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Tuning white dwarf clocks with space-based asteroseismology

jjhermes
July 12, 2022

Tuning white dwarf clocks with space-based asteroseismology

Conference presentation, 30 min. July 2022: TASC6/KASC13 Workshop, Leueven, Belgium.

jjhermes

July 12, 2022
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  1. http://sites.bu.edu/buwd
    J.J. Hermes + WG8
    Tuning white dwarf clocks with
    space-based asteroseismology

    View Slide

  2. http://sites.bu.edu/buwd
    J.J. Hermes + WG8
    Tuning white dwarf clocks with
    space-based asteroseismology
    including Stéphane Charpinet, Keaton J. Bell, Zsófia Bognár, Steve
    Kawaler, Paulina Sowicka, Pierre Brassard, Valerie Van Grootel,
    Weikai Zong, Noemi Giammichele, Murat Uzundag, Alejandro H.
    Córsico, Agnès Bischoff-Kim, Alejandra Romero, S. O. Kepler,
    Gabriela Oliveira da Rosa, Judi Provencal, Gerald Handler, Larissa
    Antunes Amaral, Leandro G. Althaus, Paul Bradley, Uli Heber,
    Stephan Geier, Betsy Green, Dave Kilkenny, Roy Østensen, Ingrid
    Pelisoli, Roberto Silvotti, John Telting, Maya Vučković, H. L.
    Worters, Leila M. Calcaferro, Mike Montgomery, Murat Uzundag,
    Andrzej S. Baran, Hamed Ghasemi, John Debes, Piotr Kołaczek-
    Szymański, Simon J. Murphy, Andrzej Pigulski, Ádám Sódor, et al.

    View Slide

  3. ‘typical’ 0.6 solar-mass
    white dwarf
    electron degenerate
    C/O core
    (r = 8500 km)
    non-degenerate
    He layer
    (260 km) non-degenerate
    H layer
    (30 km)
    [thermal reservoir]
    [insulating blanket]
    White Dwarfs: Simple Stars, Simple Evolution*
    65,000 K (0.001 Gyr)
    25,000 K (0.02 Gyr)
    13,000 K (0.3 Gyr)
    10,500 K (0.55 Gyr)
    7100 K (1.5 Gyr)
    5100 K (5 Gyr)
    3300 K (11 Gyr)

    View Slide

  4. a 0.6 solar-mass WD evolved
    from a 1.3 solar-mass ZAMS
    star (4.5 Gyr on MS+RGB)
    in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75,
    170,000 K have the highest number of detected modes. The first class of pulsating s
    5.5 5.0 4.5
    Planetary Nebula
    Main
    sequence
    DOV
    DBV
    DAV
    4.0 3.5 3.0
    log [T
    eff
    (K)]
    4
    2
    0
    –2
    –4
    log (L/L )
    Figure 3
    White Dwarfs: Simple Stars, Simple Evolution*
    a 0.6 solar-mass WD has a
    total age of 4.5 + 0.55 =
    5.05 Gyr
    Winget & Kepler 2008
    10,500 K (0.55 Gyr)

    View Slide

  5. We Assume Stars Lose Mass Monotonically to Connect WD to ZAMS
    e.g., we can use MESA
    models to predict how
    much mass will be lost
    we calibrate with WDs
    where the total ages
    have been determined
    from cluster
    membership
    via Carl Fields
    et al. 2016
    e.g., Cummings et al. 2018

    View Slide

  6. We Have Used Gaia’s Many WDs to Empirically Test WD Ages
    Tyler Heintz, Hermes, El-Badry et al. 2022
    arXiv: 2206.00025
    eDR3: El-Badry, Rix & Heintz 2021
    Gaia revealed >1500 wide
    (>100 au) WD+WD binaries
    we have used our usual tools to assess how well
    their derived total ages agree

    View Slide

  7. We Have Used Gaia’s Many WDs to Empirically Test WD Ages
    Tyler Heintz et al. 2022
    arXiv: 2206.00025
    oops: roughly 20-35% of wide
    WD+WD have a more massive
    component that is hotter –
    its age was likely "reset”
    by a merger
    thus: 20-35% of wide WD+WD
    binaries were once triples
    in general, total WD ages are good to at least 25%
    (i.e., 4 ± 1 Gyr) but we’d like to do even better!
    (similar to pop-synth: Temmink et al. 2020)

