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.

Transcript

1. http://jjherm.es
   J.J. Hermes
   The Still-Perilous Fate of Planets and
   Asteroids that Survive Stellar Evolution
   

   View Slide

2. Today
   Boris Gänsicke
   

   View Slide

3. 5 billion years
   from now
   Boris Gänsicke
   

   View Slide

4. The life cycle of the Sun
   8 billion years
   from now
   Boris Gänsicke
   

   View Slide

5. Typical DA white dwarf log(g) = 8.0
   • Settling times << years
   • Radiative levitation inefficient <25,000 K
   • Expect pure hydrogen photospheres
   

   View Slide

6. DA white dwarf + metals
   But many
   white dwarfs
   show metals!
   

   View Slide

7. • 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
   

   View Slide

8. 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.
   

   View Slide

9. (a) Photospheric pollution
   (b) IR excess (dust disks)
   (c) Ca emission (gas disks)
   Farihi 2016
   Observational evidence of
   remnant planetary systems:
   

   View Slide

10. van Lieshout et al. 2018
    

    View Slide

11. (d) Transits of the white dwarf (WD1145+017)
    Gänsicke et al. 2016
    Vanderburg et al. 2015
    Mark Garlick
    4RWD
    model
    

    View Slide

12. 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)
    

    View Slide

13. 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
    

    View Slide

14. 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%)
    

    View Slide

15. View Slide

16. Dennihy et al. 2018
    WD gas disks
    are incredibly
    dynamic
    Some disks show cyclic
    variations with periods
    <1.5 years!
    

    View Slide

17. Cauley et al. 2018
    Circumstellar gas
    absorption in
    WD1145+017 shows cyclic
    variations with few-year
    timescale
    

    View Slide

18. 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:
    

    View Slide

19. 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!
    

    View Slide