Pulsating White Dwarfs in Kepler and K2

70d4f7eb14525537a3fd6c15a33a8ac1?s=47 jjhermes
June 16, 2015

Pulsating White Dwarfs in Kepler and K2

Conference presentation, 25 min. June 2017: KASC 8 TASC 1 Workshop, Aarhus, Denmark.

70d4f7eb14525537a3fd6c15a33a8ac1?s=128

jjhermes

June 16, 2015
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Transcript

  1. Growing the Ensemble: Pulsating White Dwarfs in Kepler and K2

    h/t: Mike Montgomery, Agnes Bischoff-Kim, Keaton Bell, Don Winget, Steve Kawaler,! Bart Dunlap, Chris Clemens, S. O. Kepler, Barbara Castanheira, Boris Gänsicke,! Paul Chote, Tom Marsh, Tom Barclay, Fergal Mullally, Detlev Koester JJ Hermes
  2. Kepler K2 Just 3 pulsating white dwarfs observed more than

    1 month,! only 2 more than 6 months before reaction wheel failure An exponentially growing sample of well-studied! white dwarfs…
  3. Winget & Kepler 2008 Fontaine & Brassard 2008 Fractional*Mass*Depth:2 N2#

    Ll 2# Propagation/Diagram# Core Surface p-modes σ2*>*Ll 2,*N2 g-modes σ2*<*Ll 2,*N2 convection! zone log*σ2*(s:2) A ‘typical’ white dwarf electron degenerate! C/O core! (r = 8500 km) non-degerate! He layer! (260 km) non-degerate H layer! (30 km)
  4. Winget & Kepler 2008 Fontaine & Brassard 2008 N2# Ll

    2# Propagation/Diagram# Core Surface p-modes σ2*>*Ll 2,*N2 g-modes σ2*<*Ll 2,*N2 convection! zone log*σ2*(s:2) A ‘typical’ white dwarf electron degenerate! C/O core! (8500 km thick) non-degerate! He layer! (260 km) non-degerate H layer! (30 km) DA: Broad hydrogen Balmer lines Fractional*Mass*Depth:2
  5. White Dwarfs Shed Much of Their Complexity •  Most*are*DA* (hydrogen*atmosphere)2

    •  Most*WDs*≈* 0.6*M!2 •  Pulsate*at*onset*of*H* partial*ionization*zone* (DAVs,*aka*ZZ*Cetis)2 The observed pulsating white dwarf stars lie in three strips in the H-R diagram, a in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 7 170,000 K have the highest number of detected modes. The first class of pulsating 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 A 13-Gyr isochrone with z = 0.019 from Marigo et al. (2007), on which we have drawn the obs locations of the instability strips, following the nonadiabatic calculations of C´ orsico, Althaus & M Annu. Rev. Astro. Astrophys. 2008.46:157-199. Downloade by University of Texas - Austin on 01/28/09. The Astrophysical Journal, 730:128 (23pp), 2011 April 1 Tremblay, Bergeron, & Gianninas Winget & Kepler 2008 Tremblay+ 2011 One*DBV*in*original* mission*(Østensen+*2011,* Bischoff:Kim+*2014)
  6. "  Core Angular Momentum Evolution "  Kepler’s View of the

    ZZ Ceti Instability Strip "  The Unexpected (?!) "  What’s On Deck
  7. Ageing Low Mass Stars: From Red Giants to White Dwarfs

    Figure 4. Prewhitening sequence for the 213 s feature. Figure 5. Prewhitening sequence for the 274 s feature. White Dwarf Rotation from the Ground Giammichele+/2013# •  ZZ/Ceti/itself://P rot (≈(1.7(d. prewhitened: prewhitened: prewhitened: prewhitened:
  8. White Dwarf Rotation Made Easy with Kepler •  Kp /=*18.0*mag2

