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Публикации по объекту
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 We include fivepreviously unpublished exoplanets orbiting the stars HD 11964, HD 66428,HD 99109, HD 107148, and HD 164922.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.
| 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.
| Chemical Composition of the Planet-harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star ofthe transiting extrasolar planet TrES-1. Based on high-resolution KeckHIRES and Hobby-Eberly Telescope HRS spectra, we have determinedabundances relative to the Sun for 16 elements (Na, Mg, Al, Si, Ca, Sc,Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The resulting averageabundance of <[X/H]>=-0.02+/-0.06 is in good agreement withinitial estimates of solar metallicity based on iron. We compare theelemental abundances of TrES-1 with those of the sample of stars withplanets, searching for possible chemical abundance anomalies. TrES-1appears not to be chemically peculiar in any measurable way. Weinvestigate possible signs of selective accretion of refractory elementsin TrES-1 and other stars with planets and find no statisticallysignificant trends of metallicity [X/H] with condensation temperatureTc. We use published abundances and kinematic information forthe sample of planet-hosting stars (including TrES-1) and severalstatistical indicators to provide an updated classification in terms oftheir likelihood to belong to either the thin disk or the thick disk ofthe Milky Way. TrES-1 is found to be very likely a member of thethin-disk population. By comparing α-element abundances of planethosts and a large control sample of field stars, we also find thatmetal-rich ([Fe/H]>~0.0) stars with planets appear to besystematically underabundant in [α/Fe] by ~0.1 dex with respect tocomparison field stars. The reason for this signature is unclear, butsystematic differences in the analysis procedures adopted by differentgroups cannot be ruled out.
| About putative Neptune-like extrasolar planetary candidates
Context: .We re-analyze the precision radial velocity (RV) data of HD208487 by the Anglo-Australian Planet Search Team, HD 190360, HD 188015,HD 114729 by the California and Carnegie Planet Search Team, and HD147513 by the Geneva Planet Search Team. All these stars are supposed tohost Jovian companions in long-period orbits. Aims.We test a hypothesisthat the residuals of the 1-planet model of the RV or an irregularscatter of the measurements around the synthetic RV curve may beexplained by the existence of additional planets in short-period orbits.Methods. We performed a global search for the best fits in the orbitalparameters space with genetic algorithms and simplex method. This makesit possible to verify and extend the results with an application ofcommonly used FFT-based periodogram analysis for identifying the leadingperiods. Results. Our analysis confirms the presence of a periodiccomponent in the RV of HD 190360 that may correspond to a hot-Neptuneplanet. We found four new cases in which the 2-planet model yieldssignificantly better fits to the RV data than the best 1-planetsolutions. If the periodic variability of the residuals of single-planetfits indeed has a planetary origin, then hot-Neptune planets may existin these extrasolar systems. We estimate their orbital periods as in therange of 7-20 d and minimal masses of about 20 masses of the Earth.
| Abundances of refractory elements in the atmospheres of stars with extrasolar planets
Aims.This work presents a uniform and homogeneous study of chemicalabundances of refractory elements in 101 stars with and 93 without knownplanetary companions. We carry out an in-depth investigation of theabundances of Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg and Al. The newcomparison sample, spanning the metallicity range -0.70< [Fe/H]<0.50, fills the gap that previously existed, mainly at highmetallicities, in the number of stars without known planets.Methods.Weused an enlarged set of data including new observations, especially forthe field "single" comparison stars . The line list previously studiedby other authors was improved: on average we analysed 90 spectral linesin every spectrum and carefully measured more than 16 600 equivalentwidths (EW) to calculate the abundances.Results.We investigate possibledifferences between the chemical abundances of the two groups of stars,both with and without planets. The results are globally comparable tothose obtained by other authors, and in most cases the abundance trendsof planet-host stars are very similar to those of the comparison sample.Conclusions.This work represents a step towards the comprehension ofrecently discovered planetary systems. These results could also beuseful for verifying galactic models at high metallicities andconsequently improve our knowledge of stellar nucleosynthesis andgalactic chemical evolution.
