Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Extrasolar planets in stellar multiple systems
Aims: Analyzing exoplanets detected by radial velocity (RV) ortransit observations, we determine the multiplicity of exoplanet hoststars in order to study the influence of a stellar companion on theproperties of planet candidates. Methods: Matching the host starsof exoplanet candidates detected by radial velocity or transitobservations with online multiplicity catalogs in addition to aliterature search, 57 exoplanet host stars are identified having astellar companion. Results: The resulting multiplicity rate of atleast 12% for exoplanet host stars is about four times smaller than themultiplicity of solar like stars in general. The mass and the number ofplanets in stellar multiple systems depend on the separation betweentheir host star and its nearest stellar companion, e.g. the planetarymass decreases with an increasing stellar separation. We present anupdated overview of exoplanet candidates in stellar multiple systems,including 15 new systems (compared to the latest summary from 2009).
| Metallicity of solar-type stars with debris discs and planets?
Context. Around 16% of the solar-like stars in our neighbourhood showIR-excesses due to dusty debris discs and a fraction of them are knownto host planets. Determining whether these stars follow any specialtrend in their properties is important to understand debris disc andplanet formation. Aims: We aim to determine in a homogeneous waythe metallicity of a sample of stars with known debris discs andplanets. We attempt to identify trends related to debris discs andplanets around solar-type stars. Methods: Our analysis includesthe calculation of the fundamental stellar parameters Teff,log g, microturbulent velocity, and metallicity by applying the ironionisation equilibrium conditions to several isolated Fe i and Fe iilines. High-resolution échelle spectra (R ~ 57 000) from 2, 3 mclass telescopes are used. Our derived metallicities are compared withother results in the literature, which finally allows us to extend thestellar samples in a consistent way. Results: The metallicitydistributions of the different stellar samples suggest that there is atransition toward higher metallicities from stars with neither debrisdiscs nor planets to stars hosting giant planets. Stars with debrisdiscs and stars with neither debris nor planets follow a similarmetallicity distribution, although the distribution of the first onesmight be shifted towards higher metallicities. Stars with debris discsand planets have the same metallicity behaviour as stars hostingplanets, irrespective of whether the planets are low-mass or gas giants.In the case of debris discs and giant planets, the planets are usuallycool, - semimajor axis larger than 0.1 AU (20 out of 22 planets), even?65% have semimajor axis larger than 0.5 AU. The data also suggestthat stars with debris discs and cool giant planets tend to have a lowdust luminosity, and are among the less luminous debris discs known. Wealso find evidence of an anticorrelation between the luminosity of thedust and the planet eccentricity. Conclusions: Our data show thatthe presence of planets, not the debris disc, correlates with thestellar metallicity. The results confirm that core-accretion modelsrepresent suitable scenarios for debris disc and planet formation. Theseconclusions are based on a number of stars with discs and planetsconsiderably larger than in previous works, in particular stars hostinglow-mass planets and debris discs. Dynamical instabilities produced byeccentric giant planets could explain the suggested dust luminositytrends observed for stars with debris discs and planets.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by the Max-PlanckInstitut für Astronomie and the Instituto de Astrofísica deAndalucía (CSIC); observations made with the Italian TelescopioNazionale Galileo (TNG) operated on the island of La Palma by theFundación Galileo Galilei of the INAF (Istituto Nazionale diAstrofisica); observations made with the Nordic Optical Telescope,operated on the island of La Palma jointly by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias; and data obtainedfrom the ESO Science Archive Facility.Full Tables 1 and 5 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/541/A40
| Evidence for enhanced chromospheric Ca II H and K emission in stars with close-in extrasolar planets
Context. The planet-star interaction is manifested in many ways. It hasbeen found that a close-in exoplanet causes small but measurablevariability in the cores of a few lines in the spectra of several stars,which corresponds to the orbital period of the exoplanet. Stars with andwithout exoplanets may have different properties. Aims: The maingoal of our study is to search for the influence that exoplanets mighthave on atmospheres of their host stars. Unlike the previous studies, wedo not study changes in the spectrum of a host star or differencesbetween stars with and without exoplanets. We aim to study a largenumber of stars with exoplanets and the current level of theirchromospheric activity and to look for a possible correlation with theexoplanetary properties. Methods: To analyse the chromosphericactivity of stars, we exploited our own and publicly available archivalspectra, measured the equivalent widths of the cores of Ca II H and Klines, and used them to trace their activity. Subsequently, we searchedfor their dependence on the orbital parameters and the mass of theexoplanet. Results: We found statistically significant evidencethat the equivalent width of the Ca II K line emission and logR'HK activity parameter of the host star varies with thesemi-major axis and mass of the exoplanet. Stars with Teff? 5500 K having exoplanets with semi-major axis a ? 0.15 AU(Porb ? 20 days) have a broad range of Ca II K emissionsand much stronger emission in general than stars at similar temperaturesbut with higher values of semi-major axes. The Ca II K emission of coldstars (Teff ? 5500 K) with close-in exoplanets (a ?0.15 AU) is also more pronounced for more massive exoplanets. Conclusions: The overall level of the chromospheric activity of starsmay be affected by their close-in exoplanets, and stars with massiveclose-in exoplanets may be more active.Table 1 is available in electronic form at http://www.aanda.org
