Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Membership Determination of Open Cluster M48 Based on BATC 13-Band Photometry
Beijing-Arizona-Taiwan-Connecticut (BATC) multiband photometric data inthe field of open cluster M48 are used to determine its membership. Bycomparing observed spectral energy distributions of M48 stars withtheoretical ones, membership probabilities of 750 stars with limitingmagnitudes of 15.0 in the BATC c band (λeff=4194Å) are determined. We find 323 stars with membership probabilitieshigher than 30% that are considered to be candidate members of M48.Comparing membership probabilities of 229 stars obtained in commonbetween the present method and proper-motion-based methods, an 80%agreement among these methods is obtained.
| Caroline Herschel's catalogue of nebulae
Not Available
| Thirteen-Color Photometry of Open Cluster M48
This paper presents 13 color CCD intermediate-band spectrophotometry ofa field centered on the open cluster M48 (NGC 2548) from 400 to nearly1000 nm, taken with Beijing-Arizona-Taiwan-Connecticut (BATC) ColorSurvey photometric system. The fundamental parameters of this clusterare derived with a new method that is based on a comparison of thespectral energy distributions (SEDs) of cluster stars and thetheoretical SEDs of Padova models. We find that the best-fitting age ofM48 is 0.32 Gyr, with a distance of 780 pc, a reddening of E(B-V)=0.04,and a solar metallicity of Z=0.019.
| Deepsky delights.
Not Available
| Caroline Herschel as observer
Not Available
| Properties of five low-contrast open clusters in the third quadrant
We derive photometric, structural and dynamical evolution-relatedparameters of five as yet unstudied low-contrast open clusters locatedin the third quadrant using 2MASS data. The target clusters are Czernik31, Czernik 32, Haffner 9, Haffner 11 and Trumpler 13. We apply astatistical field-star decontamination procedure to infer on theintrinsic colour-magnitude diagram (CMD) morphology which is criticalfor such low-contrast objects. Consequently, it became possible toderive accurate reddening, age, distance from the Sun and Galactocentricdistance for the five clusters. In the structural andluminosity/mass-function analyses we apply a colour-magnitude filterwhich encompasses the cluster evolutionary CMD sequences and excludesstars with discrepant colours. Using this procedure we derive core andlimiting radii, mass function (MF) slope, total mass, mass density andrelaxation time. We derive ages in the range 140-1100 Myr,Galactocentric distances within 7.7-11.4 kpc, and total masses within360-2900 M_ȯ. Reflecting large-scale mass segregation, the MF slopein the core is significantly flatter than that in the halo of the fiveclusters. Although some of the present clusters are relatively youngerthan the Gyr-old clusters, they present evidence of advanced dynamicalevolution. This kind of study has become possible because of thephotometric uniformity and spatial coverage of 2MASS which allows aproper subtraction of the field-star contamination on the target CMDs.The present study indicates that low-contrast clusters can be studiedwith 2MASS, particularly after field-star subtraction, which isimportant since most of the unstudied open clusters belong to thisclass.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| Detailed analysis of open clusters: A mass function break and evidence of a fundamental plane
We derive photometric, structural and dynamical evolution-relatedparameters of 11 nearby open clusters with ages in the range 70 Myr to 7Gyr and masses in the range ≈400 M_ȯ to ≈5300 M_ȯ. Theclusters are homogeneously analysed by means of J, H and KS2MASS photometry, which provides spatial coverage wide enough toproperly take into account the contamination of the cluster field byGalaxy stars. Structural parameters such as core and limiting radii arederived from the background-subtracted radial density profiles.Luminosity and mass functions (MFs) are built for stars later than theturnoff and brighter than the 2MASS PSC 99.9% completeness limit. Thetotal mass locked up in stars in the core and the whole cluster, as wellas the corresponding mass densities, are calculated by taking intoaccount the observed stars (evolved and main sequence) and extrapolatingthe MFs down to the H-burning mass limit, 0.08 M_ȯ. We illustratethe methods by analysing for the first time in the near-infrared thepopulous open clusters NGC 2477 and NGC 2516. For NGC 2477 we derive anage of 1.1 ± 0.1 Gyr, distance from the Sun d_ȯ=1.2 ±0.1 kpc, core radius Rcore=1.4 ± 0.1 pc, limitingradius Rlim=11.6 ± 0.7 pc and total massmtot≈(5.3±1.6) × 103 M_ȯ.Large-scale mass segregation in NGC 2477 is reflected in the significantvariation of the MF slopes in different spatial regions of the cluster,and in the large number-density of giant stars in the core with respectto the cluster as a whole. For NGC 2516 we derive an age of 160 ±10 Myr, d_ȯ=0.44 ± 0.02 kpc, Rcore=0.6 ±0.1 pc, Rlim=6.2 ± 0.2 pc andmtot≈(1.3±0.2) × 103 M_ȯ.Mass-segregation in NGC 2516 shows up in the MFs. Six of the 11 clusterspresent a slope break in the MF occurring at essentially the same massas that found for the field stars in Kroupa's universal IMF. The MFbreak is not associated to cluster mass, at least in the clusters inthis paper. In two clusters the low-mass end of the