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Speckle interferometry of nearby multiple stars. III.
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| 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.
| 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
| 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 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
| 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.
| 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
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Mesures d'etoiles doubles faites a Nice, etoiles doubles nouvelles (24eme serie) decouvertes a Nice.
Table 1 gives 1182 measurements of 682 binaries observed with the 74 and50 cm refractors. Table 2 lists 26 new binaries discovered with the 50cm refractor.
| 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
| 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.
| Proper motions from Schmidt plates. II - The Hyades
COSMOS scans of photographic plates taken by the Palomar Oschin Schmidttelescope and by the UK Schmidt telescope are used to obtain propermotions for about 450,000 stars within a 112-sq-deg region covering partof the Hyades luster. With epoch differences of 33 to 37 yr, propermotions accurate to 6-12 milliarcsec/yr are obtained, and 393 candidateHyades to a limiting magnitude of about 15.5, including at least two newwhite dwarf candidates, are identified. The main-sequence luminosityfunction determined from this sample is similar to that defined by localfield stars, with a broad maximum at about +12. Both the line-of-sightand surface density distributions show evidence for significant masssegregation; the overall proper motion distribution suggests a tightcore centered within a much broader distribution. A total mass of410-480 solar masses and a gravitational binding radius of about 10.5 pcare derived.
| The chromospheric activity of low-mass stars in the Hyades
High-resolution spectra or narrow-band H-alpha photometry of 106 dwarf Kand M stars in the Hyades cluster have been used to determine H-alphaequivalent widths. These data reveal a sequence of Hyades members withH-alpha in absorption for photospheric temperatures hotter than about3500 K. Within this sequence, the dispersion about the mean equivalentwidth-color relation is only slightly larger than the measurementerrors. A second sequence of Hyades members, characterized by H-alphaemission and significant scatter at a given color, appears at effectivetemperatures cooler than about 4000 K. This bifurcation in H-alphaproperties at 4000 K coincides with a bifurcation in the rotationalcharacteristics of Hyades stars: the dispersion in the rotationalvelocities of the hotter Hyades members at a given effective temperatureis small while the cooler stars exhibit significant scatter in theirrotational velocities. On the basis of these data, it is suggested thatlow-mass stars spin down to rotational velocities dependent upon massand age, but independent of premain-sequence angular momentum.
| Magnetic structure in cool stars. XVII - Minimum radiative losses from the outer atmosphere
The emissions in several chromospheric and transition region lines andin coronal soft X-rays are analyzed for a sample of cool stars. Thenature of the lower-limit flux densities is explored, and evidence isgiven for the possibility of a basal, nonmagnetic heating mechanismbeing responsible for these emission fluxes up to, and perhapsincluding, the upper transition region. It is argued that the excessflux density, derived by subtraction of the basal flux density from theobserved stellar flux, is the proper measure of magnetic activity. Thelevel of the basal flux density as a function of color is determined tobe 2 x 10 exp 6 erg/sq cm/s for F-type stars and 2 x 10 exp 5 erg/sqcm/s for K-type stars.
| Parallaxes of stars in the Hyades Cluster region - A comparison of hand and automatic measures
Parallaxes and proper motions are presented for 30 members of the HyadesCluster and 223 field stars in 13 fields located near the center of thecluster. The series of photographic plates are extensive and they weremeasured twice; first, by hand, using a conventional two-screw measuringmachine, and also with a PDS microdensitometer. A comparison of the twosets of measures reveals that the internal and external errors inparallax average about + or - 0.005 arcsec for the central stars fromautomatic PDS measures and about twice this amount for the data measuredby hand. The parallaxes of the member stars yield a distance modulus of3.30, in excellent agreement with the average of many prior distancedeterminations for the cluster. The parallaxes of the field starsconfirm a small amount of coma or higher-order terms in the opticalsystem of the Van Vleck refractor. They also confirm that, within afield of one half degree radius centered on the optical axis and over arange in visual magnitude from 8.5 to 13, the errors in parallax varyonly slightly over the most optimum conditions.
| 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.
| Very active chromosphere stars and the age, chromosphere activity relation
The wide range of objects in stellar superclusters and groups near thesun is used in an attempt to define normal stellar chromosphericbehavior, with which 'very active chromosphere' (VAC) stars can beisolated. Two chromosphere signatures, soft X-ray flux, and Mg II h andk line flux, are discussed. The X-ray flux is of limited use in thisregard because of a wide range of variation with time, although themaximum values are well defined for stars of a given age. The VAC stars,which have an excessive X-ray flux, also have an excessive bolometricflux. The ratio of the Mg II h and k (and Ca II H and K) line emissionand the total bolometric emission, R(hk) decreases with bolometricluminosity. The rate of decrease in log R(hk), 0.175 (35.00 - logLBOL), is not very dependent on stellar age, but the zeropoint at log LBOL = 35.00 decades varies from log R(hk) =-4.45 decades for main-sequence stars in the Pleiades supercluster(200-300 million yr) to - 4.91 decades for those in the HR 1614 group (8billion yr). The age dependence of R(hk) is clearly demonstrated notonly by the supercluster and group stars but by the 'Mount Wilsonsample' of objects that have been observed in Ca II H and K for over 15years (e.g., Noyes et al., 1984). Several determinations (e.g.,Soderblom and Clements, 1987) have established a linear relation betweenR(hk) and R(HK). Some 50 stars in the Mount Wilson sample havewell-established luminosities and space motions (e.g., Eggen, 1989) thatallow the separation of young and old disk stars in velocity space(Eggen, 1989). The young disk stars all have values of R(hk) thatidentify them as having ages less than the youngest Hyades superclustermembers (about 600 million yr).
