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Discovery of a Transiting Planet and Eight Eclipsing Binaries in HATNet Field G205
We report the discovery of HAT-P-8b, a transiting planet with mass Mp = 1.52+0.18 -0.16 MJ, radius R p = 1.50+0.08-0.06 R J, and photometric period P = 3.076days. HAT-P-8b has a somewhat inflated radius for its mass, and asomewhat large mass for its period. The host star is a solar-metallicityF dwarf, with mass M sstarf = 1.28 ± 0.04 Msun and R sstarf = 1.58+0.08-0.06 R sun. HAT-P-8b was initiallyidentified as one of the 32 transiting-planet candidates in HATNet fieldG205. We describe the procedures that we have used to follow up thesecandidates with spectroscopic and photometric observations, and wepresent a status report on our interpretation for 28 of the candidates.Eight are eclipsing binaries with orbital solutions whose periods areconsistent with their photometric ephemerides; two of thesespectroscopic orbits are single-lined and six are double-lined.Based in part on observations obtained at the W. M. Keck Observatory,which is operated by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by NOAO (A285Hr).
| Inflating and Deflating Hot Jupiters: Coupled Tidal and Thermal Evolution of Known Transiting Planets
We examine the radius evolution of close in giant planets with a planetevolution model that couples the orbital-tidal and thermal evolution.For 45 transiting systems, we compute a large grid ofcooling/contraction paths forward in time, starting from a large phasespace of initial semimajor axes and eccentricities. Given observationalconstraints at the current time for a given planet (semimajor axis,eccentricity, and system age), we find possible evolutionary paths thatmatch these constraints, and compare the calculated radii toobservations. We find that tidal evolution has two effects. First,planets start their evolution at larger semimajor axis, allowing them tocontract more efficiently at earlier times. Second, tidal heating cansignificantly inflate the radius when the orbit is being circularized,but this effect on the radius is short-lived thereafter. Oftencircularization of the orbit is proceeded by a long period while thesemimajor axis slowly decreases. Some systems with previouslyunexplained large radii that we can reproduce with our coupled model areHAT-P-7, HAT-P-9, WASP-10, and XO-4. This increases the number ofplanets for which we can match the radius from 24 (of 45) to as many as35 for our standard case, but for some of these systems we are requiredto be viewing them at a special time around the era of current radiusinflation. This is a concern for the viability of tidal inflation as ageneral mechanism to explain most inflated radii. Also, large initialeccentricities would have to be common. We also investigate theevolution of models that have a floor on the eccentricity, as may be dueto a perturber. In this scenario, we match the extremely large radius ofWASP-12b. This work may cast some doubt on our ability to accuratelydetermine the interior heavy element enrichment of normal, noninflatedclose in planets, because of our dearth of knowledge about theseplanets' previous orbital-tidal histories. Finally, we find that the endstate of most close in planetary systems is disruption of the planet asit moves ever closer to its parent star.
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