A Large and Variable Leading Tail of Helium in HAT-P-67b, a Sub-Saturn Undergoing Runaway Inflation

Transcript

1. Michael Gully-Santiago
   The University of Texas at Austin
   DPS- EPSC 2023
   Division for Planetary Sciences
   the American Astronomical Society
   October 3, 2023
   San Antonio, TX
   A Large and Variable Leading Tail of Helium in HAT-P-67b,
   a Sub-Saturn Undergoing Runaway Inflation
   Caroline V. Morley, Jessica Luna, Morgan MacLeod,
   Antonija Oklopčić, Aishwarya Ganesh, Quang H. Tran,
   Zhoujian Zhang, Brendan P. Bowler, William D.
   Cochran, Daniel M. Krolikowski, Suvrath Mahadevan,
   Joe P. Ninan, Guðmundur Stefánsson, Andrew
   Vanderburg, Joseph A. Zalesky, Gregory R. Zeimann
   Gully-Santiago et al. arXiv 2307.08959
   

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2. The observed mass-radius diagram for Solar System planets
   

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3. The observed mass-radius diagram for exoplanets
   

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4. Why so few
   inflated sub-
   Saturns?
   The Inflated Sub-Saturn Cliff
   

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5. Scenario 1: Nature does not make them.
   Scenario 2: Nature makes them, but they are unstable.
   Why so few
   inflated sub-
   Saturns?
   

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6. Scenario 1: Migration prevents sub-Saturns from reaching high Teq
   .
   Scenario 2: They reach high Teq
   , but quickly undergo Runaway Inflation.
   Thorngren & Fortney 2018
   

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7. Scenario 1: Migration prevents sub-Saturns from reaching high Teq
   .
   Scenario 2: They reach high Teq
   , but quickly undergo Runaway Inflation.
   Thorngren & Fortney 2018
   What does planetary theory expect?
   

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8. The steady state Radius-Mass slope steepens with increasing Teq
   .
   Thorngren & Fortney 2018
   

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9. Thorngren & Fortney 2018
   The steady state Radius-Mass slope steepens with increasing Teq
   .
   

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10. Thorngren & Fortney 2018
    The steady state Radius-Mass slope steepens with increasing Teq
    .
    

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11. Thorngren & Fortney 2018
    A positive feedback loop ensues.
    

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12. Thorngren & Fortney 2018
    A positive feedback loop ensues.
    

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13. Thorngren & Fortney 2018
    A positive feedback loop ensues.
    Losing mass makes you larger, which makes you lose mass faster.
    

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14. Inflated sub-Saturns should exhibit profound mass loss rates.
    Thorngren & Fortney 2018
    

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15. Inflated sub-Saturns are rare.
    Thorngren & Fortney 2018
    

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16. This talk: Helium 10833 Å observations of HAT-P-67 b
    for HAT-P-32 b, see--
    Zhang, Morley, Gully-Santiago et al. 2023 DOI: (10.1126/sciadv.adf8736)
    

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17. HAT-P-67
    an F subgiant
    Zhou et al. 2017
    

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18. HAT-P-67 b
    a very low density, inflated hot Saturn
    Zhou et al. 2017
    

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19. Habitable Zone Planet Finder (HPF)
    Helium Exospheres Survey
    λ = 8100 – 12,800 Å
    R = 55,000
    Hobby Eberly Telescope (HET), Texas, USA
    We get abundant orbital phase coverage:
    Large orbital phase coverage
    Visits
    In–Transit Out-of-Transit
    HAT-P-67 b 7 35
    

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20. HAT-P-67 b
    with HPF
    39 nights over 3 years
    13.8 hours of on-sky integration time
    152 individual exposures
    

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21. HAT-P-67 b shows conspicuous variability in He I 10833 Å.
    

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22. Up to 10% transit depths.
    

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23. HAT-P-67 b also has an extended ingress.
    

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30. Leading tail resides in the stellar rest frame.
    

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31. Weak trailing tail blueshifts
    indicating acceleration away from the planet.
    

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32. The leading tail
    is direct evidence for preferential dayside mass loss.
    

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33. ̇
    𝑴 ~ 2 ×1013 g/s (105 M
    ⨁
    / Gyr )
    with 1D Parker Winds models † (p-winds)
    †Significant uncertainty:
    - XUV radiation
    - T0
    - 3D effects (streams)
    - self-shielding
    Dos Santos et al. 2022
    with Mp
    < 100 M
    ⨁
    implies inflationary timescale
    𝜏infl
    < 1 Gyr
    

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34. Thorngren, Lee & Lopez 2023
    XUV irradiation removes hot Saturns from the mass-radius plane.
    Mass loss is a positive feedback loop near the 0.1 g/cm3 threshold.
    

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35. Ohmic Dissipation and XUV irradiation
    make different quantitative predictions for inflation timescales.
    HAT-P-67 b
    Theory:
    𝜏infl
    ~ 5-50 Myr
    Observed:
    𝜏infl
    < 1000 Myr
    

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36. XUV irradiation
    better matches the population of hot Saturns
    0.1 g cm-3 threshold
    divides observed
    planet sample from
    sub-Saturn cliff.
    

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37. Conclusions
    We have detected up to 10% transit depth of He I 10833 Å from HPF spectra of HAT-P-67 b.
    The excess absorption preceeds the transit by up to 130 planetary radii in a large leading tail.
    The prominence of this leading tail is direct evidence for preferential dayside mass loss.
    We estimate a mass loss rate of 2 x 1013 g/s, and lifetime less than a Gyr.
    This pattern broadly agrees with theoretical predictions and explains the lack of inflated sub-Saturns.
    Gully-Santiago et al. arXiv 2307.08959
    

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