Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Are Debris Disks and Massive Planets Correlated?
Using data from the Spitzer Space Telescope Legacy Science ProgramFormation and Evolution of Planetary Systems (FEPS), we have searchedfor debris disks around nine FGK stars (2-10 Gyr), known from radialvelocity (RV) studies to have one or more massive planets. Only one ofthe sources, HD 38529, has excess emission above the stellarphotosphere; at 70 μm the signal-to-noise ratio in the excess is 4.7,while at λ<30 μm there is no evidence of excess. Theremaining sources show no excesses at any Spitzer wavelengths. Applyingsurvival tests to the FEPS sample and the results for the FGK surveyrecently published in Bryden et al., we do not find a significantcorrelation between the frequency and properties of debris disks and thepresence of close-in planets. We discuss possible reasons for the lackof a correlation.
| 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.
| Habitability of Known Exoplanetary Systems Based on Measured Stellar Properties
Habitable planets are likely to be broadly Earth-like in composition,mass, and size. Masses are likely to be within a factor of a few of theEarth's mass. Currently, we do not have sufficiently sensitivetechniques to detect Earth-mass planets, except in rare circumstances.It is thus necessary to model the known exoplanetary systems. Inparticular, we need to establish whether Earth-mass planets could bepresent in the classical habitable zone (HZ) or whether the giantplanets that we know to be present would have gravitationally ejectedEarth-mass planets or prevented their formation. We have answered thisquestion by applying computer models to the 152 exoplanetary systemsknown by 2006 April 18 that are sufficiently well characterized for ouranalysis. For systems in which there is a giant planet, inside the HZ,which must have arrived there by migration, there are two cases: (1)where the migration of the giant planet across the HZ has not ruled outthe existence of Earth-mass planets in the HZ; and (2) where themigration has ruled out existence. For each case, we have determined theproportion of the systems that could contain habitable Earth-massplanets today, and the proportion for which this has been the case forat least the past 1000 Myr (excluding any early heavy bombardment). Forcase 1 we get 60% and 50%, respectively, and for case 2 we get 7% and7%, respectively.
| 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.
| 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.
| A search for wide visual companions of exoplanet host stars: The Calar Alto Survey
We have carried out a search for co-moving stellar and substellarcompanions around 18 exoplanet host stars with the infrared camera MAGICat the 2.2 m Calar Alto telescope, by comparing our images with imagesfrom the all sky surveys 2MASS, POSS I and II. Four stars of the samplenamely HD 80606, 55 Cnc, HD 46375 and BD-10°3166, arelisted as binaries in the Washington Visual Double Star Catalogue (WDS).The binary nature of HD 80606, 55 Cnc, and HD 46375 is confirmed withboth astrometry as well as photometry, thereby the proper motion of thecompanion of HD 46375 was determined here for the first time. We derivedthe companion masses as well as the longterm stability regions foradditional companions in these three binary systems. We can rule outfurther stellar companions around all stars in the sample with projectedseparations between 270 AU and 2500 AU, being sensitive to substellarcompanions with masses down to 60 {MJup} (S/N=3).Furthermore we present evidence that the two components of the WDSbinary BD-10°3166 are unrelated stars, i.e this system isa visual pair. The spectrophotometric distance of the primary (a K0dwarf) is 67 pc, whereas the presumable secondaryBD-10°3166 B (a M4 to M5 dwarf) is located at a distanceof 13 pc in the foreground.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Chemical Composition of the Planet-harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star ofthe transiting extrasolar planet TrES-1. Based on high-resolution KeckHIRES and Hobby-Eberly Telescope HRS spectra, we have determinedabundances relative to the Sun for 16 elements (Na, Mg, Al, Si, Ca, Sc,Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The resulting averageabundance of <[X/H]>=-0.02+/-0.06 is in good agreement withinitial estimates of solar metallicity based on iron. We compare theelemental abundances of TrES-1 with those of the sample of stars withplanets, searching for possible chemical abundance anomalies. TrES-1appears not to be chemically peculiar in any measurable way. Weinvestigate possible signs of selective accretion of refractory elementsin TrES-1 and other stars with planets and find no statisticallysignificant trends of metallicity [X/H] with condensation temperatureTc. We use published abundances and kinematic information forthe sample of planet-hosting stars (including TrES-1) and severalstatistical indicators to provide an updated classification in terms oftheir likelihood to belong to either the thin disk or the thick disk ofthe Milky Way. TrES-1 is found to be very likely a member of thethin-disk population. By comparing α-element abundances of planethosts and a large control sample of field stars, we also find thatmetal-rich ([Fe/H]>~0.0) stars with planets appear to besystematically underabundant in [α/Fe] by ~0.1 dex with respect tocomparison field stars. The reason for this signature is unclear, butsystematic differences in the analysis procedures adopted by differentgroups cannot be ruled out.
