Poster Abstracts - Kepler - NASA

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POSTER ABSTRACTSP0401. POSTER SESSION ISPIN-ORBIT ALIGNMENT OF TRANSITING PLANETARY SYSTEMS FROM RM EFFECTOBSERVATIONS USING CYCLOPS.Brett Addison 1 , Duncan Wright 1 ,and Chris Tinney 1 , 1 Department of Astrophysics and Optics,University of New South Wales, NSW 2052, Australia. b.addison@student.unsw.edu.auIntroduction: Over 500 extrasolar planets havebeen discovered over the last decade and a half withmany more to be discovered in the next couple ofyears. In addition to discovering new extrasolar planets,a detailed analysis of their structure, composition,and other bulk properties is also needed in order togain an understanding of the processes involved in theformation of planets in other systems as well as in ourown solar system.The Exoplanetary Science group at UNSW iscommissioning a Cassegrain-fed optical-fiber bundlecalled CYCLOPS at the Anglo-Australian Telescope(AAT) to carry out Doppler spectroscopy of transitingplanet candidate stars arising from Southern Hemispheretransit searches. In addition, our team willcarry out measurments of the Rossiter-McLaughlin(RM) effect in transiting exoplanets. The RM effect isa spectroscopic anomaly in the radial velocity curvethat arises when a planet occults a small spot on therotating disk of its host star. This in turn causes asymmetricdistortions in the line profiles of a star's spectrumcreating the apparent anomaly seen in the radialvelocity curve (1). The detection of this effect allowsus to estimate the spin-orbit alignment of transitingplanetary system which is a critical component in orderto study the processes involved in planetary formationand migration.CYCLOPS: CYCLOPS is an upgrade for theAAT’s existing UCLES coude-echelle spectrograph. Itreplaces the five mirror Coude train, with aCassegrain-fed optical-fiber bundle, which reformatsan area of 4.7 square arcseconds on the sky (formattedas fifteen 0.6” diameter hexagons) into a pseudo-slit of15 fibers at the entrance of UCLES. Each fibre at theentrance slit has a diameter of 0.61”, which delivers aresolution of λ/Δλ = 70,000. Commissioning testsdemonstrate CYCLOPS delivers 70% more photons toour spectrograph than the old mirror train, and does soat 50% higher resolution (2).Spin-orbit Alignment of Transiting Exoplanetsand the Rossiter-McLaughlin Effect: Observing theRM effect provides an estimate of the alignment of theprojected stellar spin axis to the orbital plane of theplanet known as “spin-orbit” alignment, measured bythe angle (λ). This information is critical in order toplace constraints and test different theories on planetaryformation and migration (1). Using bothCYCLOPS and UCLES, our team will follow up anumber of transiting planet candidate stars arising fromthe HAT-South transit search with high precision radialvelocity both during and out of the transit phase.Our team has also developed a chi squared minimizationanalysis model called ExOSAM (ExoplanetaryOrbital and Simulation Analysis Model) to estimatevsini and λ by comparing the observed RM effect datato our theoretical model. We have tested ExOSAMwith actual data obtained for Wasp-18 (3). We findthat λ = 4° and vsini = 11.6 km/s for this system. Figure1 shows the RM anomaly in the radial velocitymodeled using ExOSAM with Wasp-18 data duringtransit.Conclusion: The Exoplanetary Science group atUNSW has commissioned a Cassegrain-fed opticalfibrebundle spectrograph called Cyclops at the AATto carry out Doppler spectroscopy and measurmenetsof the RM effect of transiting planet candidate starsarising from the HAT South transit survey. This researchwill allow us to estimate the orbital parametersand mass of transiting exoplanets, critical componentsneeded to study their structure and formation processesas well as their migration history.Figure 1 RM anomaly in the radial velocity modeledby ExOSAM with data obtained during the transit ofWASP-18 b (Triaud et al. 2010). The underlying Kepleriantrend of the star’s orbit due to the planet hasbeen removed for clarity.References: [1] Ohta, Taruya & Suto (2004) Nat.,90, 1151–1154.[2] http://www.phys.unsw.edu.au/~cgt/CYCLOPS/CYCLOPS.html. [3] Triaud et al. (2010) A&A, 524, A25.1602011 Kepler Science Conference - NASA Ames Research Center