| Toward Precise Ages for Single Stars in the Field. Gyrochronology Constraints at Several Gyr Using Wide Binaries. I. Ages for Initial Sample
We present a program designed to obtain age-rotation measurements ofsolar-type dwarfs to be used in the calibration of gyrochronologyrelations at ages of several Gyr. This is a region of parameter spacecrucial for the large-scale study of the Milky Way, and where the onlyconstraint available today is that provided by the Sun. Our programtakes advantage of a set of wide binaries selected so that one componentis an evolved star and the other is a main-sequence star of FGK type. Inthis way, we obtain the age of the system from the evolved star, whilethe rotational properties of the main-sequence component provide theinformation relevant for gyrochronology regarding the spin-down ofsolar-type stars. By mining currently available catalogs of widebinaries, we assemble a sample of 37 pairs well positioned for ourpurposes: 19 with turnoff or subgiant primaries and 18 with white dwarfcomponents. Using high-resolution optical spectroscopy, we measureprecise stellar parameters for a subset of 15 of the pairs withturnoff/subgiant components and use these to derive isochronal ages forthe corresponding systems. Ages for 16 of the 18 pairs with white dwarfcomponents are taken from the literature. The ages of this initialsample of 31 wide binaries range from 1 to 9 Gyr, with precisions betterthan ~20% for almost half of these systems. When combined withmeasurements of the rotation period of their main-sequence components,these wide binary systems would potentially provide a similar number ofpoints useful for the calibration of gyrochronology relations at veryold ages.
| Optimizing exoplanet transit searches around low-mass stars with inclination constraints
Aims: We investigate a method to increase the efficiency of atargeted exoplanet search with the transit technique by preselecting asubset of candidates from large catalogs of stars. Assuming spin-orbitalignment, this can be achieved by considering stars that have a higherprobability to be oriented nearly equator-on (inclination close to90°). Methods: We used activity-rotation velocity relationsfor low-mass stars with a convective envelope to study the dependence ofthe position in the activity-vsini diagram on the stellar axisinclination. We composed a catalog of G-, K-, M-type main-sequencesimulated stars using isochrones, an isotropic inclination distributionand empirical relations to obtain their rotation periods and activityindexes. Then the activity-vsini diagram was completed and statisticswere applied to trace the areas containing the higher ratio of starswith inclinations above 80°. A similar statistics was applied tostars from real catalogs with log(R'HK) and vsini data tofind their probability of being oriented equator-on. Results: Wepresent our method to generate the simulated star catalog and thesubsequent statistics to find the highly inclined stars from realcatalogs using the activity-vsini diagram. Several catalogs from theliterature are analyzed and a subsample of stars with the highestprobability of being equator-on is presented. Conclusions:Assuming spin-orbit alignment, the efficiency of an exoplanet transitsearch in the resulting subsample of probably highly inclined stars isestimated to be two to three times higher than with a general searchwithout preselection.Table 4 is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/537/A147
| Silicon and Oxygen Abundances in Planet-host Stars
The positive correlation between planet detection rate and host stariron abundance lends strong support to the core accretion theory ofplanet formation. However, iron is not the most significant masscontributor to the cores of giant planets. Since giant planet cores arethought to grow from silicate grains with icy mantles, the likelihood ofgas giant formation should depend heavily on the oxygen and siliconabundance of the planet formation environment. Here we compare thesilicon and oxygen abundances of a set of 76 planet hosts and a controlsample of 80 metal-rich stars without any known giant planets. Our new,independent analysis was conducted using high resolution, highsignal-to-noise data obtained at McDonald Observatory. Because we do notwish to simply reproduce the known planet-metallicity correlation, wehave devised a statistical method for matching the underlying [Fe/H]distributions of our two sets of stars. We find a 99% probability thatplanet detection rate depends on the silicon abundance of the host star,over and above the observed planet-metallicity correlation. We do notdetect any such correlation for oxygen. Our results would thus seem tosuggest that grain nucleation, rather than subsequent icy mantle growth,is the important limiting factor in forming giant planets via coreaccretion. Based on our results and interpretation, we predict thatplanet detection should correlate with host star abundance forrefractory elements responsible for grain nucleation and that no suchtrends should exist for the most abundant volatile elements responsiblefor icy mantle growth.