| A massive planet to the young disc star HD 81040
We report the discovery of a massive planetary companion orbiting theyoung disc star HD 81040. Based on five years of precise radial-velocitymeasurements with the HIRES and ELODIE spectrographs, we derive aspectroscopic orbit with a period P =1001.0 days and eccentricity e =0.53. The inferred minimum mass for the companion of m_2 sin i = 6.86M_Jup places it in the high-mass tail of the extrasolar planet massdistribution. From the ELODIE spectra we derive a Lithium abundance oflogɛ(Li) = 1.90, and from the HIRES spectra of the cores of theCa II H and K lines we derive an activity index of < log R'_HK> =-4.48, suggesting an age of about 0.8 Gyr. The radial-velocity residualsexhibit a scatter significantly larger than the typical internalmeasurement precision of the instruments. We attribute this excessvelocity jitter to activity on the surface of the moderately young hoststar. However, the amplitude of the jitter is much too small and theexpected period of rotation is much too short to explain the observedorbital motion, which we conclude is due to a massive planetarycompanion.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| Obliquity variations of terrestrial planets in habitable zones
We have investigated obliquity variations of possible terrestrialplanets in habitable zones (HZs) perturbed by a giant planet(s) inextrasolar planetary systems. All the extrasolar planets so fardiscovered are inferred to be jovian-type gas giants. However,terrestrial planets could also exist in extrasolar planetary systems. Inorder for life, in particular for land-based life, to evolve and surviveon a possible terrestrial planet in an HZ, small obliquity variations ofthe planet may be required in addition to its orbital stability, becauselarge obliquity variations would cause significant climate change. It isknown that large obliquity variations are caused by spin-orbitresonances where the precession frequency of the planet's spin nearlycoincides with one of the precession frequencies of the ascending nodeof the planet's orbit. Using analytical expressions, we evaluated theobliquity variations of terrestrial planets with prograde spins in HZs.We found that the obliquity of terrestrial planets suffers largevariations when the giant planet's orbit is separated by several Hillradii from an edge of the HZ, in which the orbits of the terrestrialplanets in the HZ are marginally stable. Applying these results to theknown extrasolar planetary systems, we found that about half of thesesystems can have terrestrial planets with small obliquity variations(smaller than 10°) over their entire HZs. However, the systems withboth small obliquity variations and stable orbits in their HZs are only1/5 of known systems. Most such systems are comprised of short-periodgiant planets. If additional planets are found in the known planetarysystems, they generally tend to enhance the obliquity variations. On theother hand, if a large/close satellite exists, it significantly enhancesthe precession rate of the spin axis of a terrestrial planet and islikely to reduce the obliquity variations of the planet. Moreover, if aterrestrial planet is in a retrograde spin state, the spin-orbitresonance does not occur. Retrograde spin, or a large/close satellitemight be essential for land-based life to survive on a terrestrialplanet in an HZ.
| 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.
| Are beryllium abundances anomalous in stars with giant planets?
In this paper we present beryllium (Be) abundances in a large sample of41 extra-solar planet host stars, and for 29 stars without any knownplanetary-mass companion, spanning a large range of effectivetemperatures. The Be abundances were derived through spectral synthesisdone in standard Local Thermodynamic Equilibrium, using spectra obtainedwith various instruments. The results seem to confirm that overall,planet-host stars have ``normal'' Be abundances, although a small, butnot significant, difference might be present. This result is discussed,and we show that this difference is probably not due to any stellar``pollution'' events. In other words, our results support the idea thatthe high-metal content of planet-host stars has, overall, a``primordial'' origin. However, we also find a small subset ofplanet-host late-F and early-G dwarfs that might have higher thanaverage Be abundances. The reason for the offset is not clear, and mightbe related either to the engulfment of planetary material, to galacticchemical evolution effects, or to stellar-mass differences for stars ofsimilar temperature.Based on observations collected with the VLT/UT2 Kueyen telescope(Paranal Observatory, ESO, Chile) using the UVES spectrograph (Observingruns 66.C-0116 A, 66.D-0284 A, and 68.C-0058 A), and with the WilliamHerschel and Nordic Optical Telescopes, operated on the island of LaPalma by the Isaac Newton Group and jointly by Denmark, Finland,Iceland, and Norway, respectively, in the Spanish Observatorio del Roquede los Muchachos of the Instituto de Astrofísica de Canarias.
