http://jjherm.es J.J. Hermes Hubble Fellow University of North Carolina at Chapel Hill Improved white dwarf cooling ages using asteroseismology and eclipsing binaries
40 Eri, S. Smith Star Trek writer James Blish put planet Vulcan in orbit around 40 Eri A 40 Eri B: coeval white dwarf with total age ~1.8 Gyr I have evolved telepathy in less than 2 billion years…
Bond, Bergeron & Bédard 2017, arXiv: 1709.00478 0.573±0.018 M¤ 17,200±110 K WD Cooling Age: ~122 Myr + Cluster-Calibrated Initial-to-Final Mass Relation (Kalirai’s talk): 1.8 M¤ Progenitor: ~1.7 Gyr MS age 40 Eri, S. Smith ~35 AU ~400 AU Thin H-layer Thick H-layer Precision mass-radius measurements can constrain envelope masses à Better cooling ages (Dynamical) (Parallax) 40 Eri B Total Age ~1.8 Gyr
WD+dM Eclipsing Binaries: <2% WD Masses, Radii No evidence for very thin H layers in 13 white dwarfs in close WD+dM binaries: All have <10-8 MH /M Parsons et al. 2017, MNRAS, 470, 4473 He-core models C/O-core models Thick H (10-4) Thin H (10-10)
Asteroseismology: Pulsations Constrain Envelope Masses Detailed study of two superficially similar pulsating WDs: GD 165 and Ross 548 Noemi Giammichele et al. 2015, ApJ, 815, 56 Time (s) Rel. Flux Rel. Flux Both white dwarfs have Teff ~ 12,100 K and are ~0.64 Msun but quite different pulsation properties
Original Kepler Mission (4 years): Just 20 white dwarfs observed, 6 pulsating WDs (just two >3 months) K2 through Campaign 13: >1200 white dwarf candidates observed 53 more pulsating WDs K2 has given us hundreds of candidate pulsating white dwarfs to observe
l = 2 l = 2 l = 1 l = 1 SDSSJ0106+0145, K2 Campaign 8 Hermes et al. 2017, ApJS, in press; k2wd.org K2 is giving us exceptional data for WD asteroseismology k k = Number of radial nodes l = Number of vertical nodes m = Number of horizontal + vertical nodes
Asteroseismology: Insights from the Aggregated Periods Chris Clemens, Bart Dunlap et al. 2017, in prep. 239 periods from 75 hot DAVs (mostly ground-based) Histogram of periods 0 5 10 15 20 25 30 50 100 150 200 250 300 350 400 450 500 0 5 10 15 20 25 30 50 100 150 200 250 300 350 400 450 Mode Amplitude (ppt) N Mode Period (s) Mode Period (s)
Asteroseismology: Insights from the Aggregated Periods If we only plot identified l=1 modes: 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l = 1 k = 1 l = 1 k = 2 l = 1 k = 3 Kepler makes mode identification relatively trivial Mode Period (s) N Clemens et al. 2017, in prep. SDSSJ0051+0339, g=17.6, K2 Campaign 8 k2wd.org k = 1 k = 2 k = 3 k = 4
Asteroseismology: Insights from the Aggregated Periods If we only plot identified l=1 modes: 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 Kepler makes mode identification relatively trivial Mode Period (s) N Clemens et al. 2017, in prep. l = 1 k = 1 l = 1 k = 2 l = 1 k = 3 k = 1 k = 2 k = 3 k = 4
Asteroseismology: Insights from the Aggregated Periods If we only plot identified l=1 modes: 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 Kepler makes mode identification relatively trivial Mode Period (s) N k = 1 k = 2 k = 3 k = 4 Clemens et al. 2017, in prep. l = 1 k = 1 l = 1 k = 2 l = 1 k = 3
Asteroseismology: Insights from the Aggregated Periods Clemens et al. 2017, in prep. Drawing from a random distribution of models with a range of thick (10-4 MH /M ) to thin (10-10 MH /M ) hydrogen layer masses, using the measured spectroscopic Teff & masses for each pulsating WD Full evolutionary models computed by Alejandra Romero et al. 2012, MNRAS, 420, 1462 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 hDAV 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
Asteroseismology: Insights from the Aggregated Periods Clemens et al. 2017, in prep. Ross 548 GD 165 l = 1, k = 2 l = 1, k = 1 Thick H Layer: ~10-4 MH /M He Layer: ~10-1.7 MHe /M “Canonical” nuclear burning sets envelope masses Thin H Layer: <10-7 MH /M ~He Layer: 10-2.9 MHe /M Very late thermal pulses? Giammichele et al. 2016, ApJS, 223, 10 size = amplitude of mode
Asteroseismology: Insights from the Aggregated Periods Clemens et al. 2017, in prep. Ross 548 GD 165 l = 1, k = 2 l = 1, k = 1 Thick H Layer: ~10-4 MH /M He Layer: ~10-1.7 MHe /M “Canonical” nuclear burning sets envelope masses Thin H Layer: <10-7 MH /M ~He Layer: 10-2.9 MHe /M Very late thermal pulses? Interpulse interaction? Giammichele et al. 2016, ApJS, 223, 10 size = amplitude of mode ~80% of DAs have canonically thick (~10-4 MH /M ) envelopes ~20% of DAs have thinner (~10-7-9 MH /M ) envelopes à WDs with 1 dex thinner He envelopes cool >10% slower! N = 14 N = 4
Asteroseismology: Insights from the Aggregated Periods Clemens et al. 2017, in prep. 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 hDAV periods, observed 0 1 2 3 4 5 6 7 8 50 100 150 200 250 300 350 400 450 l=1 canonical MH simulation Full evolutionary models computed by Alejandra Romero et al. 2012, MNRAS, 420, 1462 10-15 s offset: Suggests He-layer masses too thick in canonical models à Would lead to systematically younger WD cooling ages Only drawing from the models with canonically thick MH
Tuning the White Dwarf Clocks with Eclipses & Pulsations A ‘typical’ 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] - Seismology: ~80% of WDs have canonically thick envelopes - Those with thinner He layers can cool >10-25% more slowly - Seismic evidence that those with thick MH may have thinner MHe (are systematically older than we think) - K2 data still coming in: Expect many core C/O ratio constraints very soon!
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