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Elemental abundances of intermediate-age open cluster NGC 3680
We present a new abundance analysis of the intermediate-age Galacticopen cluster NGC 3680, based on high-resolution, high signal-to-noiseratio VLT/UVES spectroscopic data. Several element abundances arepresented for this cluster for the first time, but most notably wederive abundances for the light and heavy s-process elements Y, Ba, Laand Nd. The serendipitous measurement of the rare-earth r-processelement Gd is also reported. This cluster exhibits a significantenhancement of Na in giants as compared to dwarfs, which may be a proxyfor an O to Na anticorrelation as observed in Galactic globular clustersbut not open clusters. We also observe a step-like enhancement of heavys-process elements towards higher atomic number, contrary toexpectations from asymptotic giant branch nucleosynthesis models,suggesting that the r process played a significant role in thegeneration of both La and Nd in this cluster.
| Distance determination for RAVE stars using stellar models. III. The nature of the RAVE survey and Milky Way chemistry
We apply the method of Burnett & Binney (2010, MNRAS, 407, 339) forthe determination of stellar distances and parameters to the internalcatalogue of the RAdial Velocity Experiment (RAVE; Steinmetz et al.2006, AJ, 132, 1645). Subsamples of stars that either have Hipparcosparallaxes or belong to well-studied clusters inspire confidence in theformal errors. Distances to dwarfs cooler than ~6000 K appear to beunbiased, but those to hotter dwarfs tend to be too small by ~10% of theformal errors. Distances to giants tend to be too large by about thesame amount. The median distance error in the whole sample of 216 000stars is 28% and the error distribution is similar for both giants anddwarfs. Roughly half the stars in the RAVE survey are giants. The giantfraction is largest at low latitudes and in directions towards theGalactic Centre. Near the plane the metallicity distribution isremarkably narrow and centred on [M/H] = -0.04 dex; with increasing |z|it broadens out and its median moves to [M/H] ? -0.5. Mean age as afunction of distance from the Galactic centre and distance |z| from theGalactic plane shows the anticipated increase in mean age with |z|.
| The RAdial Velocity Experiment (RAVE): Third Data Release
We present the third data release of the RAdial Velocity Experiment(RAVE) which is the first milestone of the RAVE project, releasing thefull pilot survey. The catalog contains 83,072 radial velocitymeasurements for 77,461 stars in the southern celestial hemisphere, aswell as stellar parameters for 39,833 stars. This paper describes thecontent of the new release, the new processing pipeline, as well as anupdated calibration for the metallicity based upon the observation ofadditional standard stars. Spectra will be made available in a futurerelease. The data release can be accessed via the RAVE Web site.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Distance determination for RAVE stars using stellar models . II. Most likely values assuming a standard stellar evolution scenario
The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of theMilky Way which already collected over 400 000 spectra of ~ 330 000different stars. We use the subsample of spectra with spectroscopicallydetermined values of stellar parameters to determine the distances tothese stars. The list currently contains 235 064 high quality spectrawhich show no peculiarities and belong to 210 872 different stars. Thenumbers will grow as the RAVE survey progresses. The public version ofthe catalog will be made available through the CDS services along withthe ongoing RAVE public data releases. The distances are determined witha method based on the work by Breddels et al. (2010, A&A, 511, A16).Here we assume that the star undergoes a standard stellar evolution andthat its spectrum shows no peculiarities. The refinements include: theuse of either of the three isochrone sets, a better account of thestellar ages and masses, use of more realistic errors of stellarparameter values, and application to a larger dataset. The deriveddistances of both dwarfs and giants match within ~ 21% to theastrometric distances of Hipparcos stars and to the distances ofobserved members of open and globular clusters. Multiple observations ofa fraction of RAVE stars show that repeatability of the deriveddistances is even better, with half of the objects showing a distancescatter of ? 