| A giant planet in the triple system HD 132563
As part of our radial velocity planet-search survey performed with SARGat TNG, we monitored the components of HD 132563 for ten years. It is abinary system formed by two rather similar solar type stars with aprojected separation of 4.1 arcsec, which corresponds to 400 AU at thedistance of 96 pc. The two components are moderately metal-poor ([Fe/H]= -0.19), and the age of the system is about 5 Gyr. We detected RVvariations of HD 132563B with period of 1544 days and semi-amplitude of26 m/s. From the star characteristics and line profile measurements, weinfer their Keplerian origin. Therefore HD 132563B turns out to host aplanet with a projected mass msini = 1.49 MJ at 2.6 AU with amoderately eccentric orbit (e = 0.22). The planet around HD 132563B isone of the few that are known in triple stellar systems, as we foundthat the primary HD 132563A is itself a spectroscopic binary with aperiod longer than 15 years and an eccentricity higher than 0.65. Thespectroscopic component was not detected in adaptive-optics images takenwith the instrument AdOpt mounted at the TNG, since it expected at aprojected separation that was smaller than 0.2 arcsec at the time of ourobservations. A small excess in K band difference between the componentswith respect to the difference in V band is compatible with a companionof about 0.55 M&sun;. A preliminary statistical analysis ofwhen planets occur in triple systems indicate a similar frequency ofplanets around the isolated component in a triple system, components ofwide binaries and single stars. There is no significant iron abundancedifference between the components. The lack of stars in binary systemsand open clusters showing strong enhancements of iron abundance, whichare comparable to the typical metallicity difference between stars withand without giant planets, agrees with the idea that accretion ofplanetary material producing iron abundance anomalies over 0.1 dex israre.Based on observations made with the Italian Telescopio Nazionale Galileo(TNG) operated on the island of La Palma by the Fundacion GalileoGalilei of the INAF (Istituto Nazionale di Astrofisica) at the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.Tables 4 and 5 are available in electronic form at http://www.aanda.org and at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/533/A90
| On the use of the Virtual Observatory to select calibrators for phase-referenced astrometry of exoplanet-host stars
Phase-referenced interferometric astrometry offers the possibility tolook for exoplanets around bright stars. Instruments like PRIMA(Phase-Referenced Imaging and Micro-arcsecond Astrometry) will measurethe astrometric wobble of a candidate star due to an exoplanet relativeto a close-by 'calibrator' star, located within the instrument'sobserving field (1 arcmin in the PRIMA case). Stars with already knownexoplanets will constitute the first targets for this technique, as itwill provide a way to further specify the characteristics of the knownexoplanets, such as the inclinations. The main requirement is to have acalibrator in the vicinity of the star. We provide here a list ofcalibrators for all stars with known exoplanets obtained using datamining and Virtual Observatory techniques. This list is available onlineand revised regularly. The calibrators are found from cataloguesavailable at Centre de Données astronomiques de Strasbourg (CDS)using the SEARCHCAL software developed at Jean-Marie Mariotti Center(JMMC). In our test case, the calibrators are found within 1 arcminangular distance for approximately 50 per cent of the stars tested, andoften closer. They are all faint objects from the Two Micron All SkySurvey (2MASS) with K magnitudes between 13 and 15. A list of the mostpromising targets is also given.
| Chromospheric activity of stars with planets
Context. Signatures of chromospheric activity enhancement have beenfound for a dozen stars, pointing to a possible star-planet interaction.Nevertheless in the coronal activity regime, there is no conclusiveobservational evidence of such an interaction. Does star-planetinteraction manifest itself only for a few particular cases, withouthaving a major effect on stars with planets in general? Aims: Weaim to add additional observational constraints to support or reject themajor effects of star-planet interactions in stellar activity, based onCa II chromospheric emission flux. Methods: We performed astatistical analysis of Ca II emission flux of stars with planets, aswell as a comparison between Ca II and X-ray emission fluxes, searchingfor dependencies on planetary parameters. Results: In the presentsample of stars with planets, there are no significant correlationsbetween chromospheric activity indicator log(R'HK) andplanetary parameters. Furthermore, the distribution of the chromosphericactivity indicator for stars without planets is indistinguishable fromthe one with planets.
| Density Estimation for Projected Exoplanet Quantities
Exoplanet searches using radial velocity (RV) and microlensing (ML)produce samples of "projected" mass and orbital radius, respectively. Wepresent a new method for estimating the probability density distribution(density) of the unprojected quantity from such samples. For a sample ofn data values, the method involves solving n simultaneous linearequations to determine the weights of delta functions for the raw,unsmoothed density of the unprojected quantity that cause the associatedcumulative distribution function (CDF) of the projected quantity toexactly reproduce the empirical CDF of the sample at the locations ofthe n data values. We smooth the raw density using nonparametric kerneldensity estimation with a normal kernel of bandwidth ?. Wecalibrate the dependence of ? on n by Monte Carlo experimentsperformed on samples drawn from a theoretical density, in which theintegrated square error is minimized. We scale this calibration to theranges of real RV samples using the Normal Reference Rule. Theresolution and amplitude accuracy of the estimated density improve withn. For typical RV and ML samples, we expect the fractional noise at thePDF peak to be approximately 80 n -log 2. For illustrations,we apply the new method to 67 RV values given a similar treatment byJorissen et al. in 2001, and to the 308 RV values listed atexoplanets.org on 2010 October 20. In addition to analyzingobservational results, our methods can be used to develop measurementrequirements—particularly on the minimum sample size n—forfuture programs, such as the microlensing survey of Earth-likeexoplanets recommended by the Astro 2010 committee.
