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Публикации по объекту
A Complicated Pulsation δ Scuti Variable in Praesepe: HD 74028
We report the pulsation characteristics of the δ Scuti star HD74028, a low-amplitude pulsator in the Praesepe cluster. Amplitudespectra of 126 hr of observations spanning 16 nights indicatemultiperiodic pulsation behavior. We identify three frequencies,f1=22.6652, f2=23.8505, and f3=20.5254cycles day-1, and find four additional candidate frequencies,f4=17.3060, f5=12.0643, f6=14.8160, andf7=17.1143 cycles day-1. This complicatedfrequency distribution requires an explanation that includes rotationalsplitting.
| Zero-Age Main Sequence in the HR Diagram of the Vilnius Photometric System
The zero-age main sequence for solar metallicity stars in the absolutemagnitude vs. color diagram of the Vilnius seven-color photometricsystem is determined. The calibration is based on the results ofphotoelectric photometry of stars in the Hyades, Pleiades and Praesepeopen clusters and the Ori OB1 association. A theoretical Victoria-Reginaisochrone, corresponding to an age of 10 million years, coincides wellwith the lower envelope of the unevolved main sequence.
| Is Praesepe really different from the coeval Hyades cluster? The XMM-Newton view
The Praesepe open cluster represents a puzzle since it has about thesame age as the Hyades, and only slightly different metallicity, yetprevious ROSAT observations resulted in a detection rate of clustersources significantly lower than for the Hyades. We present a new 50ksec observation of Praesepe performed with the EPIC instrument on boardXMM-Newton, which resulted in the detection of ~ 200 sources, including48 cluster members. We detected all solar-type (F-G) stars in the fieldof view, ~ 90% of the K stars and ~ 70% of the M stars. We find thatthe distribution of X-ray luminosities of solar-type Praesepe members iscomparable to that of the Hyades, in contrast with the previous ROSATresults; however, the disagreement between the ROSAT and XMM-Newtonresults appears to be mostly due to X-ray faint Praesepe members fallingoutside the XMM-Newton field of view, while it is considerably reducedwhen considering only the subsample of stars in the ROSAT survey incommon with the present observation. The finding supports an earliersuggestion that Praesepe may be formed by two merged clusters ofdifferent age.
| A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters
As part of our continuing search for peculiar A-type stars, especiallyλ Bootis stars, in open clusters of all ages, we have obtainedclassification spectra of 130 late B, A, and early F-type stars in 12intermediate-age open clusters, including NGC 1039, 2281, 2548, 6633,7039, 7063, 7092, and 7209, IC 4665, IC 4756, Stock 2, and Praesepe. Thespectra were obtained with resolutions of 1.8 and 3.6 Å on the 0.8m telescope of Appalachian State University and were classified on theMK system. Numerous classical Ap and Am stars were found among the 130,including two new Ap stars in NGC 7092. In addition, three emission-linestars and two candidate λ Bootis stars were found. Neither ofthese λ Bootis candidates turned out to be members of theirrespective clusters. Combined with 184 stars previously classified in 10other intermediate-age open clusters, also devoid of λ Bootisstars, a statistically significant null result is obtained. We discussthe implications of this null result for our understanding of theλ Bootis mechanism.
| A study of correlation between the oscillation amplitude and stellar parameters of delta Scutis in open clusters. Toward selection rules for delta Scuti star oscillations
In the present work, we study correlations between stellar fundamentalparameters and the oscillation amplitude for delta Scuti stars. Wepresent this study for a sample of 17 selected delta Scutis belonging to5 young open clusters. Taking advantage of properties of delta Scutis inclusters, we correct the photometric parameters of our objects for theeffects of fast rotation. We confirm the benefit of applying suchcorrections in this kind of studies. In addition, the technique used forthis correction allows us to obtain an estimate of stellar parameterssuch as the angle of inclination and the rotation rate, usually notaccessible. A significant correlation between the parameteri'(estimation of the angle of inclination of the star) andthe oscillation amplitude is found. A discussion and interpretation ofthese a priori surprising results is proposed, in terms of a possibleselection rule for oscillation modes of delta Scuti stars.
