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|Virtual planet sleuths.|
|The Effects of Multiple Companions on the Efficiency of Space Interferometry Mission Planet Searches|
The Space Interferometry Mission (SIM) is expected to make preciseastrometric measurements that can be used to detect low-mass planetsaround nearby stars. Since most nearby stars are members ofmultiple-star systems, many of them will have a measurable accelerationdue to their companion, which must be included when solving forastrometric parameters and searching for planetary perturbations. Inaddition, many of the stars with one radial velocity planet showindications of additional planets. Therefore, astrometric surveys suchas SIM must be capable of detecting planets and measuring orbitalparameters in systems with multiple stellar and/or planetary companions.We have conducted Monte Carlo simulations to investigate how thepresence of multiple companions affects the sensitivity of anastrometric survey such as SIM. We find that the detection efficiencyfor planets in wide binary systems is relatively unaffected by thepresence of a binary companion if the planetary orbital period is lessthan half the duration of the astrometric survey. For longer orbitalperiods, there are significant reductions in the sensitivity of anastrometric survey. In addition, we find that the signal required todetect a planet can be increased significantly due to the presence of anadditional planet orbiting the same star. Fortunately, adding a modestnumber of precision radial velocity observations significantly improvesthe sensitivity for many multiple-planet systems. Thus, the combinationof radial velocity observations and astrometric observations by SIM willbe particularly valuable for studying multiple-planet systems.
|Condensation temperature trends among stars with planets|
Results from detailed spectroscopic analyses of stars hosting massiveplanets are employed to search for trends between abundances andcondensation temperatures. The elements C, S, Na, Mg, Al, Ca, Sc, Ti, V,Cr, Mn, Fe, Ni and Zn are included in the analysis of 64 stars withplanets and 33 comparison stars. No significant trends are evident inthe data. This null result suggests that accretion of rocky material onto the photospheres of stars with planets is not the primary explanationfor their high metallicities. However, the differences between the solarphotospheric and meteoritic abundances do display a weak but significanttrend with condensation temperature. This suggests that the metallicityof the Sun's envelope has been enriched relative to its interior byabout 0.07 dex.
|Extrasolar planets, stellar winds and chromospheric hotspots|
Recent observations have shown what is believed to be planet-inducedchromospheric activity on stars with hot Jupiters. We present a model ofthe magnetic interaction between a planet and a star with a dipolarmagnetic field. Reconnection between the fields of the star and planetaccelerates electrons along the field lines that connect the star andplanet. By determining the locations at which these field lines connectto the stellar surface, we can model the surface pattern of thechromospheric response to the planet-star interaction. We find that theinclination of the rotation axis of the star determines the magnitude ofthe emission, while a misalignment of the magnetic and rotation axesproduces a phase shift between the peak of the observed chromosphericemission and the phase where the planet is directly in front of thestar. This phase shift increases as the extent of the stellar coronaincreases. This model reproduces the cyclic signature of chromosphericenhancement seen in stars with hot Jupiters. It can reproduce the65° phase lag reported for HD 179949 if the closed corona of thestar extends out to the orbital radius of the planet at8.5R*. It cannot, however, reproduce the phase lag of169° reported for υ And.
|Colour-differential interferometry for the observation of extrasolar planets|
We present the high angular resolution technique of colour-differentialinterferometry for direct detection of extrasolar giant planets (EGPs).The measurement of differential phase with long-baseline ground-basedinterferometers in the near-infrared could allow the observation ofseveral hot giant extrasolar planets in tight orbit around the nearbystars, and thus yield their low- or mid-resolution spectroscopy,complete orbital data set and mass. Estimates of potentially achievablesignal-to-noise ratios are presented for a number of planets alreadydiscovered by indirect methods. The limits from the instrumental andatmospheric instability are discussed, and a subsequent observationalstrategy is proposed.
|Metallicity, debris discs and planets|
We investigate the populations of main-sequence stars within 25 pc thathave debris discs and/or giant planets detected by Doppler shift. Themetallicity distribution of the debris sample is a very close match tothat of stars in general, but differs with >99 per cent confidencefrom the giant planet sample, which favours stars of above averagemetallicity. This result is not due to differences in age of the twosamples. The formation of debris-generating planetesimals at tens of authus appears independent of the metal fraction of the primordial disc,in contrast to the growth and migration history of giant planets withina few au. The data generally fit a core accumulation model, with outerplanetesimals forming eventually even from a disc low in solids, whileinner planets require fast core growth for gas to still be present tomake an atmosphere.
