Open Cluster Study Research Articles

Age Metallicity Relation in the LMC

The age metallicity relation (AMR) is known to be very important for understanding the chemical evolution in a galaxy. LMC, our nearest galaxy offers an ideal target for such studies, considering that with the SMC and our Galaxy are an interacting group, influencing each other's star formation rate and production of metals. An observing program for the determination of AMR from a study of small open LMC clusters using Stroemgren phorometry has been initiated. Three observing runs were granted with the 1.5m Danish Telescope at La Silla. We report on our search within 8 clusters, scattered all over the LMC to cover a wide spatial distribution and metallicity. CMDs using Stroemgren photometry have been produced, in order to find the age of the stellar content. The available isochrones used, although very few are able to give us a good age estimate. The calibration of the y, b, v, magnitudes and colours to metallicity used, is the one by Richter et al.(A&A, 1999), to obtain the adopted metallicities of the clusters. Although our sample is still small, a clear trend is observed in AMR showing a significant increase of metallicity with age. Comparison with previous AMRs from other investigations shows good agreement within the errors. The bursting model of chemical evolution by Pagel and Tautvaisiene (MNRAS, 1999) shows that the burst of star formation (SF) produces a change of slope in their AMRs from 2 Gyr to the present time, the burst assumed to occur from –0.4 dex to 0.0 dex. Although our sample is small the observed trend favours the expected change of the AMRs rather towards the 1 Gyr. Therefore our observations support a bursting model of chemical evolution. More obervations are needed and new theoretical models to strengthen these results. Finally it is found that all young metal rich clusters occupy the central LMC regions whereas the old metal poor ones are found in the LMC periphery giving evidence for a metallicity gradient as well. We would like to acknowledge financial support by the NATO grant GRG.GRGP/972234and the Greek Secretariat of Research and Technology.

A photometric study of the intermediate age open cluster King 5

We report on near IR (J and K bands) observations of an $8^{\prime} \times 8^{\prime}$ region centered on the poorly studied open cluster King 5, for which only optical photometry existed. We found that the cluster is of moderate age (1.0 Gry old), intermediate in age between the Hyades and NGC 752. Combining optical and IR photometry we obtain estimates for cluster parameters. The color excess E(J-K), E(V-I) and E(V-K) are 0.50, 1.10 and 2.45, respectively. The true distance modulus turns out to be $(m-M)_0) = 11.40\pm 0.15$. As a consequence, King 5 is 1.9 kpc far from the Sun.

WIYN Open Cluster Study. III. The Observed Variation of the Red Clump Luminosity and Color with Metallicity and Age

The recent controversy regarding the variation of the I-band red clump (RC) luminosity (M) with metallicity and age has prompted us to examine this question, using precise photometry of Galactic open clusters. Because these data extend well down to the unevolved main sequence, it is possible to use main-sequence fitting to estimate the cluster distance moduli, thereby providing a straightforward measure of the absolute magnitude of the red clump. Using this technique and comparing the observed quantities with theoretical ones, we draw the following conclusions. Cluster M values are much less sensitive to metal abundance than their M counterparts, making the former more amenable for use as a distance indicator. However, the range in the observed values of M is much larger than that expected from the measurement errors alone. This fact suggests that the value of M is influenced to a significant degree by properties of the stellar population, such as metal abundance and age. In particular, the observed variation of M and M with metallicity and age, as inferred from the open clusters in this study, agrees qualitatively with the predictions of the theoretical models. These results indicate that application of the solar-neighborhood M to red clumps of other stellar populations with a different age/abundance mix, such as the Magellanic Clouds, may produce spurious results.

A Group-Group Merger at a Redshift of [ITAL]z[/ITAL] = 0.84?

