Mining the future of low-mass, core-He-burning hot subdwarfs

Conference presentation, 20 min. June 2019: 9th Hot Subdwarf Meeting, Hendaye, France.

Transcript

1. Mining the Future of Low-Mass, Core-He-Burning Hot Subdwarfs http://jjherm.es @jotajotahermes J.J. Hermes
2. JJ Hermes, Boston University | sdOB9-Hendaye | 2 David Schneider (on Tuesday) Let’s talk about non-canonical-mass hot subdwarfs!
3. • There is good evidence for <0.4 M¤ sdBs • Core-He-burning subdwarfs descending from >2 M ¤ stripped progenitors should exist • These sdBs will evolve into <0.4 M¤ CO-core WDs • Is there evidence for <0.4 M¤ CO-core WDs? • Gaia CMD • Asteroseismology • Eclipsing binaries JJ Hermes, Boston University | sdOB9-Hendaye | 3
4. Observational Evidence of Low-Mass Hot Subdwarfs 2M 1533+3759 0.376 ± 0.055 M¤ 0.166 ± 0.007 R¤ JJ Hermes, Boston University | sdOB9-Hendaye | 4 For et al. 2010 from lightcurve fits
5. Observational Evidence of Low-Mass Hot Subdwarfs 2M 1938+4603 0.372 ± 0.024 M¤ (if e < 10-4) Barlow et al. 2012 JJ Hermes, Boston University | sdOB9-Hendaye | 5 from Rømer delay
6. Observational Evidence of Low-Mass Hot Subdwarfs TIC 278659026 0.391 ± 0.013 M¤ 0.1694 ± 0.0081 R¤ Charpinet et al. 2019 (from Tuesday) JJ Hermes, Boston University | sdOB9-Hendaye | 6 from seismology
7. Hot Subdwarfs Could Have Masses Down to 0.31 M ¤ • Stripped progenitors >1.7 M¤ can nondegenerately ignite He with core masses at ~0.31 M¤ JJ Hermes, Boston University | sdOB9-Hendaye | 7 Han et al. 2013 Han et al. 2012 Z=0.02 Z=0.02, normal tip of FGB Z=0.004 First CE ejection First stable RLOF channel Merger
8. Hot Subdwarfs Could Have Masses Down to 0.31 M ¤ • sdBs are the only way to make a <0.4 M¤ CO-core WD JJ Hermes, Boston University | sdOB9-Hendaye | 8 Prada Moroni & Straniero 2009 Mass of the H-exhausted core see also Iben & Tutukov 1985
9. Can We Find <0.4 M ¤ CO-Core White Dwarfs? • CO-core white dwarfs have much smaller radii than He-core white dwarf of the same mass • At 17,000 K, an He-core WD has a >10% bigger radius than a CO-core WD JJ Hermes, Boston University | sdOB9-Hendaye | 9 Prada Moroni & Straniero 2009
10. Can We Find <0.4 M ¤ CO-Core White Dwarfs? • Gaia CMD position of WDs w/ log(g) < 7.5 and high- quality (σ < 0.035 dex) spectroscopy JJ Hermes, Boston University | sdOB9-Hendaye | 10 spectroscopic log(g) Montreal White Dwarf Database log(g) = 7.0 log(g) = 7.5 25kK 5kK
11. Can We Find <0.4 M ¤ CO-Core White Dwarfs? JJ Hermes, Boston University | sdOB9-Hendaye | 11 spectroscopic log(g) – photometric log(g) log(g) = 7.0 log(g) = 7.5 Smaller difference: WD is underluminous
12. Can We Find <0.4 M ¤ CO-Core White Dwarfs? • Asteroseismology is another precise way to determine mean stellar density • Asymptotic mean period spacing for l=1 dipole modes • 0.3 M¤ He-core: Δπ = 75 s • 0.3 M¤ CO-core: Δπ < 60 s JJ Hermes, Boston University | sdOB9-Hendaye | 12
13. Can We Find <0.4 M ¤ CO-Core White Dwarfs? JJ Hermes, Boston University | sdOB9-Hendaye | 13 Known Pulsating WD
14. Can We Find <0.4 M ¤ CO-Core White Dwarfs? • Double-lined eclipsing (WD+dM) binaries JJ Hermes, Boston University | sdOB9-Hendaye | 14 Parsons et al. 2017 He-core models C/O-core models Thick H (10-4) Thin H (10-10)
15. Can We Find <0.4 M ¤ CO-Core White Dwarfs? JJ Hermes, Boston University | sdOB9-Hendaye | 15 Hallakoun et al. 2016 SDSSJ1152+0248: WD+WD from K2 Campaign 1 T1 = 25,500 ± 1000 K log(g)1 = 7.42 ± 0.25 SED: T2 = 14,340 K
16. Can We Find <0.4 M ¤ CO-Core White Dwarfs? JJ Hermes, Boston University | sdOB9-Hendaye | 16 SDSSJ1152+0248 Parsons et al. 2019 (in prep., please no Tweets) X-shooter HiPERCAM
17. Can We Find <0.4 M ¤ CO-Core White Dwarfs? JJ Hermes, Boston University | sdOB9-Hendaye | 17 SDSSJ1152+0248 M1 : 0.362 ± 0.014 M¤ M2 : 0.325 ± 0.013 M¤ R1 : 0.0212 ± 0.0003 R¤ R2 : 0.0191 ± 0.0004 R¤ Parsons et al. 2019 (in prep., please no Tweets)
18. Can We Find <0.4 M ¤ CO-Core White Dwarfs? JJ Hermes, Boston University | sdOB9-Hendaye | 18 21.9 min (1312 s) @ 0.5% amp ZZ Ceti pulsations! Parsons et al. 2019 (in prep., please no Tweets)
19. Evidence for 0.3-0.4 M ¤ sdBs Evolving Into 0.3-0.4 M ¤ WDs JJ Hermes, Boston University | sdOB9-Hendaye • There is good evidence for <0.4 M¤ sdBs • Core-He-burning subdwarfs descending from >2 M ¤ stripped progenitors should exist • These sdBs will evolve into <0.4 M¤ CO-core WDs • Is there evidence for <0.4 M¤ CO-core WDs? • Gaia CMD • Asteroseismology • Eclipsing binaries possible CO-core WD(s) in the pulsating WD+WD binary SDSSJ1152+0248 (maybe)