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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 We include fivepreviously unpublished exoplanets orbiting the stars HD 11964, HD 66428,HD 99109, HD 107148, and HD 164922.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.
| Atmosphere, Interior, and Evolution of the Metal-rich Transiting Planet HD 149026b
We investigate the atmosphere and interior of the new transiting planetHD 149026b, which appears to be very rich in heavy elements. We firstcompute model atmospheres at metallicities ranging from solar to 10times solar and show how for cases with high metallicity or inefficientredistribution of energy from the dayside, the planet may develop a hotstratosphere due to absorption of stellar flux by TiO and VO. Thespectra predicted by these models are very different than cooleratmosphere models without stratospheres. The spectral effects arepotentially detectable with the Spitzer Space Telescope. In addition,the models with hot stratospheres lead to a large limb brightening,rather than darkening. We compare the atmosphere of HD 149026b to otherwell-known transiting planets, including the recently discovered HD189733b, which we show has a planet-to-star flux ratio twice that of HD209458 and TrES-1. The methane abundance in the atmosphere of HD 189733bis a sensitive indicator of atmospheric temperature and metallicity andcan be constrained with Spitzer IRAC observations. We then turn tointerior studies of HD 149026b and use a grid of self-consistent modelatmospheres and high-pressure equations of state for all components tocompute thermal evolution models of the planet. We estimate that themass of heavy elements within the planet is in the range of 60-93M⊕. Finally, we discuss trends in the radii oftransiting planets with metallicity in light of this new member of theclass.
| The N2K Consortium. III. Short-Period Planets Orbiting HD 149143 and HD 109749
We report the detection of two short-period planets discovered at KeckObservatory. HD 149143 is a metal-rich G0 IV star with a planet ofMsini=1.33MJ and an orbital radius of 0.053 AU. The best-fitKeplerian model has an orbital period, P=4.072 days, semivelocityamplitude, K=149.6 m s-1, and eccentricity, e=0.016+/-0.01.The host star is chromospherically inactive and metal-rich, with[Fe/H]=0.26. Based on the Teff and stellar luminosity, wederive a stellar radius of 1.49 Rsolar. Photometricobservations of HD 149143 were carried out using the automatedphotometric telescopes at Fairborn Observatory. HD 149143 isphotometrically constant over the radial velocity period to0.0003+/-0.0002 mag, supporting the existence of the planetarycompanion. No transits were detected down to a photometric limit ofapproximately 0.02%, eliminating transiting planets with a variety ofcompositions and constraining the orbital inclination to less than83°. A short-period planet was also detected around HD 109749, a G3IV star. HD 109749 is chromospherically inactive, with [Fe/H]=0.25 and astellar radius of 1.24. The radial velocities for HD 109749 are modeledby a Keplerian with P=5.24 days and K=28.7 m s-1. Theinferred planet mass is Msini=0.28MJ and the semimajor axisof this orbit is 0.0635 AU. Photometry of HD 109749 was obtained withthe SMARTS consortium telescope, the PROMPT telescope, and bytransitsearch.org observers in Adelaide and Pretoria. These observationsdid not detect a decrement in the brightness of the host star at thepredicted ephemeris time, and they constrain the orbital inclination toless than 85° for gas giant planets with radii down to0.7RJ.Based on observations obtained at the W. M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration (NASA). The Observatory was made possible bythe generous financial support of the W. M. Keck Foundation. The authorswish to recognize and acknowledge the very significant cultural role andreverence that the summit of Mauna Kea has always had within theindigenous Hawaiian community. We are most fortunate to have theopportunity to conduct observations from this mountain. Keck time hasbeen granted by the National Optical Astronomy Observatory (NOAO) andNASA.
