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Formation of Earth-like Planets During and After Giant Planet Migration
Close-in giant planets are thought to have formed in the cold outerregions of planetary systems and migrated inward, passing through theorbital parameter space occupied by the terrestrial planets in our ownsolar system. We present dynamical simulations of the effects of amigrating giant planet on a disk of protoplanetary material and thesubsequent evolution of the planetary system. We numerically investigatethe dynamics of postmigration planetary systems over 200 million yearsusing models with a single migrating giant planet, one migrating and onenonmigrating giant planet, and excluding the effects of a gas disk.Material that is shepherded in front of the migrating giant planet bymoving mean motion resonances accretes into ``hot Earths,'' but survivalof these bodies is strongly dependent on dynamical damping. Furthermore,a significant amount of material scattered outward by the giant planetsurvives in highly excited orbits; the orbits of these scattered bodiesare then damped by gas drag and dynamical friction over the remainingaccretion time. In all simulations Earth-mass planets accrete onapproximately 100 Myr timescales, often with orbits in the habitablezone. These planets range in mass and water content, with bothquantities increasing with the presence of a gas disk and decreasingwith the presence of an outer giant planet. We use scaling arguments andprevious results to derive a simple recipe that constrains which giantplanet systems are able to form and harbor Earth-like planets in thehabitable zone, demonstrating that roughly one-third of the knownplanetary systems are potentially habitable.
| Properties of planets in binary systems. The role of binary separation
Aims.The statistical properties of planets in binaries wereinvestigated. Any difference to planets orbiting single stars can shedlight on the formation and evolution of planetary systems. As planetswere found around components of binaries with very different separationand mass ratio, it is particularly important to study thecharacteristics of planets as a function of the effective gravitationalinfluence of the companion. Methods: .A compilation of planets inbinary systems was made; a search for companions orbiting stars recentlyshown to host planets was performed, resulting in the addition of twofurther binary planet hosts (HD 20782 and HD 109749). The probableoriginal properties of the three binary planet hosts with white dwarfscompanions were also investigated. Using this updated sample of planetsin binaries we performed a statistical analysis of the distributions ofplanet mass, period, and eccentricity, fraction of multiplanet systems,and stellar metallicity for planets orbiting components of tight andwide binaries and single stars. Results: .The only highlysignificant difference revealed by our analysis concerns the massdistribution of short-period planets. Massive planets in short periodorbits are found in most cases around the components of rather tightbinaries. The properties of exoplanets orbiting the components of widebinaries are compatible with those of planets orbiting single stars,except for a possible greater abundance of high-eccentricity planets.The previously suggested lack of massive planets with P>100 days inbinaries is not confirmed. Conclusions: .We conclude that thepresence of a stellar companion with separation smaller than 100-300 AUis able to modify the formation and/or migration and/or the dynamicalevolution history of giant planets while wide companions play a morelimited role.Table 1 and Appendices A-C are only available in electronic form athttp://www.aanda.org
| Habitability of Known Exoplanetary Systems Based on Measured Stellar Properties
Habitable planets are likely to be broadly Earth-like in composition,mass, and size. Masses are likely to be within a factor of a few of theEarth's mass. Currently, we do not have sufficiently sensitivetechniques to detect Earth-mass planets, except in rare circumstances.It is thus necessary to model the known exoplanetary systems. Inparticular, we need to establish whether Earth-mass planets could bepresent in the classical habitable zone (HZ) or whether the giantplanets that we know to be present would have gravitationally ejectedEarth-mass planets or prevented their formation. We have answered thisquestion by applying computer models to the 152 exoplanetary systemsknown by 2006 April 18 that are sufficiently well characterized for ouranalysis. For systems in which there is a giant planet, inside the HZ,which must have arrived there by migration, there are two cases: (1)where the migration of the giant planet across the HZ has not ruled outthe existence of Earth-mass planets in the HZ; and (2) where themigration has ruled out existence. For each case, we have determined theproportion of the systems that could contain habitable Earth-massplanets today, and the proportion for which this has been the case forat least the past 1000 Myr (excluding any early heavy bombardment). Forcase 1 we get 60% and 50%, respectively, and for case 2 we get 7% and7%, respectively.
| The N2K Consortium. VI. Doppler Shifts without Templates and Three New Short-Period Planets
We present a modification to the iodine cell Doppler technique thateliminates the need for an observed stellar template spectrum. For agiven target star, we iterate toward a synthetic template spectrumbeginning with an existing template of a similar star. We then perturbthe shape of this first-guess template to match the program observationof the target star taken through an iodine cell. The elimination of aseparate template observation saves valuable telescope time, a featurethat is ideally suited for the quick-look strategy employed by the``Next 2000 Stars'' (N2K) planet search program. Tests using Keck HIRES(High Resolution Echelle Spectrometer) spectra indicate that synthetictemplates yield a short-term precision of 3 m s-1 and along-term, run-to-run precision of 5 m s-1. We used this newDoppler technique to discover three new planets: a 1.50MJplanet in a 2.1375 day orbit around HD 86081; a 0.71MJ planetin circular, 26.73 day orbit around HD 224693; and a Saturn-mass planetin an 18.179 day orbit around HD 33283. The remarkably short period ofHD 86081b bridges the gap between the extremely short period planetsdetected in the Optical Gravitational Lensing Experiment (OGLE) surveyand the 16 Doppler-detected hot Jupiters (P < 15 days), which have anorbital period distribution that piles up at about 3 days. We haveacquired photometric observations of two of the planetary host starswith the automated photometric telescopes at Fairborn Observatory. HD86081 and HD 224693 both lack detectable brightness variability on theirradial velocity periods, supporting planetary-reflex motion as the causeof the radial velocity variability. HD 86081 shows no evidence ofplanetary transits in spite of a 17.6% transit probability. We have toofew photometric observations to detect or rule out transits for HD224693.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology.
| Catalog of Nearby Exoplanets
We present a catalog of nearby exoplanets. It contains the 172 knownlow-mass companions with orbits established through radial velocity andtransit measurements around stars within 200 pc. We include fivepreviously unpublished exoplanets orbiting the stars HD 11964, HD 66428,HD 99109, HD 107148, and HD 164922. We update orbits for 83 additionalexoplanets, including many whose orbits have not been revised sincetheir announcement, and include radial velocity time series from theLick, Keck, and Anglo-Australian Observatory planet searches. Both thesenew and previously published velocities are more precise here due toimprovements in our data reduction pipeline, which we applied toarchival spectra. We present a brief summary of the global properties ofthe known exoplanets, including their distributions of orbital semimajoraxis, minimum mass, and orbital eccentricity.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. The Keck Observatory was made possible by thegenerous financial support of the W. M. Keck Foundation.
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