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Galactic archaeology and asteroseismology of white dwarf stars

jjhermes
March 11, 2021

Galactic archaeology and asteroseismology of white dwarf stars

Colloquium, 45 min. March 2021: SAC Seminar, Aarhus University, Aarhus, Denmark

jjhermes

March 11, 2021
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  1. Galactic archaeology
    and asteroseismology of
    white dwarf stars
    http://jjherm.es
    @jotajotahermes
    J.J. Hermes

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  2. View Slide

  3. View Slide

  4. JJ Hermes, Boston University | SAC Seminar | 4
    1. White Dwarfs
    are Stellar Fossils
    that We Can
    Directly Age-Date
    2. We Are Using TESS
    to Better Model These
    Stellar Fossils

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  5. • a stellar remnant that is
    no longer fusing in its
    core
    • the endpoints of
    everything < 8 M¤
    • electron degeneracy
    limits WD mass to <
    1.4 M¤
    A ‘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]
    JJ Hermes, Boston University | SAC Seminar | 5
    What Do We Mean by ‘White Dwarf’?

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  6. A ‘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]
    JJ Hermes, Boston University | SAC Seminar | 6
    White Dwarfs are Excellent for Ages: They Simply Radiate
    Their Stored Heat, Which is Not Replenished
    65,000 K (0.001 Gyr)
    25,000 K (0.02 Gyr)
    13,000 K (0.31 Gyr)
    10,500 K (0.56 Gyr)
    7100 K (1.5 Gyr)
    5100 K (5 Gyr)
    3300 K
    (11 Gyr)

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  7. Gaia has revolutionized our ability to nd white dwarfs
    Gaia Collaboration,
    Babusiaux et al. 2018
    • Before Gaia we knew of
    ~35,000 white dwarfs
    (mostly from SDSS)
    • Gentile Fusillo et al. 2019
    catalog nearly half
    a million candidates
    from Gaia DR2
    JJ Hermes, Boston University | SAC Seminar | 7

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  8. Gaia eDR3: We Are Directly Testing Ages in Wide WD+WD
    Tyler Heintz (BU), also
    Kareem El-Badry (Berkeley)
    JJ Hermes, Boston University | SAC Seminar | 8
    El-Badry, Rix & Heintz 2021:
    arXiv: 2101.05282
    1565 high-confidence, wide
    (>100 au) binaries with 2 WDs!

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  9. Soon We Will Have a Better-Calibrated Sample of Wide WD
    Co-PI: Jennifer Van Saders JJ Hermes, Boston University | SAC Seminar | 9
    200 pc sample from
    El-Badry et al. 2018, 2021
    >16,000 high-confidence, wide (>100 au) binaries with 1 WD!

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  10. 0.6 M¤
    0.9 M¤
    1.1 M¤
    Gaia Reveals Interesting Physics in White Dwarf Cooling
    JJ Hermes, Boston University | SAC Seminar | 10
    Tremblay et al. 2019

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  11. 0.6 M¤
    0.9 M¤
    1.1 M¤
    JJ Hermes, Boston University | SAC Seminar | 11
    Tremblay et al. 2019
    White dwarfs within 100 pc in Gaia
    • Gaia CMD showed an
    overdensity aside from
    expected cooling tracks

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  12. JJ Hermes, Boston University | SAC Seminar | 12
    Tremblay et al. 2019
    DA (H-atmosphere) white dwarfs within 100 pc in Gaia
    • The overdensity
    appears better focusing only
    on DA white dwarfs

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  13. 20% of core is
    crystallized
    80% of core is
    crystallized
    JJ Hermes, Boston University | SAC Seminar | 13
    Tremblay et al. 2019
    DA (H-atmosphere) white dwarfs within 100 pc in Gaia
    • The overdensity
    appears better focusing only
    on DA white dwarfs

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  14. 107.5 yr,
    0.4 M¤
    107.5 yr,
    1.3 M¤
    +100.02 yr
    Onset of crystallization
    80% of mass is
    crystallized
    JJ Hermes, Boston University | SAC Seminar | 14
    Tremblay et al. 2019
    Crystallization causes a pile-up in white dwarf cooling
    Predicted theoretically by
    Van Horn 1968

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  15. No crystallization
    Latent heat from crystallization
    Gaia Observed
    Latent heat from
    crystallization, plus
    gravitational energy
    from 16O sedimentation
    JJ Hermes, Boston University | SAC Seminar | 15
    Tremblay et al. 2019
    This overdensity is exactly where we expect crystallization!
    Gaia WD Luminosity Function