| Transit Photometry of the Core-dominated Planet HD 149026b
We report g, V, and r photometric time series of HD 149026 spanningpredicted times of transit of the Saturn-mass planetary companion, whichwas recently discovered by Sato and collaborators. We present a jointanalysis of our observations and the previously reported photometry andradial velocities of the central star. We refine the estimate of thetransit ephemeris toTc=(2,453,527.87455+0.00085-0.00091)+(2.87598+0.00012-0.00017)N(HJD). Assuming that the star has a radius of 1.45+/-0.10Rsolar and a mass of 1.30+/-0.10 Msolar, weestimate the planet radius to be (0.726+/-0.064)RJup, whichimplies a mean density of 1.07+0.42-0.30 gcm-3. This density is significantly greater than predictedfor models that include the effects of stellar insolation and in whichthe planet has only a small core of solid material. Thus, we confirmthat this planet likely contains a large core and that the ratio of coremass to total planet mass is more akin to that of Uranus and Neptunethan to either Jupiter or Saturn.
| A correlation between the heavy element content of transiting extrasolar planets and the metallicity of their parent stars
Context.Nine extrasolar planets with masses between 110 and 430M_⊕ are known to transit their star. The knowledge of their massesand radii allows an estimate of their composition, but uncertainties onequations of state, opacities and possible missing energy sources implythat only inaccurate constraints can be derived when considering eachplanet separately.Aims.We seek to better understand thecomposition of transiting extrasolar planets by considering them as anensemble, and by comparing the obtained planetary properties to that ofthe parent stars.Methods.We use evolution models and constraintson the stellar ages to derive the mass of heavy elements present in theplanets. Possible additional energy sources like tidal dissipation dueto an inclined orbit or to downward kinetic energy transport areconsidered.Results.We show that the nine transiting planetsdiscovered so far belong to a quite homogeneous ensemble that ischaracterized by a mass of heavy elements that is a relatively steepfunction of the stellar metallicity, from less than 20 earth masses ofheavy elements around solar composition stars, to up to ~100 M_⊕for three times the solar metallicity (the precise values beingmodel-dependant). The correlation is still to be ascertained however.Statistical tests imply a worst-case 1/3 probability of a falsepositive.Conclusions.Together with the observed lack of giantplanets in close orbits around metal-poor stars, these results appear toimply that heavy elements play a key role in the formation of close-ingiant planets. The large masses of heavy elements inferred for planetsorbiting metal rich stars was not anticipated by planet formation modelsand shows the need for alternative theories including migration andsubsequent collection of planetesimals.
| High resolution spectroscopy of stars with transiting planets. The cases of OGLE-TR-10, 56, 111, 113, and TrES-1
Context: .During the past years photometric surveys, later complementedby follow-up radial-velocity measurements, have revealed the presence ofseveral new extra-solar transiting planets, in very short-period orbits.Many of the host stars are extremely faint (V16), makinghigh-precision spectroscopic measurements challenging. Aims: .Weused the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolutionspectra of 5 stars hosting transiting planets, namely for OGLE-TR-10,56, 111, 113, and TrES-1. The immediate objective is to derive accuratestellar parameters and chemical abundances. Methods: .The stellarparameters were derived from an LTE analysis of a set of Fe I and Fe IIlines. Results: .Complementing the spectroscopic information withphotometric transit curves and radial-velocity data from the literature,we then refined the stellar and planetary radii and masses. The obtaineddata were also used to study the relation between the stellarmetallicity and orbital period of the planets.
| Hipparcos astrometric orbits for two brown dwarf companions: HD 38529 and HD 168443
Context: .HD 38529 and HD 168443 have previously been identified assystems with two substellar companion candidates using precise radialvelocity measurements.Aims.We want to further constrain their orbits andthe nature of the outer companions.Methods.We fit astrometric orbits ofthe outer substellar companions in the two systems to the HipparcosIntermediate Astrometric Data.Results.The fit constrains all possiblesolutions to a small region in the parameter space of the two missingorbital parameters (inclination i and ascending node Ω). This canbe interpreted as a possible real detection of the astrometricsignatures of the companions in the Hipparcos data, although there isstill a 14-18% chance that the signal is not detectable in the data,according to an F-test. However, even in the case of a non-detection ofthe companion signal in the astrometric data, the knowledge of thespectroscopic orbital parameters enables us to place tight constraintson these two missing parameters, so that the astrometric orbit is fullydetermined (with confidence levels of around 80% for HD 38529, 95% forHD 168443). Inclinations derived from these astrometric fits enable usto calculate masses for the substellar companions rather than lower orupper limits. The best fit solution for HD 38529, (i, Ω) =(160°, 52°), yields a mass of 37+36-19M_Jup for the outer companion. For HD 168443, we derive best fitparameters of (i, Ω) = (150°, 19°), which imply acompanion mass of 34± 12 M_Jup.Conclusions.The outer companionsin both systems are thus brown dwarfs.
