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The Status of ROSAT X-ray Active Young Stars toward Taurus-Auriga
We present an astrometric study of the candidates of T Tauri stars (TTS)and non-TTS X-ray sources around Tau-Aur, based on the HipparcosCatalogue and the ACT Reference Catalogue. The ROSAT selected X-raysources are found to be a mixed population. A few of them areassociated with the Tau-Aur or Orion Star Forming Regions (SFR). Some,with distances similar to that of Tau-Aur but with discrepant propermotions, are probable or sure Pleiades super-cluster members or otherlate type young active stars with unresolved nature, more likely tooriginate in rapidly moving cloudlets, or else having originated fromdifferent sites other than Tau-Aur and moved to the present locations. Agood many of the non-TTS X-ray sources are considered as Hyades clustermembers. Some TTS candidates could be foreground pre-main sequencestars or actually young dwarfs not yet depleted of their Lithium. Underthe hypothesis that the sources we studied are representative of theROSAT selected TTS candidates discovered in the outskirts of the Tau-Aurregion, we conclude that only up to one third of the weak-line TTScandidates could be expected to be physically associated with theTau-Aur association. Along with the parallax and proper motion analysisof the non-TTS X-ray sources around the Tau-Aur SFR, our result suggeststhat the vast majority of the young active X-ray sources within anangular diameter of about 30 ° of the Tau-Aur SFR, belong to fourmain subgroups that are spatially separate.
| 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.
| X-ray flares on zero-age- and pre-main sequence stars in Taurus-Auriga-Perseus
We present the results of a systematic search for X-ray flares on youngstars observed during ROSAT PSPC observations of theTaurus-Auriga-Perseus sky region. All pointed PSPC observationscurrently available from the ROSAT Public Data Archive with knownpre-main sequence T Tauri Stars or young Pleiads or Hyads in the fieldof view are analyzed. A study of the activity of late-type stars ofdifferent ages provides information on the evolution of their coronalactivity, which may be linked to their angular momentum. We develop acriterion for the detection of flares based on the shape of the X-raylightcurve. Applying our detection method to all 104 PSPC pointings fromthe archive we find 52 flares. Among them 15 are detected on T TauriStars, 20 on Pleiads, and 17 on Hyads. Only the 38 events which candefinitely be attributed to late-type stars (i.e. stars of spectral typeG and later) are considered in the statistical analysis of theproperties of flaring stars. We investigate the influence of stellarparameters such as age, rotation and multiplicity on individual flareparameters and flare frequency. From the total exposure time falling tothe share of each sample and the duration of the individual flares wecompute a flare rate. We take into account that the detectionsensitivity for large X-ray flares depends on the S/N and hence on thestellar distance. The values we derive for the flare rates are 0.86 +/-0.16% for T Tauri Stars, 0.67 +/- 0.13% for Pleiads and 0.32 +/- 0.17%for Hyads. The flare rate of classical T Tauri Stars may be somewhathigher than that of weak-line T Tauri Stars (F_c = 1.09 +/- 0.39% versusF_w = 0.65 +/- 0.16%). Hardness ratios are used to track the heatingthat takes place during stellar flares. Hardness ratios are evaluatedfor three distinct phases of the flare: the rise, the decay, and thequiescent (pre- and post-flare) stage. In most cases the hardnessincreases during the flares as compared to the quiescent state. Duringboth quiescence and flare phase TTSs display the largest hardnessratios, and the Hyades stars show the softest spectrum.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Newly discovered candidate weak-line T Tauri stars in the surrounding area of the Taurus-Auriga region
We present results of an extensive search for weak-line T Tauri stars(WTTS) in the outskirts of the Taurus-Auriga molecular cloud on thebasis of the ROSAT All-Sky Survey Bright Source Catalog. Our surveyedregion extends from 2() h40() m to 5() h40() m in right ascension andfrom 10(deg) to 40(deg) in declination, with the central part ofTaurus-Auriga (4() h
| 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
| Rotational Velocities and Chromospheric Activity of M Dwarfs in the Hyades
We have obtained high-resolution spectra of 52 K and M dwarf members ofthe Hyades open cluster. We have used these spectra to derive radialvelocities, rotational velocities, and H alpha equivalent widths. Sevenof the stars in our sample are double-lined spectroscopic binaries, andone is a spectroscopic triple. Of the apparently single stars, 13 haverotational velocities above our detection limit of 6 km s-1, with themaximum rotational velocity being about 25 km s-1. Given the relativelylow mass for these stars, this modest spectroscopic rotational velocityof 25 km s-1 corresponds to a rotational period of order 17 hr, and thusthe most rapidly rotating Hyades M dwarfs actually are quite rapidrotators. Somewhat surprisingly, the components of the spectroscopicbinaries are, if anything, on average apparently more slowly rotatingthan the single stars. Forty-nine of the stars in our sample are Mdwarfs. There is a good rotation-activity correlation for this sample,with stars with v sin i > 12 km s-1 having log (LX/LBol) ~ -3 and Halpha equivalent widths saturating at ~4 Angstroms. There appear to betwo branches of the rotation-activity relation as one approachessaturation, however---one set of stars approaches the saturation levelat a very slow rotation rate (v sin i <= 6 km s-1), whereas thesecond set does not reach saturation until about v sin i = 12 km s-1.The components of the double-lined spectroscopic binaries are generallymembers of the first set since they are quite active but generallyslowly rotating.
