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The Menagerie of Hydrogen-Deficient White Dwarfs

jjhermes
September 11, 2018

The Menagerie of Hydrogen-Deficient White Dwarfs

Conference presentation, 30 min. September 2018: Hydrogen Deficient Stars 2018, Armagh, Northern Ireland, UK.

jjhermes

September 11, 2018
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  1. The menagerie of
    hydrogen-deficient
    white dwarfs
    http://jjherm.es
    J.J. Hermes
    Hubble Fellow
    University of North Carolina
    at Chapel Hill

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  2. Outline: The Menagerie of Hydrogen-Deficient WDs
    via single-star
    progenitors
    via binary
    coalescence
    DA
    DB
    hot DQ
    LP 40-365

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  3. Outline: The Menagerie of Hydrogen-Deficient WDs
    • Spectral evolution of descendants of single stars
    • Asteroseismic constraints of H layers in DA (H-dominant) WDs
    • Kinematics and masses of DAs and non-DAs
    • Evidence for a population of WD+WD mergers: the hot DQs
    • New class partially burnt supernova remnants slungshot from
    the Galaxy (e.g., LP 40-365)

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  4. What Do We Mean by ‘White Dwarf’?
    • a stellar remnant that
    is no longer fusing
    in its core
    • the endpoints of
    everything < 8 M¤
    • electron degeneracy
    limits WD mass to
    < 1.4 M¤
    A ‘typical’ white dwarf
    electron degenerate
    C/O core
    (r = 8500 km)
    non-degenerate
    He layer
    (260 km) non-degenerate
    H layer
    (30 km)
    [thermal reservoir]
    [insulating blanket]
    DA

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  5. 4000 4500 5000 5500 6500
    DA DA: H
    DB: He
    DQ: C2
    (‘Swan bands’)
    DC: [continuum]
    DZ: [metals]
    DB
    DZ
    DQ
    DC
    The Most Common White Dwarf Flavours in Nature
    adapted from
    Wesemael et al. 1993

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  6. Appeal to the Modern: the Gaia Colour-Magnitude Diagram
    Gaia Collaboration, Babusiaux et al. 2018

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  7. 100 pc sample: 18,702 high-probability WDs
    100 pc sample: Gentile Fusillo et al. 2018

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  8. 100 pc sample: 2145 WDs with spectroscopy
    DA: log(g) = 8.0
    DA: log(g) = 9.0
    100 pc sample: Gentile Fusillo et al. 2018
    crossed with the Montreal White Dwarf Database: Dufour et al. 2015

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  9. 100 pc sample w/ spectra: 1578 (~75%) are DAs
    DA: log(g) = 8.0
    DA: log(g) = 9.0
    100 pc sample: Gentile Fusillo et al. 2018
    crossed with the Montreal White Dwarf Database: Dufour et al. 2015

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  10. 100 pc sample w/ spectra: 88 (~4%) are DBs
    DA: log(g) = 8.0
    DA: log(g) = 9.0
    100 pc sample: Gentile Fusillo et al. 2018
    crossed with the Montreal White Dwarf Database: Dufour et al. 2015

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  11. Gaia Shows Spectral Types are Temperature-Dependent

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  12. The Balmer Jump Strongly Affects WD Atmospheres
    DA: log(g) = 8.0
    200 pc sample: Gentile Fusillo et al. 2018
    crossed with the Montreal White Dwarf Database: Dufour et al. 2015

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  13. Gaia CMD Shows Spectral Types are Evolution-Dependent
    DA: log(g) = 8.0
    200 pc sample: Gentile Fusillo et al. 2018
    crossed with the Montreal White Dwarf Database: Dufour et al. 2015

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  14. 100 pc sample w/ spectra: ~25% non-DA

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  15. DA vs. non-DA Ratio is a Function of Sample Selection
    100 pc sample (volume-limited):
    DA: ~65%
    non-DA: ~35%
    SDSS sample (magnitude-limited):
    DA: ~80%
    non-DA: ~20%
    e.g., Kleinman et al. 2013
    Kilic et al. 2018

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  16. Gaia CMD Shows Spectral Types are Evolution-Dependent
    200 pc sample: Gentile Fusillo et al. 2018
    crossed with the Montreal White Dwarf Database: Dufour et al. 2015

