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When flux standards go wild: White dwarfs in the era of space photometry

jjhermes
February 19, 2020

When flux standards go wild: White dwarfs in the era of space photometry

Colloquium, 45 min. February 2020: Joint STScI/JHU Colloquium, Baltimore, MD, USA.

jjhermes

February 19, 2020
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  1. When Flux Standards Go Wild:
    White Dwarfs in the Era of Space
    Photometry
    http://jjherm.es
    @jotajotahermes
    J.J. Hermes

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  2. summary slide
    white dwarfs are empirically excellent flux standards
    caveats: binarity, pulsations, and magnetism
    when variable, white dwarfs reveal dynamic physics

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  3. How you may see white
    dwarf stars: through the
    eyes of Oke
    ESO
    JJ Hermes, Boston University | STScI/JHU Colloquium | 3

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  4. G191-B2B
    DA0 (61,300 K)
    GD 71
    DA1 (32,300 K)
    GD 153
    DA1 (38,500 K)
    Bohlin, Colina & Finley 1995
    HZ 43
    DA1 (50,000 K)
    Nearby (3”) dM
    … these 3 white dwarfs have 1-2% internal precision on absolute flux
    CALSPEC white dwarfs
    JJ Hermes, Boston University | STScI/JHU Colloquium | 4
    Bohlin 2007
    “primary reference standards
    ... from 1000 to 10,000 Å”

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  5. CALSPEC white dwarfs
    jwst-docs.stsci.edu
    JJ Hermes, Boston University | STScI/JHU Colloquium | 5
    … many frontiers are pushing towards <1% absolute flux calibration
    see also Calamida et al. 2019;
    Narayan et al. 2019

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  6. Sun
    White Dwarf
    (60% Mass of Sun)
    Earth
    (0.0003% Mass of Sun)
    JJ Hermes, Boston University | STScI/JHU Colloquium | 6

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  7. Kepler
    12 May 2009 –
    11 May 2013
    JJ Hermes, Boston University | STScI/JHU Colloquium | 7

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  8. =
    Steve Howell
    The solar pressure on the Kepler spacecraft was ~50 µN m-2
    JJ Hermes, Boston University | STScI/JHU Colloquium | 9

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  9. Ecliptic
    JJ Hermes, Boston University | STScI/JHU Colloquium | 10

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  10. Original Kepler Mission:
    46 white dwarfs observed,
    20 every 1-min
    K2, through Campaign 18:
    2166 white dwarfs observed,
    552 every 1-min
    Kepler
    K2 provided a large,
    empirical test of white dwarf
    flux stability
    (e.g., Maoz et al. 2015)
    JJ Hermes, Boston University | STScI/JHU Colloquium | 11

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  11. Kp
    = 16.7 mag, 52,000 K DA
    JJ Hermes, Boston University | STScI/JHU Colloquium | 12
    1 hr
    24 hr 6 hr 2 hr
    Hermes et al. 2017,
    MNRAS
    not variable to 0.05%

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  12. • Before Gaia: ~35,000 white
    dwarfs (mostly from SDSS)
    • Nearly half a million
    candidates from Gaia DR2
    JJ Hermes, Boston University | STScI/JHU Colloquium | 13
    Gaia Collaboration,
    Babusiaux et al. 2018
    Gentile Fusillo
    et al. 2019

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  13. JJ Hermes, Boston University | STScI/JHU Colloquium | 14
    7.5
    log(g) = 9 8.5 8.0
    Grey: Only photometry
    Black: 72% of K2 WDs w/ spectra
    White dwarf cooling tracks
    Gaia CMD of all 2166 white dwarfs observed by Kepler

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  14. JJ Hermes, Boston University | STScI/JHU Colloquium | 15
    7.5
    8.5 8.0
    Red: WD+MS from SDSS log(g) = 9
    Gaia CMD of all 2166 white dwarfs observed by Kepler