    •  1*month*Kepler*data2 •  P rot (=(0.9(±(0.3(d. 2 •  0.62*±*0.05*M! *WD:* 2~2.2*M! *(A)*progenitor2
  9. Greiss+/2014# their Ck,l values should not be identical, and are

    not exactly 0.5. If we adopt the Ck,l values of the model from Romero et al. (2012) discussed in Section 4.2, we obtain a rotation rate of 3.5 ± 0.2 d. To best reflect the systematic uncertainties, we adopt a rotation rate of 3.5 ± 0.5 d. Notably, the small but significant deviations in the observed fre- quency splittings provide additional asteroseismic information, es- pecially useful for constraining which modes are trapped by com- position transition zones (Brassard et al. 1992). The shorter-period g modes have lower radial order, and these splittings are observed to have values of 1.97 µHz for f1 , 1.77 µHz for f2 , 2.03 µHz for f3 and 1.94 µHz for f4 . This value is in agreement with previous rotation frequencies found in ZZ Ceti stars. Fontaine & Brassard (2008) give an overview on pulsating WDs and provide the asteroseismic rotation rates of seven ZZ Ceti stars, spanning from 9 to 55 h, i.e. 0.4 to 2.3 d. In the case of non-pulsating WDs, the sharp NLTE core of the Hα line in their spectra has been used in many studies to measure the projected rotation velocities of the stars (Heber, Napiwotzki & Reid 1997; Koester et al. 1998; Karl et al. 2005). In all cases, the same conclusion was drawn: isolated WDs are generally slow rotators. 5 CONCLUSION We report on the discovery of the second ZZ Ceti in the Kepler field: KIC 11911480. It was discovered using colour selections from the Kepler-INT Survey and confirmed with ground-based time series photometry from the RATS-Kepler survey. Follow-up Kepler short- cadence observations during Q12 and Q16 are analysed: five inde- •  Kp /=*18.1*mag*DAV2 •  6*months*Kepler*data2 •  Clean*rotational* spli\ings:* 2P rot (=(3.5(±(0.5(days. •  0.57*±*0.06*M! *WD:* 2~1.5*M! *(F)*progenitor2 Web Formulas ⌫ = m(1 Ck,` )⌦ l. 4.3 Rotation rate We see what appears to be multiplet splitting of some modes, which is a direct manifestation of the star’s rotation rate (Fig. 5). In the limit of slow rotation, the difference between the frequency of one mode of indices l, k, m (σk,lm ) and the frequency in the non-rotating case (σk,l ) is: σk,l,m − σk,l = m(1 − Ck,l ) (1) where Ck,l comes from the Coriolis force term in the momentum equation and is the rotation frequency (Winget et al. 1991; Vau- clair 1997). Note that this equation is the classical first-order ex- pansion. In the asymptotic limit for g modes, Ck,l only depends on the degree of the mode: Ck,l ≃ 1 l(l+1) . When a pulsating WD ro- tates, each mode of degree l can be split into 2l+1 components. We see splitting into three components in several modes in the power spectrum of KIC 11911480 (see Fig. 5), which likely corre- sponds to an ℓ = 1 mode in those cases, leading to Ck,l ≃ 0.5. The frequency spacing between the split components of the modes is quite consistent, 1.93 ± 0.10 µHz, suggesting these modes are all of the same spherical degree. This corresponds to a rotation rate of 3.0 ± 0.2 d. However, f1 − f4 (with periods from 172.9 to 324.5s) are likely low-radial-order and far from the asymptotic limit, so their Ck,l values should not be identical, and are not exactly 0.5. If we adopt the Ck,l values of the model from Romero et al. (2012) discussed in Section 4.2, we obtain a rotation rate of 3.5 ± 0.2 d. To best reflect the systematic uncertainties, we adopt a rotation rate of 3.5 ± 0.5 d. White Dwarf Rotation Made Easy with Kepler
  10. The Astrophysical Journal, 788:93 (7pp), 2014 June 10 Figure 5.

    Evolution of the average core rotational period as a function of Boundary Cond’s: Angular Momentum Transport Cantiello+/2014# Core Rotation Surface! Rotation WD$rotation$constrains$ RGB$core1envelope$ coupling7
  11. A New K2 View on Common-Envelope Evolution •  WD+dM*in*K2*Campaign*1:* SDSS*J1136+04092

    SDSS SOAR VLT Hermes+/2015,/arXiv:/1505.01848#
  12. A New K2 View on Common-Envelope Evolution M-dwarf RV (VLT/FORS2)

