Rumblings in the stellar graveyard: White dwarf pulsations with K2 and TESS

70d4f7eb14525537a3fd6c15a33a8ac1?s=47 jjhermes
July 18, 2017

Rumblings in the stellar graveyard: White dwarf pulsations with K2 and TESS

Conference presentation, 25 min. July 2017: TASC3 KASC 10 Workshop, Birmingham, UK.

70d4f7eb14525537a3fd6c15a33a8ac1?s=128

jjhermes

July 18, 2017
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  1. 1.

    http://jjherm.es J.J. Hermes Hubble Fellow University of North Carolina at

    Chapel Hill Rumblings in the Stellar Graveyard: White Dwarf Pulsations with K2 and TESS
  2. 2.

    U. North Carolina: Chris Clemens, Bart Dunlap, Erik Dennihy, Josh

    Fuchs, Stephen Fanale U. Warwick: Boris Gaensicke, Roberto Raddi, N. P. Gentile Fusillo, P.-E. Tremblay, Paul Chote U. Texas: Keaton J. Bell, Mike Montgomery, Don Winget, Zach Vanderbosch + Steve Kawaler, Agnes Bischoff-Kim, Judi Provencal, S.O. Kepler, Alejandra Romero Rumblings in the Stellar Graveyard: White Dwarf Pulsations with K2 and TESS
  3. 3.

    Kepler/K2 pulsating white dwarfs have provided opportunity to: • Establish

    the range of WD envelope masses • Empirically constrain the efficiency of convection in WDs • Witness nonlinear mode coupling • Measure the endpoints of angular momentum evolution • Test for radial differential rotation All without extremely detailed asteroseismic fits
  4. 4.

    Sandra Greiss et al. 2016 http://www2.warwick.ac.uk/fac/sci/physics/ research/astro/research/catalogues/kis stars WDs Just

    two known WDs at Kepler launch In 2012 we started Kepler INT Survey (U,g,r,i,Hα ) down to 20th mag: Found 10 new pulsating WDs
  5. 5.
  6. 6.

    Original Kepler Mission (4 years): Just 20 white dwarfs observed,

    6 pulsating WDs (just two >3 months) K2 through Campaign 10: >1000 white dwarf candidates observed 35 more pulsating WDs K2 has given us hundreds of candidate pulsating white dwarfs to observe
  7. 7.

    GD 1212, Hermes et al. 2014 Data from the 9-day

    K2 engineering test run V=13.3 mag
  8. 8.

    WET, and KASC4 Boulder (7/2011 so SIX YEARS AGO!) He

    P.I. zone (30-20 kK) H P.I. zone (13-10 kK) DBV aka V477 Her DAV aka ZZ Ceti
  9. 9.

    White Dwarfs are Finally Getting the Space Treatment PG1159-035, V=14.9

    mag -- poster child for WET (March 1989, 9 sites, 90.8% duty cycle over 12.0 days) SDSSJ0106+0145, g=16.2 mag -- typical K2 light curve (K2 Campaign 8, 96.0% duty cycle over 78.7 days) Winget et al. 1991 Hermes et al. 2017, in prep. l = 1 l = 2 l = 2 l = 2 l = 1 l = 1
  10. 10.

    White Dwarfs Seismologist’s Dilemma: Often Few Modes For any one

    hot DAV: 1. Small number of independent modes observed 2. Best model hinges on mode identification 3. Hidden free parameters (core profile, layer masses), with 8+ degrees of freedom e.g., WD0111+0018, 6 hr ground-based data e.g., WD0111+0018, 78.7-d K2 data Hermes et al. 2013 Hermes et al. 2017, in prep.
  11. 11.

    White Dwarfs Seismologist’s Dilemma: Often Few Modes For any one

    hot DAV: 1. Small number of independent modes observed 2. Best model hinges on mode identification 3. Hidden free parameters (core profile, layer masses), with 8+ degrees of freedom e.g., WD0111+0018, 6 hr ground-based data e.g., WD0111+0018, 78.7-d K2 data Hermes et al. 2013 Hermes et al. 2017, in prep.
  12. 12.

    Spectroscopy Yields Effective Temperatures and Masses SDSS SOAR spectroscopy yields

    WD mass We have obtained SOAR spectra of all DAVs observed by K2 so far: k2wd.org
  13. 13.

    The Kepler/K2 DAV Instability Strip Our DAVs span all edge

    to edge of DAV instability strip (We will address purity by the end of K2) Hermes et al. 2017, k2wd.org Josh Fuchs et al. 2017, in prep. Stay tuned: Recent UNC Ph.D. Josh Fuchs is exploring strip with minimal systematics (same instrument, methods, models) Empirical edges by Tremblay+ 2015
  14. 14.

    As Convection Zone Deepens, Longer Mode Periods Driven Known DAV

    from ground WMP > 500 s Outbursting DAV WMP > 500 s
  15. 17.

