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Sample records for open cluster distance

  1. A revised moving cluster distance to the Pleiades open cluster

    NASA Astrophysics Data System (ADS)

    Galli, P. A. B.; Moraux, E.; Bouy, H.; Bouvier, J.; Olivares, J.; Teixeira, R.

    2017-01-01

    Context. The distance to the Pleiades open cluster has been extensively debated in the literature over several decades. Although different methods point to a discrepancy in the trigonometric parallaxes produced by the Hipparcos mission, the number of individual stars with known distances is still small compared to the number of cluster members to help solve this problem. Aims: We provide a new distance estimate for the Pleiades based on the moving cluster method, which will be useful to further discuss the so-called Pleiades distance controversy and compare it with the very precise parallaxes from the Gaia space mission. Methods: We apply a refurbished implementation of the convergent point search method to an updated census of Pleiades stars to calculate the convergent point position of the cluster from stellar proper motions. Then, we derive individual parallaxes for 64 cluster members using radial velocities compiled from the literature, and approximate parallaxes for another 1146 stars based on the spatial velocity of the cluster. This represents the largest sample of Pleiades stars with individual distances to date. Results: The parallaxes derived in this work are in good agreement with previous results obtained in different studies (excluding Hipparcos) for individual stars in the cluster. We report a mean parallax of 7.44 ± 0.08 mas and distance of pc that is consistent with the weighted mean of 135.0 ± 0.6 pc obtained from the non-Hipparcos results in the literature. Conclusions: Our result for the distance to the Pleiades open cluster is not consistent with the Hipparcos catalog, but favors the recent and more precise distance determination of 136.2 ± 1.2 pc obtained from Very Long Baseline Interferometry observations. It is also in good agreement with the mean distance of 133 ± 5 pc obtained from the first trigonometric parallaxes delivered by the Gaia satellite for the brightest cluster members in common with our sample. Full Table B.2 is only

  2. The Membership and Distance of the Open Cluster Collinder 419

    NASA Technical Reports Server (NTRS)

    Roberts, Lewis C., Jr.; Gies, Douglas R.; Parks, J. Robert; Grundstrom, Erika D.; McSwain, M. Virginia; Berger, David H.; Mason, Brian D.; tenBrummelaar, Theo A.; Turner, Nils H.

    2010-01-01

    The young open cluster Collinder 419 surrounds the massive O star, HD 193322, that is itself a remarkable multiple star system containing at least four components. Here we present a discussion of the cluster distance based upon new spectral classifications of the brighter members, UBV photometry, and an analysis of astrometric and photometric data from the third U. S. Naval Observatory CCD Astrograph Catalog and Two Micron All Sky Survey Catalog. We determine an average cluster reddening of E(B - V) = 0.37 +/-.05 mag and a cluster distance of 741 plus or minus 36 pc. The cluster probably contains some very young stars that may include a reddened M3 III star, IRAS 20161+4035.

  3. THE MEMBERSHIP AND DISTANCE OF THE OPEN CLUSTER COLLINDER 419

    SciTech Connect

    Roberts, Lewis C.; Gies, Douglas R.; Parks, J. Robert; Grundstrom, Erika D.; McSwain, M. Virginia; Berger, David H.; Mason, Brian D.; Ten Brummelaar, Theo A.; Turner, Nils H. E-mail: gies@chara.gsu.ed E-mail: erika.grundstrom@vanderbilt.ed E-mail: dberger@sysplan.co E-mail: theo@chara-array.or

    2010-09-15

    The young open cluster Collinder 419 surrounds the massive O star, HD 193322, that is itself a remarkable multiple star system containing at least four components. Here we present a discussion of the cluster distance based upon new spectral classifications of the brighter members, UBV photometry, and an analysis of astrometric and photometric data from the third U. S. Naval Observatory CCD Astrograph Catalog and Two Micron All Sky Survey Catalog. We determine an average cluster reddening of E(B - V) = 0.37 {+-} 0.05 mag and a cluster distance of 741 {+-} 36 pc. The cluster probably contains some very young stars that may include a reddened M3 III star, IRAS 20161+4035.

