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Decay of Planetary Debris Disks
We report new Spitzer 24 μm photometry of 76 main-sequence A-typestars. We combine these results with previously reported Spitzer 24μm data and 24 and 25 μm photometry from the Infrared SpaceObservatory and the Infrared Astronomy Satellite. The result is a sampleof 266 stars with mass close to 2.5 Msolar, all detected toat least the ~7 σ level relative to their photospheric emission.We culled ages for the entire sample from the literature and/orestimated them using the H-R diagram and isochrones; they range from 5to 850 Myr. We identified excess thermal emission using an internallyderived K-24 (or 25) μm photospheric color and then compared allstars in the sample to that color. Because we have excluded stars withstrong emission lines or extended emission (associated with nearbyinterstellar gas), these excesses are likely to be generated by debrisdisks. Younger stars in the sample exhibit excess thermal emission morefrequently and with higher fractional excess than do the older stars.However, as many as 50% of the younger stars do not show excessemission. The decline in the magnitude of excess emission, for thosestars that show it, has a roughly t0/time dependence, witht0~150 Myr. If anything, stars in binary systems (includingAlgol-type stars) and λ Boo stars show less excess emission thanthe other members of the sample. Our results indicate that (1) there issubstantial variety among debris disks, including that a significantnumber of stars emerge from the protoplanetary stage of evolution withlittle remaining disk in the 10-60 AU region and (2) in addition, it islikely that much of the dust we detect is generated episodically bycollisions of large planetesimals during the planet accretion end game,and that individual events often dominate the radiometric properties ofa debris system. This latter behavior agrees generally with what we knowabout the evolution of the solar system, and also with theoreticalmodels of planetary system formation.
| 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.
| 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 IMF of open star clusters with Tycho-2
We studied the fields of nine nearby open star clusters based on theTycho-2 catalogue. We determined membership probabilities for the starsin the cluster fields from the stellar proper motions and used theTycho-2 photometry to compute the initial mass function (IMF) of theclusters from the main sequence turn-off point down to approx. 1 M_sun.We found IMF slopes ranging from Gamma =-0.69 down to Gamma =-2.27 (whenthe Salpeter \cite{salpeter} value would be Gamma =-1.35). We alsostudied the membership of individual stars of special astrophysicalinterest. In some cases previous results had to be revised. As aby-product, we investigated some general properties of the Tycho-2catalogue; we confirmed that the Tycho-2 proper motions show onlymarginal deviations from the Hipparcos catalogue. On the other hand, insome regions the completeness of the catalogue seems to decrease atmagnitudes brighter than claimed by Høg et al. (\cite{tycho2}).Based on observations of the ESA Hipparcos satellite.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Spectroscopy of Blue Stragglers and Turnoff Stars in M67 (NGC 2682)
We have analyzed high-resolution spectra of relatively cool bluestragglers and main-sequence turnoff stars in the old open cluster M67(NGC 2682). We attempt to identify blue stragglers whose spectra areleast contaminated by binary effects (contamination by a binarycompanion or absorption by circumstellar material). These ``best''stragglers have metallicities ([Fe/H]=-0.05) and abundance ratios notsignificantly different from those of the turnoff stars. Based onarguments from hydrodynamical models of stellar collisions, we assertthat the current upper limits for the lithium abundances of all bluestragglers observed in M67 (by us and others) are consistent with aformation process without mixing, assuming pre-main-sequence andmain-sequence depletion patterns observed for M67 main-sequence stars.We discuss composition signatures that could more definitivelydistinguish between blue straggler formation mechanisms in open clusterstars. We confirm the spectroscopic detection of a binary companion tothe straggler S1082. From our spectra, we measure a projected rotationalspeed of 90+/-20 km s-1 for the secondary and find that itsradial velocity varies with a peak-to-peak amplitude of >~25 kms-1. Because the radial velocities do not vary with a periodcorresponding to the partial eclipses in the system, we believe thissystem is currently undergoing mass transfer. In addition we presentevidence that S984 is a true blue straggler (not an unresolved pair). Ifthis can be proved, our detection of lithium may indicate a collisionalorigin. Based in part on observations obtained with the Hobby-EberlyTelescope, which is a joint project of the University of Texas atAustin, the Pennsylvania State University, Stanford University,Ludwig-Maximillians-Universität, München, andGeorg-August-Universität, Göttingen.
| 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.
| 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 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.
| Photoelectric photometry and period analysis of selected Delta Scuti stars in Praesepe
Photoelectric photometry of seven Delta Scuti stars in Praesepe wassecured. Three of them were observed simultaneously at observatorieslocated at different longitudes. Period analysis has been carried outfor each star with different computing packages and the results comparedto those in the literature. Their physical characteristics have beendetermined from the Stroemgren photometry and theoretical and empiricalcalibrations. The observations are available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.70.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Delta a and Stroemgren photometry of stars in the Renson-catalogue of AP and AM stars
We have observed 131 stars of \cite[Renson's (1991)]{re91} catalogue ofAp and Am stars both in the Stroemgren & Maitzen's (1976) Delta asystem as a contribution to the photometric studies of the lambda 5200broad band flux depression feature in chemically peculiar stars. Withfew exceptions the probability grouping of Renson for membership in theCP2 group of peculiar stars is nicely reflected by peculiar values ofDelta a. Comparison with already available Delta a values yieldsslightly larger values due to a minor shift in the filter g_1 samplingthe depression. As found by \cite[Maitzen & Vogt (1983)]{ma83} theGeneva system peculiarity parameters correlate well with Delta a. Thisstudy demonstrates the advantageous performance of a photoelectricphotometer with a rapidly rotating filter wheel moving in a stop and gomode. Tables 3 and 4 are also available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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)
| Blue stragglers in open clusters. I. NGC 2632
We present the results of a spectroscopic study of four blue stragglersfrom old galactic open cluster NGC 2632 (Praesepe). The LTE analysisbased on Kurucz's atmosphere models and synthetic spectra technique hasshown that three stars, including the hottest star of the clusterHD73666, possess an uniform chemical composition: they show a solar-likeabundance (or slight overabundance) of iron and an apparent deficiencyof oxygen and silicon. Two stars exhibit a remarkable bariumoverabundance. The chemical composition of their atmospheres is typicalfor Am stars. One star of our sample does not share such uniformelemental distribution, being generally deficient in metals. For allstars Teff and log g values were estimated. A shortdiscussion of the obtained results is given.
