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The Structure of the Local Interstellar Medium. IV. Dynamics, Morphology, Physical Properties, and Implications of Cloud-Cloud Interactions
We present an empirical dynamical model of the LISM based on 270 radialvelocity measurements for 157 sight lines toward nearby stars. Physicalparameter measurements (i.e., temperature, turbulent velocity,depletions) are available for 90 components, or one-third of the sample,enabling initial characterizations of the physical properties of LISMclouds. The model includes 15 warm clouds located within 15 pc of theSun, each with a different velocity vector. We derive projectedmorphologies of all clouds and estimate the volume filling factor ofwarm partially ionized material in the LISM to be between ~5.5% and 19%.Relative velocities of potentially interacting clouds are oftensupersonic, consistent with heating, turbulent, and metal depletionproperties. Cloud-cloud collisions may be responsible for thefilamentary morphologies found in ~1/3 of LISM clouds, the distributionof clouds along the boundaries of the two nearest clouds (LIC and G),the detailed shape and heating of the Mic Cloud, the location of nearbyradio scintillation screens, and the location of an LISM cold cloud.Contrary to previous claims, the Sun appears to be located in thetransition zone between the LIC and G Cloud.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. These observations areassociated with programs 9525 and 10236.
| Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
We derive detailed theoretical models for 1074 nearby stars from theSPOCS (Spectroscopic Properties of Cool Stars) Catalog. The Californiaand Carnegie Planet Search has obtained high-quality (R~=70,000-90,000,S/N~=300-500) echelle spectra of over 1000 nearby stars taken with theHamilton spectrograph at Lick Observatory, the HIRES spectrograph atKeck, and UCLES at the Anglo Australian Observatory. A uniform analysisof the high-resolution spectra has yielded precise stellar parameters(Teff, logg, vsini, [M/H], and individual elementalabundances for Fe, Ni, Si, Na, and Ti), enabling systematic erroranalyses and accurate theoretical stellar modeling. We have created alarge database of theoretical stellar evolution tracks using the YaleStellar Evolution Code (YREC) to match the observed parameters of theSPOCS stars. Our very dense grids of evolutionary tracks eliminate theneed for interpolation between stellar evolutionary tracks and allowprecise determinations of physical stellar parameters (mass, age,radius, size and mass of the convective zone, surface gravity, etc.).Combining our stellar models with the observed stellar atmosphericparameters and uncertainties, we compute the likelihood for each set ofstellar model parameters separated by uniform time steps along thestellar evolutionary tracks. The computed likelihoods are used for aBayesian analysis to derive posterior probability distribution functionsfor the physical stellar parameters of interest. We provide a catalog ofphysical parameters for 1074 stars that are based on a uniform set ofhigh-quality spectral observations, a uniform spectral reductionprocedure, and a uniform set of stellar evolutionary models. We explorethis catalog for various possible correlations between stellar andplanetary properties, which may help constrain the formation anddynamical histories of other planetary systems.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Kinematics, ages and metallicities for F- and G-type stars in the solar neighbourhood
A new metallicity distribution and an age-metallicity relation arepresented for 437 nearby F and G turn-off and sub-giant stars selectedfrom radial velocity data of Nidever et al. Photometric metallicitiesare derived from uvby- Hβ photometry, and the stellar ages from theisochrones of Bergbusch & VandenBerg as transformed to uvbyphotometry using the methods of Clem et al.The X (stellar population) criterion of Schuster et al., which combinesboth kinematic and metallicity information, provides 22 thick-discstars. σW= 32 +/- 5 km s-1,= 154 +/- 6 km s-1 and<[M/H]>=-0.55 +/- 0.03 dex for these thick-disc stars, which is inagreement with values from previous studies of the thick disc.α-element abundances which are available for some of thesethick-disc stars show the typical α-element signatures of thethick disc, supporting the classification procedure based on the Xcriterion.Both the scatter in metallicity at a given age and the presence of old,metal-rich stars in the age-metallicity relation make it difficult todecide whether or not an age-metallicity relation exists for the olderthin-disc stars. For ages greater than 3 Gyr, our results agree with theother recent studies that there is almost no correlation between age andmetallicity, Δ([M/Fe])/Δ(age) =-0.01 +/- 0.005 dexGyr-1. For the 22 thick-disc stars there is a range in agesof 7-8 Gyr, but again almost no correlation between age and metallicity.For the subset of main-sequence stars with extra-solar planets, theage-metallicity relation is very similar to that of the total sample,very flat, the main difference being that these stars are mostlymetal-rich, [M/H]>~-0.2 dex. However, two of these stars have[M/H]~-0.6 dex and have been classified as thick-disc stars. As for thetotal sample, the range in ages for these stars with extra-solarplanetary systems is considerable with a nearly uniform distributionover 3 <~ age <~ 13 Gyr.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| 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