|Secular apsidal configuration of non-resonant exoplanetary systems|
Using a high-order (order 12) expansion of the perturbative potential inpowers of eccentricities [Libert, A.-S., Henrard, J., 2005. Celest.Mech. Dynam. Astron. 93, 187 200], we study the secular effects of twocoplanar planets which are not in mean motion resonances. The mainresults concern eccentricity variations, oscillation amplitude of theangular difference of the apsidal lines (Δϖ) and frequency ofsuch an oscillation. We show that this analytical approach describescorrectly the behaviour of most of the exosystems and underlines theknown limitations of the linear Laplace Lagrange theory. Apsidalconfiguration of υ Andromedae, HD 168443, HD 169830, HD 38529, HD74156 and HD 12661 are examined. We also point out the great sensitivityof the υ Andromedae system to the initial values (e(0),e(0) or Δϖ(0)).
|Modeling the 3-D secular planetary three-body problem|
The three-dimensional secular behavior of a system composed of a centralstar and two massive planets is modeled semi-analytically in the frameof the general three-body problem. The main dynamical features of thesystem are presented in geometrical pictures allowing us to investigatea large domain of the phase space of this problem without time-expensivenumerical integrations of the equations of motion and without anyrestriction on the magnitude of the planetary eccentricities,inclinations and mutual distance. Several regimes of motion of thesystem are observed. With respect to the secular angle Δϖ,possible motions are circulations, oscillations (around 0° and180°), and high-eccentricity/inclination librations in secularresonances. With respect to the arguments of pericenter,ω and ω, possible motions are directcirculation and high-inclination libration around ±90° in theLidov Kozai resonance. The regions of transition between domains ofdifferent regimes of motion are characterized by chaotic behavior. Weapply the analysis to the case of the two outer planets of the υAndromedae system, observed edge-on. The topology of the 3-D phase spaceof this system is investigated in detail by means of surfaces ofsection, periodic orbits and dynamical spectra, mapping techniques andnumerical simulations. We obtain the general structure of the phasespace, and the boundaries of the spatial secular stability. We find thatthis system is secularly stable in a large domain of eccentricities andinclinations.
|Stability and 2:1 resonance in the planetary system HD 829431|
We have explored the secular dynamical evolution of the HD 82943 systemwith two resonant giant planets, by simulating various planetaryconfigurations via direct numerical integration. We also studied theirorbital motions in phase space. In the numerical integrations over107 yr, we found that all the stable orbits are connectedwith the 2:1 resonance. Typically, there exists the libration of the tworesonant arguments 1 and (or) 2 on the sametimescale. Hence, both of the semi-major axes are strongly constrainedto behave in a regular way, due to the confinement of the libration ofthe related angles. Using the analytical model we considered the motionof the inner planet in phase space for different values of the outerplanet's eccentricity e2 and of the relative apsidallongitude . We found that the 2:1 orbital resonance is easily preservedwhen= 0† and when e2 is not too large. A moderatee2 can lock the two planets into deep resonance. The resultsby the analytical method agree well with those by the numericalsimulation, both revealing the 2:1 resonance architecture.
|An Upper Limit on the Albedo of HD 209458b: Direct Imaging Photometry with the MOST Satellite|
We present space-based photometry of the transiting exoplanetary systemHD 209458 obtained with the Microvariablity and Oscillations of Stars(MOST) satellite, spanning 14 days and covering 4 transits and 4secondary eclipses. The HD 209458 photometry was obtained in MOST'slower precision direct imaging mode, which is used for targets in thebrightness range 6.5>=V>=13. We describe the photometric reductiontechniques for this mode of observing, in particular the corrections forstray earthshine. We do not detect the secondary eclipse in the MOSTdata, to a limit in depth of 0.053 mmag (1 σ). We set a 1 σupper limit on the planet-star flux ratio of 4.88×10-5corresponding to a geometric albedo upper limit in the MOST bandpass(400-700 nm) of 0.25. The corresponding numbers at the 3 σ levelare 1.34×10-4 and 0.68, respectively. HD 209458b ishalf as bright as Jupiter in the MOST bandpass. This low geometricalbedo value is an important constraint for theoretical models of the HD209458b atmosphere, in particular ruling out the presence of reflectiveclouds. A second MOST campaign on HD 209458 is expected to be sensitiveto an exoplanet albedo as low as 0.13 (1 σ), if the star does notbecome more intrinsically variable in the meantime.MOST is a Canadian Space Agency mission, operated jointly by Dynacon,Inc., and the Universities of Toronto and British Columbia, withassistance from the University of Vienna.
