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Ýlgili Makaleler
Temperature Behavior of Elemental Abundances in the Atmospheres of Magnetic Peculiar Stars
We analyze the temperature dependence of the abundances of the chemicalelements Si, Ca, Cr, and Fe in the atmospheres of normal, metallic-line(Am), magnetic peculiar (Ap), and pulsating magnetic peculiar (roAp)stars in the range 6000 15000 K. The Cr and Fe abundances in theatmospheres of Ap stars increase rapidly as the temperature rises from6000 to 9000 10000 K. Subsequently, the Cr abundance decreases to valuesthat exceed the solar abundance by an order of magnitude, while the Feabundance remains enhanced by approximately +1.0 dex compared to thesolar value. The temperature dependence of the abundances of theseelements in the atmospheres of normal and Am stars is similar in shape,but its maximum is several orders of magnitude lower than that observedfor Ap stars. In the range 6000 9500 K, the observed temperaturedependences for Ap stars are satisfactorily described in terms ofelement diffusion under the combined action of gravitational settlingand radiative acceleration. It may well be that diffusion also takesplace in the atmospheres of normal stars, but its efficiency is very lowdue to the presence of microturbulence. We show that the magnetic fieldhas virtually no effect on the Cr and Fe diffusion in Ap stars in therange of effective temperatures 6000 9500 K. The Ca abundance and itsvariation in the atmospheres of Ap stars can also be explained in termsof the diffusion model if we assume the existence of a stellar wind witha variable moderate rate of (2 4) × 10- 15 M ȯ yr-1.
| A Catalog of Temperatures and Red Cousins Photometry for the Hyades
Using Hyades photometry published by Mendoza and other authors,Pinsonneault et al. have recently concluded that Cousins V-I photometrypublished by Taylor & Joner is not on the Cousins system. Extensivetests of the Taylor-Joner photometry and other pertinent results aretherefore performed in this paper. It is found that in part, thePinsonneault et al. conclusion rests on (1) a systematic error inMendoza's (R-I)J photometry and (2) a small error in anapproximate Johnson-to-Cousins transformation published by Bessell. Forthe Taylor-Joner values of (V-R)C, it is found that there arepossible (though not definite) differences of several mmag with otherresults. However, the Taylor-Joner values of (R-I)C data aresupported at the 1 mmag level. Using the (R-I)C data andother published results, an (R-I)C catalog is assembled for146 Hyades stars with spectral types earlier than about K5. For singlestars with multiple contributing data, the rms errors of the catalogentries are less than 4.4 mmag. Temperatures on the Di Benedettoangular-diameter scale are also given in the catalog and are used tohelp update published analyses of high-dispersion values of [Fe/H] forthe Hyades. The best current mean Hyades value of [Fe/H] is found to be+0.103+/-0.008 dex and is essentially unchanged from its previous value.In addition to these numerical results, recommendations are made aboutimproving attitudes and practices that are pertinent to issues likethose raised by Pinsonneault et al.
| Differential photometry of speckle-interferometric binary and multiple stars
A method for differential photometry of speckle-interferometric binaryand multiple stars is presented. Both the accuracy and sources ofsystematic errors of the method are analysed. The photometric accuracyranges between 0.02 m and 0.20 m, depending on the atmospheric seeing,the brightness and the separation of the system components. A comparisonbetween our magnitude differences and those of other authors ispresented.
| Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential Photometry
Five hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory.
| Speckle interferometry of nearby multiple stars. II.
