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Stellar Autopsies from White Dwarf Pulsations

Stellar Autopsies from White Dwarf Pulsations

Colloquium, 45 min. May 2018: University of Hawaii, Manoa, HI.

jjhermes

May 16, 2018
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  1. http://jjherm.es
    J.J. Hermes
    Hubble Fellow
    University of North Carolina
    at Chapel Hill
    Stellar Autopsies from
    White Dwarf Pulsations

    View Slide

  2. All low-mass stars eventually run out of fuel, lose
    their envelope, and become a white dwarf
    More than 97% of all stars in our Galaxy
    are or will become white dwarfs

    View Slide

  3. D. Berry, GSFC
    White dwarf stars mark the endpoints
    of stellar, binary and planetary evolution

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  4. Outline: Kepler/K2 Insights into White Dwarfs
    • Rotation
    § White dwarfs relatively slow (0.5-2.2 d), solid-body rotation
    • Ages
    § Seismology constrains white dwarf H and He layers
    § Cooling ages in our models could be wrong by up to 10%
    • A New Phase of Low-Mass Stellar Evolution
    § Rogue waves on the coolest pulsating white dwarfs

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  5. Kepler
    12 May 2009 –
    11 May 2013

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  6. View Slide


  7. Steve Howell
    The solar pressure on the Kepler spacecraft is ~50 µN m-2

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  8. Ecliptic
    K2 Campaign 18
    began on Sunday!

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  9. Original 4-year Kepler Mission:
    Just 20 white dwarfs observed
    K2 through Campaign 8:
    >900 white dwarfs
    K2 through Campaign 15:
    >1750 white dwarfs
    K1
    K2, as of 2016
    K2, today
    Through Campaign 17:
    >2250 white dwarfs

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  10. In K2 Campaign 6 we found an interacting
    WD+WD binary (AM CVn-type) orbiting one
    another every 15.7 minutes!
    Green, Hermes et al. 2018

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  11. Vanderburg et al. 2015
    The first transits of a white
    dwarf were discovered in
    K2 Campaign 1
    (rare: so far a one-off in
    >1750 WDs with K2 data)
    The object is disintegrating
    4RWD
    model
    Gänsicke et al. 2016

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  12. GD 1212, Hermes et al. 2014a
    Data from the 9-day K2 engineering test run, 2014 January
    V=13.3 mag

    View Slide

  13. View Slide

  14. (Astero)Seismology
    White Dwarf Earth
    We match the observed periods to
    models to discern stellar interior!

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  15. A ‘typical’ 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 are cosmic timepieces:
    They are excellent age indicators
    But we must tune the clocks!

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  16. Gaia will eventually uncover more than 300,000 new
    white dwarfs (just ~35,000 known today)
    GBP
    - GRP
    MG
    >31,000 WDs w/in 200pc!

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  17. SLoWPoKES:
    Dhital et al. 2015
    Lots of science using white dwarfs in wide
    binaries as age calibrators
    5” 5” 5”

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  18. g-modes—remarkably similar to the large-amplitude DAV pulsators (Winget et al. 19
    The observed pulsating white dwarf stars lie in three strips in the H-R diagram,
    in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 7
    170,000 K have the highest number of detected modes. The first class of pulsating
    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
    A 13-Gyr isochrone with z = 0.019 from Marigo et al. (2007), on which we have drawn the obs
    Annu. Rev. Astro. Astrophys. 2008.46:157-199. Downloaded fr
    by University of Texas - Austin on 01/28/09. For
    Winget & Kepler 2008
    H
    He
    C/O
    Not all white dwarfs pulsate: We must select them!

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  19. GBP
    - GRP
    MG
    >31,000 WDs w/in 200pc
    MG
    GBP
    - GRP
    4% “most variable”
    WDs w/in 200pc
    DAV (H-atm)

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  20. Mike Montgomery
    Pulsations are periodic
    brightness changes,
    caused by surface
    temperature
    variations
    hotter
    cooler

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  21. m = -1
    m = +1
    m = 0
    1000 s 200 s
    500 s 125 s
    316.8 s
    345.3 s
    n = Number of radial nodes
    l = Number of vertical nodes
    m = Number of horizontal + vertical nodes
    n
    l = 1
    n = 5
    l = 1
    n = 6
    Prot
    = 0.9
    ± 0.2 day
    Typical K2 data from a
    pulsating white dwarf

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  22. Model-Independent Rotation Falls Readily from K2 Data
    Hermes et al. 2017d
    k2wd.org

