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מאמרים קשורים
Ages for Illustrative Field Stars Using Gyrochronology: Viability, Limitations, and Errors
We here develop an improved way of using a rotating star as a clock, setit using the Sun, and demonstrate that it keeps time well. Thistechnique, called gyrochronology, derives ages for low-massmain-sequence stars using only their rotation periods and colors. Thetechnique is developed here and used to derive ages for illustrativegroups of nearby field stars with measured rotation periods. We firstdemonstrate the reality of the interface sequence, the unifying featureof the rotational observations of cluster and field stars that makes thetechnique possible, and extend it beyond the proposal of Skumanich byspecifying the mass dependence of rotation for these stars. We delineatewhich stars it cannot currently be used on. We then calibrate the agedependence using the Sun. The errors are propagated to understand theirdependence on color and period. Representative age errors associatedwith the technique are estimated at ~15% (plus possible systematicerrors) for late F, G, K, and early M stars. Gyro ages for the MountWilson stars are shown to be in good agreement with chromospheric agesfor all but the bluest stars, and probably superior. Gyro ages are thencalculated for each of the active main-sequence field stars studied byStrassmeier and collaborators. These are shown to have a median age of365 Myr. The sample of single field stars assembled by Pizzolato andcollaborators is then assessed and shown to have gyro ages ranging fromunder 100 Myr to several Gyr, with a median age of 1.2 Gyr. Finally, wedemonstrate that the individual components of the three wide binariesξ Boo AB, 61 Cyg AB, and α Cen AB yield substantially the samegyro ages.
| The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| High-Resolution Spectroscopy of Ursa Major Moving Group Stars
We use new and extant literature spectroscopy to address abundances andmembership for UMa moving group stars. We first compare the UMa, Coma,and Hyades H-R diagrams via a homogeneous set of isochrones and findthat these three aggregates are essentially coeval; this (near)coevality can explain the indistinguishable distributions of UMa andHyades dwarfs in the chromospheric emission versus color plane. Ourspectroscopy of cool UMa dwarfs reveals striking abundanceanomalies-trends with Teff, ionization state, and excitationpotential-like those recently seen in young, cool M34, Pleaides, andHyades dwarfs. In particular, the trend of rising λ7774-based O Iabundance with declining Teff is markedly subdued in UMacompared to the Pleiades, suggesting a dependence on age or metallicity.Recent photometric metallicity estimates for several UMa dwarfs aremarkedly low compared to the group's canonical metallicity, and similardeviants are seen among cool Hyads as well. Our spectroscopy does notconfirm these curious photometric estimates, which seem to be calledinto question for cool dwarfs. Despite disparate sources of Li data, ourhomogeneous analysis indicates that UMa members evince remarkably smallscatter in the Li-Teff plane for Teff>=5200 K.Significant star-to-star scatter suggested by previous studies is seenfor cooler stars. Comparison with the consistently determined HyadesLi-Teff trend reveals differences that are qualitativelyconsistent with this cluster's larger [Fe/H] (and perhaps slightlygreater age). However, quantitative comparison with standard stellarmodels indicates the differences are smaller than expected, suggestingthe action of a fourth parameter beyond age, mass, and [Fe/H]controlling Li depletion. The UMa-Coma cool star Li abundances may showa slight 0.2 dex difference; however, this may be mass-independent andthus more consistent with a modest initial Li abundance difference.This paper includes data taken at the McDonald Observatory of theUniversity of Texas at Austin.Based on observations obtained at Kitt Peak National Observatory, adivision of the National Optical Astronomy Observatories, which isoperated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation.
| 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
| Binary Star Speckle Interferometry: Measurements and Orbits
Results of our second observational run of binary star interferometricmeasurements with an ICCD speckle camera attached to the 1.52 mtelescope of the Observatorio Astronómico Nacional at Calar Alto(Almería, Spain) in 2000 June-July are presented. The measuredangular separations range from 0.096" to 6.558". With the use of the newspeckle data, the orbits of the visual binaries WDS 14369+4813 and WDS21597+4908 are improved.
| Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group
Utilizing Hipparcos parallaxes, original radial velocities and recentliterature values, new Ca II H and K emission measurements,literature-based abundance estimates, and updated photometry (includingrecent resolved measurements of close doubles), we revisit the UrsaMajor moving group membership status of some 220 stars to produce afinal clean list of nearly 60 assured members, based on kinematic andphotometric criteria. Scatter in the velocity dispersions and H-Rdiagram is correlated with trial activity-based membership assignments,indicating the usefulness of criteria based on photometric andchromospheric emission to examine membership. Closer inspection,however, shows that activity is considerably more robust at excludingmembership, failing to do so only for <=15% of objects, perhapsconsiderably less. Our UMa members demonstrate nonzero vertex deviationin the Bottlinger diagram, behavior seen in older and recent studies ofnearby young disk stars and perhaps related to Galactic spiralstructure. Comparison of isochrones and our final UMa group membersindicates an age of 500+/-100 Myr, some 200 Myr older than thecanonically quoted UMa age. Our UMa kinematic/photometric members' meanchromospheric emission levels, rotational velocities, and scattertherein are indistinguishable from values in the Hyades and smaller thanthose evinced by members of the younger Pleiades and M34 clusters,suggesting these characteristics decline rapidly with age over 200-500Myr. None of our UMa members demonstrate inordinately low absolutevalues of chromospheric emission, but several may show residual fluxes afactor of >=2 below a Hyades-defined lower envelope. If one defines aMaunder-like minimum in a relative sense, then the UMa results maysuggest that solar-type stars spend 10% of their entire main-sequencelives in periods of precipitously low activity, which is consistent withestimates from older field stars. As related asides, we note six evolvedstars (among our UMa nonmembers) with distinctive kinematics that liealong a 2 Gyr isochrone and appear to be late-type counterparts to diskF stars defining intermediate-age star streams in previous studies,identify a small number of potentially very young but isolated fieldstars, note that active stars (whether UMa members or not) in our samplelie very close to the solar composition zero-age main sequence, unlikeHipparcos-based positions in the H-R diagram of Pleiades dwarfs, andargue that some extant transformations of activity indices are notadequate for cool dwarfs, for which Ca II infrared triplet emissionseems to be a better proxy than Hα-based values for Ca II H and Kindices.
| Statistics of spectroscopic sub-systems in visual multiple stars
A large sample of visual multiples of spectral types F5-M has beensurveyed for the presence of spectroscopic sub-systems. Some 4200 radialvelocities of 574 components were measured in 1994-2000 with thecorrelation radial velocity meter. A total of 46 new spectroscopicorbits were computed for this sample. Physical relations are establishedfor most of the visual systems and several optical components areidentified as well. The period distribution of sub-systems has a maximumat periods from 2 to 7 days, likely explained by a combination of tidaldissipation with triple-star dynamics. The fraction of spectroscopicsub-systems among the dwarf components of close visual binaries withknown orbits is similar to that of field dwarfs, from 11% to 18% percomponent. Sub-systems are more frequent among the components of widevisual binaries and among wide tertiary components to the known visualor spectroscopic binaries - 20% and 30%, respectively. In triple systemswith both outer (visual) and inner (spectroscopic) orbits known, we findan anti-correlation between the periods of inner sub-systems and theeccentricities of outer orbits which must be related to dynamicalstability constraints. Tables 1, 2, and 6 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/118
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| Speckle Observations of Double Stars with PISCO at Pic du Midi: Measurements in 1998
We present astrometric measurements of binary stars based on speckleobservations of 164 independent sequences of observations(~104 frames each) made with the PISCO speckle camera at Picdu Midi. These measurements concern 147 objects, of which 134 were foundto be double with a separation in the range 0.1"-1.0". These objectswere mainly selected among grade 3 orbits to improve the accuracy oftheir orbits and to constrain their masses. We discovered the binarityof 59 Aql with an angular separation of 0.09"+/-0.01".
| ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New Orbits
We present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses.
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Speckle camera for the Astronomical Observatory
Not Available
| Visual binary orbits and masses POST HIPPARCOS
The parallaxes from Hipparcos are an important ingredient to derive moreaccurate masses for known orbital binaries, but in order to exploit theparallaxes fully, the orbital elements have to be known to similarprecision. The present work gives improved orbital elements for some 205systems by combining the Hipparcos astrometry with existing ground-basedobservations. The new solutions avoid the linearity constraints andomissions in the Hipparcos Catalog by using the intermediate TransitData which can be combined with ground-based observations in arbitarilycomplex orbital models. The new orbital elements and parallaxes give newmass-sum values together with realistic total error-estimates. To getindividual masses at least for main-sequence systems, the mass-ratioshave been generally estimated from theoretical isochrones and observedmagnitude-differences. For some 25 short-period systems, however, trueastrometric mass-ratios have been determined through the observedorbital curvature in the 3-year Hipparcos observation interval. Thefinal result is an observed `mass-luminosity relation' which falls closeto theoretical expectation, but with `outliers' due to undetectedmultiplicity or to composition- and age-effects in the nonuniformnear-star sample. Based in part on observations collected with the ESAHipparcos astrometry satellite. Tables~ 1, 3, 4 and 6 are also availablein electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr~(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Mass determination of astrometric binaries with Hipparcos. II. Selection of candidates and results
In a previous paper (\cite{Mar97}) we have shown that for double starswith orbital periods smaller than about 25 years, it was possible todetermine from the Hipparcos data, the mass ratio B of the components orthe difference between the mass and intensity ratios, beta -B, providedthe orbital elements of the relative orbit are available. From anextensive literature search we have selected 145 potential systems, ofwhich 46 yielded eventually a satisfactory solution. For eight systemswith the largest separations, the peculiarities of the natural directionassociated to the Hipparcos observations, the 'hippacentre', have beenfully exploited to derive the mass ratio of the components without anyadditional assumption. For the remaining 38, the derivation of the massratio was possible only by taking the magnitude difference between thetwo components from other sources. The parallax determinedsimultaneously, is then used to produce the individual masses of thecomponents. The astrophysical relevance of the results is discussed andwhen possible (17 systems) the masses are compared to ground-basedvalues.
