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New catalogue of blue stragglers in open clusters
We present a catalogue of blue-straggler candidates in galactic openclusters. It is based on the inspection of the colour-magnitude diagramsof the clusters, and it updates and supersedesthe first version(Ahumada & Lapasset 1995). A new bibliographical search was made foreach cluster, and the resulting information is organised into twotables. Some methodological aspects have been revised, in particularthose concerning the delimitation of the area in the diagrams where thestragglers are selected.A total of 1887 blue-straggler candidates have been found in 427 openclusters of all ages, doubling the original number. The catalogued starsare classified into two categories mainly according to membershipinformation.The whole catalogue (Tables 8, 9, notes, and references) is onlyavailable 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/qcat?J/A+A/463/789
| New magnetic chemically peculiar stars
Spectropolarimetric observations of 96 chemically peculiar (CP)main-sequence stars have been carried out at the 6-m telescope at theSpecial Astrophysical Observatory of the Russian Academy of Sciences(SAO RAS) with the aim of searching for the presence of stellar magneticfields. The stars selected for investigation were CP stars known to havestrong anomalies in the wavelength region of the continuum fluxdepression around λ 5200Å. This selection was conductedwith the aid of low-resolution spectral observations, made with the SAORAS 1-m telescope, and of published differential photometric data.Magnetic fields have been successfully detected in 72 stars of whichonly three stars were previously known to have magnetic fields. For twostars, the longitudinal component of the magnetic field Beexceeds 5 kG: HD178892 - 7.4 kG, and HD258686 - 6.7 kG. We failed toreliably detect the magnetic field in the other 24 CP stars. These starsare mostly fast rotators, a feature which hampers accurate measurementsof Be. It is demonstrated in this paper that selectingcandidate magnetic stars by considering their photometric indices Z orΔa, or alternatively, by inspecting low-resolution spectra aroundthe λ5200Å flux depression, considerably increases thedetection rate.This paper is based on data obtained at the 6-m telescope of the RussianAcademy of Sciences.E-mail: dkudr@sao.ru
| On the current status of open-cluster parameters
We aim to characterize the current status of knowledge on the accuracyof open-cluster parameters such as the age, reddening and distance.These astrophysical quantities are often used to study the globalcharacteristics of the Milky Way down to the very local stellarphenomena. In general, the errors of these quantities are neglected orset to some kind of heuristic standard value. We attempt to give somerealistic estimates for the accuracy of available cluster parameters byusing the independently derived values published in the literature. Intotal, 6437 individual estimates for 395 open clusters were used in ourstatistical analysis. We discuss the error sources depending ontheoretical as well as observational methods and compare our resultswith those parameters listed in the widely used catalogue by Dias et al.In addition, we establish a list of 72 open clusters with the mostaccurate known parameters which should serve as a standard table in thefuture for testing isochrones and stellar models.
| Kinematics of the Open Cluster System in the Galaxy
Absolute proper motions and radial velocities of 202 open clusters inthe solar neighborhood, which can be used as tracers of the Galacticdisk, are used to investigate the kinematics of the Galaxy in the solarvicinity, including the mean heliocentric velocity components(u1,u2,u3) of the open cluster system,the characteristic velocity dispersions(σ1,σ2,σ3), Oortconstants (A,B) and the large-scale radial motion parameters (C,D) ofthe Galaxy. The results derived from the observational data of propermotions and radial velocities of a subgroup of 117 thin disk young openclusters by means of a maximum likelihood algorithm are:(u1,u2,u3) =(-16.1+/-1.0,-7.9+/-1.4,-10.4+/-1.5) km s-1,(σ1,σ2,σ3) =(17.0+/-0.7,12.2+/-0.9,8.0+/-1.3) km s-1,(A,B) =(14.8+/-1.0,-13.0+/-2.7) km s-1 kpc-1, and (C,D) =(1.5+/-0.7,-1.2+/-1.5) km s-1 k pc-1. A discussionon the results and comparisons with what was obtained by other authorsis given.