| Radial Velocities for 889 Late-Type Stars
We report radial velocities for 844 FGKM-type main-sequence and subgiantstars and 45 K giants, most of which had either low-precision velocitymeasurements or none at all. These velocities differ from the standardstars of Udry et al. by 0.035 km s-1 (rms) for the 26 FGKstandard stars in common. The zero point of our velocities differs fromthat of Udry et al.: =+0.053km s-1. Thus, these new velocities agree with the best knownstandard stars both in precision and zero point, to well within 0.1 kms-1. Nonetheless, both these velocities and the standardssuffer from three sources of systematic error, namely, convectiveblueshift, gravitational redshift, and spectral type mismatch of thereference spectrum. These systematic errors are here forced to be zerofor G2 V stars by using the Sun as reference, with Vesta and day sky asproxies. But for spectral types departing from solar, the systematicerrors reach 0.3 km s-1 in the F and K stars and 0.4 kms-1 in M dwarfs. Multiple spectra were obtained for all 889stars during 4 years, and 782 of them exhibit velocity scatter less than0.1 km s-1. These stars may serve as radial velocitystandards if they remain constant in velocity. We found 11 newspectroscopic binaries and report orbital parameters for them. Based onobservations obtained at the W. M. Keck Observatory, which is operatedjointly by the University of California and the California Institute ofTechnology, and on observations obtained at the Lick Observatory, whichis operated by the University of California.
| The Structure of the Local Interstellar Medium. I. High-Resolution Observations of Fe II, Mg II, and Ca II toward Stars within 100 Parsecs
High-resolution absorption measurements(λ/Δλ>~100,000) of the resonance lines of Fe II,Mg II, and Ca II are presented for all available observed targets within100 pc. The Fe II and Mg II spectra were obtained with the Goddard HighResolution Spectrograph (GHRS) and the Space Telescope ImagingSpectrograph (STIS) instruments aboard the Hubble Space Telescope (HST).Of the 63 observations of targets within 100 pc, we present newmeasurements for 24 lines of sight. We also compiled all publishedabsorption measurements based on Ca II spectra obtained by variousground-based instruments. For each observation we provide measurementsof the central velocity, Doppler parameter, and column density for eachabsorption component. These three ions provide the best opportunity tomeasure the component velocity structure. Because these are the heaviestions observed in absorption through the warm local interstellar medium(LISM), the narrow line widths minimize significant blending ofcomponents and allow for accurate measurements of the central velocity.We present a statistical analysis of the LISM absorption measurements,which provides an overview of some physical characteristics of warmclouds in the LISM, such as, temperature, turbulent velocity, ionizationdegree, and depletion. The complete collection and reduction of all LISMabsorption measurements provides an important database for studying thestructure of nearby warm clouds. Subsequent papers will present modelsfor the morphology and physical properties of individual structures(clouds) in the LISM.
| 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.
| Microstructure of the Local Interstellar Cloud and the Identification of the Hyades Cloud
We analyze high-resolution UV spectra of the Mg II h and k lines for 18members of the Hyades to study inhomogeneity along these proximate linesof sight. The observations were taken by the Space Telescope ImagingSpectrograph (STIS) instrument on board the Hubble Space Telescope(HST). Three distinct velocity components are observed. All 18 lines ofsight show absorption by the Local Interstellar Cloud (LIC); 10 starsshow absorption by an additional cloud, which we name the Hyades Cloud;and one star exhibits a third absorption component. The LIC absorptionis observed at a lower radial velocity than predicted by the LICvelocity vector derived by Lallement & Bertin in 1992 and Lallementet al. in 1995[vpredicted(LIC)-vobserved(LIC)=2.9+/-0.7 kms-1], which may indicate a compression or deceleration at theleading edge of the LIC. We propose an extension of the Hyades Cloudboundary based on previous HST observations of other stars in thegeneral vicinity of the Hyades, as well as ground-based Ca IIobservations. We present our fits of the interstellar parameters foreach absorption component. The availability of 18 similar lines of sightprovides an excellent opportunity to study the inhomogeneity of thewarm, partially ionized local interstellar medium (LISM). We find thatthese structures are roughly homogeneous. The measured Mg II columndensities do not vary by more than a factor of 2 for angular separationsof <~8°, which at the outer edge of the LIC correspond tophysical separations of <~0.6 pc.
