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

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

Transcript

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. 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. How many of our fellow AAS-goers see white dwarf stars: through the eyes of Oke
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”
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!
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
7. Caveats: Binarity, Magnetism, Pulsations Reflection effect in close binary
8. Caveats: Binarity, Magnetism, Pulsations
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
10. EC 14012-1446, r= 15.7 mag 98.2% duty cycle for 78.9 days Caveats: Binarity, Magnetism, Pulsations
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%)
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
13. HST primary standards DAs surface convection <13,000 K DBs surface convection <30,000 K PG 0112+104
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
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