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1. Amplitudes of Solar Gravity Modes: A Review

Author

K. Belkacem, C. Pinçon, and G. Buldgen

Subjects
Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, FOS: Physical sciences, Astronomy and Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

Solar gravity modes are considered as the {\it Rosetta Stone} for probing and subsequently deciphering the physical properties of the solar inner-most layers. Recent claims of positive detection therefore shed some new light on the long-standing issue of estimating solar gravity mode amplitudes. In this article, our objective is to review the theoretical efforts intended to predict solar gravity mode amplitudes. Because most of these studies assumed analogous driving and damping properties to those for the observed acoustic modes, we also provide a short overview of our current knowledge for these modes in the Sun and solar-type stars (which show solar-like oscillations) before diving into the specific problem of solar gravity modes. Finally, taking recent estimates into account, we conclude and confirm that the low-frequency domain (typically between $10\,\mu$Hz and $100\,\mu$Hz) is certainly more suited to focus on for detecting solar gravity modes. More precisely, around $60\,\mu$Hz, the theoretical estimates are slightly lower than the observational detection threshold as provided by the GOLF (Global Oscillations at Low Frequencies) instrument by about a factor of two only. This is typically within the current uncertainties associated with theoretical estimates and should motivate us for improving our knowledge on turbulence in the whole solar convective region, which is key for improving the accuracy of $g$-mode amplitude estimates. The recent detection of solar inertial modes (Gizon et al. 2021) combined with the continuous development of numerical simulations provide interesting prospects for future studies., Comment: Accepted for publication in Solar Physics

Published
2022
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2. Coupling between turbulence and solar-like oscillations: A combined Lagrangian PDF/SPH approach

Author

J. Philidet, K. Belkacem, and M.-J. Goupil

Subjects
Plasma Physics (physics.plasm-ph), Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Fluid Dynamics (physics.flu-dyn), FOS: Physical sciences, Astronomy and Astrophysics, Physics - Fluid Dynamics, Solar and Stellar Astrophysics (astro-ph.SR), Physics - Plasma Physics
Abstract

The first paper of this series established a linear stochastic wave equation for solar-like p-modes, correctly taking the effect of turbulence thereon into account. In this second paper, we aim at deriving simultaneous expressions for the excitation rate, damping rate, and modal surface effect associated with any given p-mode, as an explicit function of the statistical properties of the turbulent velocity field. We reduce the stochastic wave equation to complex amplitude equations for the normal oscillating modes of the system. We then derive the equivalent Fokker-Planck equation for the real amplitudes and phases of all the oscillating modes of the system simultaneously. The effect of the finite-memory time of the turbulent fluctuations (comparable to the period of the modes) on the modes themselves is consistently and rigorously accounted for, by means of the simplified amplitude equation formalism. This formalism accounts for mutual linear mode coupling in full, and we then turn to the special single-mode case. This allows us to derive evolution equations for the mean energy and mean phase of each mode, from which the excitation rate, the damping rate, and the modal surface effect naturally arise. We show that the expression for the excitation rate of the modes is identical to previous results obtained through a different modelling approach, thus supporting the validity of the formalism presented here. We also recover the fact that the damping rate and modal surface effect correspond to the real and imaginary part of the same single complex quantity. We explicitly separate the different physical contributions to these observables, in particular the turbulent pressure contribution and the joint effect of the pressure-rate-of-strain correlation and the turbulent dissipation. We show that the former dominates for high-frequency modes and the latter for low-frequency modes., Accepted for publication in A&A. 23 pages, 2 figures

Published
2022

4. First-Principles Study of the New Half-Metallic Ferromagnetic Quaternary-Heusler Alloys NaXNO (X=Ca, Sr, Ba)

Author

L. Beldi, K. Belkacem, S. Amari, B. Bouhafs, and Y. Zaoui

Subjects
010302 applied physics, Materials science, Condensed matter physics, Magnetism, Astrophysics::Instrumentation and Methods for Astrophysics, Computer Science::Computation and Language (Computational Linguistics and Natural Language and Speech Processing), 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Metal, Condensed Matter::Materials Science, Ferromagnetism, visual_art, 0103 physical sciences, visual_art.visual_art_medium, Computer Science::General Literature, Density functional theory, Electrical and Electronic Engineering, 0210 nano-technology, Quaternary
Abstract