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  15. Reflection effect in close binary
    Kp
    = 16.5 mag
    Kp
    = 16.7 mag
    19.898 hr
    9.923 hr
    Most overluminous white dwarfs: WD+dM binaries
    JJ Hermes, Boston University | STScI/JHU Colloquium | 16
    >2%
    >6%

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  16. Parsons et al. 2017 JJ Hermes, Boston University | STScI/JHU Colloquium | 17 Casewell et al. 2018
    71.2 min
    100%
    >11%
    68.2 min
    Some overluminous white dwarfs have nearby brown dwarfs
    ~58 Jupiter-mass
    companion
    surviving common-
    envelope (shortest-
    period WD+BD
    system known)
    Companion:
    51 ± 6 Jupiter masses
    0.081-0.087 solar radii

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  17. JJ Hermes, Boston University | STScI/JHU Colloquium | 18
    7.5
    8.5 8.0
    Red: WD+MS from SDSS log(g) = 9
    We can generally omit suspected binaries as
    overluminous, based on their Gaia CMD position

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  18. JJ Hermes, Boston University | STScI/JHU Colloquium | 19
    7.5
    8.5 8.0
    log(g) = 9
    We can generally omit suspected binaries as
    overluminous, based on their Gaia CMD position
    HZ 43
    DA1 (50,000 K)
    Nearby (3”) dM

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  19. JJ Hermes, Boston University | STScI/JHU Colloquium | 20
    Sub-stellar transiting systems are rare, but present
    Gänsicke et al. 2016;
    Rappaport et al. 2016
    Vanderburg et al. 2015
    WD 1145+017: a disintegrating asteroid transiting a white dwarf
    >50%

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  20. JJ Hermes, Boston University | STScI/JHU Colloquium | 21
    Vanderbosch et al.
    arXiv: 1908.09839
    ~107 days
    >45%
    Sub-stellar transiting systems are rare, but present
    ZTF 0139+5245: transiting debris far outside the white dwarf
    tidal disruption radius
    2019

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  21. JJ Hermes, Boston University | STScI/JHU Colloquium | 22
    7.5
    8.5 8.0
    log(g) = 9
    So what fraction of white dwarfs are good flux standards?

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  22. Landolt 1968
    JJ Hermes, Boston University | STScI/JHU Colloquium | 23
    So what fraction of white dwarfs are good flux standards?

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  23. JJ Hermes, Boston University | STScI/JHU Colloquium | 24
    7.5
    8.5 8.0
    Blue: WD Pulsations log(g) = 9
    Pulsations in white dwarfs are confined to
    narrow instability strips in temperature
    30,000 K
    20,000 K
    10,000 K

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  24. 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
    H
    He
    CO
    Peering 6 Gyr into
    our Sun’s future…
    white dwarfs have
    non-radial g-mode
    pulsations driven
    by partial
    ionization of He
    or H
    See reviews by:
    Winget & Kepler 2008
    Fontaine & Brassard 2008
    Althaus, Córsico, Isern & García-Berro 2010
    JJ Hermes, Boston University | STScI/JHU Colloquium | 25

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  25. JJ Hermes, Boston University | STScI/JHU Colloquium | 26
    7.5
    8.5 8.0
    Blue: Pulsations log(g) = 9
    >95% of isolated white dwarfs are <1% constant on 1-hr to 10-
    d timescales (omitting known/likely binaries & pulsators)

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  26. white dwarfs are empirically excellent flux standards
    caveats: binarity, pulsations
    >95% of isolated WDs are <1% constant on 1-hr to 10-d timescales
    eclipses, reflection effect from close companions, (debris) transits
    pulsations

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  27. Pulsating WD: EC 14012-1446, r = 15.7 mag
    98.2% duty cycle for
    78.9 days with K2
    JJ Hermes, Boston University | STScI/JHU Colloquium | 28
    10 min
    >13%