  4. An updated maximum likelihood approach to open cluster distance determination

    NASA Astrophysics Data System (ADS)

    Palmer, M.; Arenou, F.; Luri, X.; Masana, E.

    2014-04-01

    Aims: An improved method for estimating distances to open clusters is presented and applied to Hipparcos data for the Pleiades and the Hyades. The method is applied in the context of the historic Pleiades distance problem, with a discussion of previous criticisms of Hipparcos parallaxes. This is followed by an outlook for Gaia, where the improved method could be especially useful. Methods: Based on maximum likelihood estimation, the method combines parallax, position, apparent magnitude, colour, proper motion, and radial velocity information to estimate the parameters describing an open cluster precisely and without bias. Results: We find the distance to the Pleiades to be 120.3 ± 1.5 pc, in accordance with previously published work using the same dataset. We find that error correlations cannot be responsible for the still present discrepancy between Hipparcos and photometric methods. Additionally, the three-dimensional space velocity and physical structure of Pleiades is parametrised, where we find strong evidence of mass segregation. The distance to the Hyades is found to be 46.35 ± 0.35 pc, also in accordance with previous results. Through the use of simulations, we confirm that the method is unbiased, so will be useful for accurate open cluster parameter estimation with Gaia at distances up to several thousand parsec. Appendices are available in electronic form at http://www.aanda.org

  5. Strengthening the open cluster distance scale via VVV photometry

    NASA Astrophysics Data System (ADS)

    Majaess, D.; Turner, D.; Moni Bidin, C.; Geisler, D.; Borissova, J.; Minniti, D.; Bonatto, C.; Gieren, W.; Carraro, G.; Kurtev, R.; Mauro, F.; Chené, A.-N.; Forbes, D.; Lucas, P.; Dékány, I.; Saito, R. K.; Soto, M.

    2012-01-01

    Approximately 14% of known Galactic open clusters possess absolute errors ≤ 20% as evaluated from n ≥ 3 independent distance estimates, and the statistics for age estimates are markedly worse. That impedes such diverse efforts as calibrating standard candles and constraining masses for substellar companions. New data from the VVV survey may be employed to establish precise cluster distances with comparatively reduced uncertainties ( ≤ 10%). This is illustrated by deriving parameters for Pismis 19 and NGC 4349, two pertinent open clusters which hitherto feature sizable uncertainties (60%). Fundamental parameters determined for Pismis 19 from new VVV JHKs photometry are d = 2.40 ± 0.15 kpc, ⟨EJ - H⟩ = 0.34 ± 0.04, and log τ = 9.05 ± 0.10, whereas for NGC 4349 the analysis yielded d = 1.63 ± 0.13 kpc, EJ - H = 0.09 ± 0.02, log τ = 8.55 ± 0.10. The results exhibit a significant ( ≥ 5 × ) reduction in uncertainties, and indicate that: i) existing parameters for the substellar object NGC 4349 127b require revision, in part because the new cluster parameters imply that the host is 20% less-massive (ℳ∗/ℳ⊙ ~ 3.1); ii) R Cru is not a member of NGC 4349 and should be excluded from period-Wesenheit calibrations that anchor the distance scale; iii) and results for Pismis 19 underscore the advantages gleaned from employing deep VVV JHKs data to examine obscured (AV ~ 4) and differentially reddened intermediate-age clusters. Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002.

  6. The distance to the young open cluster Westerlund 2

    NASA Astrophysics Data System (ADS)

    Carraro, G.; Turner, D.; Majaess, D.; Baume, G.

