Galactic archaeology and asteroseismology of white dwarf stars

Colloquium, 45 min. March 2021: SAC Seminar, Aarhus University, Aarhus, Denmark

Transcript

1. Galactic archaeology and asteroseismology of white dwarf stars http://jjherm.es @jotajotahermes J.J. Hermes
4. JJ Hermes, Boston University | SAC Seminar | 4 1. White Dwarfs are Stellar Fossils that We Can Directly Age-Date 2. We Are Using TESS to Better Model These Stellar Fossils
5. • a stellar remnant that is no longer fusing in its core • the endpoints of everything < 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) [thermal reservoir] [insulating blanket] JJ Hermes, Boston University | SAC Seminar | 5 What Do We Mean by ‘White Dwarf’?
6. 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) [thermal reservoir] [insulating blanket] JJ Hermes, Boston University | SAC Seminar | 6 White Dwarfs are Excellent for Ages: They Simply Radiate Their Stored Heat, Which is Not Replenished 65,000 K (0.001 Gyr) 25,000 K (0.02 Gyr) 13,000 K (0.31 Gyr) 10,500 K (0.56 Gyr) 7100 K (1.5 Gyr) 5100 K (5 Gyr) 3300 K (11 Gyr)
7. Gaia has revolutionized our ability to nd white dwarfs Gaia Collaboration, Babusiaux et al. 2018 • Before Gaia we knew of ~35,000 white dwarfs (mostly from SDSS) • Gentile Fusillo et al. 2019 catalog nearly half a million candidates from Gaia DR2 JJ Hermes, Boston University | SAC Seminar | 7
8. Gaia eDR3: We Are Directly Testing Ages in Wide WD+WD Tyler Heintz (BU), also Kareem El-Badry (Berkeley) JJ Hermes, Boston University | SAC Seminar | 8 El-Badry, Rix & Heintz 2021: arXiv: 2101.05282 1565 high-confidence, wide (>100 au) binaries with 2 WDs!
9. Soon We Will Have a Better-Calibrated Sample of Wide WD Co-PI: Jennifer Van Saders JJ Hermes, Boston University | SAC Seminar | 9 200 pc sample from El-Badry et al. 2018, 2021 >16,000 high-confidence, wide (>100 au) binaries with 1 WD!
10. 0.6 M¤ 0.9 M¤ 1.1 M¤ Gaia Reveals Interesting Physics in White Dwarf Cooling JJ Hermes, Boston University | SAC Seminar | 10 Tremblay et al. 2019
11. 0.6 M¤ 0.9 M¤ 1.1 M¤ JJ Hermes, Boston University | SAC Seminar | 11 Tremblay et al. 2019 White dwarfs within 100 pc in Gaia • Gaia CMD showed an overdensity aside from expected cooling tracks
12. JJ Hermes, Boston University | SAC Seminar | 12 Tremblay et al. 2019 DA (H-atmosphere) white dwarfs within 100 pc in Gaia • The overdensity appears better focusing only on DA white dwarfs
13. 20% of core is crystallized 80% of core is crystallized JJ Hermes, Boston University | SAC Seminar | 13 Tremblay et al. 2019 DA (H-atmosphere) white dwarfs within 100 pc in Gaia • The overdensity appears better focusing only on DA white dwarfs
14. 107.5 yr, 0.4 M¤ 107.5 yr, 1.3 M¤ +100.02 yr Onset of crystallization 80% of mass is crystallized JJ Hermes, Boston University | SAC Seminar | 14 Tremblay et al. 2019 Crystallization causes a pile-up in white dwarf cooling Predicted theoretically by Van Horn 1968
15. No crystallization Latent heat from crystallization Gaia Observed Latent heat from crystallization, plus gravitational energy from 16O sedimentation JJ Hermes, Boston University | SAC Seminar | 15 Tremblay et al. 2019 This overdensity is exactly where we expect crystallization! Gaia WD Luminosity Function