| Mg II Emission Lines of Hyades F Stars
With the Hubble Space Telescope (HST) we have observed Hyades F stars,using the Space Telescope Imaging Spectrograph (STIS), in order to getmore information about the heating mechanism(s) for the chromospheresand transition layers and their dependence on rotation and age. In thispaper we study the Mg II lines at 2800 Å. We include earlierobservations with the International Ultraviolet Explorer (IUE)satellite. The Mg II emission lines become observable for B-V>0.3.The emission line fluxes increase steeply until B-V~0.40. For singlestars there is a steep decrease in flux between B-V=0.41 and B-V=0.44,similar to the behavior of the Ca II emission line cores. For larger B-Vthe Mg II emission line fluxes again increase, but much more slowly thanfor the Ca II lines. Generally, the low point of the emission is reachedbetween B-V=0.43 and B-V=0.45, i.e., similar to the Ca II emissioncores. For the Hyades F stars there appears to be a difference betweenthe emissions for single stars and those for binaries. We find that forHyades stars with surface line fluxes larger than 106 ergscm-2 s-1 the emission line fluxes decrease withincreasing vsini. For smaller fluxes they may increase with increasingvsini. We have only three stars that perhaps show this. We study theflux ratios of the Mg II k and h lines at 2795.7 and 2802.5 Å inorder to determine where the lines fall on the curve of growth. For theearliest F stars studied here the ratio is close to 2, as expected foroptically thin lines. Generally, it seems that the optical depths in theline centers are less than 10. There remain problems in understandingthe size of the line widths. We discuss the interpretation of theWilson-Bappu effect. For the Hyades F stars there is a strong dependenceof the line width on the effective temperature. Based on observationswith the NASA/ESA Hubble Space Telescope obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy. Incorporated, under NASA contract NAS5-26555.
| Binary star speckle measurements during 1992-1997 from the SAO 6-m and 1-m telescopes in Zelenchuk
We present the results of speckle interferometric measurements of binarystars made with the television photon-counting camera at the 6-m BigAzimuthal Telescope (BTA) and 1-m telescope of the Special AstrophysicalObservatory (SAO) between August 1992 and May 1997. The data contain 89observations of 62 star systems on the large telescope and 21 on thesmaller one. For the 6-m aperture 18 systems remained unresolved. Themeasured angular separation ranged from 39 mas, two times above the BTAdiffraction limit, to 1593 mas.
| 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.
| 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.
| 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
| 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
| CN variations among asymptotic giant branch and horizontal branch stars in the intermediate metallicity globular clusters M5, M4, and NGC 6752
An investigation is conducted of the 3883-A CN band strengths amongstars in the asymptotic giant branch evolutionary phase in the M5 andNGC 6752 globular clusters. It is suggested that the differences in CNdistributions among the evolved stars in these clusters may be aconsequence of the varying degrees of C-to-N processing to which theywere subjected in the preceding, red giant phase of evolution.
| 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
| UBV photometry of stars whose positions are accurately known. III
UBV photometric observations of 417 stars at BD declination 35-49 degfrom the NPZT(74) catalog of Yasuda et al. (1982) and the AGK3R catalogof Corben (1978), obtained with the 40-cm Cassegrain reflector atKvistaberg Observatory during 1984-1985, are reported. The data arepresented in tables, and the mean errors per observation are given as0.016 mag in V, 0.011 mag in B-V, 0.012 mag in U-B for U less than 10,and 0.026 mag in U-B for U greater than 10.
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Perseus |
| Ascensió Recta: | 03h32m39.92s |
| Declinació: | +35°39'33.5" |
| Magnitud Aparent: | 7.299 |
| Distancia: | 48.9 parsecs |
| Moviment propi RA: | 133 |
| Moviment propi Dec: | -58.5 |
| B-T magnitude: | 7.89 |
| V-T magnitude: | 7.348 |
Catàlegs i designacions:
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