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The impact of stellar duplicity on planet occurrence and properties. I. Observational results of a VLT/NACO search for stellar companions to 130 nearby stars with and without planets
Context: Although it is commonly agreed that the presence of a closestellar companion is likely to affect planet formation and evolution,the precise effects and their actual impact on planet occurrence arestill debated. Different conclusions have been reached on thetheoretical side, while observational constraints are sparse, aconsequence of the discrimination against close binaries in Dopplerplanet searches. Accordingly, basic questions such as how hospitablebinaries are to planets and how binary separation and mass ratio impacton planet formation, remain poorly known. Aims: In an effort to bringobservational constraints on the occurrence and properties of planets inbinaries and multiple stars, we have been conducting a dedicatedinvestigation, the results of which will be presented in this series. Methods: Our investigation follows two different approaches, one basedon radial-velocity monitoring, the other based on direct imaging. Inthis first paper, we present the observational results from oursystematic adaptive optics search with VLT/NACO for close stellarcompanions to 130 nearby stars, 57 with planets and 73 without, forcomparison. The inclusion of a control sub-sample is a unique feature ofour program that will enable a meaningful and rigorous comparisonbetween the properties of planet-host stars and the properties of fieldstars subject to the same selection effects against close binaries, butshowing no evidence for planetary companions. Results: Our data reveal95 companion candidates found in the vicinity of 33 of our targets.Nineteen of these candidates are true companions and 2 are likely boundobjects. Among planet-host stars, we discovered a tight pair of very lowmass companions to HD 65216 (projected separation of 255 AU), an early Mcompanion to HD 177830 (projected separation of 97 AU), and we resolvedthe previously known companion to HD 196050 into a close pair of Mdwarfs. Our data additionally confirm the bound nature of the companionsto HD 142, HD 16141, and HD 46375. Among control stars, we detected truecompanions to HD 7895, HD 24331, HD 31412, HD 40397, HD 43834, HD 70923,HD 78351, HD 104263, HD 129642, HD 154682, and HD 223913, and likelybound companions to HD 82241 and HD 134180. Most of these objects are Mdwarfs and have projected separations between 7 and 505 AU.Based on observations collected at the ESO VLT Yepun telescope,proposals 70.C-0557, 71.C-0125, 73.C-0124, 74.C-0048, 75.C-0069, and76.C-0057. Tables 1, 2, and Figs. 3, 4 are only available in electronicform at http://www.aanda.org
| Stability and formation of the resonant system HD 73526
Context: Based on radial velocity measurements, it has been found thatthe two giant planets detected around the star HD 73526 are in 2:1resonance. However, as our numerical integration shows, the derivedorbital data for this system result in chaotic behavior of the giantplanets, which is uncommon among the resonant extrasolar planetarysystems. Aims: We present regular (non-chaotic) orbital solutions forthe giant planets in the system HD 73526 and offer formation scenariosbased on combining planetary migration and sudden perturbative effectssuch as planet-planet scattering or rapid dispersal of theprotoplanetary disk. A comparison with the already-studied resonantsystem HD 128311, exhibiting similar behavior, is given. Methods: Thenew sets of orbital solutions were derived using the Systemic Console.The stability of these solutions was investigated using the RelativeLyapunov indicator, while the migration and scattering effects arestudied by gravitational N-body simulations applying non-conservativeforces. Additionally, hydrodynamic simulations of embedded planets inprotoplanetary disks were performed to follow the capture intoresonance. Results: For the system HD 73526 we demonstrate that theobservational radial velocity data are consistent with a coplanarplanetary system in a stable 2:1 resonance exhibiting apsidalcorotation. We have shown that, similarly to the system HD 128311, thepresent dynamical state of HD 73526 could be the result of a mixedevolutionary process combining planetary migration and a perturbativeevent.
