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The Still-Perilous Fate of Planets and Asteroids that Survive Stellar Evolution

January 15, 2019

The Still-Perilous Fate of Planets and Asteroids that Survive Stellar Evolution

Conference presentation, 20 min. January 2019: Boston Area Exoplanet Science Meeting #5, Boston, MA, USA.


January 15, 2019

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  1. Typical DA white dwarf log(g) = 8.0 • Settling times

    << years • Radiative levitation inefficient <25,000 K • Expect pure hydrogen photospheres
  2. • Consensus: Metals are from accreted, tidally disrupted debris –

    30-50% of all WDs are metal polluted when look in UV (Koester et al. 2014) – WD debris is comparable to bulk Earth (dominated by Fe, O, S, Mg) – Some of this debris is water-rich! (Farihi et al. 2013) WDs Directly Measure Exoplanet Compositions Abundances of rocks falling on 10 different white dwarfs: Xu et al. 2014 Bulk Earth Comet Halley
  3. 1. We are observing the future of planetary systems around

    2-3 solar- mass ZAMS stars. 2. As the host evolves, the orbits of surviving planets expand. Objects destabilize, some scatter in. 3. Ancient solar systems have leftover debris. We can see it if it pollutes a pristine white dwarf.
  4. (a) Photospheric pollution (b) IR excess (dust disks) (c) Ca

    emission (gas disks) Farihi 2016 Observational evidence of remnant planetary systems:
  5. (d) Transits of the white dwarf (WD1145+017) Gänsicke et al.

    2016 Vanderburg et al. 2015 Mark Garlick 4RWD model
  6. van Sluijs & Van Eylen 2018 >1100 white dwarfs observed

    by K2 through Campaign 13 Only 1 (WD1145+017) shows transits (Gaia: 2113 bona fide WDs observed through K2 Campaign 18)
  7. tasoc.dk 175 white dwarfs observed (2-min) by TESS through Sector

    2 815 WDs in Cycle 1 with T<16 mag Expect >1400 WDs proposed in Cycle 2 (thanks Gaia!) T = 15.2 mag WD in Sector 2
  8. Rowan et al. 2019, arXiv: 1812.05614 >15,000 WDs with GALEX

    light curves longer than 10-min Still no new transits detected! (observed occurrence rate <0.5%)
  9. Dennihy et al. 2018 WD gas disks are incredibly dynamic

    Some disks show cyclic variations with periods <1.5 years!
  10. Manser et al. 2019, in review (no tweets, plz) evidence

    of "a solid body with significant internal strength" 123.4-min periodic modulation of Ca II:
  11. Mark Garlick 30-50% of WDs are being actively polluted by

    rocks Few dozen show IR excess from dusty debris Less than a dozen show gas emission (Ca II) One (WD1145+017) shows transiting rocky debris No surviving, in-tact planets yet discovered: Gaia end-of-mission astrometry beckons!