目录
图像
上传图像
DSS Images Other Images
相关文章
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.
| 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.
| Stars of Extragalactic Origin in the Solar Neighborhood
For 77 main-sequence F-G stars in the solar neighborhood with publishediron, magnesium, and europium abundances determined from high-dispersionspectra and with the ages estimated from theoretical isochrones, wecalculated the spatial velocities using Hipparcos data and the Galacticorbital elements. A comparison with the orbital elements of the globularclusters that are known to have been accreted by our Galaxy in the pastreveals stars of extragalactic origin. We show that the abundance ratiosof r- and alpha-elements in all the accreted stars differ sharply fromthose in the stars that are genetically associated with the Galaxy.According to current theoretical models, europium is produced mainly inlow-mass type-II supernovae (SNe II), while magnesium is synthesized inlarge quantities in high-mass SN II progenitors. Since all the oldaccreted stars of our sample exhibit a significant Eu overabundancerelative to Mg, we conclude that the maximum masses of the SN IIprogenitors outside the Galaxy were much lower than those inside it. Onthe other hand, only a small number of young accreted stars exhibit lownegative ratios [Eu/Mg] < 0. This can be explained by the delay ofprimordial star formation and the explosions of high-mass SNe II in arelatively small part of extragalactic space. We provide evidence thatthe interstellar medium was weakly mixed at the early evolutionarystages of the Galaxy formed from a single protogalactic cloud, and thatthe maximum mass of the SN II progenitors increased in it with timesimultaneously with the increase in mean metallicity.
| The Atmospheric Lithium Abundances of Solar Analogues
We have analyzed the lithium abundance in the atmospheres of 20 starsthat are solar analogues based on high-resolution echelle spectra usingmodel atmospheres in a non-LTE approach. In terms of their lithiumabundances, the stars (which are located in a narrow range oftemperatures of 5650 5900 K) can be divided into two groups: one withlow lithium abundances, as in the solar atmosphere, and one with lithiumabundances that are higher than the solar value by about 1 dex (with theaccuracy of the lithium abundances being 0.15 dex).
| Neutron-Capture Elements in Halo, Thick-Disk, and Thin-Disk Stars: Neodymium
We have derived the LTE neodymium abundances in 60 cool stars withmetallicities [Fe/H] from 0.25 to -1.71 by applying a synthetic-spectrumanalysis to spectroscopic observations of NdII lines with a resolutionof λ/Δλ⋍60 000 and signal-to-noise ratios of100 200. We have improved the atomic parameters of NdII and blendinglines by analyzing the corresponding line pro files in the solarspectrum. Neodymium is overabundant with respect to iron in halo stars,[Nd/Fe]=0.33±0.09, with the [Nd/Fe] ratio decreasingsystematically with metallicity when [Fe/H]>-1. This reflects anonset of efficient iron production in type I supernovae during theformation of the thick disk. The [Nd/Ba] and [Nd/Eu] abundance ratiosbehave differently in halo, thick-disk, and thin-disk stars. Theobserved abundance ratios in halo stars, [Nd/Ba]=0.34±0.08 and[Nd/Eu]=-0.27±0.05, agree within the errors with the ratios ofthe elemental yields for the r-process. These results support theconclusion of other authors based on analyses of other elements that ther-process played the dominant role in the synthesis of heavy elementsduring the formation of the halo. The [Nd/Ba] and [Nd/Eu] ratios forthick-disk stars are almost independent of metallicity([Nd/Ba]=0.28(±0.03)-0.01(±0.04) [Fe/H] and[Nd/Eu]=-0.13(±0.03)+0.05(±0.04) [Fe/H]) but are smallerin absolute value than the corresponding ratios for halo stars,suggesting that the synthesis of s-process nuclei started during theformation of the thick disk. The s-process is estimated to havecontributed ⋍30% of the neodymium produced during this stage ofthe evolution of the Galaxy. The [Nd/Ba] ratio decreases abruptly by0.17 dex in the transition from the thick to the thin disk. Thesystematic decrease of [Nd/Ba] and increase of [Nd/Eu] with increasingmetallicity of thin-disk stars point toward a dominant role of thes-process in the synthesis of heavy elements during this epoch.
| 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.
| Nearby stars of the Galactic disk and halo. III.
