Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
The Effects of Multiple Companions on the Efficiency of Space Interferometry Mission Planet Searches
The Space Interferometry Mission (SIM) is expected to make preciseastrometric measurements that can be used to detect low-mass planetsaround nearby stars. Since most nearby stars are members ofmultiple-star systems, many of them will have a measurable accelerationdue to their companion, which must be included when solving forastrometric parameters and searching for planetary perturbations. Inaddition, many of the stars with one radial velocity planet showindications of additional planets. Therefore, astrometric surveys suchas SIM must be capable of detecting planets and measuring orbitalparameters in systems with multiple stellar and/or planetary companions.We have conducted Monte Carlo simulations to investigate how thepresence of multiple companions affects the sensitivity of anastrometric survey such as SIM. We find that the detection efficiencyfor planets in wide binary systems is relatively unaffected by thepresence of a binary companion if the planetary orbital period is lessthan half the duration of the astrometric survey. For longer orbitalperiods, there are significant reductions in the sensitivity of anastrometric survey. In addition, we find that the signal required todetect a planet can be increased significantly due to the presence of anadditional planet orbiting the same star. Fortunately, adding a modestnumber of precision radial velocity observations significantly improvesthe sensitivity for many multiple-planet systems. Thus, the combinationof radial velocity observations and astrometric observations by SIM willbe particularly valuable for studying multiple-planet systems.
| 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.
| 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.
| 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.
| Predicting Planets in Known Extrasolar Planetary Systems. III. Forming Terrestrial Planets
Recent results have shown that many of the known extrasolar planetarysystems contain regions that are stable for both Earth-mass andSaturn-mass planets. Here we simulate the formation of terrestrialplanets in four planetary systems, 55 Cancri, HD 38529, HD 37124, and HD74156, under the assumption that these systems of giant planets arecomplete and that their orbits are well determined. Assuming that thegiant planets formed and migrated quickly, terrestrial planets may formfrom a second generation of planetesimals. In each case, Moon- toMars-sized planetary embryos are placed in between the giant planets andevolved for 100 Myr. We find that planets form relatively easily in 55Cnc, with masses up to 0.6 M⊕ and, in some cases,substantial water content and orbits in the habitable zone. HD 38529 islikely to support an asteroid belt, but no terrestrial planets ofsignificant mass. No terrestrial planets form in HD 37124 and HD 74156,although in some cases 1-2 lone embryos survive for 100 Myr. Ifmigration occurred later, depleting the planetesimal disk, then massiveterrestrial planets are unlikely to form in any of these systems.
| Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets
Precise radial velocity measurements have led to the discovery of ~170extrasolar planetary systems. Understanding the uncertainties in theorbital solutions will become increasingly important as the discoveryspace for extrasolar planets shifts to planets with smaller masses andlonger orbital periods. The method of Markov chain Monte Carlo (MCMC)provides a rigorous method for quantifying the uncertainties in orbitalparameters in a Bayesian framework (Paper I). The main practicalchallenge for the general application of MCMC is the need to constructMarkov chains that quickly converge. The rate of convergence is verysensitive to the choice of the candidate transition probabilitydistribution function (CTPDF). Here we explain one simple method forgenerating alternative CTPDFs that can significantly speed convergenceby 1-3 orders of magnitude. We have numerically tested dozens of CTPDFswith simulated radial velocity data sets to identify those that performwell for different types of orbits and suggest a set of CTPDFs forgeneral application. In addition, we introduce other refinements to theMCMC algorithm for radial velocity planets, including an improvedtreatment of the uncertainties in the radial velocity observations, analgorithm for automatically choosing step sizes, an algorithm forautomatically determining reasonable stopping times, and the use ofimportance sampling for including the dynamical evolution ofmultiple-planet systems. Together, these improvements make it practicalto apply MCMC to multiple-planet systems. We demonstrate theimprovements in efficiency by analyzing a variety of extrasolarplanetary systems.
| 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.
| Dwarfs in the Local Region
We present lithium, carbon, and oxygen abundance data for a sample ofnearby dwarfs-a total of 216 stars-including samples within 15 pc of theSun, as well as a sample of local close giant planet (CGP) hosts (55stars) and comparison stars. The spectroscopic data for this work have aresolution of R~60,000, a signal-to-noise ratio >150, and spectralcoverage from 475 to 685 nm. We have redetermined parameters and derivedadditional abundances (Z>10) for the CGP host and comparison samples.From our abundances for elements with Z>6 we determine the meanabundance of all elements in the CGP hosts to range from 0.1 to 0.2 dexhigher than nonhosts. However, when relative abundances ([x/Fe]) areconsidered we detect no differences in the samples. We find nodifference in the lithium contents of the hosts versus the nonhosts. Theplanet hosts appear to be the metal-rich extension of local regionabundances, and overall trends in the abundances are dominated byGalactic chemical evolution. A consideration of the kinematics of thesample shows that the planet hosts are spread through velocity space;they are not exclusively stars of the thin disk.