11%. RAVE dwarfs are ~ 300 pc from the Sun, and giantsare at distances of 1 to 2 kpc, and up to 10 kpc. This places the RAVEdataset between the more local Geneva-Copenhagen survey and the moredistant and fainter SDSS sample. As such it is ideal to address some ofthe fundamental questions of Galactic structure and evolution in thepre-Gaia era. Individual applications are left to separate papers, herewe show that the full 6-dimensional information on position and velocityis accurate enough to discuss the vertical structure and kinematicproperties of the thin and thick disks.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/522/A54
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Lithium in the Intermediate-Age Open Cluster, NGC 3680
High-dispersion spectra centered on the Li 6708 Å line have beenobtained for 70 potential members of the intermediate-age open clusterNGC 3680, with an emphasis on stars in the turnoff region of the clustercolor-magnitude diagram (CMD). A measurable Li abundance has beenderived for 53 stars, 39 of which have radial velocities and propermotions consistent with cluster membership. After being transferred tocommon temperature and abundance scales, previous Li estimates have beencombined to generate a sample of 49 members, 40 of which bracket thecluster Li-dip. Spectroscopic elemental analysis of eight giants andfive turnoff stars produces [Fe/H] = -0.17 ± 0.07 (sd) and -0.07± 0.02 (sd), respectively. We also report measurements of Ca, Si,and Ni which are consistent with scaled-solar ratios within the errors.Adopting [Fe/H] = -0.08 (Section 3.6), Y 2 isochronecomparisons lead to an age of 1.75 ± 0.1 Gyr and an apparentmodulus of (m - M) = 10.30 ± 0.15 for the cluster, placing thecenter of the Li-dip at 1.35 ± 0.03 M sun. Among thegiants, five of the nine cluster members are now known to havemeasurable Li with A(Li) near 1.0. A combined sample of dwarfs in theHyades and Praesepe is used to delineate the Li-dip profile at 0.7 Gyrand [Fe/H] = +0.15, establishing its center at 1.42 ± 0.02 Msun and noting the possible existence of a secondary dip onits red boundary. When evolved to the typical age of the clusters NGC752 (age = 1.45 Gyr, (m - M) = 8.4), IC 4651 (age = 1.5 Gyr, (m - M) =10.4), and NGC 3680, the Hyades/Praesepe Li-dip profile reproduces theobserved morphology of the combined Li-dip within the CMDs of theintermediate-age clusters while implying a metallicity dependence forthe central mass of the Li-dip given by M/M sun = 1.38± 0.04 + 0.4 ± 0.2 [Fe/H]. The implications of thesimilarity of the Li-dichotomy among giants in NGC 752 and IC 4651 andthe disagreement with the pattern among NGC 3680 giants are discussed.
| Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars. Stellar metallicity, stellar mass, and giant planets
We present a study of accurate stellar parameters and iron abundancesfor 39 giants and 16 dwarfs in the 13 open clusters IC2714, IC 4651, IC 4756,NGC 2360, NGC 2423, NGC2447 (M 93), NGC 2539, NGC2682 (M 67), NGC 3114, NGC3680, NGC 4349, NGC5822, NGC 6633. The analysis was done usinga set of high-resolution and high-S/N spectra obtained with the UVESspectrograph (VLT). These clusters are currently being searched forplanets using precise radial velocities. For all the clusters, thederived average metallicities are close to solar. Interestingly, thevalues derived seem to depend on the line-list used. This dependence andits implications for the study of chemical abundances in giants starsare discussed. We show that a careful choice of the lines may be crucialfor the derivation of metallicities for giant stars on the samemetallicity scale as those derived for dwarfs. Finally, we discuss theimplications of the derived abundances for the metallicity- andmass-giant planet correlation. We conclude that a good knowledge of thetwo parameters is necessary to correctly disentangle their influence onthe formation of giant planets.Based on observations collected at the La Silla Parana Observatory, ESO(Chile) with the UVES spectrograph at the 8.2-m Kueyen telescope, underprograms 079.C-0131 and 66.D-0457.
