Contents
Images
Upload your image
DSS Images Other Images
Related articles
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 We include fivepreviously unpublished exoplanets orbiting the stars HD 11964, HD 66428,HD 99109, HD 107148, and HD 164922.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.
| 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.
| 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 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.
| 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.
| 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.
| 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.
| C, S, Zn and Cu abundances in planet-harbouring stars
We present a detailed and uniform study of C, S, Zn and Cu abundances ina large set of planet host stars, as well as in a homogeneous comparisonsample of solar-type dwarfs with no known planetary-mass companions.Carbon abundances were derived by EW measurement of two C I opticallines, while spectral syntheses were performed for S, Zn and Cu. Weinvestigated possible differences in the behaviours of the volatiles C,S and Zn and in the refractory Cu in targets with and without knownplanets in order to check possible anomalies due to the presence ofplanets. We found that the abundance distributions in stars withexoplanets are the high [Fe/H] extensions of the trends traced by thecomparison sample. All volatile elements we studied show [X/Fe] trendsdecreasing with [Fe/H] in the metallicity range -0.8< [Fe/H] <0.5, with significantly negative slopes of -0.39±0.04 and-0.35±0.04 for C and S, respectively. A comparison of ourabundances with those available in the literature shows good agreementin most cases.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and with the FEROS spectrograph at the 1.52-m and 2.2-m ESOtelescopes, at the Paranal Observatory, ESO (Chile), using the UVESspectrograph at the VLT/UT2 Kueyen telescope, and with the UES and SARGspectrographs at the 4-m William Hershel Telescope (WHT) and at the3.5-m TNG telescope, respectively, both at La Palma (Canary Islands).Tables 4-16 are only available in electronic form athttp://www.edpsciences.org
| The 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
| 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.
| 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).
| Search for periodicities in distribution of orbits of planets.
Not Available
| Target Selection for SETI. I. A Catalog of Nearby Habitable Stellar Systems
In preparation for the advent of the Allen Telescope Array, the SETIInstitute has the need to greatly expand its former list of ~2000targets compiled for Project Phoenix, a search for extraterrestrialtechnological signals. In this paper we present a catalog of stellarsystems that are potentially habitable to complex life forms (includingintelligent life), which comprises the largest portion of the new SETItarget list. The Catalog of Nearby Habitable Systems (HabCat) wascreated from the Hipparcos Catalogue by examining the information ondistances, stellar variability, multiplicity, kinematics, and spectralclassification for the 118,218 stars contained therein. We also make useof information from several other catalogs containing data for Hipparcosstars on X-ray luminosity, Ca II H and K activity, rotation, spectraltypes, kinematics, metallicity, and Strömgren photometry. Combinedwith theoretical studies on habitable zones, evolutionary tracks, andthird-body orbital stability, these data are used to remove unsuitablestars from HabCat, leaving a residue of stars that, to the best of ourcurrent knowledge, are potentially habitable hosts for complex life.While this catalog will no doubt need to be modified as we learn moreabout individual objects, the present analysis results in 17,129Hipparcos ``habstars'' near the Sun (75% within 140 pc), ~2200 of whichare known or suspected to be members of binary or triple star systems.
| Seven New Keck Planets Orbiting G and K Dwarfs
Planetary mass companions orbiting seven nearby G and K dwarfs have beenfound from the Keck Precision Doppler Survey. A ``51 Peg-like'' planetorbiting HD 49674 has the smallest mass yet found, Msini=0.12MJ. This system does not transit. A double-planet systemorbits HD 37124, with periods of 153 days and 6 yr and minimum masses of0.91 and 1.70 MJ. Single companions with moderateeccentricity have been found orbiting HD 108874, HD 72659, HD 114729,and HD 145675 with orbital periods ranging from 1.09 to 5.98 yr,yielding minimum masses ranging from 0.90 to 4.87 MJ.Periodic Doppler velocity variations, consistent with a mildly eccentricplanet in a 1 AU orbit, are reported for the chromospherically active K0dwarf HD 128311. It remains plausible that these velocity variations aredue to stellar photospheric ``jitter.'' Based on observations obtainedat the W. M. Keck Observatory, which is operated jointly by theUniversity of California and the California Institute of Technology.Keck time has been granted by both NASA and the University ofCalifornia.
