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Secular apsidal configuration of non-resonant exoplanetary systems
Using a high-order (order 12) expansion of the perturbative potential inpowers of eccentricities [Libert, A.-S., Henrard, J., 2005. Celest.Mech. Dynam. Astron. 93, 187 200], we study the secular effects of twocoplanar planets which are not in mean motion resonances. The mainresults concern eccentricity variations, oscillation amplitude of theangular difference of the apsidal lines (Δϖ) and frequency ofsuch an oscillation. We show that this analytical approach describescorrectly the behaviour of most of the exosystems and underlines theknown limitations of the linear Laplace Lagrange theory. Apsidalconfiguration of υ Andromedae, HD 168443, HD 169830, HD 38529, HD74156 and HD 12661 are examined. We also point out the great sensitivityof the υ Andromedae system to the initial values (e(0),e(0) or Δϖ(0)).
| Stability and 2:1 resonance in the planetary system HD 829431
We have explored the secular dynamical evolution of the HD 82943 systemwith two resonant giant planets, by simulating various planetaryconfigurations via direct numerical integration. We also studied theirorbital motions in phase space. In the numerical integrations over107 yr, we found that all the stable orbits are connectedwith the 2:1 resonance. Typically, there exists the libration of the tworesonant arguments 1 and (or) 2 on the sametimescale. Hence, both of the semi-major axes are strongly constrainedto behave in a regular way, due to the confinement of the libration ofthe related angles. Using the analytical model we considered the motionof the inner planet in phase space for different values of the outerplanet's eccentricity e2 and of the relative apsidallongitude . We found that the 2:1 orbital resonance is easily preservedwhen= 0† and when e2 is not too large. A moderatee2 can lock the two planets into deep resonance. The resultsby the analytical method agree well with those by the numericalsimulation, both revealing the 2:1 resonance architecture.
| 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.
| Orbital Configurations and Dynamical Stability of Multiplanet Systems around Sun-like Stars HD 202206, 14 Herculis, HD 37124, and HD 108874
We perform a dynamical analysis of the recently published radialvelocity (RV) measurements of a few solar-type stars that host multipleJupiter-like planets. In particular, we reanalyze the data for HD202206, 14 Her, HD 37124, and HD 108874. We derive dynamically stableconfigurations that reproduce the observed RV signals, using GAMP (thegenetic algorithm with MEGNO penalty). GAMP relies on N-body dynamicsand makes use of genetic algorithms merged with a stability criterion.For this purpose, we use the maximal Lyapunov exponent computed with thedynamical fast indicator MEGNO. Through a dynamical analysis of thephase space in a neighborhood of the obtained best-fit solutions, wederive meaningful limits on the parameters of the planets. Wedemonstrate that GAMP is especially well suited to the analysis of theRV data that only partially cover the longest orbital period and/or arerelated to multiplanet configurations involved in low-order mean motionresonances (MMRs). Our analysis reveals a presence of a secondJupiter-like planet in the 14 Her system (14 Her c) that is involved ina 3:1 or 6:1 MMR with the known companion 14 Her b. We also show thatthe dynamics of the HD 202206 system may be qualitatively different whencoplanar and mutually inclined orbits of the companions are considered.We demonstrate that the two outer planets in the HD 37124 system mayreside in a close neighborhood of the 5:2 MMR. Our results confirm thatthe HD 108874 system may be very close to a, or locked in an exact, 4:1MMR.
| 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.
| A Comparative Study on Lithium Abundances in Solar-Type Stars With and Without Planets
We have investigated the abundance anomalies of lithium for stars withplanets in the temperature range of 5600-5900 K reported by Israelianand coworkers, as compared to 20 normal stars in the same temperatureand metallicity ranges. Our result indicates a higher probability oflithium depletion for stars with planets in the main-sequence stage. Itseems that stellar photospheric abundances of lithium in stars withplanets may be somewhat affected by the presence of planets. Twopossible mechanisms are considered to account for the lower Liabundances of stars with planets. One is related to the rotation-inducedmixing due to the conservation of angular momentum by the protoplanetarydisk, and the other is a shear instability triggered by planetmigration. These results provide new information on stellar evolutionand the lithium evolution of the Galaxy.
| Abundance ratios of volatile vs. refractory elements in planet-harbouring stars: hints of pollution?
