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Searching for signposts of failed white dwarf supernovae

jjhermes
April 18, 2022

Searching for signposts of failed white dwarf supernovae

Colloquium, 45 min. April 2022: Pitt/CMU Astrophysics Colloquium, Pittsburgh, PA, USA.

jjhermes

April 18, 2022
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  1. Searching for signposts of
    failed white dwarf supernovae
    sites.bu.edu/buwd
    @jotajotahermes
    J.J. Hermes
    Mark Garlick

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  2. JJ Hermes, Boston University | Pitt/CMU | 2
    White Dwarf Stars are the Endpoints of Stellar Evolution
    • a stellar remnant
    that is no longer
    fusing in its core
    • the endpoints of all
    stars that begin
    their lives < 8 M¤
    • electron degeneracy
    limits WD mass to
    < 1.4 M¤
    A typical 0.6 solar-mass
    white dwarf
    electron degenerate
    C/O core
    (r = 8500 km)
    non-degenerate He
    layer
    (260 km)
    non-degenerate H
    layer
    (30 km)

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  3. JJ Hermes, Boston University | Pitt/CMU | 3
    Type Ia Supernova: Standardizable Fully Disrupted White Dwarfs
    SN1994D
    Pearson

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  4. JJ Hermes, Boston University | Pitt/CMU | 4
    We Now Often Observe WDs in the Act of Merging!
    Average distance between Earth and Moon:
    Brown et al. 2011;
    Hermes et al. 2012
    M
    2
    = 0.51 M
    ¤
    M
    1
    = 0.26 M
    ¤
    SDSSJ0651+2844 is a 12.75-min WD+WD binary

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  5. JJ Hermes, Boston University | Pitt/CMU | 5
    We Now Often Observe WDs in the Act of Merging!
    SDSSJ0651+2844 is a 12.75-min WD+WD binary
    Brown et al. 2011;
    Hermes et al. 2012

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  6. Hermes et al. 2022, in prep.
    JJ Hermes, Boston University | Pitt/CMU | 6
    Expected dPorb
    /dt =
    (-0.263 ± 0.020) ms/yr from GR
    Observed dPorb
    /dt =
    (-0.28688 ± 0.00072) ms/yr!
    M
    tot
    = 0.770 ± 0.039 M
    ¤
    L
    GW
    = 2.85 L
    ¤
    L
    EM
    = 0.05 L
    ¤
    SDSSJ0651+2844 is a 12.75-min WD+WD binary

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  7. JJ Hermes, Boston University | Pitt/CMU | 7
    M
    tot
    = 0.770 ± 0.039 M
    ¤
    that will merge in less than 1 million years
    D. Berry, GSFC
    SDSSJ0651+2844 is a 12.75-min WD+WD binary
    There should be many merger byproducts masquerading as
    ‘normal’ white dwarfs in the field

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  8. JJ Hermes, Boston University | Pitt/CMU | 8
    Zwicky Transient Facility (ZTF) has found >15 WD+WD binaries with Porb
    < 1 hr
    that will all merge within 60 Myr, but none have total mass >1.1 M¤
    Burdge et al. 2020
    There should be many merger byproducts masquerading as
    ‘normal’ white dwarfs in the field

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  9. JJ Hermes, Boston University | Pitt/CMU | 9
    We can also search for WD+WD binaries from radial-velocity changes
    Maoz, Hallakoun & Badenes 2018
    Badenes & Maoz 2012
    Modeling RV changes shows WDs have a ~10% binary fraction <4 au
    The observed WD merger rate is 6-7 times higher than the SN Ia rate
    Chandra et al. 2021, using SDSS-V

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  10. JJ Hermes, Boston University | Pitt/CMU | 10
    Simulated Populations of Evolved Binaries Predicts Many Mergers
    Temmink et al. 2020
    Population synthesis modeling expects >25% of
    all white dwarfs to arise from stellar mergers

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  11. Gaia has Revolutionized Our Ability to Find White Dwarfs
    Gaia Collaboration,
    Babusiaux et al. 2018
    JJ Hermes, Boston University | Pitt/CMU | 11
    Sun-like stars
    white dwarfs
    Bluer (hotter) Redder (cooler)
    Absolute G Magnitude (Distance Normalized)
    • Before Gaia we knew of
    ~35,000 white dwarfs
    (mostly from SDSS)
    • Gentile Fusillo et al. 2021
    catalog of ~360,000 high-
    confidence WDs from
    Gaia eDR3

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  12. We Can Test Ages with Wide Pairs of White Dwarfs
    JJ Hermes, Boston University | Pitt/CMU | 12
    El-Badry, Rix & Heintz 2021
    Gaia has revealed >1500 wide
    (>100 au) WD+WD binaries
    Tyler Heintz (BU)
    • Both WD components should be coeval, so we
    should infer the same total age!
    • We have used this sample to empirically test
    WD age determination (good to at least 25%)

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  13. We Can Test Ages with Wide Pairs of White Dwarfs
    JJ Hermes, Boston University | Pitt/CMU | 13
    El-Badry, Rix & Heintz 2021
    Tyler Heintz (BU)
    Gaia has revealed >1500 wide
    (>100 au) WD+WD binaries