| 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.
| 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.
| An Analysis of the Condensation Temperature of Elements of Extrasolar Planetary Systems
Using high signal-to-noise ratio spectra of extrasolar planet-hostingstars, we obtained the atmospheric parameters, accurate metallicitiesand the differential abundance for 15 elements (C, O, Na, Mg, Al, Si, S,Ca, Sc, Ti, V, Cr, Mn, Ni and Ba). In a search for possible signaturesof metal-rich material accreting onto the parent stars, we found that ,for a given element, there is no significant trend of increasing [X/H]with increasing condensation temperature Tc. In our sample ofplanet-harboring stars, the volatile and refractory elements behavesimilarly, and we can not confirm if there exists any significantdependence on the condensation temperature Tc.
| A link between the semimajor axis of extrasolar gas giant planets and stellar metallicity
The fact that most extrasolar planets found to date are orbitingmetal-rich stars lends credence to the core accretion mechanism of gasgiant planet formation over its competitor, the disc instabilitymechanism. However, the core accretion mechanism is not refined to thepoint of explaining orbital parameters such as the unexpected semimajoraxes and eccentricities. We propose a model that correlates themetallicity of the host star with the original semimajor axis of itsmost massive planet, prior to migration, assuming that the coreaccretion scenario governs giant gas planet formation. The modelpredicts that the optimum regions for planetary formation shift inwardsas stellar metallicity decreases, providing an explanation for theobserved absence of long-period planets in metal-poor stars. We compareour predictions with the available data on extrasolar planets for starswith masses similar to the mass of the Sun. A fitting procedure producesan estimate of what we define as the zero-age planetary orbit (ZAPO)curve as a function of the metallicity of the star. The model hints thatthe lack of planets circling metal-poor stars may be partly caused by anenhanced destruction probability during the migration process, becausethe planets lie initially closer to their central star.
| On the ages of exoplanet host stars
We obtained spectra, covering the CaII H and K region, for 49 exoplanethost (EH) stars, observable from the southern hemisphere. We measuredthe chromospheric activity index, R'{_HK}. We compiled previouslypublished values of this index for the observed objects as well as theremaining EH stars in an effort to better smooth temporal variations andderive a more representative value of the average chromospheric activityfor each object. We used the average index to obtain ages for the groupof EH stars. In addition we applied other methods, such as: Isochrone,lithium abundance, metallicity and transverse velocity dispersions, tocompare with the chromospheric results. The kinematic method is a lessreliable age estimator because EH stars lie red-ward of Parenago'sdiscontinuity in the transverse velocity dispersion vs dereddened B-Vdiagram. The chromospheric and isochrone techniques give median ages of5.2 and 7.4 Gyr, respectively, with a dispersion of 4 Gyr. The medianage of F and G EH stars derived by the isochrone technique is 1-2 Gyrolder than that of identical spectral type nearby stars not known to beassociated with planets. However, the dispersion in both cases is large,about 2-4 Gyr. We searched for correlations between the chromosphericand isochrone ages and L_IR/L* (the excess over the stellarluminosity) and the metallicity of the EH stars. No clear tendency isfound in the first case, whereas the metallicy dispersion seems toslightly increase with age.