| Abundance Analysis of Planetary Host Stars. I. Differential Iron Abundances
We present atmospheric parameters and iron abundances derived fromhigh-resolution spectra for three samples of dwarf stars: stars that areknown to host close-in giant planets (CGP), stars for which radialvelocity data exclude the presence of a close-in giant planetarycompanion (no-CGP), as well as a random sample of dwarfs with a spectraltype and magnitude distribution similar to that of the planetary hoststars (control). All stars have been observed with the same instrumentand have been analyzed using the same model atmospheres, atomic data,and equivalent width modeling program. Abundances have been deriveddifferentially to the Sun, using a solar spectrum obtained with Callistoas the reflector with the same instrumentation. We find that the ironabundances of CGP dwarfs are on average 0.22 dex greater than that ofno-CGP dwarfs. The iron abundance distributions of both the CGP andno-CGP dwarfs are different than that of the control dwarfs, while thecombined iron abundances have a distribution that is very similar tothat of the control dwarfs. All four samples (CGP, no-CGP, combined, andcontrol) have different effective temperature distributions. We showthat metal enrichment occurs only for CGP dwarfs with temperatures justbelow solar and ~300 K higher than solar, whereas the abundancedifference is insignificant at Teff around 6000 K.
| Parent Stars of Extrasolar Planets. VII. New Abundance Analyses of 30 Systems
The results of new spectroscopic analyses of 30 stars with giant planetand/or brown dwarf companions are presented. Values for Teffand [Fe/H] are used in conjunction with Hipparcos data and Paduaisochrones to derive masses, ages, and theoretical surface gravities.These new data are combined with spectroscopic and photometricmetallicity estimates of other stars harboring planets and publishedsamples of F, G, and K dwarfs to compare several subsets of planetbearing stars with similarly well-constrained control groups. Thedistribution of [Fe/H] values continues the trend uncovered in previousstudies in that stars hosting planetary companions have a higher meanvalue than otherwise similar nearby stars. We also investigate therelationship between stellar mass and the presence of giant planets, andwe find statistically marginal but suggestive evidence of a decrease inthe incidence of radial velocity companions orbiting relatively lessmassive stars. If confirmed with larger samples, this would represent acritical constraint to both planetary formation models, as well as toestimates of the distribution of planetary systems in our Galaxy.
| Effective temperatures and radii of planet-hosting stars from IR photometry
In this paper we present and analyse determinations of effectivetemperatures of planet-hosting stars using infrared (IR) photometry. Oneof our goals is the comparison with spectroscopic temperatures toevaluate the presence of systematic effects that could alter thedetermination of metal abundances. To estimate the stellar temperatureswe have followed a new approach based on fitting the observed 2MASS IRphotometry with accurately calibrated synthetic photometry. Special carehas been put in evaluating all sources of possible errors andincorporating them in the analysis. A comparison of our temperaturedeterminations with spectroscopic temperatures published by differentgroups reveals the presence of no systematic trends and a scattercompatible with the quoted uncertainties of 0.5-1.3%. This mutualagreement strengthens the results of both the spectroscopic and IRphotometry analyses. Comparisons with other photometric temperaturecalibrations, generally with poorer performances, are also presented. Inaddition, the method employed of fitting IR photometry naturally yieldsdeterminations of the stellar semi-angular diameters, which, whencombined with the distances, results in estimations of the stellar radiiwith remarkable accuracies of ~ 2-4%. A comparison with the only starin the sample with an empirically determined radius (HD 209458 - fromtransit photometry) indicates excellent agreement.
| Chemical abundances of planet-host stars. Results for alpha and Fe-group elements
In this paper, we present a study of the abundances of Si, Ca, Sc, Ti,V, Cr, Mn, Co, and Ni in a large set of stars known to harbor giantplanets, as well as in a comparison sample of stars not known to haveany planetary-mass companions. We have checked for possible chemicaldifferences between planet hosts and field stars without known planets.Our results show that overall, and for a given value of [Fe/H], theabundance trends for the planet hosts are nearly indistinguishable fromthose of the field stars. In general, the trends show nodiscontinuities, and the abundance distributions of stars with giantplanets are high [Fe/H] extensions to the curves traced by the fielddwarfs without planets. The only elements that might present slightdifferences between the two groups of stars are V, Mn, and to a lesserextent Ti and Co. We also use the available data to describe galacticchemical evolution trends for the elements studied. When comparing theresults with former studies, a few differences emerge for the high[Fe/H] tail of the distribution, a region that is sampled withunprecedented detail in our analysis.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 ESO telescope, withthe VLT/UT2 Kueyen telescope (Paranal Observatory, ESO, Chile) using theUVES spectrograph (Observing run 67.C-0206, in service mode), with theTNG and William Herschel Telescopes, both operated at the island of LaPalma, and with the ELODIE spectrograph at the 1.93-m telescope at theObservatoire de Haute Provence.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Coma Berenices |
| Right ascension: | 12h30m26.88s |
| Declination: | +22°52'47.4" |
| Apparent magnitude: | 8.746 |
| Distance: | 68.54 parsecs |
| Proper motion RA: | 128.4 |
| Proper motion Dec: | -90.1 |
| B-T magnitude: | 9.684 |
| V-T magnitude: | 8.824 |
Catalogs and designations:
|
