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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.
| Metallicity, debris discs and planets
We investigate the populations of main-sequence stars within 25 pc thathave debris discs and/or giant planets detected by Doppler shift. Themetallicity distribution of the debris sample is a very close match tothat of stars in general, but differs with >99 per cent confidencefrom the giant planet sample, which favours stars of above averagemetallicity. This result is not due to differences in age of the twosamples. The formation of debris-generating planetesimals at tens of authus appears independent of the metal fraction of the primordial disc,in contrast to the growth and migration history of giant planets withina few au. The data generally fit a core accumulation model, with outerplanetesimals forming eventually even from a disc low in solids, whileinner planets require fast core growth for gas to still be present tomake an atmosphere.
| 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.
| HD 98618: A Star Closely Resembling Our Sun
Despite the observational effort carried out in the last few decades, noperfect solar twin has been found to date. An important milestone wasachieved a decade ago by Porto de Mello & da Silva, who showed that18 Sco is almost a solar twin. In the present work, we use extremelyhigh resolution (R=105), high signal-to-noise ratio KeckHIRES spectra to carry out a differential analysis of 16 solar-twincandidates. We show that HD 98618 is the second-closest solar twin andthat the fundamental parameters of both HD 98618 and 18 Sco are verysimilar (within a few percent) to the host star of our solar system,including the likelihood of hosting a terrestrial planet within theirhabitable zones. We suggest that these stars should be given toppriority in exoplanet and SETI surveys.The data presented herein were obtained at the W. M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California, and the NationalAeronautics and Space Administration.
| Gas Giant Protoplanets Formed by Disk Instability in Binary Star Systems
Gas giant planets have been discovered in binary or triple star systemswith a range of semimajor axes. We present a new suite ofthree-dimensional radiative gravitational hydrodynamics modelssuggesting that binary stars may be quite capable of forming planetarysystems similar to our own. One difference between the new and previouscalculations is the inclusion of artificial viscosity in the previouswork, leading to significant conversion of disk kinetic energy intothermal energy in shock fronts and elsewhere. New models are presentedshowing how vigorous artificial viscosity can help to suppress clumpformation. The new models with binary companions do not employ anyexplicit artificial viscosity and also include the third (vertical)dimension in the hydrodynamic calculations, allowing for transientphases of convective cooling. The new calculations of the evolution ofinitially marginally gravitationally stable disks show that the presenceof a binary star companion may actually help to trigger the formation ofdense clumps that could become giant planets. Earth-like planets wouldform much later in the inner disk regions by the traditional collisionalaccumulation of progressively larger, solid bodies. We also show that inmodels without binary companions, which begin their evolution asgravitationally stable disks, the disks evolve to form dense rings,which then break up into self-gravitating clumps. The latter modelssuggest that the evolution of any self-gravitating disk with sufficientmass to form gas giant planets is likely to lead to a period of diskinstability, even in the absence of a trigger such as a binary starcompanion.
| Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer MIPS Survey
We have searched for infrared excesses around a well-defined sample of69 FGK main-sequence field stars. These stars were selected withoutregard to their age, metallicity, or any previous detection of IRexcess; they have a median age of ~4 Gyr. We have detected 70 μmexcesses around seven stars at the 3 σ confidence level. Thisextra emission is produced by cool material (<100 K) located beyond10 AU, well outside the ``habitable zones'' of these systems andconsistent with the presence of Kuiper Belt analogs with ~100 times moreemitting surface area than in our own planetary system. Only one star,HD 69830, shows excess emission at 24 μm, corresponding to dust withtemperatures >~300 K located inside of 1 AU. While debris disks withLdust/L*>=10-3 are rare around oldFGK stars, we find that the disk frequency increases from 2%+/-2% forLdust/L*>=10-4 to 12%+/-5% forLdust/L*>=10-5. This trend in thedisk luminosity distribution is consistent with the estimated dust inour solar system being within an order of magnitude greater or less thanthe typical level around similar nearby stars. Although there is nocorrelation of IR excess with metallicity or spectral type, there is aweak correlation with stellar age, with stars younger than a gigayearmore likely to have excess emission.
