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Variable Stars in the Field of NGC 6882/6885: The Case of V381 Vulpeculae and V382 Vulpeculae
We present photometric and spectroscopic results for two reportedδ Scuti stars in the field of NGC 6882/6885. We find that V381 Vulhas a period of 0.1185 days and is a δ Scuti variable, aspreviously reported. The spectra of V382 Vul shows it to be a B3 starand therefore not a δ Scuti. All evidence points to V382 Vul beinga β Cephei star with a period of 0.1808 days. Additionally, wereport five new variables and eight suspected variable stars. Of thefive new variables, two are pulsators and three are eclipsing binarysystems. In our search for new variable stars, we use a ``robust medianstatistic'' that is proven to be better at finding low-amplitudevariables than the traditional error curve approach.
| 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.
| Delta Scuti Variables in the Field of NGC 6882/85
In the constellation Vulpecula reside two open clusters NGC 6882 and NGC6885. The smaller cluster NGC 6885 is superimposed onto NGC 6882. Recentobservations of the field have led to discoveries that challenge thecurrent classification of these two clusters. We present the resultsfrom a variable star campaign of regions surrounding the heart of thecluster that resulted in the discovery of four new δ Scuti starsand five other candidates. Of the four, one star was found to be a highamplitude pulsator with a period of about 0.205557 days. The remainingcandidates consist of low amplitude stars of which two were found toundergo rapid pulsations. The observations were performed utilizing anapplication of time series CCD photometry using VRI Bessel filters. Datawere obtained using the 0.4-m David Derrick Telescope.Funding for this research was provided by the National ScienceFoundation Research Experience for Undergraduates program hosted by theDept. of Physics and Astronomy at Brigham Young University.
| Seeing double in the local group: extragalactic binaries
Eclipsing binaries, both inside and outside our Galaxy, are proving tobe powerful tools for studying a wide spectrum of astrophysicalproblems. They are also are extremely valuable for providing fundamentalquantities such as stellar masses, radii, luminosities, ages anddistances. Recently, eclipsing binaries are turning out to be accuratedistance indicators for star clusters inside our Galaxy and fordetermining accurate distances to nearby galaxies - such as theMagellanic Clouds and the Andromeda Galaxy. Also with eclipsingbinaries, it is possible to study the physical properties and determineevolution for a wide variety of objects that are lucky enough to bebinary members. These objects include pre-main sequence stars, mainsequence stars, giants, supergiants, various pulsating stars, whitedwarfs, black holes and even exosolar planets. At the present time over7000 eclipsing binaries have been discovered in Local Group galaxies.These systems are mostly members of the Magellanic Clouds and theAndromeda Galaxy. But also an increasing number of extragalacticbinaries are being found as members of dwarf elliptical galaxies and lowsurface density irregular galaxy members of the Local Group. It will beimportant to study the properties of eclipsing binaries that have formedin galaxies with vastly different dynamical, star formation, andchemical histories than our home Galaxy. The study of these binaries mayprovide clues about the star formation rates and dynamics of their hostgalaxies as well as the possible effects of varying chemical abundanceon stellar evolution and structure. An overview of eclipsing andinteracting binary star systems in exterior galaxies is presented thattraces the development of this emerging field of research. Alsodiscussed are some recent developments and future expectations for thestudy of extragalactic binaries.
| 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.
| tex2html_wrap_inlineuvbyb#beta; Photoelectric Photometry of the Open Cluster NGC823
Absolute uvby beta photoelectric photometry of the brightest stars inthe direction of the Open Cluster NGC823 has been secured and ispresented. From the data analysis, reddening, distance, temperature andgravity are determined for the B, A, F stars and, from these, reddeningand a mean distance modulus ( 12.475+/-0.414) to the cluster aredetermined. Also, their membership in the cluster has been establishedand a numerical value of the age is determined through direct comparisonwith theoretical models. A brief analysis of the short period variablestars in the direction of NGC823 is made. We have concluded that theymight not be pre-MS delta Scuti stars.
