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Binarity of Am stars in Praesepe and Hyades
CORAVEL radial-velocity observations of Am stars in the Hyades andPraesepe have allowed the determination of orbital elements for 10spectroscopic binaries, among which 3 are first determinations. One Amstar (KW 40) is found to be a well hierarchisedtriple system. KW 538 has a rather long period (435days) for an Am star. Orbits of systems with periods shorter than 8.5days are circularized, or present eccentricities smaller than 0.04. For19 Am stars, the number of quadruple-, triple-, double-, single systemsis 1:2:14(10+4?):(2?). The Am stars in a (beta , B-V) diagram clearlystand away by 0.03 mag from the sequence defined by normal main-sequencestars. This diagram could be a powerful method to identify Am stars inmore distant open clusters, provided there is no differential reddening.In the colour-magnitude diagram (M_V, beta ), double-lined binaries are0.6 - 0.7 mag above the ZAMS as expected, while most single-lined areclose to or on the ZAMS because the secondary does not contribute muchlight. The absence of X-ray detection of 4 systems in the Hyades is anargument for the presence of a white dwarf secondary. based onobservations collected at the Haute-Provence Observatory(France)}\fnmsep \thanks{Table~2 is available only in electronic form atCDS by ftp at 130.79.128.5 or on the Web athttp://cdsweb.u-strasbg.fr/CDS.html
| The Age Range of Hyades Stars
On the basis of canonical models, the age of Hyades supercluster stars,whether in the Hyades and Praesepe clusters or the noncluster field,ranges from (5-6) x 10^8 to 10^9 yr. The difference between the parallaxderived from the supercluster motion and that obtained from Hipparcosobservations has a dispersion only twice that of the mean dispersion ofthe individual Hipparcos values. The supercluster appears not to containred giants on the first ascent of the red giant branch, but onlyasymptotic giant branch (``clump'') stars. The masses obtained forindividual components of binary stars in the supercluster show adispersion of less than 10% when compared with model predictions.
| The Praesepe open cluster: abundances of Li, Al, Si, S, Fe, Ni, and EU in A stars.
In the second of a series of papers on the A stars in open clusters, thePraesepe cluster is investigated; in the first paper, it was thePleiades. Ten A Praesepe stars were observed with theCanada-France-Hawaii telescope at high spectral resolution and highsignal-to-noise ratios. Photospheric abundances of the sample, which hasturned out to be composed exclusively with Am stars, have beendetermined for Li, Al, Si, S, Fe, Ni, and Eu from model atmosphereabundance analysis. The A stars of Praesepe are well advanced in theMain Sequence evolution: several of the observed stars are in theturn-off (and one is a blue straggler). The Li abundance in Am stars isthe same as in non-evolved Praesepe F stars on the hot side of the Lidip, and Fe is twice its original value as given by Praesepe F stars.The abundances of the studied elements were found remarkably uniform inthe cluster over a large range of T_eff, i.e., for various structureenvelopes and evolution. Surface abundances of Li and Fe remainunchanged in Am stars at both ages of the Pleiades and Praesepeclusters. The Li results for the Am stars challenge predictions fromevolutionary model envelopes in the framework of a diffusion-dominantdescription. Based on observations collected at the Canada-France-Hawaiitelescope (Hawaii)
| Evolution of mass segregation in open clusters: some observational evidences
On the basis of the best available member list and duplicityinformation, we have studied the radial structure of Praesepe and of thevery young open cluster NGC 6231. We have found mass segregation amongthe cluster members and between binaries and single stars, which isexplained by the greater average mass of the multiple systems. However,the degree of mass segregation for stars between 1.5 and 2.3 M_sun isless pronounced in Praesepe than in the Pleiades. Furthermore, masssegregation is already present in the very young open cluster NGC 6231although this cluster is likely still not dynamically relaxed. Wediscuss the implications of these results and propose a qualitativescenario for the evolution of mass segregation in open clusters. InPraesepe the mass function of single stars and primaries appears to besignificantly different, like in the Pleiades. We observe an absence ofellipticity of the outer part of Praesepe. Tables 2 and 3 are availableonly in electronic form from the Strasbourg ftp server at 130.79.128.5
| High-precision study of proper motions and membership of 924 stars in the central region of Praesepe.