This paper is a continuation of diffraction-limited speckleinterferometry of binary and multiple stars carried out at the 6-mtelescope of the Special Astrophysical Observatory in Zelenchuk. Theprogram has concentrated on nearby (π>10 mas) close binariesdiscovered or measured during the Hipparcos mission. Here, we present132 measurements of relative positions and magnitude differences for 99pairs and 8 measurements for 6 triple systems. 54 entries in the paperare new Hipparcos binaries. New triple systems with late-type dwarfcomponents, discovered in the course of observations, are HIP 8533 andHIP 25354.Based on data collected at the Special Astrophysical Observatory,Russia.{Tables 1-3 are 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?/A+A/422/627
| 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 Archive of IUE Low-Dispersion Spectra of the White Dwarf Stars
We have produced an archive of the ultraviolet low-dispersion spectrafor the full set of white dwarf stars observed with the InternationalUltraviolet Explorer (IUE) satellite over the course of its 18 yrmission. This archive contains the spectra of 322 individual degeneratestars which have been processed to optimize the signal-to-noise for eachstar. In particular, all spectra have been corrected for residualtemporal and thermal effects and placed on the Hubble Space TelescopeFaint Object Spectrograph absolute flux scale using procedures describedby Massa & Fitzpatrick. Wherever possible, multiple observations ofindividual stars have been co-added to further enhance signal-to-noiseand have been combined into a single spectrum including the full 1150 to3150 Å wavelength region observed by IUE. The contents of thisspectral archive are described and the details of data reductionprocedures are provided, along with the url for access to the electronicfiles of the processed spectra.
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| What Is Happening at Spectral Type F5 in Hyades F Stars?
Aiming at a better understanding of the mechanisms heating thechromospheres, transition regions, and coronae of cool stars, we studyultraviolet, low-resolution Hubble Space Telescope/Space TelescopeImaging Spectrograph spectra of Hyades main-sequence F stars. We studythe B-V dependence(s) of the chromospheric and transition layer emissionline fluxes and their dependences on rotational velocities. We find thatthe transition layer emission line fluxes and also those of strongchromospheric lines decrease steeply between B-V=0.42 and 0.45, i.e., atspectral type F5, for which the rotational velocities also decreasesteeply. The magnitude of the line-flux decrease increases for lines ofions with increasing degree of ionization. This shows that the line-fluxdecrease is not due to a change in the surface filling factor but ratherdue to a change of the relative importance of different heatingmechanisms. For early F stars with B-V<0.42 we find for thetransition layer emission lines increasing fluxes for increasing vsini,indicating magnetohydrodynamic heating. The vsini dependence isstrongest for the high-ionization lines. On the other hand, the lowchromospheric lines show no dependence on vsini, indicating acousticshock heating for these layers. This also contributes to the heating ofthe transition layers. The Mg II and Ca II lines show decreasing fluxesfor increasing vsini, as long as vsini is less than ~40 kms-1. The coronal X-ray emission also decreases for increasingvsini, except for vsini larger than ~100 km s-1. We have atpresent no explanation for this behavior. For late F stars thechromospheric lines show vsini dependences similar to those observed forearly F stars, again indicating acoustic heating for these layers. Wewere unable to determine the vsini dependence of the transition layerlines because of too few single star targets. The decrease of emissionline fluxes at the spectral type F5, with steeply decreasing vsini,indicates, however, a decreasing contribution of magnetohydrodynamicheating for the late F stars. The X-ray emission for the late F starsincreases for increasing vsini, indicating magnetohydrodynamic heatingfor the coronae of the late F stars, different from the early F stars.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Incorporated,under NASA contract NAS5-26555.
| Speckle Observations of Binary Stars with the WIYN Telescope. II. Relative Astrometry Measures during 1998-2000
Five hundred twelve relative astrometry measures are presented for 253double stars, including 53 double stars discovered by Hipparcos. In 15cases, relative astrometry is reported for the first time for newlyconfirmed pairs. In addition, 20 high-quality nondetections ofcompanions are reported for stars suspected of being nonsingle byHipparcos. Observations were taken using a fast-readout CCD camerasystem at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparingthese measures with ephemeris predictions for binary stars with verywell known orbits, we find that the measurement precision is better than3 mas in separation and 1° in position angle per individualobservation. Measurement precision and detection capabilities are fullydiscussed, and confirmed orbital motion is reported in four cases of theHipparcos double star discoveries. The WIYN Observatory is a jointfacility of the University of Wisconsin-Madison, Indiana University,Yale University, and the National Optical Astronomy Observatory.