High-resolution spectroscopic observations of about 150 nearby stars orstar systems are presented and discussed. The study of these and another100 objects of the previous papers of this series implies that theGalaxy became reality 13 or 14 Gyr ago with the implementation of amassive, rotationally-supported population of thick-disk stars. The veryhigh star formation rate in that phase gave rise to a rapid metalenrichment and an expulsion of gas in supernovae-driven Galactic winds,but was followed by a star formation gap for no less than three billionyears at the Sun's galactocentric distance. In a second phase, then, thethin disk - our ``familiar Milky Way'' - came on stage. Nowadays ittraces the bright side of the Galaxy, but it is also embedded in a hugecoffin of dead thick-disk stars that account for a large amount ofbaryonic dark matter. As opposed to this, cold-dark-matter-dominatedcosmologies that suggest a more gradual hierarchical buildup throughmergers of minor structures, though popular, are a poor description forthe Milky Way Galaxy - and by inference many other spirals as well - if,as the sample implies, the fossil records of its long-lived stars do notstick to this paradigm. Apart from this general picture that emergeswith reference to the entire sample stars, a good deal of the presentwork is however also concerned with detailed discussions of manyindividual objects. Among the most interesting we mention the bluestraggler or merger candidates HD 165401 and HD 137763/HD 137778, thelikely accretion of a giant planet or brown dwarf on 59 Vir in itsrecent history, and HD 63433 that proves to be a young solar analog at\tau200 Myr. Likewise, the secondary to HR 4867, formerly suspectednon-single from the Hipparcos astrometry, is directly detectable in thehigh-resolution spectroscopic tracings, whereas the visual binary \chiCet is instead at least triple, and presumably even quadruple. Withrespect to the nearby young stars a complete account of the Ursa MajorAssociation is presented, and we provide as well plain evidence foranother, the ``Hercules-Lyra Association'', the likely existence ofwhich was only realized in recent years. On account of its rotation,chemistry, and age we do confirm that the Sun is very typical among itsG-type neighbors; as to its kinematics, it appears however not unlikelythat the Sun's known low peculiar space velocity could indeed be thecause for the weak paleontological record of mass extinctions and majorimpact events on our parent planet during the most recent Galactic planepassage of the solar system. Although the significance of thiscorrelation certainly remains a matter of debate for years to come, wepoint in this context to the principal importance of the thick disk fora complete census with respect to the local surface and volumedensities. Other important effects that can be ascribed to this darkstellar population comprise (i) the observed plateau in the shape of theluminosity function of the local FGK stars, (ii) a small thoughsystematic effect on the basic solar motion, (iii) a reassessment of theterm ``asymmetrical drift velocity'' for the remainder (i.e. the thindisk) of the stellar objects, (iv) its ability to account for the bulkof the recently discovered high-velocity blue white dwarfs, (v) itsmajor contribution to the Sun's 220 km s-1 rotationalvelocity around the Galactic center, and (vi) the significant flatteningthat it imposes on the Milky Way's rotation curve. Finally we note ahigh multiplicity fraction in the small but volume-complete local sampleof stars of this ancient population. This in turn is highly suggestivefor a star formation scenario wherein the few existing single stellarobjects might only arise from either late mergers or the dynamicalejection of former triple or higher level star systems.
| Some anomalies in the occurrence of debris discs around main-sequence A and G stars
Debris discs consist of large dust grains that are generated bycollisions of comets or asteroids around main-sequence stars, and thequantity and distribution of debris may be used to detect the presenceof perturbing planets akin to Neptune. We use stellar and disc surveysto compare the material seen around A- and G-type main-sequence stars.Debris is detected much more commonly towards A stars, even when acomparison is made only with G stars of comparable age. Detection ratesare consistent with disc durations of ~0.5 Gyr, which may occur at anytime during the main sequence. The higher detection rate for A stars canresult from this duration being a larger fraction of the main-sequencelifetime, possibly boosted by a globally slightly larger disc mass thanfor the G-type counterparts. The disc mass range at any given age is afactor of at least ~100 and any systematic decline with time is slow,with a power law estimated to not be steeper than t-1/2.Comparison with models shows that dust can be expected as late as a fewGyr when perturbing planetesimals form slowly at large orbital radii.Currently, the Solar system has little dust because the radius of theKuiper Belt is small and hence the time-scale to produce planetesimalswas less than 1 Gyr. However, the apparently constant duration of ~0.5Gyr when dust is visible is not predicted by the models.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| 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.