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  23. 1 10 100
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    N
    Kepler & K2
    Kawaler (2015)
    Most isolated white
    dwarfs rotate between
    0.5-2.2 days
    Hermes et al. 2017d: k2wd.org
    None of the stars are
    currently in binaries:
    Representative of
    single-star evolution
    of mostly 1-3 M¤
    stars
    Model-Independent Rotation Falls Readily from K2 Data
    0.5 d 1 d 2 d 4 d

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  24. SDSS
    SOAR spectroscopy
    yields
    WD mass
    We have
    obtained SOAR
    spectra of all
    pulsating white
    dwarfs observed
    so far by K2
    Hermes et al. 2017d: k2wd.org

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  25. 1 10 100
    WD Rotation Period (hr)
    0.4
    0.5
    0.6
    0.7
    0.8
    0.9
    WD Mass (M⊙
    )
    1.0
    1.5
    2.0
    2.5
    3.0
    3.5
    4.0
    ZAMS Progenitor Mass (M⊙
    )
    1 10 100
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    N
    Kepler & K2
    Kawaler (2015)
    1 d 2 d 4 d
    We Can Finally Probe WD Rotation as a Function of Mass
    The fastest-rotating pulsating white dwarf (1.13 hr) is also the most
    massive (0.87 M¤
    ) – descended from a single 4.0 M¤
    ZAMS progenitor
    Hermes et al. 2017c
    Hermes et al. 2017d: k2wd.org

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  26. Most white dwarfs evolve
    from 0.9-3.0 M¤
    ZAMS stars,
    and rotate at 0.5-2.2 days
    (Possible link emerging between
    higher white dwarf mass and
    faster rotation)
    1 10 100
    0
    1
    2
    3
    4
    N
    1.7 2.0 M ZAMS
    WD Prot = 1.48 ± 0.94 d
    1 10 100
    0
    1
    2
    3
    4
    N
    2.0 2.5 M ZAMS
    WD Prot = 1.35 ± 0.74 d
    1 10 100
    0
    1
    2
    3
    4
    N
    2.5 3.0 M ZAMS
    WD Prot = 1.32 ± 1.04 d
    1 10 100
    White Dwarf Rotation Period (hr)
    0
    1
    2
    3
    4
    N
    3.5 4.0 M ZAMS
    WD Prot = 0.17 ± 0.15 d
    We Can Finally Probe WD Rotation as a Function of Mass
    Hermes et al. 2017d: k2wd.org

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  27. in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75,000 K to
    170,000 K have the highest number of detected modes. The first class of pulsating stars to be
    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
    A 13-Gyr isochrone with z = 0.019 from Marigo et al. (2007), on which we have drawn the observed
    locations of the instability strips, following the nonadiabatic calculations of C´
    orsico, Althaus & Miller
    Bertolami (2006) for the DOVs, the pure He fits to the observations of Beauchamp et al. (1999) for the
    DBVs, and the observations of Gianninas, Bergeron & Fontaine (2006) and Castanheira et al. (2007, and
    references therein) for the DAVs.
    172 Winget ·Kepler
    2.5 M¤
    A star:
    Prot,ZAMS
    ~ 10 hr
    Core-He RGB: modes
    ~0.02-0.10 R¤
    Prot
    : 30-180 d
    White dwarf: ~0.005-0.013 R¤
    Prot
    : 0.5-2.2 d
    10 100
    Secondary Clump Rotation Period (d)
    0
    1
    2
    3
    4
    5
    6
    7
    8
    N
    Deheuvels et al. 2015
    Tayar et al., in prep.
    1 10 100
    WD Rotation Period (hr)
    0.4
    0.5
    0.6
    0.7
    0.8
    0.9
    WD Mass (M⊙
    )
    1.0
    1.5
    2.0
    2.5
    3.0
    3.5
    4.0
    ZAMS Progenitor Mass (M⊙
    )
    1 10 100
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    N
    Kepler & K2
    Kawaler (2015)
    Kepler has
    mapped internal
    rotation evolution
    all the way from
    MS to WD

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  28. White Dwarfs Do Not Rotate Differentially (Solid Body)
    Based on detailed
    asteroseismic model:
    PG0112+104 rotates
    rigidlyover its outer
    70% in radius with a
    period of
    Prot
    = 10.18 ± 0.27 hr
    White dwarfs
    appear to lack
    radial differential
    rotation
    Giammichele et al. 2018, in prep.