The first-principles approach based on density functional theory (DFT) and the full-potential linearized augmented plane-wave method were employed to investigate the structural, elastic, electronic and magnetic properties of Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys. The generalized gradient approximation (GGA) as parameterized by Perdew, Burke and Ernzerhof (PBE) and the modified Becke–Johnson exchange potential were used. As far as we know, we present our results which for the first time quantitatively account for the electronic structures and magnetic properties of Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys. From the total energy calculation using three possible atomic configurations ([Formula: see text], [Formula: see text] and [Formula: see text]), it is found that the Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys are more stable in the ferromagnetic [Formula: see text]-phase. From our estimated elastic constants [Formula: see text], it is found that all the considered Heusler alloys are mechanically stable in the [Formula: see text]-phase. We have also investigated the robustness of the half-metallicity with respect to the variation of lattice constants in these alloys. We have found that these alloys are half-metallic ferromagnets (HMFs) with a magnetic moment of 2[Formula: see text][Formula: see text] per formula unit at their equilibrium volumes. The spin-polarized electronic band structure and density of states of these quaternary half-Heusler alloys calculated by GGA (mBJ-GGA) show that the minority spin channels have metallic nature and the majority spin channels have a semiconductor character with half-metallic gaps of 0.49[Formula: see text]eV (2.17[Formula: see text]eV), 0.72[Formula: see text]eV (2.28[Formula: see text]eV) and 0.96[Formula: see text]eV (2.22[Formula: see text]eV) for NaCaNO, NaSrNO and NaBaNO quaternary half-Heusler alloys, respectively. Analysis of the density of states and the spin charge density of these quaternary alloys indicates that their magnetic moments mainly originate from the strong spin-polarization of 2[Formula: see text] states of N atoms and O atoms.