| Kinematics of Hipparcos Visual Binaries. II. Stars with Ground-Based Orbital Solutions
This paper continues kinematical investigations of the Hipparcos visualbinaries with known orbits. A sample, consisting of 804 binary systemswith orbital elements determined from ground-based observations, isselected. The mean relative error of their parallaxes is about 12% andthe mean relative error of proper motions is about 4%. However, even 41%of the sample stars lack radial velocity measurements. The computedGalactic velocity components and other kinematical parameters are usedto divide the stars with known radial velocities into kinematical agegroups. The majority (92%) of binaries from the sample are thin diskstars, 7.6% have thick disk kinematics and only two binaries have halokinematics. Among them, the long-period variable Mira Ceti has a verydiscordant {Hipparcos} and ground-based parallax values. From the wholesample, 60 stars are ascribed to the thick disk and halo population.There is an urgent need to increase the number of the identified halobinaries with known orbits and substantially improve the situation withradial velocity data for stars with known orbits.
| Radial Velocities for 889 Late-Type Stars
We report radial velocities for 844 FGKM-type main-sequence and subgiantstars and 45 K giants, most of which had either low-precision velocitymeasurements or none at all. These velocities differ from the standardstars of Udry et al. by 0.035 km s-1 (rms) for the 26 FGKstandard stars in common. The zero point of our velocities differs fromthat of Udry et al.: =+0.053km s-1. Thus, these new velocities agree with the best knownstandard stars both in precision and zero point, to well within 0.1 kms-1. Nonetheless, both these velocities and the standardssuffer from three sources of systematic error, namely, convectiveblueshift, gravitational redshift, and spectral type mismatch of thereference spectrum. These systematic errors are here forced to be zerofor G2 V stars by using the Sun as reference, with Vesta and day sky asproxies. But for spectral types departing from solar, the systematicerrors reach 0.3 km s-1 in the F and K stars and 0.4 kms-1 in M dwarfs. Multiple spectra were obtained for all 889stars during 4 years, and 782 of them exhibit velocity scatter less than0.1 km s-1. These stars may serve as radial velocitystandards if they remain constant in velocity. We found 11 newspectroscopic binaries and report orbital parameters for them. Based onobservations obtained at the W. M. Keck Observatory, which is operatedjointly by the University of California and the California Institute ofTechnology, and on observations obtained at the Lick Observatory, whichis operated by the University of California.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| Heavy element abundances in cool dwarf stars: An implication for the evolution of the Galaxy
We present revised strontium, barium and europium abundances for 63 coolstars with metallicities [Fe/H] ranging from -2.20 to 0.25. The stellarsample has been extracted from Fuhrmann's lists (\cite{Fuhr3, Fuhr5}).It is confined to main-sequence and turnoff stars. The results are basedon NLTE line formation obtained in differential model atmosphereanalyses of spectra that have a typical S/N of 200 and a resolution of40 000 to 60 000. The element abundance ratios reveal a distinctchemical history of the halo and thick disk compared with that of thethin disk. Europium is overabundant relative to iron and barium in haloand thick disk stars suggesting that during the formation of thesegalactic populations high-mass stars exploding as SNe II dominatednucleosynthesis on a short time scale of the order of 1 Gyr. We note theimportance of [Eu/Mg] determinations for halo stars. Our analysis leadsto the preliminary conclusion that Eu/Mg ratios found in halo stars donot support current theoretical models of the r-process based onlow-mass SNe; instead they seem to point at a halo formation time muchshorter than 1 Gyr. A steep decline of [Eu/Fe] and a slight decline of[Eu/Ba] with increasing metallicity have been first obtained for thickdisk stars. This indicates the start of nucleosynthesis in the lowermass stars, in SN I and AGB stars, which enriched the interstellar gaswith iron and the most abundant s-process elements. From a decrease ofthe Eu/Ba ratio by ~ 0.10 ... 