    2013-07-01

    A new X-ray, UBVRIc, and JHKs study of the young cluster Westerlund 2 was undertaken to resolve discrepancies tied to the cluster's distance. Existing spectroscopic observations for bright cluster members and new multi-band photometry imply a reddening relation toward Westerlund 2 described by EU - B/EB - V = 0.63 + 0.02EB - V. Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based upon spectroscopic distance moduli and ZAMS fitting yield values of RV = AV/EB - V = 3.88 ± 0.18 and 3.77 ± 0.19, respectively, and confirm prior assertions that anomalous interstellar extinction is widespread throughout Carina. The results were confirmed by applying the color-difference method to UBVRIcJHKs data for 19 spectroscopically observed cluster members, yielding RV = 3.85 ± 0.07. The derived distance to Westerlund 2 of d = 2.85 ± 0.43 kpc places the cluster on the far side of the Carina spiral arm. The cluster's age is no more than τ ~ 2 × 106 yr as inferred from the cluster's brightest stars and an X-ray (Chandra) cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet stars in the cluster core and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are very likely cluster members, and their inferred luminosities are consistent with those of other late-WN stars in open clusters. The color-magnitude diagram for Westerlund 2 also displays a gap at spectral type B0.5 V with associated color spread at higher and lower absolute magnitudes that might be linked to close binary mergers. These features, in conjunction with the evidence for mass loss from the WR stars, may help to explain the high flux of γ-rays, cosmic rays, and X-rays from the direction toward Westerlund 2. Based on observations carried out at Las Campanas Observatory.Full photometric data are available at the CDS via anomymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A50

  7. 3D cluster members and near-infrared distance of open cluster NGC 6819

    NASA Astrophysics Data System (ADS)

    Gao, Xin-Hua; Xu, Shou-Kun; Chen, Li

    2015-12-01

    In order to obtain clean members of the open cluster NGC 6819, the proper motions and radial velocities of 1691 stars are used to construct a three-dimensional (3D) velocity space. Based on the DBSCAN clustering algorithm, 537 3D cluster members are obtained. From the 537 3D cluster members, the average radial velocity and absolute proper motion of the cluster are Vr = +2.30 ± 0.04 km s-1 and (PMRA, PMDec) = (-2.5 ± 0.5, -4.3 ± 0.5) mas yr-1, respectively. The proper motions, radial velocities, spatial positions and color-magnitude diagram of the 537 3D members indicate that our membership determination is effective. Among the 537 3D cluster members, 15 red clump giants can be easily identified by eye and are used as reliable standard candles for the distance estimate of the cluster. The distance modulus of the cluster is determined to be (m - M)0 = 11.86 ± 0.05 mag (2355 ± 54 pc), which is quite consistent with published values. The uncertainty of our distance modulus is dominated by the intrinsic dispersion in the luminosities of red clump giants (˜ 0.04 mag).

  8. Distance estimates to five open clusters based on 2mass data of red clump giants

    NASA Astrophysics Data System (ADS)

    Chen, Li; Gao, Xinhua

    2013-02-01

    Red clump (RC) giants are excellent standard candles in the Milky Way and the Large Magellanic Cloud. The near-infrared K-band intrinsic luminosity of RC giants exhibits only a small variance and a weak dependence on chemical composition and age. In addition, RCs are often easily recognizable in the color-magnitude diagrams of open clusters, which renders them extremely useful distance indicators for some intermediate-age or old open clusters. Here we determine the distance moduli of five Galactic open clusters covering a range of metallicities and ages, based on RC giants in the cluster regions using 2mass photometric data. We compare our result with those from main-sequence fitting and also briefly discuss the advantages and disadvantages of RC-based cluster distance determination.

  9. Distance moduli of open cluster NGC 6819 from Red Giant Clump stars

    NASA Astrophysics Data System (ADS)

    Abedigamba, O. P.; Balona, L. A.; Medupe, R.

    2016-07-01

    In this paper we study Kepler open cluster NGC 6819 using Kepler data of Red Giant Clump (RGC) single member (SM) stars. The Kepler data spans a period of 4 years starting in 2009. In particular, we derive distance moduli for each individual RGC star, from which we get the mean distance modulus of μ0 = 11.520 ± 0.105 mag for the cluster when we use reddening from the Kepler Input Catalogue (KIC) for each RGC star. A value of μ0 = 11.747 ± 0.086 mag is obtained when uniform reddening value E(B - V) = 0.15 is used for the cluster. The values of μ0 obtained with RGC stars are in agreement with the values in the literature with other methods. We report for the case of Kepler open cluster NGC 6819 that RGC stars can be used as 'distance candles' as has been done in the literature with other open clusters.

