Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Watching stellar evolution all the way to the closing credits

jjhermes
September 19, 2016

Watching stellar evolution all the way to the closing credits

Conference presentation, 25 min. September 2016: Understanding the roles of rotation, pulsation and chemical peculiarities in the upper main sequence, Windermere, Cumbria, UK.

jjhermes

September 19, 2016
Tweet

More Decks by jjhermes

Other Decks in Science

Transcript

  1. http://jjherm.es
    J.J. Hermes
    Hubble Fellow
    University of North Carolina at Chapel Hill
    Watching Stellar Evolution All
    the Way to the Closing Credits

    View full-size slide

  2. U. North Carolina: Chris Clemens, Bart Dunlap, Erik Dennihy, Josh Fuchs, Stephen Fanale
    U. Warwick: Boris Gaensicke, Paul Chote, Roberto Raddi, Nicola Gentile Fusillo, Dave Armstrong,
    Pier-Emmanuel Tremblay
    U. Texas: Keaton J. Bell, Mike Montgomery, Don Winget
    U. Oklahoma: Mukremin Kilic, Alex Gianninas Harvard/Smithsonian: Warren R. Brown
    + S.O. Kepler, Alejandra Romero, Agnes Bischoff-Kim, Steve Kawaler, Alex Gianninas
    Watching Stellar Evolution All
    the Way to the Closing Credits

    View full-size slide

  3. Watching Stellar Evolution All
    the Way to the Closing Credits

    View full-size slide

  4. • White dwarfs are a remarkably homogenous byproduct of stellar evolution
    – Clustered mean mass, compositional stratification, simple evolution (just cooling)
    • Exploiting deviations from that simplicity yields rich insights
    Don Winget: “White Dwarfs Shed Their Complexity”

    View full-size slide

  5. Chemical Peculiarities

    View full-size slide

  6. Typical DA white dwarf log(g) = 8.0
    • Settling times << years
    • Radiative levitation inefficient <25,000 K
    • Expect pure hydrogen photospheres

    View full-size slide

  7. DA white dwarf + metals
    But many show metals!

    View full-size slide

  8. • Consensus: Metals are from accreted, tidally disrupted debris
    – 25-50% of all WDs are metal polluted (Koester et al. 2014)
    – WD debris is comparable to bulk Earth (dominated by Fe, O, S, Mg)
    – Some of this debris is
    water-rich! (Farihi et al. 2013)
    • Planetary systems around
    A stars are very common
    Metals in Typical WDs: Planetary Debris

    View full-size slide

  9. Tremblay et al. 2016
    Kleinman et al. 2013
    • 80%+ of WDs have hydrogen-dominated atmospheres (DA)
    • Estimate masses from observed Balmer line profiles: Teff
    /log(g)
    Most White Dwarfs: 0.6 Solar Masses
    He-Core WDs
    G+ progenitors
    CO-Core WDs
    A/F/G progenitors
    ONe-Core WDs
    B+ progenitors
    < 0.45 M¤
    excluded
    here

    View full-size slide

  10. • The Galaxy is not old enough for a
    single star to evolve into a < 0.30 M¤
    white dwarf
    • “Low-mass white dwarfs need friends”
    (Marsh et al. 1995)
    • Friends à binary companions
    – Effectively strip mass on RGB,
    leaving behind an ELM WD
    David A. Aguilar, CfA
    Extremely Low-Mass (ELM) White Dwarf Stars

    View full-size slide

  11. phase = 0
    • This is the most compact detached binary
    system currently known! In <1 Myr they’ll be
    really good friends.
    J0651+2844: A 12.75-min WD+WD Binary
    Brown et al. 2011

    View full-size slide

  12. (from Phase 0 to Phase 1 is 12.75 minutes)
    Hermes et al. 2012
    Porb
    = 765.20644(95) s
    i = 86.3 ± 1.0 deg
    K1
    = 616.9 ± 5.0 km s-1
    Teff,1
    = 16,340 ± 260 K
    M1
    = 0.247 ± 0.04 M¤
    Teff,2
    = 10,370 ± 360 K
    M2
    = 0.49 ± 0.04 M¤
    J0651+2844: A 12.75-min WD+WD Binary

    View full-size slide

  13. We expect dPorb
    /dt = (-0.26 ± 0.05)ms/yr; observe (-0.2891 ± 0.0028)ms/yr!
    – a measurement to <1% !
    An Optical Detection of Gravitational Waves!
    Hermes et al. 2012, 2016 (in prep.)