| Open Clusters as Galactic Disk Tracers. I. Project Motivation, Cluster Membership, and Bulk Three-Dimensional Kinematics
We have begun a survey of the chemical and dynamical properties of theMilky Way disk as traced by open star clusters. In this firstcontribution, the general goals of our survey are outlined and thestrengths and limitations of using star clusters as a Galactic disktracer sample are discussed. We also present medium-resolution (R ~ 15,0000) spectroscopy of open cluster stars obtained with the Hydramulti-object spectrographs on the Cerro Tololo Inter-AmericanObservatory 4 m and WIYN 3.5 m telescopes. Here we use these data todetermine the radial velocities of 3436 stars in the fields of openclusters within about 3 kpc, with specific attention to stars havingproper motions in the Tycho-2 catalog. Additional radial velocitymembers (without Tycho-2 proper motions) that can be used for futurestudies of these clusters were also identified. The radial velocities,proper motions, and the angular distance of the stars from clustercenter are used to derive cluster membership probabilities for stars ineach cluster field using a non-parametric approach, and the clustermembers so identified are used, in turn, to derive the reliable bulkthree-dimensional motion for 66 of 71 targeted open clusters. Thehigh-probability cluster members that we identify help to clarify thecolor-magnitude sequences for many of the clusters, and are primetargets for future echelle resolution spectroscopy as well asastrometric study with the Space Interferometry Mission (SIMPlanetquest).
| Red giants in open clusters. XIV. Mean radial velocities for 1309 stars and 166 open clusters
Context: Radial velocities have proved to be an efficient method formembership determination if there are at least 2 or 3 red giants in acluster. They are necessary for galactic studies, but are still missingfor many open clusters. Aims: We present the final catalogues of along-term observing programme performed with the two coravelspectrovelocimeters for red giants in open clusters. The main aims wereto detect spectroscopic binaries and determine their orbital parameters,determine the membership, and compute mean velocities for the stars andopen clusters. Methods: We computed weighted mean radial velocities for1309 stars from 10 517 individual observations, including the systemicradial velocities from spectroscopic orbits and for cepheids. Results:The final results are contained in three catalogues collecting 10 517individual radial velocities, mean radial velocities for 1309 redgiants, and mean radial velocities for 166 open clusters among whichthere are 57 new determinations. We identified 891 members and 418non-members. We discovered a total of 288 spectroscopic binaries, amongwhich 57 are classified as non-members. In addition 27 stars were judgedto be variable in radial velocities and they are all red supergiants. Conclusions: The present material, combined with recent absolute propermotions, will permit various investigation of the galactic distributionand space motions of a large sample of open clusters. However, thedistance estimates still remain the weakest part of the necessary data.This paper is the last one in this series devoted to the study of redgiants in open clusters based on radial velocities obtained with thecoravel instruments.Based on observations collected at the Haute-Provence Observatory(France) and on observations collected with the Danish 1.54-m telescopesat the European Southern Observatory, La Silla, Chile. Full Tables [seefull textsee full textsee full textsee full textsee full text] to [seefull textsee full textsee full textsee full textsee full text] are onlyavailable and Tables [see full textsee full textsee full textsee fulltextsee full text] and [see full textsee full textsee full textsee fulltextsee full text] are also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/485/303
| uvbyCaHβ CCD Photometry of Clusters. IV. Solving the Riddle of NGC 3680
CCD photometry on the intermediate-band uvbyCaHβ system ispresented for the open cluster, NGC 3680. Restricting the data toprobable cluster members using the color-magnitude diagram (CMD) and thephotometric indices alone defines a sample of 34 stars at the clusterturnoff that imply E(b-y)=0.042+/-0.002 (s.e.m.) or E(B-V)=0.058+/-0.003(s.e.m.), where the errors refer to internal errors alone. With thisreddening, [Fe/H] is derived from both m1 and hk using bothb-y and Hβ as the temperature indices. The agreement among the fourapproaches is excellent, leading to final value of [Fe/H]=-0.14+/-0.03for the cluster and removing the apparent discrepancy between the pastuvby analyses and extensive results from the red giants. The primarysource of the photometric anomaly appears to be a zero-point offset inthe original m1 indices. Using the homogenized and combinedV, b-y data from a variety of studies transformed to B-V, the clusterCMD is compared with NGC 752, IC 4651, and the core-convective-overshootisochrones of Girardi et al. By interpolation to the proper metallicity,it is found that the E(B-V), m-M, and age for NGC 752, IC 4651, and NGC3680 are (0.03, 8.30, 1.55 Gyr), (0.10, 10.20, 1.7 Gyr), and (0.06,10.20, 1.85 Gyr), respectively. The revised age and metallicity sequenceand the color distribution of the giants provide evidence for thesuggestion that the giants defining the apparent clump in NGC 3680 arepredominantly first-ascent giants, as indicated by their Li abundance,while the clump stars in NGC 752, 0.1 mag bluer in B-V, areHe-core-burning stars. When combined with the color distribution in IC4651, it is suggested that over this modest age range where He-coreflash becomes important, the distribution of so-called clump starsswitches from being dominated by He-core-burning stars to first-ascentgiants in the bump phase.