| Chemical abundances of 22 extrasolar planet host stars*
We present observations of 22 extrasolar planet host stars and derivetheir stellar parameters. With the high signal-to-noise ratio spectra,we acquire accurate metallicities and the differential abundances for 15other elements and we discuss the relation between the abundance ratioand the metallicity. These sample stars are metal-rich relative to theSun, covering the range from -0.04 to 0.54 dex with the average [Fe/H]value of 0.15 +/- 0.12 dex, except for HD 37124, which has [Fe/H]=-0.45.The stars with planets show a slight overabundance pattern for [C/Fe]and [Mg/Fe], but [Na/Fe], [Al/Fe], [Si/Fe], [Ti/Fe], [Cr/Fe], [Sc/Fe],[V/Fe], [Ni/Fe] and [Ba/Fe] are approximately solar in the sample stars.These stars also show slight underabundances for [O/Fe], [Ca/Fe] and[Mn/Fe]. The sulphur displays enhanced values, ranging from -0.10 to0.40 through the sample stars. These results are used to investigate theconnection between giant planets and high metallicity and to probe theinfluence of the process on the other elements.
| Sulphur abundance in Galactic stars
We investigate sulphur abundance in 74 Galactic stars by using highresolution spectra obtained at ESO VLT and NTT telescopes. For the firsttime the abundances are derived, where possible, from three opticalmultiplets: Mult. 1, 6, and 8. By combining our own measurements withdata in the literature we assemble a sample of 253 stars in themetallicity range -3.2 [Fe/H] +0.5. Two important features,which could hardly be detected in smaller samples, are obvious from thislarge sample: 1) a sizeable scatter in [S/Fe] ratios around [Fe/H]-1; 2) at low metallicities we observe stars with [S/Fe] 0.4, aswell as stars with higher [S/Fe] ratios. The latter do not seem to bekinematically different from the former ones. Whether the latter findingstems from a distinct population of metal-poor stars or simply from anincreased scatter in sulphur abundances remains an open question.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| Abundances of Na, Mg and Al in stars with giant planets
We present Na, Mg and Al abundances in a set of 98 stars with knowngiant planets, and in a comparison sample of 41 “single”stars. The results show that the [X/H] abundances (with X = Na, Mg andAl) are, on average, higher in stars with giant planets, a resultsimilar to the one found for iron. However, we did not find any strongdifference in the [X/Fe] ratios, for a fixed [Fe/H], between the twosamples of stars in the region where the samples overlap. The data wasused to study the Galactic chemical evolution trends for Na, Mg and Aland to discuss the possible influence of planets on this evolution. Theresults, similar to those obtained by other authors, show that the[X/Fe] ratios all decrease as a function of metallicity up to solarvalues. While for Mg and Al this trend then becomes relatively constant,for Na we find indications of an upturn up to [Fe/H] values close to0.25 dex. For metallicities above this value the [Na/Fe] becomesconstant.