| 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.
| Infrared 3-4 μm Spectroscopy of Infrared Luminous Galaxies with Possible Signatures of Obscured Active Galactic Nuclei
We present the results of infrared 2.8-4.1 μm (L-band) spectroscopyof nearby infrared luminous galaxies with possible signatures ofdust-obscured active galactic nuclei (AGNs) in data at otherwavelengths. The samples are chosen to include sources with a radioexcess relative to far-infrared emission, strong absorption features inmid-infrared 5-11.5 μm spectra, unusually weak [C II] 158 μmemission relative to the far-infrared continuum, and radio galaxiesclassified optically as narrow-line objects. Our aim is to investigatewhether the signatures of possible obscured AGNs can be detected in ourL-band spectra based on the strengths of emission and absorptionfeatures. Six of nine observed sources clearly show 3.3 μm polycyclicaromatic hydrocarbon emission features, a good starburst indicator. Anabsorption feature at 3.1 μm due to ice-covered dust is detected inIRAS 04154+1755 and IRAS 17208-0014. The signature of a barecarbonaceous dust absorption feature at 3.4 μm is seen in NGC 1377.Our L-band spectra reveal strong signatures of obscured AGNs in allthree optical Seyfert 2 galaxies (IRAS 04154+1755, Cygnus A, and 3C 234)and two galaxies classified optically as non-Seyfert galaxies (NGC 828and NGC 1377). Among the remaining optical non-Seyfert galaxies, IRAS17208-0014 might also show a buried AGN signature, whereas no explicitAGN evidence is seen in the L-band spectra of the mid-infraredabsorption feature source IRAS 15250+3609 and two weak [C II] emitters,IC 860 and CGCG 1510.8+0725.Based in part on data collected at the Subaru Telescope, which isoperated by the National Astronomical Observatory of Japan.
| 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.
| Can stellar wobble in triple systems mimic a planet?
The first extrasolar planets were detected by the measurement of thewobble of the parent star. This wobble leads to the periodic modulationof three observables: the radial velocity, the position on the sky andthe time of arrival of periodic signals. We show that the same wobble,and therefore the same modulation of the three observables, can be dueto the presence of a more distant binary stellar companion. Thus, the observation of the wobble does not, by itself, constitute a proof of aplanet detection. In particular, astrometric confirmation of a wobbledoes not necessarily provide a sufficient proof of the existence of aplanet candidate detected by radial velocity. Additional conditions,which we discuss here, must be fulfilled. We investigate the observedwobble for the planet candidates already detected and we find that, foreach case, a wobble due to a binary stellar companion can beexcluded.
However, for apparent Saturn-like planets in wideorbits, there may be an ambiguity in future detections, especially inspaceborne astrometric missions. We conclude that, in some cases, adefinitive proof of the presence of a planet requires furtherobservations such as direct imaging.
| 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.
| Prospects for brown dwarf and extrasolar planet research with the GTC and the LMT
The topic of brown dwarf and extrasolar planet research with the GTC andthe LMT was discussed during a half day workshop at Universidad NacionalAutonoma de Mexico. This paper summarizes the contributions presented atthat Workshop plus additional contributions from members of the SpanishNetwork for extrasolar planets. Specific observational projects, whichcan be carried out with the planned instruments for the GTC, includingfirst light ones, are explained in some detail. These projects are thefollowing: our coolest neighbors, brown dwarfs in wide binaries, browndwarfs and planetary mass objects in Orion, follow-up of transitingextrasolar planets and verification of planet candidates, the search forultracool companions to nearby stars, brown dwarf binaries and disksaround brown dwarfs.
