http://sites.bu.edu/buwd J.J. Hermes + WG8 Tuning white dwarf clocks with space-based asteroseismology including Stéphane Charpinet, Keaton J. Bell, Zsófia Bognár, Steve Kawaler, Paulina Sowicka, Pierre Brassard, Valerie Van Grootel, Weikai Zong, Noemi Giammichele, Murat Uzundag, Alejandro H. Córsico, Agnès Bischoff-Kim, Alejandra Romero, S. O. Kepler, Gabriela Oliveira da Rosa, Judi Provencal, Gerald Handler, Larissa Antunes Amaral, Leandro G. Althaus, Paul Bradley, Uli Heber, Stephan Geier, Betsy Green, Dave Kilkenny, Roy Østensen, Ingrid Pelisoli, Roberto Silvotti, John Telting, Maya Vučković, H. L. Worters, Leila M. Calcaferro, Mike Montgomery, Murat Uzundag, Andrzej S. Baran, Hamed Ghasemi, John Debes, Piotr Kołaczek- Szymański, Simon J. Murphy, Andrzej Pigulski, Ádám Sódor, et al.
‘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] White Dwarfs: Simple Stars, Simple Evolution* 65,000 K (0.001 Gyr) 25,000 K (0.02 Gyr) 13,000 K (0.3 Gyr) 10,500 K (0.55 Gyr) 7100 K (1.5 Gyr) 5100 K (5 Gyr) 3300 K (11 Gyr)
a 0.6 solar-mass WD evolved from a 1.3 solar-mass ZAMS star (4.5 Gyr on MS+RGB) in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75, 170,000 K have the highest number of detected modes. The first class of pulsating s 5.5 5.0 4.5 Planetary Nebula Main sequence DOV DBV DAV 4.0 3.5 3.0 log [T eff (K)] 4 2 0 –2 –4 log (L/L ) Figure 3 White Dwarfs: Simple Stars, Simple Evolution* a 0.6 solar-mass WD has a total age of 4.5 + 0.55 = 5.05 Gyr Winget & Kepler 2008 10,500 K (0.55 Gyr)
We Assume Stars Lose Mass Monotonically to Connect WD to ZAMS e.g., we can use MESA models to predict how much mass will be lost we calibrate with WDs where the total ages have been determined from cluster membership via Carl Fields et al. 2016 e.g., Cummings et al. 2018
We Have Used Gaia’s Many WDs to Empirically Test WD Ages Tyler Heintz, Hermes, El-Badry et al. 2022 arXiv: 2206.00025 eDR3: El-Badry, Rix & Heintz 2021 Gaia revealed >1500 wide (>100 au) WD+WD binaries we have used our usual tools to assess how well their derived total ages agree
We Have Used Gaia’s Many WDs to Empirically Test WD Ages Tyler Heintz et al. 2022 arXiv: 2206.00025 oops: roughly 20-35% of wide WD+WD have a more massive component that is hotter – its age was likely "reset” by a merger thus: 20-35% of wide WD+WD binaries were once triples in general, total WD ages are good to at least 25% (i.e., 4 ± 1 Gyr) but we’d like to do even better! (similar to pop-synth: Temmink et al. 2020)
One Motivation for Better WD Ages: Wide WD+MS Systems (El-Badry, Rix & HeinB 2021) >15,000 wide (>100 au) WD+MS binaries from Gaia DR3 improving WD total ages can improve, e.g., old K/M gyrochronology h/t Jennifer Van Saders see also talk Friday by Diego Godoy-Riviera
Testing Assumptions in Our White Dwarf Cooling Models • M H / M WD ~ 0.01% 6 dex thinner H envelope cools ~3% slower to 6000 K • M He / M WD ~ 1% 1 dex thinner He envelope cools ~10% slower to 6000 K • C/O ratio: 50% C A 100% O-rich core cools ~15-20% faster to 6000 K • Core crystallization Model ignoring release of latent heat cools ~40% faster to 6000 K ‘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]
Testing Assumptions in Our White Dwarf Cooling Models • M H / M WD ~ 0.01% 106 times thinner H envelope cools ~3% slower to 6000 K • M He / M WD ~ 1% 1 dex thinner He envelope cools ~10% slower to 6000 K • C/O ratio: 50% C a 100% O-rich core cools ~15-20% faster to 6000 K • Core crystallization a model ignoring release of latent heat cools ~40% faster to 6000 K ‘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]
pulsations driven at onset of partial ionization zone, we think, for all white dwarfs ~130,000 K for C/O-atm, DOV ~30,000 K for He-atm, DBV ~12,000 K for H-atm, DAV in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75 170,000 K have the highest number of detected modes. The first class of pulsating s 5.5 5.0 4.5 Planetary Nebula Main sequence DOV DBV DAV 4.0 3.5 3.0 log [T eff (K)] 4 2 0 –2 –4 log (L/L ) Figure 3 Testing Assumptions in Our White Dwarf Cooling Models Winget & Kepler 2008