High-precision proper motions for 257 and 296 stars in a 90'x90' regioncentered on BD+20 2170 were obtained from seven plates taken with the40cm refractor (f=6895mm) at Zo-Se station of Shanghai Observatory withsix AC plates and the stellar positions in Russell's (1976) catalogue,respectively. Combining with the data given by Klein-Wassink (1927),Jones (1971), Artyukhina (1971), and Jones & Cudworth (1983), theseproper motions give a sample of 924 stars in the region mentioned above.With membership probabilities estimated by an improved maximumlikelihood method, a very good sample of 198 members is obtained withproper motion accuracies ranging from +/-0.2 to +/-5.0mas/yr, of which60 per cent are better than +/-1.0mas/yr, and the completeness nearlydown to B=15.5.
| ICCD speckle observations of binary stars. IX - A duplicity survey of the Pleiades, Praesepe, and IC 4665 clusters
Multiplicity of stars within clusters is a well-studied phenomenon.However, recent survey work done on the Hyades by Mason et al. (1993)would seem to indicate that even in the most often studied clusters,there may be binaries yet undiscovered. In order to expand the sample ofcluster binaries with potentially short-period visual orbits, a specklesurvey of 45 Pleiades, 54 Praesepe, and 22 IC 4665 bright stars (V isless than 10) for possible multiplicity was conducted at the KPNO 4 mMayall telescope between 1987 October and 1991 November. Of these, threenew binaries have been discovered: one in the Pleiades where the newcomponent may be spectroscopic, another in Praesepe which has beenconfirmed from examinations of archival observations and also has beenresolved by occultation, and the third in IC 4665. Continued study ofthese new binary stars could further refine the cluster distance modulias well as the cluster mass-luminosity relations.
| Liste des étoiles Ap et Am dans les amas ouverts (édition révisée)
Not Available
| Washington photometry of open cluster giants - Nine old disk clusters in the third Galactic quadrant
Washington photoelectric photometry for 136 stars in nine old openclusters is presented and used to determine the luminosity class, T(e),and metallicity. The virtually unstudied cluster NGC 2324 is found tohave a metallicity one tenth that of the sun, as is the cluster NGC 2660for which previous estimates have ranged from about +0.1 to -0.5. Athird cluster, NGC 3960, with a Galactocentric distance of only 8 kpc,is found to have a metallicity of -0.7, also substantially lower thanpublished values. Such clusters indicate that substantial scatteractually exists in the tight relation found by Friel and Janes (1992)between the metallicity of an open cluster and its currentGalactocentric distance. Outer disk clusters have a metallicity at agiven age that is much more like that of the LMC counterparts than thatof solar neighborhood disk field stars or clusters.
| The Hyades supercluster in the FK5
The members of the Hyades supercluster brighter than about M(V) = + 4mag and contained in the FK5, or having nearly FK5 quality propermotions, show a convergent point of (A,D) = (6h, + 6.5 deg). The Hyadescluster stars in the FK5 have a mean distance of 46.7 pc. Thesupercluster, as well as the Hyades and Praesepe cluster, populationsrepresent at least three age groups. Standard models indicate ages of 3to 4, 6, and 8 x 10 exp 8 yr, whereas model ages with convectiveovershoot are nearly twice this. Most of the Am and USPC stars in thesupercluster are of the same age. The Ap stars mark the onset of shellhydrogen burning. The photometry of the red giants confirms the agespread and indicates a weakening of CN strength with age. Attention iscalled to the need for further study of NGC 2423 as an effectiveprolusion to understanding the evolution of the supercluster.
| J 2000.0 positions and proper motions of 257 stars in the central part of the Praesepe astrometric standard region
Data are presented on the J2000.0 positions and proper motions of 257stars in the central 1.5 deg x 1.5 deg area of the Praesepe astrometricstandard region. These data obtained with accuracies of 0.005-0.10arcsec for the positions in each direction and 0.0002-0.006 arcsec/yrfor the proper motions in each direction. The list includes stars forwhich proper motions were not given in the Russell (1976) catalog.
| Photometry of astrometric reference stars
UBVRI, DDO, and uvby, H-beta photometry of astrometric reference starsis presented. Spectral types and luminosity classifications made fromthe colors are used to determine their spectroscopic parallaxes. In thispaper, colors for 309 stars in 25 regions are given, and classificationsfor 210 stars have been made. These stars form reference frames in theAllegheny Observatory Multichannel Astrometric Photometer astrometricprogram, and in the Praesepe cluster reduced by Russell (1976). It isfound that the present photometric spectral types are reliable to within2.5 spectral subclasses.
| Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
| Chemically peculiar stars in open clusters. I - The catalog
The largest existing compilation is presented of Ap and Am open clusterstars. The catalog contains information on 381 chemically peculiar (CP)stars of the upper main sequence in 79 open clusters. The catalog iscomposed of the following tables: (1) the main body, which lists CP (orsuspected CP) stars which are kinematical (or suspected kinematical)members of open clusters; (2) the list of CP (or suspected CP) starssometimes numbered among cluster members but which are actuallykinematical nonmembers; (3) the list of stars sometimes designated as'peculiar' but, in fact, probably not CP; (4) references for numberingsystems of cluster stars; (5) references for membership; and (6)references for spectral and/or peculiarity types.