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  29. Used to Be, Getting Data Required
    Going to the Telescope

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  30. View Slide

  31. *PG 1159 star = hot pre-white-dwarf (aka DOV)

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  32. Vauclair et al. 2002
    Maidanak Observatory,
    Uzbekistan
    2-week coordinated, global (14-site)
    Whole Earth Telescope run in 1994

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  33. THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev

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  34. Jul 27th
    Uzbeks introduced new rules for the visas ... spent long
    8 night hours in the old stinking Russian bus, which,
    using longest possible route and stopping more than ten
    times for the repairs, after which passengers were
    supposed to push the bus to start the engine, brought us
    to Shakhrisabz.
    Jul 28th
    Old military jeep, which exhaust went more inside
    than via its pipes, after 5 hours brought us to
    Maidanak [Observatory]. ... Some windows of our
    living house were broken, no clean sheets ... no
    butter, meat, sugar. Running water system was not
    working anymore, not to mention hot water.
    THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev

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  35. Jul 29th
    I checked telescope; tracking and positioning were
    working, but telescope mirrors needed cleaning...
    Jul 30th
    Managed to repair distiller and to get 3 L of water late
    in the evening only. Decided to wash mirrors next day.
    Still lots of yellow Afghanistan dust in the sky.
    Jul 31st
    Washed mirrors, cleaned telescope inner surfaces from
    thick dust layer. Started the full scale system test.
    THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev

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  36. Aug 1st
    All day no clouds, but wind increasing to the
    evening. Worked all night.
    Aug 3rd
    All day clear sky with some clouds. Quite strong wind in
    day time but diminished before the night.
    THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev

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  37. Aug 5th
    It was first night there on the mountain without me. I was
    at that time in Kitab Hospital severely injured by the
    Tashkent Astrophysical Institute Director son Iskander
    Yuldashbaev, apparently mentally ill young man of about 21.
    THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev

    View Slide

  38. Aug 5th
    It was first night there on the mountain without me. I was
    at that time in Kitab Hospital severely injured by the
    Tashkent Astrophysical Institute Director son Iskander
    Yuldashbaev, apparently mentally ill young man of about 21.
    He did some cleaning ... suddenly saying no words grabbed my
    hair with his left hand and hit my throat with a broken
    knife from our kitchen. I ran in horror, but he managed to
    hit me twice into my back. I ran to the Russian house for
    the help all in the blood. It was no phone connection with
    outside world and two of them had to run all the way to
    Maidanak to soldiers, and in three hours at last I was
    delivered to Kitab hospital in rather weak condition.
    THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev

    View Slide

  39. THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev
    Aug 5th
    It was first night there on the mountain without me. I was
    at that time in Kitab Hospital severely injured by the
    Tashkent Astrophysical Institute Director son Iskander
    Yuldashbaev, apparently mentally ill young man of about 21.
    He did some cleaning ... suddenly saying no words grabbed my
    hair with his left hand and hit my throat with a broken
    knife from our kitchen. I ran in horror, but he managed to
    hit me twice into my back. I ran to the Russian house for
    the help all in the blood. It was no phone connection with
    outside world and two of them had to run all the way to
    Maidanak to soldiers, and in three hours at last I was
    delivered to Kitab hospital in rather weak condition.
    ... He is in a custody now and cannot say the reason either,
    says he did not like the way I looked at him. But he was
    smart enough to steal before that event good sum of my money
    ... Until helicopter arrived I explained the basics of the
    work with the quilt program to Alexey -- my assistant.
    Luckily I trained him on almost everything...

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  40. Aug 10th
    Alexey arrived from the Maidanak in the afternoon.
    Everything seems OK.
    Aug 11th Aug 12th
    I lived in the Russian hotel in Kitab ... working with
    data: writing logs, marking bad points. Tomorrow night
    Uzbeks promised to bring me to the Samarkand airport.
    My throat is swollen, still hurts and ugly.
    END OF CAMPAIGN HERE IN THE UZBEKISTAN
    ------------------------------------------------------------------------
    THE MAIN LOG
    Observations at Maidanak observatory in Uzbekistan. Aug 1994
    Observers: E. Meistas, and local assistant Alexey V. Chernyshev
    Aug 8th
    I ... practically defected from Kitab hospital, where
    black bugs were running on the walls at night even in
    the patient's beds, over the face too. Throat is badly
    swollen and hurts.