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  16. JJ Hermes, Boston University | SAC Seminar | 16
    (What is latent heat? Why does it stall cooling?)
    • Latent heat: extra energy
    required to carry out a
    first-order phase transition
    • (When smoking a brisket
    the moisture in the meat
    undergoes a 1st-order
    phase transition at 160F
    [70C] from evaporative
    cooling)

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  17. “Long after our roiling, boiling life-giving star runs out of fuel,
    it will slowly form a cold, dead, super-dense crystal sphere
    about the size of the Earth that will linger like a translucent
    tombstone.” – Deborah Netburn, The Los Angeles Times
    JJ Hermes, Boston University | SAC Seminar | 17

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  18. Adding tangential velocities to the Gaia CMD…
    100 pc sample from
    Gentile Fusillo et al. 2019 JJ Hermes, Boston University | SAC Seminar | 18
    0.6 M¤
    1.2 M¤

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  19. 1. Fundamental physics from White Dwarfs in Gaia CMD
    JJ Hermes, Boston University | SAC Seminar | 19
    • Most (>90%) of WDs Should Cool
    Predictably & Eventually Crystallize,
    Releasing Latent Heat
    • We are Testing Expectations with Wide,
    Coeval WD+WD Binaries
    65,000 K (0.001 Gyr)
    25,000 K (0.02 Gyr)
    13,000 K (0.31 Gyr)
    10,500 K (0.56 Gyr)
    7100 K (1.5 Gyr)
    5100 K (5 Gyr)
    3300 K
    (11 Gyr)

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  20. He
    P.I. zone
    (30-20 kK)
    H
    P.I. zone
    (13-10 kK)
    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
    DBV:
    aka V477 Her
    DAV:
    aka ZZ Ceti
    Fontaine & Brassard 2008
    Aerts, JCD, Kurtz 2010 JJ Hermes, Boston University | SAC Seminar | 20

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  21. White Dwarfs: g-modes, not all
    modes are observed excited
    (much like delta Scuti p-modes)
    5 min 4 min
    6 min
    Solar p-modes
    BiSON; Thompson et al. 2003
    2 min
    3 min
    4 min
    5 min
    6 min
    10 min
    JJ Hermes, Boston University | SAC Seminar | 21
    n

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  22. White Dwarfs: g-modes, not all
    modes are observed excited
    (much like delta Scuti p-modes)
    Adiabatic Model: 11,245 K, 0.632 M¤
    ,
    10-4.12 MH
    /MWD
    (Romero et al. 2012)
    2 min
    3 min
    4 min
    5 min
    6 min
    10 min
    JJ Hermes, Boston University | SAC Seminar | 22
    l=1
    l=2

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  23. KIC 08626021: Østensen et al.
    2011, 2013
    JJ Hermes, Boston University | SAC Seminar | 23
    The Most Studied Kepler Pulsating WD: A Hot DBV
    Red: Location of
    m=0 models of
    Giammichele et
    al. 2018
    Blue: Location of
    m=0 models of
    Bischoff-Kim et
    al. 2014

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  24. Core Surface
    ß 99% of mass
    X(O) = 78.03% ± 4.2%
    X(C) = 21.96% ± 4.2%
    X(He) = 0.0113% ± 0.006%
    KIC 08626021: Giammichele et
    al. 2018
    JJ Hermes, Boston University | SAC Seminar | 24
    Toulouse Models Predict A Large, O-Dominated Core

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  25. JJ Hermes, Boston University | SAC Seminar | 25
    Toulouse Models Neglected to Include Neutrino Cooling
    Timmes et al. 2018
    KIC 08626021: Giammichele et
    al. 2018

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  26. JJ Hermes, Boston University | SAC Seminar | 26
    Toulouse Models Now Updated to Include Neutrino Cooling
    KIC 08626021: Charpinet et al.
    2019
    8 observed modes &
    many free parameters
    There is great potential
    in getting this right!
    Gaia CMD position
    infers: 0.73 ± 0.12 M¤
    Black: Models of Giammichele et al. 2018
    Red: Models of Charpinet et al. 2019 including
    neutrino cooling

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  27. JJ Hermes, Boston University | SAC Seminar | 27
    7.5
    8.5 8.0
    Blue: K2 Pulsating WDs log(g) = 9
    20,000 K
    10,000 K
    Kepler/K2 Observed 90 Pulsating White Dwarfs
    Hermes et al. 2021, in prep.
    81 DAV (H-atm.) WDs
    First 27 published in Hermes et al. 2017
    Grey: All 2166 WDs
    7 DBV (He-atm.) WDs
    Analysis in Vanderbosch et al. 2021
    2 DOV (pre-WDs, C/O-atm.)

