Astronomy and Astrophysics – Astrophysics – Earth and Planetary Astrophysics
Scientific paper
2012-04-04
Astronomy and Astrophysics
Astrophysics
Earth and Planetary Astrophysics
Scientific paper
We show that ongoing direct imaging experiments may detect a new class of long-period, highly luminous, tidally powered extrasolar gas giants. Even though they are hosted by Gyr-"old" main-sequence stars, they can be as "hot" as young Jupiters at ~100 Myr, the prime targets of direct imaging surveys. These planets, with years-long orbits, are presently migrating to "feed" the "hot Jupiters" in steady state. Their existence is expected from a class of "high-e" migration mechanisms, in which gas giants are excited to highly eccentric orbits and then shrink their semi-major axis by factor of ~ 10-100 due to tidal dissipation at successive close periastron passages. The dissipated orbital energy is converted to heat, and if it is deposited deep enough into the planet atmosphere, the planet likely radiates steadily at luminosity ~2-3 orders of magnitude larger than that of our Jupiter during a typical Gyr migration time scale. Their large orbital separations and expected high planet-to-star flux ratios in IR make them potentially accessible to high-contrast imaging instruments on 10m-class telescopes at present and in the near future. A dozen or so such planets are expected to exist around FGK dwarfs within ~50 pc. Long-period planets around nearby stars found by RV are viable candidates to follow up, and in particular, the highly eccentric planet HD 20782b at maximum angular separation ~ 0.08" is the most promising candidate. Directly imaging these tidally powered Jupiters would enable a direct test of high-e migration mechanisms. Once detected, the luminosity would provide a direct measurement of the migration rate, and together with mass (and possibly radius) estimate, they would serve as a laboratory to study planetary spectral formation and tidal physics.
Dong Subo
Katz Boaz
Socrates Aristotle
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