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| 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
| 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
| Testing the Least Action principle in an Ω0 =1 universe
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| Testing the least action principle in an omegamicron = 1 Universe
The least action principle (LAP) is a dynamically rigorous method forderiving the history of galaxy orbits. In particular it is an omegatest, predicting current epoch galaxy velocities as a function ofposition and of the cosmological background. It is most usefully appliedto in-falling structures, such as the local group, where its applicationindicates that the preferred cosmological model isomegamicron = 0.1 and h = 0.75 (h is the Hubble parameter inunits of 100 km/s/Mpc). The method assumes that all the mass acts as ifit were distributed as the visible galaxies. We test the reliability ofthe LAP to Local Group-like systems extracted fromomegamicron = 1 n-body simulations. While the orbits of thegalaxies are qualitatively well reconstructed, the LAP systematicallyunderestimates the mass of the system. This failure is attributed to thepresence of extended halos weakly clustered around visible galaxieswhich prevent a large fraction of the group mass from being detected bythe LAP technique. We conclude that the LAP method cannot rule out anomegamicron = 1 value of the Local Group scale. Betterconstraints on omegamicron may be obtained by applying thistechnique to in-falling systems, such as clusters, containing objectswith separations large compared to galaxy sizes.
| Open cluster chemical composition. 1: Later type stars in eight clusters
Abundance analyses of 36 stars associated with eight open clusters (IC2581, NGC 3532, NGC 5822, NGC 6067, NGC 6087, IC 4725 (M25), IC 4756,and NGC 6882/6885) are presented. The stars are primarily evolved G andK giants and supergiants. Cepheids in NGC 6067, NGC 6087, and IC 4725are included as are non-cluster Cepheids near the clusters NGC 3532, NGC6067, and IC 4725. With the addition of a background K giant in IC 4725,the total number of stars is 40. Elemental abundances derived includeLi, C, N, O, the alpha-elements, the Fe peak, and limited data on theheavy elements. The Na abundances of the sample show a gravitydependence in the sense of an increase in the abundance as the gravitydecreases. The CNO abundances indicate that these objects are processed(on the whole), and that they show the O deficiency previously noted inintermediate mass stars by Luck & Lambert (1981, 1985). There arefour stars in the sample which appear to be unprocessed: two giants andtwo supergiants. There are also two super-Li stars in the sample, one ofwhich is most likely a weak G-band star. It is suggested that thesuper-Li F supergiants could be evolved blue stragglers. The moststriking result of the study is the finding that the (O/Na) ratiocorrelates strongly with the gravity and the stellar mass, thus implyingthat there is a nonstandard additional mixing process affecting thesurface abundances of these stars. A promising candidate for the mixingprocess is the turbulent diffusive mixing process proposed byDenissenkov (1993) which brings Na to the surface and which could alsolead to a modification of the oxygen content.
| Development of the Galactic disk: A search for the oldest open clusters
In an extensive charge coupled devices (CCD) photometric survey ofpotential old open clusters, we have identified a number of systems thatare indeed old; some of them are among the oldest of the open clusters.Using our versions of two well-known morphological age indices, onebased on the luminosity difference between the main sequence turnoff andthe horizontal branch and the other on the color difference between theturnoff and the giant branch, we have ranked the open clusters inapproximate order of age. Our data together with previously publishedphotometry of other old open clusters, yields a catalogue of 72 clustersof the age of Hyades or older with 19 of the clusters as old or olderthan M67 (about 5 Gyr). Among the oldest open clusters are Be 17, Cr261, NGC 6791, Be 54, and AM 2. Be 17 and another old cluster, Lynga 7,are possibly as old as the youngest globulars. The data also suggestthat the formation rate of open clusters may have been higher early inthe history of the disk than at intermediate times since numerousclusters have survived from that time.
| 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.
| Blue stragglers - A search for binaries in the infrared
Infrared photometry in the J, H and K bands, performed on a sample of 33blue stragglers (BS) belonging to 8 open clusters is presented. Thisphotometry has been combined with published Johnson UBV photometry tosearch for possible cold companions among the BS, as expected for Case Bclose binary evolution. Probable binaries were identified by comparisonwith standard mean color relations for single stars. The number ofbinary detections is discussed together with the results of a previousspectroscopic search for binaries among BS (Manteiga et al. 1989), andthe consequences for the hypothesis of binarity for the origin of BS areanalyzed.
| 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.