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  28. 1000 s 200 s
    500 s 125 s
    White Dwarfs: g-modes
    (buoyancy restoring force)
    BiSON; Thompson et al. 2003
    5 min 4 min
    6 min
    Solar p-modes
    JJ Hermes, Boston University | STScI/JHU Colloquium | 29

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  29. Giammichele et al. 2015
    5 nights on 3.6-m CFHT
    on Mauna Kea:
    V = 14.2 mag
    Actual signal
    The view from one
    telescope on the ground
    JJ Hermes, Boston University | STScI/JHU Colloquium | 30

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  30. Today We Are Spoiled with
    Telescopes in Space

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  31. JJ Hermes, Boston University | STScI/JHU Colloquium | 32 k2wd.org
    Hermes et al. 2017, ApJS
    K2 seismology: enabled bulk white dwarf rotation rates

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  32. JJ Hermes, Boston University | STScI/JHU Colloquium | 33
    1 d 2 d 4 d
    None of the stars are
    currently in binaries:
    representative of
    single-star evolution
    of mostly 1-3 M¤
    stars
    Isolated pulsating WDs rotate between 0.5-2.2 days
    k2wd.org
    Hermes et al. 2017, ApJS

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  33. JJ Hermes, Boston University | STScI/JHU Colloquium | 34
    7.5
    8.5 8.0
    log(g) = 9
    >95% of isolated white dwarfs are <1% constant on 1-hr to 10-
    d timescales (omitting known/likely binaries & pulsators)
    Blue: Pulsations

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  34. JJ Hermes, Boston University | STScI/JHU Colloquium | 35
    7.5
    8.5 8.0
    log(g) = 9
    >95% of isolated white dwarfs are <1% constant on 1-hr to 10-
    d timescales (omitting known/likely binaries & pulsators)
    Orange: Spots
    Blue: Pulsations

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  35. Kp
    = 17.7 mag
    2.0409 days
    >4%
    Kp
    = 18.5 mag
    2.2229 days
    >6%
    K2 uncovered a modest population of spotted white dwarfs!
    JJ Hermes, Boston University | STScI/JHU Colloquium | 36
    Hermes et al. 2017,
    MNRAS

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  36. JJ Hermes, Boston University | STScI/JHU Colloquium | 37
    1 d 2 d 4 d
    Magnetic spotted WDs can reach extreme rotation rates

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  37. Long-cadence (30-min)
    exposures showed a
    significant peak in FT
    at 3 ppt = 0.3%
    5 hr 2 hr 1 hr
    SDSS
    νNyq
    JJ Hermes, Boston University | STScI/JHU Colloquium | 38
    SDSSJ082547.52+174818.4
    g=18.9 mag
    K2 Campaign 5
    A strongly magnetic WD observed in K2

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  38. JJ Hermes, Boston University | STScI/JHU Colloquium | 39
    0.0 0.5 1.0 1.5 2.0
    Rotational Phase
    °6
    °4
    °2
    0
    2
    4
    6
    Relative Flux (%)
    νNyq
    2νNyq
    3νNyq
    2 hr 30 min 20 min
    Folded SOAR
    High-speed photometry from
    SOAR shows this was a super-
    Nyquist signal at 18 min!
    K2 Campaign 5
    SOAR, 5-pt smoothed
    A strongly magnetic WD observed in K2 rotating at 18 min!
    18.0441 min
    >7%

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  39. JJ Hermes, Boston University | STScI/JHU Colloquium | 40
    In K2 Campaign 10,
    CCD Module 4 failed
    one week into the
    campaign
    νNyq
    1% FAP
    K2 discovered the fastest-rotating isolated WD
    Reding et al., in prep.

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  40. JJ Hermes, Boston University | STScI/JHU Colloquium | 41
    A 317.287 s (5.29 min) signal!
    νNyq
    3νNyq
    7νNyq
    11νNyq
    Reding et al., in prep.
    K2 discovered the fastest-rotating isolated WD
    317.287 s
    >10%
    The signal seen in 30-min
    K2 data was reflected off
    the Nyquist 11 times!

