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uvby - β Photoelectric Photometry of the Open Cluster α Per
Absolute photoelectric photometry of stars in the direction of the OpenCluster α Per has been secured and is presented along with ananalysis reinforced with all the available data in Strömgrenuvby-β photometry compiled from the literature. Cluster membershipis analyzed and the physical characteristics of the stars have beendeduced. The membership determined in this paper is compared with thatof proper motion studies and Hipparcos.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| An extensive library of 2500 10 500 Å synthetic spectra
We present a complete library of synthetic spectra based on Kurucz'scodes that covers the 2500 10 500 Å wavelength range at resolvingpowers R{P}=20 000, 11 500 (≡GAIA), 8500 (≡RAVE),2000 (≡SLOAN) and uniform dispersions of 1 and 10 Å/pix. Thelibrary maps the whole HR diagram, exploring 51 288 combinations ofatmospheric parameters spanning the ranges: 3500 ≤ T_eff ≤ 47500 K, 0.0≤ log g ≤ 5.0 , -2.5 ≤ [M/H] ≤ 0.5, [α/Fe] = 0.0,+0.4, ξ = 1, 2, 4 km s-1, 0 ≤ V_rot≤ 500 km s-1. The spectra are available both as absolutefluxes as well as continuum normalized. Performance tests andspectroscopic applications of the library are discussed, includingautomatic classification of data from spectroscopic surveys like RAVE,SLOAN, GAIA. The entire library of synthetic spectra is accessible viathe web.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Spectroscopy, Photometry and Micro-arcsec Astrometry of Binaries with the GAIA Space Mission and with the RAVE Experiment
The GAIA astrometric mission of ESA will be very efficient indiscovering binary and multiple stars with any orbital period, fromminutes to millions of years. The main parameters of the revised missiondesign are presented. Next we estimate the fraction of binary starsdiscovered by means of astrometry, photometry and on-board spectroscopy.Finally we summarize observations that confirm the ability to measurephysical parameters like masses, radii and spectroscopic distance fromGAIA data alone. GAIA will fly only in 2010, but the radial velocityexperiment (RAVE) has started this year. We show that its spectroscopicobservations have the capacity to discover a large fraction of so farunknown binary systems.
| 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
| An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks
We have assembled a database of stars having both masses determined frommeasured orbital dynamics and sufficient spectral and photometricinformation for their placement on a theoretical H-R diagram. Our sampleconsists of 115 low-mass (M<2.0 Msolar) stars, 27pre-main-sequence and 88 main-sequence. We use a variety of availablepre-main-sequence evolutionary calculations to test the consistency ofpredicted stellar masses with dynamically determined masses. Despitesubstantial improvements in model physics over the past decade, largesystematic discrepancies still exist between empirical and theoreticallyderived masses. For main-sequence stars, all models considered predictmasses consistent with dynamical values above 1.2 Msolar andsome models predict consistent masses at solar or slightly lower masses,but no models predict consistent masses below 0.5 Msolar,with all models systematically underpredicting such low masses by5%-20%. The failure at low masses stems from the poor match of mostmodels to the empirical main sequence below temperatures of 3800 K, atwhich molecules become the dominant source of opacity and convection isthe dominant mode of energy transport. For the pre-main-sequence samplewe find similar trends. There is generally good agreement betweenpredicted and dynamical masses above 1.2 Msolar for allmodels. Below 1.2 Msolar and down to 0.3 Msolar(the lowest mass testable), most evolutionary models systematicallyunderpredict the dynamically determined masses by 10%-30%, on average,with the Lyon group models predicting marginally consistent masses inthe mean, although with large scatter. Over all mass ranges, theusefulness of dynamical mass constraints for pre-main-sequence stars isin many cases limited by the random errors caused by poorly determinedluminosities and especially temperatures of young stars. Adopting awarmer-than-dwarf temperature scale would help reconcile the systematicpre-main-sequence offset at the lowest masses, but the case for this isnot compelling, given the similar warm offset at older ages between mostsets of tracks and the empirical main sequence. Over all age ranges, thesystematic discrepancies between track-predicted and dynamicallydetermined masses appear to be dominated by inaccuracies in thetreatment of convection and in the adopted opacities.
| Evaluating GAIA performances on eclipsing binaries. I. Orbits and stellar parameters for V505 Persei, V570 Persei and OO Pegasi
The orbits and physical parameters of three detached, double-lined A-Feclipsing binaries have been derived combining HP,VT, BT photometry from the Hipparcos/Tycho missionwith 8500-8750 Å ground-based spectroscopy, mimicking thephotometric+spectroscopic observations that should be obtained by GAIA,the approved Cornerstone 6 mission by ESA. This study has two mainobjectives, namely (a) to derive reasonable orbits for a number of neweclipsing binaries and (b) to evaluate the expected performances by GAIAon eclipsing binaries and the accuracy achievable on the determinationof fundamental stellar parameters like masses and radii. It is shownthat a 1% precision in the basic stellar parameters can be achieved byGAIA on well observed detached eclipsing binaries provided that thespectroscopic observations are performed at high enough resolution.Other types of eclipsing binaries (including semi-detached and contacttypes) and different spectral types will be investigated in subseguentpapers in this series.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Eigenbewegungen in der Umgebung von α Persei
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| Takýmyýldýz: | Kahraman |
| Sað Açýklýk: | 03h09m34.94s |
| Yükselim: | +48°37'28.7" |
| Görünürdeki Parlaklýk: | 8.094 |
| Uzaklýk: | 117.233 parsek |
| özdevim Sað Açýklýk: | 47.1 |
| özdevim Yükselim: | -39.8 |
| B-T magnitude: | 8.641 |
| V-T magnitude: | 8.14 |
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