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  28. 1000 s 200 s
    500 s 125 s
    l=1
    l=2
    White Dwarf Seismologist’s Dilemma: Often Few Modes
    JJ Hermes, Boston University | SAC Seminar | 28

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  29. 1000 s 200 s
    500 s 125 s
    l=1
    l=2
    White Dwarf Seismologist’s Dilemma: Often Few Modes
    (consecutive g-modes evenly
    spaced in period, not frequency)
    JJ Hermes, Boston University | SAC Seminar | 29

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  30. l = 1
    n = 1
    l = 1
    n = 2
    l = 1
    n = 3
    SDSSJ0051+0339, g=17.6, K2 Campaign 8
    White Dwarf Seismologist’s Dilemma: Often Few Modes
    Chris Clemens et al. in prep.
    Kepler and TESS makes some short-period
    mode identification relatively trivial
    JJ Hermes, Boston University | SAC Seminar | 30

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  31. 0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    Mode Period (s)
    N
    l = 1
    n = 1
    l = 1
    n = 2
    l = 1
    n = 3
    n = 1 n = 2 n = 3 n = 4
    If we only plot identified l=1 (m=0) modes:
    White Dwarf Seismologist’s Dilemma: Often Few Modes
    Chris Clemens et al. in prep.
    JJ Hermes, Boston University | SAC Seminar | 31

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  32. 0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    Mode Period (s)
    N
    n = 1 n = 2 n = 3 n = 4
    l = 1
    n = 1
    l = 1
    n = 2
    l = 1
    n = 3
    If we only plot identified l=1 (m=0) modes:
    White Dwarf Seismologist’s Dilemma: Often Few Modes
    Chris Clemens et al. in prep.
    JJ Hermes, Boston University | SAC Seminar | 32

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  33. 0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 DAV periods, observed
    Full evolutionary models computed
    by Romero et al. 2012
    Chris Clemens et al. in prep.
    White Dwarf Seismologist’s Dilemma: Often Few Modes
    JJ Hermes, Boston University | SAC Seminar | 33

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  34. Drawing from a random distribution of all
    hydrogen layer masses
    Full evolutionary models computed
    by Romero et al. 2012
    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
    Chris Clemens et al. in prep.
    White Dwarf Seismologist’s Dilemma: Often Few Modes
    JJ Hermes, Boston University | SAC Seminar | 34

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  35. 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
    Full evolutionary models computed
    by Romero et al. 2012
    Only drawing from the models with
    canonically thick (10-4 MH
    /M★
    )
    hydrogen layers
    Chris Clemens et al. in prep.
    Most (>80%) of DAs Have Thick H Layers
    JJ Hermes, Boston University | SAC Seminar | 35

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  36. 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
    Full evolutionary models computed
    by Romero et al. 2012
    Only drawing from the models with
    canonically thick (10-4 MH
    /M★
    )
    hydrogen layers
    Chris Clemens et al. in prep.
    Most (>80%) of DAs Have Thick H Layers
    10-15 s offset: Could be that He-layer
    masses too thick in canonical models
    à Would lead to systematically
    younger WD cooling ages (~10%)
    JJ Hermes, Boston University | SAC Seminar | 36

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  37. JJ Hermes, Boston University | SAC Seminar | 37
    We Have Strong Motivation to Keep Going with TESS

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  38. JJ Hermes, Boston University | SAC Seminar | 38
    We Have Strong Motivation to Keep Going with TESS
    Blue: TESS Pulsating WDs
    Grey: All 3383 WDs with T < 17 mag 7.5
    8.5 8.0
    log(g) = 9
    20,000 K
    10,000 K
    So Far TESS Has Detected Oscillations in 62 Pulsating WDs

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  39. White Dwarfs Are Faint, But TESS Data is Still Valuable
    JJ Hermes, Boston University | SAC Seminar | 39

    View Slide

  40. White Dwarfs Are Faint, But TESS Data is Still Valuable
    JJ Hermes, Boston University | SAC Seminar | 40

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  41. WD 0158-160 (TIC 257459955): T=14.1 mag
    JJ Hermes, Boston University | SAC Seminar | 41
    Bell et al. 2019
    TESS DAVs: Bognar et al. 2020
    9 observed l=1 modes
    Gaia parallax implies a
    distance of 68.14 ± 0.28 pc
    Seismic distance, Model 2: 66.5 ± 2.5 pc
    Seismic distance, Model 1/3: 87.7 ± 7.9 pc