| Precise Differential Analysis of Stellar Metallicities: Application to Solar Analogs Including 16 Cyg A and B
A method is presented for very accurately establishing the differencesof the atmospheric parameters (the effective temperature, the surfacegravity, the microturbulent velocity, and the Fe abundance) between twosimilar stars by using the equivalent widths of Fe I and Fe II lines,which is a variant of the numerical solution-search approach developedby Takeda et al. (2002, PASJ, 54, 451), while being inspired by thespirit of the orthodox ``differential curve-of-growth'' procedure. Byapplying this technique to eight selected stars similar to the Sun [HD20630, 76151, 134987, 181655, 186408 (16 Cyg A), 186427 (16 Cyg B),195019, and 217014] along with the Sun itself, the parameter differencesbetween any pairs of these stars could be successfully determined toprecisions of 10 K (in ΔTeff), 0.02dex (inΔlog g), 0.02 km s-1 (in Δv t), and 0.01 dex (in ΔA Fe). Regarding 16 Cyg A and B, awell-known ``solar twin'' system where a planet has been detected onlyin B, the metallicities of these two components were concluded to beessentially the same to a level of ≲ 0.01 dex.
| Photospheric CNO Abundances of Solar-Type Stars
We determined the C, N, and O abundances of 160 nearby F, G, and Kdwarfs and subgiants by using spectra obtained with the HIDESspectrograph at Okayama Astrophysical Observatory, with the purposes of(1) establishing the runs of [C/Fe], [N/Fe], and [O/Fe] for thesegalactic disk stars in the metallicity range of -1 ≲ [Fe/H] ≲+0.4, (2) searching for any difference in the CNO abundances ofplanet-host stars as compared to non-planet-host stars, and (3)examining the consistency of the abundances derived from different linesto check the validity of the analysis. The non-LTE effect on theabundance determination was taken into consideration based on ourextensive statistical-equilibrium calculations. We confirmed thatconsistent abundances are mostly accomplished between different lines,and that [C/Fe] as well as [O/Fe] progressively increase with a decreasein [Fe/H] with the slope of the former ( 0.2‑0.3) beingshallower than the latter ( 0.4‑0.5), while [N/Fe] does notshow any clear systematic trend with the metallicity. The [C/Fe],[N/Fe], and [O/Fe] values of 27 planet-harboring stars (included in oursample of 160 stars) were shown to be practically indistinguishable fromthose exhibited by non-planet-harboring stars of similar metallicities.
| Lithium Abundances of F-, G-, and K-Type Stars: Profile-Fitting Analysis of the Li I 6708 Doublet
An extensive profile-fitting analysis was performed for the Li(+Fe)6707-6708Å feature of nearby 160 F-K dwarfs/subgiants (including27 planet-host stars) in the Galactic disk ( 7000 K ≳Teff ≳ 5000 K, -1 ≲ [Fe/H] ≲ +0.4), in orderto establish the photospheric lithium abundances of these stars. Thenon-LTE effect (though quantitatively insignificant) was taken intoaccount based on our statistical equilibrium calculations, which werecarried out on an adequate grid of models. Our results confirmed most ofthe interesting observational characteristics revealed by recentlypublished studies, such as the bimodal distribution of the Li abundancesfor stars at Teff ≳ 6000 K, the satisfactory agreementof the upper envelope of the A(Li) vs. [Fe/H] distribution with thetheoretical models, the existence of a positive correlation betweenA(Li) and the stellar mass, and the tendency of lower lithium abundancesof planet-host stars (as compared to stars without planets) at thenarrow ``transition'' region of 5900 K ≳ Teff ≳5800 K. The solar Li abundance derived from this analysis is 0.92 (H =12.00), which is by 0.24dex lower than the widely referenced standardvalue of 1.16.
| Spectroscopic Study on the Atmospheric Parameters of Nearby F--K Dwarfs and Subgiants
Based on a collection of high-dispersion spectra obtained at OkayamaAstrophysical Observatory, the atmospheric parameters (Teff,log g, vt, and [Fe/H]) of 160 mid-F through early-K starswere extensively determined by the spectroscopic method using theequivalent widths of Fe I and Fe II lines along with the numericaltechnique of Takeda et al. (2002, PASJ, 54, 451). The results arecomprehensively discussed and compared with the parameter values derivedby different approaches (e.g., photometric colors, theoreticalevolutionary tracks, Hipparcos parallaxes, etc.) as well as with thepublished values found in various literature. It has been confirmed thatour purely spectroscopic approach yields fairly reliable and consistentresults.