| delta Scuti stars in Praesepe I. The STACC 1998 campaign - the photometry
We present the results of the multisite differential CCD photometry forthe two delta Scuti stars, BN and BV Cnc, in the open cluster Praesepe.The main objective was to identify the character of the pulsation modesin BN Cnc deriving their accurate periods, amplitudes and phases. Theseparameters are essential for the mode identification which uses combinedphotometric and spectroscopic data and is presented in the secondarticle. For BN Cnc, six pulsation modes with amplitudes above thedetection limit ( ~ 0.5 mmag) were detected. Using the same CCD framesit was possible to verify the presence of the four pulsation modes in BVCnc, the faintest of delta Scuti stars in Praesepe. It is shown that inthis very low-amplitude pulsator, substantial amplitude variations areseen between 1997 and 1998. Based in part on observations obtained atthe European Southern Observatory at La Silla, Chile (Application60D-0148).
| 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
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Photometric parameters for rotating models of A- and F-type stars
We have computed the photometric magnitudes of rotatingatmospheres-based on the simple model of Collins-for a grid suitable formain-sequence and slightly evolved stars of spectral type A0 to F5. Agravity-darkening law valid for radiative and convective envelopes hasbeen considered. The general results are given as magnitude differencesbetween rotating and non-rotating copartners to allow for the use of anyphotometric calibration. A simple interpolation on these results givesthe photometric parameters for interior rotating models but we alsoindicate how they can be used to correct for the effect of rotation whenan investigation with non-rotating models is carried out. We illustratethe procedure with the interesting case of the Praesepe Cluster.
| Amplitude investigation of delta Scuti variables in open clusters
We report here the results of a statistical analysis of 28 delta Scutistars from five open clusters, alpha Persei, Pleiades, Hyades, Praesepeand Coma. These delta Scuti variables, most of which are on the mainsequence, tend to show a positive correlation between oscillationamplitude and absolute luminosity. No correlation is found betweenamplitude and effective temperature.
| Seismology of delta Scuti stars in the Praesepe cluster. I. Ranges of unstable modes as predicted by linear analysis versus observations
We consider here a representative set of delta Scuti stars observed inthe Praesepe cluster, thanks to recent efforts of multi-site networks.We show that the effect of rotation on the determination of fundamentalparameters {Mbol} and {Teff} cannot be neglectedwhen modelling fast rotators as delta Scuti stars. We propose a methodto take this effect into account and gain some indication on therotation rate of the stars. We then use this unique homogeneous set ofobservational data to investigate the pulsational behaviour of deltaScuti stars for different masses, corresponding to differentevolutionary stages at the age of the Praesepe cluster. We propose herean alternative approach to seismology of delta Scuti stars, trying toavoid specific but questionable mode identifications. Via a large set ofmodels, we compare the observed modes with the unstable modes asobtained from a linear stability analysis including a nonlocaltime-dependent treatment of convection. We show that, in the frameworkof the linear analysis adopted here, a satisfying agreement can bereached between the predicted ranges of unstable modes and the rangesderived from observations. However we found that for ``low-mass'' deltaScuti stars (1.6-1.80 Msun) the agreement is found only for arestricted range of values of the mixing length parameter. These starsthus bring a valuable observational constraint on the description of theconvection in the outer layers of stars.
