Pre- and post- hot subdwarfs with uncommon core masses

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

Transcript

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

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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
   

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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)
   

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

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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
   

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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
   

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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
   

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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¤
   

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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
   

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

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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:
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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?!
    

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