| 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
| Beryllium anomalies in solar-type field stars
We present a study of beryllium (Be) abundances in a large sample offield solar-type dwarfs and sub-giants spanning a large range ofeffective temperatures. The Be abundances, computed using a very uniformset of stellar parameters and near-UV spectra obtained with 3 differentinstruments, are used to study the depletion of this light element. Theanalysis shows that Be is severely depleted for F stars, as expected bythe light-element depletion models. However, we also show that berylliumabundances decrease with decreasing temperature for stars cooler than6000 K, a result that cannot be explained by current theoreticalmodels including rotational mixing, but that is, at least in part,expected from the models that take into account internal wave physics.In particular, the light element abundances of the coolest and youngeststars in our sample suggest that Be, as well as lithium (Li), hasalready been burned early during their evolution. Furthermore, we findstrong evidence for the existence of a Be-gap for solar-temperaturestars. The analysis of Li and Be abundances in the sub-giants of oursample also shows the presence of one case that has still detectableamounts of Li, while Be is severely depleted. Finally, we compare thederived Be abundances with Li abundances derived using the same set ofstellar parameters. This gives us the possibility to explore thetemperatures for which the onset of Li and Be depletion occurs.Based on observations collected with the VLT/UT2 Kueyen telescope(Paranal Observatory, ESO, Chile) using the UVES spectrograph (Observingruns 66.C-0116 A, 66.D-0284 A, and 68.C-0058 A), and with the WilliamHerschel and Nordic Optical Telescopes, operated at the island of LaPalma by the Isaac Newton Group and jointly by Denmark, Finland,Iceland, and Norway, respectively, in the Spanish Observatorio del Roquede los Muchachos of the Instituto de Astrofísica de Canarias.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Nitrogen abundances in planet-harbouring stars
We present a detailed spectroscopic analysis of nitrogen abundances in91 solar-type stars, 66 with and 25 without known planetary masscompanions. All comparison sample stars and 28 planet hosts wereanalysed by spectral synthesis of the near-UV NH band at 3360 Åobserved at high resolution with the VLT/UVES, while the near-IR N I7468 Å was measured in 31 objects. These two abundance indicatorsare in good agreement. We found that nitrogen abundance scales with thatof iron in the metallicity range -0.6 < [Fe/H] <+0.4 with theslope 1.08 ± 0.05. Our results show that the bulk of nitrogenproduction at high metallicities was coupled with iron. We found thatthe nitrogen abundance distribution in stars with exoplanets is the high[Fe/H] extension of the curve traced by the comparison sample of starswith no known planets. A comparison of our nitrogen abundances withthose available in the literature shows a good agreement.
| Spectroscopic [Fe/H] for 98 extra-solar planet-host stars. Exploring the probability of planet formation
We present stellar parameters and metallicities, obtained from adetailed spectroscopic analysis, for a large sample of 98 stars known tobe orbited by planetary mass companions (almost all known targets), aswell as for a volume-limited sample of 41 stars not known to host anyplanet. For most of the stars the stellar parameters are revisedversions of the ones presented in our previous work. However, we alsopresent parameters for 18 stars with planets not previously published,and a compilation of stellar parameters for the remaining 4 planet-hostsfor which we could not obtain a spectrum. A comparison of our stellarparameters with values of Teff, log g, and [Fe/H] availablein the literature shows a remarkable agreement. In particular, ourspectroscopic log g values are now very close to trigonometric log gestimates based on Hipparcos parallaxes. The derived [Fe/H] values arethen used to confirm the previously known result that planets are moreprevalent around metal-rich stars. Furthermore, we confirm that thefrequency of planets is a strongly rising function of the stellarmetallicity, at least for stars with [Fe/H] > 0. While only about 3%of the solar metallicity stars in the CORALIE planet search sample werefound to be orbited by a planet, this number increases to more than 25%for stars with [Fe/H] above +0.3. Curiously, our results also suggestthat these percentages might remain relatively constant for values of[Fe/H] lower than about solar, increasing then linearly with the massfraction of heavy elements. These results are discussed in the contextof the theories of planetary formation.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and the FEROS spectrograph at the 1.52-m and 2.2-m ESOtelescopes, with the VLT/UT2 Kueyen telescope (Paranal Observatory, ESO,Chile) using the UVES spectrograph (Observing run 67.C-0206, in servicemode), with the TNG and William Herschel Telescopes, both operated atthe island of La Palma, and with the ELODIE spectrograph at the 1.93-mtelescope at the Observatoire de Haute Provence.