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  14. We Can Test Ages with Wide Pairs of White Dwarfs
    JJ Hermes, Boston University | Pitt/CMU | 14
    Roughly 40% of wide WD+WD
    have a more massive component
    that is hotter – its age was “reset”
    by a merger
    Thus ~40% of wide WD+WD
    binaries were once triples
    Heintz, Hermes, El-Badry et al. 2022 Tyler Heintz (BU)

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  15. JJ Hermes, Boston University | Pitt/CMU | 15
    Can We Distinguish Merged WDs? What is a Normal WD?
    Composition | Mass | Rotation
    adapted from Wesemael
    et al. 1993
    The majority (>2/3) of white dwarfs are H dominated
    Mostly H-dominated
    4000 4500 5000 5500 6500
    DA: H

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  16. JJ Hermes, Boston University | Pitt/CMU | 16
    Composition | Mass | Rotation
    Tremblay et al. 2016
    Mostly H-dominated ~0.6 M
    ¤
    The vast majority
    of white dwarfs
    have a mass near
    0.55-0.65 M¤
    Can We Distinguish Merged WDs? What is a Normal WD?

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  17. JJ Hermes, Boston University | Pitt/CMU | 17
    Composition | Mass | Rotation
    Winget & Kepler
    2008
    Mostly H-dominated ~0.6 M
    ¤
    maximum associated with the onset of significant partial ionization.
    Observations soon caught up. A systematic survey of the DB white dwarf stars de
    that the brightest DB with the broadest He I lines, GD 358, did indeed pulsate i
    g-modes—remarkably similar to the large-amplitude DAV pulsators (Winget et al. 19
    The observed pulsating white dwarf stars lie in three strips in the H-R diagram,
    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 ob
    Annu. Rev. Astro. Astrophys. 2008.46:157-199. Downloaded from arjour
    by University of Texas - Austin on 01/28/09. For personal
    Asteroseismology can probe
    core composition, mass, and
    WD rotation
    Can We Distinguish Merged WDs? What is a Normal WD?

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  18. JJ Hermes, Boston University | Pitt/CMU | 18 Hermes et al. 2017
    1000 s 200 s
    500 s 125 s
    Typical K2 data from a
    pulsating white dwarf
    345.3 s
    l = 1
    n = 6
    Prot
    = 0.9 ±
    0.2 day
    Composition | Mass | Rotation
    Mostly H-dominated ~0.6 M
    ¤
    Asteroseismology can probe
    core composition, mass, and
    WD rotation
    Can We Distinguish Merged WDs? What is a Normal WD?

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  19. JJ Hermes, Boston University | Pitt/CMU | 19
    Prot
    = 0.5-2 days
    1 10 100
    WD Rotation Period (hr)
    0.4
    0.5
    0.6
    0.7
    0.8
    0.9
    WD Mass (MØ)
    1.0
    1.5
    2.0
    2.5
    3.0
    3.5
    4.0
    ZAMS Progenitor Mass (MØ)
    1 10 100
    White Dwarf Rotation Period (hr)
    0
    2
    4
    6
    8
    10
    12
    14
    16
    N
    TESS
    Kepler/K2
    pre-Kepler
    1 d 2 d 4 d
    Hermes et al. 2017
    The vast majority of pulsating
    white dwarfs rotate between
    0.5-2 days
    Composition | Mass | Rotation
    Mostly H-dominated ~0.6 M
    ¤
    TESS update from
    Romero, Kepler, Hermes et al. 2022
    Can We Distinguish Merged WDs? What is a Normal WD?

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  20. JJ Hermes, Boston University | Pitt/CMU | 20
    What is a normal ‘White Dwarf’?
    A ‘typical’ 0.6 solar-mass
    white dwarf
    H-dominated atmosphere
    ~0.6 M
    ¤
    Prot
    = 0.5-2 days
    The majority of white dwarfs are
    pretty boring – that’s why they’re
    great flux standards!

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  21. JJ Hermes, Boston University | Pitt/CMU | 21
    What are possible signposts of merged WDs?
    Composition | Mass | Rotation | Kinematics
    Mostly H-dominated ~0.6 M
    ¤ Prot
    = 0.5-2 days
    4000 4500 5000 5500 6500
    DA: H
    Some strongly
    magnetic white
    dwarfs show large
    Zeeman splitting of
    the Balmer lines
    Gaensicke et al. 2002

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  22. JJ Hermes, Boston University | Pitt/CMU | 22
    An extreme example of a clear merger remnant
    Composition | Mass | Rotation | Kinematics
    Mostly H-dominated ~0.6 M
    ¤ Prot
    = 0.5-2 days
    Caiazzo et al. 2021
    P
    rot
    = 416.2 s
    B = 600-900 MG R ~ 2100 km
    M > 1.3 M
    ¤
    ZTF J1901+1458
    "A highly magnetized and rapidly rotating
    white dwarf as small as the Moon"