| Lithium in the intermediate age cluster NGC 3680: Following Li evolution along the C-M diagram
We present an analysis of high resolution spectroscopic observations (R~ 30 000, S/N=60-150) of 24 members of the intermediate age ( ~ 1.5 Gyr)open cluster NGC 3680, covering all regions of the clustercolour-magnitude (C-M) diagram where cluster members are known to exist.These observations represent in many aspects challenges to ourunderstanding of stellar interior and mixing. Four main sequence G starshave, within the errors, the same Li abundance, 0.3 dex lower thansimilar stars in the ~ 1 Gyr younger Hyades but comparable with thoseobserved in the coeval cluster IC 4651. The clustershows a clear Li-dip located around the turn-off; two stars on the upperpart of the turn-off are out of the dip and reach solar systemmeteoritic Li abundances. Just above the turn-off, in a very small rangeof magnitudes ( ~ 0.2 in V), a factor of ~ 5 Li depletion occurs. Thissudden decrease explains puzzling results recently obtained on fieldsubgiants but it is not at all reproduced by standard (e.g. no rotation,no diffusion) models, whereas it is in somewhat better agreement withthe predictions of recent models which include rotational mixing andatomic diffusion. Out of the six cluster giants, one is probably abinary; of the remaining five single cluster members, three have a Liabundance log n(Li) ~ 1.1 while two have Li abundances from a factor 6to more than a factor 30 lower than the other three. The star with nodetected Li is the coolest and most luminous object in the sample and ismost likely an AGB star; the other has instead a similar magnitude andeffective temperature as the three more Li rich giants. The reasons forthis difference in Li abundance among otherwise similar stars can beascribed either to differential depletion during main-sequence orpost-main sequence evolution, possibly induced by rotation, or todifferences in the evolutionary status of these evolved stars. Bycomparing our results with those found for clusters of similar age andfor field stars, we find that none of the possible scenarios gives afully satisfactory explanation if the present population of NGC 3680giants reflect the expected ratio of clump vs. first-ascent RGB stars.If the more abundant Li-rich giants in NGC 3680 are indeed clump giants,their relatively high Li content requires that Li is produced, orbrought to the surface, between the tip of the RGB and the clump, whichis not consistent with observations of the similar age cluster NGC 752,where the more abundant, presumably clump giants have low Li abundances.Finally, we have used our spectra to determine the metallicity of thecluster giants, finding [Fe/H]=-0.17+/-0.12. This value is in very goodagreement with that derived from spectral indexes analysis, butsubstantially lower than the value inferred from Strömgrenphotometry. Based on observations collected at ESO, la Silla, and at theVLT.
| 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
| Critical tests of stellar evolution in open clusters. II. Membership, duplicity, and stellar and dynamical evolution in NGC 3680.