| A 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.
| Circumstellar and circumbinary discs in eccentric stellar binaries
We explore test particle orbits in the orbital plane of eccentricstellar binary systems, searching for `invariant loops': closed curvesthat change shape periodically as a function of binary orbital phase asthe test particles in them move under the gravity of the stars. Stableinvariant loops play the same role in this periodically varyingpotential as stable periodic orbits do in stationary potentials; inparticular, when dissipation is weak, gas will most likely follow thenon-intersecting loops, while nearby particle orbits librate aroundthem. We use this method to set bounds on the sizes of discs around thestars, and on the gap between those and the inner edge of a possiblecircumbinary disc. Gas dynamics may impose further restrictions, but ourstudy sets upper bounds for the size of circumstellar discs, and a lowerbound for the inner radius of a circumbinary disc. We find thatcircumstellar discs are sharply reduced as the eccentricity of thebinary grows. For the disc around the secondary star, the tidal (Jacobi)radius calculated for circular orbits at the periastron radius gives agood estimate of the maximum size. Discs change in size and shape onlymarginally with the binary phase, with no strong preference to increaseor decrease at any particular phase. The circumstellar discs inparticular can be quite asymmetric. We compare our results with othernumerical and theoretical results and with observations of the αCentauri and L1551 systems, finding very good agreement. The calculatedchanges in the shapes and crowding of the circumstellar orbits can beused to predict how the disc luminosity and mass inflow should vary withbinary phase.
| Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids
The first verifiable near-infrared absorption features in the0.9-μm spectral region are reported for Asteroids 16 Psyche, 69Hesperia, 110 Lydia, 125 Liberatrix, 201 Penelope, and 216 Kleopatra.These weak features (1 3%) are attributed to orthopyroxenes presenton the surfaces of these asteroids. 16 Psyche and 125 Liberatrix havefull rotational coverage while 69 Hesperia, 110 Lydia, 201 Penelope, and216 Kleopatra have 75% rotational coverage. Qualitative2-μm absorption features are present, but are very weak(<1%). Absorption band positions suggest relatively low abundances ofcalcium and iron in the pyroxenes. This indicates relatively reducingredox conditions for these asteroids, their parent bodies, and thenebular regions in which they formed. Four potential interpretations forthese asteroids include: (1) they are exposed metallic cores or corefragments of differentiated parent bodies with residual orthopyroxenemantle material, (2) they are the result of a smelting-like reactionthat converts olivine to pyroxene and metallic iron in the presence ofcarbon at high temperatures, (3) they are analogs to the primitivemetal-rich Bencubbinite meteorites, or (4) they represent metallicsurfaces which have accumulated silicate debris from external sources.Of the two original interpretations for the M-asteroids, the enstatitechondrite interpretation (Chapman and Salisbury, 1973, Icarus 19, 507522; Gaffey and McCord, 1979, Mineralogical and petrologicalcharacterizations of asteroids. In: Gehrels T. (Ed.), Asteroids. Univ.of Arizona Press, Tucson, pp. 688 723) can be eliminated for theseasteroids because the pyroxene in enstatite chondrites is iron-free anddoes not exhibit such absorption features. The iron meteoriteinterpretation remains valid, but with modification. For M-Asteroids 16Psyche and 216 Kleopatra, these spectral results combined with previousdeterminations of high radar albedos indicate that these bodies are mostprobably exposed core fragments of differentiated bodies. M-Asteroids 69Hesperia, 110 Lydia, 125 Liberatrix, and 201 Penelope exhibit similarspectral features consistent with exposed core fragments, but radarobservations would be needed to confirm a high metal abundance.Observations of M-Asteroids 136 Austria and 325 Heidelberga suggest theabsence of absorption features in the 0.4- to 2.5-μm regionwithin the scatter of the data. Verification of the presence or absenceof features across the surfaces of these two asteroids requires fullrotational coverage. The interpretations for these“featureless” M-asteroids are not well-constrained, butremain consistent with the iron meteorite and enstatite chondriteinterpretations.