|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.
|Predictions for the Correlation between Giant and Terrestrial Extrasolar Planets in Dynamically Evolved Systems|
The large eccentricities of many giant extrasolar planets may representthe endpoint of gravitational scattering in initially more crowdedsystems. If so, the early evolution of the giant planets is likely to bemore restrictive of terrestrial planet formation than would be inferredfrom the current, dynamically quiescent configurations. Here we studystatistically the extent of the anticorrelation between giant planetsand terrestrial planets expected in a scattering model. We usemarginally stable systems of three giant planets, with a realistic rangeof planetary masses, as a simple model for the initial conditions priorto scattering, and we show that after scattering the surviving planetsreproduce well the known extrasolar planet eccentricities beyonda>0.5 AU. By tracking the minimum periastron values of all planetsduring the evolution, we derive the distribution of orbital radii acrosswhich strong perturbations (from crossing orbits) are likely to affectlow-mass planet formation. We find that scattering affects inner planetformation at orbital separations less than 50% of the final periastrondistance, qfm, of the innermost massive planet inapproximately 30% of the realizations and can occasionally influenceplanet formation at orbital separations less than 20% of qfm.The domain of influence of the scattering massive planets increases asthe mass differential between the massive planets decreases.Observational study of the correlation between massive and terrestrialextrasolar planets in the same system has the potential to constrain theorigin of planetary eccentricity.
|Dynamical Stability and Habitability of the γ Cephei Binary-Planetary System|
It has been suggested that the long-lived residual radial velocityvariations observed in the precision radial velocity measurements of theprimary of γ Cephei (HR 8974, HD 222404, HIP 116727) are likelydue to a Jupiter-like planet orbiting this star. In this paper, thedynamics of this planet is studied, and the possibility of the existenceof a terrestrial planet around its central star is discussed.Simulations, which have been carried out for different values of theeccentricity and semimajor axis of the binary, as well as the orbitalinclination of its Jupiter-like planet, expand on previous studies ofthis system and indicate that, for the values of the binary eccentricitysmaller than 0.5, and for all values of the orbital inclination of theJupiter-like planet ranging from 0° to 40°, the orbit of thisplanet is stable. For larger values of the binary eccentricity, thesystem becomes gradually unstable. Integrations also indicate that,within this range of orbital parameters, a terrestrial planet, such asan Earth-like object, can have a long-term stable orbit only atdistances of 0.3-0.8 AU from the primary star. The habitable zone of theprimary, at a range of approximately 3.05-3.7 AU, is, however, unstable.
|Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets|
Precise radial velocity measurements have led to the discovery of ~170extrasolar planetary systems. Understanding the uncertainties in theorbital solutions will become increasingly important as the discoveryspace for extrasolar planets shifts to planets with smaller masses andlonger orbital periods. The method of Markov chain Monte Carlo (MCMC)provides a rigorous method for quantifying the uncertainties in orbitalparameters in a Bayesian framework (Paper I). The main practicalchallenge for the general application of MCMC is the need to constructMarkov chains that quickly converge. The rate of convergence is verysensitive to the choice of the candidate transition probabilitydistribution function (CTPDF). Here we explain one simple method forgenerating alternative CTPDFs that can significantly speed convergenceby 1-3 orders of magnitude. We have numerically tested dozens of CTPDFswith simulated radial velocity data sets to identify those that performwell for different types of orbits and suggest a set of CTPDFs forgeneral application. In addition, we introduce other refinements to theMCMC algorithm for radial velocity planets, including an improvedtreatment of the uncertainties in the radial velocity observations, analgorithm for automatically choosing step sizes, an algorithm forautomatically determining reasonable stopping times, and the use ofimportance sampling for including the dynamical evolution ofmultiple-planet systems. Together, these improvements make it practicalto apply MCMC to multiple-planet systems. We demonstrate theimprovements in efficiency by analyzing a variety of extrasolarplanetary systems.