16. JJ Hermes, Boston University | SAC Seminar | 16 (What is latent heat? Why does it stall cooling?) • Latent heat: extra energy required to carry out a first-order phase transition • (When smoking a brisket the moisture in the meat undergoes a 1st-order phase transition at 160F [70C] from evaporative cooling)
17. “Long after our roiling, boiling life-giving star runs out of fuel, it will slowly form a cold, dead, super-dense crystal sphere about the size of the Earth that will linger like a translucent tombstone.” – Deborah Netburn, The Los Angeles Times JJ Hermes, Boston University | SAC Seminar | 17
18. Adding tangential velocities to the Gaia CMD… 100 pc sample from Gentile Fusillo et al. 2019 JJ Hermes, Boston University | SAC Seminar | 18 0.6 M¤ 1.2 M¤
19. 1. Fundamental physics from White Dwarfs in Gaia CMD JJ Hermes, Boston University | SAC Seminar | 19 • Most (>90%) of WDs Should Cool Predictably & Eventually Crystallize, Releasing Latent Heat • We are Testing Expectations with Wide, Coeval WD+WD Binaries 65,000 K (0.001 Gyr) 25,000 K (0.02 Gyr) 13,000 K (0.31 Gyr) 10,500 K (0.56 Gyr) 7100 K (1.5 Gyr) 5100 K (5 Gyr) 3300 K (11 Gyr)
20. He P.I. zone (30-20 kK) H P.I. zone (13-10 kK) N2 Ll 2 DAV Propagation Diagram Core Surface p-modes σ2 > L l 2, N2 convection zone log σ2 (s-2) g-modes σ2 < L l 2, N2 DBV: aka V477 Her DAV: aka ZZ Ceti Fontaine & Brassard 2008 Aerts, JCD, Kurtz 2010 JJ Hermes, Boston University | SAC Seminar | 20
21. White Dwarfs: g-modes, not all modes are observed excited (much like delta Scuti p-modes) 5 min 4 min 6 min Solar p-modes BiSON; Thompson et al. 2003 2 min 3 min 4 min 5 min 6 min 10 min JJ Hermes, Boston University | SAC Seminar | 21 n
22. White Dwarfs: g-modes, not all modes are observed excited (much like delta Scuti p-modes) Adiabatic Model: 11,245 K, 0.632 M¤ , 10-4.12 MH /MWD (Romero et al. 2012) 2 min 3 min 4 min 5 min 6 min 10 min JJ Hermes, Boston University | SAC Seminar | 22 l=1 l=2
23. KIC 08626021: Østensen et al. 2011, 2013 JJ Hermes, Boston University | SAC Seminar | 23 The Most Studied Kepler Pulsating WD: A Hot DBV Red: Location of m=0 models of Giammichele et al. 2018 Blue: Location of m=0 models of Bischoff-Kim et al. 2014
24. Core Surface ß 99% of mass X(O) = 78.03% ± 4.2% X(C) = 21.96% ± 4.2% X(He) = 0.0113% ± 0.006% KIC 08626021: Giammichele et al. 2018 JJ Hermes, Boston University | SAC Seminar | 24 Toulouse Models Predict A Large, O-Dominated Core
25. JJ Hermes, Boston University | SAC Seminar | 25 Toulouse Models Neglected to Include Neutrino Cooling Timmes et al. 2018 KIC 08626021: Giammichele et al. 2018
26. JJ Hermes, Boston University | SAC Seminar | 26 Toulouse Models Now Updated to Include Neutrino Cooling KIC 08626021: Charpinet et al. 2019 8 observed modes & many free parameters There is great potential in getting this right! Gaia CMD position infers: 0.73 ± 0.12 M¤ Black: Models of Giammichele et al. 2018 Red: Models of Charpinet et al. 2019 including neutrino cooling
27. JJ Hermes, Boston University | SAC Seminar | 27 7.5 8.5 8.0 Blue: K2 Pulsating WDs log(g) = 9 20,000 K 10,000 K Kepler/K2 Observed 90 Pulsating White Dwarfs Hermes et al. 2021, in prep. 81 DAV (H-atm.) WDs First 27 published in Hermes et al. 2017 Grey: All 2166 WDs 7 DBV (He-atm.) WDs Analysis in Vanderbosch et al. 2021 2 DOV (pre-WDs, C/O-atm.)