| The Einstein Observatory survey of stars in the Hyades cluster region
The paper reports the results of an extensive X-ray study of the Hyadesregion and improves on previous studies by using refined X-ray sourcedetection algorithms and the complete set of Einstein Observatory IPCexposures covering the Hyades cluster region (a total of 63 1 x 1 degimages). Maximum likelihood integral X-ray luminosity functions werecomputed for the Hyades stars for given color index (B-V) ranges. Thepresent results agree substantially with a previous survey about theubiquity of the stellar activity in the Hyades cluster, especially amongsolar-type stars. The result of Stern et al. (1981) that stellar X-rayemission is dependent on stellar age is confrimed.
| Further Cousins VRI photometry of the Hyades and M67
New V magnitudes and/or (VRI)C colors are reported for 17 Hyads and 11bright M67 stars. It is found that a source of variation in the Hyads(probably chromospheric variation) can change R-I while leaving V-Runaffected. The V magnitude can also vary, but is uncorrelated with R-I.The time scale for color variation is roughly a week; V magnitudes canvary on time scales from weeks to years.
| 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.
| Chromospheric and transition-region emission from young solar-type stars in clusters, kinematic groups, and the field
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987AJ.....93..920S&db_key=AST
| Positions of 127 Hyads and 6-cm observations of 320 Hyads
Accurate positions are given for 127 Hyades cluster stars whichpreviously had only approximate positions known. The fields of 320Hyads, including 55 X-ray stars, were observed with the VLA to a 6-cmdetection level of approximately 0.5 mJy. There were no detections.
| Photometry of stars in the uvgr system
Photoelectric photometry is presented for over 400 stars using the uvgrsystem of Thuan and Gunn. Stars were selected to cover a wide range ofspectral type, luminosity class, and metallicity. A mean main sequenceis derived along with reddening curves and approximate transformationsto the UBVR system. The calibration of the standard-star sequence issignificantly improved.
| Color anomalies and starspots in Hyades dwarfs
Hyades dwarfs later than about F7 show color anomalies which are foundto correlate well with various indicators of chromospheric activity. Itis proposed that the color anomalies are due to starspots, whichapparently also cause the low level photometric variations seen in somestars. That some stars with small color anomaly are variable, plus thefinding that Hyades dwarfs show a mean color anomaly relative to fieldstars, implies that virtually all late-type Hyades are spotted.Intermediate band photometry of spotted stars could give an apparentoverestimate of the metallicity. This may explain why many Hyadesabundance estimates from photometry are larger than from spectroscopicanalyses. Similarly, starspots could explain the 'Hyades anomaly', thec1 excess of unevolved Hyades dwarfs relative to field stars. Starspotscould lead to a displacement of the Hyades from the standard mainsequence in the color-magnitude diagram, but detailed models of spottedstars are required to test this. Tentative evidence is found that Hyadesdwarfs are roughly 0.1 mag brighter in V than field stars of the same B- V and metallicity. A new value of the solar B - V color is derived inthe Appendix.
| A photometric search for halo binaries. I - New observatinal data. II - Results
Carney (1982) has reported JHK photometry for 76 Hyades dwarfs. Inconnection with the present investigation, results of similarobservations of field halo stars are provided along with some uvbyphotometry. In addition, older spectrophotometric and photometric dataused previously for temperature determinations have been collected. Theinfrared and uvby data were obtained primarily with the objective ofidentifying binaries with dissimilar components among a sample of fieldhalo dwarfs by comparing metallicity insensitive blue and infraredcolors. Attention is given to 111 spectrophotometric scans of 89 stars,67 uvby measures of 41 stars, 127 UBV measures of 87 stars, 147 (RI)Jmeasures of 127 stars, 8 JHK measures of eight stars in the 'HCO'system, and 212 JHK measures of 137 stars in the 'CIT' system. Themajority of these stars are dwarfs, and most of them are metal poor. Theresults of a search for binaries in 71 halo dwarf stars are alsopresented, taking into account a few other dwarfs of special interest.
| The Hyades main sequence
Intermediate band, H-beta and RI observations of 72 Hyades cluster starsto V = 11 mag are reported and discussed. A modulus of 3.2 mag isderived on the basis of a comparison with field stars of large parallax.Also presented are observations of 98 main-sequence stars of the Hyadesgroup that were previously found to be group members from kinematicalconsiderations. Parallaxes of the group stars, computed on theassumption that they are members of an extended Hyades cluster, yieldmean values of (U, V, W) = (+40.5, -18.4, -4.9) km/s, with dispersionsof (2.3, 2.3, 6.0) km/s, compared with (+41.7, -18.4, -2.0) and (2.6,1.3, 1.9) km/s for the brightest cluster members. It is noted that allthe stars discussed can be considered as members of a supercluster inwhich only a slight relaxation control of the W velocities is presentfor stars far from the nucleus. Evidence is found, including that of thePraesepe cluster at Z = +80 pc, for some interchange between the U, V,and W velocities in stars farthest from the galactic plane, with thetotal cluster velocity being maintained.
| Infrared photometry of Hyades dwarfs
JHK infrared photometry is presented for 76 main-sequence proper motionmembers brighter than V = 12 in the Hyades. Known binaries are confirmedand new candidates proposed using color-magnitude and color-colordiagrams. The cluster binary frequency (about 40%) is discussed, as wellas its possible effects on the cluster distance modulus and stellarchromospheric/coronal activity.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Bika |
| Rektaszcenzió: | 04h25m47.56s |
| Deklináció: | +18°01'02.2" |
| Vizuális fényesség: | 9.006 |
| Távolság: | 48.1 parszek |
| RA sajátmozgás: | 104.4 |
| Dec sajátmozgás: | -28.8 |
| B-T magnitude: | 10.139 |
| V-T magnitude: | 9.1 |
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