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Statistics of binaries in the Pleiades cluster
We present a statistical analysis of binaries in galactic clusters,based on photometric properties. Synthetic clusters are used to solvethe deconvolution problem. If the colour-magnitude relation for singlestars is given and if triple stars are treated as binaries, thedistribution of systems in a colour-magnitude diagram (CMD) can be usedto determine cluster properties. They include the maximum number ofsingle stars N1max which is compatible with the distributionof systems, a standard deviation sigma (describing the scatter of starson the main sequence), a critical mass ratio q_c, and the mass ratiodistribution in the case of N_1=N1max. In the general case(N_1<= N1max) the mass ratio distribution can bedetermined for q>q_c, and in favourable cases (if N_1 is sufficientlylarge) for all mass ratios. A first application concerns thePleiades cluster in the colour range 0.2<= B-V<0.98. The concentration of systems near the main sequence in the CMDis used to derive an approximation for the colour-magnitude relation. Asmall positive number c is involved as a parameter. The mass ratiodistribution depends sensitively on c and increases towards small massratios, at least up to q =~ 0.5 and probably up to q =~ 0.3. Thedistribution is bimodal, with a peak at q=1. Photometric arguments showthat c<~ 0.02. A binary frequency of 60-70% as expected from clustersimulations (Kroupa \cite{krou}) requires c<~ 0.03. An adjustment oftwo parameters (c=0.02 and a 70% binary frequency) is sufficient toreproduce the mass ratio distribution for binaries in the galacticfield. This suggests that the mass ratio distribution in the Pleiades issimilar to the distribution in the field, in accordance with aconjecture of Bouvier et al. (\cite{brn}, BRN).
| The rotational velocity of low-mass stars in the Pleiades cluster
We present new {vsin i} measurements for 235 low-mass stars in thePleiades. The differential rotational broadening has been resolved forall the stars in our sample. These results, combined with previouslypublished measurements, provide a complete and unbiased rotation dataset for stars in the mass range from 0.6 to 1.2{Msun}.Applying a numerical inversion technique on the {vsin i} distributions,we derive the distributions of equatorial velocities for low-massPleiades members. We find that half of the Pleiades dwarfs with a massbetween 0.6 to 1 {Msun} have rotation rates lower than 10{ kms(-1) }. Comparison of the rotational distributions of low-mass membersbetween IC 2602/2391 (~ 35 Myr) and the Pleiades (~ 100 Myr) suggeststhat G dwarfs behave like solid-bodies and follow Skumanich's law duringthis time span. However, comparison between Pleiades and older clusters-M34 (~ 200 Myr) and Hyades (~ 600 Myr)- indicates that the braking ofslow rotators on the early main sequence is weaker than predicted by anasymptotical Skumanich's law. This strongly supports the view thatangular momentum tapped in the radiative core of slow rotators on thezero age main sequence (ZAMS) resurfaces into the convective envelopebetween Pleiades and Hyades age. For the G-dwarfs, we derive acharacteristic coupling time scale between the core and the envelope ofabout 100-200 Myr, which accounts for the observed evolution of surfacerotation from the ZAMS to the Hyades. The relationship between rotationand coronal activity in the Pleiades is in agreement with previousobservations in other clusters and field stars. We show that the Rossbydiagram provides an excellent description of the X-ray activity for allstars in the mass domain studied. The Pleiades data for slow andmoderate rotators fills the gap between the X-ray-rotation correlationfound for slow rotators and the X-ray ``saturation plateau'' observedfor young fast rotators. The transition between increasing X-ray fluxwith rotation and X-ray saturation is observed at log (P/tau)=0.8+/-0.1. These results strengthen the hypothesis that the``saturation'' of the angular momentum loss process depends on thestellar mass. Based on observations collected at the Observatoire deHaute-Provence with ELODIE at the 193cm telescope and with CORAVEL atthe 1m-swiss telescope
| 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.
| Rotation and chromospheric emission among F, G, and K dwarfs of the Pleiades
High-resolution echelle spectra of more than 100 F, G, and K dwarfs inthe Pleiades are reported. Chromospheric activity in these stars ismeasured via comparisons of the profiles of H-alpha and the Ca II IRtriplet to chromospherically inactive field stars. Consistent dereddenedcolors are determined from the available photometry and temperatures arederived. Most G and K dwarfs in the Pleiades rotate slowly, but about 20percent of the stars are ultrafast rotators (UFRs). That fraction ofUFRs is independent of color, and the highest rotation rates are foundamong the K dwarfs. The Pleiades exhibit a broad range in the strengthof chromospheric emission at any one color. Most G and K dwarfs in thePleiades show H-alpha and the IR triple in absorption, with filling inof the line cores.
| Investigation of the Pleiades cluster. I - Radial velocities of corona stars
Coravel radial velocities of 83 stars ranging in spectral types from F5to K0 selected frozen van Leeuwen's et al. (1986) survey of the coronaof the Pleiades show that only 56 are actually members. Sixspectroscopic binaries among the members and two among the nonmembershave been found. The large extent of the cluster over the sky alsoinduces a radial-velocity gradient from which a convergent point hasbeen determined. Since the cluster's depth is so large, the width of themain sequence is increased. The present results lead to a star densityof 1.1 stars per sq deg for r between 2.5 and 3.5 deg. However, westress that this is only a preliminary result, since the sample of starsin the corona is incomplete.
| A VBLUW photometric survey of the Pleiades cluster
Photometric data are presented for 390 known or suspected members of thePleiades cluster. The data were obtained in 1979 at ESO using theWalraven VBLUW photometer and the Dutch 91-cm telescope. A comparisonwas made with subsets obtained with the same telescope andinstrumentation at the former Leiden Southern Station at the SAAO annexduring 1976 and 1977, and with data obtained at ESO during 1980 and1981. The much improved performance of the telescope and the photometerat their new site is obvious from these comparisons. The stars measuredcomprise the selection of possible members by Hertzsprung (1947)brighter than m(pg) = 14.5 and a selection of possible members in theouter region of the cluster by Pels et al. (1975). Of the starsselected, 66 were found not to be members. A few of these are possiblyescaping members. The present data set provides a well determined mainsequence over the range K2V to B9V, as well as data on some of theprobably premain-sequence K2-to-K5 and postmain-sequence B8-to-B6 stars.Finding charts for the stars selected by Pels are presented in anappendix.
| Statistical identification of binaries in star clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87..707B&db_key=AST
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
| The physical members of the Pleiades group
Not Available
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Телец |
| Прямое восхождение: | 03h37m24.05s |
| Склонение: | +22°21'03.6" |
| Видимая звёздная величина: | 9.163 |
| Собственное движение RA: | 19.1 |
| Собственное движение Dec: | -45.4 |
| B-T magnitude: | 9.787 |
| V-T magnitude: | 9.215 |
Каталоги и обозначения:
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