    View full-size slide

  14. GALEX J1717: A 5.9-hr, Eclipsing WD+WD
    R1
    = 0.093 ± 0.013 R¤
    = 0.9 RJupiter
    i = 86.9 ± 0.4 deg
    Porb
    = 5.90724895(41) hr
    -20
    vrot
    = 50+30 km s-1
    Prot
    = 2.3+2.0 hr
    Hermes et al. 2014
    • Prot
    < Porb
    but not yet formally
    significant
    • Direct test of tidal
    synchronization!
    -1.0
    secondary primary

    View full-size slide

  15. Mean Earth--Moon
    separation
    Minimum WD+WD
    (J0651+2844, 12.75-min)
    Median ELM Survey (~5.4 hr)
    Maximum
    ELM Survey
    (J0815+2309, 25.8-hr)
    1 R¤
    The ELM Survey At a Glance
    Brown et al. 2016
    + Gianninas, Kilic
    • 80+ ELM WD binaries solved
    • M1
    range: 0.16-0.32 M¤
    • Median M2
    : 0.76 M¤

    View full-size slide

  16. • Zeeman surface field limits exclude >200 kG for all 80 ELM WDs
    • These are stripped
    descendants of
    suppressed dipole
    mode red giants
    (Stello, Fuller, Cantiello, et al.)
    • No history of
    core He burning
    • Do all ELMs have
    <1.5 M¤
    progenitors?
    Slow Ohmic diffusion?
    No strong internal B-fields?
    Aside: No ELM White Dwarf Is Strongly Magnetic
    Fit courtesy of Alex Gianninas
    Teff
    = 12240(180) K, log(g) = 5.75(04) à 0.17 M¤

    View full-size slide

  17. Insights from Asteroseismology

    View full-size slide

  18. Discovery of Pulsations in Low-Mass White Dwarfs
    Hermes et al. 2012, 2013
    Kilic et al. 2015
    • In October 2011 we discovered the first
    pulsating low-mass, He-core WD from
    McDonald Observatory: Now six known
    • The first pulsating ELM WD around a
    millisecond pulsar, PSR J1738+0333
    • ELM white dwarfs have much longer
    pulsation periods (1100-6200 s) than
    C/O-core WDs (100-1400 s): less dense!
    • g-mode period spacing of ~100 s rather
    than ~40 s

    View full-size slide

  19. Original Kepler Mission:
    20 WDs observed,
    6 pulsating WDs
    (just two >3 months)
    K2 through Campaign 8:
    >930 WDs observed
    35 pulsating WDs
    K2 through Campaign 13:
    >1200 WDs,
    >50 pulsating WDs (~240 known today)
    K1
    K2, today
    K2, by mid-2017

    View full-size slide

  20. Aside: White Dwarfs Are Good Flux Standards
    >95% of all spectroscopically
    confirmed white dwarfs in Kepler/K2
    are flux constant to <1% on 30-min to
    10-day timescales.
    Hermes et al. 2016 (in prep.)

    View full-size slide

  21. Caveats: Binarity, Magnetism, Pulsations
    Doppler beaming & eclipses in WD+WD
    EPIC 210659779, K2 C4, Kp
    = 16.5
    Reflection effect in close binary
    Hermes et al. 2016 (in prep.)

    View full-size slide

  22. Caveats: Binarity, Magnetism, Pulsations
    Hermes et al. 2016 (in prep.)

    View full-size slide

  23. 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
    Hermes et al. 2016 (in prep.)

    View full-size slide

  24. EC 14012-1446, r = 15.7 mag 98.2% duty cycle for 78.9 days
    Caveats: Binarity, Magnetism, Pulsations

    View full-size slide

  25. DA (hydrogen atmosphere)
    WDs pulsate when H partially
    ionized (DAVs, aka ZZ Cetis)
    in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75,
    170,000 K have the highest number of detected modes. The first class of pulsating st
    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 obser
    locations of the instability strips, following the nonadiabatic calculations of C´
    orsico, Althaus & Mi
    Bertolami (2006) for the DOVs, the pure He fits to the observations of Beauchamp et al. (1999) fo
    DBVs, and the observations of Gianninas, Bergeron & Fontaine (2006) and Castanheira et al. (200
    Annu. Rev. Astro. Astrophys. 2008.46:157-199. Downloa
    by University of Texas - Austin on 01/28/0
    Winget & Kepler 2008, ARA&A, 46, 157