We present a dynamical study of the Cl 0023+0423 system at a redshift of z = 0.84. This system consists of two components separated in velocity space by ~2900 km s-1 and on the plane of the sky by ~0.23 h-1 Mpc. A kinematic analysis indicates that the two components are a poor cluster with a velocity dispersion of 415 km s-1 and a mass of ~3?6 ? 1014 h-1 M?, and a less massive group with a velocity dispersion of 158 km s-1 and a mass of ~1013 h-1 M?. The dynamics of galaxy groups at high redshift can provide important insights into the creation of present-day galaxy clusters. Therefore, we have performed a dynamical study on this system in order to determine whether the two groups are infalling. This analysis includes an analytic two-body calculation and N-body simulations. The results of both studies indicate that the system is most likely not bound, but simply a chance projection on the sky; however, within the observational uncertainties, there exist bound solutions where the two galaxy groups are currently moving toward each other and will eventually merge into a larger system of galaxies. We have run 1000 N-body simulations with random initial conditions based on the observed parameters of the Cl 0023+0423 groups. A statistical analysis of these simulations indicates that there is a 20% chance that the two groups will merge. If the Cl 0023+0423 system does merge, it will appear as a cluster on the sky, as well as in velocity space, within 1?2 Gyr. The cluster will evolve dynamically for more than 3 Gyr, appearing during this time more similar to an open, irregular cluster. The final merged system has a velocity dispersion that is consistent with a local Abell richness class 1 cluster. The morphological analysis of the galaxy populations of Cl 0023+0423 suggests that both groups are largely dominated by spiral galaxies. Early-type fractions are 33% or less. These modest early-type fractions have implications for both cluster formation and group evolution. Studies of open clusters at z = 0.31?0.54 indicate that they have early-type fractions between 45%?80%. If the Cl 0023+0423 system is the predecessor of such a cluster, the comparison may suggest that some fraction of early-type galaxies are formed between redshifts of z ~ 0.8 and z ~ 0.3; however, the morphological fractions are still highly uncertain. In addition, the modest early-type fractions in both groups may be inconsistent with the strong correlation between velocity dispersion and early-type fraction observed in nearby groups of galaxies. Both groups apparently have relatively low early-type populations, irrespective of their velocity dispersion. If the groups of Cl 0023+0423 are typical of galaxy groups at high redshift, and if high-redshift groups are the progenitors of local groups, this result may also imply that some early-type formation is occurring at redshifts of z 0.8. These results do not preclude the formation of early-type galaxies at very high redshift, as many observations suggest; however, the observations of the Cl 0023+0423 system may imply that a fraction of the early-type population is forming and/or undergoing significant evolution at redshifts of z < 1.

The fine structure of luminosity functions of young open cluster stars

Abstract The luminosity function (LF) of young open cluster stars has been studied for decades to obtain a slope of the initial mass function (IMF), which is important for understanding of star formation. Young open clusters contain a lot of pre-main-sequence (PMS) stars the positions of which in the H—R diagram deviate significantly from the main sequence and consequently the PMS massluminosity relation (MLR) differs from the ZAMS one. Such features of the MLR and related details of young open cluster LFs they produce are the subject of this poster. Three peaks have been studied: (1) the main peak (H-peak)—generated by PMS stars settling on the main sequence; (2) the R-peak—generated by inversion of the radius on the stellar birthline; the D-peak—generated by changes in the MLR and associated with deuterium burning. The evolution of these features with cluster age and possible application for young open cluster study are discussed.

Very Low Mass Stars and Substellar Objects in the Pleiades

We have identified a small number of faint, red stars in optical and infrared frames taken near the center of the Pleiades cluster. The sampled masses range from 0.25 to 0.04 M<SUB>sun</SUB>. The Pleiades mass function in linear units is consistent with a M<SUP>-1</SUP> power law or with a flat dependence in logarithmic mass units. This dependence is consistent with studies of other young open clusters and suggests that massive brown dwarfs and low-mass stars do not contribute significantly to the dark matter.

Schmidt plate survey towards the Galactic centre. 2. Stellar statistics in the direction of the Sagittarius‐Carina arm

AbstractA study of the structure and kinematics of the Galaxy from Tautenburg Schmidt plates taken towards the Galactic centre (l = 17.0°, b = +0.8°) is presented. Proper motions and B, V magnitudes were determined for about 36 500 stars up to the limiting magnitude V = 16m.8 in a field of 8.95 square degrees. Proper motion accuracy of about 3 mas/year has been obtained for stars brighter than V = 15m. The rms errors of stellar magnitudes and (B–V) colours is about 0.1 mag.The majority of field stars in the survey are main sequence stars and red giants of the disk. They belong to the Local or Sagittarius‐Carina arms, or they are located between these spiral arms. Comparing the modelled and observed distributions of magnitudes and colours, we specified the interstellar extinction determined in the preceding study of open clusters in this field.The luminosity function towards the Galactic centre was determined for stars with absolute magnitudes from ‐4m.35 to +9m. Kinematical and spatial distribution parameters up to 4 kpc from the Sun were obtained as a function of galactocentric distance.