| The Effective Temperature Scale of FGK Stars. I. Determination of Temperatures and Angular Diameters with the Infrared Flux Method
The infrared flux method (IRFM) has been applied to a sample of 135dwarf and 36 giant stars covering the following regions of theatmospheric parameter space: (1) the metal-rich ([Fe/H]>~0) end(consisting mostly of planet-hosting stars), (2) the cool(Teff<~5000 K) metal-poor (-1<~[Fe/H]<~-3) dwarfregion, and (3) the very metal-poor ([Fe/H]<~-2.5) end. These starswere especially selected to cover gaps in previous works onTeff versus color relations, particularly the IRFMTeff scale of A. Alonso and collaborators. Our IRFMimplementation was largely based on the Alonso et al. study (absoluteinfrared flux calibration, bolometric flux calibration, etc.) with theaim of extending the ranges of applicability of their Teffversus color calibrations. In addition, in order to improve the internalaccuracy of the IRFM Teff scale, we recomputed thetemperatures of almost all stars from the Alonso et al. work usingupdated input data. The updated temperatures do not significantly differfrom the original ones, with few exceptions, leaving the Teffscale of Alonso et al. mostly unchanged. Including the stars withupdated temperatures, a large sample of 580 dwarf and 470 giant stars(in the field and in clusters), which cover the ranges3600K<~Teff<~8000K and -4.0<~[Fe/H]<~+0.5, haveTeff homogeneously determined with the IRFM. The meanuncertainty of the temperatures derived is 75 K for dwarfs and 60 K forgiants, which is about 1.3% at solar temperature and 4500 K,respectively. It is shown that the IRFM temperatures are reliable in anabsolute scale given the consistency of the angular diameters resultingfrom the IRFM with those measured by long baseline interferometry, lunaroccultation, and transit observations. Using the measured angulardiameters and bolometric fluxes, a comparison is made between IRFM anddirect temperatures, which shows excellent agreement, with the meandifference being less than 10 K for giants and about 20 K for dwarfstars (the IRFM temperatures being larger in both cases). This resultwas obtained for giants in the ranges 3800K
| Planets and Infrared Excesses: Preliminary Results from a Spitzer MIPS Survey of Solar-Type Stars
As part of a large Spitzer MIPS Guaranteed Time Observation program, wehave searched for infrared excesses due to debris disks toward 26 FGKfield stars known from radial velocity (RV) studies to have one or moreplanets. While none of these stars show excesses at 24 μm, we havedetected 70 μm excesses around six stars at the 3 σ confidencelevel. The excesses are produced by cool material (<100 K) locatedbeyond 10 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. Theseplanet-bearing stars are, by selection for RV studies, typically olderthan 1 Gyr, and the stars identified here with excesses have a medianage of 4 Gyr. We find a preliminary correlation of both the frequencyand the magnitude of dust emission with the presence of known planets.These are the first stars outside the solar system identified as havingboth well-confirmed planetary systems and well-confirmed IR excesses.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Prospects for Habitable ``Earths'' in Known Exoplanetary Systems
We have examined whether putative Earth-mass planets could remainconfined to the habitable zones (HZs) of the 111 exoplanetary systemsconfirmed by 2004 August. We find that in about half of these systemsthere could be confinement for at least the past 1000 Myr, though insome cases only in variously restricted regions of the HZ. The HZmigrates outward during the main-sequence lifetime, and we find that inabout two-thirds of the systems an Earth-mass planet could be confinedto the HZ for at least 1000 Myr sometime during the main-sequencelifetime. Clearly, these systems should be high on the target list forexploration for terrestrial planets. We have reached our conclusions bydetailed investigations of seven systems, which has resulted in anestimate of the distance from the giant planet within which orbitalstability is unlikely for an Earth-mass planet. This distance is givenby nRH, where RH is the Hill radius of the giantplanet and n is a multiplier that depends on the giant's orbitaleccentricity and on whether the Earth-mass planet is interior orexterior to the giant planet. We have estimated n for each of the sevensystems by launching Earth-mass planets in various orbits and followingtheir fate with a hybrid orbital integrator. We have then evaluated thehabitability of the other exoplanetary systems using nRHderived from the giant's orbital eccentricity without carrying outtime-consuming orbital integrations. A stellar evolution model has beenused to obtain the HZs throughout the main-sequence lifetime.
| 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.