| 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
| 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
| The Consistency of Stromgren-Beta Photometry for Northern Galactic Clusters. II. Praesepe and NGC 752
We have measured stars in Praesepe and NGC 752 in aninternally-consistent Stromgren-Beta system. This system is based inlarge part on published Hyades and Coma measurements. On comparing ourPraesepe results to those of Crawford and Barnes (1969, AJ, 74, 818), wefind that the published color indices require corrections of 10-18 mmagto put them on the Hyades-Coma system. This deduction applies for b-y,m_1 and Beta (but not c_1). For the NGC 752 data of Crawford and Barnes(1970, AJ, 75, 946), we obtain a nonzero correction only for Beta. Thiscorrection is about 9 mmag. Also for NGC 752, we find that the data ofTwarog (1983, ApJ, 267, 207) require corrections ranging from 4-17 mmag,with all Stromgren indices being affected and the largest correctionbeing for m_1. These corrections resolve the long-standing problem posedby the differences between the Twarog and Crawford-Barnes data. Forthree published sources of V magnitudes, we obtain offsets ranging from-14 to +27 mmag relative to our zero point, and we suggest that suchoffsets are fairly common in published photometry for galactic clusters.For Praesepe, we use new and corrected data to test for a c_1 anomalyand is indistinguishable from Coma in that regard. (SECTION: StellarClusters and Associations)
| Blue Stragglers in the Solar Vicinity: Newborn or Reborn
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110..823E&db_key=AST
| 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.
| 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.
| Catalogue of blue stragglers in open clusters.
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
| Photometry of Stars in the Field of V431 Orionis
Not Available
| Photometry of Stars in the Field of R Aurigae
Not Available
| A search for radio emission from the 'nonmagnetic' chemically peculiar stars
We have observed 23 members of the Am and HgMn subclasses of chemicallypeculiar (CP) stars with the Very Large Array (VLA) to search fornonthermal radio emission at levels comparable to those found for the Siand He peculiar subclasses of the CP stars by Linsky et al. (1992). Thisstudy was motivated by recent claims that magnetic fields of kilogaussstrength are present in at least some of the Am and HgMn stars, contraryto previous beliefs, which would indicate that radio-emittingmagnetospheres could be present in these stars. We detected none of theAm and HgMn stars as radio emitters with upper limits typically lessthan 0.20 mJy. Applying a correlation between radio luminosity, surfacemagnetic field, and effective temperature derived from previous radiostudies of the Si and He peculiar CP stars, we find that the predictedradio luminosities of alpha And (an HgMn star) and Sirius (a hot Amstar) are more than an order of magnitude larger than the observed upperlimits, indicating that these stars lack magnetospheres, and, byinference, surface magnetic fields.
| The interior structure and evolution of blue straggler stars in open clusters
We present a detailed spectroscopic determination of effectivetemperatures and surface gravities of B- and A-type blue straggler starsin four open clusters by means of model atmospheres and new optical/UVspectrograms. By using a new method of analysis which also allows toseparate objects not belonging to the cluster under investigation weshow for the first time convincingly that blue stragglers are not theresult of internal slow mixing processes as proposed by Wheeler (1979)and Saio & Wheeler (1980). Instead, their parameters are consistentwith the predictions of normal stellar evolution. We discuss theimplications of our result for possible evolutionary scenarios leadingto straggling cluster stars.
| All-sky Stromgren photometry of speckle binary stars
All-sky Stromgren photometric observations were obtained for 303 specklebinaries. Most stars were in the range of V = 5-8. These data, whencombined with ratios of intensities from the CHARA speckle photometryprogram, will allow the determination of photometric indices for theindividual components of binary stars with separations as small as 0.05arcsec. These photometric indices will complement the stellar massesfrom the speckle interferometry observations to provide a much improvedmass-luminosity relationship.
| 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.
| Effects of rotation on the colours and line indices of stars. VI - The reality of the blue straggler phenomenon
The effect of rotation on the observed colors of stars has beenconsidered as a possible cause for the blue straggler phenomenon inclusters listed by Mermilliod (1982). It appears that this phenomenon isdefinitely not real in the case of the late B and early A spectral typeblue stragglers that are intrinsic slow rotators. Among clusterscontaining the early B type blue stragglers it is found that theanomalous position of the stragglers in NGC 6633, NGC 4675, and NGC 2516cannot be accounted for by rotation effects alone.
| 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.
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | סרטן |
| התרוממות ימנית: | 08h40m11.45s |
| סירוב: | +19°58'16.1" |
| גודל גלוי: | 6.577 |
| מרחק: | 174.825 פארסק |
| תנועה נכונה: | -34.1 |
| תנועה נכונה: | -13.8 |
| B-T magnitude: | 6.606 |
| V-T magnitude: | 6.58 |
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