Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
New stellar members of the Coma Berenices open star cluster
We present the results of a survey of the Coma Berenices open starcluster (Melotte 111), undertaken using proper motions from theUSNO-B1.0 (United States Naval Observatory) and photometry from theTwo-Micron All-Sky Survey (2MASS) Point Source catalogues. We haveidentified 60 new candidate members with masses in the range 1.007
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Abundances of A/F and Am/Fm stars in open clusters as constraints to self-consistent models including transport processes
We describe the current status of a programme we started a few years agoto observe a large number of A/F and Am/Fm stars in open clusters ofvarious ages. Spectra were obtained with the AURELIE and ELODIEspectrographs at a resolving power of about 40000 and S/N ratios from100 up to 500. Abundances of 11 chemical elements have been derived byusing Takeda's (1995) procedure. A short review on previous abundancedeterminations of A and F dwarfs in open clusters and a progress reporton the current status of this project are presented. New abundancedeterminations for 24 A and F dwarfs in the Coma Berenices cluster arepresented. These abundance determinations serve to set constraints toself-consistent evolutionary models of A and F stars including transportprocesses.
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| Improved Hipparcos Parallaxes of Coma Berenices and NGC 6231
A method to reprocess the Hipparcos Intermediate Astrometry Data thatreduces the propagation of the along-scan spacecraft attitude errors wasdeveloped and successfully used to obtain a more consistent parallax ofthe Pleiades (Makarov, published in 2002). The same technique is usednow to correct the Hipparcos parallaxes of the Coma Berenices and NGC6231 open clusters, which are also in error. The new mean parallax ofComa is 12.40+/-0.17 mas (against previously 11.43 mas) and of NGC 62311.7+/-0.4 mas (against previously -0.8 mas). The new data for Coma arein excellent agreement with the pre-Hipparcos main-sequence fittingestimates. All six members of NGC 6231 that have negative parallaxes inHipparcos obtain positive parallaxes. These results suggest that themain source of astrometric error has been correctly identified, and thata more accurate Hipparcos catalog can be computed.
| 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
| The Pleiades, Coma, Hyades, and Praesepe open clusters: Li, Al, Si, S, Fe, Ni, and Eu abundances compared in A stars
In the third of a series of papers on the A stars in open clusters, theComa and Hyades clusters are revisited; in the first and second papers,the Pleiades and Praesepe were respectively investigated. All thespectra were secured with the Canada-France-Hawaii telescope at highspectral resolution and high signal-to-noise ratios. Photosphericabundances have been determined for Li, Al, Si, S, Fe, Ni, and Eu frommodel atmosphere abundance analysis. All the A stars with enough-sharplines to be studied for Li were observed in the four clusters. Abundanceresults are summarized for 31 cluster members, including 21 Am, 7 normalA, and 3 early-A stars. The Am stars have very uniform Li, Al, Si, S,and Fe abundances in a large temperature range of nearly 1000 K.Compared to normal A stars, Li is significantly deficient in Am stars(by a factor of 3), Al marginally overabundant, Si, S, and Fe are thesame, Ni and Eu (with only a few results) overabundant. Those uniformabundances of Li, Al, Si, S, or Fe in Am stars involve that abundancesare little affected by the magnitude of the rotational velocity. Forboth Am and normal A samples, no abundance trend as a function of ageand/or evolution is detected in the case of Li, Al, Si, S, or Fe. Theages considered are in the range 0.8 - 7 108 years; theevolution is limited from the ZAMS to the cluster turn-off. The build-upof the chemical abundances studied, in particular the Li differentiationbetween Am and normal A stars, could have taken place very early whenthe stars arrive on the Main Sequence. The spread in lithium found forthe A stars is reminiscent of that reported in the field and one opencluster for stars of nearly the same mass and slightly evolved out ofthe Main Sequence. The Li abundance does not change as soon as the starevolves through the subgiant phase and the convection zone becomesdeeper. There are two exceptional Am stars: one, in the Hyades, isLi-deficient and the other, in Praesepe, Li-overabundant. They are noobvious circumstances that can distinguish both stars from others in thevery same region of their respective cluster sequence. In each of thefour clusters, the maximum Li abundance is found in A stars, generallyin normal A stars. The Fe abundance of both Am and normal A groups isfound to be twice the original Fe value (on the ZAMS) in each of thefour clusters, independently of their age or metallicity. It is wellestablished for the Am group and in only a narrow range of Teff for thenormal A group. This behavior is unexpected for normal A stars which arethought to have their original abundances and Fe abundance differentfrom that of Am stars. A larger normal A sample is needed to concludeanything. Our abundance results for cluster Am stars quantitativelyagree with predictions of new models coupling atomic diffusion withturbulent transport (Richer et al. \cite{richer99}). Based onobservations collected at the Canada-France-Hawaii telescope (Hawaii)
| Binaries in the Praesepe and Coma Star Clusters and Their Implications for Binary Evolution
This completes a study of the evolution of binary systems in five openclusters of various ages. Among 21 stars observed in Praesepe, eight arefound or confirmed to be spectroscopic binaries and orbital elements arederived, while one more shows long-term binary motion. Among 18 starsobserved in the Coma Berenices cluster, five are found or confirmed tobe spectroscopic binaries and orbital elements are derived, while asixth has tentative elements. Among five clusters studied we searchedfor three expected evolutionary effects, namely an increase with age inthe mass ratios, a decrease with age of the binary periods, and anincrease in binary frequencies. We find that there is a progression (atthe 3 sigma level) from no binaries out of 10 with mass ratios greaterthan 0.5 in the youngest cluster (combined with the published resultsfor NGC 6193) to 25% such stars in the intermediate-age clusters to 43%such stars in these two oldest clusters. There is no evidence for anincrease in short-period binaries with age. And there is slight evidence(at the 1 sigma level) for an increase with age from 15% to 28% in thefraction of large-amplitude binaries. These results are mostlyconsistent with the idea that most binaries are formed or modified inthree-body interactions, and successive generations of formation anddisruptions tend to form binaries with larger mass ratios. However, partof the initial generation of binaries is probably primordial.
