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Evidence from K2 for rapid rotation in the descendant of an intermediate-mass star

jjhermes
June 21, 2017

Evidence from K2 for rapid rotation in the descendant of an intermediate-mass star

Conference presentation, 12 min. June 2017: Kepler and K2 Science Conference IV, NASA Ames Research Center, Mountain View, CA, USA.

jjhermes

June 21, 2017
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  1. http://jjherm.es
    J.J. Hermes
    Hubble Fellow
    University of North Carolina
    at Chapel Hill

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  2. View Slide

  3. View Slide

  4. 1.13 ± 0.02 hr
    a 0.87 ± 0.03 M¤
    white dwarf
    4.0±0.5 M¤
    ZAMS

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  5. White dwarfs serve as empirical final boundary
    conditions to stellar evolution. So how
    fast do white dwarfs rotate?
    Expectations if conserving angular
    momentum from main sequence:
    2.5 M¤
    ZAMS Prot,initial
    : 10 hr
    à 0.6 M¤
    WD Prot,WD
    : 2 min

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  6. • Despite 220+ known pulsating
    WDs, just 16 ground-based
    measurements:
    Typical Prot
    : 0.5-2.0 days
    (not 2 min!)
    Most White Dwarfs Rotate at Roughly 0.5-2 Days
    Stars apparently shed most
    of their angular momentum
    before they become white
    dwarfs. But how?!
    • Pulsations are the best way to measure white dwarf
    rotation rates (few known with spots, v sin i not helpful)

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  7. Giant Kepler legacy: RGB cores are rotating much slower
    than any models can predict on their first ascent up AGB
    Cantiello et al. 2014
    observed (Mosser+ 2012)
    plus Tayler-Spruit (magnetic
    torques from dynamo-driven
    fields in radiative regions)
    with hydrodynamic rotational
    instabilities (e.g. Eddington-
    Sweet; Heger+ 2000)
    Internal gravity waves also insufficient (Fuller+ 2014)
    pure angular momentum
    conservation

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  8. Cantiello et al. 2014
    observed (Mosser+ 2012)
    plus Tayler-Spruit (magnetic
    torques from dynamo-driven
    fields in radiative regions)
    with hydrodynamic rotational
    instabilities (e.g. Eddington-
    Sweet; Heger+ 2000)
    Internal gravity waves also insufficient (Fuller+ 2014)
    pure angular momentum
    conservation
    Giant Kepler legacy: RGB cores are rotating much slower
    than any models can predict on their first ascent up AGB
    Essentially all constraints on angular momentum evolution
    in stars observed by Kepler are for <3 M¤
    stars

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  9. Original Kepler Mission (4 years):
    Just 20 white dwarfs observed,
    6 pulsating WDs (just two >3 months)
    K2 through Campaign 10:
    >1000 white dwarf candidates observed
    35 more pulsating WDs
    K2 has given us hundreds of
    candidate pulsating white
    dwarfs to observe

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  10. This outburst phenomenon never seen before in
    40+ years of pulsating white dwarf studies
    See poster #6
    by Keaton Bell
    A surprising discovery with Kepler: Aperiodic Outbursts
    Quiescent pulsations
    Outburst

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  11. m = +1
    m = -1
    m = 0
    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 ± 0.1 day
    Fourier transform, 75 days
    data from K2 Campaign 1
    200 s
    500 s
    1000 s
    We Can Decompose Pulsations into Spherical Harmonics

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  12. 1 10 100
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    N
    Kepler & K2
    Kawaler (2015)
    Kepler & K2 have doubled
    the number of white
    dwarfs with measured
    internal rotation
    periods using
    asteroseismology
    Hermes et al. 2017, in prep.
    None of the stars here are
    currently in binaries:
    Representative of
    single-star evolution
    Pulsation SplittingsReveal Rotation Rates
    0.5 d 1 d 2 d 4 d

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  13. 1 10 100
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    N
    Kepler & K2
    Kawaler (2015)
    Kepler & K2 have doubled
    the number of white
    dwarfs with measured
    internal rotation
    periods using
    asteroseismology
    Hermes et al. 2017, in prep.
    None of the stars here are
    currently in binaries:
    Representative of
    single-star evolution
    Pulsation SplittingsReveal Rotation Rates
    0.5 d 1 d 2 d 4 d

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  14. • EPIC 211914185, aka SDSSJ0837+1856
    • Kp
    = 18.9 mag
    • Observed with short-cadence in C5 as part
    of a search for WD transits (PI: S. Redfield)
    The most rapidly rotating pulsating WD is massive
    SDSS
    Hermes et al. 2017, ApJL, 841, L2; arXiv: 1704.08690
    500 s 200 s 118 s
    Nyquist
    ambiguity
    EPIC 211914185

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  15. The most rapidly rotating pulsating WD is massive
    500 s 200 s 118 s
    Hermes et al. 2017, ApJL, 841, L2; arXiv: 1704.08690
    Ground-based time-series photometry
    breaks Nyquist ambiguity
    EPIC 211914185