| Optical and X-Ray Characteristics of Stars Detected in the Einstein Slew Survey
We detect X-rays for the first time from 63 cool (types AM) stars. Thesestars are part of the 229 total stellar X-ray sources identified to datein the Einstein Slew Survey (hereafter Slew). We also list new X-raydata on one A star that may have a corona, five OB stars, and reportdiscoveries of two new T Tauri stars and two new cataclysmic variables.The stellar content of the Slew high-latitude subset (currently 93%identified for |b_II_| > 20^deg^) is 26%. This agrees well with theEinstein Extended Medium Sensitivity Survey (EMSS) stellar sample, whichonly considered high latitudes. Because of the large solid angle coveredby the Slew, and its shallow limiting flux, the sample will better probethe bright end of the stellar X-ray luminosity function (L_X_ >10^30^ ergs s^-1^). Presently (based on the 221 Slew stars with knownspectral types), the sample is dominated by late-type systems (coolerthan F; 68%). These include dMe's, BY Dra, RS CVn, and FK Comae systems.Based on the limiting magnitudes of catalogs searched to date, the Slewis assessed to be complete for spectral types earlier than K. Hence, Kand M systems will be prominent in the ~50 as yet unidentified stars. Wehave embarked on an extensive program to (1) confirm the X-rayidentifications with the optical counterparts; (2) search for Ca II Hand K and Balmer line emission as activity signatures; and (3) searchfor supporting evidence of magnetic activity by measuring rotationalvelocities and relating them to X-ray luminosity level. Of 64 proposedcoronal systems observed to date, we have confirmed 44 active stars,while in the remaining 20 we have been unable to find definitiveactivity. We have confirmed an additional 19 active stars from stellardatabase searches, and reclassified nine systems as having nonstellaroptical counterparts from optical follow-up identification work andextragalactic database searches. We discuss notable new discoveries.From the sample of single active F7-MS Slew stars with measured ν sini-values, we find a strong (99.9% confidence level) linear correlationof X-ray luminosity with ν sin i and with stellar radius (R).However, L_X_ is uncorrelated with angular rotation speed at the 99%level. For the combined Slew and EMSS single star F7-MS sample, we findthe same 99.9% ν sin i-L_X_ and R-L_X_ correlations. The L_X_-νsin i relation for the combined sample appears to flatten with respectto the quadratic behavior seen for optically selected stellar samples atrotational velocities in excess of ~16 km s^-1^. For the unevolvedsubset of the Slew single star sample, we also find a correlationbetween L_X_ and Rossby number (R_0_; more than 99% confidence). Aleast-squares fit gives L_X_ ~ R_0_^-0.4^, which is similarly flatterthan the quadratic dependence seen in optical samples. Using the stellarsurface X-ray flux F_X_ versus B - V diagram, we interpret these resultsas saturation of the stellar surface by active regions at F_X_/F_bol_ ~10^-3^.
| 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).
| Chromospheric and coronal activity in low-mass Hyades dwarfs
We present an extensive survey of the chromospheric and coronal activityamong low-mass members of the Hyades open cluster. We have obtained Halpha spectroscopy of 91 probable cluster members, including 23 that liewithin three fields for which we have deep ROSAT X-ray observations. 20of the 23 stars are detected in X-rays; the non-detections are probablynot Hyades members. Combining these observations with data from theliterature, we find that the mean H alpha to bolometric luminosity ratiolog (L_H alpha/L_bol) is constant at a value of ~-3.9 for M_bol>8,with a substantial dispersion and an upper limit of -3.5. The X-ray tobolometric luminosity ratio log (L_x/L_bol) first increases withincreasing M_bol, then flattens at a value of ~-3.3 for M_bol>8.Comparing this behaviour with stars in the Pleiades cluster, there aresignificant differences: first, the log (L_H alpha/L_bol) ratioincreases with increasing M_bol while M_bol<10, but appears to turnover sharply at fainter magnitudes, with the lower luminosity starsbeing nearly an order of magnitude lower in the ratio; secondly, we findno evidence for saturation in the log (L_x/L_bol) ratio; L_x increasesmonotonically with M_bol, reaching a value of ~-2.5 at M_bol~10. Lowerluminosity stars have not yet been detected in X-ray observations. Thenearly constant H alpha to H beta ratio in the Hyades stars, coupledwith the small range in coronal temperature seen in the X-ray data,suggest that the (presumably magnetically generated) heating rate isnearly constant in the outer atmospheres of these stars. Differences inthe relative activity levels are then ascribed to differences in thefilling factor of active regions, and in the sizes of the coronalstructures.
| 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
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Seven-Color Photoelectric Photometry of Stars in the Hyades Clusters
Not Available
| Progress report on the radial velocity measurement programme of population II stars.