| Stability Limits in Resonant Planetary Systems
The relationship between the boundaries for Hill and Lagrange stabilityin orbital element space is modified in the case of resonantlyinteracting planets. Hill stability requires the ordering of the planetsto remain constant, while Lagrange stability also requires all planetsto remain bound to the central star. The Hill stability boundary isdefined analytically, but no equations exist to define the Lagrangeboundary, so we perform numerical experiments to estimate the locationof this boundary. To explore the effect of resonances, we considerorbital element space near the conditions in the HD 82943 and 55 Cncsystems. Previous studies have shown that, for nonresonant systems, thetwo stability boundaries are nearly coincident. However, the Hillstability formulae are not applicable to resonant systems, and ourinvestigation shows how the two boundaries diverge in the presence of amean-motion resonance, while confirming that the Hill and Lagrangeboundaries are similar otherwise. In resonance the region of stabilityis larger than the domain defined by the analytic formula for Hillstability. We find that nearly all known resonant interactions currentlylie in this unexpectedly stable region, i.e., where the orbits would beunstable according to the nonresonant Hill stability formula. Thisresult bears on the dynamical packing of planetary systems, showing howquantifying planetary systems' dynamical interactions (such as proximityto the Hill stability boundary) provides new constraints on planetformation models.
| Parent stars of extrasolar planets - VIII. Chemical abundances for 18 elements in 31 stars
We present the results of detailed spectroscopic abundance analyses for18 elements in 31 nearby stars with planets (SWPs). The resultingabundances are combined with other similar studies of nearby SWPs andcompared to a sample of nearby stars without detected planets. We findsome evidence for abundance differences between these two samples forAl, Si and Ti. Some of our results are in conflict with a recent studyof SWPs in the SPOCS data base. We encourage continued study of theabundance patterns of SWPs to resolve these discrepancies.
| Using Transit Timing Observations to Search for Trojans of Transiting Extrasolar Planets
Theoretical studies predict that Trojans are likely a frequentby-product of planet formation and evolution. We examine the sensitivityof transit timing observations for detecting Trojan companions totransiting extrasolar planets. We demonstrate that this method offersthe potential to detect terrestrial-mass Trojans using existingground-based observatories. We compare the transit timing variation(TTV) method with other techniques for detecting extrasolar Trojans andoutline the future prospects for this method.
| Planetary Formation Scenarios Revisited: Core-Accretion versus Disk Instability
The core-accretion and disk instability models have so far been used toexplain planetary formation. These models have different conditions,such as planet mass, disk mass, and metallicity for formation of gasgiants. The core-accretion model has a metallicity condition([Fe/H]>-1.17 in the case of G-type stars), and the mass of planetsformed is less than 6 times that of the Jupiter mass MJ. Onthe other hand, the disk instability model does not have the metallicitycondition, but requires the disk to be 15 times more massive than theminimum mass solar nebulae model. The mass of planets formed is morethan 2 MJ. These results are compared to the 161 detectedplanets for each spectral type of the central stars. The results showthat 90% of the detected planets are consistent with the core-accretionmodel regardless of the spectral type. The remaining 10% are not in theregion explained by the core-accretion model, but are explained by thedisk instability model. We derived the metallicity dependence of theformation probability of gas giants for the core-accretion model.Comparing the result with the observed fraction having gas giants, theyare found to be consistent. On the other hand, the observation cannot beexplained by the disk instability model, because the condition for gasgiant formation is independent of the metallicity. Consequently, most ofplanets detected so far are thought to have been formed by thecore-accretion process, and the rest by the disk instability process.