| Chemical Clues on the Formation of Planetary Systems: C/O Versus Mg/Si for HARPS GTO Sample
Theoretical studies suggest that C/O and Mg/Si are the most importantelemental ratios in determining the mineralogy of terrestrial planets.The C/O ratio controls the distribution of Si among carbide and oxidespecies, while Mg/Si gives information about the silicate mineralogy. Wepresent a detailed and uniform study of C, O, Mg, and Si abundances for61 stars with detected planets and 270 stars without detected planetsfrom the homogeneous high-quality unbiased HARPS GTO sample, togetherwith 39 more planet-host stars from other surveys. We determine theseimportant mineralogical ratios and investigate the nature of thepossible terrestrial planets that could have formed in those planetarysystems. We find mineralogical ratios quite different from those of theSun, showing that there is a wide variety of planetary systems which arenot similar to our solar system. Many planetary host stars present anMg/Si value lower than 1, so their planets will have a high Si contentto form species such as MgSiO3. This type of composition canhave important implications for planetary processes such as platetectonics, atmospheric composition, or volcanism.
| Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
We present time series measurements of chromospheric activity for morethan 2600 main-sequence and subgiant stars on the California PlanetSearch (CPS) program with spectral types ranging from about F5V to M4Vfor main-sequence stars and from G0IV to about K5IV for subgiants. Thelarge data set of more than 44,000 spectra allows us to identify anempirical baseline floor for chromospheric activity as a function ofcolor and height above the main sequence. We define ?S as anexcess in emission in the Ca II H and K lines above the baselineactivity floor and define radial velocity jitter as a function of?S and B - V for main-sequence and subgiant stars. Although thejitter for any individual star can always exceed the baseline level, wefind that K dwarfs have the lowest level of jitter. The lack ofcorrelation between observed jitter and chromospheric activity in Kdwarfs suggests that the observed jitter is dominated by instrumental oranalysis errors and not astrophysical noise sources. Thus, given thelong-term precision for the CPS program, radial velocities are notcorrelated with astrophysical noise for chromospherically quiet K dwarfstars, making these stars particularly well suited for the highestprecision Doppler surveys. Chromospherically quiet F and G dwarfs andsubgiants exhibit higher baseline levels of astrophysical jitter than Kdwarfs. Despite the fact that the rms in Doppler velocities iscorrelated with the mean chromospheric activity, it is rare to seeone-to-one correlations between the individual time series activity andDoppler measurements, diminishing the prospects for correctingactivity-induced velocity variations in F and G dwarfs.Based on observations obtained at the Keck Observatory and LickObservatory, which are operated by the University of California.
| Estimating the masses of extra-solar planets
All extra-solar planet masses that have been derived spectroscopicallyare lower limits since the inclination of the orbit to our line-of-sightis unknown except for transiting systems. In theory, however, it ispossible to determine the inclination angle, i, between the rotationaxis of a star and an observer's line-of-sight from measurements of theprojected equatorial velocity (vsini), the stellar rotation period(Prot) and the stellar radius (R*). For starswhich host planetary systems this allows the removal of the sinidependency of extra-solar planet masses derived from spectroscopicobservations under the assumption that the planetary orbits lieperpendicular to the stellar rotation axis.We have carried out an extensive literature search and present acatalogue of vsini,Prot and R* estimates for starshosting extra-solar planets. In addition, we have used Hipparcosparallaxes and the Barnes-Evans relationship to further supplement theR* estimates obtained from the literature. Using thiscatalogue, we have obtained sini estimates using a Markov-chain MonteCarlo analysis. This technique allows proper 1? two-tailedconfidence limits to be placed on the derived sini's along with thetransit probability for each planet to be determined.While we find that a small proportion of systems yield sini'ssignificantly greater than 1, most likely due to poor Protestimations, the large majority are acceptable. We are furtherencouraged by the cases where we have data on transiting systems, as thetechnique indicates inclinations of ~90° and high transitprobabilities. In total, we are able to estimate the true masses of 133extra-solar planets. Of these 133 extra-solar planets, only six haverevised masses that place them above the 13MJ deuteriumburning limit; four of those six extra-solar planet candidates werealready suspected to lie above the deuterium burning limit beforecorrecting their masses for the sini dependency. Our work reveals apopulation of high-mass extra-solar planets with low eccentricities, andwe speculate that these extra-solar planets may represent the signatureof different planetary formation mechanisms at work. Finally, we discussfuture observations that should improve the robustness of thistechnique.
