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When flux standards go wild: White dwarfs in the age of Kepler

jjhermes
January 05, 2017

When flux standards go wild: White dwarfs in the age of Kepler

Conference presentation, 7 min. January 2017: AAS Winter Meeting, Grapevine, TX, USA.

jjhermes

January 05, 2017
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  1. http://jjherm.es
    J.J. Hermes
    Hubble Fellow
    University of North Carolina at Chapel Hill
    When flux standards go wild:
    White dwarfs in the age of Kepler

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  2. white dwarfs are generally excellent flux standards
    caveats: binarity, magnetism, and pulsations
    beware weakly magnetic WDs >25,000 K
    summary slide (like eating breakfast for dinner)

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  3. How many of our fellow
    AAS-goers see white
    dwarf stars: through
    the eyes of Oke

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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
    The HST White Dwarf Standards
    … JWST will likely use four primary white dwarfs as absolute flux standards
    … dark energy studies with Type Ia supernovae pushing towards <1% flux calibration
    “the primary reference
    standards that are
    recommended for all
    ultraviolet and optical
    absolute calibrations from
    1000 to 10,000 Å”

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  5. Original Kepler Mission:
    20 white dwarfs observed,
    Six pulsating WDs
    (just two >3 months)
    K2 through Campaign 10:
    >1100 WDs observed
    43 pulsating WDs
    K2 through Campaign 16:
    >2000 WDs (if our GO proposal is !),
    >90 pulsating WDs (~280 known today)
    K1
    K2, today
    K2, by mid-2018
    K2 is providing a growing
    empirical test of white
    dwarf flux stability!

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  6. K2 Shows: White Dwarfs Are Good Flux Standards
    >97% of all spectroscopically confirmed
    WDs in Kepler/K2 are flux constant to
    <1% on 30-min to 10-day timescales
    5/252 spectroscopic WDs >1% var.
    9/424 with WD colors/proper motions
    Kp
    < 19.0 mag
    Cut: Pulsating WDs (SC)
    & known SDSS WD+dM
    (sdss-wdms.org)
    Zhichao Xue & Brad Schaefer are exploring white dwarf stability at mmag levels

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  7. Caveats: Binarity, Magnetism, Pulsations
    Reflection effect in close binary

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  8. Caveats: Binarity, Magnetism, Pulsations

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  9. (K2 Already Doubled WD Rotation Measurements)
    10 1 100 101 102
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    N
    K2 Asteroseismic
    Asteroseismic
    K2 Magnetic
    Magnetic
    0.5 d 1.0 d 5.0 d
    3 hr
    pre-K2: Kawaler et al. 2015

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  10. EC 14012-1446, r= 15.7 mag 98.2% duty cycle for 78.9 days
    Caveats: Binarity, Magnetism, Pulsations

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  11. We recently discovered
    pulsations and an apparent
    spot modulation in a hot
    (>31,000 K) DB:
    PG 0112+104
    No spectroscopic evidence
    for Zeeman splitting
    Hermes et al. 2017, arXiv: 1612.07807
    (Spots Appear on Weakly Magnetic WDs, As Well)
    10.17404 hr surface rotation period
    (peak-to-peak amplitude <0.3%)

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  12. • Pulsation splittings consistent
    with 10.2-hr rotation
    • Pulsation symmetry requires
    <10 kG field
    Hermes et al. 2017, arXiv: 1612.07807
    (Spots Appear on Weakly Magnetic WDs, As Well)
    l=1 modes l=2 modes

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  13. HST primary standards
    DAs surface convection <13,000 K
    DBs surface convection <30,000 K
    PG 0112+104

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  14. white dwarfs are generally excellent flux standards
    caveats: binarity, magnetism, and pulsations
    beware weakly magnetic WDs >25,000 K
    summary slide (like eating dinner for dinner)
    >97% of isolated WDs are constant to <1% on 30-min to 10-d timescales
    reflection, eclipses, spots, pulsations, outbursts
    surface spots visible even with <10 kG magnetic fields

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  15. Dufour et al. 2010
    PG 0112+104
    Teff
    = 31,300 ± 500 K
    log g = 7.8 ± 0.1
    (M = 0.52 ± 0.05 M
    )
    log N(H)/N(He) < −4.0
    several C II and C III lines

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