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  41. View Slide

  42. View Slide

  43. Today We Are Spoiled with
    Telescopes in Space

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  44. View Slide

  45. 1000 s 200 s
    500 s 125 s
    White Dwarfs: g-modes, not all
    modes are observed excited
    BiSON; Thompson et al. 2003
    5 min 4 min
    6 min
    Solar p-modes

    View Slide

  46. n = Number of radial nodes
    l = Number of vertical nodes
    n
    Each white dwarf has a spectrum of g-modes:
    standing waves that naturally resonate
    Adiabatic Model: 11,245 K, 0.632 M¤
    ,
    10-4.12 MH
    /MWD
    (Romero et al. 2012)
    1000 s 200 s
    500 s 125 s
    l=1
    l=2

    View Slide

  47. n = Number of radial nodes
    l = Number of vertical nodes
    n
    1000 s 200 s
    500 s 125 s
    l=1
    l=2
    l=1
    l=2

    View Slide

  48. n = Number of radial nodes
    l = Number of vertical nodes
    n
    1000 s 200 s
    500 s 125 s
    l=1
    l=2
    l=1
    l=2

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  49. If we only plot identified l=1 modes:
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l = 1
    n = 1
    l = 1
    n = 2
    l = 1
    n = 3
    Kepler makes mode identification
    relatively trivial
    Mode Period (s)
    N
    SDSSJ0051+0339, g=17.6, K2 Campaign 8
    n = 1 n = 2 n = 3 n = 4
    Clemens, Dunlap, Hermes et al. 2018, in prep.

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  50. 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
    Clemens, Dunlap, Hermes et al. 2018, in prep.
    If we only plot identified l=1 (m=0) modes:
    Kepler makes mode identification
    relatively trivial

    View Slide

  51. 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
    Clemens, Dunlap, Hermes et al. 2018, in prep.
    If we only plot identified l=1 (m=0) modes:
    Kepler makes mode identification
    relatively trivial

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  52. 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
    Clemens, Dunlap, Hermes et al. 2018, in prep.

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  53. Drawing from a random distribution of
    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 hDAV 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
    Clemens, Dunlap, Hermes et al. 2018, in prep.

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  54. Most (>80%) DA White Dwarfs Have Thick H Layers
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 hDAV 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 hydrogen layers
    Clemens, Dunlap, Hermes et al. 2018, in prep.

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  55. Asteroseismology:Model He Layers Too Thick
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 hDAV periods, observed
    0
    1
    2
    3
    4
    5
    6
    7
    8
    50 100 150 200 250 300 350 400 450
    l=1 canonical MH
    simulation
    Full evolutionary models computed
    by Romero et al. 2012
    10-15 s offset: Suggests He-layer
    masses too thick in canonical models
    à Would lead to systematically
    younger WD cooling ages (~10%)
    Only drawing from the
    models with canonically
    thick hydrogen layers
    Clemens, Dunlap, Hermes et al. 2018, in prep.

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  56. We Have Only Scratched the Surface of Analyzing the
    ~100 Pulsating White Dwarfs Observed by Kepler
    WDs Evolve (Cool) à
    Blue: Observed by Kepler
    Open: Ground-based

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  57. Coming Soon: NASA/TESS will observe all bright WDs every 2 min
    All systems nominal.
    Sector 1 planned to start end of June!
    At least 28 days per sector
    ~70 I < 16 mag white dwarfs per sector

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  58. 2 Bell et al.
    Fig. 1.— Representative sections of the
    Kepler
    light curve of KIC 4552982 in units of days since the start of observations. The top p
    shows the full Q11 light curve. The one-month shaded region in the top panel is expanded in the middle panel. The one-week sh
    region in the middle panel is expanded in the bottom panel. The solid line is the light curve smoothed with a 30-minute window.
    point-to-point scatter dominates the pulsation amplitudes in the light curve, so pulsations are not apparent to the eye. The dram
    increases in brightness are discussed in detail in Section 3.
    to medium-resolution spectra for the white dwarf and fit
    the Balmer line profiles to models to determine its val-
    tion rate. We summarize our findings and conclud
    Section 5.
    KIC 4552982: Bell et al. 2015
    3 months:
    1 month:
    1 week:
    Brightenings
    every ~2.7 d,
    lasting for
    4.0-25.0 hr
    A surprising discovery with Kepler: Aperiodic Outbursts

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  59. This outburst phenomenon never seen before in
    40+ years of pulsating white dwarf studies
    A surprising discovery with Kepler: Aperiodic Outbursts
    Quiescent pulsations
    (1151.9 s, 1160.8 s, …)
    In Outburst
    (999.9 s, 896.6 s, …)
    PG 1149+057: Hermes et al. 2015b

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  60. • White dwarf Teff
    = 11,060 K
    • é 15% mean flux = é 750 K
    • ~1034 erg energy
    Black line is
    30-min running mean
    Event 1
    Event 7
    Quiescence
    Pulsations Persist in Outburst, But Surface >700 K Hotter

