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Searching for signposts of failed white dwarf supernovae

jjhermes
October 12, 2022

Searching for signposts of failed white dwarf supernovae

Colloquium, 45 min. October 2022: IfA University of Hawaii Astrophysics Colloquium, Manoa, HI, USA.

jjhermes

October 12, 2022
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  1. sites.bu.edu/buwd J.J. Hermes Mark Garlick Searching for signposts of failed

    white dwarf supernovae
  2. Mark Garlick Takeaways: 1. Every century, there are a few

    WD+WD mergers in the Milky Way. 2. Most (>80%) simply create a weird WD. ~25% of all WDs are merger byproducts. 3. We have found stars ejected from the Galaxy that were involved in a WD supernova. Searching for signposts of failed white dwarf supernovae
  3. JJ Hermes, Boston University | UHIfA | 3 a white

    dwarf staris • a stellar remnant that is no longer fusing in its core • the endpoint 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)
  4. JJ Hermes, Boston University | UHIfA | 4 Type Ia

    Supernova: Standardizable, Exploded White Dwarfs SN1994D Pearson
  5. JJ Hermes, Boston University | UHIfA | 5 Today, We

    Can Observe WDs in the Act of Merging! Average distance between Earth and Moon: Brown et al. 2011; Hermes et al. 2012 M2 = 0.51 M ¤ M1 = 0.26 M ¤ SDSSJ0651+2844 is a 12.75-min WD+WD binary
  6. JJ Hermes, Boston University | UHIfA | 6 Today, We

    Can 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
  7. Hermes et al. 2022, in prep. JJ Hermes, Boston University

    | UHIfA | 7 Expected dP orb /dt = (-0.263 ± 0.020)ms/yr from GR Observed dP orb /dt = (-0.28688 ± 0.00072)ms/yr! M tot = 0.770 ±0.039 M ¤ L GW = 2.85 L ¤ LEM = 0.05 L ¤ SDSSJ0651+2844 is a 12.75-min WD+WD binary
  8. JJ Hermes, Boston University | UHIfA | 8 that will

    merge into a single WD 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 M tot = 0.770 ±0.039 M ¤
  9. JJ Hermes, Boston University | UHIfA | 9 Transient surveys

    havefound tens of WD+WD binaries with P orb < 1 hr They will all merge within 60 Myr, but none have total mass >1.1 M ¤ ZTF: Burdge et al. 2020 There should be many merger byproducts masquerading as ‘normal’ white dwarfs in the field
  10. JJ Hermes, Boston University | UHIfA | 10 Simulated Populations

    of Evolved Binaries Predicts Many Mergers Temmink et al. 2020 Population synthesis modeling expects >25% of all field white dwarfs to arise from stellar mergers
  11. Gaia has Revolutionized Our Ability to Find White Dwarfs Gaia

    Collaboration, Babusiaux et al. 2018 JJ Hermes, Boston University | UHIfA | 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 by accident from SDSS) • Gentile Fusillo et al. 2021 catalog of ~360,000 high- confidence WDs from Gaia eDR3
  12. We Can Test Ages with Wide Pairs of White Dwarfs

    JJ Hermes, Boston University | UHIfA | 12 El-Badry, Rix & Heintz 2021 Gaia has revealed >1500 wide (>100 au) WD+WD binaries that should be coeval We can estimate the total age of both WDs and make sure they agree (they usually do OK, with ~25% age uncertainties) Heintz, Hermes, El-Badry et al. 2022
  13. We Can Test Ages with Wide Pairs of White Dwarfs

    JJ Hermes, Boston University | UHIfA | 13 However, roughly 30% of wide WD+WD have a more massive component that is hotter It should be cooler since it was a more-massive main-sequence star Thus ~30%of wide WD+WD binaries have had an age reset (once triples that merged). How do post-merger WDs look? Heintz, Hermes, El-Badry et al. 2022 (M1 is more massive component)
  14. How Do Post-Merger WDs Look? What is a Normal WD?

    Composition | Mass | Rotation adapted from Wesemael et al. 1993 The majority (>2/3) of white dwarfs are Hydrogen dominated Mostly H-dominated 4000 4500 5000 5500 6500 DA: H JJ Hermes, Boston University | UHIfA | 14
  15. 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 ¤ What Does a Merged WD Look Like? What is a Normal WD? JJ Hermes, Boston University | UHIfA | 15
  16. 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 What Does a Merged WD Look Like? What is a Normal WD? JJ Hermes, Boston University | UHIfA | 16
  17. JJ Hermes, Boston University | UHIfA | 17 What is

    a Normal ‘White Dwarf’? A ‘typical’ 0.6 solar-mass white dwarf H-dominated atmosphere ~0.6 M ¤ P rot = 0.5-2 days The majority of white dwarfs are pretty boring – that’s why they’re great flux standards!
  18. JJ Hermes, Boston University | UHIfA | 18 What are

    Possible Signposts of Merged WDs? Composition | Mass | Rotation | Kinematics Mostly H-dominated ~0.6 M ¤ Prot = 0.5-2 days Some strongly magnetic white dwarfs show large Zeeman splitting of the Balmer lines Gaensicke et al. 2002
  19. JJ Hermes, Boston University | UHIfA | 19 An Extreme

    Example of a Clear Merger Remnant 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" Composition | Mass | Rotation | Kinematics Mostly H-dominated ~0.6 M ¤ Prot = 0.5-2 days
  20. What are Possible Signposts of Merged WDs? JJ Hermes, Boston