| Extrasolar Planetary Dynamics with a Generalized Planar Laplace-Lagrange Secular Theory
The dynamical evolution of nearly half of the known extrasolar planetsin multiple-planet systems may be dominated by secular perturbations.The commonly high eccentricities of the planetary orbits calls intoquestion the utility of the traditional Laplace-Lagrange (LL) seculartheory in analyses of the motion. We analytically generalize this theoryto fourth order in the eccentricities, compare the result with thesecond-order theory and octupole-level theory, and apply these theoriesto the likely secularly dominated HD 12661, HD 168443, HD 38529, andυ And multiplanet systems. The fourth-order scheme yields amultiply branched criterion for maintaining apsidal libration andimplies that the apsidal rate of a small body is a function of itsinitial eccentricity, dependencies which are absent from the traditionaltheory. Numerical results indicate that the primary difference thesecond- and fourth-order theories reveal is an alteration in secularperiodicities and to a smaller extent amplitudes of the planetaryeccentricity variation. Comparison with numerical integrations indicatesthat the improvement afforded by the fourth-order theory over thesecond-order theory sometimes is dwarfed by the improvement needed toreproduce the actual dynamical evolution. We conclude that LL seculartheory, to any order, generally represents a poor barometer forpredicting secular dynamics in extrasolar planetary systems, but doesembody a useful tool for extracting an accurate long-term dynamicaldescription of systems with small bodies and/or near-circular orbits.
| On the Extrasolar Multiplanet System around HD 160691
We reanalyze the precision radial velocity (RV) observations of HD160691 (μ Ara) by the Anglo-Australian Planet Search Team. The staris supposed to host two Jovian companions (HD 160691b, HD 160691c) inlong-period orbits (~630 days and ~2500 days, respectively) and a hotNeptune (HD 160691d) in ~9 day orbit. We perform a global search for thebest fits in the orbital parameter space with a hybrid code employingthe genetic algorithm and simplex method. The stability of Keplerianfits is verified with the N-body model of the RV signal that takes intoaccount the dynamical constraints (so called GAMP method). Our analysisreveals a signature of the fourth, as yet unconfirmed, Jupiter-likeplanet HD 160691e in ~307 day orbit. Overall, the global architecture offour-planet configuration recalls the solar system. All companions ofμ Ara move in quasi-circular orbits. The orbits of two inner Jovianplanets are close to the 2:1 mean motion resonance. The alternativethree-planet system involves two Jovian planets in eccentric orbits(e~0.3), close to the 4:1 MMR, but it yields a significantly worse fitto the data. We also verify a hypothesis of the 1:1 MMR in the subsystemof two inner Jovian planets in the four-planet model.
| A Bayesian Kepler periodogram detects a second planet in HD208487
An automatic Bayesian Kepler periodogram has been developed foridentifying and characterizing multiple planetary orbits in precisionradial velocity data. The periodogram is powered by a parallel temperingMarkov chain Monte Carlo (MCMC) algorithm which is capable ofefficiently exploring a multiplanet model parameter space. Theperiodogram employs an alternative method for converting the time of anobservation to true anomaly that enables it to handle much larger datasets without a significant increase in computation time. Improvements inthe periodogram and further tests using data from HD208487 have resultedin the detection of a second planet with a period of90982-92d, an eccentricity of0.370.26-0.20, a semimajor axis of1.870.13-0.14au and an M sini =0.45+0.11-0.13 MJ. The revisedparameters of the first planet are period = 129.8 +/- 0.4d, eccentricity= 0.20 +/- 0.09, semimajor axis = 0.51 +/- 0.02au and M sini = 0.41 +/-0.05MJ. Particular attention is paid to several methods forcalculating the model marginal likelihood which is used to compare theprobabilities of models with different numbers of planets.
| Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
We derive detailed theoretical models for 1074 nearby stars from theSPOCS (Spectroscopic Properties of Cool Stars) Catalog. The Californiaand Carnegie Planet Search has obtained high-quality (R~=70,000-90,000,S/N~=300-500) echelle spectra of over 1000 nearby stars taken with theHamilton spectrograph at Lick Observatory, the HIRES spectrograph atKeck, and UCLES at the Anglo Australian Observatory. A uniform analysisof the high-resolution spectra has yielded precise stellar parameters(Teff, logg, vsini, [M/H], and individual elementalabundances for Fe, Ni, Si, Na, and Ti), enabling systematic erroranalyses and accurate theoretical stellar modeling. We have created alarge database of theoretical stellar evolution tracks using the YaleStellar Evolution Code (YREC) to match the observed parameters of theSPOCS stars. Our very dense grids of evolutionary tracks eliminate theneed for interpolation between stellar evolutionary tracks and allowprecise determinations of physical stellar parameters (mass, age,radius, size and mass of the convective zone, surface gravity, etc.).Combining our stellar models with the observed stellar atmosphericparameters and uncertainties, we compute the likelihood for each set ofstellar model parameters separated by uniform time steps along thestellar evolutionary tracks. The computed likelihoods are used for aBayesian analysis to derive posterior probability distribution functionsfor the physical stellar parameters of interest. We provide a catalog ofphysical parameters for 1074 stars that are based on a uniform set ofhigh-quality spectral observations, a uniform spectral reductionprocedure, and a uniform set of stellar evolutionary models. We explorethis catalog for various possible correlations between stellar andplanetary properties, which may help constrain the formation anddynamical histories of other planetary systems.
| Co-orbital terrestrial planets in exoplanetary systems: a formation scenario
Aims.We study the formation of a hypothetical terrestrial-type body inthe equilateral Lagrange points of a giant extrasolar planet. Startingfrom a swarm of planetesimals in stable tadpole orbits, we simulate itsdynamical and collisional evolution under a wide range of differentinitial conditions and masses for both the Trojan population and itsplanetary companion. We also analyze the effects of gas drag from theinteraction of the planetesimals with the nebular disk. Methods: Theformation process is simulated with an N-body code that considers fullgravitational interactions between the planetesimals and the giantplanet. Gas interaction is modeled with Stokes and Epstein drags, wherethe drag coefficients are chosen following the results of fullhydrodynamic simulations performed with the 2D public hydro-code FARGO. Results: In both gas-free and gas-rich scenarios, we have been able toobtain a single final terrestrial-type body in a stable tadpole orbitaround one of the triangular Lagrange points of the system. However, dueto gravitational instabilities within the swarm, the accretional processis not very efficient and the mass of the final planet never seems toexceed ~0.6 Earth masses, even when the total mass of the swarm is fivetimes this value. Finally, we also included an orbital decay of thegiant planet due to a type II migration. Although the accretionalprocess shows evidence of a lower efficiency, a small terrestrial planetis still able to form, and follows the giant planet towards thehabitable zone of the hosting star.
| On the stability of test particles in extrasolar multiple planet systems
We have studied the dynamical evolution of test particles in theplanetary systems of υ Andromedae, GJ 876, 47 UMa and 55 Cnc. Usingrecent radial velocity data of these stars and also utilizing arelatively new radial velocity fitting routine, we have obtained theorbital parameters of the giant planets of these systems, and studiedthe possibility of their harbouring of terrestrial-class planets andsmaller objects. Our results indicate that, unlike the stable orbit ofthe newly discovered Earth-like planet of GJ 876, the orbit of therecently announced planet of 55 Cnc is unstable. Our simulations alsoshow that the outer planet of 47 UMa may contain Trojan-type asteroids.We present the results of our detailed study of the orbital stabilityand dynamical behaviour of test particles throughout these systems, andinvestigate the possibility of stable orbits in their habitable zones.Within the context of the latter, it seems that the two systems of 47UMa and 55 Cnc are still the only ones with the capability of harbouringhabitable planets, although the new influence zones of their giantplanets have caused their habitable regions to be different from theones reported in the literature.
| Stable satellites around extrasolar giant planets
In this work, we study the stability of hypothetical satellites ofextrasolar planets. Through numerical simulations of the restrictedelliptic three-body problem we found the borders of the stable regionsaround the secondary body. From the empirical results, we derivedanalytical expressions of the critical semimajor axis beyond which thesatellites would not remain stable. The expressions are given as afunction of the eccentricities of the planet, eP, and of thesatellite, esat. In the case of prograde satellites, thecritical semimajor axis, in the units of Hill's radius, is given byaE ~ 0.4895 (1.0000 - 1.0305eP -0.2738esat). In the case of retrograde satellites, it isgiven by aE ~ 0.9309 (1.0000 - 1.0764eP -0.9812esat). We also computed the satellite stability region(aE) for a set of extrasolar planets. The results indicatethat extrasolar planets in the habitable zone could harbour theEarth-like satellites.