    •  WD+dM*in*K2*Campaign*1:* SDSS*J1136+04092 WD atmospheric parameters (SOAR) Teff *=*12,330*±*260*K2 log(g)*=*7.99*±*0.06*(0.601(±(0.036(M! ) . SDSS SOAR VLT Hermes+/2015,/arXiv:/1505.01848# Porb *=*6.8976*hr2
  13. A New K2 View on Common-Envelope Evolution M-dwarf RV (VLT/FORS2)

    Porb *=*6.8976*hr2 (Model:/Doppler/beaming,/reflection,/ellipsoidal/ variations/using/spectroscopic/parameters)2 •  WD+dM*in*K2*Campaign*1:* SDSS*J1136+04092 WD atmospheric parameters (SOAR) Teff *=*12,330*±*260*K2 log(g)*=*7.99*±*0.06*(0.601(±(0.036(M! ) . SDSS SOAR VLT Hermes+/2015,/arXiv:/1505.01848# Folded K2 light curve
  14. A New K2 View on Common-Envelope Evolution 10500 11000 11500

    12000 12500 White dwarf effective temperature (K) 0.54 0.56 0.58 0.60 0.62 0.64 0.66 0.68 0.70 White dwarf mass (Msun) 10500 11000 11500 12000 12500 White dwarf effective temperature (K) −5.6 −5.4 −5.2 −5.0 −4.8 −4.6 −4.4 Hydrogen layer mass (log MH/Mstar) 20 22 24 26 28 30 32 34 7 independent pulsation modes 19σ(Spectroscopic( Teff( /(mass. Best( asteroseismic(fit. Hermes+/2015,/arXiv:/1505.01848# See(poster(#3(by(A.(Bischoff9Kim.
  15. A New K2 View on Common-Envelope Evolution Hermes+/2015,/arXiv:/1505.01848# J1136+0409/Prot :*

    2.49*±*0.53*hr2
  16. A New K2 View on Common-Envelope Evolution 10 1 100

    101 102 White Dwarf Rotation Period (hr) 0 1 2 3 4 5 6 N Non-magnetic CVs Pulsating white dwarfs J1136+0409 J1136+0409/Prot :* 2.49*±*0.53*hr2 ~Days ~Minutes •  No*isolated*WD*rotates*this*fast2 •  No*accretion*history*in*J1136+04092 •  RGB(core(evolution(influenced(by( common(envelope(ejection. Hermes+/2015,/arXiv:/1505.01848#
  17. "  Core Angular Momentum Evolution "  Kepler’s View of the

    ZZ Ceti Instability Strip "  The Unexpected (?!) "  What’s On Deck
  18. The Empirical DAV Instability Strip Today # Gianninas+/2011# Tremblay+/2011# 3DRCorrected/Atmospheric/Parameters,/ML2/α/=/0.8

  19. Convective Driving: WD Cools, Periods Increase

  20. Convective Driving: WD Cools, Periods Increase Mukadam+/2006# V. Van Grootel

    et al.: The instab Fig. 2. Structure of the envelope of our representative evolving 0.6 M DA white dwarf. The ordinate gives the fractional mass depth in loga rithmic units. The small dots define “isocontours” of opacity, and som Surface Core Base(of( convection(zone( deepens(as(WD(cools. Van/Grootel+/2012#
  21. 1000 s 200 s 500 s

  22. "  Core Angular Momentum Evolution "  Kepler’s View of the

    ZZ Ceti Instability Strip "  The Unexpected (?!) "  What’s On Deck
  23. KASC6 Sydney: ‘Large-Scale Flux Excursions’ 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+/2015,/in/review# 3 months: 1 month: 1 week:
  24. KASC6 Sydney: ‘Large-Scale Flux Excursions’ 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+/2015,/in/review# 3 months: 1 month: 1 week: e measured equivalent durations of the 186 outbursts at were recorded without interruption from gaps in the ta is displayed in Figure 4 and the continua used for e example outbursts are the dashed lines in Figure 3. e median outburst equivalent duration is 6.8 minutes he corresponding outburst is displayed in the second nel of Figure 3). Since the Kepler point-to-point scat- is 1.8% for this target, we are limited to detecting ly large outbursts by eye and so are undoubtedly in-
  25. KASC6 Sydney: ‘Large-Scale Flux Excursions’ 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+/2015,/submi^ed# 3 months: 1 month: 1 week: e measured equivalent durations of the 186 outbursts at were recorded without interruption from gaps in the ta is displayed in Figure 4 and the continua used for e example outbursts are the dashed lines in Figure 3. e median outburst equivalent duration is 6.8 minutes he corresponding outburst is displayed in the second nel of Figure 3). Since the Kepler point-to-point scat- is 1.8% for this target, we are limited to detecting ly large outbursts by eye and so are undoubtedly in- Broad power bands reminiscent of stochastic driving
  26. A Second Case of Outbursts in a Cool DAV PG/1149+057:/Hermes+/2015,/submi^ed#