Not Available
| 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
| The low mass Hyades and the evaporation of clusters
The 135 single stars and 85 binary systems, redder than R-I = +0.34 magand brighter than V = 17 mag, between alpha = 3.75 h and 5.0 h and delta= +5 deg and + 25 deg show a luminosity function that differsconsiderably from that of the general field stars within 20 pc of theSun. The ratio of double star components to single cluster membersincreases markedly with decreasing luminosity. Forty-three single starsand 16 binary systems that are members of the Hyades supercluster within20 pc of the Sun show the same luminosity function as the field stars inthat region. Fifty percent of the cluster members and 40 percent of thesupercluster members are components of binary stars. The equivalentwidths of H-alpha appear to support a range of ages (approximately 8 to16 x 108 yr) for the cluster stars and demonstrate that theoldest objects are in the supercluster. A list of cluster members, whichmay include the end of the stable main sequence, but for which accurate(R-I) photometry is not available, is included. The half-dozen knownparallax stars of the faintest luminosity contain at least onesupercluster member, TVLM 868-110639, which is probably beyond thestable, nuclear burning main sequence as a 'transitional' or 'brown'dwarf.
| 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.
| First results from ROSAT all-sky survey observations of the Hyades cluster
We present preliminary ROSAT all-sky survey results for the Hyadescluster. We detected 108 Hyades cluster members as X-ray sources withL(y) greater than about 3 x 10 exp 28 ergs/s. A number of short-period,chromospherically active binary systems and the giants Theta1 Tau andGamma Tau are among the most X-ray-luminous objects in the cluster. Thesecond brightest X-ray source, HR 1394 = 71 Tau = VB 141, is along-period lunar occultation binary. Seven cluster members were alsoseen in the Wide Field Camera EUV all-sky survey. Among the starsdetected in both X-rays and EUV is the Hyades white dwarf EG 37 (= VR16), confirming an earlier serendipitous EXOSAT detection. We alsoreport the first X-ray detection of the Hyades K0 giant Epsilon Tau, atroughly the survey limit. This new result establishes all four Hyadesgiants as X-ray emitters, although with an about 50:1 range in L(x). Acomparison of Einstein and ROSAT data for three of the giants suggeststhat long-term X-ray variability, perhaps due to activity cycles, may bepartly responsible for the wide dispersion in L(x).
| 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.
| A Hyades distance modulus from trigonometric parallaxes from Northern and Southern Hemisphere observatories
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991AJ....102.1091P&db_key=AST
| 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 Possible Members of the Hyades Cluster - Part Four
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982PASP...94..475W&db_key=AST
| 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.
| Luminosity distribution and shape of the Hyades cluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&A....78..312O&db_key=AST
| Intermediate band photometry of late-type stars. II - Some stellar groups
Observations on the (R, I) system and a modified Stromgren system ofmembers of six stellar groups are used to demonstrate the chemicalhomogeneity of some 70% or 80% of the members assigned to the groups onthe basis of kinematics. The groups discussed are the Hyades, Wolf 630,Arcturus, Groombridge 1830, and Kapteyn's Star Groups as well as ananonymous group of a half dozen subdwarfs with (U, V) near (-150, -320)km/s. Standards for a previously described photometric system areextended, and additional F- and G-type standards for the (R, I) systemare presented. A simple relation is derived for computing the Fe/Habundance ratio for most stars in the corrected (R-I) interval from +0.2to +0.45 magnitude.
| Photometry of new possible members of the Hyades cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82..978U&db_key=AST
| Intermediate-band photometry of late-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..732E&db_key=AST
| A study of the motion, membership, and distance of the Hyades cluster
Particular attention is given to the role of the convergent-point, ormoving cluster, method in the determination of the Hyades distance, andthe apparent discrepancy between its results and those of other Hyadesdistance indicators. The Hyades photographic plate material isconsidered along with the approaches used in the measurements, propermotion reductions, coordinate reductions, and aspects of photography.Problems of cluster membership determination are also discussed.
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Toro |
| Ascensione retta: | 04h32m25.66s |
| Declinazione: | +13°06'47.7" |
| Magnitudine apparente: | 11.142 |
| Moto proprio RA: | 103 |
| Moto proprio Dec: | -20.3 |
| B-T magnitude: | 12.222 |
| V-T magnitude: | 11.232 |
Cataloghi e designazioni:
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