| An astrometric catalogue for the area of Coma Berenices
A catalogue of stellar positions and proper motions down to the 14thphotographic magnitude in the area of the open cluster in Coma Berenicesis compiled from data of 12 different sources. The accuracy of theproper motion data is comparable to that of the Hipparcos Catalogue. Thecatalogue Table 5 is 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/Abstract.html
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| The Coma Berenices star cluster and its moving group
We report on the analysis of astrometric and photometric data fromHipparcos, Tycho and the ACT catalogue in a 1200 sq. degree field aroundthe nearby open star cluster in Coma Berenices and infer thecharacteristic features of this cluster. From a sample of 51 kinematicmembers we derive the cluster's distance, size and spatial structure aswell as its stellar content, mass and age. We find that the clusterconsists of an elliptical core-halo system with major axis parallel tothe direction of galactic motion, and of a moving group of extratidalstars. The latter have tangential distances >= 10 pc from the clustercenter, but have the same distance from the Sun, the same motion and thesame age as the stars in the core and halo. The luminosity function ofthe core-halo system steeply declines beyond absolute magnitude M_V=4.5,but that of the moving group rises towards fainter magnitudes andsuggests the existence of further low-mass members below the currentmagnitude limit. The cloud of extratidal stars witnesses the process ofdissolution of the cluster.
| Metal abundances of A-type stars in galactic clusters. II. Pleiades, Coma Berenices, Hyades, and Praesepe
A study of chemical composition for 23 A-type stars in four nearby openclusters (Pleiades, Coma, Hyades and Praesepe) has derived detailedabundances for Mg, Ca, Sc, Cr, Fe, and Ni from high resolutionspectroscopy. These results are discussed using the microscopicdiffusion model, which yields time-dependent element stratifications asin the case of Am stars. For the Pleiades, the youngest cluster, we findseveral atypical abundance patterns, which may be transient phases ofthe Am phenomenon. The members of the older clusters show globally moreclassical patterns. Based on observations collected at the Observatoirede Haute-Provence (France)
| Spectrophotometry of 237 Stars in 7 Open Clusters
Spectrophotometry is presented for 237 stars in 7 nearby open clusters:Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, andM39. The observations were taken by Lee McDonald and David Bursteinusing the Wampler single-channel scanner on the Crossley 0.9m telescopeat Lick Observatory from July 1973 through December 1974. Sixteenbandpasses spanning the spectral range 3500 Angstroms to 7780 Angstromswere observed for each star, with bandwidths 32Angstroms, 48 Angstromsor 64 Angstroms. Data are standardized to the Hayes-Latham system tomutual accuracy of 0.016 mag per passband. The accuracy of thespectrophotometry is assessed in three ways on a star-by-star basis.First, comparisons are made with previously published spectrophotometryfor 19 stars observed in common. Second, (B-V) colors and uvby colorsare compared for 236 stars and 221 stars, respectively. Finally,comparsions are made for 200 main sequence stars to the spectralsynthesis models of Kurucz, fixing log g = 4.0 and [Fe/H] = 0.0, andonly varying effective temperature. The accuracy of tests using uvbycolors and the Kurucz models are shown to track each other closely,yielding an accuracy estimate (1 sigma ) of 0.01 mag for the 13 colorsformed from bandpasses longward of the Balmer jump, and 0.02 mag for the3 colors formed from the three bandpasses below the Balmer jump. Incontrast, larger scatter is found relative to the previously publishedspectrophotometry of Bohm-Vitense & Johnson (16 stars in common) andGunn & Stryker (3 stars). We also show that the scatter in the fitsof the spectrophotometric colors and the uvby filter colors is areasonable way to identify the observations of which specific stars areaccurate to 1 sigma , 2 sigma , .... As such, the residuals from boththe filter color fits and the Kurucz model fits are tabulated for eachstar where it was possible to make a comparison, so users of these datacan choose stars according to the accuracy of the data that isappropriate to their needs. The very good agreement between the modelsand these data verifies the accuracy of these data, and also verifiesthe usefulness of the Kurucz models to define spectrophotometry forstars in this temperature range (>5000 K). These data define accuratespectrophotometry of bright, open cluster stars that can be used as asecondary flux calibration for CCD-based spectrophotometric surveys.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Atmospheric chemical composition of Am stars in the Coma cluster
Not Available
| Coronal activity in the Coma Berenices open cluster.