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  17. Dredge-Up from Convection Leads to Spectral Evolution
    • DB à DQ when He convection reaches c2
    =nC
    /(nHe
    +nC
    ) > 10-6
    • This naturally explains the cool DQs
    • Eventually all line opacities fade the WD into a DC
    Fontaine & Wesemael 1991
    45 kK 18 kK 8 kK
    He convection
    zone
    c2
    = nC
    /(nHe
    +nC
    )
    c2
    = 10-10
    c2
    = 0.99
    core
    photosphere
    log M/M★

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  18. When Cool Enough, a DA can Transform to a DB
    • With a thin enough H layer (figure shows 10-11 MH
    /M

    ),
    a DA convection zone dredges up He
    • Again, eventually all line opacities fade the WD into a DC
    Fontaine & Wesemael 1991
    H convection
    zone
    towards core
    log M/M★

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  19. First Clue to Spectral Evolution: The ‘DB gap’
    • First big clue of spectral evolution: the ‘DB gap’, which is a
    dearth of DBs between 30-45 kK
    • Requires H to be very thin (<10-14 MH
    /M

    )
    45 kK 10 kK 6 kK
    Greenstein et al. 1986

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  20. How Thick Is the Hydrogen Layer in Typical DA WDs?
    • We can explore
    chemical layers via
    asteroseismology as
    well as eclipsing
    binaries!
    See wonderful reviews by:
    Winget & Kepler 2008
    Fontaine & Brassard 2008
    Althaus, Córsico, Isern & García-Berro 2010
    A ‘typical’ white dwarf
    electron degenerate
    C/O core
    (r = 8500 km), 99% M

    non-degenerate
    He layer
    (260 km)
    1% MHe
    /M★
    non-degenerate
    H layer
    (30 km)
    <0.01% MH
    /M★
    [thermal reservoir]
    [insulating blanket]
    DA

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  21. WD+dM Eclipsing Binaries: <2% WD Masses, Radii
    • No evidence for very
    thin H layers in 13 WD in
    close WD+dM binaries
    • All have <10-8 MH
    /M

    Parsons et al. 2017
    He-core models
    C/O-core
    models
    Thick H (10-4)
    Thin H (10-10)

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  22. Asteroseismology: Pulsations Constrain Envelope Masses
    Detailed study of two superficially similar
    pulsating WDs: GD 165 and Ross 548
    Giammichele et al. 2015
    Time (s)
    Rel. Flux
    Rel. Flux
    Both white dwarfs have
    Teff
    ~ 12,100 K and are ~0.64 Msun
    but quite different pulsation properties

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  23. Asteroseismology: Pulsations Constrain Envelope Masses
    Thick H Layer: 10-4.23±0.15 MH
    /M

    He Layer: 10-1.70±0.13 MHe
    /M

    Giammichele et al. 2016
    Thin H Layer: 10-7.45±0.12 MH
    /M

    He Layer: 10-2.92±0.10 MHe
    /M

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  24. Asteroseismology: Insights from the Aggregated Periods
    Clemens et al. 2018, in prep.
    Ross 548
    GD 165
    l = 1, k = 2 l = 1, k = 1
    Thick H Layer: ~10-4 MH
    /M

    He Layer: ~10-1.7 MHe
    /M

    “Canonical” nuclear burning
    sets envelope masses
    Thin H Layer: <10-7 MH
    /M

    ~He Layer: 10-2.9 MHe
    /M

    Very late thermal pulses?
    Giammichele et al. 2016
    size = amplitude
    of mode

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  25. Asteroseismology: Insights from the Aggregated Periods
    Clemens et al. 2018, in prep.
    Ross 548
    GD 165
    l = 1, k = 2 l = 1, k = 1
    Thick H Layer: ~10-4 MH
    /M

    He Layer: ~10-1.7 MHe
    /M

    “Canonical” nuclear burning
    sets envelope masses
    Thin H Layer: <10-7 MH
    /M

    ~He Layer: 10-2.9 MHe
    /M

    Very late thermal pulses?
    Interpulse interaction?
    Giammichele et al. 2016
    size = amplitude
    of mode
    ~80% of DAs have canonically thick (~10-4 MH
    /M

    ) envelopes
    ~20% of DAs have thinner (~10-7-9 MH
    /M

    ) envelopes
    N = 14 N = 4

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  26. (Photometric) Mass Distribution of DA vs. DB
    200 pc sample: Gentile Fusillo et al. 2018
    DA: = 0.65 M¤
    DB: = 0.61 M¤
    Mass (M¤
    )