We present the [ X/H] trends as a function of the elemental condensationtemperature TC in 88 planet host stars and in avolume-limited comparison sample of 33 dwarfs without detected planetarycompanions. We gathered homogeneous abundance results for many volatileand refractory elements spanning a wide range of T_C, from a few dozento several hundred kelvin. We investigate possible anomalous trends ofplanet hosts with respect to comparison sample stars to detect evidenceof possible pollution events. No significant differences are found inthe behaviour of stars with and without planets. This is consistent witha "primordial" origin of the metal excess in planet host stars. However,a subgroup of 5 planet host and 1 comparison sample stars stands out ashaving particularly high [ X/H] vs. TC slopes.
| 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.
| Planetary Harmony
Not Available
| 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.
| 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.
| Five New Multicomponent Planetary Systems
We report Doppler measurements for six nearby G- and K-typemain-sequence stars that show multiple low-mass companions, at least oneof which has planetary mass. One system has three planets, the fourthtriple-planet system known around a normal star, and another has anextremely low minimum mass of 18 M⊕. HD 128311 (K0 V)has two planets (one previously known) with minimum masses (Msini) of2.18MJ and 3.21MJ and orbital periods of 1.26 and2.54 yr, suggesting a possible 2:1 resonance. For HD 108874 (G5 V), thevelocities reveal two planets (one previously known) having minimummasses and periods of (Msinib=1.36MJ,Pb=1.08 yr) and (Msinic=1.02MJ,Pc=4.4 yr). HD 50499 (G1 V) has a planet with P=6.8 yr andMsini=1.7MJ, and the velocity residuals exhibit a trend of-4.8 m s-1 yr-1, indicating a more distantcompanion with P>10 yr and minimum mass of 2MJ. HD 37124(G4 IV-V) has three planets, one having Msini=0.61MJ andP=154.5 days, as previously known. We find two plausible triple-planetmodels that fit the data, both having a second planet near P=840 days,with the more likely model having its third planet in a 6 yr orbit andthe other one in a 29 day orbit. For HD 190360, we confirm the planethaving P=7.9 yr and Msini=1.5MJ as found by the Geneva team,but we find a distinctly noncircular orbit with e=0.36+/-0.03, renderingthis not an analog of Jupiter as had been reported. Our velocities alsoreveal a second planet with P=17.1 days and Msini=18.1M⊕. HD 217107 (G8 IV) has a previously known ``hotJupiter'' with Msini=1.4MJ and P=7.13 days, and we confirmits high eccentricity, e=0.13. The velocity residuals reveal an outercompanion in an eccentric orbit, having minimum mass ofMsini>2MJ, eccentricity e~0.5, and a period P>8 yr,implying a semimajor axis a>4 AU and providing an opportunity fordirect detection. We have obtained high-precision photometry of five ofthe six planetary host stars with three of the automated telescopes atFairborn Observatory. We can rule out significant brightness variationsin phase with the radial velocities in most cases, thus supportingplanetary reflex motion as the cause of the velocity variations.Transits are ruled out to very shallow limits for HD 217107 and are alsoshown to be unlikely for the prospective inner planets of the HD 37124and HD 108874 systems. HD 128311 is photometrically variable with anamplitude of 0.03 mag and a period of 11.53 days, which is much shorterthan the orbital periods of its two planetary companions. This rotationperiod explains the origin of periodic velocity residuals to thetwo-planet model of this star. All of the planetary systems here wouldbe further constrained with astrometry by the Space InterferometryMission.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by both NASA and theUniversity of California.
| The Dynamics of the HD 12661 Extrasolar Planetary System
The main goal of this work is to analyze the possible dynamicalmechanisms that dominate the motion of the HD 12661 extrasolar planetarysystem. By an analytical approach using the expansion of the disturbingfunction given by Ellis and Murray, we solve the equation of motionworking in a Hamiltonian formulation with the corresponding canonicalvariables and by means of appropriate canonical transformations.Comparing these results with a direct numerical integration, we canconclude that the system is dominated by a pure secular evolution thatis very well reproduced with a disturbing function including at leastsixth-order terms in the eccentricities. Because of the uncertainties inthe orbital elements of the planets, we also contemplate the occurrenceof mean motion resonances in the system and analyze possiblecontribution from these resonant terms to the total motion.