Published
2020

5. PLATO as it is: a legacy mission for Galactic archaeology

Author

A. Miglio, C. Chiappini, B. Mosser, G. R. Davies, K. Freeman, L. Girardi, P. Jofré, D. Kawata, B. M. Rendle, M. Valentini, L. Casagrande, W. J. Chaplin, G. Gilmore, K. Hawkins, B. Holl, T. Appourchaux, K. Belkacem, D. Bossini, K. Brogaard, M.‐J. Goupil, J. Montalbán, A. Noels, F. Anders, T. Rodrigues, G. Piotto, D. Pollacco, H. Rauer, C. Allende Prieto, P. P. Avelino, C. Babusiaux, C. Barban, B. Barbuy, S. Basu, F. Baudin, O. Benomar, O. Bienaymé, J. Binney, J. Bland‐Hawthorn, A. Bressan, C. Cacciari, T. L. Campante, S. Cassisi, J. Christensen‐Dalsgaard, F. Combes, O. Creevey, M. S. Cunha, R. S. Jong, P. Laverny, S. Degl'Innocenti, S. Deheuvels, É. Depagne, J. Ridder, P. Di Matteo, M. P. Di Mauro, M.‐A. Dupret, P. Eggenberger, Y. Elsworth, B. Famaey, S. Feltzing, R. A. García, O. Gerhard, B. K. Gibson, L. Gizon, M. Haywood, R. Handberg, U. Heiter, S. Hekker, D. Huber, R. Ibata, D. Katz, S. D. Kawaler, H. Kjeldsen, D. W. Kurtz, N. Lagarde, Y. Lebreton, M. N. Lund, S. R. Majewski, P. Marigo, M. Martig, S. Mathur, I. Minchev, T. Morel, S. Ortolani, M. H. Pinsonneault, B. Plez, P. G. Prada Moroni, D. Pricopi, A. Recio‐Blanco, C. Reylé, A. Robin, I. W. Roxburgh, M. Salaris, B. X. Santiago, R. Schiavon, A. Serenelli, S. Sharma, V. Silva Aguirre, C. Soubiran, M. Steinmetz, D. Stello, K. G. Strassmeier, P. Ventura, R. Ventura, N. A. Walton, C. C. Worley, Institut d'Astrophysique et de Géophysique [Liège], Université de Liège, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Arizona State University [Tempe] (ASU), Leibniz-Institut für Astrophysik Potsdam (AIP), Department of Physics and Astronomy [Aarhus], Aarhus University [Aarhus], School of Physics and Astronomy [Birmingham], University of Birmingham [Birmingham], Heckscher-Klinikum, Danish AsteroSeismology Centre (DASC), Universidade Federal de São Paulo (UNIFESP), DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Department of Astronomy [New Haven], Yale University [New Haven], Evolution et Modélisation des Bassins Sédimentaires (EMBS), Institut des Sciences de la Terre de Paris (iSTeP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Department of Biomedical, Metabolic and Neural Sciences [Modena], Chaire Galaxies et cosmologie, Collège de France (CdF (institution)), Institut d'astrophysique spatiale (IAS), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Universidade de Aveiro, Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Las Cumbres Observatory (LCO), Observatoire Astronomique de l'Université de Genève (ObsGE), Université de Genève (UNIGE), Université de Strasbourg (UNISTRA), Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Universitat de Girona (UdG), Max-Planck-Institut für Extraterrestrische Physik (MPE), Max-Planck-Institut für Sonnensystemforschung (MPS), Max-Planck-Gesellschaft, SETI Institute, University of Illinois at Urbana Champaign (UIUC), University of Illinois at Urbana-Champaign [Urbana], University of Illinois System-University of Illinois System, Universidade Federal de Santa Catarina = Federal University of Santa Catarina [Florianópolis] (UFSC), Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Space Science Institute [Boulder] (SSI), Department of Astronomy (Ohio State University), Ohio State University [Columbus] (OSU), Laboratoire Univers et Particules de Montpellier (LUPM), Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Astrophysical Research Institute [Liverpool], Liverpool John Moore University (ljmu), Institute of Space Sciences [Barcelona] (ICE-CSIC), Spanish National Research Council [Madrid] (CSIC), Sydney Institute for Astronomy (SIfA), The University of Sydney, M2A 2017, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Leibniz Institute for Astrophysics Potsdam (AIP), Symbiose Marine (SM), Evolution Paris Seine, Université des Antilles et de la Guyane (UAG)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles et de la Guyane (UAG)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS), DNRF106, The Danish National Research Foundation, Centre National d’Etudes Spatiales, PRIN INAF 2014 - CRA 1.05.01.94.05, Science and Technology Facilities Council, Programme National Cosmologie et Galaxies (CNRS/INSU, France), IF/00894/2012/, Federación Española de Enfermedades Raras, CNES Fellowship, 615604, ERC Consolidator (STARKEY), Federaal Wetenschapsbeleid, ESP2015-66134-R, Ministerio de Economía y Competitividad, European Commission's Seventh Framework Programme, Swedish National Space Board, European Commission, DLR, FT1400147, Australian Research Council, NNX16AI09G, National Aeronautics and Space Administration, European Cooperation in Science and Technology, CH1188/2-1, DFG, CA16117, ChETEC COST Action, 10118, Villum Fonden, European Union FP7 program, 320360, ERC, UID/FIS/04434/2013, FCT, G1502, NYUAD Institute, Programme National de Physique Stellaire (PNPS), ITA, USA, GBR, FRA, DEU, ESP, Federal University of Sao Paulo (Unifesp), Université Paris-Saclay, Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Collège de France - Chaire Galaxies et cosmologie, Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Genève = University of Geneva (UNIGE), Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, University of Illinois System, Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université des Antilles et de la Guyane (UAG)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles et de la Guyane (UAG)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), Miglio A., Chiappini C., Mosser B., Davies G.R., Freeman K., Girardi L., Jofre P., Kawata D., Rendle B.M., Valentini M., Casagrande L., Chaplin W.J., Gilmore G., Hawkins K., Holl B., Appourchaux T., Belkacem K., Bossini D., Brogaard K., Goupil M.-J., Montalban J., Noels A., Anders F., Rodrigues T., Piotto G., Pollacco D., Rauer H., Prieto C.A., Avelino P.P., Babusiaux C., Barban C., Barbuy B., Basu S., Baudin F., Benomar O., Bienayme O., Binney J., Bland-Hawthorn J., Bressan A., Cacciari C., Campante T.L., Cassisi S., Christensen-Dalsgaard J., Combes F., Creevey O., Cunha M.S., Jong R.S., Laverny P., Degl'Innocenti S., Deheuvels S., Depagne E., Ridder J., Matteo P.D., Mauro M.P.D., Dupret M.-A., Eggenberger P., Elsworth Y., Famaey B., Feltzing S., Garcia R.A., Gerhard O., Gibson B.K., Gizon L., Haywood M., Handberg R., Heiter U., Hekker S., Huber D., Ibata R., Katz D., Kawaler S.D., Kjeldsen H., Kurtz D.W., Lagarde N., Lebreton Y., Lund M.N., Majewski S.R., Marigo P., Martig M., Mathur S., Minchev I., Morel T., Ortolani S., Pinsonneault M.H., Plez B., Moroni P.G.P., Pricopi D., Recio-Blanco A., Reyle C., Robin A., Roxburgh I.W., Salaris M., Santiago B.X., Schiavon R., Serenelli A., Sharma S., Aguirre V.S., Soubiran C., Steinmetz M., Stello D., Strassmeier K.G., Ventura P., Ventura R., Walton N.A., Worley C.C., Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Montpellier 2 - Sciences et Techniques (UM2), Université Nice Sophia Antipolis (... - 2019) (UNS), and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles et de la Guyane (UAG)-Université Pierre et Marie Curie - Paris 6 (UPMC)