| The CORALIE survey for southern extra-solar planets. XII. Orbital solutions for 16 extra-solar planets discovered with CORALIE
This paper summarizes the information gathered for 16 still unpublishedexoplanet candidates discovered with the CORALIE echelle spectrographmounted on the Euler Swiss telescope at La Silla Observatory. Amongstthese new candidates, 10 are typical extrasolar Jupiter-like planets onintermediate- or long-period (100 < P ≤ 1350 d) and fairlyeccentric (0.2 ≤ e ≤ 0.5) orbits (HD 19994, HD 65216, HD 92788,HD 111232, HD 114386, HD 142415, HD 147513, HD 196050, HD 216437, HD216770). Two of these stars are in binary systems. The next 3 candidatesare shorter-period planets (HD 6434, HD 121504) with lowereccentricities among which we find a hot Jupiter (HD 83443). Moreinteresting cases are given by the multiple-planet systems HD 82943 andHD 169830. The former is a resonant P2/P1 = 2/1system in which planet-planet interactions are influencing the systemevolution. The latter is more hierarchically structured.Based on observations collected with the CORALIE echelle spectrograph onthe 1.2-m Euler Swiss telescope at La Silla Observatory, ESO Chile.The precise radial velocities presented in this paper are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/391, except for themulti-planet systems that will appear in a future paper describing theirdynamical evolutions, taking planet-planet interaction into account.
| Lithium in stars with exoplanets
We present a comparison of the lithium abundances of stars with andwithout planetary-mass companions. New lithium abundances are reportedin 79 planet hosts and 38 stars from a comparison sample. When the Liabundances of planet host stars are compared with the 157 stars in thesample of field stars of Chen et al. (\cite{Chen2001}) we find that theLi abundance distribution is significantly different, and that there isa possible excess of Li depletion in planet host stars with effectivetemperatures in the range 5600-5850 K, whereas we find no significantdifferences in the temperature range 5850-6350 K. We have searched forstatistically significant correlations between the Li abundance ofparent stars and various parameters of the planetary companions. We donot find any strong correlation, although there are may be a hint of apossible gap in the Li distribution of massive planet host stars.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 ESO telescope,and using the UES spectrograph at the 4.2 m William Herschel Telescope(WHT) and SARG spectrograph at the 3.5 m Telescopio Nazional Galileo onLa Palma (Canary Islands).
| The use of orbital phase curve of an exoplanet for improvement of its mass estimate
In remote observations of a planet with the elliptic orbit around thecentral star, the planet brightness varies considerably with phaseangle. The spatial indicatrice of the visible layer reflection incontinuous spectrum for a giant planet is basically determined byoptical properties and the function of particle sizes distribution atthe levels of the leaving radiation formation. We estimate someparameters of aerosols and calculate the spectral distributions of thebrightness of the disá of a planet for a phase angle from00 to 1800. With the use of these data the valuesof spherical albedo, geometrical albedo, and the phase functions for aplanet are determined as well as the relative change of the integralbrightness for a planet revolving around the central star is calculated.Our results show that, for some star systems, the possibility exists ofreconstructing orbital phase curves. This allows one to improve theestimate of the inclination of the orbital plane to the picture planeand, in some cases, this can increase the estimate of the mass of anexoplanet almost by a factor of 6.
| Colloquium: Stars, planets, and metals
The discovery in 1995 of the first planet orbiting another Sun-like starstimulated renewed interest in planet formation and evolution processes.A number of trends among the properties of the planets have becomeevident in the years since. An interesting pattern began to emerge in1997stars hosting planets tend to be more metal rich (i.e., havemore abundant elements with Z>2) than the average nearby star. Other,more subtle, trends are beginning to appear as the sample size continuesto grow; for example, the masses of stars hosting planets are found tocorrelate with their metallicities. The author reviews the state of ourknowledge concerning the observed trends, their possible causes, andtheir possible implications for astrophysics and astrobiology.
| Search for periodicities in distribution of orbits of planets.
Not Available
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Центавр |
| Прямое восхождение: | 13h57m17.24s |
| Склонение: | -56°02'24.2" |
| Видимая звёздная величина: | 7.526 |
| Расстояние: | 44.366 парсек |
| Собственное движение RA: | -247.9 |
| Собственное движение Dec: | -85.6 |
| B-T magnitude: | 8.249 |
| V-T magnitude: | 7.586 |
Каталоги и обозначения:
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INHABITED SKY