| A revised HRD for individual components of binary systems from BaSeL BVRI synthetic photometry. Influence of interstellar extinction and stellar rotation
Johnson BVRI photometric data for individual components of binarysystems have been provided by ten Brummelaar et al. (\cite{Brummelaar}).This is essential because non-interacting binaries can be considered astwo single stars and therefore play a critical role in testing andcalibrating single-star stellar evolution sets of isochrones and theimplicit theory. While they derived the effective temperature (T_eff)from their estimated spectral type, we infer metallicity-dependent T_efffrom a minimizing method fitting the B-V, V-R and V-I colours. For thispurpose, a grid of 621 600 flux distributions were computed from theBasel Stellar Library (BaSeL 2.2) of model-atmosphere spectra, and theirtheoretical colours compared with the observed photometry. The BaSeLcolours show a very good agreement with the BVRI metallicity-dependentempirical calibrations of Alonso et al. (\cite{Alonso}), with thetemperatures being different by 3+/-3% in the range 4000-8000 K fordwarf stars. Before deriving the metallicity-dependent T_eff from theBaSeL models, we paid particular attention to the influence of reddeningand stellar rotation. We inferred the reddening from two differentmethods: (i) the MExcessNg code v1.1 (Méndez & van Altena\cite{Mendez}) and (ii) neutral hydrogen column density data. Acomparison of both methods shows a good agreement for the sample locatedinside a local sphere of ~ 500 pc, but we point out a few directionswhere the MExcess model overestimates the E(B-V) colour excess.Influence of stellar rotation on the BVRI colours can be neglectedexcept for 5 stars with large v sin i, the maximum effect on temperaturebeing less than 5%. Our final determinations provide effectivetemperature estimates for each component. They are in good agreementwith previous spectroscopic determinations available for a few primarycomponents, and with ten Brummelaar et al. below ~ 10 000 K.Nevertheless, we obtain an increasing disagreement with theirtemperatures beyond 10 000 K. Finally, we provide a revisedHertzsprung-Russell diagram (HRD) for the systems with the moreaccurately determined temperatures.
| Speckle interferometry of nearby multiple stars
We present the results of diffraction-limited optical speckleinterferometry and infrared bispectrum speckle interferometry of 111double and 10 triple systems performed in 1998-1999 with the 6-mtelescope of the Special Astrophysical Observatory in Zelenchuk. Theobservations concentrated on nearby close binaries discovered during theHipparcos mission. Many nearby fast-orbiting low-mass binaries knownbefore Hipparcos were also included in the program. New companions werefirst resolved in 4 systems: HIP 5245, ADS 3179, Kui 99, and ADS 16138.In addition to accurate relative positions, magnitude differences weremeasured for most of the pairs. We combined our results with theHipparcos parallaxes to derive absolute magnitudes and spectral typesfor 63 binaries and 4 triples. Preliminary orbital elements and themass-sum are derived for HIP 689, and improved orbits are presented forHIP 16602 (CHR 117) and HIP 21280 (CHR 17). Based on data collected atthe Special Astrophysical Observatory, Russia Table 1 is only, and Table2 also, available in electronic form at the CDS via anonymons ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/385/87
| 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
| Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Radial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be ``Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Speckle Interferometry of Southern Double Stars. II. Measures from the CASLEO 2.15 Meter Telescope, 1995-1996
Relative astrometry is presented for 198 observations of 160 doublestars. The data were obtained at the 2.15 m telescope at the ComplejoAstronómico El Leoncito (Argentina) with a multianodemicrochannel array (MAMA) detector system. Five high-qualitynondetections are also reported. When judged against ephemeris positionsfor binaries with very well determined orbits, the separation residualsexhibit a root mean square deviation of13.2+3.4-1.9 mas and the position angle residualsexhibit rms deviation of 2.9d+0.8d-0.5d. Factorsaffecting the measurement precision are discussed.