Subjects
RED-GIANT STARS, Astrophysics, 01 natural sciences, COROT ASTEROSEISMOLOGY FIELDS, Astrophysics::Solar and Stellar Astrophysics, VELOCITY EXPERIMENT RAVE, Galaxy: structure, 010303 astronomy & astrophysics, SUN-LIKE STAR, QC, QB, Physics, structure - stars: abundances - stars: fundamental parameters - stars: oscillations - surveys [Galaxy], Astrophysics - Solar and Stellar Astrophysics, stars: fundamental parameters, stars: oscillations, Astrophysics::Earth and Planetary Astrophysics, SOLAR-LIKE OSCILLATIONS, THICK DISK, stars: abundances, Relation (database), DATA RELEASE, Milky Way, surveys, Astronomy and Astrophysics, Space and Planetary Science, FOS: Physical sciences, MILKY-WAY DISK, F500, Kepler, Asteroseismology, ATMOSPHERIC PARAMETERS, Settore FIS/05 - Astronomia e Astrofisica, 0103 physical sciences, Quality (philosophy), Galaxy: structure â stars: abundances â stars: fundamental parameters â stars: oscillations â surveys, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, 010308 nuclear & particles physics, Galaxy: structure – stars: abundances – stars: fundamental parameters – stars: oscillations – surveys, [PHYS.ASTR.SR]Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Data science, Astrophysics - Astrophysics of Galaxies, Galaxy, COLD DARK-MATTER, Stars, Astrophysics of Galaxies (astro-ph.GA), Stellar physics, Galaxy: structure – stars: abundances – stars: fundamental parameters – stars: oscillations – surveys, Galaxy: structure - stars: abundances - stars: fundamental parameters - stars: oscillations - surveys
Abstract

Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps of the Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with a well-defined view of the current chemo-kinematical structure of the Milky Way, but will only enable a blurred view on the temporal sequence that led to the present-day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler, and K2, asteroseismology provides the way forward: solar-like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age-initial-mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar properties that are needed to tackle such questions. By quantifying the asteroseismic yields expected from PLATO for red-giant stars, we demonstrate that these requirements are within the capabilities of the current instrument design, provided that observations are sufficiently long to identify the evolutionary state and allow robust and precise determination of acoustic-mode frequencies. This will allow us to harvest data of sufficient quality to reach a 10% precision in age. This is a fundamental pre-requisite to then reach the more ambitious goal of a similar level of accuracy, which will only be possible if we have to hand a careful appraisal of systematic uncertainties on age deriving from our limited understanding of stellar physics, a goal which conveniently falls within the main aims of PLATO's core science., 17 pages, 9 figures, accepted for publication in Astronomical Notes

Published
2017

6. Oscillation mode linewidths and heights of 23 main-sequence stars observed byKepler(Corrigendum)

Author

Tiago L. Campante, K. Belkacem, Rasmus Handberg, Rachel Howe, Rafael A. García, William J. Chaplin, Guy R. Davies, Othman Benomar, G. Houdek, Clara Régulo, T. Appourchaux, H. M. Antia, Institut d'astrophysique spatiale (IAS), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Department of Physics and Astronomy [Aarhus], Aarhus University [Aarhus], National Solar Observatory [Tucson] (NSO/Tucson), Association of Universities for Research in Astronomy (AURA)-National Science Foundation [Arlington] (NSF), Departamento de Astrofísica [La laguna], Universidad de La Laguna [Tenerife - SP] (ULL), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institute for Astronomy [Vienna], University of Vienna [Vienna], Visio per computador i robotica (VICOROB), Universitat de Girona (UdG), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), and National Science Foundation [Arlington] (NSF)-Association of Universities for Research in Astronomy (AURA)

Subjects
interiors [stars], [PHYS]Physics [physics], Physics, 010504 meteorology & atmospheric sciences, Oscillation, Mode (statistics), Astronomy, Astronomy and Astrophysics, asteroseismology, Astrophysics, 01 natural sciences, Kepler, Asteroseismology, Space and Planetary Science, 0103 physical sciences, data analysis [methods], [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], errata, addenda, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, Main sequence, 0105 earth and related environmental sciences
Abstract

International audience

Published
2016

7. Stellar granulation as seen in disk-integrated intensity. II. Theoretical scaling relations compared with observations

Author

Elisabetta Caffau, Savita Mathur, Benoit Mosser, Hans-Günter Ludwig, Thomas Kallinger, Mikkel N. Lund, Annie Baglin, K. Belkacem, Rafael A. García, R. Samadi, Tiago L. Campante, and Guy R. Davies

Subjects
Physics, Brightness, Photosphere, 010504 meteorology & atmospheric sciences, Scale (ratio), Turbulence, Sigma, FOS: Physical sciences, Astronomy and Astrophysics, Function (mathematics), Astrophysics, 01 natural sciences, Stars, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, 010303 astronomy & astrophysics, Scaling, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences
Abstract

A large set of stars observed by CoRoT and Kepler shows clear evidence for the presence of a stellar background, which is interpreted to arise from surface convection, i.e., granulation. These observations show that the characteristic time-scale (tau_eff) and the root-mean-square (rms) brightness fluctuations (sigma) associated with the granulation scale as a function of the peak frequency (nu_max) of the solar-like oscillations. We aim at providing a theoretical background to the observed scaling relations based on a model developed in the companion paper. We computed for each 3D model the theoretical power density spectrum (PDS) associated with the granulation as seen in disk-integrated intensity on the basis of the theoretical model. For each PDS we derived tau_eff and sigma and compared these theoretical values with the theoretical scaling relations derived from the theoretical model and the Kepler measurements. We derive theoretical scaling relations for tau_eff and sigma, which show the same dependence on nu_max as the observed scaling relations. In addition, we show that these quantities also scale as a function of the turbulent Mach number (Ma) estimated at the photosphere. The theoretical scaling relations for tau_eff and sigma match the observations well on a global scale. Our modelling provides additional theoretical support for the observed variations of sigma and tau_eff with nu_m max. It also highlights the important role of Ma in controlling the properties of the stellar granulation. However, the observations made with Kepler on a wide variety of stars cannot confirm the dependence of our scaling relations on Ma. Measurements of the granulation background and detections of solar-like oscillations in a statistically sufficient number of cool dwarf stars will be required for confirming the dependence of the theoretical scaling relations with Ma., Comment: 12 pages, 6 figures,accepted for publication in A&A