| Washington photometry of open cluster giants: two moderately metal-poor anticentre clusters
New photometric data in the Washington system are presented for redgiant candidates in NGC 1817 and 2251, two open clusters located towardsthe Galactic anticentre direction. In the case of NGC 2251, theWashington data are supplemented with new UBV and David DunlapObservatory (DDO) photoelectric photometry. Published radial velocitiesare used to separate field stars from cluster giants. The photometricdata yield an effective temperature and metal abundance for each clustermember. Five independent Washington abundance indices yield meanmetallicities of [Fe/H]= 0.25 +/- 0.04 for NGC 1817 and 2251,respectively. From combined BV and DDO data, we also derive E(B-V) =0.21 +/- 0.03 and [Fe/H]DDO=-0.14 +/- 0.05 for NGC 2251. Bothobjects are then found to be on the metal-poor side of the distributionof open clusters, their metallicities being compatible with theexistence of a radial abundance gradient in the disc. Using the WEBDAOpen Cluster data base and the available literature, we re-examined theoverall properties of a sample of 30 clusters located towards theGalactic anticentre with the distances, ages and metallicitiesavailable. This cluster sample presents no evidence of an abundancegradient perpendicular to the Galactic plane, nor is an age-metallicityrelation found. However, a radial abundance gradient of -0.093 dexkpc-1 is derived over a Galactocentric distance of 14 kpc, agradient which is in keeping with most recent determinations. This valuepractically does not change when all clusters with basic parametersknown up to this date are considered.
| 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.
| A trend filtering algorithm for wide-field variability surveys
We show that various systematics related to certain instrumental effectsand data reduction anomalies in wide-field variability surveys can beefficiently corrected by a trend filtering algorithm (TFA) applied tothe photometric time-series produced by standard data pipelines.Statistical tests, performed on the data base of the HAT Networkproject, show that by the application of this filtering method thecumulative detection probability of periodic transits increases by up to0.4 for variables brighter than 11 mag, with a trend of increasingefficiency toward brighter magnitudes. We also show that the TFA can beused for the reconstruction of periodic signals by iteratively filteringout systematic distortions.
| 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.
| 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.
| 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.
| 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.
| 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
| Luminosity and mass function of galactic open clusters I. NGC 4815
We present deep V and I photometry for the open cluster NGC 4815 andfour surrounding Galactic fields down to a limiting magnitude V ~ 25.These data are used to study cluster spatial extension by means of starcounts, and to derive the luminosity (LF) and mass function (MF). Theradius turns out to be 3.6+/-0.3 arcmin at V=19.0, whereas the mass is880+/-230 msun down to V=20.8. From the color-magnitudediagram, we obtain the LFs in the V and I bands, using both the standardhistogram and an adaptive kernel. After correction for incompletenessand field star contamination, the LFs were transformed into the presentday mass functions (PDMF). The PDMFs from the V and I photometry can berepresented as a power-law with a slope alpha = 3.1+/-0.3 and alpha =2.9+/-0.3 (the (Salpeter \cite{salp55}) MF in this notation has a slopealpha = 2.35) respectively, in the mass range 2.5 <=(m)/(msun) <= 0.8. Below this mass, the MF cannot beconsidered as representative of the cluster IMF, as it is the result ofthe combined effect of strong irregularities in the stellar background,probable internal dynamical evolution of the cluster and/or interactionof the cluster with the dense Galactic field. Unresolved binaries andmass segregation can only flatten the apparent derived IMF, so we expectthat the real IMF must be steeper than the quoted slope by an unknownamount. Based on observations made at the European Southern Observatory,La Silla, Chile.
