Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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.
| Time scales of Li evolution: a homogeneous analysis of open clusters from ZAMS to late-MS
We have performed a new and homogeneous analysis of all the Li dataavailable in the literature for main sequence stars (spectral-types fromlate F to K) in open clusters. In the present paper we focus on adetailed investigation of MS Li depletion and its time scales for starsin the 6350-5500 K effective temperature range. For the first time, wewere able to constrain the age at which non-standard mixing processes,driving MS Li depletion, appear. We have also shown that MS Li depletionis not a continuous process and cannot be simply described by at-α law. We confirm that depletion becomes ineffectivebeyond an age of 1-2 Gyr for the majority of the stars, leading to a Liplateau at old ages. We compared the empirical scenario of Li as afunction of age with the predictions of three non-standard models. Wefound that models including only gravity waves as main mixing processare not able to fit the Li vs. age pattern and thus this kind of mixingcan be excluded as the predominant mechanism responsible for Lidepletion. On the other hand, models including slow mixing induced byrotation and angular momentum loss, and in particular those includingalso diffusive processes not related to rotation, can explain to someextent the empirical evidence. However, none of the currently proposedmodels can fit the plateau at old ages.
| 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.
| 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
| 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
| 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.
| 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.
| The Hyades: distance, structure, dynamics, and age
{We use absolute trigonometric parallaxes from the Hipparcos Catalogueto determine individual distances to members of the Hyades cluster, fromwhich the 3-dimensional structure of the cluster can be derived.Inertially-referenced proper motions are used to rediscuss distancedeterminations based on convergent-point analyses. A combination ofparallaxes and proper motions from Hipparcos, and radial velocities fromground-based observations, are used to determine the position andvelocity components of candidate members with respect to the clustercentre, providing new information on cluster membership: 13 newcandidate members within 20 pc of the cluster centre have beenidentified. Farther from the cluster centre there is a gradual mergingbetween certain cluster members and field stars, both spatially andkinematically. Within the cluster, the kinematical structure is fullyconsistent with parallel space motion of the component stars with aninternal velocity dispersion of about 0.3 km s(-1) . The spatialstructure and mass segregation are consistent with N-body simulationresults, without the need to invoke expansion, contraction, rotation, orother significant perturbations of the cluster. The quality of theindividual distance determinations permits the cluster zero-age mainsequence to be accurately modelled. The helium abundance for the clusteris determined to be Y =3D 0.26+/-0.02 which, combined with isochronemodelling including convective overshooting, yields a cluster age of625+/-50 Myr. The distance to the observed centre of mass (a conceptmeaningful only in the restricted context of the cluster memberscontained in the Hipparcos Catalogue) is 46.34+/-0.27 pc, correspondingto a distance modulus m-M=3D3.33+/-0.01 mag for the objects within 10 pcof the cluster centre (roughly corresponding to the tidal radius). Thisdistance modulus is close to, but significantly better determined than,that derived from recent high-precision radial velocity studies,somewhat larger than that indicated by recent ground-based trigonometricparallax determinations, and smaller than those found from recentstudies of the cluster convergent point. These discrepancies areinvestigated and explained. } Based on observations made with the ESAHipparcos astrometry satellite. Table~2 is also available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html
| A New and Comprehensive Determination of the Distance to Member Stars of the Hyades
This paper critiques the methods used in the past for estimating thedistances to the stars that make up the Hyades moving cluster, anddevelops one which is new and comprehensive. We develop a formalism forthe application of stochastic restrictions to the adjustment parameters(velocity components and distances) and test it on constructed clustermodels. We perform model calculations with fictitious model starclusters in which the `true' values of the input parameters (ie.positions, distances and velocity components) are therefore known. Thecomparison of the distances recovered by different methods with the trueinput distances shows our approach to be very superior to thetraditional ones that estimate distances by the method of streamparallaxes without restricting the adjustment parameters. Applying ouralgorithm to the Hyades, we assume a dispersion of 0.25 kps in eachcoordinate about a common value for the velocity components of thecluster members and a dispersion of 5pc about the distance to thecluster's centre for the distances to the stars in the cluster. Underthese stochastic restrictions, we analyse the known estimates (ie.measurements) of trigonometric parallaxes, sets of high-precision propermotion pairs and high-precision radial velocities subject to theabove-stated stochastic constraints, and as a result estimate thecluster's centre to be at a distance of 45.8+/-1.25 (standard error) pc.
| New weak-line T Tauri stars in Taurus-Auriga.
