Contents
Images
Upload your image
DSS Images Other Images
Related articles
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
| The impact of stellar duplicity on planet occurrence and properties. I. Observational results of a VLT/NACO search for stellar companions to 130 nearby stars with and without planets
Context: Although it is commonly agreed that the presence of a closestellar companion is likely to affect planet formation and evolution,the precise effects and their actual impact on planet occurrence arestill debated. Different conclusions have been reached on thetheoretical side, while observational constraints are sparse, aconsequence of the discrimination against close binaries in Dopplerplanet searches. Accordingly, basic questions such as how hospitablebinaries are to planets and how binary separation and mass ratio impacton planet formation, remain poorly known. Aims: In an effort to bringobservational constraints on the occurrence and properties of planets inbinaries and multiple stars, we have been conducting a dedicatedinvestigation, the results of which will be presented in this series. Methods: Our investigation follows two different approaches, one basedon radial-velocity monitoring, the other based on direct imaging. Inthis first paper, we present the observational results from oursystematic adaptive optics search with VLT/NACO for close stellarcompanions to 130 nearby stars, 57 with planets and 73 without, forcomparison. The inclusion of a control sub-sample is a unique feature ofour program that will enable a meaningful and rigorous comparisonbetween the properties of planet-host stars and the properties of fieldstars subject to the same selection effects against close binaries, butshowing no evidence for planetary companions. Results: Our data reveal95 companion candidates found in the vicinity of 33 of our targets.Nineteen of these candidates are true companions and 2 are likely boundobjects. Among planet-host stars, we discovered a tight pair of very lowmass companions to HD 65216 (projected separation of 255 AU), an early Mcompanion to HD 177830 (projected separation of 97 AU), and we resolvedthe previously known companion to HD 196050 into a close pair of Mdwarfs. Our data additionally confirm the bound nature of the companionsto HD 142, HD 16141, and HD 46375. Among control stars, we detected truecompanions to HD 7895, HD 24331, HD 31412, HD 40397, HD 43834, HD 70923,HD 78351, HD 104263, HD 129642, HD 154682, and HD 223913, and likelybound companions to HD 82241 and HD 134180. Most of these objects are Mdwarfs and have projected separations between 7 and 505 AU.Based on observations collected at the ESO VLT Yepun telescope,proposals 70.C-0557, 71.C-0125, 73.C-0124, 74.C-0048, 75.C-0069, and76.C-0057. Tables 1, 2, and Figs. 3, 4 are only available in electronicform at http://www.aanda.org
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| 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
| Additional TWA members?. Spectroscopic verification of kinematically selected TWA candidates
We present spectroscopic measurements of the 23 new candidate members ofthe TW Hydrae Association from \citet{MF}. Based on Hα and Li 6708Å strengths together with location on a color-magnitude diagramfor Hipparcos TWA candidates, we found only three possible new members(TYC 7760-0835-1, TYC 8238-1462-1, and TYC 8234-2856-1) in addition tothe already known member, TWA 19. This eliminated most of the candidatesmore distant than 100 pc. Three Tycho stars, almost certainly members ofthe Lower Centaurus Crux association, are the most distant members ofthe TWA. A claim of isotropic expansion of TWA has to be re-evaluatedbased on our new results. Generally, one cannot identify new members ofa diffuse nearby stellar group based solely on kinematic data. Toeliminate interlopers with similar kinematics, spectroscopicverification is essential.
| Internal kinematics of the TW Hya association of young stars
Thirty one probable kinematic members of the nearby TW Hya associationof young stars are selected from the RASSBSC/Tycho-2 sample of starsluminous in X-rays, detected by ROSAT. Eight of them have been listedalready as members of the association, and 23 are new candidates. Theassociation occupies a volume of some 106 pc3, thenearest member being at a distance of only 17.5 pc from the Sun. Thelower bound internal velocity dispersion is estimated at 0.8 kms-1, which is considerably larger than is expected in agravitationally bound open cluster. The total mass of the group isestimated at 31 solar masses. The centre of mass lies at 73 pc from usin the direction close to the position of the prototype star TW Hya. Arealistic kinematical model fitting both the observed trigonometricparallaxes and radial velocities involves a linear expansion of thegroup with the rate 0.12 km s-1 pc-1, whichdefines a dynamical age of 8.3 Myr, in good agreement with previous ageestimations for T Tauri members. Likewise the nearby Carina-Vela movinggroup of X-ray stars, the TW Hya association appears to be an outpost ofthe Gould Belt structure rather than an isolated open cluster.
| 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.
| Pre-Main-Sequence Stars in the Pleiades Supercluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1749E&db_key=AST
| Secondary UVBY standards in the Harvard E-regions
Photoelectric uvby photometry for 201 stars which are already UBV (RI)cstandards is presented. The photoelectric data are closely tied to theCousins uvby standards and the stars should be suitable for use asfainter (7-11 mag) secondary standards.
| Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| UBV photometry of E region standard stars of intermediate brightness
Photometry data are given for 335 stars in the nine E regions.Observations were made using a photometer and filters on the 47 cmreflector at Cape Town. The stellar dispersions are summarized. Data arepresented in tabular form.
| Photometric standard stars for the UBV and (RI)KC systems.
Not Available
| Fainter Standards for VRI Photometry in the E Regions
Not Available
| Photoelectric photometry of late type stars in the direction opposed to galactic rotation
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...16..269G&db_key=AST
| Three-color photometry of the components in 228 wide double and multiple systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963AJ.....68..483E&db_key=AST
| Standard magnitudes in the E regions.
Not Available
| Fundamental data for southern stars (First list)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1957MNRAS.117..534E&db_key=AST
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | ほ座 |
| Right ascension: | 09h29m28.57s |
| Declination: | -44°31'56.5" |
| Apparent magnitude: | 6.982 |
| Distance: | 39.667 parsecs |
| Proper motion RA: | -92.6 |
| Proper motion Dec: | 13 |
| B-T magnitude: | 7.567 |
| V-T magnitude: | 7.031 |
Catalogs and designations:
|