| Orbital Solutions to the HD 160691 (μ Arae) Doppler Signal
We perform a dynamical analysis of the recently updated set of theradial velocity (RV) measurements of HD 160691 (μ Arae). Thekinematic, double-Keplerian model of the measurements leads to abest-fit solution that is unstable and self-disrupting in less than20,000 yr. In order to derive dynamically stable configurations that aresimultaneously consistent with the RV data, we use the so-called GAMP(genetic algorithm with MEGNO penalty). Using this method, we derivemeaningful limits on the parameters of the outer planet that alsoprovide a stable behavior of the system. The best-fit solutions arelocated in a shallow valley of(χ2ν)1/2 in the (ac,ec)-plane, extending over 2 AU (for the formal 1 σconfidence interval of the best fit). We find two equally good best-fitsolutions leading to qualitatively different orbital configurations. Oneof them corresponds to the center of the 5:1 mean motion resonance(MMR), and the second one describes a configuration between the 11:2 and17:3 MMRs. If the formal best-fit errors of the orbital parameters aretaken into account, the HD 160691 system can likely be found in the zoneof the phase space filled with low-order MMRs of the type p:1, with5
| 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.
| The CORALIE survey for southern extra-solar planets. XIII. A pair of planets around HD 202206 or a circumbinary planet?
Long-term precise Doppler measurements with the CORALIE spectrographreveal the presence of a second planet orbiting the solar-type star HD202206. The radial-velocity combined fit yields companion masses ofm2sin i=17.4 MJup and 2.44 MJup,semi-major axes of a=0.83 AU and 2.55 AU, and eccentricities of e=0.43and 0.27, respectively. A dynamical analysis of the system further showsa 5/1 mean motion resonance between the two planets. This system is ofparticular interest since the inner planet is within the brown-dwarflimits while the outer one is much less massive. Therefore, either theinner planet formed simultaneously in the protoplanetary disk as asuperplanet, or the outer Jupiter-like planet formed in a circumbinarydisk. We believe this singular planetary system will provide importantconstraints on planetary formation and migration scenarios.
| 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.
| Astrophysics in 2003
Five coherent sections appear this year, addressing solar physics,cosmology (with WMAP highlights), gamma-ray bursters (and theirassociation with Type Ia supernovae), extra-solar-system planets, andthe formation and evolution of galaxies (from reionization to assemblageof Local Group galaxies). There are also eight incoherent sections thatdeal with other topics in stellar, galactic, and planetary astronomy andthe people who study them.
| 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.
| The dynamical structure of the habitable zone in the HD 38529, HD 168443 and HD 169830 systems
The dynamical structure of the habitable zone in the multipleexoplanetary systems HD 38529, HD 168443 and HD 169830 is investigated.By using long-time numerical integration and fast chaos-detectionmethods, it is shown that the habitable zone of all three systems ismostly chaotic. There is a stable region between the two known planetsonly in the system HD 38529, near the inner edge of the habitable zone,where a third planet could exist. This region is stable for a wide rangeof orbital eccentricity and mass of the larger outer planet. Thestability region is divided by higher-order mean motion resonances,which are studied in detail. It seems that higher-order resonances areimportant in exoplanetary systems due to the large planetary masses andlarge orbital eccentricities.
| 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.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| Predicting Planets in Known Extrasolar Planetary Systems. I. Test Particle Simulations
Recent work has suggested that many planetary systems lie nearinstability. If all systems are near instability, then at least oneadditional planet must exist in stable regions of well-separatedextrasolar planetary systems to push these systems to the edge ofstability. We examine the known systems by placing massless testparticles in between the planets and integrating for 1-10 million yr. Wefind that some systems, HD 168443 and HD 74156, eject nearly all testparticles within 2 million yr. However, we find that HD 37124, HD 38529,and 55 Cnc have large contiguous regions in which particles survive for10 million yr. These three systems, therefore, seem the most likelycandidates for additional companions. Furthermore, HD 74156 and HD168443 must be complete; therefore radial velocity surveys should onlyfocus on detecting more distant companions. We also find that severalsystems show stable regions that only exist at nonzero eccentricities.
| A Minimum-Mass Extrasolar Nebula
By analogy with the minimum-mass solar nebula, we construct asurface-density profile using the orbits of the 26 precise-Dopplerplanets found in multiple-planet systems:Σ=2200(a/1AU)-βgcm-2, where a is thecircumstellar radius and β=2.0+/-0.5. The minimum-mass solar nebula(β=1.5) is consistent with this model, but the uniform-αaccretion disk model (β~1) is not. In a nebula with β>2,the center of the disk is the likely cradle of planet formation.
| 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.
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Datos observacionales y astrométricos
| Constelación: | Carnero |
| Ascensión Recta: | 02h04m34.29s |
| Declinación: | +25°24'51.5" |
| Magnitud Aparente: | 7.433 |
| Distancia: | 37.161 parsecs |
| Movimiento Propio en Ascensión Recta: | -107.8 |
| Movimiento Propio en Declinación: | -174.4 |
| B-T magnitude: | 8.326 |
| V-T magnitude: | 7.507 |
Catálogos y designaciones:
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