We present ROSAT PSPC observations of the ~500Myr old Coma Berenicescluster. The X-ray survey in Coma consists of a) a raster scan of shortduration PSPC pointings, b) ROSAT All-Sky Survey data, and c) a 16ksecdeep PSPC pointing. The raster scan and the survey data were mergedtogether covering an area of about 36 square degrees, while the deeppointing was analyzed separately. No major differences were foundbetween the two datasets. Our ROSAT observations indicate that Coma ismuch more similar in its X-ray properties to the coeval Hyades than tothe also coeval Praesepe cluster. As in the Hyades, almost all late-Fand G stars were detected, also showing a comparable range in X-rayluminosity. X-ray luminosity distribution functions (XLDFs) forsolar-type members are in close agreement with those of the Hyades,confirming that the majority of Praesepe's members are less luminousthan what one would expect for stars of their age. The Coma Berenicescluster is known for its apparent deficit of low mass stars of spectraltype K and later. We present 12 new possible low-mass Coma candidates,identified through this X-ray survey.
| 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.
| Member stars of the open cluster Mel 111 in Coma Berenices
Proper motions of AGK3 stars in a 6 x 6 deg field centered on the opencluster Mel 111 in Coma Berenices have been used for selecting starswhich are probable members of the cluster. Available photometric dataand radial velocities have been used to refine the selection. Seventeennew candidates are proposed.
| Effective temperature of AP and AM stars from Geneva photometry
The determination of the effective temperature of different kinds ofchemically peculiar stars from Geneva photometry is rediscussed. Wepropose an improved method of determining T(eff) of Ap stars fromGeneva's reddening-free X and Y parameters or from the B2-G index. Theeffect of duplicity on the determination of T(eff) of Am stars isdiscussed.
| Liste des étoiles Ap et Am dans les amas ouverts (édition révisée)
Not Available
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| The initial mass function of the Coma Berenices open cluster (MEL 111)
The HR (log T(eff), M(bol)) diagram of the Coma Berenices open cluster(MEL 111), as derived from a reliable list of cluster members, isemployed to show that its IMF can be approximated by a power law ofstellar mass with a slope of x = 1.90 in the mass range 1-2.5 solarmasses. The HR diagram of the Coma Berenices open cluster, and starcounts of Coma Berenices are presented.
| Which evolution for an AM star?
The behavior of calcium abundance is examined in relation to theevolutionary stage of some Am stars in three star clusters. It appearsthat, the more the Am star is evolved, the less is its calciumdeficiency. This observation makes it possible to suppose that DeltaDelphini stars and A-F giant stars photometrically similar to classicalAm stars could be descendants of the Am stars.
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
| The catalogue of equivalent line widths in the spectra of A- and F-stars.
Not Available
| Photoelectric photometry of bright stars in the vicinity of the North Galactic Pole
Not Available
| The late A-type stars - Refined MK classification, confrontation with Stromgren photometry, and the effects of rotation
The MK spectral classification for late A-type stars is refined and theeffects of rotation of spectral classification and uvby(beta) photometryfor these stars are examined. It is found that, for A3 stars, the4417/4481 A wavelength ratio produces results that are inconsistent withthe Stark broadening of the H lines. It is suggested that this ratio isnot useful as a luminosity criterion at any spectral type.Self-consistent sequences of narrow- and broadline standards areestablished. The results of the refined classification system arecompared with Stromgren photometry, showing a set of low-v sin i A-typestars with anomalously large delta(c1) indices for theirluminosity types. It is proposed that these stars are rapid rotatorsseen at fairly low inclination angles.
| 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.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Coma Berenices |
| Ascensió Recta: | 12h27m38.36s |
| Declinació: | +25°54'43.6" |
| Magnitud Aparent: | 6.659 |
| Distancia: | 91.743 parsecs |
| Moviment propi RA: | -12.4 |
| Moviment propi Dec: | -10.1 |
| B-T magnitude: | 6.88 |
| V-T magnitude: | 6.678 |
Catàlegs i designacions:
|