VBYH-BETA CCD PHOTOMETRY OF MELOTTE 66: A DISK ANALOG OF OMEGA CENTAURI

ABSTRACT A CCD study of the peculiar open cluster, Melotte 66, on the vbyH-beta system is presented. The V, (b-y) color-magnitude diagram of this metal-deficient, old disk cluster confirms the anomalous features found in photographic BV studies and extends the main sequence to V = 20. The main sequence exhibits a (b-y) color rang significantly larger than expected from photometric errors alone; the (b-y) colors are correlated with H-beta implying that the dispersion is real and not the result of variable reddening across the cluster. The m1 indices for the turnoff stars imply a spread in [Fe/H] too small to explain the color range. Though the subgiant region is poorly defined, the region above the turnoff in the Hertzsprung gap is richly populated by a group of yellow stragglers whose membership is confirmed by radial star counts and radial velocities. The giant branch is richly populated but shows a smaller spread in color at a given V than one would expect from the turnoff region. More important, the giants exhibit a large scatter in m1, in contradiction with the turnoff observations. Various explanations for these observations are discussed, including CN variations among the gaints triggered by either binary evolution or rapid rotation among the main sequence stars.

Photometric study of the intermediate-age open cluster Be 33

We present CCD BVI photometry for Be 33, a previously unstudied open cluster located toward the Galactic Anticentre. The radial extent of the cluster is about 4 arcmin, and it contains about 285 stars with V < 20.5 mag. Examination of the derived colour-magnitude diagrams shows that Be 33 is a strongly reddened object, with an age slightly lower than the age of the Hyades. Its apparent distance modulus is (m − M) V ≃ 14.7, and its reddening is E(B − V) ≃ 0.6 for an assumed metallicity equal to the solar value. Comparison of the cluster colour-magnitude diagram with isochrones published by Bertelli et al. suggests that in fact Be 33 has a metallicity significantly lower than solar

Luminosities for two yellow supergiants - Nonvariables and the instability strip

view Abstract Citations (9) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Luminosities for Two Yellow Supergiants: Non-variables and the Instability Strip Evans, Nancy R. Abstract The luminosities for two yellow supergiants HD 183864 and Psi And = HD 223047 are determined from the IUE spectra of their hot companions. The absolute magnitudes of HD 183864 and HD 223047 are -2.3 and -2.1 mag, respectively, and their companions have spectral types of A0.0 V and B8.8 V. The companion of Psi And is compatible with the orbital motion tentatively detected by speckle interferometric observations. The supergiant luminosities are combined with the Cepheid luminosities determined in the same way, and also the variables and nonvariables from Schmidt's studies of open clusters. As found by Schmidt, the variable and nonvariable supergiants have almost no overlap in the HR diagram. The combined sample defines the locus of the helium burning blue loops of evolutionary tracks. Because no nonvariables are found to the blue of fainter Cepheids, the observed blue edge of the Cepheid region may be partly determined by the blue loops rather than by the region of pulsational instability. Publication: The Astronomical Journal Pub Date: May 1993 DOI: 10.1086/116570 Bibcode: 1993AJ....105.1956E Keywords: Companion Stars; Hertzsprung-Russell Diagram; Iue; Stellar Luminosity; Stellar Orbits; Supergiant Stars; Cepheid Variables; Magellanic Clouds; Stellar Color; Stellar Magnitude; Stellar Spectra; Astrophysics; SUPERGIANTS; STARS: FUNDAMENTAL PARAMETERS full text sources ADS | data products SIMBAD (2) MAST (1) INES (1)

Study of faint young open clusters as tracers of spiral features in our galaxy

Continuing the study of faint young open clusters as tracers of spiral features in our Galaxy, photoelectric and photographic photometry of 39 stars was done in the field of the faint open cluster NGC 2236 ≡ OCl 501 in the direction of Monoceros constellation. Out of these stars, a total of 22 down tom v ≃ 15.4 mag have been found to be probable members. There is apparently a variable extinction across the field of the cluster with E(B - V) ranging between 0.84 mag and 0.68 mag. The median age of this cluster is estimated to be 7.6 × 107 years and the cluster is thereby considered as belonging to the marginally old category. Thus, it cannot be specifically used as a spiral arm tracer in the study of our Galaxy. This cluster is located at a distance of 3.72 ± 0.13 kpc, which places it at the inner edge of the outer Perseus spiral feature of the Milky Way.