  10. Galactic Structure from Open Clusters: Photometric Characterization of Reddening, Distance and Abundance

    NASA Astrophysics Data System (ADS)

    Anthony-Twarog, Barbara; Twarog, Bruce A.; Schuster, William

    1999-02-01

    Our recent work with open clusters has indicated a surprising demarcation of the Milky Way disk's metallicity as a function of distance from the Galactic center - an apparently abrupt drop in [Fe/H] from solar to -0.3 at R_GC=10 kpc (Twarog, Ashman & Anthony- Twarog 1997). We have asserted that due to uncertain reddenings, distances and abundance data, the step-down in [Fe/H] at 10 kpc has long been masked in previous studies or interpreted as a declining radial gradient in the disk's metallicity. Current work, including observations proposed here, will address these issues for disk clusters by using uvbyCaH(beta) photometry to determine foreground reddenings, abundances and cluster distances.

  11. Open and Globular Cluster Distances for Extragalactic, Galactic, and Stellar Astrophysics

    NASA Technical Reports Server (NTRS)

    Worthey, Guy S.

    2004-01-01

    One of the hallmarks of SIM's few-milliarcsecond astrometric precision is its ability to obtain accurate parallax measurements across more than half of the Galaxy. The "open and globular" project obtains parallax distances to a set of star clusters. One important, goal is to pinpoint the zeropoint of the distance scale for main-sequence fitting. Another goal is to improve stellar evolutionary isochrones and integrated light models. Another goal is to use the clusters themselves to address unsolved problems of late-stage stellar evolution and Galactic and extragalactic chemical evolution. The clusters to be observed are chosen to span the widest possible range of abundance and age, to be as rich as possible, and to be as well-studied as possible.

  12. WIYN Open Cluster Study. VII. NGC 2451A and the Hipparcos Distance Scale

    NASA Astrophysics Data System (ADS)

    Platais, Imants; Kozhurina-Platais, Vera; Barnes, Sydney; Girard, Terrence M.; Demarque, Pierre; van Altena, William F.; Deliyannis, Constantine P.; Horch, Elliott

    2001-09-01

    We provide new evidence that NGC 2451A is undoubtedly a young open cluster, although sparsely populated. New cluster membership has been derived from relative proper motions of 5868 stars. In total, 136 stars down to V~15 have membership probability Pμ>=2%. New CCD BV photometry indicates that about 70 stars are indeed main-sequence stars of NGC 2451A. This is also supported by our measurements of radial velocities. A total of 34 very likely cluster members yield a mean heliocentric radial velocity for NGC 2451A equal to +22.9 km s-1. The high quality of our BV photometry, a confirmation of cluster membership from proper motions and radial velocities, and a recently obtained metallicity estimate for several cluster stars allow us to perform a precise isochrone fit. The Yale isochrones, updated by the latest available input physics, have been fitted to the cluster's color-magnitude diagram, yielding a distance modulus V0-MV in the range 6.35 to 6.38, which is in excellent agreement with the distance modulus (m-M)0=6.38 derived from the Hipparcos data recently by van Leeuwen and Robichon et al. For NGC 2451A the isochrone fit yields an age of 60+/-20 Myr; hence, the cluster appears to be somewhat younger than the Pleiades. We also present alternative evidence suggesting that the cluster could be slightly older than the Pleiades. The most important result of this study is an excellent match between the main-sequence fitting and Hipparcos distances to NGC 2451A. If we consider noticeable similarities between NGC 2451A and Pleiades, then the Hipparcos distance anomaly for Pleiades may not require an explanation of astrophysical nature.

  13. The Reddening Law and Distance of the Highly Reddened Massive Young Open Cluster Westerlund 2

    NASA Astrophysics Data System (ADS)

    Hur, H.; Sung, H.; Lim, B.

    2014-08-01

    Westerlund 2 is one of the most reddened massive young open clusters observable in optical bands. There is large disagreement among previous distance determinations. The main cause of the disagreement seems to be due to the abnormal reddening law. We report the reddening law and distance of Westerlund 2 using the deep UBVIC photometry data obtained with the CTIO 4m Blanco telescope and MOSAIC II CCD camera. We estimated the reddening E(B-V) using the relation E(U-B)/E(B-V)=0.72+0.025E(B-V). The foreground reddening law is found to be fairly normal, E(V-I)/E(B-V)=1.31 (i.e. RV≡ AV/E(B-V)=3.2) for E(B-V)≤ 1.05. An abnormal reddening law of RV=4.3 is determined for E(B-V)>1.05 stars using the combined optical and published near-IR data. We also report the color excess ratio E(V-I)/E(B-V) for highly reddened OB stars may not follow the relation RV=2.45E(V-I)/E(B-V) by Guetter & Vrba. Finally, we determined the distance modulus of Westerlund 2 to be V0-MV=13.9±0.2 mag (d=6.0±0.6 kpc).