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  41. JJ Hermes, Boston University | STScI/JHU Colloquium | 42
    Spectrum changes occur along the
    315.96 s (5.3 min) spin period!
    5.1 MG
    Joins GD 356 as the only DAe
    SOAR
    The fastest-rotating isolated WD has magnetic emission!
    Reding et al., in prep.

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  42. white dwarfs are empirically excellent flux standards
    caveats: binarity, pulsations, and magnetism
    >95% of isolated WDs are <1% constant on 1-hr to 10-d timescales
    eclipses, (debris) transits, pulsations, spots
    It is possible that these spotted white
    dwarfs (strongly magnetic, rapidly rotating)
    are connected to WD+WD mergers à
    failed SNe Ia

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  43. Gaia provides an
    empirical look at white
    dwarf variability
    JJ Hermes, Boston University | STScI/JHU Colloquium | 44
    Gaia Collaboration,
    Babusiaux et al. 2018
    Gaia Collaboration,
    Evans et al. 2018
    N
    obs

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  44. Hermes et al. 2018; 2020, in prep.
    see also Eyer et al. 2019,
    arXiv: 1912.07659
    >46,000 WDs within 200pc
    WDs with the
    top 1% most
    sca7er for their
    magnitude…
    …cluster near
    WD instability
    strips!
    Cooling track,
    0.6 M⊙ WD
    Using Gaia’s empirical
    photometric
    uncertainties …
    … is a good way to
    select (against) highly
    variable white dwarfs!
    JJ Hermes, Boston University | STScI/JHU Colloquium | 45

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  45. >46,000 WDs within 200pc
    Cooling track,
    0.6 M⊙ WD
    Most of these variable WDs in Gaia are pulsating or spotted
    JJ Hermes, Boston University | STScI/JHU Colloquium | 46
    Hermes et al. 2018;
    2020, in prep.
    27.9 min
    >4% >8%
    16.6 min

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  46. JJ Hermes, Boston University | STScI/JHU Colloquium | 47
    7.5
    8.5 8.0
    log(g) = 9
    Purple: Pulsations+
    Blue: Pulsations
    Orange: Spots
    Pulsating white dwarfs can reveal dynamic physics

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  47. WDs Evolve (Cool) à
    We Have Only Scratched the Surface of Analyzing the ~100
    Pulsating White Dwarfs Observed by Kepler
    JJ Hermes, Boston University | STScI/JHU Colloquium | 48
    Blue: Observed by Kepler
    Open: Ground-based
    SOAR

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  48. 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
    An unexpected, dynamic discovery in Kepler: outbursts
    JJ Hermes, Boston University | STScI/JHU Colloquium | 49

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  49. Quiescent pulsations
    (Dominant >800 s)
    PG 1149+057:
    Hermes et al. 2015
    see also Bell et al. 2016
    recurrence time:
    chaotic; days to weeks
    duration:
    2-20 hr
    excess energy:
    1033-34 erg
    15% flux increase:
    700 K T
    eff
    increase
    An unexpected, dynamic discovery confirmed in K2: outbursts
    JJ Hermes, Boston University | STScI/JHU Colloquium | 50

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  50. 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
    JJ Hermes, Boston University | STScI/JHU Colloquium | 51
    Blue: Observed by Kepler
    Red: Outbursting DAV
    Open: Ground-based

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  51. GD 1212:
    Hermes et al. 2014
    GD 1212: Data from the 9-day K2 engineering test run
    V=13.3 mag
    JJ Hermes, Boston University | STScI/JHU Colloquium | 52
    2014