On the basis of the ROSAT All-Sky-Survey, a study of the Taurus-Aurigastar forming region has been performed in order to search for hithertoundiscovered TTauri stars. Our study covers an area of about 280 squaredegrees, located between 4^h^ and 5^h^ in right ascension and between15deg and 34deg in declination. Identification of ROSAT All-Sky Surveysources in this area by means of optical spectroscopy revealed 2 newclassical T Tauri stars (CTTS) and 66 new weak-line-T Tauri stars (WTTS)with Wlambda_(Hα)<=10A. Additional pointed ROSATobservations led to the identification of 6 more WTTS and 2 CTTS, givinga total of 76 new T Tauri stars. The large area of our study, ascompared with previous works, allows us to study the spatialdistribution of WTTS in this star forming region. We find the WTTS ofour survey to be distributed over the whole region investigated. Thereis a noticeable decline of the surface density from south to northwithin our study area, but the spatial distribution extends mostprobably beyond our study region. No clustering towards the populationof TTauri stars known prior to ROSAT in Taurus-Auriga could be observed.We suggest that the WTTS found in our study might in part be somewhatolder than the previously known TTauri stars in Taurus-Auriga, and thattheir broad spatial distribution is due to the typical velocitydispersion of a few km/s measured for Taurus TTauri stars, in which casefor some of our WTTS an age on the order of 10^7^years would be requiredfor reaching the observed distances from the Taurus dark clouds. Weestimate a WTTS/CTTS ratio of about 6 within our study area, butconclude that because of the different spatial distribution of WTTS andCTTS this ratio will be most probably significantly larger for a moreextended area.
| Lithium abundance in binaries of the Hyades open cluster.
We have derived accurate and homogeneous lithium abundances in 49 MainSequence binary systems belonging to the Hyades open cluster by using adeconvolution method to determine individual magnitudes and colors forthe primary and secondary components of the binary. The input parametersof the model are the observed Li equivalent width, the actual distanceto the binary, the integrated apparent magnitude and the integratedcolors of the binaries -BV(RI)_K_. We show that the general behavior isthe same in binaries and in single stars (Li is depleted faster in Kstars than in G stars and there is a deep dip for mid-F stars). However,there is a larger scatter in the abundances of binary systems than insingle stars. Moreover, in general, binary systems have anoverabundance, which is more conspicuous in close binaries. In fact,there is a cut-off period, which can be estimated as P_orb_~9d. Thisvalue is in excellent agreement with the theoretical prediction of Zahn(1994).
| 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.
| ROSAT All-Sky Survey Observations of the Hyades Cluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...448..683S&db_key=AST
| 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
| Low-Mass Stars in the Hyades
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.265..785R&db_key=AST
| Lithium in the Hyades. I - New observations
Results are presented of new observations, carried out at Li 6707 A, on68 main-sequence members of the Hyades cluster with spectral typesranging from late F to and early K, and their surface lithium abundanceLi/H is related to their mass, age, and initial composition. It is foundthat, for the sample as a whole, the observed distribution of lithiumabundances is inconsistent with the hypothesis of a unique relationshipbetween lithium abundance and mass. Moreover, is strong observationalevidence for main-sequence lithium depletion when the data are comparedwith observations in younger clusters, even for masses that are notpredicted to experience such depletion in standard stellar models.
| ICCD speckle observations of binary stars. VII - A duplicity survey of the Hyades cluster
The Hyades cluster is the nearest open cluster to the solar system, andits distance has long been a contentious issue. In order to expand thesample of Hyades binaries with potentially short-period visual orbits, aspeckle survey of 153 bright Hyades stars for possible multiplicity wasconducted at the KPNO 4 m Mayall telescope on November 23-27, 1991. Ofthese, one is graded as a suspected new binary, three are graded aspossible new binaries, and three are graded as definite new binaries,one of which has been confirmed from examination of an archivalobservation from 1989. Of these seven new visual resolutions, six havepossible spectroscopic components, two of which are probably the objectsobserved here, three certainly are not, and one may or may not be thecomponent observed.
| UBV photometry of stars whose positions are accurately known. VI
Results are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory.
| Lithium, age, and metallicity in open clusters
It is shown that a strong relationship exists between Li abundance andage for stars in the temperature region 5950-6350 K. The relation isderived from mean Li abundances in eight open clusters ranging in agefrom 5 x 10 to the 7th to 8 x 10 to the 9th yr. The Li declinesexponentially with t exp(-0.3). It is suggested that, in thistemperature regime, simple microscopic diffusion is the cause of the Lidepletion. It is possible that there is a metallicity term in therelation, such that higher metallicity clusters with deeper convectionzones have less Li depletion, while lower metallicity cluster undergogreater depletion. This is consistent with expectations from diffusiontheory. Furthermore, the halo stars, with even lower metallicity andshallower convection zones, would have more diffusion and more Lidepletion; this is in agreement with recent theoretical work.
| The distance and main sequence of the Hyades cluster based on 145 stars with highly accurate proper motions obtained from work on the catalogues FK 5 and PPM
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&A...243..386S&db_key=AST
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| Determining the temperatures of solar-type stars - Do star spots produce color anomalies?