| 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 Relationship Between the Böhm-Vitense Gap and Stellar Activity in Open Clusters
Using published UBV photometry of nine open clusters and chromosphericactivity data in five clusters, we have performed the most completestudy to date of the supposed Böhm-Vitense gap in main-sequencelate-A and early-F stars. Using the χ2 test on thedistribution of B-V colors of the main-sequence stars of these clusters,we located gaps at the 0.90 probability level or greater in eight out ofthe nine clusters. Six of the nine clusters show a gap near B-V=0.35 atthis level. In four nearby clusters, Alpha Persei, Pleiades, Coma, andPraesepe, we compare the gaps with measurements of chromosphericactivity via the He I λ5876 (D3) line. If the Böhm-Vitensegap is related to the onset of surface convection zones, as has beensuggested, we would expect to find a direct relationship between theonset of activity and the gaps. However, in all four cases we find starson both sides of the gap showing strong activity. The observed gaps donot appear to correlate directly with any known physical mechanism andthus either point to an unknown mechanism or a statistical anomaly.
| 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
| Thirty years of research with the Baldone Schmidt Telescope
We describe the research done with the Baldone Schmidt telescope(80/120/240 cm) of the Radioastrophysical Observatory. The telescope hastwo objective prisms with reciprocal dispersions of 600 and 1130 A/mm atH-gamma. One of the main research projects is the search for andphotometric study of galactic carbon stars. The telescope has also beenused for novae studies in M 31 and stellar photometry in open clustersand fields of special interest. Comet studies, particularly during theInternational Halley Watch, proved to be another successful applicationof the telescope. The archive of the Baldone Schmidt telescope containsnearly 20,000 direct and 2000 spectral plates and films.
| Cluster membership determinations from proper motion surveys
Not Available
| On Coagulation and the Stellar Mass Spectrum
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...452..652A&db_key=AST
| A study of clusters and field stars in two regions in the Large Magellanic Cloud.II. Colour-magnitude diagrams and luminosity functions.
The stellar populations in two regions of the Large Magellanic Cloud,one in the NW and one in the SW, are analysed to a limiting absolutevisual magnitude of about M_V_=3.5mag Colour-magnitude diagrams arepresented for three faint clusters in each region as well as for thepopulations in their surrounding fields. The clusters in the NW regionhave ages between 0.1 and 0.5Gyr and metallicities close to solarwhereas those in the SW are about 1Gyr old and of lower metallicity.Also the field populations in the two regions have different characters.Both contain strong components of ages around 1 to 3Gyr. In the NWregion a young component, 0.2-0.6Gyr, exists which is completely missingin the SW region. The latter contains a weak but well identifiedgeneration about 7-10Gyr old which may be traced also in the NW region.Comparisons with other regions in the Large Cloud are carried out. TheSW part of the LMC differs from the others by an almost total lack ofyoung generations. The luminosity functions in many parts of the LargeCloud are otherwise rather similar. The generations identified hereconfirm that the initial star formation in the LMC, more than 7Gyr ago,was weak and that a much stronger star production occurred during theperiod 0.5 to 4.0Gyr ago.
| 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.
| Monte-Carlo simulations of binary stellar evolution in young open clusters
We present a model for calculating the evolution of close binaries,including mass exchange episodes, in an approximate way. Our modelcovers all parts of parameter space (initial masses and orbitalseparations) for binaries with primaries more massive than2Msun_, and calculates the evolution until both stars havebecome compact objects. The model is described in detail and itsapproximations and uncertainties are discussed. The model is applied inMonte-Carlo simulations of a large population of stars, representing theinitial population of young open clusters. The colour-magnitude diagramsof these synthetic clusters reproduce several observed features of realyoung open clusters that can be attributed to the presence of binaries.In particular, blue stragglers are produced as remnants of mass exchangein close binaries. We identify five types of blue straggler. Four ofthese types are binaries with helium-star, white-dwarf, neutron-star,and stripped main-sequence-star companions; the fifth type are single,merged main-sequence stars. We derive the expected numbers andproperties of each of these blue-straggler types as a function ofcluster age. The numbers and properties of our synthetic blue stragglers(rapid rotation, small or absent radial-velocity variations) areconsistent with the observed incidence and characteristics of bluestragglers in clusters younger than about 300 Myr. In contrast, ourmodel appears to be unable to account for all the observed bluestragglers in intermediate-age clusters (between 300 and 1500 Myr).Other observed features that are reproduced by the inclusion of binariesare: the occurrence of a second main sequence, the appearance of "yellowstraddler" giants between the giant branch and the turn-off point, andthe occurrence of "blue interlopers" below the main sequence.