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  27. Kinematic Distribution of DA vs. DB
    200 pc sample: Gentile Fusillo et al. 2018
    DB: >
    = 40.7 km/s
    DA: >
    = 39.7 km/s
    • Historically it has been found
    there is no difference in
    kinematics between DA vs. DB
    • This is consistent with 200 pc
    sample from Gaia
    Sion et al. 1988

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  28. BUT: DQ and maybe DC show bimodality at ~50 km/s
    DB
    DA
    200 pc sample
    DQ
    DC
    • Kinematics can
    give us insights
    into possible
    merger history

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  29. Stars Get Stirred Up Over Time in the Galaxy
    • Hot (>15 kK) massive WDs
    descending from single stars were
    born <1 Gyr ago
    • They should thus have low velocity
    dispersions
    Dunlap & Clemens 2015
    1.2 M¤
    WD
    cooling
    kinematics

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  30. Most Massive DAs Have Low Kinematics
    DA: M < 0.75 M¤
    Teff
    > 15,000 K
    DA: M > 0.90 M¤
    Teff
    > 15,000 K
    Wegg & Phinney 2012
    • PG & SDSS
    samples
    suggest most
    massive DAs
    are evolved
    single stars

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  31. Specifically, Hot DQs Appear to be Merger Byproducts
    • Hot DQs: 18,000-26,000 K
    Dunlap et al. 2018, submitted
    DA < 0.75 M¤
    DA > 0.75 M¤
    hot DQs
    (all >0.90 M¤
    ) Dufour et al. 2008
    see especially Dunlap & Clemens 2015
    • Hot DQs: No H: Mostly C
    Williams et al. 2013

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  32. Specifically, Hot DQs Appear to be Merger Byproducts
    Dufour et al. 2013
    • Hot DQs: 18,000-26,000 K
    • 0.9-1.2 M¤
    WDs (massive)
    • ~70% strongly magnetic
    (>2 MG)
    • Most 5-20 min monoperiodic
    variables (very fast rotation;
    most WD rotate 0.5-2 d)
    Dunlap et al. 2018, submitted
    DA < 0.75 M¤
    DA > 0.75 M¤
    hot DQs
    (all >0.90 M¤
    ) Dufour et al. 2008
    Dunlap et al. 2018
    see especially Dunlap & Clemens 2015
    Williams et al. 2016
    • Hot DQs: No H: Mostly C
    Williams et al. 2013

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  33. Can We Find Further Evidence of Mergers in the CMD?
    100 pc sample: Gentile Fusillo et al. 2018

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  34. Tangential Velocity Cuts in the Gaia CMD
    100 pc sample: Gentile Fusillo et al. 2018

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  35. Tangential Velocity Cuts in the Gaia CMD
    100 pc sample: Gentile Fusillo et al. 2018

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  36. Tangential Velocity Cuts in the CMD
    100 pc sample: Gentile Fusillo et al. 2018

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  37. Using Gaia to Revisit the GD Sample
    Hermes et al. 2018, in prep.
    0.50 0.25 0.00 0.25 0.50 0.75 1.00 1.25
    GBP
    GRP
    [mag]
    0
    2
    4
    6
    8
    10
    12
    14
    MG
    = G + 5 ⇥ log $ 10 [mag]
    DA, log(g) = 8.0
    Z=0.019
    Z=10 2
    Z=10 3
    0
    100
    200
    300
    400
    500
    v? [km s 1]
    • Gaia CMD: <400 WDs among >1700
    WD suspects in Giclas Dwarf catalog
    (Giclas, Burnham & Thomas 1980)

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  38. Using Gaia to Revisit the GD Sample
    Hermes et al. 2018, in prep.
    0.50 0.25 0.00 0.25 0.50 0.75 1.00 1.25
    GBP
    GRP
    [mag]
    0
    2
    4
    6
    8
    10
    12
    14
    MG
    = G + 5 ⇥ log $ 10 [mag]
    DA, log(g) = 8.0
    Z=0.019
    Z=10 2
    Z=10 3
    0
    100
    200
    300
    400
    500
    v? [km s 1]
    • Gaia CMD: <400 WDs among >1700
    WD suspects in Giclas Dwarf catalog
    (Giclas, Burnham & Thomas 1980)
    GD 492

