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Tertiary companions to close spectroscopic binaries
We have surveyed a sample of 165 solar-type spectroscopic binaries (SB)with periods from 1 to 30 days for higher-order multiplicity. Asubsample of 62 targets were observed with the NACO adaptive opticssystem and 13 new physical tertiary companions were detected. Anadditional 12 new wide companions (5 still tentative) were found usingthe 2MASS all-sky survey. The binaries belong to 161 stellar systems; ofthese 64 are triple, 11 quadruple and 7 quintuple. After correction forincompleteness, the fraction of SBs with additional companions is foundto be 63% ± 5%. We find that this fraction is a strong functionof the SB period P, reaching 96% for P<3d and dropping to34% for P>12^d. Period distributions of SBs with and withouttertiaries are significantly different, but their mass ratiodistributions are identical. The statistical data on the multiplicity ofclose SBs presented in this paper indicates that the periods and massratios of SBs were established very early, but the periods of SB systemswith triples were further shortened by angular momentum exchange withcompanions.
| 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
| 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.
| 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.
| 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.
| 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).
| 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.
| Spectroscopic binaries - 15th complementary catalog
Published observational data on the orbital characteristics of 436spectroscopic binaries, covering the period 1982-1986, are compiled intables. The data sources and the organization of the catalog are brieflydiscussed, and notes are provided for each item.
| 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.
| Synchronization in late-type binary stars
The synchronism between rotation and revolution in late-type closebinaries is rediscussed by an inspection of the published rotationvelocities and rotation (photometric) periods of about 50 binarycomponents. Basically, it is found that, as a rule, dwarfs havingfractional radii of more than 0.05 appear to be in synchronous rotationand those with radii of less than 0.03 are in asynchronous rotation;asynchronism is more frequently observed in giants. Remarkably, theobserved degree of synchronism appears to be in substantial agreementwith current theoretical views (Zahn, 1977) on tidal friction inlate-type binaries.
| 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.
| Spectroscopic Orbits for Three Double-Lined Binaries in the Hyades Field 22DEG669 VA771 VB166
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&A...106..221G&db_key=AST
| 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
| 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.
| The Distance to the Hyades Cluster from R - i Photometry
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974ApJ...193..359U&db_key=AST
| Low-luminosity members of the Hyades cluster. II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74....2V&db_key=AST
| Low-luminosity members of the Hyades cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..482V&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Toro |
| Ascensione retta: | 04h35m33.92s |
| Declinazione: | +12°06'01.8" |
| Magnitudine apparente: | 8.964 |
| Distanza: | 74.019 parsec |
| Moto proprio RA: | 41.1 |
| Moto proprio Dec: | -14.4 |
| B-T magnitude: | 9.638 |
| V-T magnitude: | 9.02 |
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