| Lithium Abundances of F-, G-, and K-Type Stars: Profile-Fitting Analysis of the Li I 6708 Doublet
An extensive profile-fitting analysis was performed for the Li(+Fe)6707-6708Å feature of nearby 160 F-K dwarfs/subgiants (including27 planet-host stars) in the Galactic disk ( 7000 K ≳Teff ≳ 5000 K, -1 ≲ [Fe/H] ≲ +0.4), in orderto establish the photospheric lithium abundances of these stars. Thenon-LTE effect (though quantitatively insignificant) was taken intoaccount based on our statistical equilibrium calculations, which werecarried out on an adequate grid of models. Our results confirmed most ofthe interesting observational characteristics revealed by recentlypublished studies, such as the bimodal distribution of the Li abundancesfor stars at Teff ≳ 6000 K, the satisfactory agreementof the upper envelope of the A(Li) vs. [Fe/H] distribution with thetheoretical models, the existence of a positive correlation betweenA(Li) and the stellar mass, and the tendency of lower lithium abundancesof planet-host stars (as compared to stars without planets) at thenarrow ``transition'' region of 5900 K ≳ Teff ≳5800 K. The solar Li abundance derived from this analysis is 0.92 (H =12.00), which is by 0.24dex lower than the widely referenced standardvalue of 1.16.
| Spectroscopic Study on the Atmospheric Parameters of Nearby F--K Dwarfs and Subgiants
Based on a collection of high-dispersion spectra obtained at OkayamaAstrophysical Observatory, the atmospheric parameters (Teff,log g, vt, and [Fe/H]) of 160 mid-F through early-K starswere extensively determined by the spectroscopic method using theequivalent widths of Fe I and Fe II lines along with the numericaltechnique of Takeda et al. (2002, PASJ, 54, 451). The results arecomprehensively discussed and compared with the parameter values derivedby different approaches (e.g., photometric colors, theoreticalevolutionary tracks, Hipparcos parallaxes, etc.) as well as with thepublished values found in various literature. It has been confirmed thatour purely spectroscopic approach yields fairly reliable and consistentresults.
| A new Böhm-Vitense gap in the temperature range 5560 to 5610 K in the main sequence hm-Vitense gap in the main sequence
Highly precise temperatures (σ = 10-15 K) have been determinedfrom line depth ratios for a set of 248 F-K field dwarfs of about solarmetallicity (-0.5 < [Fe/H] < +0.4), based on high resolution (R=42000), high S/N echelle spectra. A new gap has been discovered in thedistribution of stars on the Main Sequence in the temperature range 5560to 5610 K. This gap coincides with a jump in the microturbulent velocityVt and the well-known Li depression near 5600 K in fielddwarfs and open clusters. As the principal cause of the observeddiscontinuities in stellar properties we propose the penetration of theconvective zone into the inner layers of stars slightly less massivethan the Sun and related to it, a change in the temperature gradient.Based on spectra collected with the ELODIE spectrograph at the 1.93-mtelescope of the Observatoire de Haute-Provence (France).Full Table 1 is only available in electronic form athttp://www.edpsciences.org
| On the possible correlation between the orbital periods of extrasolar planets and the metallicity of the host stars
We investigate a possible correlation between the orbital periods P ofthe extrasolar planet sample and the metallicity [Fe/H] of their parentstars. Close-in planets, on orbits of a few days, are more likely to befound around metal-rich stars. Simulations show that a weak correlationis present. This correlation becomes stronger when only single starswith one detected planet are considered. We discuss several potentialsources of bias that might mimic the correlation, and find that they canbe ruled out, but not with high significance. If real, the absence ofvery short-period planets around the stellar sample with [Fe/H] < 0.0can be interpreted as evidence of a metallicity dependence of themigration rates of giant planets during formation in the protoplanetarydisc. The observed P-[Fe/H] correlation can be falsified or confirmed byconducting spectroscopic or astrometric surveys of metal-poor stars([Fe/H] < -0.5) in the field.