Study of young open clusters as tracers of spiral features in our galaxy. Paper 4: Czernik 20 (OCl 427)

Photoelectric and photographic photometry of 72 stars was done in the field of the not-well-studied open cluster Czernik 20= OCl 427 in the direction of the Auriga constellation. Of these stars, a total of 43 have been found to be probable members down tomv− 15.75 mag. There is apparently a variable extinction across the field of the cluster withE(B-V) ranging from 0.53 to 0.38 mag. The cluster stars show a range in their ages from 1.0 × 107 to 7.1 × 107 years, indicating that Czernik 20 is young enough to be considered as a spiral-arm tracer in the study of our Galaxy. The distance of this cluster is found to be 4.27 ±0.14 kpc and it is located inside the outer Perseus arm of the Milky Way

The mass of the open star cluster M35 as derived from proper motions

view Abstract Citations (64) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Mass of the Open Star Cluster M35 as Derived from Proper Motions Leonard, Peter J. T. ; Merritt, David Abstract Proper-motion studies of several open and globular clusters have yielded accurate, two-component (radial and tangential) velocity dispersion profiles for the brighest stars in these systems. It is shown that velocity dispersions derived from proper motions, unlike those derived from radial velocities, contain enough information to determine the shape and amplitude of the velocity ellipsoid at all radii in a spherical cluster. This information, in turn, is sufficient to yield the cluster potential without any additional assumptions about the kinematics or the mass-to-light ratio. Proper-motion data for the open star cluster M35 imply a dynamical mass within the central 3.75 pc between 1600 and 3200 solar masses (95 percent confidence), consistent with the mass of a realistic stellar population within the same radius. Publication: The Astrophysical Journal Pub Date: April 1989 DOI: 10.1086/167287 Bibcode: 1989ApJ...339..195L Keywords: Open Clusters; Stellar Motions; Velocity Distribution; Density Distribution; Doppler Effect; Mass To Light Ratios; Radial Velocity; Stellar Luminosity; Stellar Mass; Astrophysics; CLUSTERS: OPEN; STARS: STELLAR DYNAMICS full text sources ADS | data products SIMBAD (4)

The virial mass of the open cluster M11

Abstract In statistical studies of open clusters, great attention should be paid to possible field contamination. The importance of correct handling of membership probabilities in the calculation of the virial mass of a cluster is emphasized. Our analysis shows that reasonable virial mass can be obtained only if we use only those member stars with large membership probabilities. Our re-calculation for M11 gives a virial mass of 5094 μ ⊙, in good agreement with the latest result of 4671 μ ⊙, directly derived from observed luminosities, giving a virial coefficient of 0.9.

A study of faint young open clusters as tracers of spiral features in our galaxy paper 3: Collinder 97 (OC1 506)

Photoelectric and photographic photometry of twenty-nine stars was done in the field of the open cluster Collinder 97 ≡ OC1 506. Of these stars, a total of twenty-four have been found to be possible members. There is apparently no interstellar extinction in the direction of this cluster which is in the constellation of Monoceros: itsE(B-V) = 0.0 mag. This cluster is situated at a distance of 0.63 ± 0.01 kpc, which is well within the local arm of our Galaxy. The age of this cluster is in the range of 1 × 108 to 5.9 × l08 yr, which puts it in an older age group. Thus, it cannot be specifically considered as a spiral-arm tracer in the study of our Galaxy.

On determining membership of open clusters from relative proper motion

We discuss the determination of membership of 42 open clusters. Our analysis shows that Vasilevskis' mathematical model can be reasonably applied to this case. Our improved version of Sanders' method and our definition of cluster member based on the principles of discriminatory analysis effectively exclude stars of low probabilities. It is important in the study of open cluster to use only those with high probabilities. The effectiveness of the statistical method is closely related to the velocity distributions of the member and field stars. For fields where the error rate is high, it is better to combine other data than proper motion in determining membership.

A radial-velocity study of open clusters containing blue stragglers.

A radial-velocity study of open clusters containing blue stragglers.

The contribution of Hipparcos to the study of open clusters

The observation by the projected ESA astrometric satellite Hipparcos (HIghPrecisionPARallaxesCOllectingSatellite) of stars in nearby open clusters is studied and the expected precision and accuracy of their parallax measurements are evaluated. The amplitude of local systematic errors will certainly be smaller than the precision of the results, a feature which is very seldom realized in global astrometric sets of data; this will have far-reaching consequences.With the exception of Hyades, these measures will be the first trigonometric parallaxes ever obtained for open clusters. The precision of astronomical interferences from clusters properties will be greatly improved.

Commission 33. (Stellar Statistics.)

A recommendation to the Union concerning the construction of certain tables was accepted.A discussion was opened on the subject of collaboration in the study of open clusters. An application to the General Assembly was passed for a recommendation as follows: “That the Union call attention to the important problems connected with the open clusters and determinations of proper motions, radial velocities, magnitudes and spectra along the lines already inaugurated at several observatories.”It was agreed that Dr Mineur should approach the observatories of the Carte du Ciel on the subject of photographing the open clusters for the future determinations of proper motions.