MF occurs above theMF break. However, in three clusters the MF break does not occur, atleast for the mass range m≥0.7 M_ȯ. One possibility isdynamical evolution affecting the MF slope distribution. We also searchfor relations of structural and evolutionary parameters with age andGalactocentric distance. The main results for the present sample are:(i) cluster size correlates both with age and Galactocentric distance;(ii) because of size and mass scaling, core and limiting radii, and coreand overall mass correlate; (iii) massive (m≥1000 M_ȯ) andless-massive clusters follow separate correlation paths on the planecore radius and overall mass; (iv) MF slopes of massive clusters arerestricted to a narrow range, while those of the less-massive onesdistribute over a wider range. Core and overall MF flattening is relatedto the ratio (τ) of age to relaxation time. For large values ofτ the effects of large-scale mass segregation and low-mass starsevaporation can be observed in the MFs. In this sense, τ appears tocharacterize the evolutionary state of the clusters. We conclude thatappreciable slope flattenings in the overall MFs of the less-massiveclusters take ~6 times longer to occur than in the core, while in themassive clusters they take a time ~13 times longer. We investigatecluster parameters equivalent to those determining the fundamental planeof ellipticals. These parameters are: overall mass, projected massdensity and core radius. We conclude that in the present sample there isevidence of a fundamental plane. Larger samples are necessary to pindown this issue.
| uvby Hβ CCD photometry and membership segregation of the open cluster NGC 2548; gaps in the Main Sequence of open clusters
Deep CCD photometry in the uvby-Hβ intermediate-bandsystem is presented for the cluster NGC 2548 (M 48). A completemembership analysis based on astrometric and photometric criteria isapplied. The photometric analysis of a selected sample of stars yields areddening value of E(b-y)= 0.06±0.03, a distance modulus ofV_0-M_V= 9.3±0.5 (725 pc) and a metallicity of [ Fe/H] = - 0.24±0.27. Through isochrone fitting we find an age of log t = 8.6±0.1 (400 Myr). Our optical photometry and JHK from 2MASS arecombined to derive effective temperatures of cluster member stars. Theeffective temperature distribution along the main sequence of thecluster shows several gaps. A test to study the significance of thesegaps in the main sequence of the HR diagram has been applied. The methodis also applied to several other open clusters (Pleiades, Hyades, NGC1817 and M 67) to construct a sequence of metallicities and ages. Thecomparison of the results of each cluster gives four gaps with highsignificance (one of them, centred at 4900 K, has not been previouslyreported).
| Spatial dependence of 2MASS luminosity and mass functions in the old open cluster NGC 188
Luminosity and mass functions in the old open cluster NGC 188 areanalysed by means of J and H 2MASS photometry, which provides uniformityand spatial coverage for a proper background subtraction. With an age ofabout 6-8 Gyr, NGC 188 is expected to be suffering the effects ofadvanced dynamical evolution. Indeed, previous works in optical bandshave suggested the presence of mass segregation. Within theuncertainties, the observed projected radial density profile of NGC 188departs from the two-parameter King model in two inner regions, whichreflects the non-virialized dynamical state and possibly, some degree ofnon-sphericity in the spatial shape of this old open cluster. Fits withtwo and three-parameter King models to the radial distribution of starsresulted in a core radius Rcore=1.3±0.1 pc and a tidalradius Rtidal=21±4 pc, about twice as large as thevisual limiting radius. The concentration parameter c=1.2±0.1 ofNGC 188 makes this open cluster structurally comparable to the looseglobular clusters. The present 2MASS analysis resulted in significantslope variations with distance in the mass function φ(m)∝m-(1+χ), being flat in the central parts(χ=0.6±0.7) and steep in the cluster outskirts(χ=7.2±0.6). The overall mass function has a slopeχ=1.9±0.7, slightly steeper than a standard Salpeter massfunction. In this context, NGC 188 is similar to the 3.2 Gyr,dynamically evolved open cluster M 67. Solar metallicity Padovaisochrone fits to the near-infrared colour-magnitude diagram of NGC 188resulted in an age of 7.0±1.0 Gyr. The best fit, obtained withthe 7.1 Gyr isochrone, produced a distance modulus(m-M)0=11.1±0.1, E(B-V)=0.0, and a distance to the Sundȯ=1.66±0.08 kpc. The observed stellar mass (inthe range 0.98 Mȯ- 1.08 Mȯ) in NGC 188is mobs=380±12 Mȯ. A simpleextrapolation of the observed overall mass function to stars with 0.08Mȯ resulted in a total present mass ofmtot(1.8±0.7)×104Mȯ. On the other hand, for a more realistic initial massfunction which flattens in the low-mass range, the total mass in NGC 188drops to mtot(3.8±1.6)×103Mȯ. Since mass-loss processes such as evaporation andtidal stripping have been occurring in this old open cluster for about 7Gyr, the primordial mass in NGC 188 must have been significantly largerthan 4×103 Mȯ. We also examinedthe consequences of the presence of unresolved binaries and concludedthat, even if dominant in the CMD, binaries alone are not responsiblefor the flat central mass function, which supports the mass-segregationscenario.