Based on new, accurate photometry, radial velocities, and proper motionsfor the intermediate-age open cluster NGC 3680, we identify individualsingle and binary cluster members and field stars in thecolour-magnitude diagram (CMD). This basic step turns out to be crucialfor a proper understanding of the cluster CMD: ~60% of the stars arefound to be field stars, and over 50% of the cluster stars are binaries.No bona fide cluster star is found more than 1.5mag below the turnoff,and cluster stars below 1.4Msun_ are only found in binarysystems. The total present mass of NGC 3680 is ~100Msun_,excluding any as yet unseen stellar remnants, and its half-mass radiusis 3.3' (1.2pc). Comparison with plausible IMFs indicates that only ~3%of the original stars and <~10% of the mass now survive, ~30% of theinitial mass being in the form of massive stars that have now completedtheir evolution, and ~60% in low-mass stars which may now be located ina distant cluster halo or perhaps have been lost entirely. The singlemain-sequence cluster members form an extremely tight sequence in theCMD, with E_(b-y)_=0.034 and [Fe/H]=+0.11. A direct fit to the Hyadesmain sequence yields (m-M)_0_=10.5+/-0.2 for NGC 3680. Isochrones fromseveral stellar models have been fit to the cluster sequence. When basedon consistent uvby colour transformations and the above clusterparameters, these fits are very stable and show that standard models arenot acceptable for stars with the turnoff mass of NGC 3680. Overshootingmodels perform much better, but further refinement of the overshootingformalism seems to be needed. The age derived for NGC 3680 is1.45+/-0.3Gyr. The limiting factor in a precise comparison of theory andobservations is now the transformation from theoretical to observedparameters, particularly (broad-band) colours.
| The Age of NGC 3680 and a Test of Convective Overshoot
A new CCD BV color-magnitude diagram has been derived for theintermediate age open cluster NGC 3680. The quality of photometrycoupled with the best-to-date knowledge of cluster memberships allowsfor a detailed isochrone fit to the CMD. The theoretical isochrones havebeen constructed using the Yale Rotating Evolution Code (YREC) in itsnon-rotating mode and the OPAL opacities (circa 1991). Four sets ofisochrones have been calculated: one for the standard stellar modelcalibrated to the Sun and three others for models with different amountsof convective overshoot at the edge of the convective core, namely,0.15, 0.20 and 0.25Hp, where Hp is the pressurescale height at the core edge. All four sets of theoretical isochroneswere adjusted to an adopted distance modulus ofVdeg-MV=10.20 and reddening E(B-V)=0.075 whichleads to ages of 1.3+/-0.15, 1.5+/-0.15, 1.6+/-0.15 and 1.7+/-0.15 Gyr,respectively. The uncertainties in age mainly reflect a subjectivedecision in differentiating a good fit from a poorer one. The model witha convective overshoot of 0.20Hp seems to yield the best fitto the sharply curved upper main-sequence. Hence, the estimated age ofNGC 3680 is 1.6+/-0.15 Gyr. The adopted overshoot parameter ostensiblyis uncertain by +/-0.05H_p. For comparison, the same stellar models withovershoot of 0.25Hp were fit to the color-magnitude diagramof the cluster NGC 752, which is similar in age and composition to NGC3680. The age estimate for NGC 752 is 1.6+/-0.2 Gyr, assumingVdeg-MV=8.20 and E(B-V)=0.030 for the cluster.
| Critical tests of stellar evolution in open clusters. I. New photometry and radial velocities for NGC 3680.
We present new CCD photometry in the b and y colours of the Stroemgrenuvby system for 310 stars in a 13'x13' field centered on theintermediate-age open cluster NGC 3680. Careful cross-checks indicatethat previously published BV photometry of NGC 3680 is affected byrandom and/or systematic errors precluding its use in criticalcomparison with theoretical isochrone computations. Detailed notes onseveral individual stars are given. In addition, we present =~400 newphotoelectric radial-velocity observations of 109 stars obtained withthe CORAVEL scanner during the period 1988-1994. These data allowsubstantially complete identification of member and non-member stars inthe field, and of spectroscopic binaries in both groups. Rotationalvelocities have also been derived for the programme stars, and ourvelocity variability criteria for stars of all rotations are described.The further astrophysical discussion of the data, including thedefinition of radial-velocity membership criteria, theoretical isochronefitting, and the dynamical state of the cluster and the origin of its"bimodal turnoff", will appear in a separate paper (Nordstroem et al.1996).
| Red giants in open clusters. IV. NGC 3680 and IC 4651.