| A Hipparcos study of the Hyades open cluster. Improved colour-absolute magnitude and Hertzsprung-Russell diagrams
Hipparcos parallaxes fix distances to individual stars in the Hyadescluster with an accuracy of ~ 6 percent. We use the Hipparcos propermotions, which have a larger relative precision than the trigonometricparallaxes, to derive ~ 3 times more precise distance estimates, byassuming that all members share the same space motion. An investigationof the available kinematic data confirms that the Hyades velocity fielddoes not contain significant structure in the form of rotation and/orshear, but is fully consistent with a common space motion plus a(one-dimensional) internal velocity dispersion of ~ 0.30 kms-1. The improved parallaxes as a set are statisticallyconsistent with the Hipparcos parallaxes. The maximum expectedsystematic error in the proper motion-based parallaxes for stars in theouter regions of the cluster (i.e., beyond ~ 2 tidal radii ~ 20 pc) isla 0.30 mas. The new parallaxes confirm that the Hipparcos measurementsare correlated on small angular scales, consistent with the limitsspecified in the Hipparcos Catalogue, though with significantly smaller``amplitudes'' than claimed by Narayanan & Gould. We use the Tycho-2long time-baseline astrometric catalogue to derive a set of independentproper motion-based parallaxes for the Hipparcos members. The newparallaxes provide a uniquely sharp view of the three-dimensionalstructure of the Hyades. The colour-absolute magnitude diagram of thecluster based on the new parallaxes shows a well-defined main sequencewith two ``gaps''/``turn-offs''. These features provide the first directobservational support of Böhm-Vitense's prediction that (the onsetof) surface convection in stars significantly affects their (B-V)colours. We present and discuss the theoretical Hertzsprung-Russelldiagram (log L versus log T_eff) for an objectively defined set of 88high-fidelity members of the cluster as well as the delta Scuti startheta 2 Tau, the giants delta 1, theta1, epsilon , and gamma Tau, and the white dwarfs V471 Tau andHD 27483 (all of which are also members). The precision with which thenew parallaxes place individual Hyades in the Hertzsprung-Russelldiagram is limited by (systematic) uncertainties related to thetransformations from observed colours and absolute magnitudes toeffective temperatures and luminosities. The new parallaxes providestringent constraints on the calibration of such transformations whencombined with detailed theoretical stellar evolutionary modelling,tailored to the chemical composition and age of the Hyades, over thelarge stellar mass range of the cluster probed by Hipparcos.
| Binary star speckle measurements at Calar Alto. I.
We present the first results of our speckle interferometric measurementsof binary stars made with the ICCD speckle camera using the 1.52-mtelescope of the Observatorio Astronomico Nacional at Calar Alto (Spain)in September, 1999. The data contain 123 observations of 83 systems. Themeasured angular separations range from 0farcs153 to 6farcs727 . We haveused there new speckle measurements to improve the orbital elements forthe binaries COU 247 and BU 524 AB.
| Lithium.
Electronic Article Available from Elsevier Science.
| 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.
| Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory
We present photometric and astrometric results for 36 binary systemsobserved with the natural guide star adaptive optics system of the MountWilson Institute on the 100 inch (2.5 m) Hooker Telescope. Themeasurements consist of differential photometry in U, B, V, R, and Ifilters along with astrometry of the relative positions of systemcomponents. Magnitude differences were combined with absolute photometryfound in the literature of the combined light for systems to obtainapparent magnitudes for the individual components at standardbandpasses, which in turn led to color determinations and spectraltypes. The combination of these results with Hipparcos parallaxmeasurements yielded absolute magnitudes and allowed us to plot thecomponents on an H-R diagram. To further examine the reliability andself-consistency of these data, we also estimated system masses from thespectral types. Based on observations made at Mount Wilson Observatory,operated by the Mount Wilson Institute under an agreement with theCarnegie Institution of Washington.
| Kinematics versus X-ray luminosity segregation in the Hyades
State of the art Tycho-2 proper motions of bona fide Hyades members areused in combination with the ROSAT X-ray survey of this open cluster inStern et al. (1995) to study the internal velocity dispersion versusX-ray luminosity by the classical convergent point method. It is shownin this paper for the Hyades members with B-V below 0.7 mag that starsbrighter than 1.3x 1029 erg s-1 (0.1-1.8 keV) havemuch more coherent motions than those with smaller X-ray luminositiesand those not detected by ROSAT at all. In fact, the proper motions ofthe X-ray luminous members are in agreement with a null internaldispersion of velocities for this subpopulation, whereas theintermediate bright X-ray stars exhibit a dispersion at 320 ms-1. The non-emitters, despite their being more massive andoptically brighter, have a velocity dispersion of about 440 ms-1. Probably related to this fact, the strong X-ray emittersare more concentrated within the tidal radius (10 pc) of the clustercentre than the non-emitters. Nearly half of strong X-ray emitters withcoherent motions are visual or orbiting pairs with typical separations 5to 50 AU. This find implies that a group of intermediate mass (1.0 to1.5 solar masses) stars in the Hyades is significantly younger than therest and their system is not yet dynamically relaxed.
