massive white dwarf from mergers

A journal club talk on massive white dwarfs as end products of white dwarf mergers.

Transcript

1. White Dwarf Mergers Produce More Massive White Dwarfs Yuhan Yao 20200403@Journal Club Hollands et al. (2020) Gvaramadze et al. (2019)
2. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks • Chandrasekhar Mass • Mass-Radius Relation • Types of White Dwarf (based on core composition) 1.1 1.1 !2
3. Gaia White Dwarfs and Cooling Tracks White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Gentile Fusillo et al. (2019) !3
4. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks 4000 5000 6000 7000 8000 H DA DAZ DA+MS DAH Gentile Fusillo et al. (2019) • Spectral Classification: DA (Hydrogen) from hottest to coolest DO (He II), DB (He I) DC (featureless), DQ (Carbon), DZ (metal)
5. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks 1 2 3 4 5 6 Althaus et al. (2010) H, He, C, O distributions within a typical DA WD CO core He- and C-rich intershell H envelope He buffer !5
6. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Winget & Kepler (2008) Non-radial g-mode pulsations driven by partial ionization DOV: He/C/O, 120000 K DBV: He, 25000K DAV: H, 12000K (ZZ Ceti) Periods: 100—1500 s Amps: 0.1—3% (and higher…) Pulsation !6
7. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Hermes et al. (2017) Rotation Splitting in Fourier Spec !7
8. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Diagram from Ken Shen Toroidal magnetic field (G) Generation of strong magnetic field and outflow in WD mergers Ji et al. (2013)
9. Merger of two CO WDs with superChandra total mass Does the merger lead to a detonation? yes SNe Ia no Remnant evolves viscously core envelope Remnant expands and enters cool, giant phase Off-center carbon- burning ignited Does the mass loss make the remnant sub-Chandra? Does the carbon flame reach the center? Off-center neon-burning ignited Neon-oxygen flame propagates to center Subsequent silicon burning leads to formation of an iron core Los-mass NS yes no yes no Hybrid Ia Massive WD Schwab et al. (2016) White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks
10. Post Merger 0.6+0.9=1.5 Msun model Propagation of Carbon Flame (1)—(2): viscous envelope, giant phase (2)—(3): ionize material, form nebula, no H He (3)—(4): contract, C flame reaches the center Beyond: Kelvin-Helmholtz contraction White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Schwab et al. (2016) !10
11. Paper I
12. Identify high-mass white dwarf using Gaia White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Dashed curve: DAV instability strip Kinematics of the WD (high) speed~ 130 km/s Dynamical age = few Gyr Photometric age = 1.3 Gyr but 1.1—1.2 Msun
13. 1st DAQ WD White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks logg Helium fraction
14. Pulsation White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks P=832s P=843s Window function Window function Evidence for WD merger: 1. H-C atmosphere 2. Low He mass fraction 3. High velocity 4. High mass (1.14 Msun)
15. Paper II
16. Discovery of Mid-IR nebula in Cassiopeia (a, b) WISE 22-µm image at two intensity scales circle: position of the central star (c) WISE 12-µm image (d) IPHAS Hα 1 arcmin = 0.9 pc. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks 16
17. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks = = = O III? Ne III?
18. Position of central star close to fiducial model of merging white dwarf = = White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks !18 Evidence for WD merger: 1. Position on HRD 2. Ionized IR nebula 3. H- and He-free composition 4. High velocity
19. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Cheng et al. (2019) 6% of high-mass WDs experience an extra 8 Gyr cooling delay on the Q branch
20. Merger of two CO WDs with superChandra total mass Does the merger lead to a detonation? yes SNe Ia no Remnant evolves viscously core envelope Remnant expands and enters cool, giant phase Off-center carbon- burning ignited Does the mass loss make the remnant sub-Chandra? Does the carbon flame reach the center? Off-center neon-burning ignited Neon-oxygen flame propagates to center Subsequent silicon burning leads to formation of an iron core Los-mass NS yes no yes no Hybrid Ia Massive WD Schwab et al. (2016) White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Thank you to: SRK, Suoqing Ji
21. Back-up Slides
22. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks 4000 5000 6000 7000 8000 4000 5000 6000 7000 8000 H DA DAZ DA+MS DB+MS DBA DBZ DB DAH DBH He Gentile Fusillo et al. (2019)
23. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks 4000 5000 6000 7000 8000 4000 5000 6000 7000 8000 Ca DC MWD DZ DC+MS DZH hot DQ DQ DQ pec ultracool WD Gentile Fusillo et al. (2019)
24. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Chemical Composition in Ultra-Massive WDs Camisassa et al. (2019) 1.10 Msun 1.29 Msun More massive WDs: He buffer almost vanish at low Teff !24
25. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks Kinematics of the WD (high) speed~ 130 km/s Dynamical age = few Gyr Photometric age only 1.3 Gyr C H He Upper limit of He from spectral fitting Helium fraction Merger delay !25
26. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks core core • Outer chemical composition does not depend on core structures • Helium buffer is removed by diffusion, giving hydrogen/carbon interface !26
27. White dwarf basics WD merger products Hollands+2000 Gvaramadze+2019 Final remarks