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

70d4f7eb14525537a3fd6c15a33a8ac1?s=47 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.

70d4f7eb14525537a3fd6c15a33a8ac1?s=128

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
  2. summary slide white dwarfs are empirically excellent flux standards caveats:

    binarity, pulsations, and magnetism when variable, white dwarfs reveal dynamic physics
  3. How you may see white dwarf stars: through the eyes

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

    of Sun) JJ Hermes, Boston University | STScI/JHU Colloquium | 6
  7. Kepler 12 May 2009 – 11 May 2013 JJ Hermes,

    Boston University | STScI/JHU Colloquium | 7
  8. None
  9. = Steve Howell The solar pressure on the Kepler spacecraft

    was ~50 µN m-2 JJ Hermes, Boston University | STScI/JHU Colloquium | 9
  10. Ecliptic JJ Hermes, Boston University | STScI/JHU Colloquium | 10

  11. 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
  12. 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%
  13. • 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
  14. 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
  15. 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
  16. 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%
  17. 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
  18. 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
  19. 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
  20. 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%
  21. 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
  22. 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?
  23. Landolt 1968 JJ Hermes, Boston University | STScI/JHU Colloquium |

    23 So what fraction of white dwarfs are good flux standards?
  24. 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
  25. 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
  26. 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)
  27. 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
  28. 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%
  29. 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
  30. 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
  31. Today We Are Spoiled with Telescopes in Space

  32. JJ Hermes, Boston University | STScI/JHU Colloquium | 32 k2wd.org

    Hermes et al. 2017, ApJS K2 seismology: enabled bulk white dwarf rotation rates
  33. 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
  34. 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
  35. 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
  36. 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
  37. JJ Hermes, Boston University | STScI/JHU Colloquium | 37 1

    d 2 d 4 d Magnetic spotted WDs can reach extreme rotation rates
  38. 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
  39. 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%
  40. 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.
  41. 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!
  42. 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.
  43. 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
  44. 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
  45. 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
  46. >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
  47. 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
  48. 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
  49. 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
  50. 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
  51. 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
  52. 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
  53. 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
  54. K2 Campaign 12 JJ Hermes, Boston University | STScI/JHU Colloquium

    | 54 animation by Zach Vanderbosch
  55. 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
  56. 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.
  57. 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.
  58. 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
  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 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
  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) à driven damped ß ω p = 897.7 µHz (l=1, n=24) JJ Hermes, Boston University | STScI/JHU Colloquium | 60
  61. 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)
  62. 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
  63. Edward Jones (Aussie50)

  64. 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