FliPer: Checking the reliability of global seismic parameters from automatic pipelines

Our understanding of stars through asteroseismic data analysis is limited by our ability to take advantage of the huge amount of observed stars provided by space missions such as CoRoT, Kepler, K2, and soon TESS and PLATO. Global seismic pipelines provide global stellar parameters such as mass and radius using the mean seismic parameters, as well as the effective temperature. These pipelines are commonly used automatically on thousands of stars observed by K2 for 3 months (and soon TESS for at least around 1 month). However, pipelines are not immune from misidentifying noise peaks and stellar oscillations. Therefore, new validation techniques are required to assess the quality of these results. We present a new metric called FliPer (Flicker in Power), which takes into account the average variability at all measured time scales. The proper calibration of FliPer enables us to obtain good estimations of global stellar parameters such as surface gravity that are robust against the influence of noise peaks and hence are an excellent way to find faults in asteroseismic pipelines.Comment: 4 pages, 3 figures, Proceedings for SF2A 2017 (Paris

Operando analysis of a solid oxide fuel cell by environmental transmission electron microscopy

Correlating the microstructure of an energy conversion device to its performance is often a complex exercise, notably in solid oxide fuel cell (SOFC) research. SOFCs combine multiple materials and interfaces that evolve in time due to high operating temperatures and reactive atmospheres. We demonstrate here that operando environmental transmission electron microscopy can simplify the identification of structure-property links in such systems. By contacting a cathode-electrolyte-anode cell to a heating and biasing microelectromechanical system in a single-chamber configuration, a direct correlation is found between the environmental conditions (O2 and H2 partial pressures, temperature), the cell voltage, and the microstructural evolution of the fuel cell, down to the atomic scale. The results shed new insights into the impact of the anode oxidation state and its morphology on the cell electrical properties.Comment: 18 pages, 5 figure

New U-Pb ages for syn-orogenic magmatism in the SW sector of the Ossa Morena Zone (Portugal)

The Ossa-Morena Zone (OMZ) is a major geotectonic unit within the Iberian Massif (which constitutes an important segment of the European Variscan Belt) and one of its distinguishing features is the presence of a noteworthy compositional diversity of plutonic rocks. In the SW sector of the OMZ, the tonalitic Hospitais intrusion (located to the W of Montemor-o-Novo) is considered a typical example of syn-orogenic magmatism, taking into account that both the long axis of the plutonic body and its mesoscopic foliation are oriented parallel to the Variscan WNW-ESE orientation. Another relevant feature of the Hospitais intrusion is the occurrence of mafic microgranular enclaves within the main tonalite. In previous works (Moita et al., 2005; Moita, 2007), it was proposed that: (1) the Hospitais intrusion is part of a calc-alkaline suite, represented by a large number of intrusions in this sector of the OMZ, ranging from gabbros to granites; (2) the enclaves are co-genetic to the host tonalite in the Hospitais pluton. In this study, zircon populations from one sample of the main tonalite (MM-17) and one sample of the associated enclave (MM-17E) were analysed by ID-TIMS for U-Pb geochronology. In each sample, three fractions of nice glassy, euhedral, long prismatic and inclusion free crystals were analysed. The results from the three fractions of MM-17 yielded a 206Pb/238U age of 337.0 ± 2.0 Ma. Similarly, for the enclave MM-17E a 206Pb/238U zircon age of 336.5 ± 0.47 Ma was obtained. These identical ages, within error, are in agreement with a common parental magma for the tonalite and mafic granular enclaves. Similar U-Pb ages have been reported in previous works for plutonic and metamorphic events in this region (e.g.: Pereira et al., 2009; Antunes et al., 2011). Furthermore, also in the SW sector of the OMZ, palaeontological studies (Pereira et al., 2006; Machado & Hladil, 2010) carried out in Carboniferous sedimentary basins containing intercalated calc-alkaline volcanics (Santos et al., 1987; Chichorro, 2006) have shown that they are mainly of Visean age. Therefore, magmatism displaying features typical of continental arc setting seems to have been active in this part of the OMZ during the Lower Carboniferous times

Atomic-Scale Study of Metal–Oxide Interfaces and Magnetoelastic Coupling in Self-Assembled Epitaxial Vertically Aligned Magnetic Nanocomposites

Vertically aligned nanocomposites (VANs) of metal/oxide type have recently emerged as a novel class of heterostructures with great scientific and technological potential in the fields of nanomagnetism, multiferroism, and catalysis. One of the salient features of these hybrid materials is their huge vertical metal/oxide interface, which plays a key role in determining the final magnetic and/or transport properties of the composite structure. However, in contrast to their well‐studied planar counterparts, detailed information on the structural features of vertical interfaces encountered in VANs is scarce. In this work, high resolution scanning transmission electron microscopy (STEM) and electron energy‐loss spectroscopy (EELS) are used to provide an element selective atomic‐scale analysis of the interface in a composite consisting of ultrathin, self‐assembled Ni nanowires, vertically epitaxied in a SrTiO3/SrTiO3(001) matrix. Spectroscopic EELS measurements evidence rather sharp interfaces (6–7 Å) with the creation of metallic NiTi bonds and the absence of nickel oxide formation is confirmed by X‐ray absorption spectroscopy measurements. The presence of these well‐defined phase boundaries, combined with a large lattice mismatch between the oxide and metallic species, gives rise to pronounced magnetoelastic effects. Self‐assembled columnar Ni:SrTiO3 composites thus appear as ideal model systems to explore vertical strain engineering in metal/oxide nanostructures

Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi

Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called Gaia–Enceladus1, leading to substantial pollution of the chemical and dynamical properties of the Milky Way. Here we identify the very bright, naked-eye star ν Indi as an indicator of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be 11.0 ± 0.7 (stat) ± 0.8 (sys) billion years. The star bears hallmarks consistent with having been kinematically heated by the Gaia–Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 billion years ago, at 68% and 95% confidence, respectively. Computations based on hierarchical cosmological models slightly reduce the above limits

Detection and Characterization of Oscillating Red Giants: First Results from the TESS Satellite

Since the onset of the "space revolution" of high-precision high-cadence photometry, asteroseismology has been demonstrated as a powerful tool for informing Galactic archeology investigations. The launch of the NASA Transiting Exoplanet Survey Satellite (TESS) mission has enabled seismic-based inferences to go full sky-providing a clear advantage for large ensemble studies of the different Milky Way components. Here we demonstrate its potential for investigating the Galaxy by carrying out the first asteroseismic ensemble study of red giant stars observed by TESS. We use a sample of 25 stars for which we measure their global asteroseimic observables and estimate their fundamental stellar properties, such as radius, mass, and age. Significant improvements are seen in the uncertainties of our estimates when combining seismic observables from TESS with astrometric measurements from the Gaia mission compared to when the seismology and astrometry are applied separately. Specifically, when combined we show that stellar radii can be determined to a precision of a few percent, masses to 5%-10%, and ages to the 20% level. This is comparable to the precision typically obtained using end-of-mission Kepler data

Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi

Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called Gaia–Enceladus1, leading to substantial pollution of the chemical and dynamical properties of the Milky Way. Here we identify the very bright, naked-eye star ν Indi as an indicator of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be 11.0±0.7 (stat) ±0.8 (sys) billion years. The star bears hallmarks consistent with having been kinematically heated by the Gaia–Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 billion years ago, at 68% and 95% confidence, respectively. Computations based on hierarchical cosmological models slightly reduce the above limits

Age dating of an early Milky Way merger via asteroseismology of the naked-eye star νν Indi

Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies. While these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to precisely date the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called \textit{Gaia}-Enceladus, leading to a substantial pollution of the chemical and dynamical properties of the Milky Way. Here, we identify the very bright, naked-eye star $\nu$\,Indi as a probe of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric, and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be $11.0 \pm 0.7$ (stat) $\pm 0.8$ (sys)$\,\rm Gyr$. The star bears hallmarks consistent with it having been kinematically heated by the \textit{Gaia}-Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 Gyr ago at 68 and 95% confidence, respectively. Input from computations based on hierarchical cosmological models tightens (i.e. reduces) slightly the above limits

Chemically sensitive amorphization process in the nanolaminated Cr2AC (A = Al or Ge) system from TEM in situ irradiation

The effect of 320 keV Xe2+ ion-irradiation in Cr2AlC and Cr2GeC is investigated in situ in the transmission electron microscope. Both compounds amorphize at moderate fluences (1013-1014 Xe cm−2) but exhibit different amorphization mechanisms, bearing witness of the major influence of the chemical composition of the nanolaminated Mn+1AXn phases. It is proposed that amorphization takes place via a direct impact amorphization process in Cr2GeC whereas it is governed by a defect accumulation process in Cr2AlC

FliPer: A global measure of power density to estimate surface gravities of main-sequence solar-like stars and red giants

International audienceAsteroseismology provides global stellar parameters such as masses, radii, or surface gravities using mean global seismic parameters and effective temperature for thousands of low-mass stars (0.8 $M_\odot$ < M < 3 $M_\odot$). This methodology has been successfully applied to stars in which acoustic modes excited by turbulent convection are measured. Other methods such as the Flicker technique can also be used to determine stellar surface gravities, but only works for log g above 2.5 dex. In this work, we present a new metric called FliPer (Flicker in spectral power density, in opposition to the standard Flicker measurement which is computed in the time domain); it is able to extend the range for which reliable surface gravities can be obtained (0.1 < log g < 4.6 dex) without performing any seismic analysis for stars brighter than $Kp$ < 14. FliPer takes into account the average variability of a star measured in the power density spectrum in a given range of frequencies. However, FliPer values calculated on several ranges of frequency are required to better characterize a star. Using a large set of asteroseismic targets it is possible to calibrate the behavior of surface gravity with FliPer through machine learning. This calibration made with a random forest regressor covers a wide range of surface gravities from main-sequence stars to subgiants and red giants, with very small uncertainties from 0.04 to 0.1 dex. FliPer values can be inserted in automatic global seismic pipelines to either give an estimation of the stellar surface gravity or to assess the quality of the seismic results by detecting any outliers in the obtained $ν_{max}$ values. FliPer also constrains the surface gravities of main-sequence dwarfs using only long-cadence data for which the Nyquist frequency is too low to measure the acoustic-mode properties