| Speckle Observations of Binary Stars with the WIYN Telescope. I. Measures During 1997
Two hundred seventy-seven position angle and separation measures of 154double stars are presented. Three of the systems were previously unknownto be double, and 16 other systems were discovered earlier this decadeby the Hipparcos satellite. Measures are derived from speckleobservations taken with the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5 mtelescope located at Kitt Peak, Arizona. Speckle images were obtainedusing two different imaging detectors, namely, a multianode microchannelarray (MAMA) detector and a fast-readout CCD. A measurement precisionstudy was performed on a sample of binaries with extremely well knownorbits by comparing the measures obtained here to the ephemerispredictions. For the CCD, the root mean square (rms) deviation ofresiduals was found to be 3.5 milliarcseconds (mas) in separation and1.2d in position angle, while the residuals of the MAMA data varieddepending on the magnification used and seeing conditions but can becomparable or superior to the CCD values. In addition, the two cameraswere compared in terms of the detection limit in total magnitude andmagnitude difference of the systems under study. The MAMA system has theability to detect some systems with magnitude differences larger than3.5, although reliable astrometry could not be obtained on theseobjects. Reliable astrometry was obtained on a system of magnitudedifference of 5.3 with the CCD system.
| Chemical abundances of A and F-type stars: the Hyades open cluster
Abundances of 11 chemical elements have been determined for 29 F and 19A dwarfs (``normal'' and chemically peculiar with apparent rotationalvelocities ranging from 11 to 237 km.s^{-1}) members of the Hyadescluster using Takeda's (1995) iterative procedure well suited for fastrotators. High quality spectra of high to moderate resolution have beensynthesized to derive the apparent rotational velocities, microturbulentvelocities and abundances of C, O, Na, Mg, Si, Ca, Sc, Fe, Ni, Y and Ba.For the F stars, the found abundances are compared to the predictions ofTurcotte et al.'s (1998) evolutionary models for the age of the Hyades.We fail to find the expected underabundances for light elements nor theoverabundances for the iron-peak elements for stars having effectivetemperatures greater than 6500 K. This suggests that diffusion alonecannot account for the derived abundances: other transport processeswhich counteract diffusion are probably at play. For the A stars,abundances of Na, Mg, Si, Ca, Fe, Ni and Ba are anticorrelated(correlated for O) with the apparent equatorial velocities forve\sin i higher than ~ 100 km.s^{-1}. Below this value, wefind no correlation in agreement with the predictions of Charbonneau& Michaud (1991) except possibly for the abundance of Ni which mightbe anticorrelated with ve\sin i. The fastest rotators(ve\sin i >= 150 km.s^{-1}) are strongly depletted in Mg,Si, Ca, Fe, Ni and Ba (between -0.3 dex and -0.94 dex) while their Oabundance is normal. Based on observations collected at Observatoire deHaute Provence (France)
| 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
| Oxygen and Nitrogen Abundances in Hyades F Type Dwarfs
The abundances of oxygen and nitrogen were investigated for elevenHyades F type main-sequence stars, based on the line-profile of O I (+FeI) 8446 and the equivalent-widths of N I 8629/8683, in order to examinewhether any conspicuous abundance deficiency exists for O and N at T_eff~ 6700 K similar to that observed for Li, since its possibility wassuggested by the diffusion interpretation of this ``Li-chasm''. Itturned out, however, that the abundances appear to be nearly independentof T_eff (and v_e sin i ) for both O and N, without showing any apparentdip larger than ~ 0.2 dex (for O) or ~ 0.3 dex (for N), being consistentwith the results of García-Lopez et al.'s (1993, AAA 58.114.068)study for oxygen. This may indicate that the diffusion process alone isprobably not responsible for the origin of the Li-gap. Regarding theaveraged O and N abundances in these Hyades F stars, a moderate N-excessby ~ 0.3 dex relative to the Sun was suggested (though not definite),with oxygen being nearly normal.