    View full-size slide

  26. Mike Montgomery
    • Pulsations: periodic brightness
    changes, caused by surface
    temperature variations
    • White dwarfs only show
    nonradial pulsations
    (strong surface gravity)

    View full-size slide

  27. Empirical DAV instability strip
    Tremblay et al. 2011
    Gianninas et al. 2011
    Gianninas et al. 2014 (ELMs)
    3D-corrected atmospheric parameters, ML2/α= 0.8

    View full-size slide

  28. m = +1
    m = -1
    m = 0
    1000 s 200 s
    500 s 125 s
    316.8 s
    345.3 s
    n = Number of radial nodes
    l = Number of vertical nodes
    m = Number of horizontal + vertical nodes
    n
    l = 1
    n = 5
    l = 1
    n = 6
    Prot
    = 0.9
    ± 0.2 day

    View full-size slide

  29. Common-Envelope Evolution Affects
    White Dwarf Rotation Rates

    View full-size slide

  30. A K2 View on Close, Evolved Binaries
    M-dwarf RV (VLT/FORS2)
    WD atmospheric parameters (SOAR)
    Teff
    = 12,330 ± 260 K
    log(g) = 7.99 ± 0.06 (0.601 ± 0.036 M¤
    )
    SDSS
    SOAR VLT
    Porb
    = 6.8976 hr
    • WD+dM in K2 Campaign 1:
    SDSS J1136+0409
    Hermes et al. 2015

    View full-size slide

  31. A K2 View on Close, Evolved Binaries
    M-dwarf RV (VLT/FORS2)
    WD atmospheric parameters (SOAR)
    Teff
    = 12,330 ± 260 K
    log(g) = 7.99 ± 0.06 (0.601 ± 0.036 M¤
    )
    SDSS
    SOAR VLT
    Porb
    = 6.8976 hr
    (Model: Doppler beaming, reflection, ellipsoidal
    variations using spectroscopic parameters)
    Folded K2
    light curve
    • WD+dM in K2 Campaign 1:
    SDSS J1136+0409
    Hermes et al. 2015

    View full-size slide

  32. A K2 View on Close, Evolved Binaries
    M-dwarf RV (VLT/FORS2)
    WD atmospheric parameters (SOAR)
    Teff
    = 12,330 ± 260 K
    log(g) = 7.99 ± 0.06 (0.601 ± 0.036 M¤
    )
    SDSS
    SOAR VLT
    Porb
    = 6.8976 hr
    (Model: Doppler beaming, reflection, ellipsoidal
    variations using spectroscopic parameters)
    Folded K2
    light curve
    • WD+dM in K2 Campaign 1:
    SDSS J1136+0409
    Hermes et al. 2015
    5 independent
    pulsation modes

    View full-size slide

  33. A K2 View on Close, Evolved Binaries
    J1136+0409 Prot
    :
    2.49 ± 0.53 hr
    l = 1
    modes
    m = +1
    m = 0
    m = -1
    Hermes et al. 2015

    View full-size slide

  34. A K2 View on Close, Evolved Binaries
    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 hr
    ~Days
    ~Minutes
    • No isolated WD rotates this fast
    • No accretion history in J1136+0409
    • Post-RGB rotation influenced by
    common envelope ejection
    Hermes et al. 2015
    l = 1
    modes
    m = +1
    m = 0
    m = -1

    View full-size slide

  35. Convection Makes Asteroseismology of
    the Coolest White Dwarfs Very Hard

    View full-size slide

  36. Longest-period modes well-described
    by Lorentzian function
    Two modes in the DAV PG1149+057
    Two modes in the DAV ATLASJ1342-0735
    HWHM:
    0.05 µHz
    HWHM:
    1.54 µHz
    HWHM:
    0.06 µHz
    HWHM:
    2.23 µHz
    (No possible way to make this
    observation before Kepler.)
    Hermes et al. 2016 (in prep.)

    View full-size slide

  37. Results from fitting a Lorentzian to the 21
    DAVs with measured Teff
    observed so far:
    Clear dichotomy at ~800 s
    Hermes et al. 2016 (in prep.)

    View full-size slide

  38. • Damping rather than driving
    important for broadening; phase incoherence
    • ML2/α sets the base of convection zone and must be a free parameter
    Surface
    Core
    Broadened modes: bounded by the base of the convection zone!
    Montgomery et al.
    2016 (in prep.)