    239 eigenperiods from 75 hot DAVs (mostly ground-based, no combination

    frequencies) Histogram of eigenperiods (again, no combination frequencies) 0 5 10 15 20 25 30 50 100 150 200 250 300 350 400 450 500 0 5 10 15 20 25 30 50 100 150 200 250 300 350 400 450 Clemens et al. 2017, in prep. Insights from the Aggregated Periods of DAVs Mode Amplitude (ppt) N Mode Period (s) Mode Period (s)
  16. 18.

    38 eigenperiods from 16 hot DAVs (l=1, m=0, no combination

    frequencies, mostly Kepler/K2) 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 Clemens et al. 2017, in prep. Insights from the Aggregated Periods of DAVs n = 1 l = 1 n = 2 l = 1 n = 3 l = 1 Kepler makes mode identification relatively trivial Mode Period (s) N n=1 n=2 n=3 n=4
  17. 19.

    0 1 2 3 4 5 6 7 8 50

    100 150 200 250 300 350 400 450 l=1 hDAV periods, observed 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 random MH simulation Clemens et al. 2017, in prep. Romero et al. 2012 Comparing to a random distribution of models with thick (10-4 MH /M ★ ) to thin (10-10 MH /M ★ ) hydrogen layer masses, using spectroscopic Teff & masses Insights from the Aggregated Periods of DAVs
  18. 20.

    • The observed distribution supports a thick (canonical) hydrogen layers

    • Implications for improving white dwarf cooling ages (Gaia) 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 hDAV periods, observed 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 random MH simulation l=1 canonical MH simulation Clemens et al. 2017, in prep. Romero et al. 2012 Insights from the Aggregated Periods of DAVs
  19. 23.

    Kepler Has Revealed a Dichotomy of Mode Linewidths Two modes

    within the same DAV show very different linewidths Many of the broadened modes appear relatively Lorentzian in shape (Absolutely no way to have made these measurements before Kepler) Hermes et al. 2017, in prep.
  20. 24.

    Kepler Has Revealed a Dichotomy of Mode Linewidths Results from

    fitting Lorentzians to the 27 DAVs through K2 Campaign 8: Clear dichotomy at ~800 s Hermes et al. 2017, in prep. Stephen Fanale
  21. 25.

    Kepler Has Revealed a Dichotomy of Mode Linewidths • Damping

    rather than driving important for broadening; phase incoherence Broadened modes: bounded by the base of the convection zone! Mike Montgomery et al. 2017, in prep.
  22. 26.

    Kepler Has Revealed a Dichotomy of Mode Linewidths Mike Montgomery

    et al. 2017, in prep. 0.4 0.6 0.8 1.0 1.2 1.4 ↵ 0.675 0.700 0.725 0.750 0.775 0.800 0.825 0.850 Fraction Correct 0 200 400 600 800 1000 1200 1400 Period (s) 0 1 2 3 4 5 6 HWHM (µHz) ML2/↵ = 0.6 0 200 400 600 800 1000 1200 1400 Period (s) 0 1 2 3 4 5 6 HWHM (µHz) ML2/↵ = 0.9 Given spectroscopic Teff /log(g), we can calculate the critical period for a mode reflecting off the base of the convection zone This empirically constrains ML2/α
  23. 27.

    Not the Whole Linewidth Story – Lots of Resonances First

    5 days: 885.243(0.057) µHz Last 5 days: 888.285(0.067) µHz Some longer-period modes appear to change very quickly in frequency: Nonlinear mode coupling appears to be the only way the star can transfer that much energy so quickly!
  24. 28.

    Not the Whole Linewidth Story – Lots of Resonances Weikai

    Zong et al. 2016 Zong et al. have explored three-mode coupling to explain amplitude/phase changes in compact objects
  25. 31.

    This outburst phenomenon never seen before in 40+ years of

    pulsating white dwarf studies A surprising discovery with Kepler: Aperiodic Outbursts Quiescent pulsations (1151.9 s, 1160.8 s, …) In Outburst (999.9 s, 896.6 s, …) PG 1149+057: Hermes et al. 2015
  26. 32.

    A surprising discovery with Kepler: Aperiodic Outbursts Keaton Bell et

    al. 2017 We see outbursts in 6 of the 27 DAVs observed through Campaign 8 These are aperiodic brightenings causing up to 15% mean flux increases (>750 K Teff increases) Pulsations persist in outburst, and are consistent with the star having a thinner convection zone
  27. 33.

    A surprising discovery with Kepler: Aperiodic Outbursts Keaton Bell et

    al. 2017 We see outbursts in 6 of the 27 DAVs observed through Campaign 8 These are aperiodic brightenings causing up to 15% mean flux increases (>750 K Teff increases) Pulsations persist in outburst, and are consistent with the star having a thinner convection zone
  28. 37.

    1 10 100 White Dwarf Rotation Period (hr) 0 2

    4 6 8 10 N Kepler & K2 Kawaler (2015) Kepler & K2 have doubled the number of white dwarfs with measured internal rotation periods using asteroseismology Hermes et al. 2017, in prep. None of the stars here are currently in binaries: Representative of single-star evolution Rotation Rates Usually Fall Readily from K2 Data 0.5 d 1 d 2 d 4 d
  29. 38.