28. 1000 s 200 s 500 s 125 s l=1 l=2 White Dwarf Seismologist’s Dilemma: Often Few Modes JJ Hermes, Boston University | SAC Seminar | 28
29. 1000 s 200 s 500 s 125 s l=1 l=2 White Dwarf Seismologist’s Dilemma: Often Few Modes (consecutive g-modes evenly spaced in period, not frequency) JJ Hermes, Boston University | SAC Seminar | 29
30. l = 1 n = 1 l = 1 n = 2 l = 1 n = 3 SDSSJ0051+0339, g=17.6, K2 Campaign 8 White Dwarf Seismologist’s Dilemma: Often Few Modes Chris Clemens et al. in prep. Kepler and TESS makes some short-period mode identification relatively trivial JJ Hermes, Boston University | SAC Seminar | 30
31. 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 Mode Period (s) N l = 1 n = 1 l = 1 n = 2 l = 1 n = 3 n = 1 n = 2 n = 3 n = 4 If we only plot identified l=1 (m=0) modes: White Dwarf Seismologist’s Dilemma: Often Few Modes Chris Clemens et al. in prep. JJ Hermes, Boston University | SAC Seminar | 31
32. 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 Mode Period (s) N n = 1 n = 2 n = 3 n = 4 l = 1 n = 1 l = 1 n = 2 l = 1 n = 3 If we only plot identified l=1 (m=0) modes: White Dwarf Seismologist’s Dilemma: Often Few Modes Chris Clemens et al. in prep. JJ Hermes, Boston University | SAC Seminar | 32
33. 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 DAV periods, observed Full evolutionary models computed by Romero et al. 2012 Chris Clemens et al. in prep. White Dwarf Seismologist’s Dilemma: Often Few Modes JJ Hermes, Boston University | SAC Seminar | 33
34. Drawing from a random distribution of all hydrogen layer masses Full evolutionary models computed by Romero et al. 2012 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 DAV periods, observed 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 random MH simulation Chris Clemens et al. in prep. White Dwarf Seismologist’s Dilemma: Often Few Modes JJ Hermes, Boston University | SAC Seminar | 34
35. 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 DAV periods, observed 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 random MH simulation l=1 canonical MH simulation Full evolutionary models computed by Romero et al. 2012 Only drawing from the models with canonically thick (10-4 MH /M★ ) hydrogen layers Chris Clemens et al. in prep. Most (>80%) of DAs Have Thick H Layers JJ Hermes, Boston University | SAC Seminar | 35
36. 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 DAV periods, observed 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 random MH simulation l=1 canonical MH simulation Full evolutionary models computed by Romero et al. 2012 Only drawing from the models with canonically thick (10-4 MH /M★ ) hydrogen layers Chris Clemens et al. in prep. Most (>80%) of DAs Have Thick H Layers 10-15 s offset: Could be that He-layer masses too thick in canonical models à Would lead to systematically younger WD cooling ages (~10%) JJ Hermes, Boston University | SAC Seminar | 36
37. JJ Hermes, Boston University | SAC Seminar | 37 We Have Strong Motivation to Keep Going with TESS
38. JJ Hermes, Boston University | SAC Seminar | 38 We Have Strong Motivation to Keep Going with TESS Blue: TESS Pulsating WDs Grey: All 3383 WDs with T < 17 mag 7.5 8.5 8.0 log(g) = 9 20,000 K 10,000 K So Far TESS Has Detected Oscillations in 62 Pulsating WDs