| On the Search for Transits of the Planets Orbiting Gliese 876
We report the results of a globally coordinated photometric campaign tosearch for transits by the P~30 day and P~60 day outer planets of thethree-planet system orbiting the nearby M dwarf Gl 876. These twoplanets experience strong mutual perturbations, which necessitate theuse of a dynamical (four-body) model to compute transit ephemerides forthe system. Our photometric data have been collected from publishedarchival sources, as well as from our photometric campaigns that weretargeted to specific transit predictions. Our analysis indicates thattransits by planet c (P~30 days) do not currently occur, in concordancewith the best-fit i=50deg coplanar configuration obtained bydynamical fits to the most recent radial velocity data for the system.Transits by planet b (P~60 day) are not entirely ruled out by ourobservations, but our data indicate that it is very unlikely that theyoccur. Our experience with the Gl 876 system suggests that a distributedground-based network of small telescopes can be used to search fortransits of very low mass M stars by terrestrial-sized planets.
| Behavior of Apsidal Orientations in Planetary Systems
A widely considered characteristic of extrasolar planetary systems hasbeen a seeming tendency for major axes of adjacent orbits to librate instable configurations. Based on a new catalog of extrasolar planets(Butler et al.) and our numerical integrations, we find that suchsmall-amplitude oscillations are actually not common but in fact quiterare; most pairs of planets' major axes are consistent with circulatingrelative to one another. However, the new results are consistent withstudies that find that two-planet systems tend to lie near a separatrixbetween libration and circulation. Similarly, in systems of more thantwo planets, many adjacent orbits lie near a separatrix that dividesmodes of circulation.
| 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.
| Effects of Secular Interactions in Extrasolar Planetary Systems
This paper studies the effects of dynamical interactions among theplanets in observed extrasolar planetary systems, including hypotheticaladditional bodies, with a focus on secular perturbations. Theseinteractions cause the eccentricities of the planets to explore adistribution of values over timescales that are long compared toobservational time baselines but short compared to the age of thesystems. The same formalism determines the eccentricity forcing ofhypothetical test bodies (terrestrial planets) in these systems, and wefind which systems allow for potentially habitable planets. Such planetswould be driven to nonzero orbital eccentricity and we derive thedistribution of stellar flux experienced by the planets over the courseof their orbits. The general relativistic corrections to secularinteraction theory are included in the analysis, and such effects areimportant in systems with close planets (~4 day orbits). Some extrasolarplanetary systems (e.g., Υ Andromedae) can be used as a test ofgeneral relativity, whereas in other systems, general relativity can beused to constrain the system parameters (e.g., sini>~0.93 for HD160691). For the case of hot Jupiters we discuss how the absence ofobserved eccentricity implies the absence of companion planets.
| The 2:1 Resonant Exoplanetary System Orbiting HD 73526
We report the detection of a second exoplanet orbiting the G6 V dwarf HD73526. This second planet has an orbital period of 377 days, putting itin a 2:1 resonance with the previously known exoplanet, the orbitalperiod for which is updated to 188 days. Dynamical modeling of thecombined system allows solution for a self-consistent set of orbitalelements for both components. HD 73526 is the fourth exoplanetary system(of a total of 18 systems with two or more components currently known)to have components detected in 2:1 resonance. Finding such a largefraction of multiple planets (more than 20%) in 2:1 resonance stronglysuggests that orbital migration, halted by stabilization in a trappingresonance, plays an important role in the evolution of exoplanets inmultiple planet systems.Based on observations obtained at the Anglo-Australian Telescope, SidingSpring, Australia.
| Trojan Pairs in the HD 128311 and HD 82943 Planetary Systems?