| The transmission spectrum of Earth-size transiting planets
A variety of terrestrial planets with different physical parameters andexotic atmospheres might plausibly exist outside our Solar System,waiting to be detected by the next generation of space-explorationmissions. Some of these planets might be transiting their parent star.We present here a detailed study of the atmospheric signatures oftransiting Earth-size exoplanets. We focus on a limited number ofsignificant examples, for which we discuss the detectability of some ofthe possible molecules present in their atmospheres, such as water(H2O), carbon dioxide (CO2), ozone (O3), or molecular oxygen (O2). Tothis purpose, we developed a model to simulate transmission spectra ofEarth-size exoplanets from the ultraviolet (UV) to the near infrared(NIR). According to our calculations, the signatures of planetaryatmospheres represent an absorption of a few parts-per-million (ppm) inthe stellar flux. The atmospheres of a few Earth-like planets can bedetected with a 30-40 m telescope. The detection of the extensiveatmospheres of tens of small satellites of giant exoplanets and hundredsof hypothetical ocean-planets can be achieved with 20-30 m and 10-20 minstruments, respectively, provided all these planets are frequent andthey are efficiently surveyed. We also found that planets around K starsare favored, mainly because these stars are more numerous and smallercompared to G or F stars. While not addressed in this study, limitationsmight come from stellar photometric micro-variability.
| Elodie metallicity-biased search for transiting Hot Jupiters. I. Two Hot Jupiters orbiting the slightly evolved stars HD 118203 and HD 149143
We report the discovery of a new planet candidate orbiting the subgiantstar HD 118203 with a period of P = 6.1335 days. Thebest Keplerian solution yields an eccentricity e = 0.31 and a minimummass m_2 sin{i} = 2.1 M_Jup for the planet. This star has been observedwith the ELODIE fiber-fed spectrograph as one of the targets in ourplanet-search programme biased toward high-metallicity stars, on-goingsince March 2004 at the Haute-Provence Observatory. An analysis of thespectroscopic line profiles using line bisectors revealed no correlationbetween the radial velocities and the line-bisector orientations,indicating that the periodic radial-velocity signal is best explained bythe presence of a planet-mass companion. A linear trend is observed inthe residuals around the orbital solution that could be explained by thepresence of a second companion in a longer-period orbit. We also presenthere our orbital solution for another slightly evolved star in ourmetal-rich sample, HD 149143, recently proposed tohost a 4-d period Hot Jupiter by the N2K consortium. Our solution yieldsa period P = 4.09 days, a marginally significant eccentricity e = 0.08and a planetary minimum mass of 1.36 M_Jup. We checked that the shape ofthe spectral lines does not vary for this star as well.
| The N2K Consortium. II. A Transiting Hot Saturn around HD 149026 with a Large Dense Core
Doppler measurements from Subaru and Keck have revealed radial velocityvariations in the V=8.15, G0 IV star HD 149026 consistent with aSaturn-mass planet in a 2.8766 day orbit. Photometric observations atFairborn Observatory have detected three complete transit events withdepths of 0.003 mag at the predicted times of conjunction. HD 149026 isnow the second-brightest star with a transiting extrasolar planet. Themass of the star, based on interpolation of stellar evolutionary models,is 1.3+/-0.1 Msolar together with the Doppler amplitudeK1=43.3 m s-1, we derive a planet massMsini=0.36MJ and orbital radius 0.042 AU. HD 149026 ischromospherically inactive and metal-rich with spectroscopically derived[Fe/H]=+0.36, Teff=6147 K, logg=4.26, and vsini=6.0 kms-1. Based on Teff and the stellar luminosity of2.72 Lsolar, we derive a stellar radius of 1.45Rsolar. Modeling of the three photometric transits providesan orbital inclination of 85.3d+/-1.0d and (including the uncertainty inthe stellar radius) a planet radius of (0.725+/-0.05)RJ.Models for this planet mass and radius suggest the presence of a ~67M⊕ core composed of elements heavier than hydrogen andhelium. This substantial planet core would be difficult to construct bygravitational instability.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.Based on observations obtained at the W. M. Keck Observatory, which isoperated by the University of California and the California Institute ofTechnology. Keck time has been granted by NOAO and NASA.