Published
2013
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9. A new image smoothing method based on a simple model of spatial processing in the early stages of human vision

Author

Azeddine Beghdadi and K. Belkacem-Boussaid

Subjects
business.industry, Low-pass filter, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, Image processing, Filter (signal processing), Real image, Computer Graphics and Computer-Aided Design, Noise, Nonlinear filter, Computer vision, Artificial intelligence, business, Software, Linear filter, Smoothing, Mathematics
Abstract

The difficulty of preserving edges is central to the problem of smoothing images. The main problem is that of distinguishing between meaningful contours and noise, so that the image can be smoothed without loss of details. Substantial efforts have been devoted to solving this difficult problem, and a plethora of filtering methods have been proposed in the literature. Non-linear filters have proved to be more efficient than their linear counterparts. Here, a new nonlinear filter for noise smoothing is introduced. This filter is based on the psychophysical phenomenon of human visual contrast sensitivity. Results on real images are presented to demonstrate the validity of our approach compared to other known filtering methods.

Published
2008

10. Low-level vision treatments inspired from human visual system

Author

Azeddine Beghdadi, K. Belkacem-Boussaid, and Abdel-Ouahab Boudraa

Subjects
Visual perception, genetic structures, Computer science, business.industry, media_common.quotation_subject, SIGNAL (programming language), eye diseases, Edge detection, Digital image, Human visual system model, Contrast (vision), Computer vision, Sensitivity (control systems), Artificial intelligence, Set (psychology), business, media_common
Abstract

A set of low-level vision treatments inspired from some knowledge of mammalian retino-cortical mechanisms is proposed. The basic idea is to exploit the contrast sensitivity response of the human visual system (HVS) and the multichannel decomposition of the visual signal in the cortex. The scope of this work is limited to nonlinear filtering, contrast enhancement and edge detection but could be extended to other image treatments.

Published
2003

11. Edge detection using Holladay's principle

Author

Azeddine Beghdadi, H. Depoisot, and K. Belkacem-Boussaid

Subjects
Visual perception, medicine.anatomical_structure, business.industry, Human visual system model, Canny edge detector, medicine, Computer vision, Human eye, Artificial intelligence, business, Edge detection, Deriche edge detector, Mathematics
Abstract

We propose herein a new contour detection algorithm based on the human visual system. Using the proposed method, one can automatically select the thresholds that define the significant edges, such as perceived by the human eye. The threshold value is adapted to the background and surround intensities, according to criteria involved by Holladay's principle.

Published
2002

12. Non linear smoothing method based on the just-noticeable contrast

Author

K. Belkacem-Boussaid and A. Beghdadi

Subjects
business.industry, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, Contrast (statistics), Edge-preserving smoothing, Image enhancement, Nonlinear system, Computer vision, Artificial intelligence, business, Just noticeable, Algorithm, Smoothing, ComputingMethodologies_COMPUTERGRAPHICS, Mathematics
Abstract

The present paper provides a new smoothing method, based on psychophysical phenomena, in which the optimum smoothing parameters are automatically chosen. The method is a nonlinear one and it has some similarities with well-known morphological filters.