| Integrated photometric properties of open clusters
Galactic open clusters provide an abundant sample of stellar aggregatesof various sizes, ages and metal abundances, apt to constitute atemplate for comparison with star systems in other galaxies. In thispaper we present and discuss a standard methodology to synthesize U,B,Vfluxes and colours, and apply it to a set of 138 open clusters. Resultsare compared with previous ones available in the literature. We wereable to calibrate a mass-luminosity relation by which we evaluated themass of ~400 open clusters, leading to a well defined present-day massfunction. The number-complete sample of galactic open clusters presentedin Battinelli & Capuzzo-Dolcetta (1991) is enlarged of a 15%.
| 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.
| Magnetic activity in low-mass stars
The manifestations of magnetic activity in low-mass stars, particularlyM dwarfs, can be used as a tool to study their evolution, the operationof the interior dynamo with changing interior conditions, and thestructure of their outer atmospheres. Extensive background material onthe current understanding of low-mass stellar activity is presented. Twonew surveys are described which will greatly increase the number ofactive low-mass stars known in the field and in nearby open clusters.These surveys will define the characteristics of the activity inlow-mass stars, and how the activity changes with a number of parametersof interest, including mass, effective temperature, and age. The datawill also allow a rigorous determination of a possible age-activityrelation among the low-mass M dwarfs. Theoretical models of M dwarfatmospheres, and their connection to the understanding of theobservations, are also discussed.
| NGC 6603 - A young rich open cluster towards the bulge
We present B, V color magnitude diagrams of the rich open cluster NGC6603. A foreground reddening of E(B-V)(f) = 0.50 and an internal one ofE(B-V)(i) = 0.29 were derived with the additional help of integratedspectra. The resulting age is 200 +/- 100 Myr, and the distance is about3.6 kpc. The surrounding field is also studied, appearing to be part ofa star cloud which contains age components in the range 200 to 600 Myror more. The cluster appears to be spatially associated with the starcloud, being part of its youngest component. The cluster and the starcloud location in the inner disk are in agreement with other studiesshowing an enhancement of star formation in this region.
| 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.
| An improved metal abundance calibration for the Washington system
The determination of metal abundances for individual giants fromWashington photometry is revised, with several significant improvementsincorporated. The solar-abundance two-color relations are revamped withthe inclusion of new observations of a large sample of solar-abundancegiants with small reddenings, especially those with late-K spectraltypes. The new relations are very similar to the original ones derivedin C76 except for a zero-point offset. A new temperature index, M-T2, isinvestigated, as well as a new abundance index, C-T1, in addition to thestandard indices. The M-T2 index has a much broader baseline and thus amuch larger range than T1-T2, and is therefore less susceptible tophotometric errors. The significant decrease in abundance sensitivityfor cooler stars, suspected by previous investigations, is confirmed byincluding observations of a number of giants with a range in temperaturein each of a large sample of open and globular clusters. A procedure forcorrecting the abundance indices for cool stars is derived whichsignificantly improves the metallicity determination.
| An observational age-metallicity relation for the Galaxy
An observational Age-Metallicity Diagram for the Galaxy has beenconstructed on the base of star cluster data available in theliterature. This diagram exhibits two independent and simultaneousmetallicity enhancement processes identified with two dynamical galacticsubstructures: the thin and the thick disks. Within the observationaluncertainties both these processes can be satisfactory approximated byInfall-Inflow models of the chemical evolution with different high,although rapidly decaying with time, Star Formation and Infall Rates.The comparison of the galactic age-metallicity relations with that forthe Large Magellanic Cloud shows some similarities between processes ofthe chemical enhancement in the Large Magellanic Cloud and the Thin Disksubsystem in the Galaxy.
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