Mining the future of low-mass, core-He-burning hot subdwarfs

Conference presentation, 20 min. June 2019: 9th Hot Subdwarf Meeting, Hendaye, France.

Transcript

1. Mining the Future of Low-Mass,
   Core-He-Burning Hot Subdwarfs
   http://jjherm.es
   @jotajotahermes
   J.J. Hermes
   

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2. JJ Hermes, Boston University | sdOB9-Hendaye | 2
   David Schneider
   (on Tuesday)
   Let’s talk about non-canonical-mass hot subdwarfs!
   

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3. • There is good evidence for <0.4 M¤
   sdBs
   • Core-He-burning subdwarfs descending from
   >2 M
   ¤
   stripped progenitors should exist
   • These sdBs will evolve into <0.4 M¤
   CO-core WDs
   • Is there evidence for <0.4 M¤
   CO-core WDs?
   • Gaia CMD
   • Asteroseismology
   • Eclipsing binaries
   JJ Hermes, Boston University | sdOB9-Hendaye | 3
   

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4. Observational Evidence of Low-Mass Hot Subdwarfs
   2M 1533+3759
   0.376 ± 0.055 M¤
   0.166 ± 0.007 R¤
   JJ Hermes, Boston University | sdOB9-Hendaye | 4 For et al. 2010
   from lightcurve fits
   

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5. Observational Evidence of Low-Mass Hot Subdwarfs
   2M 1938+4603
   0.372 ± 0.024 M¤
   (if e < 10-4)
   Barlow et al. 2012
   JJ Hermes, Boston University | sdOB9-Hendaye | 5
   from Rømer delay
   

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6. Observational Evidence of Low-Mass Hot Subdwarfs
   TIC 278659026
   0.391 ± 0.013 M¤
   0.1694 ± 0.0081 R¤
   Charpinet et al. 2019
   (from Tuesday)
   JJ Hermes, Boston University | sdOB9-Hendaye | 6
   from seismology
   

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7. Hot Subdwarfs Could Have Masses Down to 0.31 M
   ¤
   • Stripped progenitors >1.7 M¤
   can nondegenerately
   ignite He with core
   masses at ~0.31 M¤
   JJ Hermes, Boston University | sdOB9-Hendaye | 7 Han et al. 2013
   Han et al. 2012
   Z=0.02
   Z=0.02, normal tip of FGB
   Z=0.004
   First CE ejection
   First stable RLOF channel
   Merger
   

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8. Hot Subdwarfs Could Have Masses Down to 0.31 M
   ¤
   • sdBs are the only way to make a <0.4 M¤
   CO-core WD
   JJ Hermes, Boston University | sdOB9-Hendaye | 8
   Prada Moroni &
   Straniero 2009
   Mass of the H-exhausted core
   see also Iben &
   Tutukov 1985
   

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9. Can We Find <0.4 M
   ¤
   CO-Core White Dwarfs?
   • CO-core white dwarfs have
   much smaller radii than
   He-core white dwarf of the
   same mass
   • At 17,000 K, an He-core WD
   has a >10% bigger radius
   than a CO-core WD
   JJ Hermes, Boston University | sdOB9-Hendaye | 9
   Prada Moroni &
   Straniero 2009
   

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10. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    • Gaia CMD position of WDs w/ log(g) < 7.5 and high-
    quality (σ < 0.035 dex) spectroscopy
    JJ Hermes, Boston University | sdOB9-Hendaye | 10
    spectroscopic log(g)
    Montreal White
    Dwarf Database
    log(g) = 7.0
    log(g) = 7.5
    25kK
    5kK
    

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11. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    JJ Hermes, Boston University | sdOB9-Hendaye | 11
    spectroscopic log(g) –
    photometric log(g)
    log(g) = 7.0
    log(g) = 7.5
    Smaller difference:
    WD is underluminous
    

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12. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    • Asteroseismology is another precise way to determine
    mean stellar density
    • Asymptotic mean period spacing for l=1 dipole modes
    • 0.3 M¤
    He-core: Δπ = 75 s
    • 0.3 M¤
    CO-core: Δπ < 60 s
    JJ Hermes, Boston University | sdOB9-Hendaye | 12
    

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13. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    JJ Hermes, Boston University | sdOB9-Hendaye | 13
    Known Pulsating WD
    

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14. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    • Double-lined eclipsing (WD+dM) binaries
    JJ Hermes, Boston University | sdOB9-Hendaye | 14 Parsons et al. 2017
    He-core
    models
    C/O-core
    models
    Thick H (10-4)
    Thin H (10-10)
    

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15. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    JJ Hermes, Boston University | sdOB9-Hendaye | 15 Hallakoun et al. 2016
    SDSSJ1152+0248: WD+WD from K2 Campaign 1
    T1
    = 25,500 ± 1000 K
    log(g)1
    = 7.42 ± 0.25 SED: T2
    = 14,340 K
    

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16. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    JJ Hermes, Boston University | sdOB9-Hendaye | 16
    SDSSJ1152+0248
    Parsons et al. 2019
    (in prep., please no Tweets)
    X-shooter
    HiPERCAM
    

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17. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    JJ Hermes, Boston University | sdOB9-Hendaye | 17
    SDSSJ1152+0248
    M1
    : 0.362 ± 0.014 M¤ M2
    : 0.325 ± 0.013 M¤
    R1
    : 0.0212 ± 0.0003 R¤ R2
    : 0.0191 ± 0.0004 R¤
    Parsons et al. 2019
    (in prep., please no Tweets)
    

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18. Can We Find <0.4 M
    ¤
    CO-Core White Dwarfs?
    JJ Hermes, Boston University | sdOB9-Hendaye | 18
    21.9 min (1312 s)
    @ 0.5% amp
    ZZ Ceti pulsations!
    Parsons et al. 2019
    (in prep., please no Tweets)
    

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19. Evidence for 0.3-0.4 M
    ¤
    sdBs Evolving Into 0.3-0.4 M
    ¤
    WDs
    JJ Hermes, Boston University | sdOB9-Hendaye
    • There is good evidence for <0.4 M¤
    sdBs
    • Core-He-burning subdwarfs descending from
    >2 M
    ¤
    stripped progenitors should exist
    • These sdBs will evolve into <0.4 M¤
    CO-core WDs
    • Is there evidence for <0.4 M¤
    CO-core WDs?
    • Gaia CMD
    • Asteroseismology
    • Eclipsing binaries
    possible CO-core WD(s) in
    the pulsating WD+WD
    binary SDSSJ1152+0248
    (maybe)
    

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