Published
2002

13. The underlying physical meaning of theνmax − νcrelation

Author

Reza Samadi, Arlette Noels, Frédéric Baudin, M. J. Goupil, Benoit Mosser, K. Belkacem, Marc-Antoine Dupret, Institut d'astrophysique spatiale (IAS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Institut d'Astrophysique, Géophysique et Océanographie, Université de Liège, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Etoile, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)

Subjects
Physics, Oscillation, Perturbation (astronomy), Spectral density, Astronomy and Astrophysics, Astrophysics, Plateau (mathematics), Asteroseismology, Stars, Entropy (classical thermodynamics), Space and Planetary Science, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Scaling
Abstract

International audience; Asteroseismology of stars that exhibit solar-like oscillations are enjoying a growing interest with the wealth of observational results obtained with the CoRoT and Kepler missions. In this framework, scaling laws between asteroseismic quantities and stellar parameters are becoming essential tools to study a rich variety of stars. However, the physical underlying mechanisms of those scaling laws are still poorly known. Our objective is to provide a theoretical basis for the scaling between the frequency of the maximum in the power spectrum (numax) of solar-like oscillations and the cut-off frequency (nuc). Using the SoHO GOLF observations together with theoretical considerations, we first confirm that the maximum of the height in oscillation power spectrum is determined by the so-called plateau of the damping rates. The physical origin of the plateau can be traced to the destabilizing effect of the Lagrangian perturbation of entropy in the upper-most layers, which becomes important when the modal period and the local thermal relaxation time-scale are comparable. Based on this analysis, we then find a linear relation between numax and nuc, with a coefficient that depends on the ratio of the Mach number of the exciting turbulence to the third power to the mixing-length parameter.

Published
2011

14. Solar-like oscillations in massive main-sequence stars

Author

Arlette Noels, K. Belkacem, and Marc-Antoine Dupret

Subjects
Physics, Convection, Opacity, Computation, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Amplitude, Astrophysics - Solar and Stellar Astrophysics, Convection zone, Space and Planetary Science, Excited state, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Solar-like oscillations, Solar and Stellar Astrophysics (astro-ph.SR), Main sequence
Abstract

Motivated by the recent detection of stochastically excited modes in the massive star V1449 Aql (Belkacem et al., 2009b), already known to be a $\beta$ Cephei, we theoretically investigate the driving by turbulent convection. By using a full non-adiabatic computation of the damping rates, together with a computation of the energy injection rates, we provide an estimate of the amplitudes of modes excited by both the convective region induced by the iron opacity bump and the convective core. Despite uncertainties in the dynamical properties of such convective regions, we demonstrate that both are able to efficiently excite $p$ modes above the CoRoT observational threshold and the solar amplitudes. In addition, we emphasise the potential asteroseismic diagnostics provided by each convective region, which we hope will help to identify the one responsible for solar-like oscillations, and to give constraints on this convective zone. A forthcoming work will be dedicated to an extended investigation of the likelihood of solar-like oscillations across the Hertzsprung-Russell diagram., Comment: 9 pages, 14 figures, accepter in A&A

Published
2010

15. The Milky Way stellar populations in CFHTLS fields

Author

Guittet, Mélanie, Haywood, Misha, Schultheis, Mathias, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), G. Alecian, K. Belkacem, R. Samadi, D. Valls-Gabaud, and eds.

Subjects
Astrophysics of Galaxies (astro-ph.GA), Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics::Solar and Stellar Astrophysics, FOS: Physical sciences, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - Astrophysics of Galaxies, ComputingMilieux_MISCELLANEOUS, Astrophysics::Galaxy Astrophysics
Abstract

We investigate the characteristics of the thick disk in the Canada - France - Hawaii - Telescope Legacy Survey (CFHTLS) fields, complemented at bright magnitudes with Sloan Digital Sky Survey (SDSS) data. The ([Fe/H], Z) distributions are derived in the W1 and W3 fields, and compared with simulated maps produced using the Besan\c{c}on model. It is shown that the thick disk, represented in star-count models by a distinct component, is not an adequate description of the observed ([Fe/H], Z) distributions in these fields., Comment: 4 pages, 4 figures

Published
2011
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