in Figure 3. The pulsating pre-white dwarf PG 1159 stars, the DOVs, around 75 170,000 K have the highest number of detected modes. The first class of pulsating s 5.5 5.0 4.5 Planetary Nebula Main sequence DOV DBV DAV 4.0 3.5 3.0 log [T eff (K)] 4 2 0 –2 –4 log (L/L ) Figure 3 TASC WG8 Has Focused First on Increasing Number of Observed WDs
white dwarfs are strongly stratified, and pulsations are very sensitive to chemical profile changes Fontaine & Brassard 2008 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
• M H / M WD ~ 0.01% 106 times thinner H envelope cools ~3% slower to 6000 K 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 DAV periods, observed after Clemens et al. 2017 n=1 2 3 4 Mode Period (s) Romero et al. 2022
Ensemble Seismology Can Also Test Thickness of Helium Layer • M H / M WD ~ 0.01% 106 times thinner H envelope cools ~3% slower to 6000 K • M He / M WD ~ 1% 1 dex thinner He envelope cools ~10% slower to 6000 K 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 after Clemens et al. 2017 n=1 2 3 4 Mode Period (s) Reece Boston 2022, PhD thesis The o set could imply thinner He layers (all models assume M He / M WD = 1%)
Deeper Inside: Reaction Rates In uence on C/O Ratio • M H / M WD ~ 0.01% 106 times thinner H envelope cools ~3% slower to 6000 K • M He / M WD ~ 1% 1 dex thinner He envelope cools ~10% slower to 6000 K • C/O ratio: 50% C a 100% O-rich core cools ~15-20% faster Morgan Chidester, Farag & Timmes 2022 arXiv: 2207.02046 core surface (normalized radius) Each color is changing the 12C(α,γ)16O reaction rate by up to +/- 3 sigma:
ß 99% of mass X(O) = 78.03% ± 4.2% X(C) = 21.96% ± 4.2% X(He) = 0.0113% ± 0.006% core surface Giammichele et al. 2018 + follow-up modeling of KIC 8626021 by Timmes et al. 2018, Charpinet et al. 2019, De Gerónimo et al. 2019, Chidester et al. 2021
STELUM Fits of 5 Kepler White Dwarfs All Imply Large Oxygen Cores Noemi Giammichele, Charpinet, Brassard: poster E1 the cores found are more massive (by 40%) and more oxygen-rich (by 15%) than predicted by canonical evolution models for these WD masses
• M H / M WD ~ 0.01% 106 times thinner H envelope cools ~3% slower to 6000 K • M He / M WD ~ 1% 1 dex thinner He envelope cools ~10% slower to 6000 K • C/O ratio: 50% C a 100% O-rich core cools ~15-20% faster to 6000 K • Core crystallization a model ignoring release of latent heat cools ~40% faster to 6000 K crystallization is a first-order phase transition, so releases latent heat and slows cooling we don’t effectively know the melting temperature for a C/O mixture from lab experiments
Crystallization Provides a New Inner Boundary Condition • M H / M WD ~ 0.01% 106 times thinner H envelope cools ~3% slower to 6000 K • M He / M WD ~ 1% 1 dex thinner He envelope cools ~10% slower to 6000 K • C/O ratio: 50% C a 100% O-rich core cools ~15-20% faster to 6000 K • Core crystallization a model ignoring release of latent heat cools ~40% faster to 6000 K Francisco De Gerónimo et al. 2019 also Montgomery & Winget 1999 >90% of the core of a 1.16 MsunWD will be crystallized by the time it pulsates – a strong seismic signature
we can see the imprint of crystallization in the Gaia CMD in fact, it appears ~10% of WDs have an extra multi-Gyr cooling delay, possibly from 22Ne sedimentation 0.6 M¤ 1.2 M¤ Tremblay et al. 2019 Cheng et al. 2019
Takeaway:White Dwarf Asteroseismology Can Test Cooling Models • M H / M WD ~ 0.01% 106 times thinner H envelope cools ~3% slower to 6000 K • M He / M WD ~ 1% 1 dex thinner He envelope cools ~10% slower to 6000 K • C/O ratio: 50% C a 100% O-rich core cools ~15-20% faster to 6000 K • Core crystallization a model ignoring release of latent heat cools ~40% faster to 6000 K • Improving WD ages significantly improves precision for their use in wide binaries with other stars • We are actively testing our cooling- model assumptions with seismology • C/O ratio and crystallization probe uncertain physics, including 12C(α,γ)16O reaction rate & 22Ne diffusion
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