| 1. |
- Sordo, Rosanna, et al.
(author)
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Synthetic stellar and SSP libraries as templates for Gaia simulations
- 2010
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In: Astrophysics and Space Science. - : Springer Science and Business Media LLC. - 0004-640X .- 1572-946X. ; 328:1-2, s. 331-335
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Journal article (peer-reviewed)abstract
- ESA's Gaia mission will collect low resolution spectroscopy in the optical range for 109 objects. Complete and up-to-date libraries of synthetic stellar spectra are needed to built algorithms aimed to automatically derive the classification and the parametrization of this huge amount of data. In addition, libraries of stellar spectra are one of the main ingredients of stellar population synthesis models, aiming to derive the properties of unresolved stellar populations from their integrated light. We present (a) the newly computed libraries of synthetic spectra built by the Gaia community, covering the whole optical range (300-1100 nm) at medium-high resolution of (0.3 nm) for stars spanning the most different types, from M to O, from A-peculiar to Emission lines to White Dwarfs, and (b) the implementation of those libraries in our SSP code (Tantalo in The Initial Mass Function 50 Years Later, 327:235 2005), exploring different stellar evolution models.
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| 2. |
- Reifarth, R., et al.
(author)
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Nuclear astrophysics with radioactive ions at FAIR
- 2016
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
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Conference paper (peer-reviewed)abstract
- The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
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| 3. |
- Fogle, M, et al.
(author)
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Electron-ion recombination of Be-like C, N, and O
- 2005
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 442:2, s. 757-766
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Journal article (peer-reviewed)abstract
- The absolute total recombination reaction rate coefficients for Be-like C, N, and O have been measured using the CRYRING storage ring and compared with the results from distorted-wave theory. For the theory results, it is found that shifts to NIST energy values for the core excited energies of the recombining system are not sufficient to accurately match all of the resonance positions and heights at lower energies. These theory results represent the quality of most archived theory DR data. The accurate calculation of these low energy resonances still presents a significant challenge to theory. In addition, trielectronic recombination resonances, associated with the formation of triply excited states during recombination, have been observed in the total recombination reaction rate coefficient spectra of N3+ and O4+. Finally, we construct a dielectronic recombination Maxwellian rate coefficient from the experimental results for low n resonances, and from the theoretical results for high n resonances. In the case of O4+, the trielectronic recombination resonances have a strong influence on the low temperature Maxwellian rate coefficient. Our best hybrid Maxwellian rate coefficient is compared with archived distorted-wave theory data, and is found to be in reasonable agreement, even at the low temperatures.
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| 4. |
- Edvardsson, Sverker, et al.
(author)
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Spin axis variations of Mars: numerical limitations and model dependences
- 2008
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 135:4, s. 1151-1160
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Journal article (peer-reviewed)abstract
- Celestial mechanical integrations for the whole solar system are carried out over four billion years before and after the present. The orbital solution of the solar system is stable during this whole time period. An instantaneous spin axis model including triaxiality is developed. In particular, spin axis precession, the Martian obliquity, solar torques, and the orbital eccentricity/inclination of Mars are studied. Model dependences from general relativity, solar oblateness, the Martian moons, solar mass loss, etc. are tested. Although the obliquity of Mars sometimes shows dramatic variations, some structures are robust and seem insensitive to the initial spin precession rate. A full integration is carried out during a total of 8000 Myr resulting in a Martian obliquity that is restricted between 10 and 60 degrees. The problems with numerical noise due to limited machine precision, integration step sizes, and the chaotic sensitivity of the solutions are studied and discussed. The limited machine precision (15-16 figures) alone is found to limit the duration of exact obliquity solutions to about 80 Myr.
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| 5. |
- Anastasopoulos, M., et al.
(author)
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Multi-Grid detector for neutron spectroscopy : Results obtained on time-of-flight spectrometer CNCS
- 2017
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In: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 12:4
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Journal article (peer-reviewed)abstract
- The Multi-Grid detector technology has evolved from the proof-of-principle and characterisation stages. Here we report on the performance of the Multi-Grid detector, the MG.CNCS prototype, which has been installed and tested at the Cold Neutron Chopper Spectrometer, CNCS at SNS. This has allowed a side-by-side comparison to the performance of 3He detectors on an operational instrument. The demonstrator has an active area of 0.2 m2. It is specifically tailored to the specifications of CNCS. The detector was installed in June 2016 and has operated since then, collecting neutron scattering data in parallel to the He-3 detectors of CNCS. In this paper, we present a comprehensive analysis of this data, in particular on instrument energy resolution, rate capability, background and relative efficiency. Stability, gamma-ray and fast neutron sensitivity have also been investigated. The effect of scattering in the detector components has been measured and provides input to comparison for Monte Carlo simulations. All data is presented in comparison to that measured by the 3He detectors simultaneously, showing that all features recorded by one detector are also recorded by the other. The energy resolution matches closely. We find that the Multi-Grid is able to match the data collected by 3He, and see an indication of a considerable advantage in the count rate capability. Based on these results, we are confident that the Multi-Grid detector will be capable of producing high quality scientific data on chopper spectrometers utilising the unprecedented neutron flux of the ESS.
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| 6. |
- Filgas, Robert, et al.
(author)
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Miniature semiconductor neutron spectrometer HardPix for surface mapping of lunar water
- 2022
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In: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 200, s. 620-625
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Journal article (peer-reviewed)abstract
- A current renaissance of lunar exploration enables to search for lunar water deposits directly on the surface of the Moon with robotic rovers. We present a novel miniature semiconductor neutron spectrometer capable of mapping the water deposits using non-invasive detection of neutrons created underground by cosmic rays and thermalized by hydrogen. This prospecting package consists of a radiation detector to monitor the cosmic rays background, a thermal/epithermal neutron detector to measure flux of neutrons moderated by water, and a gamma spectrometer suitable for monitoring local changes of major elemental components of the lunar regolith. Using miniature semiconductor detectors allows to deploy them even on small commercial rovers where resources are extremely limited. The prospecting package is being developed for ispace lunar rover and studied for ESA EL3 rover. It is based on Timepix pixel sensors, with space heritage onboard NASA, ESA and JAXA vessels.
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| 7. |
- Vallenari, A., et al.
(author)
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Synthetic stellar libraries and SSP simulations in the Gaia Era
- 2009
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In: Proceedings of the International Astronomical Union. ; , s. 444-445
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Conference paper (peer-reviewed)abstract
- The Gaia mission will obtain accurate positions, parallaxes and proper motions for 109 object all over the sky. In addition, it will collect low resolution spectroscopy in the optical range for ∼ 109 objects, stars, galaxies, and QSOs. Parameters of those objects are expected to be part of the final Catalog. Complete and up-to-date libraries of synthetic stellar spectra are needed to train the algorithms to classify this huge amount of data. Here we focus on the use of the synthetic libraries of spectra calculated by the Gaia community to derive grids of Single Stellar Populations as building blocks of population synthesis models. © International Astronomical Union 2010.
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