    View full-size slide

  39. Mode Coupling Transfers Pulsation Energy

    View full-size slide

  40. The First Kepler Pulsating White Dwarf was Weird
    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 pane
    shows the full Q11 light curve. The one-month shaded region in the top panel is expanded in the middle panel. The one-week shade
    region in the middle panel is expanded in the bottom panel. The solid line is the light curve smoothed with a 30-minute window. Th
    point-to-point scatter dominates the pulsation amplitudes in the light curve, so pulsations are not apparent to the eye. The dramati
    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-
    ues of Te↵ = 11, 129 ± 115 K, log g = 8.34 ± 0.06, and
    tion rate. We summarize our findings and conclude i
    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

    View full-size slide

  41. In K2, Things Got Weirder
    • In the first K2 campaign we saw another case of outbursts
    • These outbursts are essentially rogue waves (or freak waves) on a
    pulsating star!
    • Never seen before in 40+ years of pulsating white dwarfs
    PG 1149+057: Hermes et al. 2015
    Quiescence
    (1151.9 s, 1160.8 s, …)
    In Outburst
    (999.9 s, 896.6 s, …)
    g = 14.9 mag

    View full-size slide

  42. oDAV1
    10860 K
    0.70 M¤
    oDAV2
    11060 K
    0.64 M¤
    oDAV3
    10570 K
    0.56 M¤
    oDAV4
    11190 K
    0.62 M¤
    oDAV5
    10850 K
    0.53 M¤
    K2 keeps finding outbursting white dwarfs: Now 7 known! All aperiodic!

    View full-size slide

  43. 52 WDs within 2000 K of 10900 K do not
    outburst from K2 30-min-cadence data
    First 5 outbursting DAVs: Coolest DAVs, deepest convection zones
    Bell et al. 2016, arXiv: 1607.01392

    View full-size slide

  44. Potential Outburst Mechanisms in Cool DAVs
    l=1
    l=2
    Adiabatic Model: 11,245 K, 0.632 M¤
    , 10-4.12 MH
    /MWD
    Observed: 11,060(170) K, 0.64(0.03) M¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)

    View full-size slide

  45. Potential Outburst Mechanisms in Cool DAVs
    l=1
    l=2
    Adiabatic Model: 11,245 K, 0.632 M¤
    , 10-4.12 MH
    /MWD
    Observed: 11,060(170) K, 0.64(0.03) M¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)

    View full-size slide

  46. Potential Outburst Mechanisms in Cool DAVs
    • Wu & Goldreich predicted nonlinear mode coupling could transfer
    energy into damped modes in the cool DAVs Wu & Goldreich2001, ApJ, 546, 469
    l=1
    l=2
    Adiabatic Model: 11,245 K, 0.632 M¤
    , 10-4.12 MH
    /MWD
    Observed: 11,060(170) K, 0.64(0.03) M¤
    (Romero et al. 2012)
    (Gianninas et al. 2011)

    View full-size slide

  47. Enough Energy in One Mode to Power Outbursts
    (3-day sliding window)
    PG 1149+057: Hermes et al. 2015
    • Of order 1033-1034 erg per outburst
    • At least 1033 erg kinetic energy in a
    single mode (e.g., l=1,n=24 ωp
    )

    View full-size slide

  48. Zong et al. 2016
    Other KeplerWDs show observed
    amplitude/frequency evolution best explained by
    nonlinear mode coupling

    View full-size slide

  49. • White dwarfs are a remarkably homogenous byproduct of stellar evolution
    – Clustered mean mass, compositional stratification, simpleevolution (just cooling)
    • Set boundary conditions on stellarand binaryevolution
    • K2 is changing the game:
    – Will more than triple measured rotation rates
    – Common-envelope evolution insights
    – Evidence of transfer of energy from nonlinear mode coupling
    – Ensemble asteroseismology,even constraints on convective efficiency
    White Dwarfs: Beyond The Closing Credits

    View full-size slide

  50. Pulsations Persist in Outburst
    • White dwarf Teff
    = 11,060 K
    • é 14% mean flux = é 750 K
    • é >25% flux = é >1500 K
    Black line is
    30-min running mean
    Event 1
    Event 7
    Quiescence

    View full-size slide

  51. Pulsations Change in Outburst
    In outburst:
    - Larger pulsation amplitudes
    - Shorter-period pulsations
    PG 1149+057: Hermes et al. 2015

    View full-size slide