Radial-velocity observations of 35 red giants in the field of theintermediate-age open clusters NGC 3680 and IC 4651 are presented andanalysed for membership and duplicity. Five stars in NGC 3680 and one inIC 4651 were identified as non-members, and six and five spectroscopicbinaries, respectively, were discovered among the red giant members inthe two clusters. Orbits have been determined for seven of the binaries,four of which are still preliminary. The mean cluster velocities of NGC3680 and IC 4651 are 0.9+/-0.2km/s and -31.0+/-0.2km/s respectively. Themorphology of the red giant region in the colour magnitude diagramsshows a well-populated clump in both clusters. In both clusters, onecertain member star is clearly brighter and redder than the clump, whileIC 4651 shows, in addition, a probable concentration of stars on theascending giant branch.
| A proper-motion study of the open cluster NGC 3680
Relative proper motions and cluster membership probabilities have beendetermined for 2711 stars in a region containing the old open clusterNGC 3680. The Yale-Columbia 26 in. refractor plates used in this studycontain significant magnitude equation as well as color equation. Aprocedure is developed for transforming the measures from each of theplates into a common magnitude/color equation system, thus yieldingdifferential positions from plate to plate, (i.e., proper motions) whichare free of these systematic errors. For well measured stars the meanstandard error of the proper motions is +/- 0.35 mas/yr. Three differentmembership calculation techniques are described in detail. The best fitto the proper-motion distributions yields 74 cluster members. Almost allknown red giants are cluster member according to the proper motionmembership criterion. The luminosity function of NGC 3680 shows acharacteristic turnover at Mupsilon approximately equals +3mag and an essentially flat faint end. Monte-Carlo simulations are usedin order to explore the mutual dependence of the luminosity function andmembership probabilities. The bimodality of the upper main sequencefound in earlier photometric studies probably still exists even aftereliminating proper-motion nonmembers.
| Catalogue of proper motions in the region of NGC 3680.
Not Available
| Evolved GK stars near the sun. I - The old disk population
A sample of nearly two thousand GK giants with intermediate band, (R,I),DDO and Geneva photometry has been assembled. Astrometric data is alsoavailable for most of the stars. The some 800 members of the old diskpopulation in the sample yield accurate luminosities (from two sources),reddening values and chemical abundances from calibrations of thephotometric parameters. Less than one percent of the objects arepeculiar in the sense that the flux distribution is abnormal. Thepeculiarity is signaled by strong CH (and Ba II) and weak CH. The CH+stars are all spectroscopic binaries, probably with white dwarfcompanions, whereas the CH- stars are not. A broad absorption band,centered near 3500 A, is found in the CH+ stars whereas the CH- objectshave a broad emission feature in the same region. The intensity of theseabsorptions and emissions are independent of the intensity of abnormalspectral features. Ten percent of the old disk sample have a heavyelement abundance from one and a half to three times the solar value.The distribution of the heavy element abundances is nearly a normal onewith a peak near solar abundance and ranges three times to one sixthsolar. The distribution of the (U, V) velocities is independent of theheavy element abundance and does not appear to be random. Ten percent ofthe old disk stars show a CN anomaly, equally divided between CN strongand CN weak. Several stars of individual astrometric or astrophysicalimportance are isolated.
| A BV photographic and CCD analysis of the intermediate-age open cluster NGC 3680
Results are presented of a photographic, photoelectric, and CCD surveyon the BV system in the intermediate-age open cluster, NGC 3680. Directtests demonstrate significant magnitude-dependent differences betweenthe photometry of Eggen (1969) and the standard BV system. The clustercontains a well-defined red giant clump, but the turnoff region exhibitsscatter noticeably larger than expected from the derived errors. Theapparent luminosity function of the cluster shows a dramatic decline inprobable cluster members below 1 solar mass when compared to counts forthis region of the sky based upon Galactic models. Comparison with thetheoretical isochrones of VB85 produces an age of 1.9 x 10 to the 9th yrwith a large uncertainty depending upon the choice of luminosity orcolor as the primary age estimator.