The available evidence pertaining to color 'anomalies' in Hyades dwarfsare examined in detail in order to understand how the determine thetemperatures of solar-type stars. The evidence indicates that thetemperatures of these stars are not seriously skewed by their spots.Simpler explanations which can produce the observed effects arediscussed.
| A radial-velocity survey of the Hyades
Photoelectric radial-velocity measurements, obtained with external erroras small as 0.1 km/s using the 200-inch Hale telescope at PalomarObservatory during the period 1971-1986, are reported for over 400candidate members (with V magnitude between 6 and 14) of the Hyadescluster. The history of Hyades observations is recalled; the Palomarinstrumentation and observing program are described; the data-reductionand standardization procedures are discussed in detail; and the data arepresented in extensive tables and graphs. About 200 of the stars areclassified as cluster members, including 60 spectroscopic binaries.
| Photometry of the comet Halley : solar analogs selected along the path (November 1985 - Mat 1986)
Not Available
| Spectroscopic binaries - 14th complementary catalog
Orbital-element data for 380 spectroscopic binaries are compiled andannotated in tables. The catalog represents a continuation of the 13thcatalog (Pedoussaut and Nadal, 1977) and uses the same general format.The techniques used in making the magnitudes and spectral typeshomogeneous are indicated.
| Preliminary UVBY calibrations for G and K type dwarf stars
Four-color uvby photometry for several hundred late-type dwarf stars oftypes G, K and M is discussed. Mean values of photometric indices aregiven for MK spectral types between F8/G0V and M2V. Preliminary standardrelations between the four-color indices are derived. Based onparallaxes and results from high-dispersion spectroscopic analyses,calibrations of the observed indices in terms of Mv, log Te and Fe/Hhave been derived. The means errors are 0.29 mag, 0.009 dex, and 0.17dex, respectively. The calibrations are valid for class-V stars of allpopulations between G0 and M2. If extreme population-II dwarfs areexcluded, the mean error of the abundance calibration decreases to 0.13dex. Calibrations in terms of log g have been attempted,, but the lowaccuracy of the spectroscopic g determinations does not inspireconfidence in the results. The possible contribution of a'fourth-parameter' variation to the mean errors of the calibrations isbriefly discussed. This fourth parameter could be the intrinsic heliumabundance of the stars.
| The radial velocity of the Hyades cluster
Radial velocities for thirty-nine members or suspected members of theHyades cluster are determined through direct comparison with solarsystem objects. Using these new data for 17 nonvariable members, plusadditional published radial velocities, a new cluster radial velocity (+39.1 + or - 0.2 km/s) is derived. A radial-velocity convergent pointalso is obtained, which is in agreement with those derived throughproper-motion data. No significant correction to the standard Hyadesdistance is required by these new velocity data, but specific clusterdistances obtained in previous investigations are adjusted by smallamounts.
| The period distribution of unevolved close binary systems
Period distributions have been examined for various spectral types ofabout 600 (eclipsing and spectroscopic) close binaries, which are likelyto be substantially unevolved. The comparison with the previouscorresponding analyses of extensive (but heterogeneous) binary samplesallows a clarification of the extent of the evolutionary andobservational selection effects. Remarkably, this analysis reveals agreat deficiency of short period binaries (with periods corresponding tocase A mass transfer) in the whole spectral range. For the late spectraltypes, this result may be connected with postformation angular momentumloss caused by stellar wind magnetic braking; at least for the late Band A spectral range, a ready interpretation of this finding is thatclose binaries of corresponding periods and spectral types are rarelyformed.
| Binary stars unresolved by speckle interferometry. III
The KPNO's 4-m telescope was used in 1975-1981 to determine the epochsof 1164 speckle observations for 469 unresolved, known or suspectedbinary stars. The data, presented in tabular form, encompass visualbinaries with eccentric orbits, occultation binaries, astrometricbinaries, Hyades stars of known or suspected duplicity, and many longperiod spectroscopic binaries.
| The Hyades binary HD 27130 and the mass-luminosity relation and distance of the Hyades cluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982ApJ...254..606M&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Boga |
| Sað Açýklýk: | 04h15m42.44s |
| Yükselim: | +20°49'11.3" |
| Görünürdeki Parlaklýk: | 7.837 |
| Uzaklýk: | 51.335 parsek |
| özdevim Sað Açýklýk: | 110.2 |
| özdevim Yükselim: | -34.7 |
| B-T magnitude: | 8.729 |
| V-T magnitude: | 7.911 |
Kataloglar ve belirtme:
|
