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
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
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
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
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%
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
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
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)
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
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
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
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
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
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%
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!
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.
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
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
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
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
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
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
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
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
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
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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