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  23. JJ Hermes, Boston University | Pitt/CMU | 23
    Dunlap & Clemens 2015
    see also
    Wegg & Phinney 2012
    Most hot, massive WDs were
    formed recently (<1 Gyr)
    à low velocity dispersions
    M < 0.75 M¤
    Teff > 15,000 K
    M > 0.90 M¤
    Teff > 15,000 K
    within 100 pc
    Kinematics are Another Way to Reveal Actually Old Stars

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  24. JJ Hermes, Boston University | Pitt/CMU | 24
    Cheng et al. 2020
    Modeling WDs with anomalous kinematics reveals objects with older
    kinematics than cooling age suggests: mergers
    Kinematics are Another Way to Reveal Actually Old Stars
    "Double White Dwarf Merger Products
    among High-mass White Dwarfs"

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  25. Henry Giclas
    (1910-2007)
    Lowell Observatory,
    Flagstaff, AZ
    JJ Hermes, Boston University | Pitt/CMU | 25
    Kinematics reveal the most exciting merger remnants

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  26. JJ Hermes, Boston University | Pitt/CMU | 26
    • Before Gaia we found
    white dwarfs by looking
    for blue stars with high
    proper motion

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  27. GD 10
    1975
    GD: “Giclas Dwarf”
    GD 10: 10th Giclas dwarf

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  28. The GD catalog as seen by Gaia
    JJ Hermes, Boston University | Pitt/CMU | 30
    °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)
    Sun-like stars
    white dwarfs
    Bluer (hotter) Redder (cooler)
    Absolute G Magnitude (Distance Normalized)

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  29. The GD catalog as seen by Gaia
    JJ Hermes, Boston University | Pitt/CMU | 31
    °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
    Sun-like stars
    white dwarfs
    Bluer (hotter) Redder (cooler)
    Absolute G Magnitude (Distance Normalized)

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  30. discovery: Vennes et al. 2017
    follow-up: Raddi et al. 2018a, 2018b
    • LP 40-365 has vrad
    = +499 km/s; vrf
    = 852 +/- 10 km/s
    • It is unbound, a hyper-runaway not from Galactic center
    GD 492 = LP 40-365: A Hyper-Runaway WD
    JJ Hermes, Boston University | Pitt/CMU | 32

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  31. GD 492 = LP 40-365: A Hyper-Runaway WD
    • LP 40-365 is one of the most
    metal-rich stars known
    • No H or He detected (< 10-5)
    • Heavy elements indicate core
    C, Si burning
    discovery: Vennes et al. 2017
    follow-up: Raddi et al. 2018a, 2018b
    He
    H
    Ne
    O
    Mg
    all else
    all else
    <0.005% H
    GD 492: The Sun:
    JJ Hermes, Boston University | Pitt/CMU | 33

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  32. GD 492: First of a Class of Partly Burnt Runaways
    • These are the most metal-
    rich stars ever found:
    No H, He detected
    • All have similar abundances
    • All have extremely fast space
    motion
    • Hypothesis: These are the
    slung-shot remnants of an
    incomplete Type Ia
    supernova, ejected from
    <30-min binary!
    Raddi et al. 2019
    JJ Hermes, Boston University | Pitt/CMU | 34

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  33. GD 492: First of a Class of Partly Burnt Runaways
    • These are the most metal-
    rich stars ever found:
    No H, He detected
    • All have similar
    abundances
    • All have extremely fast
    space motion
    • Hypothesis: These are the
    slung-shot remnants of an
    incomplete Type Ia
    supernova, ejected from
    <30-min binary!
    JJ Hermes, Boston University | Pitt/CMU | 35
    Mark Garlick

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  34. GD 492: TESS Suggests it is a Surviving White Dwarf
    JJ Hermes, Boston University | Pitt/CMU | 36 Hermes, Putterman, et al. 2021
    • TESS data of GD 492
    showed 8.9-hr photometric
    variability; a surface spot

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  35. GD 492: TESS suggests it is a surviving white dwarf
    JJ Hermes, Boston University | Pitt/CMU | 37 Hermes, Putterman, et al. 2021
    "8.9 hr Rotation in the Partly Burnt Runaway
    Stellar Remnant LP 40-365 (GD 492)"
    • TESS data of GD 492
    showed 8.9-hr photometric
    variability; a surface spot
    • Variability confirmed from
    five orbits of archival time-
    tagged HST ultraviolet data

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  36. GD 492: TESS suggests it is a surviving white dwarf
    JJ Hermes, Boston University | Pitt/CMU | 38 Hermes, Putterman, et al. 2021
    • If angular momentum is
    mostly conserved rotation is
    likely too slow for it to have
    been the donor
    • More evidence its radius has
    increased substantially and it
    is actually a bound remnant
    from an underluminous
    supernova roughly 5 Myr ago
    Prot,i
    = Porb
    = minutes
    Prot,f
    = 8.9 hr

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  37. • Roughly 25% of all field white dwarfs have interacted or
    merged in their past
    • We can pick some merger byproducts individually via:
    strong magnetism, fast rotation, and/or high mass
    • High space motion (fast kinematics) can reveal
    apparently young but actually old systems
    • We are now also finding more partly burnt runaway
    supernova shards
    D. Berry, GSFC

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  38. Mark Garlick

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