    View Slide

  8. One Motivation for Better WD Ages: Wide WD+MS Systems
    (El-Badry, Rix & HeinB 2021)
    >15,000 wide (>100 au)
    WD+MS binaries from
    Gaia DR3
    improving WD total ages
    can improve, e.g.,
    old K/M gyrochronology
    h/t Jennifer Van Saders
    see also talk Friday by Diego Godoy-Riviera

    View Slide

  9. Testing Assumptions in Our White Dwarf Cooling Models
    • M
    H
    / M
    WD
    ~ 0.01%
    6 dex thinner H envelope
    cools ~3% slower to 6000 K
    • M
    He
    / M
    WD
    ~ 1%
    1 dex thinner He envelope
    cools ~10% slower to 6000 K
    • C/O ratio: 50% C
    A 100% O-rich core
    cools ~15-20% faster to 6000 K
    • Core crystallization
    Model ignoring release of latent heat
    cools ~40% faster to 6000 K
    ‘typical’ 0.6 solar-mass
    white dwarf
    electron degenerate
    C/O core
    (r = 8500 km)
    non-degenerate
    He layer
    (260 km) non-degenerate
    H layer
    (30 km)
    [thermal reservoir]
    [insulating blanket]

    View Slide

  10. Testing Assumptions in Our White Dwarf Cooling Models
    • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    • M
    He
    / M
    WD
    ~ 1%
    1 dex thinner He envelope
    cools ~10% slower to 6000 K
    • C/O ratio: 50% C
    a 100% O-rich core
    cools ~15-20% faster to 6000 K
    • Core crystallization
    a model ignoring release of latent heat
    cools ~40% faster to 6000 K
    ‘typical’ 0.6 solar-mass
    white dwarf
    electron degenerate
    C/O core
    (r = 8500 km)
    non-degenerate
    He layer
    (260 km) non-degenerate
    H layer
    (30 km)
    [thermal reservoir]
    [insulating blanket]

    View Slide

  11. pulsations driven at onset of
    partial ionization zone, we
    think, for all white dwarfs
    ~130,000 K for C/O-atm, DOV
    ~30,000 K for He-atm, DBV
    ~12,000 K for H-atm, DAV
    in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75
    170,000 K have the highest number of detected modes. The first class of pulsating s
    5.5 5.0 4.5
    Planetary Nebula
    Main
    sequence
    DOV
    DBV
    DAV
    4.0 3.5 3.0
    log [T
    eff
    (K)]
    4
    2
    0
    –2
    –4
    log (L/L )
    Figure 3
    Testing Assumptions in Our White Dwarf Cooling Models
    Winget & Kepler 2008

    View Slide

  12. in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75
    170,000 K have the highest number of detected modes. The first class of pulsating s
    5.5 5.0 4.5
    Planetary Nebula
    Main
    sequence
    DOV
    DBV
    DAV
    4.0 3.5 3.0
    log [T
    eff
    (K)]
    4
    2
    0
    –2
    –4
    log (L/L )
    Figure 3
    TASC WG8 Has Focused First on Increasing Number of Observed WDs

    View Slide

  13. white dwarfs are strongly
    stratified, and pulsations
    are very sensitive to
    chemical profile changes
    Fontaine & Brassard 2008
    N2
    Ll
    2
    DAV Propagation Diagram
    Core Surface
    p-modes
    σ2 > L
    l
    2, N2
    convection
    zone
    log σ2 (s-2)
    g-modes
    σ2 < L
    l
    2, N2

    View Slide

  14. • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 DAV periods, observed
    after Clemens et al. 2017
    n=1 2 3 4
    Mode Period (s)
    Romero et al. 2022

    View Slide

  15. • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 DAV periods, observed
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 random MH
    simulation
    after Clemens et al. 2017
    n=1 2 3 4
    Mode Period (s)
    Romero et al. 2012

    View Slide

  16. Most White Dwarfs Have Canonically Thick H Layer
    • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 DAV periods, observed
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 random MH
    simulation
    l=1 canonical MH
    simulation
    after Clemens et al. 2017
    Romero et al. 2012 only drawing from models
    with canonically thick MH
    n=1 2 3 4
    Mode Period (s)

