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The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| Comparative statistics and origin of triple and quadruple stars
The statistics of catalogued quadruple stars consisting of two binaries(hierarchy 2 + 2), is studied in comparison with triple stars, withrespective sample sizes of 81 and 724. Seven representative quadruplesystems are discussed in greater detail. The main conclusions are asfollows. (i) Quadruple systems of ? Lyr type with similar massesand inner periods are common, in 42 per cent of the sample the outermass ratio is above 0.5 and the inner periods differ by less than 10times. (ii) The distributions of the inner periods in triple andquadruple stars are similar and bimodal. The inner mass ratios do notcorrelate with the inner periods. (iii) The statistics of outer periodsand mass ratios in triples and quadruples are different. The medianouter mass ratio in triples is 0.39 independently of the outer period,which has a smooth distribution. In contrast, the outer periods of 25per cent quadruples concentrate in the narrow range from 10 to 100yr,the outer mass ratios of these tight quadruples are above 0.6 and theirtwo inner periods are similar to each other. (iv) The outer and innermass ratios in triple and quadruple stars are not mutually correlated.In 13 per cent of quadruples both inner mass ratios are above 0.85(double twins). (v) The inner and outer orbital angular momenta andperiods in triple and quadruple systems with inner periods above 30dshow some correlation, the ratio of outer-to-inner periods is mostlycomprised between 5 and 104. In the systems with small periodratios the directions of the orbital spins are correlated, while in thesystems with large ratios they are not. The properties of multiple starsdo not correspond to the products of dynamical decay of small clusters,hence the N-body dynamics is not the dominant process of theirformation. On the other hand, rotationally driven (cascade)fragmentation possibly followed by migration of inner and/or outerorbits to shorter periods is a promising scenario to explain the originof triple and quadruple stars.
| Masses, Luminosities, and Orbital Coplanarities of the ? Orionis Quadruple-Star System from Phases Differential Astrometry
? Orionis was identified by spectroscopic studies as a quadruple-starsystem. Seventeen high-precision differential astrometry measurements of? Ori have been collected by the Palomar High-precision AstrometricSearch for Exoplanet Systems (PHASES). These show both the motion of thelong-period binary orbit and short-period perturbations superimposed onthat caused by each of the components in the long-period system beingthemselves binaries. The new measurements enable the orientations of thelong-period binary and short-period subsystems to be determined. Recenttheoretical work predicts the distribution of relative inclinationsbetween inner and outer orbits of hierarchical systems to peak near 40and 140 degrees. The degree of coplanarity of this complex system isdetermined, and the angle between the planes of the A-B and Aa-Ab orbitsis found to be 136.7 ± 8.3 degrees, near the predicteddistribution peak at 140 degrees; this result is discussed in thecontext of the handful of systems with established mutual inclinations.The system distance and masses for each component are obtained from acombined fit of the PHASES astrometry and archival radial velocityobservations. The component masses have relative precisions of 5%(component Aa), 15% (Ab), and 1.4% (each of Ba and Bb). The median sizeof the minor axes of the uncertainty ellipses for the new measurementsis 20 micro-arcseconds (?as). Updated orbits for ? Equulei,? Pegasi, and V819 Herculis are also presented.
| The uvbyHβ Metallicity Calibration for G and K Dwarfs
The metallicity dependence of the primary indices of the uvbyphotometric system for cooler dwarfs (Te ~ 6500-5000 K) isinvestigated. The database for the analysis is composed of the overlapbetween a composite catalog of selected, high-dispersion spectroscopicabundances for 1801 stars on the metallicity scale of Valenti &Fischer and a merged catalog of high-precision uvbyHβ photometryfor over 35,000 stars. While [Fe/H] for F dwarfs is best estimated fromm1, with a modest dependence on c1 as expected,for hotter G dwarfs the pattern reverses, and c1 becomes thedominant index. For cooler G dwarfs and K stars, the c1dominance continues, but a discontinuity appears such that stars betweenb - y = 0.50 and 0.58 with [Fe/H] >= +0.25 have m1 andc1 indices that classify them as subgiants, confirming anearlier result based on a much smaller sample. The reversal in thesensitivity to m1 and c1 is traced, in part, tothe metallicity sensitivity of the b - y index. Moreover, b - y growslarger in a nonlinear fashion for stars above solar metallicity, leadingto an overestimate of the reddening for super-metal-rich stars from somestandard intrinsic color relations. Based on successful tests usingindices from synthetic spectra and the empirical trends among theobservations, metallicity calibrations tied to Hβ rather than b - yhave been derived for [Fe/H] >= -1.0, generating dispersions amongthe residuals ranging from 0.061 to 0.085 dex over the entiretemperature range of interest. The new calibrations have the addedadvantage of being significantly less sensitive to errors in reddeningthan previous calibrations.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Analysis of the Dynamical Instability of Several Multiple Stars with Weak Hierarchy
The dynamical stability of 16 multiple stars is analyzed using MonteCarlo simulations with allowance for the errors in the observationaldata. The analysis was carried out by varying the uncertainties in theinitial observational data. Six different stability criteria wereconsidered, and the dynamical evolution was studied using numericalsimulations. Eleven of the systems are probably stable, whereas fivesystems (HD 40887, HD 136176, HD 150680, HD 217675, and HD 222326) areprobably unstable (the probability that they are unstable is 0.94 ormore accordingt o the results of forward and backward simulations overintervals of 106 yr). The results of the simulations were mostconsistent with the criteria of Mardling-Aarseth (the correlationcoefficient between the probabilities of disruption inferred from thestability criterion and numerical integration was r = 0.998),Valtonen-Karttunen (r = 0.998), and Eggleton-Kiseleva (r = 0.997). Inabout 92 93% of all cases, these criteria yield results that areconsistent with the numerical simulations. These criteria also yieldhigh disruption probabilities for the unstable systems. Scenarios forthe formation of such systems are discussed: temporary capture of afield star by a close binary, perturbation of a stable multiple systemby a massive field object, and disruption of small stellar groups orclusters. The probabilities that these scenarios are realized areanalyzed.