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| Pulsation, binarity and close frequency spacing in $delta Scuti ta$ Scuti stars: BQ and BW Cancri. Results of the STEPHI VI campaign in Praesepe Cluster
New pulsation modes in two delta Scuti stars of Praesepe cluster, BQ andBW Cnc, have been detected during the STEPHI VI campaign in 1995. Inparticular, 3 frequencies for BQ Cnc and 9 frequencies for BW Cnc havebeen found above a 99% confidence level. The possibility of the presenceof a g-mode present in BQ Cnc is discussed, considering its binarity.The effect of mutual interference between very close detectedfrequencies in BW Cnc during the observations, is also considered. Thislast effect reveals the necessity of long-period observing runs, inorder to avoid its influence in the final number of detected modes. Insuch situation, studies of secular amplitude changes can be stronglyaffected.
| Seismology of delta Scuti stars in the Praesepe cluster. II. Identification of radial modes and their associated stellar parameters
An analysis based on a comparison between observations and stellarmodels has been carried out to identify radial modes of oscillations inseveral multi-periodic delta Scuti stars of the Praesepe cluster (BU,BN, BW and BS Cnc). The assumption that all the stars considered havecommon parameters, such as metallicity, distance or age, is imposed as aconstraint. Even so, there is a large number of possible solutions,partially caused by the rotational effects on the pulsation frequenciesand on the stars' positions in the HR diagram, which need to beparameterized. When pairs of radial modes are assumed to be present inevery star, only a few similar identifications are found to be possible,corresponding to a metallicity of Z ~ 0.030 and an amount ofovershooting of alpha_ov ~ 0.20. They are associated with a distancemodulus of ~ 6.43 and an age of ~ 650 Myr. Estimates of mass androtation rates for each star are also deduced.
| Chromospheric Activity in the Late A- and Early F-Type Stars of Open Clusters. I. Hyades, Praesepe, and Coma
We report observations of the He i lambda5876 (D3) line in the late A-and early F-type stars in the Hyades, Praesepe, and Coma star clustersused to determine chromospheric activity levels. The average activitylevel in the early F-type stars is statistically identical in the threeclusters and in field dwarfs, and the dispersion in activity levels ineach sample is similar. The earliest star detected in each clusterranges from B-V = 0.26 in the Hyades to B-V = 0.31 in Praesepe. However,four stars in the Hyades in the range 0.28-0.32 are not detected. Thedetection of Hyades star VB 84 at B-V = 0.26 represents the bluest starobserved to date with a statistically nonzero chromospheric D3equivalent width. In nine early F-type stars we compare D3 strengtheither during two different observing runs or in several individualintegrations. In two stars we find evidence for short-term variabilityof a factor of 2 on timescales of 1 day or less. The timescale of thevariability is consistent with rotational modulation. Finally, thesimilarity in chromospheric activity in the Hyades and Praesepe starscontrasts with the significant weakness of coronal X-ray emission ofearly F-type stars in Praesepe compared to Hyades. We have noexplanation for this difference; however, this result suggests that theobserved disappearance of D3 in the late A-type stars is not directlycaused by the weak coronal emission of these stars.
| New multi-site observations of the delta Scuti stars BS and BT Cancri. Results of the STEPHI VII campaign on the Praesepe cluster
New observations of BS and BT Cnc were performed during the STEPHI VIIcampaign in 1996 February. An overall run of 115 hours of data wascollected. Different methods have been used to analyse the time series,bringing the detection of 2 frequencies for BT Cnc and 3 frequencies forBS Cnc above the 99% confidence level. A comparison with the literaturereveals that the dominant mode of BT Cnc ( ~ 9.8 c/d) has kept excitedover tens of years, while the secondary modes have not been the same allthe time. However, during the very last years the two frequenciesdetected by us have been the only ones noticeably excited in thespectrum.
| 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.
| 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
| 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
| Oscillations of BT CANCRI in the Praesepe cluster.