| Chemical Composition of the Planet-harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star ofthe transiting extrasolar planet TrES-1. Based on high-resolution KeckHIRES and Hobby-Eberly Telescope HRS spectra, we have determinedabundances relative to the Sun for 16 elements (Na, Mg, Al, Si, Ca, Sc,Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The resulting averageabundance of <[X/H]>=-0.02+/-0.06 is in good agreement withinitial estimates of solar metallicity based on iron. We compare theelemental abundances of TrES-1 with those of the sample of stars withplanets, searching for possible chemical abundance anomalies. TrES-1appears not to be chemically peculiar in any measurable way. Weinvestigate possible signs of selective accretion of refractory elementsin TrES-1 and other stars with planets and find no statisticallysignificant trends of metallicity [X/H] with condensation temperatureTc. We use published abundances and kinematic information forthe sample of planet-hosting stars (including TrES-1) and severalstatistical indicators to provide an updated classification in terms oftheir likelihood to belong to either the thin disk or the thick disk ofthe Milky Way. TrES-1 is found to be very likely a member of thethin-disk population. By comparing α-element abundances of planethosts and a large control sample of field stars, we also find thatmetal-rich ([Fe/H]>~0.0) stars with planets appear to besystematically underabundant in [α/Fe] by ~0.1 dex with respect tocomparison field stars. The reason for this signature is unclear, butsystematic differences in the analysis procedures adopted by differentgroups cannot be ruled out.
| 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.
| 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.
| On detecting terrestrial planets with timing of giant planet transits
The transits of a distant star by a planet on a Keplerian orbit occur attime intervals exactly equal to the orbital period. If a second planetorbits the same star, the orbits are not Keplerian and the transits areno longer exactly periodic. We compute the magnitude of the variation inthe timing of the transits, δt. We investigate analyticallyseveral limiting cases: (i) interior perturbing planets with muchsmaller periods; (ii) exterior perturbing planets on eccentric orbitswith much larger periods; (iii) both planets on circular orbits witharbitrary period ratio but not in resonance; (iv) planets on initiallycircular orbits locked in resonance. Using subscripts `out' and `in' forthe exterior and interior planets, μ for planet-to-star mass ratioand the standard notation for orbital elements, our findings in thesecases are as follows. (i) Planet-planet perturbations are negligible.The main effect is the wobble of the star due to the inner planet, andthereforeδt~μin(ain/aout)Pout.(ii) The exterior planet changes the period of the interior planet byμout(ain/rout)3Pin.As the distance of the exterior planet changes due to its eccentricity,the inner planet's period changes. Deviations in its transit timingaccumulate over the period of the outer planet, and thereforeδt~μouteout(ain/aout)3Pout.(iii) Halfway between resonances the perturbations are small, of theorder ofμouta2in/(ain-aout)2Pinfor the inner planet (switch `out' and `in' for the outer planet). Thisincreases as one gets closer to a resonance. (iv) This is perhaps themost interesting case because some systems are known to be in resonancesand the perturbations are the largest. As long as the perturber is moremassive than the transiting planet, the timing variations would be ofthe order of the period regardless of the perturber mass. For lighterperturbers, we show that the timing variations are smaller than theperiod by the perturber-to-transiting-planet mass ratio. An earth-massplanet in 2:1 resonance with a three-dimensional period transitingplanet (e.g. HD 209458b) would cause timing variations of the order of 3min, which would be accumulated over a year. This signal of aterrestrial planet is easily detectable with current ground-basedmeasurements.For the case in which both planets are on eccentric orbits, we computenumerically the transit timing variations for several known multiplanetsystems, assuming they are edge-on. Transit timing measurements may beused to constrain the masses, radii and orbital elements of planetarysystems, and, when combined with radial velocity measurements, provide anew means of measuring the mass and radius of the host star.
| 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.
| 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 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.
| Predicting Planets in Known Extrasolar Planetary Systems. II. Testing for Saturn Mass Planets
Recent results have shown that many of the known extrasolar planetarysystems contain regions that are stable for massless test particles. Weexamine the possibility that Saturn mass planets exist in these systems,just below the detection threshold, and predict likely orbitalparameters for such unseen planets. We insert a Saturn mass planet intothe regions stable for massless test particles and integrate the systemfor 100 million years. We conduct 200-600 of these experiments to testparameter space in 55 Cancri, HD 37124, HD 38529, and HD 74156. In 55Cnc we find three maxima of the survival rate of Saturn mass planets,located in semimajor axis a and eccentricity e space at (a,e)=(1.0 AU,0.02), (2.0 AU, 0.08), and (3.0 AU, 0.17). In HD 37124 the maximum liesat a=0.90-98 AU, eccentricity e~0.05-0.15. In HD 38529, only 5% ofSaturn mass planets are unstable, and the region in which a Saturn massplanet could survive is very broad, centered on 0.5
| 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.
| 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.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Toro |
| Ascensione retta: | 05h37m02.53s |
| Declinazione: | +20°43'54.4" |
| Magnitudine apparente: | 7.659 |
| Distanza: | 33.245 parsec |
| Moto proprio RA: | 0 |
| Moto proprio Dec: | 0 |
| B-T magnitude: | 8.502 |
| V-T magnitude: | 7.729 |
Cataloghi e designazioni:
|