| A Differential Abundance Analysis of HD219175A and B
The abundances of the wide binary pair HD 219175 A and B are determinedand compared using a line-by-line differential analysis. No evidence fordifference has been found in the abundances of Fe, O, Na, Mg, Al, Si, K,Ca, Sc, Ti, V, Cr, Mn, Ni, Cu and Ba. Our results support a physicalrelation between the two components of HD 219175.
| 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.
| Planets and Infrared Excesses: Preliminary Results from a Spitzer MIPS Survey of Solar-Type Stars
As part of a large Spitzer MIPS Guaranteed Time Observation program, wehave searched for infrared excesses due to debris disks toward 26 FGKfield stars known from radial velocity (RV) studies to have one or moreplanets. While none of these stars show excesses at 24 μm, we havedetected 70 μm excesses around six stars at the 3 σ confidencelevel. The excesses are produced by cool material (<100 K) locatedbeyond 10 AU, well outside the ``habitable zones'' of these systems andconsistent with the presence of Kuiper Belt analogs with ~100 times moreemitting surface area than in our own planetary system. Theseplanet-bearing stars are, by selection for RV studies, typically olderthan 1 Gyr, and the stars identified here with excesses have a medianage of 4 Gyr. We find a preliminary correlation of both the frequencyand the magnitude of dust emission with the presence of known planets.These are the first stars outside the solar system identified as havingboth well-confirmed planetary systems and well-confirmed IR excesses.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Prospects for Habitable ``Earths'' in Known Exoplanetary Systems
We have examined whether putative Earth-mass planets could remainconfined to the habitable zones (HZs) of the 111 exoplanetary systemsconfirmed by 2004 August. We find that in about half of these systemsthere could be confinement for at least the past 1000 Myr, though insome cases only in variously restricted regions of the HZ. The HZmigrates outward during the main-sequence lifetime, and we find that inabout two-thirds of the systems an Earth-mass planet could be confinedto the HZ for at least 1000 Myr sometime during the main-sequencelifetime. Clearly, these systems should be high on the target list forexploration for terrestrial planets. We have reached our conclusions bydetailed investigations of seven systems, which has resulted in anestimate of the distance from the giant planet within which orbitalstability is unlikely for an Earth-mass planet. This distance is givenby nRH, where RH is the Hill radius of the giantplanet and n is a multiplier that depends on the giant's orbitaleccentricity and on whether the Earth-mass planet is interior orexterior to the giant planet. We have estimated n for each of the sevensystems by launching Earth-mass planets in various orbits and followingtheir fate with a hybrid orbital integrator. We have then evaluated thehabitability of the other exoplanetary systems using nRHderived from the giant's orbital eccentricity without carrying outtime-consuming orbital integrations. A stellar evolution model has beenused to obtain the HZs throughout the main-sequence lifetime.
| Jumping Jupiters in Binary Star Systems
We investigate the outcomes of the dynamical interaction of Jupiter-massplanets orbiting the central star in a binary system. These systems areunstable and lead to the hyperbolic ejection of one or more planets,while the surviving bodies are inserted in inner eccentric orbits. Thegravitational perturbations of the companion star, set at anintermediate distance (50 AU) and typically on an eccentric orbit,influence both the development of instability and the outcome of thesubsequent chaotic evolution. We compute the statistical properties ofthe resulting planetary systems when they reach a stable configuration.The binary eccentricity and the number of initial planets (two or three)are strong predictors of the final configuration of the planetarysystem. Cases of apsidal resonance between two final planets, Kozairesonance between a single surviving planet and the companion star, andretrograde orbits with respect to the binary orbit are naturallyproduced.
| 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.
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לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 19h41m52.00s |
| סירוב: | +50°31'03.0" |
| גודל גלוי: | 6.2 |
| מרחק: | 21.413 פארסק |
| תנועה נכונה: | -132 |
| תנועה נכונה: | -163 |
| B-T magnitude: | 6.963 |
| V-T magnitude: | 6.231 |
קטלוגים וכינוים:
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INHABITED SKY