| Catalog of AP and AM stars in open clusters
The previous results of Raab (1922), Markarian (1951), and Collinder(1931) have been used to catalog Ap and Am stars that are in the fieldof open clusters. Tabular data are presented for the clusterdesignation, the HD or HDE number, the right ascension (1900), thedeclination (1900), and the magnitude. Also listed are the spectraltypes and, for certain stars, the probability of cluster membership.
| Photoelectric search for CP2-stars in open clusters. XII - Alpha Persei, Praesepe and NGC 7243
Observations of 95 stars in the open clusters Alpha Persei, Praesepe,and NGC 7243 have been performed by Delta-a photometry in order tosearch for the presence of the 5200-A feature of CP2 (or CP4) stars.Although peculiarity has been claimed for half a dozen stars in AlphaPersei, the photometry detects only the CP4 star (= He-weak) HL 985among the cluster members. The behavior of 3 Be/shell stars (HL 861,1164, 904) concerning the 5200-A feature is discussed. Praesepe, by farthe oldest cluster in the survey program, presents a very new andspecial case: 3 stars, previously classified as Am have Delta-a valuesaround 0.020 mag, i.e., they exhibit photometric peculiarity likeCP2-stars. Such values are incompatible with preceding results for fieldand cluster Am-stars (= CP3). These objects deserve further attentionboth photometrically and spectroscopically. NGC 7243 exhibits anoutstanding high frequency of CP2-stars; two certain Delta a-peculiarstars have been found: L 370, already known as peculiar, and the newlyidentified L 114. Two stars are near the detection level: L 58 and 121.According to Geneva photometry, L 487 is markedly peculiar.
| MK classification of the brighter praesepe stars
MK classifications have been obtained for the 42 brightest stars in therich open cluster Praesepe. In the H-R diagram, 10 of the 12 starsbrighter than V = 7.0 mag have luminosity classes brighter than V or areAm stars. Only two of the stars fainter than V = 7.0 mag are ofluminosity class IV. The nine Am stars discovered by Bidelman (1956) areconfirmed. The frequency of these among the late A stars is consistentwith results for field stars, but there is only one Ap star. The reasonsfor that deficiency are discussed.
| Metallicism among A and F giant stars
132 stars considered as A and F giants have been studied for theirproperties in the Geneva photometric system. It is shown that thissystem to derive the temperature, absolute magnitude and Fe/H value forstars in this part of the HR diagram. 36 percent of the stars of oursample exhibit an enhanced value Delta m2 that can be interpreted interms of Fe/H. The red limit of stars having an enhanced Fe/H value is0.225 in B2-V1 or 6500 K in Teff. This corresponds to the limit definedby Vauclair and Vauclair (1982) where the diffusion timescale is equalto the stellar lifetime and permits the assumption that the diffusion isthe process responsible for the metallicism observed in the A and Fgiants.
| A Proper Motion Membership Study of Praesepe
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983AJ.....88..215J&db_key=AST
| Properties of AM stars in the Geneva photometric system
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....92..289H&db_key=AST
| The rotational velocity effect on the main sequence AM stars metallicity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&A....74...38B&db_key=AST
| Metal abundance in the Praesepe and Hyades clusters
Calcium K-line photometry is reported for 27 A-type stars in thePraesepe cluster, and the data obtained are compared with previousK-line observations of Hyades stars. It is found that calcium and othermetals are generally overabundant in Praesepe relative to field starsand that there is a considerable scatter in metal-abundance indices.Comparison with the Hyades results indicates that the Praesepe stars areas metal-enriched as the Hyades stars. These results are taken asevidence favoring Eggen's (1960) proposal that the Hyades and Praesepeclusters should be regarded as a single group having, on the average,about a factor-of-two higher metal abundance than solar-neighborhoodfield stars as well as a high internal dispersion in metal-linestrengths. The questions of where and how the Praesepe-Hyades starsacquired their high average metal abundances, K-line strengths, andassociated dispersions are briefly considered.
| Multicolor photometry of metallic-line stars. III. A photometric catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974RMxAA...1..175M&db_key=AST
| Catalogue of AM stars with known spectral types
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&AS...10..385H&db_key=AST
| Faint members of the Praesepe cluster.
Not Available
| Internal Motions in Praesepe
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..470J&db_key=AST
| Metallic-Line a Stars and Pulsation
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJ...162..597B&db_key=AST
| Photoelectric observations of early A stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....1..165J&db_key=AST
| Four-color and H-bet photometry of open clusters. III. Praesepe.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..818C&db_key=AST
| Effect of rotation on the colors and magnitudes of stars in Praesepe.
Not Available
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Cancro |
| Ascensione retta: | 08h40m56.93s |
| Declinazione: | +19°56'05.5" |
| Magnitudine apparente: | 8.652 |
| Moto proprio RA: | -36.2 |
| Moto proprio Dec: | -15.2 |
| B-T magnitude: | 9.068 |
| V-T magnitude: | 8.687 |
Cataloghi e designazioni:
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