| Analysis of the Dynamic Stability of Selected Multiple Stars with Weak Hierarchy
The stability of multiple systems with known orbital elements and withsubsystems occupying adjacent hierarchy levels is analyzed using sixstability criteria and numerical simulations of their dynamicalevolution. All the stability criteria considered are in qualitativeagreement with the numerical computations. Of the 16 systems studied, 11are confirmed to be stable and five (HD 40887, HD 136176, HD 150680, HD217675, and HD 222326) may be unstable on time scales of 106 yr orless. The small dynamical ages of the unstable systems may indicate thatthey have captured components during encounters between close binariesand field or moving cluster stars. The instability could also resultfrom the perturbation of a stable system when it approaches a massiveobject (star, black hole, or molecular cloud). It is possible that someof the unstable systems are remnants of small clusters or stellargroups.
| 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
| 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.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| A Multiplicity Survey of Chromospherically Active and Inactive Stars
Surveys of three samples of solar-type stars, segregated bychromospheric emission level, were made to determine their multiplicityfractions and to investigate the evolution of multiplicity with age. Intotal, 245 stars were searched for companions with DeltaV <= 3.0 andseparations of 0.035" to 1.08" using optical speckle interferometry. Byincorporating the visual micrometer survey for duplicity of theLamontHussey Observatory, the angular coverage was extended to 5.0" withno change in the DeltaV limit. This magnitude difference allows massratios of 0.63 and larger to be detected throughout a search region of2-127 AU for the stars observed. The 84 primaries observed in thechromospherically active sample are presumably part of a youngpopulation and are found to have a multiplicity fraction of 17.9% +/-4.6%. The sample of 118 inactive, presumably older, primaries wereselected and observed using identical methods and are found to have amultiplicity fraction of only 8.5% +/- 2.7%. Given the known linkbetween chromospheric activity and age, these results tentatively implya decreasing stellar multiplicity fraction from 1 to 4 Gyr, theapproximate ages of the two samples. Finally, only two of the 14 veryactive primaries observed were found to have a companion meeting thesurvey detection parameters. In this case, many of the systems areeither very young, or close, RS CVn type multiples that are unresolvableusing the techniques employed here.
| A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars
More than 800 southern stars within 50 pc have been observed forchromospheric emission in the cores of the Ca II H and K lines. Most ofthe sample targets were chosen to be G dwarfs on the basis of colors andspectral types. The bimodal distribution in stellar activity first notedin a sample of northern stars by Vaughan and Preston in 1980 isconfirmed, and the percentage of active stars, about 30%, is remarkablyconsistent between the northern and southern surveys. This is especiallycompelling given that we have used an entirely different instrumentalsetup and stellar sample than used in the previous study. Comparisons tothe Sun, a relatively inactive star, show that most nearby solar-typestars have a similar activity level, and presumably a similar age. Weidentify two additional subsamples of stars -- a very active group, anda very inactive group. The very active group may be made up of youngstars near the Sun, accounting for only a few percent of the sample, andappears to be less than ~0.1 Gyr old. Included in this high-activitytail of the distribution, however, is a subset of very close binaries ofthe RS CVn or W UMa types. The remaining members of this population maybe undetected close binaries or very young single stars. The veryinactive group of stars, contributting ~5%--10% to the total sample, maybe those caught in a Maunder Minimum type phase. If the observations ofthe survey stars are considered to be a sequence of snapshots of the Sunduring its life, we might expect that the Sun will spend about 10% ofthe remainder of its main sequence life in a Maunder Minimum phase.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| The chemical evolution of the solar neighborhood. I - A bias-free reduction technique and data sample
The possible ways of measuring the age-metallicity relation for thegalactic disk in the neighborhood of the sun are discussed. It is shownthat the use of a field star sample chosen on the basis of effectivetemperature introduces a bias which results in a monotonic increase inthe metal abundance of the disk with time. However, if theage-metallicity relation for the disk can be shown to satisfy certaincriteria, the bias introduced in such a sample can be neglected: thegalactic disk apparently satisfies the criteria. It is concluded that asample analyzed through the use of uvby and H(beta) photometry inconjunction with a self-consistent set of theoretical isochronesprovides the least biased, most accurate estimate of the age-metallicityrelation for the disk.
| Photoelectric photometry of galactic cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1957MNRAS.117..406E&db_key=AST
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Pozíciós és asztrometriai adatok
| Csillagkép: | Dél Keresztje |
| Rektaszcenzió: | 12h28m16.87s |
| Deklináció: | -61°45'56.9" |
| Vizuális fényesség: | 7.254 |
| Távolság: | 48.567 parszek |
| RA sajátmozgás: | 83.1 |
| Dec sajátmozgás: | -150.4 |
| B-T magnitude: | 8.082 |
| V-T magnitude: | 7.323 |
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