| Interactions between hot Jupiters and their host stars
A young hot Jupiter might have been tidally inflated beyond its Rocheradius when its orbit was being circularized. This scenario has thepotential to explain a couple of solid or tentative observations such asa pile-up of hot Jupiters around 0.04-0.05 AU, the mass-periodcorrelation of transiting planets, as well as the existence of hotNeptunes. Other scenarios such as tidal dissipation in a planet-hoststar as well as the magnetic interaction will be also discussed.
| ELODIE metallicity-biased search for transiting Hot Jupiters. II. A very hot Jupiter transiting the bright K star HD 189733
Context: .Among the 160 known exoplanets, mainly detected in largeradial-velocity surveys, only 8 have a characterization of their actualmass and radius thanks to the two complementary methods of detection:radial velocities and photometric transit. Aims: .We started inMarch 2004 an exoplanet-search programme biased toward high-metallicitystars which are more frequently host extra-solar planets. This surveyaims to detect close-in giant planets, which are most likely to transittheir host star. Methods: .For this programme, high-precisionradial velocities are measured with the ELODIE fiber-fed spectrograph onthe 1.93-m telescope, and high-precision photometry is obtained with theCCD Camera on the 1.20-m telescope, both at the Haute-ProvenceObservatory. Results: .We report here the discovery of a newtransiting hot Jupiter orbiting the star HD 189733. The planetary natureof this object is confirmed by the observation of both the spectroscopicand photometric transits. The exoplanet HD 189733 b, with an orbitalperiod of 2.219 days, has one of the shortest orbital periods detectedby radial velocities, and presents the largest photometric depth in thelight curve (3%) observed to date. We estimate for the planet amass of 1.15±0.04 MJ and a radius of 1.26±0.03RJ. Considering that HD 189733 has the same visual magnitudeas the well known exoplanet host star HD 209458, further ground-basedand space-based follow-up observations are very promising and willpermit a characterization of the atmosphere and exosphere of this giantexoplanet.
| On the potential of extrasolar planet transit surveys
We analyse the respective benefits and drawbacks of ground-based andspace-based transit surveys for extrasolar planets. Based on simple butrealistic assumptions about the fraction of lower main sequence starsharboring telluric and giant planets within the outer limit of thehabitable zone, we predict the harvests of fictitious surveys with threeexisting wide field optical and near-IR cameras: the CFHT-Megacam,SUBARU-Suprime and VISTA-IR. An additional promising instrument isconsidered, VISTA-Vis, currently under development. The results arecompared with the harvests predicted under exactly the same assumptions,for the space missions COROT and KEPLER. We show that ground-based widefield surveys may discover more giant planets than space missions.However, space surveys seem to constitute the best strategy to searchfor telluric planets. In this respect, the KEPLER mission appears 50times more efficient than any of the ground-based surveys consideredhere. KEPLER might even discover telluric planets in the habitable zoneof their host star.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
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Observation and Astrometry data
| Constellation: | Hercules |
| Right ascension: | 16h30m29.62s |
| Declination: | +38°20'50.3" |
| Apparent magnitude: | 8.146 |
| Distance: | 78.864 parsecs |
| Proper motion RA: | -78.1 |
| Proper motion Dec: | 53.3 |
| B-T magnitude: | 8.887 |
| V-T magnitude: | 8.208 |
Catalogs and designations:
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