    University | UHIfA | 20 Follow-up spectroscopy of one of the 30% of ill-behaved WD+WDs shows the hotter, more-massive WD is strongly magnetic Heintz, Hermes, El-Badry et al. 2022 s = 415 au d = 62 pc ! = 0.65 ± 0.02 !⊙ )"## = 7500 ± 100 , -$%$ = 3.03&'.)* +'.),/01 ! = 0.83 ± 0.02 !⊙ )"## = 10600 ± 100 , -$%$ = 1.10&'.-' +'.-'/01 f λ (10-16 erg cm-2 s-1 Å-1) f λ (10-16 erg cm-2 s-1 Å-1) Wavelength (nm) Wavelength (nm)
  21. Kinematics are Another Way to Reveal Actually Old Stars Older

    stars are stirred up in the Galaxy àlarger velocity dispersions APOGEE+Gaia: Mackereth et al. 2019 JJ Hermes, Boston University | UHIfA | 21
  22. Cheng et al. 2020 Modeling WDs with anomalous proper motion

    reveals objects with older kinematics than cooling age suggests: evidence for age reset by merger Kinematics Can Reveal White Dwarf Mergers "Double White Dwarf Merger Products among High-mass White Dwarfs" JJ Hermes, Boston University | UHIfA | 22
  23. Cheng et al. 2020 Modeling WDs with anomalous proper motion

    reveals objects with older kinematics than cooling age suggests: evidence for age reset by merger Kinematics Can Reveal White Dwarf Mergers "Double White Dwarf Merger Products among High-mass White Dwarfs" JJ Hermes, Boston University | UHIfA | 23
  24. Henry Giclas (1910-2007) Lowell Observatory, Flagstaff, AZ JJ Hermes, Boston

    University | UHIfA | 24 Kinematics Reveal the Most Exciting Merger Remnants
  25. JJ Hermes, Boston University | UHIfA | 25 • Before

    Gaia we found white dwarfs by looking for blue stars with high proper motion
  26. GD 10 1975 GD: “GiclasDwarf” GD 10: 10th Giclasdwarf

  27. GD 10 1988

  28. GD 10 1988

  29. The GD catalog as Seen by Gaia JJ Hermes, Boston

    University | UHIfA | 29 °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 GiclasDwarf catalog (Giclas, Burnham & Thomas 1980) Sun-like stars white dwarfs Bluer (hotter) Redder (cooler) Absolute G Magnitude (Distance Normalized)
  30. The GD catalog as Seen by Gaia JJ Hermes, Boston

    University | UHIfA | 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 GiclasDwarf catalog (Giclas, Burnham & Thomas 1980) GD 492 Sun-like stars white dwarfs Bluer (hotter) Redder (cooler) Absolute G Magnitude (Distance Normalized)
  31. discovery: Vennes et al. 2017 follow-up: Raddi et al. 2018a,

    2018b • LP 40-365 has v rad = +499 km/s • It is unbound to the Milky Way (v rf = 852 +/-10 km/s), a hyper-runaway not from Galactic center GD 492 (aka LP 40-365): A Star Unbound to the Milky Way JJ Hermes, Boston University | UHIfA | 31
  32. GD 492 (aka LP 40-365): A Star Unbound to the

    Milky Way • LP 40-365 is one of the most metal-rich stars known • No H or He detected (<10-5 solar) • Heavy elements indicate near- Chandrasekhar-mass burning: [Mn/Fe] = 0.82 ± 0.18 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 (surface): The Sun: JJ Hermes, Boston University | UHIfA | 32
  33. GD 492: First of a Class of Partly Burnt Runaways

    Raddi et al. 2019 JJ Hermes, Boston University | UHIfA | 33 • These are the most metal-rich stars ever found: No H, He detected • All have similar abundances • All have wild fast space motion • 0.20-0.28 M ¤ & 0.16-0.60 R ¤ • Hypothesis: These are the slung-shot remnants of an incomplete Type Iasupernova, ejected from <30-min binary!
  34. • These are the most metal-rich stars ever found: No

    H, He detected • All have similar abundances • All have wild fast space motion • 0.20-0.28 M ¤ & 0.16-0.60 R ¤ • Hypothesis: These are the slung-shot remnants of an incomplete Type Iasupernova, ejected from <30-min binary! GD 492: First of a Class of Partly Burnt Runaways JJ Hermes, Boston University | UHIfA | 34 Mark Garlick • Are they remnants of a He-star donor, or are they a fraction of the WD that mostly exploded?
  35. GD 492: TESS Adds Evidence it is the Surviving White

    Dwarf JJ Hermes, Boston University | UHIfA | 35 • TESS data of GD 492 showed 8.9-hr photometric variability; a surface spot Hermes, Putterman, et al. 2021
  36. GD 492: TESS Adds Evidence it is the Surviving White

    Dwarf JJ Hermes, Boston University | UHIfA | 36 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
  37. GD 492: TESS Adds Evidence it is the Surviving White

    Dwarf JJ Hermes, Boston University | UHIfA | 37 • If angular momentum is mostly conserved, 8.9-hr rotation today is too slow for it to have been the He-star donor: the donor would inflate in radius >20x less than a near-M Ch WD • Instead, is more likely to be a bound remnant from an underluminous supernova roughly 5 Myr ago ( P rot,i = P orb < 20 min P rot,f = 8.9 hr Hermes, Putterman, et al. 2021
  38. • ~25% of all field white dwarfs have interacted or

    merged in their past (a few every century in Milky Way) • We can pick some merger byproducts individually via: strong magnetism (>1 MG) & very fast (<1 hr) rotation • High space motion (fast kinematics) can reveal mergers as apparently young but actually old stars • We are now also finding more partly burnt, runaway supernova shards, likely failed Type Ia (Type Iax) events D. Berry, GSFC JJ Hermes, Boston University | UHIfA | 38
  39. Mark Garlick