depths depending on the particle's energy. This allows the mean fluxes of solar and Galactic Cosmic Rays to be assessed on the very long timescales of millions of years. Methods. Here we show that lunar rocks can serve as a very good particle integral spectrometer in the energy range 20-80 MeV. We have developed a new method based on precise modeling, that is applied to measurements of $^{26}$Al (half-life ~0.7 megayears) in lunar samples from the Apollo mission, and present the first direct reconstruction (i.e., without any a priori assumptions) of the mean energy spectrum of solar and Galactic energetic particles over a million of years. Results. We show that the reconstructed spectrum of solar energetic particles is totally consistent with that over the last decades, despite the very different levels of solar modulation of Galactic Cosmic Rays ($\phi=496\pm 40$ MV over a million years versus $\phi= 660\pm 20$ MV for the modern epoch). We also estimated the occurrence probability of extreme solar events and argue that no events with the F(>30 MeV) fluence exceeding $5*10^{10}$ and $10^{11}$ cm$^2$ are expected on timescales of a thousand and million years, respectively. Conclusions. We conclude that the mean flux of solar energetic particles hardly depends on the level of solar activity, in contrast to the solar modulation of Galactic Cosmic Rays. This puts new observational constraints on solar physics and becomes important for assessing radiation hazards for the planned space missions.
-
Solar energetic particles and Galactic Cosmic Rays over millions of years as inferred from data on cosmogenic
'EDP Sciences', 2018Co-Authors: Stepan Poluianov, Gennady A Kovaltsov, I G UsoskinAbstract:Aims. Lunar soil and rocks are not protected by a magnetic field or an atmosphere and are continuously irradiated by energetic particles that can produce cosmogenic radioisotopes directly inside rocks at different depths depending on the particle’s energy. This allows the mean fluxes of solar and Galactic Cosmic Rays to be assessed on the very long timescales of millions of years. Methods. Here we show that lunar rocks can serve as a very good particle integral spectrometer in the energy range 20–80 MeV. We have developed a new method based on precise modeling, that is applied to measurements of 26Al (half-life ≈0.7 megayears) in lunar samples from the Apollo mission, and present the first direct reconstruction (i.e., without any a priori assumptions) of the mean energy spectrum of solar and Galactic energetic particles over a million of years. Results. We show that the reconstructed spectrum of solar energetic particles is totally consistent with that over the last decades, despite the very different levels of solar modulation of Galactic Cosmic Rays (ϕ = 496 ± 40 MV over a million years versus (ϕ = 660 ± 20 MV for the modern epoch). We also estimated the occurrence probability of extreme solar events and argue that no events with the F(>30 MeV) fluence exceeding 5×1010 and 1011 cm−2 are expected on timescales of a thousand and million years, respectively. Conclusions. We conclude that the mean flux of solar energetic particles hardly depends on the level of solar activity, in contrast to the solar modulation of Galactic Cosmic Rays. This puts new observational constraints on solar physics and becomes important for assessing radiation hazards for the planned space missions
-
influence of Galactic Cosmic Rays on atmospheric composition and dynamics
Atmospheric Chemistry and Physics, 2011Co-Authors: M Calisto, I G Usoskin, E Rozanov, Thomas PeterAbstract:Abstract. This study investigates the influence of the Galactic Cosmic Rays (GCRs) on the atmospheric composition, temperature and dynamics by means of the 3-D Chemistry Climate Model (CCM) SOCOL v2.0. Ionization rates were parameterized according to CRAC:CRII (Cosmic Ray induced Cascade: Application for Cosmic Ray Induced Ionization), a detailed state-of-the-art model describing the effects of GCRs in the entire altitude range of the CCM from 0–80 km. We find statistically significant effects of GCRs on tropospheric and stratospheric NO x , HO x , ozone, temperature and zonal wind, whereas NO x , HO x and ozone are annually averaged and the temperature and the zonal wind are monthly averaged. In the Southern Hemisphere, the model suggests the GCR-induced NO x increase to exceed 10 % in the tropopause region (peaking with 20 % at the pole), whereas HO x is showing a decrease of about 3 % caused by enhanced conversion into HNO 3 . As a consequence, ozone is increasing by up to 3 % in the relatively unpolluted southern troposphere, where its production is sensitive to additional NO x from GCRs. Conversely, in the northern polar lower stratosphere, GCRs are found to decrease O 3 by up to 3 %, caused by the additional heterogeneous chlorine activation via ClONO 2 + HCl following GCR-induced production of ClONO 2 . There is an apparent GCR-induced acceleration of the zonal wind of up to 5 m s −1 in the Northern Hemisphere below 40 km in February, and a deceleration at higher altitudes with peak values of 3 m s −1 around 70 km altitude. The model also indentifies GCR-induced changes in the surface air, with warming in the eastern part of Europe and in Russia (up to 2.25 K for March values) and cooling in Siberia and Greenland (by almost 2 K). We show that these surface temperature changes develop even when the GCR-induced ionization is taken into account only above 18 km, suggesting that the stratospherically driven strengthening of the polar night jet extends all the way down to the Earth's surface.