  14. Reddening, distance, and stellar content of the young open cluster Westerlund 2

    NASA Astrophysics Data System (ADS)

    Hur, Hyeonoh; Park, Byeong-Gon; Sung, Hwankyung; Bessell, Michael S.; Lim, Beomdu; Chun, Moo-Young; Sohn, Sangmo Tony

    2015-02-01

    We present deep UBVIC photometric data of the young open cluster Westerlund 2. An abnormal reddening law of RV, cl = 4.14 ± 0.08 was found for the highly reddened early-type members (E(B-V)≥q 1.45), whereas a fairly normal reddening law of RV, fg = 3.33 ± 0.03 was confirmed for the foreground early-type stars (E(B - V)fg < 1.05). The distance modulus was determined from zero-age main-sequence fitting to the reddening-corrected colour-magnitude diagram of the early-type members to be V0 - MV = 13.9 ± 0.14 (random error) _{-0.1}^{+0.4} (the upper limit of systematic error) mag (d = 6.0 ± 0.4 _{-0.3}^{+1.2} kpc). To obtain the initial mass function, pre-main-sequence (PMS) stars were selected by identifying the optical counterparts of Chandra X-ray sources and mid-infrared emission stars from the Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) source catalogue. The initial mass function shows a shallow slope of Γ = -1.1 ± 0.1 down to log m = 0.7. The total mass of Westerlund 2 is estimated to be at least 7 400 M⊙. The age of Westerlund 2 from the main-sequence turn-on and PMS stars is estimated to be ≲ 1.5 Myr. We confirmed the existence of a clump of PMS stars located ˜1 arcmin north of the core of Westerlund 2, but we could not find any clear evidence for an age difference between the core and the northern clump.

  15. The Problem of Hipparcos Distances to Open Clusters. Report 1; Constraints from Multicolor a Main-Sequence Fitting

    NASA Technical Reports Server (NTRS)

    Pinsonneault, Marc H.; Stauffer, John; Soderblom, David R.; King, Jeremy R.; Hanson, Robert B.

    1998-01-01

    Parallax data from the Hipparcos mission allow the direct distance to open clusters to be compared with the distance inferred from main-sequence (MS) fitting. There are surprising differences between the two distance measurements. indicating either the need for changes in the cluster compositions or reddening, underlying problems with the technique of MS fitting, or systematic errors in the Hipparcos parallaxes at the 1 mas level. We examine the different possibilities, focusing on MS fitting in both metallicity-sensitive B-V and metallicity-insensitive V-I for five well-studied systems (the Hyades, Pleiades, alpha Per, Praesepe, and Coma Ber). The Hipparcos distances to the Hyades and alpha Per are within 1 sigma of the MS-fitting distance in B-V and V-I, while the Hipparcos distances to Coma Ber and the Pleiades are in disagreement with the MS-fitting distance at more than the 3 sigma level. There are two Hipparcos measurements of the distance to Praesepe; one is in good agreement with the MS-fitting distance and the other disagrees at the 2 sigma level. The distance estimates from the different colors are in conflict with one another for Coma but in agreement for the Pleiades. Changes in the relative cluster metal abundances, age related effects, helium, and reddening are shown to be unlikely to explain the puzzling behavior of the Pleiades. We present evidence for spatially dependent systematic errors at the 1 mas level in the parallaxes of Pleiades stars. The implications of this result are discussed.

  16. The Problem of Hipparcos Distances to Open Clusters. II. Constraints from Nearby Field Theory. Report 2; ClustersConstraints from nearly Field Stars

    NASA Technical Reports Server (NTRS)

    Soderblom, David R.; King, Jeremy R.; Hanson, Robert B.; Jones, Burton F.; Fischer, Debra; Stauffer, John R.; Pinsonneault, Marc H.