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  52. Quiescent pulsations
    (1135.2 s, 856.9 s, …)
    In Outburst
    (864.1 s, 846.4 s, …)
    GD 1212: Hermes et al.
    2020, in prep.
    >60 days between outbursts!
    K2 Campaign 12
    GD 1212: Revisited in K2 Campaign 12
    JJ Hermes, Boston University | STScI/JHU Colloquium | 53
    2017

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  53. K2 Campaign 12
    JJ Hermes, Boston University | STScI/JHU Colloquium | 54
    animation by
    Zach Vanderbosch

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  54. These outbursts may be responsible for shutting down
    pulsations in white dwarfs
    Outbursting
    DAVs
    JJ Hermes, Boston University | STScI/JHU Colloquium | 55
    (see Wu & Goldreich 2001)
    Blue: Observed by Kepler
    Red: Outbursting DAV
    Open: Ground-based

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  55. n
    l=1
    l=2
    Solar p-modes, evenly spaced in frequency
    JJ Hermes, Boston University | STScI/JHU Colloquium | 56
    How might outbursts work? Parametric resonance.

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  56. n
    l=1
    l=2
    JJ Hermes, Boston University | STScI/JHU Colloquium | 57
    White dwarf g-modes, evenly spaced in period
    How might outbursts work? Parametric resonance.

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  57. n
    l=1
    l=2
    JJ Hermes, Boston University | STScI/JHU Colloquium | 58
    White dwarf g-modes, evenly spaced in period
    1000 s 200 s
    500 s 125 s
    l=1
    l=2

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  58. l=1
    l=2
    Adiabatic Model: 11,245 K, 0.632 M
    ¤
    , 10-4.12 M
    H
    /M
    WD
    Observed: 11,060(170) K, 0.64(0.03) M
    ¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)
    à driven
    damped ß
    outbursts are likely “limit cycles arising from sufficiently
    resonant 3-mode couplings between overstable parent
    modes and pairs of radiatively damped daughter
    modes”
    Luan & Goldreich 2018
    JJ Hermes, Boston University | STScI/JHU Colloquium | 59

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  59. l=1
    l=2
    Adiabatic Model: 11,245 K, 0.632 M
    ¤
    , 10-4.12 M
    H
    /M
    WD
    Observed: 11,060(170) K, 0.64(0.03) M
    ¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)
    à driven
    damped ß
    ω
    p
    = 897.7 µHz
    (l=1, n=24)
    JJ Hermes, Boston University | STScI/JHU Colloquium | 60

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  60. l=1
    l=2
    Adiabatic Model: 11,245 K, 0.632 M
    ¤
    , 10-4.12 M
    H
    /M
    WD
    Observed: 11,060(170) K, 0.64(0.03) M
    ¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)
    ω
    d1
    = 435.9 µHz
    (l=2, n=88)
    ω
    d2
    = 461.9 µHz
    (l=1, n=48)
    Wu & Goldreich 2001
    ω
    d1
    + ω
    d2
    = ω
    p
    + δω
    Limit cycle if: δω < γ
    d
    (typical 1/γ
    d
    < 1 day)
    JJ Hermes, Boston University | STScI/JHU Colloquium | 61
    ω
    p
    = 897.7 µHz
    (l=1, n=24)

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  61. These outbursts may be responsible for shutting down
    pulsations in white dwarfs
    Outbursting
    DAVs
    JJ Hermes, Boston University | STScI/JHU Colloquium | 62
    (see Wu & Goldreich 2001)
    Blue: Observed by Kepler
    Red: Outbursting DAV
    Open: Ground-based

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  62. Edward Jones (Aussie50)

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  63. white dwarfs are empirically excellent flux standards
    caveats: binarity, pulsations, and magnetism
    when variable, white dwarfs reveal dynamic physics
    summary slide
    >95% of isolated WDs are <1% constant; Gaia can assess variability
    eclipses, (debris) transits, pulsations, outbursts, spots
    some spots may reveal failed Type Ia supernovae
    outbursts (nonlinear mode coupling) could quench observable pulsations

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