POSTER ABSTRACTSP0402. POSTER SESSION IORBITAL MIGRATION MODELS OF EARTHS AND SUPER-EARTHS. G. D'Angelo 1,2 and U. Gorti 2,1 ,1NASA-ARC, MS245-3, Moffett Field, CA 94035 (gennaro.dangelo@nasa.gov), 2 SETI Institute, 189 Bernardo Ave.,Mountain View, CA 94043 (uma.gorti-1@nasa.gov).Introduction: Transit data from the Kepler missionindicate that over 10% of solar-type stars mayhost planets with radii between 2 and 4 R ⊕ and orbitalperiods shorter than 50 days [1]. Radial velocity datashow that nearly 20% of solar-type stars may harborplanets with masses smaller than 10 M ⊕ and periodsless than 50 days [2].The assembly of a planet of a few Earth masses at0.25 AU from a solar-mass star requires high surfacedensities of solid material, on the order of 2000 g/cm 2or higher. Additionally, a large fraction of it should beicy material. In fact, recent studies, e.g., [1,3], implythat Super-Earths may have a wide range of possiblecompositions, including ice/water-dominated planets.It appears therefore improbable that all these planetsformed at their current locations. More likely, most ofthem formed at larger orbital distances and afterwardmoved closer to the star. One mechanism that may explainthis long-range mobility is orbital migration drivenby tidal torques exerted by a gaseous protoplanetarydisk. We present detailed models of such mechanism.Model Description: We have constructed time-dependentmodels that describe the orbital evolution ofplanets in the Earth-to-Super-Earth mass range. Thesemodels self-consistently take into account the viscousevolution of the gaseous disk, the photo-evaporation ofthe gas that originates from Far-Ultraviolet (FUV), Extreme-Ultraviolet(EUV), and X-ray radiation emittedby a solar-mass star, and the gravitational torques thatare exchanged between the planet and the disk.Viscous model. The disk evolution driven by viscousstresses is obtained from the solution of a 1-Dequation that governs conservation of angular momentumand accounts for photo-evaporation and tidaltorques [4]. The equation is solved numerically usingan implicit scheme, allowing us to include disk regionsextending very close to the star.Photo-evaporation model. The rates at which diskgas evaporates are computed by solving the 1+1-D radial-verticalstructure of the disk [5]. These rates dependon both radial distance and time, and their calculationis embedded in the disk evolution calculationoutlined above.Tidal torque model. Gravitational perturbationsproduced by the planet give rise to a torque densitydistribution that acts on the disk. In response, the diskexerts the same torques on the planet. We use torquedensity fields derived from 3-D hydrodynamics, highresolutioncalculations of disk-planet interactions [6].Physical Parameters: We have performed simulationsof radially extended disks, from 0.02 AU to 1000AU, surrounding a solar-mass star. The initial surfacedensity follows that derived from [7] for an early SolarNebula. The X-rays and EUV luminosities are ~10 -3 L ⊙ ,whereas FUV luminosities depend on the time-varyingaccretion rate of the star, but lies in the range from~10 -4 to ~0.1 L ⊙ . We have investigated different viscosityregimes, with characteristic kinematic viscosityν=ν 1 (R/AU) 1/2 , where viscosity ν 1 is between 10 -6 and2×10 -5 in units of (G M ⊙ AU) 1/2 . The planet massgrows from 0.1 M ⊕ to M iso , the isolation mass, over thetime T iso . The growth proceeds at an oligarchic rate,dM/dt∝M 2/3 . The values of M iso and T iso are chosen randomlywithin the ranges, respectively, from 1 to 10 M ⊕and from 10 4 to 10 5 local orbital periods. The initial orbitalradius varies randomly between 1 and 10 AU.10.80.60.40.20Total1e-61e-52e-5-1.5 -1 -0.5 0 0.5 1log(a [AU])Results: We find that the final orbital distributionsare dependent on the applied viscosity regime. Whenν 1 ~10 -6 , about 90% of the planets orbit within ~0.5 AU,whereas, for ν 1 ~10 -5 , only ~30% have orbital radiismaller than 1 AU. About 50% of the planets settle onorbits beyond ~3 AU when ν 1 ~2×10 -5 . The total distributionshows that ~6% of the planets orbit within 0.07AU and ~50% within 1 AU. No region appears devoidof planets. Cumulative distributions for the total populationand for selected values of ν 1 are shown above.References: [1] Howard A. W. et al. (2011)arXiv:1103.2541. [2] Wittenmyer R. A. et al. (2011)ApJ, 738, 81-86. [3] Pont F. et al. (2011) MNRAS, 411,1953-1962. [4] D'Angelo G. et al. (2010) in EXO-PLANETS, S. Seager ed., 319-346. [5] Gorti U. et al.(2009) ApJ, 705, 1237-1251. [6] D'Angelo G. and LubowS. H. (2010) ApJ, 724, 730-747. [7] Davis S. S.(2005) ApJ, 627, L153-L155.2011 Kepler Science Conference - NASA Ames Research Center 161
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