Marcel Arnould - One of the best experts on this subject based on the ideXlab platform.
-
Cosmic ray neon wolf rayet stars and the superbubble origin of Galactic Cosmic Rays
The Astrophysical Journal, 2005Co-Authors: Marcel Arnould, J S George, Stephane Goriely, Georges MeynetAbstract:We report the abundances of neon isotopes in the Galactic Cosmic Rays (GCRs) using data from the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE). These abundances have been measured for seven energy intervals over the energy range of 84 ≤ E/M ≤ 273 MeV nucleon^(-1). We have derived the ^(22)Ne/^(20)Ne ratio at the Cosmic-ray source using the measured ^(21)Ne, ^(19)F, and ^(17)O abundances as "tracers" of secondary production of the neon isotopes. Using this approach, the ^(22)Ne/^(20)Ne abundance ratio that we obtain for the Cosmic-ray source is 0.387 ± 0.007(statistical) ± 0.022(systematic). This corresponds to an enhancement by a factor of 5.3 ± 0.3 over the ^(22)Ne/^(20)Ne ratio in the solar wind. This Cosmic-ray source ^(22)Ne/^(20)Ne ratio is also significantly larger than that found in anomalous Cosmic Rays, solar energetic particles, most meteoritic samples of matter, and interplanetary dust particles. We compare our ACE CRIS data for neon and refractory isotope ratios, and data from other experiments, with recent results from two-component Wolf-Rayet (W-R) models. The three largest deviations of GCR isotope ratios from solar system ratios predicted by these models, ^(12)C/^(16)O, ^(22)Ne/^(20)Ne, and ^(58)Fe/^(56)Fe, are indeed present in the GCRs. In fact, all of the isotope ratios that we have measured are consistent with a GCR source consisting of about 80% material with solar system composition and about 20% W-R material. Since W-R stars are evolutionary products of OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of these data with W-R models suggests that superbubbles are the likely source of at least a substantial fraction of GCRs.
-
Cosmic ray neon wolf rayet stars and the superbubble origin of Galactic Cosmic Rays
arXiv: Astrophysics, 2005Co-Authors: W R Binns, A C Cummings, M H Israel, R A Leske, R A Mewaldt, M E Wiedenbeck, Marcel Arnould, J S George, Stephane Goriely, Georges MeynetAbstract:The abundances of neon isotopes in the Galactic Cosmic Rays (GCRs) are reported using data from the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE). We compare our ACE-CRIS data for neon and refractory isotope ratios, and data from other experiments, with recent results from two-component Wolf-Rayet (WR) models. The three largest deviations of GCR isotope ratios from solar-system ratios predicted by these models are indeed present in the GCRs. Since WR stars are evolutionary products of OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of these data with WR models suggests that superbubbles are the likely source of at least a substantial fraction of GCRs.