| Capture and escape in the elliptic restricted three-body problem
Several families of irregular moons orbit the giant planets. These moonsare thought to have been captured into planetocentric orbits afterstraying into a region in which the gravitation of the planet dominatessolar perturbations (the Hill sphere). This mechanism requires a sourceof dissipation, such as gas drag, in order to make capture permanent.However, capture by gas drag requires that particles remain inside theHill sphere long enough for dissipation to be effective. Recently wehave proposed that in the circular restricted three-body problem (CRTBP)particles may become caught up in sticky chaotic layers, which tends toprolong their sojourn within the Hill sphere of the planet therebyassisting capture. Here, we show that this mechanism survivesperturbations due to the ellipticity of the orbit of the planet.However, Monte Carlo simulations indicate that the ability of the planetto capture moons decreases with increasing orbital eccentricity. At theactual orbital eccentricity of Jupiter, this results in approximately anorder of magnitude lower capture probability than estimated in thecircular model. Eccentricities of planetary orbits in the Solar systemare moderate but this is not necessarily the case for extrasolarplanets, which typically have rather eccentric orbits. Therefore, ourfindings suggest that these extrasolar planets are unlikely to havesubstantial populations of irregular moons.
| C, S, Zn and Cu abundances in planet-harbouring stars
We present a detailed and uniform study of C, S, Zn and Cu abundances ina large set of planet host stars, as well as in a homogeneous comparisonsample of solar-type dwarfs with no known planetary-mass companions.Carbon abundances were derived by EW measurement of two C I opticallines, while spectral syntheses were performed for S, Zn and Cu. Weinvestigated possible differences in the behaviours of the volatiles C,S and Zn and in the refractory Cu in targets with and without knownplanets in order to check possible anomalies due to the presence ofplanets. We found that the abundance distributions in stars withexoplanets are the high [Fe/H] extensions of the trends traced by thecomparison sample. All volatile elements we studied show [X/Fe] trendsdecreasing with [Fe/H] in the metallicity range -0.8< [Fe/H] <0.5, with significantly negative slopes of -0.39±0.04 and-0.35±0.04 for C and S, respectively. A comparison of ourabundances with those available in the literature shows good agreementin most cases.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and with the FEROS spectrograph at the 1.52-m and 2.2-m ESOtelescopes, at the Paranal Observatory, ESO (Chile), using the UVESspectrograph at the VLT/UT2 Kueyen telescope, and with the UES and SARGspectrographs at the 4-m William Hershel Telescope (WHT) and at the3.5-m TNG telescope, respectively, both at La Palma (Canary Islands).Tables 4-16 are only available in electronic form athttp://www.edpsciences.org
| The Radiometric Bode's Law and Extrasolar Planets
We predict the radio flux densities of the extrasolar planets in thecurrent census, making use of an empirical relation-the radiometricBode's law-determined from the five ``magnetic'' planets in the solarsystem (the Earth and the four gas giants). Radio emission from theseplanets results from solar wind-powered electron currents depositingenergy in the magnetic polar regions. We find that most of the knownextrasolar planets should emit in the frequency range 10-1000 MHz and,under favorable circumstances, have typical flux densities as large as 1mJy. We also describe an initial, systematic effort to search for radioemission in low radio frequency images acquired with the Very LargeArray (VLA). The limits set by the VLA images (~300 mJy) are consistentwith, but do not provide strong constraints on, the predictions of themodel. Future radio telescopes, such as the Low Frequency Array and theSquare Kilometer Array, should be able to detect the known extrasolarplanets or place austere limits on their radio emission. Planets withmasses much lower than those in the current census will probably radiatebelow 10 MHz and will require a space-based array.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Ikizler |
| Sað Açýklýk: | 06h54m42.83s |
| Yükselim: | +24°14'44.0" |
| Görünürdeki Parlaklýk: | 6.854 |
| Uzaklýk: | 31.027 parsek |
| özdevim Sað Açýklýk: | -36.5 |
| özdevim Yükselim: | -96.8 |
| B-T magnitude: | 7.532 |
| V-T magnitude: | 6.91 |
Kataloglar ve belirtme:
|