39. White Dwarfs Are Faint, But TESS Data is Still Valuable JJ Hermes, Boston University | SAC Seminar | 39
40. White Dwarfs Are Faint, But TESS Data is Still Valuable JJ Hermes, Boston University | SAC Seminar | 40
41. WD 0158-160 (TIC 257459955): T=14.1 mag JJ Hermes, Boston University | SAC Seminar | 41 Bell et al. 2019 TESS DAVs: Bognar et al. 2020 9 observed l=1 modes Gaia parallax implies a distance of 68.14 ± 0.28 pc Seismic distance, Model 2: 66.5 ± 2.5 pc Seismic distance, Model 1/3: 87.7 ± 7.9 pc
42. The 20-Second Cadence Is Often Necessary for Our Science JJ Hermes, Boston University | SAC Seminar | 42 Pulsation amplitudes have been, on average, 35% underestimated by the 2-min cadence so far in Cycle 3
43. 2. TESS Will Keep Refining Models of White Dwarf Interiors JJ Hermes, Boston University | SAC Seminar | 43 • Boutique Asteroseismology of WDs Still Hard, But Improving, Especially With Ensemble Approaches at Short Periods • In Many Cases, 20-second TESS Data Is Crucial • We Are Working Onwards Towards Constraining WD Core Compositions and Envelopes! 65,000 K (0.001 Gyr) 25,000 K (0.02 Gyr) 13,000 K (0.31 Gyr) 10,500 K (0.56 Gyr) 7100 K (1.5 Gyr) 5100 K (5 Gyr) 3300 K (11 Gyr)
44. Adding tangential velocities to the Gaia CMD… 100 pc sample from Gentile Fusillo et al. 2019 JJ Hermes, Boston University | SAC Seminar | 44 0.6 M¤ 1.2 M¤
45. Massive WDs descended from 4-8 solar-mass ZAMS stars Cheng et al. 2019 JJ Hermes, Boston University | SAC Seminar | 45 • Massive WDs should come from stars that spend <0.5 Gyr on the main sequence
46. Something is delaying cooling in some massive WDs JJ Hermes, Boston University | SAC Seminar | 46 • Models include crystallization: something else is slowing them down! • Fast kinematics suggests these have had their ages “reset”! • But why are they piling up? Cheng et al. 2019
47. 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Sedimentation Cooling Delay [Gyr] °3.5 °3.0 °2.5 °2.0 °1.5 0 2 4 Q Branch 0.9 MØ C/O WD Z = 0.035 Clustering, hNi = 3,000 Clustering, hNi = 1,000 Clustering, hNi = 300 Single-particle Diffusion °3.5 °3.0 °2.5 °2.0 °1.5 0 2 4 Q Branch 1.0 MØ C/O WD Z = 0.035 °3.5 °3.0 °2.5 °2.0 °1.5 0 2 4 Q Branch 1.1 MØ C/O WD Z = 0.035 °3.5 °3.0 °2.5 °2.0 °1.5 log(L/LØ) 0 2 4 Q Branch 1.18 MØ C/O WD Z = 0.035 0.0 0.2 0.4 0.6 0.8 1.0 m [MØ] 0.0 0.2 0.4 0.6 Mass Fraction 22Ne 12C 16O initial final Something is delaying cooling in some massive WDs JJ Hermes, Boston University | SAC Seminar | 47 • That something could be 22Ne sedimentation (perhaps in clusters) in C/O-rich cores Bauer et al. 2020 Bildsten & Hall 2001
48. 1. Fundamental physics from White Dwarfs in Gaia CMD JJ Hermes, Boston University | SAC Seminar | 48 • Most (>90%) of WDs Should Cool Predictably & Crystallize, Releasing Latent Heat • We are Testing Expectations with Wide, Coeval WD+WD Binaries • Pile-ups among ~7% of massive WDs reveal crystallization PLUS poorly modeled physics (perhaps related to mergers & sedimentation of 22Ne clusters?) 65,000 K (0.001 Gyr) 25,000 K (0.02 Gyr) 13,000 K (0.31 Gyr) 10,500 K (0.56 Gyr) 7100 K (1.5 Gyr) 5100 K (5 Gyr) 3300 K (11 Gyr)