| Color indices of the Sun and Hyades stars in the WBVR system
Using an original setup at high altitudes, we measured the color indicesof the Sun in the WBVR photometric system relative to standard stars: (W- B)_solar = -0.05, (B - V)_solar = +0.67, and (V - R)_solar = +0.53. Wepresent the WBVR photometry for the Hyades members selected by vanBueren by their space velocities. The solar position is shown intwo-color diagrams relative to Hyades stars and bright G2 V stars. Acomparison of our results with Kurucz's models reveals a discrepancybetween the metallicities of the models and the Hyades members.
| The Age Range of Hyades Stars
On the basis of canonical models, the age of Hyades supercluster stars,whether in the Hyades and Praesepe clusters or the noncluster field,ranges from (5-6) x 10^8 to 10^9 yr. The difference between the parallaxderived from the supercluster motion and that obtained from Hipparcosobservations has a dispersion only twice that of the mean dispersion ofthe individual Hipparcos values. The supercluster appears not to containred giants on the first ascent of the red giant branch, but onlyasymptotic giant branch (``clump'') stars. The masses obtained forindividual components of binary stars in the supercluster show adispersion of less than 10% when compared with model predictions.
| The Multiplicity of the Hyades and Its Implications for Binary Star Formation and Evolution
A 2.2 μm speckle imaging survey of 167 bright (K < 8.5 mag) Hyadesmembers reveals a total of 33 binaries with separations spanning 0.044"to 1.34" and magnitude differences as large as 5.5 mag. Of thesebinaries, 9 are new detections and an additional 20 are now spatiallyresolved spectroscopic binaries, providing a sample from which dynamicalmasses and distances can be obtained. The closest three systems,marginally resolved at Palomar Observatory, were reobserved with the 10m Keck Telescope in order to determine accurate binary star parameters.Combining the results of this survey with previous radial velocity,optical speckle, and direct-imaging Hyades surveys, the detectedmultiplicity of the sample is 98 singles, 59 binaries, and 10 triples. Astatistical analysis of this sample investigates a variety of multiplestar formation and evolution theories. Over the binary separation range0.1"-1.07" (5-50 AU), the sensitivity to companion stars is relativelyuniform, with = 4 mag, equivalent to a mass ratio = 0.23. Accounting for the inability to detect high fluxratio binaries results in an implied companion star fraction (CSF) of0.30 +/- 0.06 in this separation range. The Hyades CSF is intermediatebetween the values derived from observations of T Tauri stars (CSF_TTS =0.40 +/- 0.08) and solar neighborhood G dwarfs (CSF_SN = 0.14 +/- 0.03).This result allows for an evolution of the CSF from an initially highvalue for the pre-main sequence to that found for main-sequence stars.Within the Hyades, the CSF and the mass ratio distribution provideobservational tests of binary formation mechanisms. The CSF isindependent of the radial distance from the cluster center and theprimary star mass. The distribution of mass ratios is best fitted by apower law q^-1.3+/-0.3 and shows no dependence on the primary mass,binary separation, or radial distance from the cluster center. Overall,the Hyades data are consistent with scale-free fragmentation, butinconsistent with capture and disk-assisted capture in small clusters.Without testable predictions, scale-dependent fragmentation and diskfragmentation cannot be assessed with the Hyades data.
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| Takýmyýldýz: | Avci |
| Sað Açýklýk: | 04h51m12.53s |
| Yükselim: | +11°04'04.9" |
| Görünürdeki Parlaklýk: | 6.75 |
| Uzaklýk: | 49.628 parsek |
| özdevim Sað Açýklýk: | 85.4 |
| özdevim Yükselim: | -12 |
| B-T magnitude: | 7.418 |
| V-T magnitude: | 6.806 |
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