K2-97b: A (RE-?)INFLATED PLANET ORBITING A RED GIANT STAR

Publication: Research - peer-reviewJournal article

DOI

  • Samuel K. Grunblatt
    Samuel K. GrunblattUniv Hawaii, University of Hawaii System, Inst Astron
  • Daniel Huber
    Daniel HuberUniv Sydney, University of Sydney, Sydney Inst Astron SIfA, Sch PhysSETI InstAarhus Univ, Aarhus University, Dept Phys & Astron, Stellar Astrophys Ctr
  • Eric J. Gaidos
    Eric J. GaidosUniv Bern, University of Bern, Ctr Space & Habitabil
  • Eric D. Lopez
    Eric D. LopezUniv Edinburgh, University of Edinburgh, Royal Observ Edinburgh, Inst Astron
  • Benjamin J. Fulton
    Benjamin J. FultonUniv Hawaii, University of Hawaii System, Inst Astron
  • Andrew Vanderburg
    Andrew VanderburgHarvard Smithsonian Ctr Astrophys, Harvard University, Smithsonian Institution
  • Thomas Barclay
    Thomas BarclayNASA, Ames Research Center, National Aeronautics & Space Administration (NASA), Ames Res Ctr
  • Jonathan J. Fortney
    Jonathan J. FortneyUniv Calif Santa Cruz, University of California Santa Cruz, University of California System, Dept Astron & Astrophys
  • Andrew W. Howard
    Andrew W. HowardUniv Hawaii, University of Hawaii System, Inst AstronCALTECH, California Institute of Technology
  • Howard T. Isaacson
    Howard T. IsaacsonUniv Calif Berkeley, University of California Berkeley, University of California System, Dept Astron
  • Andrew W. Mann
    Andrew W. MannUniv Texas Austin, University of Texas Austin, Dept Astron
  • Erik Petigura
    Erik PetiguraCALTECH, California Institute of Technology
  • Victor Silva Aguirre
  • Evan J. Sinukoff
    Evan J. SinukoffUniv Hawaii, University of Hawaii System, Inst Astron

Strongly irradiated giant planets are observed to have radii larger than thermal evolution models predict. Although these inflated planets have been known for over 15 years, it is unclear whether their inflation is caused by the. deposition of energy from the host star. or the. inhibited cooling of the planet. These processes can be distinguished if the planet becomes highly irradiated only when the host star evolves onto the red giant branch. We report the discovery of K2-97b, a 1.31 +/- 0.11 R-J, 1.10 +/- 0.11 M-J planet orbiting a 4.20 +/- 0.14 R-circle dot, 1.16 +/- 0.12 M-circle dot red giant star with an orbital period of 8.4 days. We precisely constrained stellar and planetary parameters by combining asteroseismology, spectroscopy, and granulation noise modeling along with transit and radial velocity measurements. The uncertainty in planet radius is dominated by systematic differences in transit depth, which we measure to be up to 30% between different light-curve reduction methods. Our calculations indicate the incident flux on this planet was 170(-60)(+140) times the incident flux on Earth, while the star was on the main sequence. Previous studies suggest that this incident flux is insufficient to delay planetary cooling enough to explain the present planet radius. This system thus provides the first evidence that planets may be inflated directly by incident stellar radiation rather than by delayed loss of heat from formation. Further studies of planets around red giant branch stars will confirm or contradict this hypothesis. and may reveal a new class of re-inflated planets.

Original languageEnglish
Article number185
JournalThe Astronomical Journal
Volume152
Issue number6
Number of pages12
ISSN0004-6256
DOIs
StatePublished - Dec 2016

    Keywords

  • asteroseismology, planets and satellites: detection, planets and satellites: gaseous planets, planets and satellites: physical evolution, planet-star interactions, SOLAR-LIKE OSCILLATIONS, TRANSITING EXTRASOLAR PLANETS, HOT JUPITERS, LIGHT CURVES, M-DWARF, FUNDAMENTAL PROPERTIES, STELLAR EVOLUTION, ERROR-CORRECTION, BROWN DWARFS, HOST STARS

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