|IRS Spectra of Solar-Type Stars: A Search for Asteroid Belt Analogs|
We report the results of a spectroscopic search for debris diskssurrounding 41 nearby solar-type stars, including eight planet-bearingstars, using the Infrared Spectrometer (IRS) on the Spitzer SpaceTelescope. With the accurate relative photometry of the IRS between 7and 34 μm we are able to look for excesses as small as ~2% ofphotospheric levels, with particular sensitivity to weak spectralfeatures. For stars with no excess, the 3 σ upper limit in a bandat 30-34 μm corresponds to ~75 times the brightness of our zodiacaldust cloud. Comparable limits at 8.5-13 μm correspond to ~1400 timesthe brightness of our zodiacal dust cloud. These limits correspond tomaterial located within the <1 to ~5 AU region that, in our solarsystem, originates predominantly from debris associated with theasteroid belt. We find excess emission longward of ~25 μm from fivestars, of which four also show excess emission at 70 μm. Thisemitting dust must be located in a region starting around 5-10 AU. Onestar has 70 μm emission but no IRS excess. In this case, the emittingregion must begin outside 10 AU; this star has a known radial velocityplanet. Only two stars of the five show emission shortward of 25 μm,where spectral features reveal the presence of a population of small,hot dust grains emitting in the 7-20 μm band. One of these stars, HD72905, is quite young (300 Myr), while the other, HD 69830, is olderthan 2 Gyr. The data presented here strengthen the results of previousstudies to show that excesses at 25 μm and shorter are rare: only 1out of 40 stars older than 1 Gyr or ~2.5% shows an excess. Asteroidbelts 10-30 times more massive than our own appear are rare amongmature, solar-type stars.
|Extrasolar Planetary Systems Near a Secular Separatrix|
Extrasolar planetary systems display a range of behavior that can beunderstood in terms of the secular theory of classical celestialmechanics, including the motions of the major axes. Four planet pairs inthe seventeen known extrasolar planetary systems with multiple planets(υ And, 47 UMa, 55 Cnc, and HD 128311), have trajectories inorbital element space that lie close to the separatrix between librationand circulation. Here we examine the dynamics of the first two, whichare not in mean motion resonance. The basics of secular theory arereviewed in order to develop insight into this behavior. The definitionof a secular resonance is discussed, correcting misconceptions in theliterature; it is not synonymous with libration and is not acommensurability of eigenfrequencies. The behavior of these twonear-separatrix systems is evaluated with updated orbital elements bycomparing both analytical and numerical results. We find that theapsidal motion from secular theory does not match the predictions fromN-body simulations and conclude that first-order secular theory shouldbe used with caution on extrasolar planetary systems. While theexistence of one near-separatrix system could be explained simply bychance initial conditions, the fact that there are several is improbableunless some physical process tends to set up systems near theseparatrix. Explanations based on an impulsive increase in theeccentricity of one planet are promising, but key issues remain open.
|Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer MIPS Survey|
We have searched for infrared excesses around a well-defined sample of69 FGK main-sequence field stars. These stars were selected withoutregard to their age, metallicity, or any previous detection of IRexcess; they have a median age of ~4 Gyr. We have detected 70 μmexcesses around seven stars at the 3 σ confidence level. Thisextra emission is produced by cool material (<100 K) located beyond10 AU, well outside the ``habitable zones'' of these systems andconsistent with the presence of Kuiper Belt analogs with ~100 times moreemitting surface area than in our own planetary system. Only one star,HD 69830, shows excess emission at 24 μm, corresponding to dust withtemperatures >~300 K located inside of 1 AU. While debris disks withLdust/L*>=10-3 are rare around oldFGK stars, we find that the disk frequency increases from 2%+/-2% forLdust/L*>=10-4 to 12%+/-5% forLdust/L*>=10-5. This trend in thedisk luminosity distribution is consistent with the estimated dust inour solar system being within an order of magnitude greater or less thanthe typical level around similar nearby stars. Although there is nocorrelation of IR excess with metallicity or spectral type, there is aweak correlation with stellar age, with stars younger than a gigayearmore likely to have excess emission.