Two nearby stars, HD 128311 and HD 82943, are believed to host pairs ofJupiter-like planets involved in a strong first-order 2:1 mean motionresonance (MMR). In this work, we reanalyze available radial velocity(RV) measurements and demonstrate that it is also possible to explainthe observed RV variations of the parent stars as being induced by apair of Trojan planets (i.e., in a 1:1 MMR). We show that these Trojanconfigurations reside in extended zones of stability in which suchsystems can easily survive in spite of the large masses of the planets,large eccentricities, and nonzero mutual inclinations of their orbits.We also show that HD 82943 could harbor a previously unknown thirdplanet of ~0.5MJ in ~2 AU orbit.
| The abundance distribution of stars with planets
We present the results of a uniform, high-precision spectroscopicmetallicity study of 136 G-type stars from the Anglo-Australian PlanetSearch, 20 of which are known to harbour extrasolar planets (as at 2005July). Abundances in Fe, C, Na, Al, Si, Ca, Ti and Ni are presented,along with Strömgen photometric metallicities. This study is one ofseveral recent studies examining the metallicities of a sample ofplanet-host and non-planet-host stars that were obtained from a singlesample, and analysed in an identical manner, providing an unbiasedestimate of the metallicity trends for planet-bearing stars. We findthat non-parametric tests of the distribution of metallicities forplanet-host and non-planet-host stars are significantly different at alevel of 99.4 per cent confidence. We confirm the previously observedtrend for planet-host stars to have higher mean metallicities thannon-planet-host stars, with a mean metallicity for planet-host stars of[Fe/H] = 0.06 +/- 0.03dex compared with [Fe/H] = -0.09 +/- 0.01dex fornon-host-stars in our sample. This enrichment is also seen in the otherelements studied. Based on our findings, we suggest that this observedenhancement is more likely a relic of the original gas cloud from whichthe star and its planets formed, rather than being due to `pollution' ofthe stellar photosphere.
| Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems
We present results of a reconnaissance for stellar companions to all 131radial velocity-detected candidate extrasolar planetary systems known asof 2005 July 1. Common proper-motion companions were investigated usingthe multiepoch STScI Digitized Sky Surveys and confirmed by matching thetrigonometric parallax distances of the primaries to companion distancesestimated photometrically. We also attempt to confirm or refutecompanions listed in the Washington Double Star Catalog, in the Catalogsof Nearby Stars Series by Gliese and Jahreiß, in Hipparcosresults, and in Duquennoy & Mayor's radial velocity survey. Ourfindings indicate that a lower limit of 30 (23%) of the 131 exoplanetsystems have stellar companions. We report new stellar companions to HD38529 and HD 188015 and a new candidate companion to HD 169830. Weconfirm many previously reported stellar companions, including six starsin five systems, that are recognized for the first time as companions toexoplanet hosts. We have found evidence that 20 entries in theWashington Double Star Catalog are not gravitationally bound companions.At least three (HD 178911, 16 Cyg B, and HD 219449), and possibly five(including HD 41004 and HD 38529), of the exoplanet systems reside intriple-star systems. Three exoplanet systems (GJ 86, HD 41004, andγ Cep) have potentially close-in stellar companions, with planetsat roughly Mercury-Mars distances from the host star and stellarcompanions at projected separations of ~20 AU, similar to the Sun-Uranusdistance. Finally, two of the exoplanet systems contain white dwarfcompanions. This comprehensive assessment of exoplanet systems indicatesthat solar systems are found in a variety of stellar multiplicityenvironments-singles, binaries, and triples-and that planets survive thepost-main-sequence evolution of companion stars.
| 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.