    1145.7 s, 998.1 s, 1052.8 s
  27. A Second Case of Outbursts in a Cool DAV PG/1149+057:/Hermes+/2015,/submi^ed#

    1145.7 s, 998.1 s, 1052.8 s
  28. A Second Case of Outbursts in a Cool DAV PG/1149+057:/Hermes+/2015,/submi^ed#

    •  No(companion(earlier(than(L3:( This*is*happening*on*the*white*dwarf2 SDSS image K2 pixels 11,000*K,*log(g)=8.0*model* (3σ*uncertainties*smaller*than*each*point)
  29. (An Aside: The Ecliptic is Full of Asteroids!) •  Always*check*the*target*

    pixels*if*you*see*a* blip*in*your*K2*light*curve2 Data*from*J1136+0409* (WD+dM*from*earlier)/ h9p://barentsen.github.io/k2flix/7 K2flix
  30. The Outbursts are Not Blips from Asteroids! PG/1149+057:/Hermes+/2015,/submi^ed# K2 Campaign

    1 full light curve Prot *≈*1.2*d2
  31. Pulsations Persist in Outburst •  White*dwarf*Teff *=*11,060*K2 •  #*14%*mean*flux**=**#*750*K2 • 

    #*>25%*flux**=**#*>1500*K2
  32. A Second Case of Outbursts in a Cool DAV PG/1149+057:/Hermes+/2015,/submi^ed#

    •  Pulsations(change(after(outburst2
  33. A Second Case of Outbursts in a Cool DAV PG/1149+057:/Hermes+/2015,/submi^ed#

    (3Rday/sliding/window)
  34. Potential Outburst Mechanisms in Cool DAVs •  Magnetism(unlikely:*τdynamical * only*a*few*s2

    •  Nuclear(burning(unlikely:* T*<*106*K*at*τthermal *of*recurrence* timescale*(~7.7*d)2 •  Rocky(accretion(unlikely:*No* spectroscopic*metal*lines2 •  Most(likely(connected(to( pulsations. Base of convection zone Surface Deeper
  35. Most Modes Bounded by Base of Convection Zone •  Growth*time*~days:**

    2 2γ:1*≈*nτω****2 •  For/~1000/s/modes:# –  Radial/order/n/~/20# –  τω* =* τthermal*at*top* 22 2of*mode*cavity* τω* ~*hrs2 Goldreich/&/Wu/I,/1999#
  36. Most Modes Bounded by Base of Convection Zone •  Growth*time*is*days*for*~1000*s*(~1000*mHz)*modes2

    Full K2 light curve: PG1149+057
  37. Potential Outburst Mechanisms in Cool DAVs •  Nonlinear*mode* coupling,*parametric* instability?(

    (Wu*&*Goldreich*IV,*1999)2 •  ?2 The/two/outbursting/ DAVs/in/Kepler2 One quarter: KIC 4552982
  38. "  Core Angular Momentum Evolution "  Kepler’s View of the

    ZZ Ceti Instability Strip "  The Unexpected (?!) "  What’s On Deck
  39. The Future: K2’s Expanding View of DAVs •  So*far,* 10*pulsating*white*dwarfs*with*

    >1*month*short:cadence*data2 •  45*excellent*candidates*through* Campaign*10*(7*known*DAVs)2
  40. Conclusion: Pulsating WDs in Kepler and K2 •  Rotation*rates*of*isolated*WDs*and*now*a*close*binary*WD* constrain*core*angular*momentum*evolution2

    •  Biggest*white*dwarf*discovery*so*far:*Outbursts*in*the*coolest* DAVs*with*very*deep*convection*zones2
  41. None