|No Detectable H+3 Emission from the Atmospheres of Hot Jupiters|
H+3 emission is the dominant cooling mechanism inJupiter's thermosphere and a useful probe of temperature and iondensities. The H+3 ion is predicted to form in thethermospheres of close-in ``hot Jupiters,'' where its emission would bea significant factor in the thermal energy budget, affecting temperatureand the rate of hydrogen escape from the exosphere. Hot Jupiters arepredicted to have up to 105 times Jupiter'sH+3 emission because they experience extremestellar irradiation and enhanced interactions may occur between theplanetary magnetosphere and the stellar wind. Direct (but unresolved)detection of an extrasolar planet, or the establishment of useful upperlimits, may be possible because a small but significant fraction of thetotal energy received by the planet is reradiated in a few narrow linesof H+3 within which the flux from the star islimited. We present the observing strategy and results of our search foremission from the Q(1,0) transition of H+3 (3.953μm) from extrasolar planets orbiting six late-type dwarfs usingCSHELL, the high-resolution echelle spectrograph on NASA's InfraredTelescope Facility. We exploited the time-dependent Doppler shift of theplanet, which can be as large as 150 km s-1, by differencingspectra between nights, thereby removing the stellar photospheric signaland telluric lines. We set limits on the H+3emission from each of these systems and compare them with models in theliterature. Ideal candidates for future searches are intrinsically faintstars, such as M dwarfs, at very close distances.
|Dwarfs in the Local Region|
We present lithium, carbon, and oxygen abundance data for a sample ofnearby dwarfs-a total of 216 stars-including samples within 15 pc of theSun, as well as a sample of local close giant planet (CGP) hosts (55stars) and comparison stars. The spectroscopic data for this work have aresolution of R~60,000, a signal-to-noise ratio >150, and spectralcoverage from 475 to 685 nm. We have redetermined parameters and derivedadditional abundances (Z>10) for the CGP host and comparison samples.From our abundances for elements with Z>6 we determine the meanabundance of all elements in the CGP hosts to range from 0.1 to 0.2 dexhigher than nonhosts. However, when relative abundances ([x/Fe]) areconsidered we detect no differences in the samples. We find nodifference in the lithium contents of the hosts versus the nonhosts. Theplanet hosts appear to be the metal-rich extension of local regionabundances, and overall trends in the abundances are dominated byGalactic chemical evolution. A consideration of the kinematics of thesample shows that the planet hosts are spread through velocity space;they are not exclusively stars of the thin disk.
|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.
|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.
|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.
|Ground-based direct detection of close-in extra-solar planets with nulling and high order adaptive optics|
Ground-based direct detection of extra-solar planets is very challengingdue to high planet to star brightness contrasts. For giant close-inplanets, such as have been discovered by the radial velocity method,closer than 0.1 AU, the reflected light is predicted to be fairly highyielding a contrast ratio ranging from 10-4 to10-5 at near infra-red wavelengths. In this paper, weinvestigate direct detection of reflected light from such planets usingnulling interferometry, and high-order adaptive optics in conjunctionwith large double aperture ground-based telescopes. In thisconfiguration, at least 10-3 suppression of the entirestellar Airy pattern with small loss of planet flux as close as 0.03arcsec is achievable. Distinguishing residual starlight from the planetsignal is achieved by using the center of gravity shift method ormulticolor differential imaging. Using these assumptions, we deriveexposure times from a few minutes to several hours for direct detectionof many of the known extra-solar planets with several short-baselinedouble aperture telescopes such as the Large Binocular Telescope (LBT),the Very Large Telescope (VLT) and the Keck Telescope.
|Oxygen abundances in planet-harbouring stars. Comparison of different abundance indicators|
We present a detailed and uniform study of oxygen abundances in 155solar type stars, 96 of which are planet hosts and 59 of which form partof a volume-limited comparison sample with no known planets. EWmeasurements were carried out for the [O I] 6300 Å line and the OI triplet, and spectral synthesis was performed for several OH lines.NLTE corrections were calculated and applied to the LTE abundanceresults derived from the O I 7771-5 Å triplet. Abundances from [OI], the O I triplet and near-UV OH were obtained in 103, 87 and 77dwarfs, respectively. We present the first detailed and uniformcomparison of these three oxygen indicators in a large sample ofsolar-type stars. There is good agreement between the [O/H] ratios fromforbidden and OH lines, while the NLTE triplet shows a systematicallylower abundance. We found that discrepancies between OH, [O I] and the OI triplet do not exceed 0.2 dex in most cases. We have studied abundancetrends in planet host and comparison sample stars, and no obviousanomalies related to the presence of planets have been detected. Allthree indicators show that, on average, [O/Fe] decreases with [Fe/H] inthe metallicity range -0.8< [Fe/H] < 0.5. The planet host starspresent an average oxygen overabundance of 0.1-0.2 dex with respect tothe comparison sample.