| CCD ubvy photometry of the bimodal main-sequence cluster NGC 3680
CCD uvby photometry for the intermediate age, southern open cluster, NGC3680, is analyzed. For a reddening of E(b-y) = 0.034, a true clustermodulus of 9.74 + or - 0.20 and a cluster metallicity of Fe/H abundance= 0.10 + or - 0.09, based on 18 probable nonbinary members of thecluster brighter than V = 14. The color-magnitude diagram for thecluster suggests that, although the main sequence may be subject to thesame bimodal distibution as NGC 752, the likely source in both clustersis a combination of binaries and a sharply curved turnoff. Thecolor-magnitude diagram is compared to the theoretical isochrones ofBertelli et al. (1988), showing an age of (1.9 + or - 0.3) X 10 to the9th yr.
| Large and kinematically unbiased samples of G- and K-type stars. IV - Evolved stars of the old disk population
Modified Stromgren and (R,I) photometry, along with DDO and Genevaphotometry, are presented for a complete sample of evolved old-disk Gand K giants in the Bright Star Catalogue. Stars with ages of between1.5 x 10 to the 9th and 10 to the 10th yr are found to have anear-normal distribution of heavy element abundances, centered on anFe/H abundance ratio of -0.1 dex. The old disk clusters NGC 3680 and IC4651 contain red-straggler young-disk giants that are probablycontemporaries of the blue stragglers in the clusters.
| Washington photometry of open cluster giants - The metal-rich clusters
Abundances of more than one hundred giants in a large sample ofmetal-rich open clusters in the Galaxy are investigated with Washingtonphotometry. Most of these clusters have no high-dispersion spectroscopicabundance determinations. A revision of the empirical abundancecalibrations for Population I giants, based on a much improved data setover previous calibrations, is first presented. The M-T(1) (Feabundance) calibration changes slightly for stars with Fe/H of about-0.5. The C-M (Fe + CN abundance) calibration is substantially alteredfor abundances above solar. The net effect brings the two abundanceindices into close agreement and eliminates the apparent CN enhancementspreviously determined for several open clusters. An enhanced sensitivityto Fe abundance is found for both the M - T(1) and especially the C - Mindex over that determined in previous investigations. Indeed, Delta(C -M) has an Fe abundance sensitivity that exceeds any other photometricabundance index. In view of the relative rarity of CN strengthvariations in Pop I giants, this index is most useful as a metallicityindicator for these stars. Abundances with an uncertainty of about 0.1dex are derived for a total of 18 open clusters observed with theWashington system. The abundances are generally in good agreement withprior abundance analyses. No strong evidence is found for CN variationsor anomalies in any of the clusters. A comparison with Population Ifield giants shows that the open cluster giants have normal CNabundances for their FE abundances.
| Astrophysical properties of red giants in three open clusters older than the Hyades
The application to the program stars of two independent membershipcriteria based on BV and DDO photometry makes it possible to distinguisha few red field stars from the physical members of the clusters. Inparticular, two stars previously thought to be members of NGC 3680 byEggen (1969) and McClure (1972) are found not to be physically connectedwith this cluster. It is also found that the cluster giants in NGC 2482and IC 4651 have CN strengths nearly identical with the Hyades giants,whereas NGC 3680 is considerably poorer in CN than the above clusters.Within the limits of the DDO photometry, no firm evidence is seen forany intrinsic differences in CN strength among the giants in the threeclusters. This result is valid for the clump stars at the blue end ofthe giant branch in NGC 3680 and IC 4651. Both CMT(1)T(2) and DDO datalend support to the conclusion that IC 4651 is on the metal-rich side ofthe distribution of intermediate and old open clusters. The mass resultsindicate that the clumps stars in NGC 3680 and IC 4651 could haveundergone mass loss before reaching their core burning phase ofevolution.
| The color excesses and metallicities of the open clusters NGC 2360 and NGC 3680
Abstract image available at:http://adsabs.harvard.edu/abs/1972ApJ...172..615M
| The Old Galactic Cluster NGC 3680
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...155..439E&db_key=AST
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Observation and Astrometry data
| Constellation: | Centaure |
| Right ascension: | 11h25m48.54s |
| Declination: | -43°09'52.5" |
| Apparent magnitude: | 10.929 |
| Proper motion RA: | -4.9 |
| Proper motion Dec: | -0.2 |
| B-T magnitude: | 12.676 |
| V-T magnitude: | 11.074 |
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