| The Hill stability of the possible moons of extrasolar planets
The dynamical Hill stability has been derived for a full three-bodysystem composed of a binary moving on an inclined elliptical orbitrelative to a third body where the binary mass is very small comparedwith the mass of the third body. This physical situation arises in anumber of important astronomical contexts including extrasolar planetarysystems with a star-planet-moon configuration. The Hill stabilitycriterion against disruption and component exchange was applied to allthe known extrasolar planetary systems and the critical separation of apossible moon from the planet determined for moon/planet mass ratios of0.1, 0.01 and 0.001 assuming that the moon moves on a circular orbit. Itis clear that in those cases where the planet moves on a circular orbitabout the central star, the critical separation of the moon from theplanet does not change significantly as the value of the moon/planetmass ratio is reduced. In contrast, for eccentric systems there can bebig changes in the critical separation as the mass ratio decreases. Thevariation in size depends crucially on the size of the eccentricity ofthe planetary orbit.To determine the effect of an eccentrically orbiting moon, the Hillstability criterion was applied generally to the planet-moon binary fora range of moon/planet mass ratios assuming that the planet moved on acircular orbit around the central star. It was found that in all casesthe critical distance ratio increased, and hence the regions of Hillstability decreased as the binary eccentricity increased and also as theinclination of the third body to the binary was increased. The stabilityincreased slightly as the moon/planet ratio was decreased. Also as thebinary/third body mass ratio decreased the effects of the moon/planetmass ratio became less important and the stability curves tended tomerge. These types of changes make exchange or disruption of thecomponent masses more likely.
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| How Eccentric Orbital Solutions Can Hide Planetary Systems in 2:1 Resonant Orbits
The Doppler technique measures the reflex radial motion of a starinduced by the presence of companions and is the most successful methodto detect exoplanets. If several planets are present, their signals willappear combined in the radial motion of the star, leading to potentialmisinterpretations of the data. Specifically, two planets in 2:1resonant orbits can mimic the signal of a single planet in an eccentricorbit. We quantify the implications of this statistical degeneracy for arepresentative sample of the reported single exoplanets with availabledata sets, finding that (1) around 35% of the published eccentricone-planet solutions are statistically indistinguishable from planetarysystems in 2:1 orbital resonance, (2) another 40% cannot bestatistically distinguished from a circular orbital solution, and (3)planets with masses comparable to Earth could be hidden in known orbitalsolutions of eccentric super-Earths and Neptune mass planets.
| Planets and Debris Disks: Results from a Spitzer/MIPS Search for Infrared Excess
Using the MIPS camera on the Spitzer Space Telescope, we have searchedfor debris disks around 104 stars known from radial velocity studies tohave one or more planets. Combining this new data with 42 alreadypublished observations of planet-bearing stars, we find that 14 of the146 systems have IR excess at 24 and/or 70 μm. Only one star, HD69830, has IR excess exclusively at 24 μm, indicative of warm dust inthe inner system analogous to that produced by collisions in the solarsystem's asteroid belt. For the other 13 stars with IR excess theemission is stronger at 70 μm, consistent with cool dust (<100 K)located beyond 10 AU, well outside of the orbital location of the knownplanets. Selection effects inhibit detection of faint disks around theplanet-bearing stars (e.g., the stars tend to be more distant),resulting in a lower detection rate for IR excess than in acorresponding control sample of nearby stars not known to have planets(9% ± 3% versus 14% ± 3%). Even taking into account theselection bias, we find that the difference between the dust emissionaround stars with planets and stars without known planets is notstatistically significant.
| The Role of Planet Accretion in Creating the Next Generation of Red Giant Rapid Rotators
Rapid rotation in field red giant stars is a relatively rare butwell-studied phenomenon; here we investigate the potential role ofplanet accretion in spinning up these stars. Using Zahn's theory oftidal friction and stellar evolution models, we compute the decay of aplanet's orbit into its evolving host star and the resulting transfer ofangular momentum into the stellar convective envelope. This experimentassesses the frequency of planet ingestion and rapid rotation on the redgiant branch (RGB) for a sample of 99 known exoplanet host stars. Wefind that the known exoplanets are indeed capable of creating rapidrotators; however, the expected fraction due to planet ingestion is only~ 10% of the total seen in surveys of present-day red giants. Of theplanets ingested, we find that those with smaller initial semimajor axesare more likely to create rapid rotators because these planets areaccreted when the stellar moment of inertia is smallest. We also findthat many planets may be ingested prior to the RGB phase, contrary tothe expectation that accretion would generally occur when the stellarradii expand significantly as giants. Finally, our models suggest thatthe rapid rotation signal from ingested planets is most likely to beseen on the lower RGB, which is also where alternative mechanisms forspin-up, e.g., angular momentum dredged up from the stellar core, do notoperate. Thus, rapid rotators on the lower RGB are the best candidatesto search for definitive evidence of systems that have experiencedplanet accretion.
