A New Transiting Extrasolar Giant Planet.pdf

a r X i v : a s t r o - p h / 0 3 0 1 0 5 2 v 1 4 J a n 2 0 0 3 A new transiting extrasolar giant planet Maciej Konacki?, Guillermo Torres?, Saurabh Jha?? Dimitar D. Sasselov? ? Div. of Geological Planetary Sciences 150-21, California Institute of Technology, Pasadena, CA 91125, USA ? Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA ? Department of Astronomy, University of California, Berkeley, CA 94720, USA A conceptually simple and technologically feasible approach to finding plan- ets orbiting other stars is to observe the periodic dimming of starlight due to a planet transiting in front of its star. Despite many intense photomet- ric searches, no transiting planet had yet been discovered in this way. The only known transiting extrasolar planet,1,2 HD 209458b, was first detected by precise radial velocity measurements.2,3 We have measured radial velocities of a star, OGLE-TR-56, which shows a 1.2-day transit-like light curve found photometrically by Udalski et al.4,5 Here we show that the velocity changes we detect are probably induced by an object of 0.9 Jupiter masses — a very close- in gas-giant planet only 0.023 AU from its star, with a planetary radius of 1.3 Jupiter radii and a mean density of ～0.5 g cm?3. At its small orbital distance, OGLE-TR-56b is hotter than any known planet, approaching 1900 K, but it is stable against long-term evaporation or tidal disruption. As the planet with the tightest known orbit, OGLE-TR-56b will place strong constraints on planet formation and migration models. The advent of high-precision Doppler and timing techniques in the past decade has brought a rich bounty of giant planets6–8 as well as smaller, terrestrial-mass pulsar plan- ets.9 To date over one hundred extrasolar giant planets have been found by different groups using precise radial velocity measurements.8 Photometric observations of tran- siting planets, when combined with radial velocities, yield entirely new diagnostics