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

70d4f7eb14525537a3fd6c15a33a8ac1?s=47 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.

70d4f7eb14525537a3fd6c15a33a8ac1?s=128

jjhermes

January 05, 2017
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  1. 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
  2. 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)
  3. 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”
  4. 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!
  5. 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
  6. 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
  7. 10.

    EC 14012-1446, r= 15.7 mag 98.2% duty cycle for 78.9

    days Caveats: Binarity, Magnetism, Pulsations
  8. 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%)
  9. 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
  10. 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
  11. 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