0.15 dex the time interval correspondingto the thick disk formation phase can be estimated. The step-like changeof element abundance ratios at the thick to thin disk transition foundin our previous analysis (Mashonkina & Gehren \cite{euba}) isconfirmed in this study: [Eu/Ba] and [Eu/Fe] are reduced by ~ 0.25 dexand ~ 0.15 dex, respectively; [Ba/Fe] increases by ~ 0.1 dex. This isindicative of an intermediate phase before the early stage of the thindisk developed, during which only evolved middle and low mass (<8M_sun) stars contributed to nucleosynthesis. Our data provide anindependent method to calculate the duration of this phase. The mains-process becomes dominant in the production of heavy elements beyondthe iron group during the thin disk evolution. We find that in the thindisk stars Ba/Fe ratios increase with time from [Ba/Fe] = -0.06 in starsolder than 8 Gyr to [Ba/Fe] = 0.06 in stars that are between 2 and 4 Gyrold. Based on observations collected at the German Spanish AstronomicalCenter, Calar Alto, Spain.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Parallaxes and Proper Motions From the MCCormick Observatory: List 47
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..492I&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Radial velocities of the components of wide visual double stars.
Not Available
| Radial velocities of the components of wide visual double stars
Not Available
| Determination of the relative radial velocities of the components of visual binary stars from observations with the six-meter telescope
Not Available
| The photometric method of extrasolar planet detection revisited
We investigate the geometry concerning the photometric method ofextrasolar planet detection, i.e., the detection of dimunition of aparent star's brightness during a planetary transit. Under theassumption that planetary orbital inclinations can be defined by aGaussian with a sigma of 10 deg centered on the parent star's equatorialplane, Monte Carlo simulations suggest that for a given star observed atan inclination of exactly 90 deg, the probability of at least oneEarth-sized or larger planet being suitably placed for transits isapproximately 4%. This probability drops to 3% for a star observed at aninclination of 80 deg, and is still approximately 0.5% for a starobserved at an inclination of 60 deg. If one can select 100 stars with apre-determined inclination equal or greater than 80 deg, the probabilityof at least one planet being suitably configured for transits is 95%.The majority of transit events are due to planets in small-a orbitssimilar to the Earth and Venus; thus, the photometric method inprinciple is the method best suited for the detection of Earthlikeplanets. The photometric method also allows for testing whether or notplanets can exist within binary systems. This can ge done by selectingbinary systems observed at high orbital inclinations, both eclipsingbinaries and wider visual binaries. For a 'real-world' example, we lookat the alpha Centauri system (i = 79.2 deg). If we assume that theequatorial planes of both components coincide with the system's orbitalplane, Monte Carlo simulations suggest that the probability of at leastone planet (of either component) being suitably configured for transitsis approximately 8%. In conclusion, we present a non-exhaustive list ofsolar-type stars, both single and within binary systems, which exhibit ahigh equatorial inclination. These objects may be considered aspreliminary candidates for planetary searches via the photometricmethod.