| Proper motion measurements as indicators of binarity in open clusters
We analyze 9 open clusters with ages in the range 70 Myr to 3.2 Gyrusing UCAC2 proper motion data and 2MASS photometry, which allows us toreach stellar masses down to ≈0.7 M_ȯ. We employ in this work anapproach in which the background proper motion contribution isstatistically subtracted in order to obtain the cluster's intrinsicproper motion distribution. For each cluster we consider the projectedvelocity distributions in the core and off-core regions separately. Inthe projected velocity distribution of all sample clusters we find awell-defined low-velocity peak, as well as an excess in the number ofstars at larger velocities. The low-velocity peak is accounted for bythe random motion of the single stars, while the high-velocity excesscan be attributed to the large velocity changes produced by asignificant fraction of unresolved binaries in a cluster. We derivekinematic parameters of the single-star distribution, in particular theprojected velocity dispersion. The relatively large velocity dispersionsderived in this work may reflect the non-virialized state of theclusters. Based on the relative number of high-velocity (binary) andsingle stars, we inferred for the sample clusters unresolved binaryfractions in the range 15%≤f_bin≤54%, for both core and off-coreregions. Stars with a projected velocity exceeding the maximum reachedby the single-star distribution are identified in 2MASS J×(J-H)colour magnitude diagrams. The asymmetry observed in the distribution ofthese stars around the main sequence is consistent with models ofmain-sequence widening resulting from unresolved binaries combined with2MASS photometric uncertainties. The present results suggest that caremust be taken when applying proper-motion filters to sort out members,especially binaries in a star cluster. This paper shows that propermotions turn out to be a useful tool for identifying high-velocity starsas unresolved binary cluster members, and as a consequence, map andquantify the binary component in colour magnitude diagrams.
| Astrophysical supplements to the ASCC-2.5. II. Membership probabilities in 520 Galactic open cluster sky areas
We present a catalogue (CSOCA ) of stars residing in 520 Galactic opencluster sky areas which is the result of the kinematic (proper motion)and photometric member selection of stars listed in the homogeneousAll-sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5). We describethe structure and contents of the catalogue, the selection procedureapplied, and the proper motion and photometric membership constraintsadopted. In every cluster area the CSOCA contains the complete list ofthe ASCC-2.5 stars regardless of their membership probability. Forevery star the CSOCA includes accurate J2000 equatorial coordinates,proper motions in the Hipparcos system, BV photometric data in theJohnson system, proper motion and photometric membership probabilities,as well as angular distances from the cluster centers for about 166 000ASCC-2.5 stars. If available, trigonometric parallaxes, spectral types,multiplicity and variability flags from the ASCC-2.5, and radialvelocities with their errors from the Catalogue of Radial Velocities ofGalactic Stars with high precision Astrometric Data (CRVAD) are alsogiven.