CCD observations in Johnson B of BT Cancri = HD 73575, the brightestδ Scuti variable in the Praesepe cluster, obtained on three nightsin February 1994 are described. Using least squares Fourierdecomposition, two modes of oscillation frequencies 9.783 and 7.005c/dand amplitudes of 18.0 and 9.9mmag, respectively, are determined.Comparison with data from the literature indicate that BT Cnc may showsecular variations in the oscillation spectrum.
| 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.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
| A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
| Post-main-sequence and POST red giant branch variables with pulsation periods less than one day
Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5to 1 solar mass) pulsators are discussed on the basis of four color andH beta light curves published elsewhere. The post-main-sequencevariables, called ultrashort period cepheid (USPC) (delta Sct), pulsatein the fundamental and first harmonic modes of radial pulsation and, inmany cases, in nonradial modes. The variables for which photometryallows accurate, luminosity estimates and are known to pulsatesimultaneously in the fundamental and first harmonic or in thefundamental mode alone, define a PL relation (MV = -2.80 logP - 0.60, fundamental). It is notable that the slope of this relation isin the range of slopes found for classical cepheids. Accurate Vphotometry is lacking for many of the variables known as 'anomalouscepheids', but the available data divide them into low mass,pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC(delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, forwhich accurate photometry is available, give remarkably consistentmoduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for theclusters, in which they are blue stragglers similar to SX Phe inKapteyn's star group. The assumption that the four post-giant branchvariables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn'sstar group and RR Lyr in the Groombridge 1830 group, are physicalmembers of these groups and share their V-velocities, leads to acalibration of the photometry for the derivation of reddening,luminosity, and heavy element abundance of 45 field variables. Theresulting reddenings are consistent with values obtained by othermethods and the metallicities are consistent with the most accuratelyavailable spectroscopic determinations of delta S and of Ca II K. Theluminosities of the bulk of the variables confirm Sandage's (1993)relation between MV and (Fe/H). Four or five of the fieldvariables are probably binary, including BB Vir which Kinman &Carreta (1992) have independently noted as double. The PL relation forUSPC (delta Sct) variables intersects the horizontal branch (HB) near P= 0.3d and at least two field very short period cepheid (VSPC) (RR Lyr)star, FW Lup (0.484 d) and ST Pic (0.486 d) may be first overtonepulsators of the USPC (delta Sct) variety. A dozen field VSPC (RR Lyr)stars populate a (Fe/H), MV relation with the same slope asthe other stars but displaced 0.7 mag toward higher luminosities. Theonly cluster variable found to populate this diplaced relation is No. 9in 47 Tuc, although ST Vir, which may be a member of the Arcturus group,should also be considered. The elevated luminosities are unlikely to becaused by either evolution or errors in the photometric indices. Apossible source of these apparently young VSPC(RR Lyr) variables withhalo metallicity is in second (or third) generation globular clustersformed during an episodic collapse of the galaxy that produced metalpoor stars but in a dynamical situation that hastened the disruption ofthe clusters, currently formed, before the still older globularclusters, created under conditions that have kept them in a moredisruptive free environment.
| 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.
| Ages and masses of Delta Scuti stars in the Praesepe cluster
The study derives physical parameters and radial pulsation modes forthree Delta Scuti stars in the Praesepe cluster: HD 73345, HD 73712, andHD 73746. Their ages and evolutionary masses are interpolated in thetrack systems of Iben (1967) and Paczynski (1970). These age estimatesare combined with previous results for nine other Delta Scuti stars inthe Praesepe cluster to obtain the following mean age estimates of thiscluster: (14.2 +/- 1.3) x 10 exp 8 yr and (5.4 +/- 0.4) x 10 exp 8 yr.Age and evolutionary mass estimates of the 12 cluster variables are alsoobtained in the modern track system of Maeder and Meynet (1988), inwhich the weighted mean cluster age is (15.3 +/- 1.0) x 10 exp 8 yr.
| 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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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Рак |
| Прямое восхождение: | 08h39m09.10s |
| Склонение: | +19°35'32.6" |
| Видимая звёздная величина: | 8.465 |
| Собственное движение RA: | -35.3 |
| Собственное движение Dec: | -11.7 |
| B-T magnitude: | 8.707 |
| V-T magnitude: | 8.485 |
Каталоги и обозначения:
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