| Orbital coplanarity in solar-type binary systems: Implications for planetary system formation and detection
The equatorial inclinations of solar-type stars within visual binarysystems are computed by combining v sin i measurements with rotationalperiod information, or with expected rotational velocities based uponthe age of the star in question. These inclinations are then comparedwith the orbital inclinations of the systems to test the alignmentbetween the equatorial and orbital planes, and how the tendency for oragainst coplanarity varies as a function of parameters such as spectraltype, separation, eccentricity, etc. The results are extended toplanetary systems in order to determine the appropriateness of basingplanetary search strategies upon a parent star's equatorial inclination,and to address issues in planetary system formation and evolution,including the stability of planetary orbits within binary systems.During the course of this project new or improved v sin i measurementsare made for over 30 solar-type stars within binary systems, and (forthe purposes of the study) tentative orbits are computed for thirteenlong-period systems. The results suggest that approximate coplanaritybetween the equatorial and orbital planes exists solar-type binarysystems with separations less than 30-40 AU. The coplanarity tendency,as well as this 'critical separation,' is not significantly affected bymost of the other parameters studied. The one significant exceptionoccurs with hierarchical multiple systems, where noncoplanarity mayexist at relatively small separations. If it is assumed that planetarydistances in our solar system are typical, the results suggest there isno reason to expect planets to orbit in planes significantly differentfrom that of the parent star's equator, in turn suggesting thatplanetary formation models and search strategies dependent upon thisassumption are valid from this standpoint. The results also suggest thatnoncoplanarity between the components of a binary system is not asignificant issue in addressing the stability of planetary orbits withinthe system.
| Stromgren Four-Colour UVBY Photometry of G5-TYPE Hd-Stars Brighter than MV=8.6
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...89O&db_key=AST
| CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
| The chromospheric emission-age relation for stars of the lower main sequence and its implications for the star formation rate
An attempt is made to formulate the relationship between age andchromospheric emission (CE) in late-type dwarf stars. Evidence isreviewed that a deterministic relationship of this type actually exists,and that for stars of known age, either a power-law relation or a curvecorresponding to a constant star formation rate fits equally well.Further observations should be able to demonstrate either that there isa real excess of young stars near the sun or that the evolution of CEfor a low-mass star goes through a slow initial decline, a rapid declineat intermediate ages, and finally a slow decline for old stars like thesun.
| A complete sample of wide binaries in the solar neighborhood
A well-defined sample of unambiguously bound wide binaries in the solarneighborhood is presented. The sample appears complete for physicalsystems where s is greater than 0.32 mpc, M(V) is less than 9.0, pi is0.040 arcsec or greater, and delta is larger than -12 deg. The samplecontains 39 systems, of which about 41 percent are hierarchical systems.The distribution of the separations from the sample obeys a simple powerlaw relation. A sharp cutoff in number density is indicated at about 0.1pc. Based on the sample, number densities for wide binaries arecalculated as a function of separation. It appears that about 3 percentof local stars should be members of systems wider than 0.01 pc.
| Chromospheric activity in evolved stars - The rotation-activity connection and the binary-single dichotomy
A tabulation of measured values of the Ca II H and K (S) index aretransformed to the original Mount Wilson definition of the index. Thetabulation includes main-sequence, evolved, single, and tidally coupled(RS CVn) binary stars. The (S) indices are analyzed against Wilson's(1976) I(HK) intensity estimates, showing that Wilson's estimates areonly a two-state indicator. Ca II H and K fluxes are computed andcalibrated with published values of rotation periods. It is found thatthe single and binary stars are consistent with a single relationshipbetween rotation and Ca II excess emission flux.
| Mean positions and proper motions of 224 stars based on PZT observations at Ondrejov in 1973-1986
An improvement of the positions and proper motions for the Ondrejov PZTstar list based on observations of 224 stars in the period 1973-1986 ispresented. The mean epoch of the PZT 86 catalogue is found to be 1981.56with a standard error in right ascension equal to + or - 0.0015 s/ andin delination equal to + or - 0.017 arcsec. The proper motions in rightascension and declination were obtained with an accuracy characterizedby the average standard errors of + or - 0.051 s/cy and + or - 0.57arcsec/cy, respectively. The PZT 86 catalogue is compared with theprevious PZT (1978 and 1983) catalogues, and with the AGK 3 (Dieckvoss,1975) catalogue.
| The chromospheric age dependence of the birthrate, composition, motions, and rotation of late F and G dwarfs within 25 parsecs of the sun
The chromospheric ages of 115 late F and G dwarfs within 25 parsecs ofthe sun are calculated. Rotational velocities are plotted againstchromospheric age to reveal the rotational spin-down trajectories ofsolar-type stars of various masses. Also, plots of metal abundance andpeculiar velocity versus chromospheric age are used to determine trendswith age.
| UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars
Not Available
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
INHABITED SKY