| Measurements of close binaries performed at PIC DU Midi
A total of 241 measurements of 119 close binaries observed with the 2-mTelescope Bernard Lyot at Pic du Midi Observatory are given. Themeasurements were performed with a micrometer with illuminated wires.
| Observations of double stars and new pairs. XV
The study reports visual and photographic measures listed for 1150 pairsobtained in the time frame 1989.91-1992.15, including 221 new doublestars. Magnitudes were estimated for a part of the objects, especiallythe fainter ones. Plate orientations were calculated from field stars ofknown positions and were precessed to the epoch; numbers of nights andof measured exposures are given. Reobservation of faint, neglected pairsreveal many corrections to the data from the old discovery lists.
| Precise equatorial coordinates of double and multiple systems - an astronomical support to the HIPPARCOS mission
Results are presented on determinations of precise positions (to theaccuracy required for their possible inclusion in the Hipparcos InputCatalogue) of 623 double and multiple stars (126 of them newlydiscovered) from the measurement of 39 plates taken at the ESO and theAstronomical Observatory of Torino, obtained between 1984 and 1987. Thetable includes the index number, the name of the discoverer, binarycomponent according to the designation by the Catalogue de Composantesd'etoiles Doubles et Multiples (CCDM), the magnitude of the componentsas given in the CCDM, epoch of observation, right ascension referred tothe J2000.0 equinox, declination, position angle referred to the J2000.0North Pole, angular separation, and DM and ADS numbers.
| Observations of double stars and new pairs. XIV
Results of a continuing survey of visual double stars are presented,including 4880 measurements made from February 1987 to November 1989.The positions in WDS format and Durchmusterung numbers are given for 194pairs first reported here. Micrometer measurements of 1142 doubles madewith the Swarthmore 61 cm refractor are presented. Magnitudes areestimated for some of the objects. Plate measurements, plateorientations, position angles, number of nights, and measured exposuresare given. Visual observations of 342 pairs obtained in May 1989 atCerro Tololo, mostly with the 1.0 m reflector, are reported.
| Micrometric measurements of visual double stars (IV list)
The results of 301 micrometric measurements of 88 double stars aregiven. The measurements were made at Brera-Merate, Collurania (Teramo),and La Silla Observatories during the period 1986.000-1986.999.
| Micrometer observations of double stars and new pairs. XIII
From a program of double star observations which emphasizes orbital,neglected, and newly discovered pairs, results obtained from October1984 to January 1987 are presented. A total of 3030 visual and 550photographic measures are listed. The positions in WDS format andDurchmusterung numbers are shown for 117 pairs for which firstobservations appear in this paper. Magnitudes are estimated for some ofthe objects.
| Measurements of binary stars made at Nice
Results are presented for 753 measurements of 267 binary stars that weremade with the 50- and 74-cm refractors at Nice Observatory. Coordinatesfor the equinox of 1950 are provided, along with apparent magnitudes,spectral types, and probable periods. It is noted that three-quarters ofthese systems are recently discovered close binaries.
| Double star measures at Lick Observatory Mount Hamilton California.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..325H&db_key=AST
| Micrometric measures of visual double stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87..253H&db_key=AST
| Mesures d'étoiles doubles faites à Nice
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....6..185C&db_key=AST
| Mesures d'étoiles doubles faites à Nice aux lunettes de 50 et de 74 CM
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....3...51C&db_key=AST
| MK Classification of 142 Visual Binaries
Not Available
| Mesures d'etoiles doubles faites AU 38cm de l'Observatoire de Paris.
Not Available
| Effect of Blending on the Orbital Elements of a Double-Line B-Type Binary
Not Available
| Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice
Not Available
| Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice
Not Available
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| קבוצת-כוכבים: | נבל |
| התרוממות ימנית: | 18h46m34.63s |
| סירוב: | +38°21'03.3" |
| גודל גלוי: | 8.107 |
| מרחק: | 37.023 פארסק |
| תנועה נכונה: | 16.2 |
| תנועה נכונה: | -84.1 |
| B-T magnitude: | 9.14 |
| V-T magnitude: | 8.193 |
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