    1 10 100 WD Rotation Period (hr) 0.4 0.5 0.6

    0.7 0.8 0.9 WD Mass (M⊙ ) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 ZAMS Progenitor Mass (M⊙ ) 1 10 100 White Dwarf Rotation Period (hr) 0 2 4 6 8 10 N Kepler & K2 Kawaler (2015) 1 d 2 d 4 d Hermes et al. 2017, in prep. We Can Finally Probe WD Rotation as a Function of Mass The fastest-rotating pulsating white dwarf (1.13 hr) is also the most massive (0.87 M¤ ) – descended from a single 4.0 M¤ ZAMS progenitor Hermes et al. 2017c, ApJL, 841, L2; arXiv: 1704.08690
  30. 39.

    >70% of Field WDs between 0.51-0.73 M¤ (evolved 1.7-3.0 M¤

    ZAMS) These WDs rotate at 0.5-2.2 d (WD Prot : 35 ± 28 hr) Link emerging between higher WD mass and faster rotation 1 10 100 0 1 2 3 4 N 1.7 2.0 M ZAMS WD Prot = 1.48 ± 0.94 d 1 10 100 0 1 2 3 4 N 2.0 2.5 M ZAMS WD Prot = 1.35 ± 0.74 d 1 10 100 0 1 2 3 4 N 2.5 3.0 M ZAMS WD Prot = 1.32 ± 1.04 d 1 10 100 White Dwarf Rotation Period (hr) 0 1 2 3 4 N 3.5 4.0 M ZAMS WD Prot = 0.17 ± 0.15 d We Can Finally Probe WD Rotation as a Function of Mass
  31. 41.

    PG 0112+104: Hermes et al. 2017a l=1 modes l=2 modes

    The Most Evolved Test of Radial Differential Rotation PG 0112+104 is a ~31,000 K pulsating He-atmosphere WD (DBV)
  32. 42.

    The Most Evolved Test of Radial Differential Rotation PG 0112+104:

    Hermes et al. 2017a l=1 modes n (n) n=2 n=3 n=4 n=5 n=6 Frequency splittings and overtone spacings behave in concert: Modes trapped to different depths Early hints: rigid rotation Period spacing difference (s)
  33. 43.

    We also see a surface spot Surface: 10.17404 hr Towards

    core: 10.1±0.9hr PG 0112+104: Hermes et al. 2017a 10.17404 hr surface spot rotation period The Most Evolved Test of Radial Differential Rotation Using l=1 and l=2 modes we measure a rotation period of 10.1±0.9 hr in PG 0112+104 (better asteroseismic modeling will improve this uncertainty)
  34. 44.

    The Most Evolved Test of Radial Differential Rotation “PG0112+104 rotates

    rigidlyover its outer 70% in radius with a period of Prot = 10.18 ± 0.27 hr” Based on full seismic model See Poster 2.7 by Noemi Giammichele et al.
  35. 46.

    WG8: TESS White Dwarf Candidate Follow-Up Ongoing! Zsófia Bognár et

    al., in prep. Time (d) Amplitude (mag) KonkolyObservatory: New I=14.3 mag DAV! S. Charpinet
  36. 47.

    Conclusion: More White Dwarfs Yield Firmer Conclusions! Kepler/K2 pulsating white

    dwarfs provide opportunity to: • Establish the range of WD envelope masses § Most have canonically thick (10-4 MH /M ★ ) hydrogen envelopes • Empirically constrain the efficiency of convection in WDs § ML2/α > 0.8 from mode linewidths bounded by base of convection zone • Witness nonlinear mode coupling § Outbursts (and frequency changes) on day-week timescales • Measure the endpoints of angular momentum evolution § Endpoints of 1.7-3.0 M¤ stars rotate at 35 ± 28 hr, but >3.0 M¤ faster • Test for radial differential rotation § White dwarfs appear to rotate rigidly, but more tests on the way! All of these constraints significantly improve by observing more pulsating WDs with K2 and TESS!
  37. 48.

    >70% of Field WDs between 0.51-0.73 M¤ (evolved 1.7-3.0 M¤

    ZAMS) These WDs rotate at 0.5-2.2 d (WD Prot : 35 ± 28 hr) Link emerging between higher WD mass and faster rotation 1 10 100 0 1 2 3 4 N 1.7 2.0 M ZAMS WD Prot = 1.48 ± 0.94 d 1 10 100 0 1 2 3 4 N 2.0 2.5 M ZAMS WD Prot = 1.35 ± 0.74 d 1 10 100 0 1 2 3 4 N 2.5 3.0 M ZAMS WD Prot = 1.32 ± 1.04 d 1 10 100 White Dwarf Rotation Period (hr) 0 1 2 3 4 N 3.5 4.0 M ZAMS WD Prot = 0.17 ± 0.15 d We Can Finally Probe WD Rotation as a Function of Mass