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  16. The most rapidly rotating pulsating WD is massive
    500 s 200 s 118 s
    Prot
    : 1.13 ± 0.02 hr
    Hermes et al. 2017, ApJL, 841, L2; arXiv: 1704.08690
    Ground-based time-series photometry
    breaks Nyquist ambiguity
    EPIC 211914185

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  17. The most rapidly rotating pulsating WD is massive
    SDSS
    Hermes et al. 2017, ApJL, 841, L2; arXiv: 1704.08690
    SOAR spectroscopy
    yields
    WD mass
    Teff
    : 13,590± 340 K
    log(g) = 8.434 ± 0.052
    MWD
    : 0.87 ± 0.03 M¤
    Using cluster-calibrated
    initial-to-final mass relation:
    MProg.
    : 4.0 ± 0.5 M¤
    The fastest-rotating
    pulsating white dwarf is
    also the most massive

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  18. Could This Massive White Dwarf Be a Merger Byproduct?
    Hermes et al. 2017, ApJL, 841, L2; arXiv: 1704.08690
    Evolution models suggest that <110 s
    l=1 modes can only exist in white
    dwarfs with maximally thick
    hydrogen envelopes
    à Prefer single-star evolution,
    (but main-sequence merger not
    completely ruled out)
    HST far UV
    ?

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  19. 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
    Hermes et al. 2017, in prep.
    We Can Finally Probe WD Rotation as a Function of Mass
    We have obtained WHT/SOAR spectra of all pulsating white dwarfs in
    Kepler/K2: All will be publicly available soon at k2wd.org

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  20. >70% of Field WDs between
    0.51-0.73 M¤
    (evolved 1.7-3.0 M¤
    ZAMS)
    These WDs rotate at 0.5-2.2 d
    (WD Prot
    : 35 ± 28 hr)
    Link emerging between higher
    WD mass and faster rotation
    Expect dozens to 100more
    pulsating WDs before K2 runs
    out of fuel!
    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

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  21. View Slide

  22. 100 101 102
    White Dwarf Rotation Period (hr)
    0.5
    0.6
    0.7
    0.8
    0.9
    1.0
    1.1
    1.2
    1.3
    1.4
    WD Mass (M )
    100 101 102
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    12
    14
    N
    K2 Asteroseismic
    Asteroseismic
    J1136+0409
    K2 Magnetic
    Magnetic
    1 hr 0.5 d 5 d
    2.5 M¤
    6.5 M¤
    4.5 M¤
    ZAMS
    Progenitor:
    10 min
    Burleigh et al. 1999
    2 d
    REJ0317-853, the fastest
    rotating isolated white
    dwarf (727.5 s), is both
    massive (>1.28 M¤
    )
    and strongly magnetic
    (>200 MG)
    REJ0317-853is very likely a
    merger byproduct

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  23. 0.4 0.5 0.6 0.7 0.8 0.9
    WD Mass (M⊙
    )
    0
    50
    100
    150
    WD Rotation Period (hr)
    1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
    ZAMS Progenitor Mass (M⊙
    )
    0
    50
    100
    150
    WD Rotation Period (hr)
    1 10 100
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    N
    Kepler & K2
    Kawaler (2015)
    SDSS
    SOAR VLT
    Porb
    = 6.8976 hr
    WD+dM in K2 Campaign 1
    Hermes et al. 2015, MNRAS, 451, 6219
    Close Binary Evolution Appears to Affect WD Rotation
    WD Mass: 0.60 ± 0.04 M¤
    Prot
    :
    2.5 ± 0.5 hr

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  24. Cantiello et al. 2014
    Evolution models
    including Tayler-Spruit
    0.5-2.2 d
    1.1 hr
    tHe
    = core He ignition
    Stellar evolution models including Tayler-Spruit still predict too-fast
    WD rotation, but only by factors of a few

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  25. The most rapidly rotating pulsating WD is massive
    Prot
    : 1.13 ± 0.02 hr
    Hermes et al. 2017, ApJL, 841, L2; arXiv: 1704.08690
    δf1
    = 138.626 µHz δf2
    = 124.541 µHz
    Representative weight function

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  26. Ground-based rotation rates
    of pulsating white dwarfs are hard:
    1-day (11.57 µHz) aliasing
    (18.9 hr over 5 nights on
    a 3.6-m telescope)
    V = 14.2 mag
    Actual signal
    Still, 16 WDs well-constrained
    with ground-based data:
    Prot
    = 2 hr to 2.4 d
    Giammichele et al. 2015
    1 10 100
    White Dwarf Rotation Period (hr)
    0
    1
    2
    3
    4
    5
    N
    Kawaler (2015)
    1 d 2 d

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  27. 1 d 2 d 4 d
    1.7-3.0 M¤
    ZAMS stars evolve to
    rotate at 0.5-2.2 d as WDs
    > = 0.621
    σ = 0.059
    within 1σ of
    field WDs
    (0.51-0.73)
    > =
    35 ± 28 hr
    Tremblay
    et al. 2016
    Hermes et al. 2017, in prep.

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