| On the evolution of the resonant planetary system HD 128311
Context.A significant number of the known multiple exoplanetary systemscontain a pair of giant planets engaged in low-order mean-motionresonance. Such a resonant condition protects the dynamics of theseplanets resulting in very stable orbits. According to recent studies,this capture into a resonance is the result of a planetary migrationprocess induced by interaction of the planets with a protoplanetarydisk. If the migration is slow enough (adiabatic) near a mean motionresonance, the two planets will also be in apsidal corotation. Aims.The recently refined orbital parameters of the system HD 128311suggest that the two giant planets are in a 2:1 mean motion resonance,however, without exhibiting apsidal corotation. Thus the evolution ofthis system cannot be described by an adiabatic migration process alone.We present possible evolution scenarios of this system by combiningmigration processes and sudden perturbations. Methods.We modelmigration scenarios through numerical integration of the gravitationalN-body problem with additional non-conservative forces. Planet-planetscattering has been investigated by N-body simulations. Results.Weshow that the present dynamical state of the system HD 128311 may beexplained by such evolutionary processes.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Chemical Composition of the Planet-harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star ofthe transiting extrasolar planet TrES-1. Based on high-resolution KeckHIRES and Hobby-Eberly Telescope HRS spectra, we have determinedabundances relative to the Sun for 16 elements (Na, Mg, Al, Si, Ca, Sc,Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The resulting averageabundance of <[X/H]>=-0.02+/-0.06 is in good agreement withinitial estimates of solar metallicity based on iron. We compare theelemental abundances of TrES-1 with those of the sample of stars withplanets, searching for possible chemical abundance anomalies. TrES-1appears not to be chemically peculiar in any measurable way. Weinvestigate possible signs of selective accretion of refractory elementsin TrES-1 and other stars with planets and find no statisticallysignificant trends of metallicity [X/H] with condensation temperatureTc. We use published abundances and kinematic information forthe sample of planet-hosting stars (including TrES-1) and severalstatistical indicators to provide an updated classification in terms oftheir likelihood to belong to either the thin disk or the thick disk ofthe Milky Way. TrES-1 is found to be very likely a member of thethin-disk population. By comparing α-element abundances of planethosts and a large control sample of field stars, we also find thatmetal-rich ([Fe/H]>~0.0) stars with planets appear to besystematically underabundant in [α/Fe] by ~0.1 dex with respect tocomparison field stars. The reason for this signature is unclear, butsystematic differences in the analysis procedures adopted by differentgroups cannot be ruled out.
| About putative Neptune-like extrasolar planetary candidates
Context: .We re-analyze the precision radial velocity (RV) data of HD208487 by the Anglo-Australian Planet Search Team, HD 190360, HD 188015,HD 114729 by the California and Carnegie Planet Search Team, and HD147513 by the Geneva Planet Search Team. All these stars are supposed tohost Jovian companions in long-period orbits. Aims.We test a hypothesisthat the residuals of the 1-planet model of the RV or an irregularscatter of the measurements around the synthetic RV curve may beexplained by the existence of additional planets in short-period orbits.Methods. We performed a global search for the best fits in the orbitalparameters space with genetic algorithms and simplex method. This makesit possible to verify and extend the results with an application ofcommonly used FFT-based periodogram analysis for identifying the leadingperiods. Results. Our analysis confirms the presence of a periodiccomponent in the RV of HD 190360 that may correspond to a hot-Neptuneplanet. We found four new cases in which the 2-planet model yieldssignificantly better fits to the RV data than the best 1-planetsolutions. If the periodic variability of the residuals of single-planetfits indeed has a planetary origin, then hot-Neptune planets may existin these extrasolar systems. We estimate their orbital periods as in therange of 7-20 d and minimal masses of about 20 masses of the Earth.
| Abundance ratios of volatile vs. refractory elements in planet-harbouring stars: hints of pollution?