| A Search for Multi-Planet Systems Using the Hobby-Eberly Telescope
Extrasolar multiple-planet systems provide valuable opportunities fortesting theories of planet formation and evolution. The architectures ofthe known multiple-planet systems demonstrate a fascinating level ofdiversity, which motivates the search for additional examples of suchsystems in order to better constrain their formation and dynamicalhistories. Here we describe a comprehensive investigation of 22planetary systems in an effort to answer three questions: (1) are thereadditional planets? (2) where could additional planets reside in stableorbits? and (3) what limits can these observations place on suchobjects? We find no evidence for additional bodies in any of thesesystems; indeed, these new data do not support three previouslyannounced planets (HD 20367 b: Udry et al. HD 74156 d: Beanet al. and 47 UMa c: Fischer et al.). The dynamicalsimulations show that nearly all of the 22 systems have large regions inwhich additional planets could exist in stable orbits. Thedetection-limit computations indicate that this study is sensitive toclose-in Neptune-mass planets for most of the systems targeted. Weconclude with a discussion on the implications of these nondetections.Based on observations obtained with the Hobby-Eberly Telescope, which isa joint project of the University of Texas at Austin, the PennsylvaniaState University, Stanford University,Ludwig-Maximilians-Universität München, andGeorg-August-Universität Göttingen.
| Extrasolar Giant Planets and X-Ray Activity
We have carried out a survey of X-ray emission from stars with giantplanets, combining both archival and targeted surveys. Over 230 starshave been currently identified as possessing planets, and roughlyone-third of these have been detected in X-rays. We carry out detailedstatistical analysis on a volume-limited sample of main-sequence starsystems with detected planets, comparing subsamples of stars that haveclose-in planets with stars that have more distant planets. Thisanalysis reveals strong evidence that stars with close-in giant planetsare on average more X-ray active by a factor of ~4 than those withplanets that are more distant. This result persists for various sampleselections. We find that even after accounting for observational samplebias, a significant residual difference still remains. Thisobservational result is consistent with the hypothesis that giantplanets in close proximity to the primary stars influence the stellarmagnetic activity.
| Comparative statistics and origin of triple and quadruple stars
The statistics of catalogued quadruple stars consisting of two binaries(hierarchy 2 + 2), is studied in comparison with triple stars, withrespective sample sizes of 81 and 724. Seven representative quadruplesystems are discussed in greater detail. The main conclusions are asfollows. (i) Quadruple systems of ? Lyr type with similar massesand inner periods are common, in 42 per cent of the sample the outermass ratio is above 0.5 and the inner periods differ by less than 10times. (ii) The distributions of the inner periods in triple andquadruple stars are similar and bimodal. The inner mass ratios do notcorrelate with the inner periods. (iii) The statistics of outer periodsand mass ratios in triples and quadruples are different. The medianouter mass ratio in triples is 0.39 independently of the outer period,which has a smooth distribution. In contrast, the outer periods of 25per cent quadruples concentrate in the narrow range from 10 to 100yr,the outer mass ratios of these tight quadruples are above 0.6 and theirtwo inner periods are similar to each other. (iv) The outer and innermass ratios in triple and quadruple stars are not mutually correlated.In 13 per cent of quadruples both inner mass ratios are above 0.85(double twins). (v) The inner and outer orbital angular momenta andperiods in triple and quadruple systems with inner periods above 30dshow some correlation, the ratio of outer-to-inner periods is mostlycomprised between 5 and 104. In the systems with small periodratios the directions of the orbital spins are correlated, while in thesystems with large ratios they are not. The properties of multiple starsdo not correspond to the products of dynamical decay of small clusters,hence the N-body dynamics is not the dominant process of theirformation. On the other hand, rotationally driven (cascade)fragmentation possibly followed by migration of inner and/or outerorbits to shorter periods is a promising scenario to explain the originof triple and quadruple stars.