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  61. A surprising discovery with Kepler: Aperiodic Outbursts
    Keaton Bell 2017 (PhD thesis)
    Outbursts seen in at least 13 white
    dwarfs (this is not rare!)
    None of the outbursts in pulsating
    WDs are periodic; appear chaotic
    Outburst recurrence times can be
    as short as a few hours and as long
    as 45+ days

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  62. The vast majority of cool pulsating white dwarfs outburst!
    All white dwarfs pulsate at the appropriate temperature,
    and it appears all outburst at some point, too.
    This is likely a new phase of stellar evolution!
    Outbursting
    DAVs
    Blue: Observed by Kepler
    Open: Ground-based

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  63. GD 1212, Hermes et al. 2014a
    Data from the 9-day K2 engineering test run
    V=13.3 mag

    View Slide

  64. A surprising discovery with Kepler: Aperiodic Outbursts
    Quiescent pulsations
    (1135.2 s, 856.9 s, …)
    In Outburst
    (864.1 s, 846.4 s, …)
    GD 1212: Hermes et al. 2018, in prep.
    >60 days between outbursts!
    K2 Campaign 12

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  65. The vast majority of cool pulsating white dwarfs outburst!
    All white dwarfs pulsate at the appropriate temperature,
    and it appears all outburst at some point, too.
    This is likely a new phase of stellar evolution!
    Outbursting
    DAVs
    Blue: Observed by Kepler
    Open: Ground-based

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  66. 150 s
    1000 s
    The coolest
    pulsating white
    dwarfs have
    longer-period
    pulsations
    à Higher mode
    density for coupling

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  67. • Wu & Goldreich (2001) predicted nonlinear mode coupling could
    transfer energy into damped modes in the cool DAVs
    l=1
    l=2
    Adiabatic Model: 11,245 K, 0.632 M¤
    , 10-4.12 MH
    /MWD
    Observed: 11,060(170) K, 0.64(0.03) M¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)
    Likely Cause: Mode Coupling via Parametric Resonance
    ωp
    = 897.7 µHz
    (l=1, m=0, n=24)
    à Standing waves
    Evanesce ß

    View Slide

  68. • Wu & Goldreich (2001) predicted nonlinear mode coupling could
    transfer energy into damped modes in the cool DAVs
    ωp
    = 897.7 µHz
    (l=1, m=0, n=24)
    ωd1
    = 435.9 µHz
    (l=2, m=0, n=88)
    l=1
    l=2
    ωd2
    = 461.9 µHz
    (l=1, m=0, n=48)
    Adiabatic Model: 11,245 K, 0.632 M¤
    , 10-4.12 MH
    /MWD
    Observed: 11,060(170) K, 0.64(0.03) M¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)
    Likely Cause: Mode Coupling via Parametric Resonance
    ωd1
    + ωd2
    = ωp
    + δω
    Limit cycle if: δω < γd

    View Slide

  69. ωp
    = 897.7 µHz
    (l=1, m=0, n=24)
    ωd1
    = 435.9 µHz
    (l=2, m=0, n=88)
    l=1
    l=2
    ωd2
    = 461.9 µHz
    (l=1, m=0, n=48)
    Adiabatic Model: 11,245 K, 0.632 M¤
    , 10-4.12 MH
    /MWD
    Observed: 11,060(170) K, 0.64(0.03) M¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)
    Likely Cause: Mode Coupling via Parametric Resonance
    ωd1
    + ωd2
    = ωp
    + δω
    Limit cycle if: δω < γd

    View Slide

  70. View Slide

  71. Key Takeaways
    • Kepler/K2 has us in a new regime of looking at white dwarfs
    • Rotation: Stars lose most core angular momentum before WD stage
    § The endpoints of 1-3 solar-mass stars rotate at 0.5-2.2 days
    § They are not rotating with any detectable radial differential rotation
    § Evidence for trend of faster rotation with higher mass
    • Ages: It is rare for white dwarfs to have thin H layers
    § Seismology suggests >80% of DAs have H layers ~10-4 MH
    /Mstar
    § We see evidence that the He layers from models are 10x too thick
    § Cooling ages may be overestimated by up to 10%
    • Outbursts: Nonlinear mode coupling rampant in pulsating WDs
    § Nearly all cool pulsating WDs undergo stochastic outbursts ~1034 erg
    § Parametric resonance of excited mode(s) with damped daughter modes

    View Slide

  72. KIC08626021: Giammichele et al. 2018
    Core Surface
    ß 99% of mass
    X(O) = 78.03% ± 4.2%
    X(C) = 21.96% ± 4.2%
    X(He) = 0.0113% ± 0.006%
    With enough pulsation modes we can model entire white dwarf
    C/O ratio
    constrains
    12C(α,γ)16O
    reaction rate

    View Slide