    View Slide

  17. Ensemble Seismology Can Also Test Thickness of Helium Layer
    • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    • M
    He
    / M
    WD
    ~ 1%
    1 dex thinner He envelope
    cools ~10% slower to 6000 K
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 DAV periods, observed
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 random MH
    simulation
    l=1 canonical MH
    simulation
    after Clemens et al. 2017
    n=1 2 3 4
    Mode Period (s)
    Reece Boston 2022, PhD thesis
    The o set could imply
    thinner He layers
    (all models assume
    M
    He
    / M
    WD
    = 1%)

    View Slide

  18. Deeper Inside: Reaction Rates In uence on C/O Ratio
    • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    • M
    He
    / M
    WD
    ~ 1%
    1 dex thinner He envelope
    cools ~10% slower to 6000 K
    • C/O ratio: 50% C
    a 100% O-rich core
    cools ~15-20% faster
    Morgan Chidester, Farag & Timmes 2022
    arXiv: 2207.02046
    core surface
    (normalized radius)
    Each color is changing the 12C(α,γ)16O
    reaction rate by up to +/- 3 sigma:

    View Slide

  19. ß 99% of mass
    X(O) = 78.03% ± 4.2%
    X(C) = 21.96% ± 4.2%
    X(He) = 0.0113% ± 0.006%
    core surface
    Giammichele et al. 2018
    + follow-up modeling of KIC 8626021 by
    Timmes et al. 2018, Charpinet et al. 2019,
    De Gerónimo et al. 2019, Chidester et al. 2021

    View Slide

  20. STELUM Fits of 5 Kepler White Dwarfs All Imply Large Oxygen Cores
    Noemi Giammichele,
    Charpinet, Brassard: poster E1
    the cores found are more massive (by 40%) and
    more oxygen-rich (by 15%) than predicted by
    canonical evolution models for these WD masses

    View Slide

  21. • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    • M
    He
    / M
    WD
    ~ 1%
    1 dex thinner He envelope
    cools ~10% slower to 6000 K
    • C/O ratio: 50% C
    a 100% O-rich core
    cools ~15-20% faster to 6000 K
    • Core crystallization
    a model ignoring release of latent heat
    cools ~40% faster to 6000 K
    crystallization is a first-order
    phase transition, so releases
    latent heat and slows cooling
    we don’t effectively know the
    melting temperature for a C/O
    mixture from lab experiments

    View Slide

  22. Crystallization Provides a New Inner Boundary Condition
    • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    • M
    He
    / M
    WD
    ~ 1%
    1 dex thinner He envelope
    cools ~10% slower to 6000 K
    • C/O ratio: 50% C
    a 100% O-rich core
    cools ~15-20% faster to 6000 K
    • Core crystallization
    a model ignoring release of latent heat
    cools ~40% faster to 6000 K
    Francisco De Gerónimo et al. 2019
    also Montgomery & Winget 1999
    >90% of the core of a 1.16 MsunWD
    will be crystallized by the time it
    pulsates – a strong seismic signature

    View Slide

  23. we can see the imprint of crystallization in the Gaia CMD
    in fact, it appears ~10% of WDs have an extra multi-Gyr
    cooling delay, possibly from 22Ne sedimentation
    0.6 M¤
    1.2 M¤
    Tremblay et al. 2019
    Cheng et al. 2019

    View Slide

  24. Takeaway:White Dwarf Asteroseismology Can Test Cooling Models
    • M
    H
    / M
    WD
    ~ 0.01%
    106 times thinner H envelope
    cools ~3% slower to 6000 K
    • M
    He
    / M
    WD
    ~ 1%
    1 dex thinner He envelope
    cools ~10% slower to 6000 K
    • C/O ratio: 50% C
    a 100% O-rich core
    cools ~15-20% faster to 6000 K
    • Core crystallization
    a model ignoring release of latent heat
    cools ~40% faster to 6000 K
    • Improving WD ages significantly
    improves precision for their use in wide
    binaries with other stars
    • We are actively testing our cooling-
    model assumptions with seismology
    • C/O ratio and crystallization probe
    uncertain physics, including
    12C(α,γ)16O reaction rate & 22Ne diffusion

    View Slide

  25. View Slide