| XO-2b: Transiting Hot Jupiter in a Metal-rich Common Proper Motion Binary
We report on a V=11.2 early K dwarf, XO-2 (GSC 03413-00005), that hostsa Rp=0.98+/-0.030.01 RJ,Mp=0.57+/-0.06 MJ transiting extrasolar planet,XO-2b, with an orbital period of 2.615857+/-0.000005 days. XO-2 has highmetallicity, [Fe/H]=0.45+/-0.02, high proper motion,μtot=157 mas yr-1, and a common proper motionstellar companion with 31" separation. The two stars are nearlyidentical twins, with very similar spectra and apparent magnitudes. Dueto the high metallicity, these early K dwarf stars have a mass andradius close to solar, M*=0.98+/-0.02 Msolar andR*=0.97+/-0.020.01 Rsolar.The high proper motion of XO-2 results from an eccentric orbit (Galacticpericenter, Rper<4 kpc) well confined to the Galactic disk(Zmax~100 pc). In addition, the phase-space position of XO-2is near the Hercules dynamical stream, which points to an origin of XO-2in the metal-rich, inner thin disk and subsequent dynamical scatteringinto the solar neighborhood. We describe an efficient Markov chain MonteCarlo algorithm for calculating the Bayesian posterior probability ofthe system parameters from a transit light curve.
| Speckle Interferometry at the US Naval Observatory. XIII.
The results of 1424 speckle interferometric observations of doublestars, made with the 26 inch (66 cm) refractor of the US NavalObservatory, are presented. Each speckle interferometric observation ofa system represents a combination of over 2000 short-exposure images.These observations are averaged into 1053 mean relative positions andrange in separation from 0.36″ to 61.92″, with a medianseparation of 10.31″. This is the 13th in a series of paperspresenting measurements obtained with this system and covers the period2006 January 12-December 29. Included in these data are nine oldermeasurements whose positions were previously deemed possibly aberrantbut are no longer classified this way following a confirmingobservation. This paper also includes the first data obtained using anew "secondary" camera, designed and built at USNO.
| The multiplicity of exoplanet host stars. Spectroscopic confirmation of the companions GJ 3021 B and HD 27442 B, one new planet host triple-star system, and global statistics
Aims.We present new results from our ongoing multiplicity study ofexoplanet host stars and present a list of 29 confirmed planet hostmultiple-star systems. Furthermore, we discuss the properties of thesestellar systems and compare the properties of exoplanets detected inthese systems with those of planets orbiting single stars. Methods: Weused direct imaging to search for wide stellar and substellar companionsof exoplanet host stars. With infrared and/or optical spectroscopy, wedetermined the spectral properties of the newly-found co-movingcompanions. Results: We obtained infrared H- and K-band spectra of theco-moving companion GJ 3021 B. The infrared spectra and the apparentH-band photometry of the companion is consistent with an M3-M5 dwarf atthe distance of the exoplanet host star. HD 40979 AB is a wide planethost stellar system, with a separation of ~ 6400 AU. The companion tothe exoplanet host star turned out to be a close stellar pair with aprojected separation of ~130 AU, hence, this system is a new member ofthose rare planet host triple-star systems of which only three othersystems are presently known. HD 27442 AB is a wide binary system listedin the Washington Double Star Catalogue, whose common proper motion wasrecently confirmed. This system is composed of the subgiant HD 27442 Ahosting the exoplanet, and its faint companion HD 27442 B. The visibleand infrared J-, H-, and K_S-band photometry of HD 27442 B at thedistance of the primary star shows that the companion is probably awhite dwarf. Our multi-epochs SofI imaging observations confirm thisresult and even refine the suggested physical characteristics of HD27442 B. This companion should be a relatively young, hot white dwarfwith an effective temperature of ~14 400 K, and cooling age of ~220 Myr.Finally, we could unambiguously confirm the white dwarf nature of HD27442 B with follow-up optical and infrared spectroscopy. The spectra ofthe companion show Hydrogen absorption features of the Balmer, Paschen,and Bracket series. With its subgiant primary and the white-dwarfcompanion, the HD 27442 AB system is the most evolved planet hoststellar system known today. The mass-period and eccentricity-periodcorrelation of planets around single stars and those residing inmultiple-star systems seem different for the short-period planets. Thedistribution functions of planet orbital elements (P, e) are identical,while the mass-distribution (m sin(i)) exhibits one difference. Whileboth planet populations exhibit a peak in their mass-distribution atabout 1 M_Jup, the frequency of more massive planets continuallydecreases in single-star systems, whereas the mass-distribution ofplanets residing in multiple-star systems exhibits a further peak atabout 4 M_Jup. This indicates that the mass-distributions of the twoplanet populations might differ in the intermediate mass-range between 2and 6 M_Jup.Based on observations obtained on La Silla in ESO programs 70.C-0116(A),71.C-0140(A), 73.C-0103(A), and on Paranal in ESO runs 074.C-0144(B),074.C-0144(C), 073.C-0370(A), on Mauna Kea in UKIRT program U/02A/16, aswell as at the Munich LMU University Observatory on Mount Wendelstein.
| High Resolution Spectroscopy of Planet Bearing Stars
We present here the first steps of an extended spectroscopic survey inorder to characterize the stellar hosts of extra-solar planets. We haveselected several known stars with planets and using high resolutionspectroscopy, we have studied their properties.
