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Pre- and post- hot subdwarfs with uncommon core masses

jjhermes
June 15, 2022

Pre- and post- hot subdwarfs with uncommon core masses

Conference presentation, 20 min. June 2022: sdOB10, Liege, Belgium.

jjhermes

June 15, 2022
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  1. Pre- and post- hot subdwarfs
    with uncommon core masses
    http://sites.bu.edu/buwd
    JJ Hermes

    View Slide

  2. Zooming out to the before & after of sdOBs
    uncommon (non-
    canonical) core
    masses: <0.4 M¤
    pre-sdOBs:
    Core He-burning
    giants
    post-sdOBs:
    low-mass CO-core
    white dwarfs
    Heber 2009,
    ARA&A

    View Slide

  3. Nature can form non-canonical sdBs <0.4 M¤
    Han et al. 2002
    (lines of different Z)
    sdB progenitors
    >1.8 M¤
    can ignite
    He nondegenerately,
    with core masses as
    low as ~0.32 M¤
    observationally, we measure <0.4 M¤
    sdBs in:
    • 2M 1533+3759: For et al. 2010 (eclipsing binary)
    • 2M 1938+4603: Barlow et al. 2012 (Rømer delay)
    • TIC 278659026: Charpinet et al. 2019 (seismology)

    View Slide

  4. Zooming out to the before & after of sdOBs
    Heber 2009,
    ARA&A
    What are the
    lowest-mass
    CO-core WDs?

    View Slide

  5. What is the lowest-mass CO-core white dwarf?
    Non-canonical sdBs
    will evolve into < 0.4 M¤
    CO-core WDs
    Prada Moroni &
    Straniero 2009
    He vs. CO WD could be
    distinguished by:
    • Precise mass/radius
    observations
    • Asteroseismology
    Asymptotic mean period
    spacing for dipole modes:
    • 0.3 M¤
    He-core: Δπ = 75 s
    • 0.3 M¤
    CO-core: Δπ < 60 s

    View Slide

  6. What is the lowest-mass CO-core white dwarf?
    Parsons et al. 2017
    He-core
    models
    C/O-core
    models
    Thick H
    (10-4)
    Thin H
    (10-10)
    Double-lined WD+dM best
    test for He vs. CO core

    View Slide

  7. What is the lowest-mass CO-core white dwarf?
    Parsons et al. 2020
    Double-lined WD+dM best
    test for He vs. CO core
    (Still no CO-cores detected
    with significance)
    SDSS J115219.99+024814.4

    View Slide

  8. What is the lowest-mass CO-core white dwarf?
    Kosakowski et al. 2022
    Double-lined WD+dM best
    test for He vs. CO core
    ZTF is finding many more
    systems with eclipsing WDs
    3 of 4 recent eclipsing have log(g)
    which imply 0.36 < M
    WD
    < 0.45 M¤

    View Slide

  9. Zooming out to the before & after of sdOBs
    What can core
    He-burning giants
    tell us about non-
    canonical sdBs?
    Heber 2009,
    ARA&A

    View Slide

  10. RGB pulsations driven by turbulent convection
    Chaplin & Miglio 2013, ARA&A
    Max. peak of solar-like
    oscillations scales with
    surface gravity

    View Slide

  11. RGB pulsations driven by turbulent convection
    García & Ballot 2019
    Max. peak of solar-like
    oscillations scales with
    surface gravity
    Large frequency
    separation scales with
    mean density
    Leads to scaling relations:

    View Slide

  12. Red giants also have core-probing g-modes
    Bedding et al. 2011
    He-burning
    H-burning
    We can separate
    H- vs. He-burning
    stars on RGB by
    period spacing of
    the mixed-modes
    ~7000 CHeB with
    Kepler monitoring

    View Slide

  13. Some He-burning giants are likely stripped!
    Yaguang Li et al. 2022
    Of the 7000 CHeB RGB stars in Kepler:
    • ~7 are underluminous – smaller cores
    • ~32 are too low-mass for single-star evolution

    View Slide

  14. Some He-burning giants are likely stripped!
    Yaguang Li et al. 2022
    Of the 7000 CHeB RGB stars in Kepler:
    • ~7 are underluminous – smaller cores
    • ~32 are too low-mass for single-star evolution

    View Slide

  15. Some He-burning giants are likely stripped!
    Of the 7000 CHeB RGB stars in Kepler:
    • ~7 are underluminous – smaller cores
    • ~32 are too low-mass for single-star evolution
    MESA models with
    and without mass loss
    Yaguang Li et al. 2022

    View Slide

  16. Some He-burning giants are likely stripped!
    Of the 7000 CHeB RGB stars in Kepler:
    • ~7 are underluminous – smaller cores
    • ~32 are too low-mass for single-star evolution
    MESA models with
    and without mass loss
    Models >1.8 M¤
    end
    up underluminous
    after RLOF
    Yaguang Li et al. 2022

    View Slide

  17. Some He-burning giants are likely stripped!
    Yaguang Li et al. 2022
    Of the 7000 CHeB RGB stars in Kepler:
    • ~7 are underluminous – smaller cores
    • ~32 are too low-mass for single-star evolution
    None of the three
    underluminous
    CHeB giants with
    multi-epoch
    APOGEE/LAMOST
    spectra show large
    RV variability yet
    eRV
    < 0.1 km/s

    View Slide

  18. Pre- and post- sdOBs with small core masses
    <0.4 M¤
    CO-core
    white dwarfs likely
    exist, but eclipses
    not yet revelatory
    New analysis of
    Kepler data shows
    core He-burning
    giants with small
    cores: stripped,
    sdB analogues
    0.09% ± 0.04% of
    all CHeB are
    underluminous Heber 2009,
    ARA&A
    : where are the companions?!

    View Slide