| A Survey of Open Clusters in the u'g'r'i'z' Filter System. I. Results for NGC 2548 (M48)
We present initial results of a photometric survey of open starclusters, primarily in the southern hemisphere, taken in the u'g'r'i'z'filter system. While our entire observed sample covers more than 100clusters, here we present data for NGC 2548 (M48), which is a clustercharacterized in the UBV and DDO photometric systems. We compare ourresults to the published values from other observers and to the Padovatheoretical isochrones and metallicity curves. These observationsdemonstrate that the u'g'r'i'z' filters can play an important role indetermining the metallicity of stars and clusters. We begin this seriesof papers with a study of NGC 2548 because we have obtained data on thiscluster not only with our main program telescope, the CTIO CurtisSchmidt, but also with the US Naval Observatory (USNO) 1.0 m telescope(the telescope used to define the u'g'r'i'z' system), and with the SloanDigital Sky Survey (SDSS) 0.5 m Photometric Telescope (the photometricmonitoring telescope used to calibrate the SDSS 2.5 m telescope imagingdata). We have used the data from this study to validate our ability totransform measurements obtained on other telescopes to the standard USNO1.0 m u'g'r'i'z' system. This validation is particularly important forvery red stars, for which the original u'g'r'i'z' standard star networkis poorly constrained.
| Recent developments on studies of open clusters
Studies on open clusters are of great significance for astronomy andastrophysics, for which distinct developments have been made recently inboth observational and theoretical respects. In this paper, currentresearch of open cluster is reviewed, and membership determination,basic parameters determination, evolution of cluster and clustermembers, structure and dynamics of open cluster are also described indetail.
| Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| Urban Astronomy: Observing the Messier Objects from the City
Not Available
| Abundance Gradient from Open Clusters and Implications for the Galactic Disk Evolution
We compile a new sample of 89 open clusters with ages, distances andmetallicities available. We derive a radial iron gradient of about-0.099±0.008 dexkpc (unweighted) for the whole sample, which issomewhat greater than the most recent determination of oxygen gradientfrom nebulae and young stars. By dividing the clusters into age groups,we show that the iron gradient was steeper in the past and has evolvedslowly in time. Current data show a substantial scatter of the clustermetallicities indicating that the Galactic disk has undergone a veryrapid, inhomogeneous enrichment.Also, based on a simple, but quitesuccessful model of chemical evolution of the Milky Way disk, we make adetailed calculation of the iron abundance gradient and its timeevolution. The predicted current iron gradient is about -0.072 dexkpc.The model also predicts a steady flattening of the iron gradient withtime, which agrees with the result from our open cluster sample.
| 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.
| Determination of proper motions and membership of the open star cluster NGC 2548
Absolute proper motions, their corresponding errors and membershipprobabilities of 501 stars in the intermediate-age open cluster NGC 2548region are determined from MAMA measurements of 10 photographic plates.The plates have the maximum epoch difference of 82 years and they weretaken with the double astrograph at Zô-Sèstation ofShanghai Observatory, which has an aperture of 40 cm and a plate scaleof 30 arcsec mm-1. The average proper motion precision is1.18 mas yr-1. These proper motions are used to determine themembership probabilities of stars in the region. The number of starswith membership probabilities higher than 0.7 is 165. Table 5 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/ A+A/381/464, and by e-mail requestto Lola.Balaguer@am.ub.es MAMA (Machine Automatique àMesurer pourl'Astronomie, http://dsmama.obspm.fr) is developed and operated byINSU/CNRS and Observatoire de Paris.
| Gravitational tidal effects on galactic open clusters
We have investigated the 2-D stellar distribution in the outer parts ofthree nearby open clusters: NGC 2287 (equiv M 41),NGC 2516, and NGC 2548 (equiv M48). Wide-field star counts have been performed in two colours on pairsof digitized ESO and SRC Schmidt plates, allowing us to select likelycluster members in the colour-magnitude diagrams. Cluster tidalextensions were emphasized using a wavelet transform. Taking intoaccount observational biases, namely the galaxy clustering anddifferential extinction in the Galaxy, we have associated these stellaroverdensities with real open cluster structures stretched by thegalactic gravitational field. As predicted by theory and simulations,and despite observational limitations, we detected a general elongated(prolate) shape in a direction parallel to the galactic Plane, combinedwith tidal tails extended perpendicularly to it. This geometry is dueboth to the static galactic tidal field and the heating up of thestellar system when crossing the Disk. The time varying tidal field willdeeply affect the cluster dynamical evolution, and we emphasize theimportance of adiabatic heating during the Disk-shocking. In the case ofNGC 2548, our dating of the last shocking with the Plane (based on atidal clump) is consistent with its velocity. During the 10-20Z-oscillations experienced by a cluster before its dissolution in theGalaxy, crossings through the galactic Disk contribute to at least 15%of the total mass loss. Using recent age estimations published for openclusters, we find a destruction time-scale of about 600 Myr for clustersin the solar neighbourhood. Plate scanning was done at the Centred'Analyse des Images (CAI) with M.A.M.A. (Machine AutomatiqueàMesurer pour l'Astronomie), a facility located at theObservatoire de Paris, developed and operated by INSU (Institut Nationaldes Sciences de l'Univers, CNRS). Web site http://dsmama.obspm.fr
| Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
We present mean absolute proper motions of 112 open clusters, determinedusing the data from the Tycho2 Catalogue. For 28 clusters, this is thefirst determination of proper motion. The measurements made use of alarge number of stars (usually several tens) for each cluster. The totalnumber of stars studied in the fields of the 164 open clusters is 5016,of which 4006 were considered members. The mean proper motions of theclusters and membership probability of individual stars were obtainedfrom the proper motion data by applying the statistical method proposedby Sanders (\cite{Sanders71}). Based on observations of the ESAHipparcos satellite. Tables 1, 2 and 5 to 117 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/441
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The hot side of the lithium dip - LiBeB abundances beyond the main sequence
We extend to the case of A and early-F type stars our study of thetransport of matter and angular momentum by wind-driven meridionalcirculation and shear turbulence. We show that our fully consistenttreatment of the same hydrodynamical processes which can account for Cand N anomalies in B type stars (Talon et al. 1997) and for the shape ofthe hot side of the Li dip in the open clusters (Talon & Charbonnel1998) also explains LiBeB observations in stars with T_eff higher than7000 K on the main sequence as well as in their evolved counterparts.
| 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
| HIPPARCOS absolute magnitudes for metal-rich K giants and the calibration of DDO photometry
Parallaxes for 581 bright K giants have been determined using theHipparcos satellite. We combine the trigonometric parallaxes withground-based photometric data to determine the K giant absolutemagnitudes. For all these giants, absolute magnitude estimates can alsobe made using the intermediate-band photometric David Dunlop Observatory(DDO) system. We compare the DDO absolute magnitudes with the veryaccurate Hipparcos absolute magnitudes, finding various systematicoffsets in the DDO system. These systematic effects can be corrected,and we provide a new calibration of the DDO system allowing absolutemagnitude to be determined with an accuracy of 0.35 mag in the Mv rangebetween 2 and -1. The new calibration performs well when tested on Kgiants with DDO photometry in a selection of low-reddening open clusterswith well-measured distance moduli.
| Some Revised Observational Constraints on the Formation and Evolution of the Galactic Disk
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2556T&db_key=AST
| Chemical Evolution of the Galactic Disk: Evidence for a Gradient Perpendicular to the Galactic Plane
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2813P&db_key=AST
| 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.
| CNO isotopes in red giants: theory versus observations
Evolutionary models in the mass range 1.7 to 15 Msun_ havingsolar-like initial composition are presented. The models are calculatedwith the latest opacities and with the Schwarzschild criterion forconvective instability. In test cases, core overshooting has beenincluded in a parameterized way. Up-dated nuclear reactions have beenused to follow the nucleosynthesis during the evolution which has beencarried out beyond core He-burning at masses > 2 Msun_.The 2 Msun_ model has been evolved through the core He-flash.The resulting surface CNO isotopic ratios after the first and seconddredge-up phases are compared with observations of field giants as wellas with data obtained for galactic open clusters. A comparison betweenrecent theoretical predictions of these ratios is also presented. Thegoal of this work is twofold: (i) to test mass estimations of theobserved giants on the basis of the predicted surface abundance ratiosof ^12^C/^13^C, ^16^O/^17^O and ^16^O/^18^O, and the evolutionarytracks, (ii) to show that ^16^O/^17^O ratio obtained in giant models atM>2 Msun_ is rather sensitive to the still uncertain^17^O(p,α)^14^N reaction. The main results of the present work areas follows: (i) our one-dimensional dynamical calculations show that the2 Msun_ model survives the core He-flash, (ii) we are able toestimate the masses of 6 observed giants out of 11. In addition, thesupergiant star α Sco is well described by a model of initially 15Msun_. (iii) the observed low ^12^C/^13^C ratios in manygiants with M>2 Msun_ cannot be explained in terms of asimple dredge-up scenario or by the variation of the initial value.These ratios are barely influenced by the effect of "moderate"overshooting, (iv) We find that the calculated Na enrichment resultingfrom the Ne-Na cycle does not match the values suggested by currentobservations.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
Cataloghi e designazioni:
|
INHABITED SKY