| The frequency of planets in multiple systems
Context: The frequency of planets in binaries is an important issue inthe field of extrasolar planet studies, because of its relevance inestimating of the global planet population of our Galaxy and the cluesit can give to our understanding of planet formation and evolution.However, only preliminary estimates are available in the literature. Aims: We analyze and compare the frequency of planets in multiplesystems to the frequency of planets orbiting single stars. We also tryto highlight possible connections between the frequency of planets andthe orbital parameters of the binaries (such as the periastron and massratio.) Methods: A literature search was performed for binariesand multiple systems among the stars of the sample with uniform planetdetectability defined by Fischer & Valenti (2005, ApJ, 622, 1102),and 202 of the 850 stars of the sample turned out to be binaries,allowing a statistical comparison of the frequency of planets inbinaries and single stars and a study of the run of the planet frequencyas a function of the binary separation. Results: We found that theglobal frequency of planets in the binaries of the sample is notstatistically different from that of planets in single stars. Evenconservatively taking the probable incompleteness of binary detection inour sample into account, we estimate that the frequency of planets inbinaries can be no more than a factor of three lower than that ofplanets in single stars. There is no significant dependence of planetfrequency on the binary separation, except for a lower value offrequency for close binaries. However, this is probably not as low asrequired to explain the presence of planets in close binaries only asthe result of modifications of the binary orbit after the planetformation. Table 8 and Appendix A are only available in electronic form athttp://www.aanda.org
| The N2K Consortium. VII. Atmospheric Parameters of 1907 Metal-rich Stars: Finding Planet-Search Targets
We report high-precision atmospheric parameters for 1907 stars in theN2K low-resolution spectroscopic survey, designed to identify metal-richFGK dwarfs likely to harbor detectable planets. Of these stars, 284 arein the ideal temperature range for planet searches,Teff<=6000 K, and have a 10% or greater probability ofhosting planets based on their metallicities. The stars in thelow-resolution spectroscopic survey should eventually yield >60 newplanets, including 8-9 hot Jupiters. Short-period planets have alreadybeen discovered orbiting the survey targets HIP 14810 and HD 149143.
| A stability catalogue of the habitable zones in extrasolar planetary systems
In the near future, space missions will be launched (e.g. COROT, KEPLER)to detect Earth-like extrasolar planets. The orbital elements of these(still hypothetic) planets will contain some uncertainties that can onlybe eliminated by careful dynamical investigations of the hostingplanetary systems. The proportion of extrasolar planetary systems withone known giant planet is high (~90 per cent). Therefore, as a firststep we have investigated the possible existence of terrestrial planetsin these systems. In this paper, the development of a stabilitycatalogue of the habitable zones of exoplanetary systems is reported.This catalogue is formed by a series of stability maps, which can helpto establish where Earth-like planets could exist in extrasolarplanetary systems having one giant planet. After a description of thedynamical model and the numerical methods, details of the stability mapsare discussed. An application of the stability catalogue to 15 knownexoplanetary systems is also shown, and a characterization of thestability properties of their habitable zones is given.
| New Distant Companions to Known Nearby Stars. II. Faint Companions of Hipparcos Stars and the Frequency of Wide Binary Systems
We perform a search for faint, common proper motion companions ofHipparcos stars using the recently published Lépine-Shara ProperMotion-North catalog of stars with proper motionμ>0.15'' yr-1. Our survey uncovers a totalof 521 systems with angular separations3''<Δθ<1500'', with 15 triplesand 1 quadruple. Our new list of wide systems with Hipparcos primariesincludes 130 systems identified here for the first time, including 44 inwhich the secondary star has V>15.0. Our census is statisticallycomplete for secondaries with angular separations20''<Δθ<300'' and apparentmagnitudes V<19.0. Overall, we find that at least 9.5% of nearby(d<100 pc) Hipparcos stars have distant stellar companions withprojected orbital separations s>1000 AU. We observe that thedistribution in orbital separations is consistent with Öpik's law,f(s)ds~s-1ds, only up to a separation s~4000 AU, beyond whichit follows a more steeply decreasing power law f(s)ds~s-ldswith l=1.6+/-0.1. We also find that the luminosity function of thesecondaries is significantly different from that of the single stars'field population, showing a relative deficiency in low-luminosity(8
| 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.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Calgi |
| Sað Açýklýk: | 19h09m03.10s |
| Yükselim: | +34°35'59.5" |
| Görünürdeki Parlaklýk: | 7.8 |
| Uzaklýk: | 46.729 parsek |
| özdevim Sað Açýklýk: | 69.1 |
| özdevim Yükselim: | 196.6 |
| B-T magnitude: | 8.723 |
| V-T magnitude: | 7.877 |
Kataloglar ve belirtme:
|
INHABITED SKY