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  42. The 20-Second Cadence Is Often Necessary for Our Science
    JJ Hermes, Boston University | SAC Seminar | 42
    Pulsation amplitudes have been, on
    average, 35% underestimated by the
    2-min cadence so far in Cycle 3

    View Slide

  43. 2. TESS Will Keep Refining Models of White Dwarf Interiors
    JJ Hermes, Boston University | SAC Seminar | 43
    • Boutique Asteroseismology of WDs Still
    Hard, But Improving, Especially With
    Ensemble Approaches at Short Periods
    • In Many Cases, 20-second TESS
    Data Is Crucial
    • We Are Working Onwards Towards
    Constraining WD Core Compositions
    and Envelopes!
    65,000 K (0.001 Gyr)
    25,000 K (0.02 Gyr)
    13,000 K (0.31 Gyr)
    10,500 K (0.56 Gyr)
    7100 K (1.5 Gyr)
    5100 K (5 Gyr)
    3300 K
    (11 Gyr)

    View Slide

  44. Adding tangential velocities to the Gaia CMD…
    100 pc sample from
    Gentile Fusillo et al. 2019 JJ Hermes, Boston University | SAC Seminar | 44
    0.6 M¤
    1.2 M¤

    View Slide

  45. Massive WDs descended from 4-8 solar-mass ZAMS stars
    Cheng et al. 2019 JJ Hermes, Boston University | SAC Seminar | 45
    • Massive WDs
    should come from
    stars that spend
    <0.5 Gyr on the
    main sequence

    View Slide

  46. Something is delaying cooling in some massive WDs
    JJ Hermes, Boston University | SAC Seminar | 46
    • Models include
    crystallization:
    something else is
    slowing them down!
    • Fast kinematics
    suggests these have
    had their ages
    “reset”!
    • But why are they
    piling up?
    Cheng et al. 2019

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  47. 0.0 0.2 0.4 0.6 0.8 1.0
    0.0
    0.2
    0.4
    0.6
    0.8
    1.0
    Sedimentation Cooling Delay [Gyr]
    °3.5
    °3.0
    °2.5
    °2.0
    °1.5
    0
    2
    4
    Q Branch
    0.9 MØ C/O WD
    Z = 0.035
    Clustering, hNi = 3,000
    Clustering, hNi = 1,000
    Clustering, hNi = 300
    Single-particle Diffusion
    °3.5
    °3.0
    °2.5
    °2.0
    °1.5
    0
    2
    4
    Q Branch
    1.0 MØ C/O WD
    Z = 0.035
    °3.5
    °3.0
    °2.5
    °2.0
    °1.5
    0
    2
    4
    Q Branch
    1.1 MØ C/O WD
    Z = 0.035
    °3.5
    °3.0
    °2.5
    °2.0
    °1.5
    log(L/LØ)
    0
    2
    4
    Q Branch
    1.18 MØ C/O WD
    Z = 0.035
    0.0 0.2 0.4 0.6 0.8 1.0
    m [MØ]
    0.0
    0.2
    0.4
    0.6
    Mass Fraction
    22Ne
    12C
    16O
    initial
    final
    Something is delaying cooling in some massive WDs
    JJ Hermes, Boston University | SAC Seminar | 47
    • That something could be 22Ne
    sedimentation (perhaps in
    clusters) in C/O-rich cores
    Bauer et al. 2020
    Bildsten & Hall 2001

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  48. 1. Fundamental physics from White Dwarfs in Gaia CMD
    JJ Hermes, Boston University | SAC Seminar | 48
    • Most (>90%) of WDs Should Cool
    Predictably & Crystallize, Releasing Latent
    Heat
    • We are Testing Expectations with Wide,
    Coeval WD+WD Binaries
    • Pile-ups among ~7% of massive WDs
    reveal crystallization PLUS poorly
    modeled physics (perhaps related to
    mergers & sedimentation of 22Ne
    clusters?)
    65,000 K (0.001 Gyr)
    25,000 K (0.02 Gyr)
    13,000 K (0.31 Gyr)
    10,500 K (0.56 Gyr)
    7100 K (1.5 Gyr)
    5100 K (5 Gyr)
    3300 K
    (11 Gyr)

    View Slide