Pre- and post- hot subdwarfs with uncommon core masses

Conference presentation, 20 min. June 2022: sdOB10, Liege, Belgium.

Transcript

1. Pre- and post- hot subdwarfs with uncommon core masses http://sites.bu.edu/buwd JJ Hermes
2. Zooming out to the before & after of sdOBs uncommon (non- canonical) core masses: <0.4 M¤ pre-sdOBs: Core He-burning giants post-sdOBs: low-mass CO-core white dwarfs Heber 2009, ARA&A
3. Nature can form non-canonical sdBs <0.4 M¤ Han et al. 2002 (lines of different Z) sdB progenitors >1.8 M¤ can ignite He nondegenerately, with core masses as low as ~0.32 M¤ observationally, we measure <0.4 M¤ sdBs in: • 2M 1533+3759: For et al. 2010 (eclipsing binary) • 2M 1938+4603: Barlow et al. 2012 (Rømer delay) • TIC 278659026: Charpinet et al. 2019 (seismology)
4. Zooming out to the before & after of sdOBs Heber 2009, ARA&A What are the lowest-mass CO-core WDs?
5. What is the lowest-mass CO-core white dwarf? Non-canonical sdBs will evolve into < 0.4 M¤ CO-core WDs Prada Moroni & Straniero 2009 He vs. CO WD could be distinguished by: • Precise mass/radius observations • Asteroseismology Asymptotic mean period spacing for dipole modes: • 0.3 M¤ He-core: Δπ = 75 s • 0.3 M¤ CO-core: Δπ < 60 s
6. What is the lowest-mass CO-core white dwarf? Parsons et al. 2017 He-core models C/O-core models Thick H (10-4) Thin H (10-10) Double-lined WD+dM best test for He vs. CO core
7. What is the lowest-mass CO-core white dwarf? Parsons et al. 2020 Double-lined WD+dM best test for He vs. CO core (Still no CO-cores detected with significance) SDSS J115219.99+024814.4
8. What is the lowest-mass CO-core white dwarf? Kosakowski et al. 2022 Double-lined WD+dM best test for He vs. CO core ZTF is finding many more systems with eclipsing WDs 3 of 4 recent eclipsing have log(g) which imply 0.36 < M WD < 0.45 M¤
9. Zooming out to the before & after of sdOBs What can core He-burning giants tell us about non- canonical sdBs? Heber 2009, ARA&A
10. RGB pulsations driven by turbulent convection Chaplin & Miglio 2013, ARA&A Max. peak of solar-like oscillations scales with surface gravity
11. RGB pulsations driven by turbulent convection García & Ballot 2019 Max. peak of solar-like oscillations scales with surface gravity Large frequency separation scales with mean density Leads to scaling relations:
12. Red giants also have core-probing g-modes Bedding et al. 2011 He-burning H-burning We can separate H- vs. He-burning stars on RGB by period spacing of the mixed-modes ~7000 CHeB with Kepler monitoring
13. Some He-burning giants are likely stripped! Yaguang Li et al. 2022 Of the 7000 CHeB RGB stars in Kepler: • ~7 are underluminous – smaller cores • ~32 are too low-mass for single-star evolution
14. Some He-burning giants are likely stripped! Yaguang Li et al. 2022 Of the 7000 CHeB RGB stars in Kepler: • ~7 are underluminous – smaller cores • ~32 are too low-mass for single-star evolution
15. Some He-burning giants are likely stripped! Of the 7000 CHeB RGB stars in Kepler: • ~7 are underluminous – smaller cores • ~32 are too low-mass for single-star evolution MESA models with and without mass loss Yaguang Li et al. 2022
16. Some He-burning giants are likely stripped! Of the 7000 CHeB RGB stars in Kepler: • ~7 are underluminous – smaller cores • ~32 are too low-mass for single-star evolution MESA models with and without mass loss Models >1.8 M¤ end up underluminous after RLOF Yaguang Li et al. 2022
17. Some He-burning giants are likely stripped! Yaguang Li et al. 2022 Of the 7000 CHeB RGB stars in Kepler: • ~7 are underluminous – smaller cores • ~32 are too low-mass for single-star evolution None of the three underluminous CHeB giants with multi-epoch APOGEE/LAMOST spectra show large RV variability yet eRV < 0.1 km/s
18. Pre- and post- sdOBs with small core masses <0.4 M¤ CO-core white dwarfs likely exist, but eclipses not yet revelatory New analysis of Kepler data shows core He-burning giants with small cores: stripped, sdB analogues 0.09% ± 0.04% of all CHeB are underluminous Heber 2009, ARA&A : where are the companions?!