|Astrometric Methods and Instrumentation to Identify and Characterize Extrasolar Planets: A Review|
I present a review of astrometric techniques and instrumentation used tosearch for, detect, and characterize extrasolar planets. First, Ibriefly summarize the properties of the current sample of extrasolarplanets, in connection with predictions from theoretical models ofplanet formation and evolution. Next, the generic approach to planetdetection with astrometry is described, with significant discussion of avariety of technical, statistical, and astrophysical issues to be facedby future ground-based and space-borne efforts in order to achieve therequired degree of measurement precision. After a brief summary of pastand present efforts to detect planets via milliarcsecond astrometry, Ithen discuss the planet-finding capabilities of future astrometricobservatories aiming at microarcsecond precision. Finally, I outline anumber of experiments that can be conducted by means of high-precisionastrometry during the next decade, to illustrate its potential forimportant contributions to planetary science, compared to other indirectand direct methods for the detection and characterization of planetarysystems.
|TRIDENT: An Infrared Differential Imaging Camera Optimized for the Detection of Methanated Substellar Companions|
We describe a near-infrared camera in use at the Canada-France-HawaiiTelescope (CFHT) and at the 1.6 m telescope of the Observatoire du montMégantic (OMM). The camera is based on a Hawaii-1 1024 ×1024 HgCdTe array detector. Its main feature is the acquisition of threesimultaneous images at three wavelengths across the methane absorptionbandhead at 1.6 μm, enabling, in theory, an accurate subtraction ofthe stellar point-spread function (PSF) and the detection of faintclose, methanated companions. The instrument has no coronagraph andfeatures fast data acquisition, yielding high observing efficiency onbright stars. The performance of the instrument is described, and it isillustrated by laboratory tests and CFHT observations of the nearbystars GL 526, υ And, and χ And. TRIDENT can detect (6 σ)a methanated companion with ΔH=9.5 at 0.5" separation from thestar in 1 hr of observing time. Non-common-path aberrations andamplitude modulation differences between the three optical paths arelikely to be the limiting factors preventing further PSF attenuation.Instrument rotation and reference-star subtraction improve the detectionlimit by a factor of 2 and 4, respectively. A PSF noise attenuationmodel is presented to estimate the non-common-path wave-front differenceeffect on PSF subtraction performance.Based on observations obtained at the Canada-France-Hawaii Telescope(CFHT), which is operated by the National Research Council of Canada,the Institut National des Science de l'Univers of the Centre National dela Recherche Scientifique of France, and the University of Hawaii.
|Photospheric CNO Abundances of Solar-Type Stars|
We determined the C, N, and O abundances of 160 nearby F, G, and Kdwarfs and subgiants by using spectra obtained with the HIDESspectrograph at Okayama Astrophysical Observatory, with the purposes of(1) establishing the runs of [C/Fe], [N/Fe], and [O/Fe] for thesegalactic disk stars in the metallicity range of -1 ≲ [Fe/H] ≲+0.4, (2) searching for any difference in the CNO abundances ofplanet-host stars as compared to non-planet-host stars, and (3)examining the consistency of the abundances derived from different linesto check the validity of the analysis. The non-LTE effect on theabundance determination was taken into consideration based on ourextensive statistical-equilibrium calculations. We confirmed thatconsistent abundances are mostly accomplished between different lines,and that [C/Fe] as well as [O/Fe] progressively increase with a decreasein [Fe/H] with the slope of the former ( 0.2‑0.3) beingshallower than the latter ( 0.4‑0.5), while [N/Fe] does notshow any clear systematic trend with the metallicity. The [C/Fe],[N/Fe], and [O/Fe] values of 27 planet-harboring stars (included in oursample of 160 stars) were shown to be practically indistinguishable fromthose exhibited by non-planet-harboring stars of similar metallicities.