| Metallicities of open clusters
An examination is conducted of available metallicity data on openclusters, gathering the largest possible set of homogeneous estimationsof this parameter and determining whether open cluster metallicities arerelated to the spatial and age distributions of such objects. The'composite' C-M diagrams for the two metallicity groups discussedexhibit interesting morphological differences which may be characterizedas the presence of numbered blue stragglers at the two metal-richclusters and a lack of such members in two metal-poor ones.
| Some characteristics of complexes of open star clusters
Mean coordinates and velocities, phase sizes, mean elements of galacticorbits, mean ages, and metal abundances are given for 11 complexes ofopen clusters, and correlations between these characteristics arediscussed. The possible existence of a supercomplex encompassing 9 or 10complexes, and probably a number of individual clusters, is discussed.This rotates at an angular velocity of 10 to 13 km/s kpc.
| Groups of open clusters with common motion in the Galaxy
A method of identifying star groups with common motion in space isapplied to a sample of 66 open clusters with known space velocitycomponents. Eight groups are obtained; out of these, five are probablyreal. It is shown that the motions of the cepheids and the open clustersare analogous in the vicinity of the sun.
| Two populations of open clusters
The paper proposes a division of the local open clusters into twodifferent dislike subpopulations on the base of the metallicityenhancement history, spatial distribution in the Galaxy and morphologyof their C-M diagrams. The thin disk population objects exhibit highermetallicities and are more closely concentrated to the center and thedisk of the Galaxy than the thick disk clusters. The former contain alsofrequently blue stragglers while the later exhibit the presence of Clumpgiant members, typical for the thick disk globular clusters. Kinematicalproperties of the two considered open cluster subpopulations remainunknown due to the lack of observational data.
| Young stellar-gas complexes in the Galaxy
It is found that about 90 percent of OB-associations and o-b2 clusterssituated within 3 kpc of the sun can be united into complexes withdiameters of 150-700 pc. Almost all of these clusters contain giantmolecular clouds with a mass greater than about 100,000 solar masses. Anumber of complexes are associated with giant H I clouds; a few of thesmall complexes are situated in the HI caverns. The concentration ofOB-associations and young clusters in star complexes attests to theircommon origin in the supergiant gaseous clouds.
| Radial velocities of stars in five old open clusters
Radial velocities are derived from 76 medium-resolution spectra of 57stars in the old open clusters NGC 2158, NGC 6791 NGC 6882/5, NGC 6939,and NGC 6940. The mean cluster radial velocities are determined to lessthan about 3 km/s. Cluster membership is discussed, and the results arecompared to previous investigations.
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| A catalog of some observational data and elements of the galactic orbits of open star clusters
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| A Possible Rotation of the System of Open Cluster Complexes
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| A photometric study of short period variable stars in open clusters
The photoelectric photometry of known Delta Scuti variable stars inselected open clusters (Coma, Praesepe, Pleiades, Alpha Per, and NGC2264) was carried out in order to determine the periods of pulsation.Multicolor uvby-beta photometry and a search for new variables in otheropen clusters (NGC 2539, NGC 6494, NGC 6882-5, NGC 7062, NGC 7063 andNGC 7686) were also performed.
| Yellow evolved stars in open clusters
This paper describes a program in which Galactic cluster post-AGBcandidates were first identified and then analyzed for clustermembership via radial velocities, monitored for possible photometricvariations, examined for evidence of mass loss, and classified ascompletely as possible in terms of their basic stellar parameters. Theintrinsically brightest supergiants are found in the youngest clusters.With increasing cluster age, the absolute luminosities attained by thesupergiants decline. It appears that the evolutionary tracks ofluminosity class II stars are more similar to those of class I than ofclass III. Only two superluminous giant star candidates are found inopen clusters.
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
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| 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.
| On determining membership of open clusters from relative proper motion
We discuss the determination of membership of 42 open clusters. Ouranalysis shows that Vasilevskis' mathematical model can be reasonablyapplied to this case. Our improved version of Sanders' method and ourdefinition of cluster member based on the principles of discriminatoryanalysis effectively exclude stars of low probabilities. It is importantin the study of open cluster to use only those with high probabilities.The effectiveness of the statistical method is closely related to thevelocity distributions of the member and field stars. For fields wherethe error rate is high, it is better to combine other data than propermotion in determining membership.
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