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    TESS first look at evolved compact pulsators

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    Author
    Charpinet, S.
    Brassard, P.
    Fontaine, G.
    Van Grootel, V.
    Zong, W.
    Giammichele, N.
    Heber, U.
    Bognár, Zs.
    Geier, S.
    Green, E. M.
    Hermes, J. J.
    Kilkenny, D.
    Østensen, R. H.
    Pelisoli, I.
    Silvotti, R.
    Telting, J. H.
    Vučković, M.
    Worters, H. L.
    Baran, A. S.
    Bell, K. J.
    Bradley, P. A.
    Debes, J. H.
    Kawaler, S. D.
    Kołaczek-Szymański, P.
    Murphy, S. J.
    Pigulski, A.
    Sódor, À.
    Uzundag, M.
    Handberg, R.
    Kjeldsen, H.
    Ricker, G. R.
    Vanderspek, R. K.
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    Affiliation
    Univ Arizona, Steward Observ
    Issue Date
    2019-12-06
    Keywords
    asteroseismology
    stars
    interiors
    stars
    oscillations
    stars
    horizontal-branch
    stars
    individual
    TIC 278659026
    subdwarfs
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    Metadata
    Show full item record
    Publisher
    EDP SCIENCES S A
    Citation
    Charpinet, S., Brassard, P., Fontaine, G., Van Grootel, V., Zong, W., & Giammichele, N. et al. (2019). TESS first look at evolved compact pulsators. Astronomy & Astrophysics, 632, A90. doi: 10.1051/0004-6361/201935395
    Journal
    ASTRONOMY & ASTROPHYSICS
    Rights
    Copyright © S. Charpinet et al. 2019. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
    Collection Information
    This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.
    Abstract
    Context. The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology. Aims. We present the discovery and detailed asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence. Methods. The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star. Results. The light curve analysis reveals that EC 21494-7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 +/- 0.009x2006;M-circle dot) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (greater than or similar to 2;M-circle dot) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 +/- 0.0010;M-circle dot), radius (0.1694 +/- 0.0081;R-circle dot), and luminosity (8.2 +/- 1.1;L-circle dot). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494-7018 has burnt similar to 43% (in mass) of its central helium and possesses a relatively large mixed core (M-core;=;0.198 +/- 0.010;M-circle dot), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)(core) = 0.16(-0.05)(+0.13)X(O)core=0.16-0.05+0.13$ X(\mathrm{O})_{\mathrm{core}}=0.16_{-0.05}<^>{+0.13} $) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain C-12(alpha,;gamma)O-16 nuclear reaction rate.
    Note
    Open access article
    ISSN
    0004-6361
    DOI
    10.1051/0004-6361/201935395
    Version
    Final published version
    Sponsors
    Centre National d'Etudes Spatiales (CNES, France)Centre National D'etudes Spatiales; Agence Nationale de la Recherche (ANR, France)French National Research Agency (ANR) [ANR-17-CE31-0018]; INSIDE project [2018-p0205, 2019-p0205]; NASA Explorer ProgramNational Aeronautics & Space Administration (NASA); Danish National Research FoundationDanmarks Grundforskningsfond [DNRF106]; ESA PRODEXEuropean Space Agency [PEA 4000119301]; Stellar Astrophysics Centre (SAC) at Aarhus University; Canada Research Chair ProgramCanada Research Chairs; National Natural Science Foundation of China (NSFC)National Natural Science Foundation of China [11833002]; China Postdoctoral Science FoundationChina Postdoctoral Science Foundation [2018M641244]; Chinese Academy of Sciences (CAMS) [GINOP-2.3.2-15-2016-00003, K-115709, K-113117, K-119517, PD-123910]; Hungarian National Research, Development and Innovation O ffice (NKFIH); Lendulet Program of the Hungarian Academy of Sciences [LP2018-7/2018]; University of the Western Cape; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [GE2506/12-1]; NCN [2016/21/B/ST9/01126]; Polish National Science Center [UMO-2017/26/E/ST9/00703, UMO-2017/25/B ST9/02218]; Australian Research CouncilAustralian Research Council; NSF Astronomy and Astrophysics Postdoctoral FellowshipNational Science Foundation (NSF) [AST-1903828]; ARC LIEF grantAustralian Research Council [LE130100104]; Australian National UniversityAustralian National University; Australian Astronomical Observatory; SkyMapper Team at ANU; Astronomy Australia Limited (AAL); Australian Government through the Commonwealth's Education Investment Fund (EIF); National Collaborative Research Infrastructure Strategy (NCRIS)Australian GovernmentDepartment of Industry, Innovation and Science; National eResearch Collaboration Tools and Resources (NeCTAR); Australian National Data Service Projects (ANDS) - National Aeronautics and Space Administration; National Aeronautics and Space AdministrationNational Aeronautics & Space Administration (NASA); National Science FoundationNational Science Foundation (NSF)
    ae974a485f413a2113503eed53cd6c53
    10.1051/0004-6361/201935395
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