We present the [ X/H] trends as a function of the elemental condensationtemperature TC in 88 planet host stars and in avolume-limited comparison sample of 33 dwarfs without detected planetarycompanions. We gathered homogeneous abundance results for many volatileand refractory elements spanning a wide range of T_C, from a few dozento several hundred kelvin. We investigate possible anomalous trends ofplanet hosts with respect to comparison sample stars to detect evidenceof possible pollution events. No significant differences are found inthe behaviour of stars with and without planets. This is consistent witha "primordial" origin of the metal excess in planet host stars. However,a subgroup of 5 planet host and 1 comparison sample stars stands out ashaving particularly high [ X/H] vs. TC slopes.
| A search for water masers toward extrasolar planets
Context: .Water is the most common triatomic molecule in the universeand the basis of life on Earth. Astrophysical masers have been widelystudied in recent years and have been shown to be invaluable probes ofthe details of the environment in which they are found. Water masers,for instance, are often detected toward low-mass star-forming regions.Doppler radial-velocity surveys have detected about 160exoplanets.Aims.Observations of water masers from exoplanetary systemswould give us a new detailed window through which to explorethem.Methods.We present a search for water masers toward eighteenextrasolar planets using the newly upgraded Australia Telescope CompactArray at 12 mm. A sensitivity of 25 mJy beam-1 and anangular resolution of ~10'' were achieved at 22.235 GHz. Results.Nomaser lines are clearly observed.
| Abundances of refractory elements in the atmospheres of stars with extrasolar planets
Aims.This work presents a uniform and homogeneous study of chemicalabundances of refractory elements in 101 stars with and 93 without knownplanetary companions. We carry out an in-depth investigation of theabundances of Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg and Al. The newcomparison sample, spanning the metallicity range -0.70< [Fe/H]<0.50, fills the gap that previously existed, mainly at highmetallicities, in the number of stars without known planets.Methods.Weused an enlarged set of data including new observations, especially forthe field "single" comparison stars . The line list previously studiedby other authors was improved: on average we analysed 90 spectral linesin every spectrum and carefully measured more than 16 600 equivalentwidths (EW) to calculate the abundances.Results.We investigate possibledifferences between the chemical abundances of the two groups of stars,both with and without planets. The results are globally comparable tothose obtained by other authors, and in most cases the abundance trendsof planet-host stars are very similar to those of the comparison sample.Conclusions.This work represents a step towards the comprehension ofrecently discovered planetary systems. These results could also beuseful for verifying galactic models at high metallicities andconsequently improve our knowledge of stellar nucleosynthesis andgalactic chemical evolution.
| A link between the semimajor axis of extrasolar gas giant planets and stellar metallicity
The fact that most extrasolar planets found to date are orbitingmetal-rich stars lends credence to the core accretion mechanism of gasgiant planet formation over its competitor, the disc instabilitymechanism. However, the core accretion mechanism is not refined to thepoint of explaining orbital parameters such as the unexpected semimajoraxes and eccentricities. We propose a model that correlates themetallicity of the host star with the original semimajor axis of itsmost massive planet, prior to migration, assuming that the coreaccretion scenario governs giant gas planet formation. The modelpredicts that the optimum regions for planetary formation shift inwardsas stellar metallicity decreases, providing an explanation for theobserved absence of long-period planets in metal-poor stars. We compareour predictions with the available data on extrasolar planets for starswith masses similar to the mass of the Sun. A fitting procedure producesan estimate of what we define as the zero-age planetary orbit (ZAPO)curve as a function of the metallicity of the star. The model hints thatthe lack of planets circling metal-poor stars may be partly caused by anenhanced destruction probability during the migration process, becausethe planets lie initially closer to their central star.
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Osservazione e dati astrometrici
| Costellazione: | Vele |
| Ascensione retta: | 08h37m16.48s |
| Declinazione: | -41°19'08.8" |
| Magnitudine apparente: | 8.98 |
| Distanza: | 94.607 parsec |
| Moto proprio RA: | -62.7 |
| Moto proprio Dec: | 161 |
| B-T magnitude: | 9.875 |
| V-T magnitude: | 9.054 |
Cataloghi e designazioni:
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INHABITED SKY