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  39. GD 492 = LP 40-365: A Hyper-Runaway WD
    discovery: Vennes et al. 2017
    follow-up: Raddi et al. 2018a, 2018b
    • LP 40-365 has vrad
    = +499(6) km/s and vrf
    = 852(10) km/s
    • It is unbound, a hyper-runaway not from Galactic center
    • Gaia: 0.18(1) R¤
    , crossed Z = 0 <5.3 Myr ago

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  40. GD 492 = LP 40-365: A Hyper-Runaway, Ne-rich WD
    discovery: Vennes et al. 2017
    follow-up: Raddi et al. 2018a, 2018b
    Iax unburnt remnants
    Iax yields C/O or C/O/Ne
    Iax models from Fink et al. 2014
    and Kromer et al. 2015
    • LP 40-365 is >30% Ne
    and ~2% O by mass
    • H/He < 10-5
    • (He invisible at 8900 K)
    • Alpha elements indicate
    C, Si processing
    • [Mn/Fe] > 7x solar
    • Hypothesis: Remnant
    of SN Iax, near-MCh
    ,
    ejected from <40-min
    binary! (Flip side of coin
    from D6 stars Shen et al. 2018)

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  41. A New Class of Hyper-Runaway, Mg/Ne-rich WD
    Raddi et al. 2018c, in prep.
    • With Gaia we
    found 2 more! (a)
    (b)
    a) 3 mag brighter
    than GD 492;
    much hotter
    and larger; on
    retrograde but
    bound orbit
    b) Complete twin
    to GD 492;
    vRV
    = -480 km/s

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  42. Spectroscopic Twin and Kinematic Doppelgänger to GD 492
    Raddi et al. 2018c, in prep.
    • Nearly identical radius
    and mass; vrf
    = 800 km/s
    (also unbound)
    • GD 492 has a slightly
    higher Mg abundance
    • Otherwise, they are
    startlingly similar
    • Formation mechanism
    for these slung-shot
    remnants must be
    similar

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  43. LP 40-365 and D6 Friends
    LP 40-365
    LP 40-365
    D6
    LP 40-365: Raddi et al. 2018b
    D6: Shen et al. 2018
    DOx

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  44. Are ’DOx’ Cooled-Down, Non-Ejected Versions of LP 40-365?
    first O-rich WDs: Gänsicke et al. 2008
    Most O-rich: Kepler, Koester & Ourique 2016
    • SDSSJ1240+6710 is 21 kK
    • Composed of 99.9% O
    • log(g) suggests 0.56 M¤
    • Vrf
    = 260 km/s, but on a
    retrograde orbit
    Kepler, Koester & Ourique 2016
    • SDSS has found spectra
    of a few log(g) ~ 8.0 WDs
    with no H and very high
    O content: so-called DOx
    LP 40-365
    D6
    DOx

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  45. Summary: The Menagerie of Hydrogen-Deficient WDs
    • Gaia shows WD spectral types are strongly dependent on cooling
    • Spectral evolution (DAà DB à DQ, etc.) involves both convective dredge-
    up and requires a range of H-layer masses (>10-4 to <10-15 MH
    /M

    )
    • Asteroseismology: ~80% of DAs have canonically thick H layers (>10-4 MH
    /M

    )
    • Gaia: Possible evidence of kinematic difference between DA and DQ?
    • Gaia: No difference in mean mass between DA and DB
    • The hot DQs (>18 kK) are massive, magnetic, rapid rotators, kinematicallyhot
    • LP 40-365 is the first in a class of Mg- and Ne-rich, hyper-runaway remnants
    work led by Roberto Raddi
    work led by Bart Dunlap
    work led by Chris Clemens

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  46. 10-4-6
    MH
    /M

    10-6-14
    <10-15
    DAO DA DC
    DAO DA DC
    PG1159 DO DA DB DQ DC
    ~60 kK ~6 kK
    ~60 kK ~10 kK
    ~100 kK ~45 kK ~30 kK ~12 kK ~6 kK
    WD+WD hot DQ DC
    SN Iax LP 40-365 DOx?
    Mostly from single-star evolution
    Mostly from binary coalescence
    ~65%
    DA
    ~35%
    non-DA
    <1%
    DQ
    ~80% DAs
    (~50% total)
    ~20% DAs
    (~15% total)
    bound remnant unbound; Ne-rich O/C > 1
    kinematics; mass; magnetic; fast Prot
    DA CZ
    <13 kK
    DB CZ
    <13 kK
    gravitation settling dominates <80 kK
    radiative levitation impactful >25 kK
    winds possible > 35 kK?

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