    1998-01-01

    This paper examines the discrepancy between distances to nearby open clusters as determined by parallaxes from Hipparcos compared to traditional main-sequence fitting. The biggest difference is seen for the Pleiades, and our hypothesis is that if the Hipparcos distance to the Pleiades is correct, then similar subluminous zero-age main-sequence (ZAMS) stars should exist elsewhere, including in the immediate solar neighborhood. We examine a color-magnitude diagram of very young and nearby solar-type stars and show that none of them lie below the traditional ZAMS, despite the fact that the Hipparcos Pleiades parallax would place its members 0.3 mag below that ZAMS. We also present analyses and observations of solar-type stars that do lie below the ZAMS, and we show that they are subluminous because of low metallicity and that they have the kinematics of old stars.

  17. Ghostly Open Clusters (Invited)

    NASA Astrophysics Data System (ADS)

    de La Fuente Marcos, R.

    We review theory and observations of the final stages of the evolution of open clusters. The distinguishing features of these ghostly objects depend upon the original membership of the cluster, the fraction of primordial binaries, and the initial mass function. Remnants of rich open clusters are difficult to detect and might exist in large numbers. We then examine the limited observational data available in this field, and discuss how to use the results of numerical integrations to plan future surveys and evaluate the quality of the available observational information. Current observational results render it very hard to distinguish between a poor open cluster, an open cluster remnant, or part of an association.

  18. Flow distances on open flow networks

    NASA Astrophysics Data System (ADS)

    Guo, Liangzhu; Lou, Xiaodan; Shi, Peiteng; Wang, Jun; Huang, Xiaohan; Zhang, Jiang

    2015-11-01

    An open flow network is a weighted directed graph with a source and a sink, depicting flux distributions on networks in the steady state mode of an open flow system. Energetic food webs, economic input-output networks, and international trade networks are open flow network models of energy flows between species, money or value flows between industrial sectors, and goods flows between countries, respectively. An open flow network is different from a closed flow network because it considers the flows from or to the environment (the source and the sink). For instance, in energetic food webs, species obtain energy not only from other species but also from the environment (sunlight), and species also dissipate energy to the environment. Flow distances between any two nodes i and j are defined as the average number of transition steps of a random walker along the network from i to j. The conventional method for the calculation of the random walk distance on closed flow networks cannot be applied to open flow networks. Therefore, we derive novel explicit expressions for flow distances of open flow networks according to their underlying Markov matrix of the network in this paper. We apply flow distances to two types of empirical open flow networks, including energetic food webs and economic input-output networks. In energetic food webs, we visualize the trophic level of each species and compare flow distances with other distance metrics on the graph. In economic input-output networks, we rank sectors according to their average flow distances and cluster sectors into different industrial groups with strong connections. Other potential applications and mathematical properties are also discussed. To summarize, flow distance is a useful and powerful tool to study open flow systems.

  19. The open cluster NGC 6716

    SciTech Connect

    Grice, N.A.; Dawson, D.W. Western Connecticut State Univ., Danbury, CT )

    1990-08-01

    NGC 6716 is a young open star cluster in Sagittarius. Lindoff (1971) obtained photoelectric photometry for 12 stars and photographic UBV photometry for 115 stars in the cluster field down to V = 13.8. This work has been expanded to include more photoelectric standards and IRIS photometry for 332 stars in the cluster field down to V = 16. A reddening E(B-V) = 0.17 mag, a distance modulus of 8.69 + or - 0.15 mag (d = 547 pc), and an age of around 100 million years for the cluster are derived. Of the stars studied, 75 were judged as likely cluster members, 63 as possible members, and 194 as probable nonmembers. 13 refs.

  20. Galaxy Cluster Smashes Distance Record

    NASA Astrophysics Data System (ADS)

    2009-10-01

    he most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes. The cluster is located about 10.2 billion light years away, and is observed as it was when the Universe was only about a quarter of its present age. The galaxy cluster, known as JKCS041, beats the previous record holder by about a billion light years. Galaxy clusters are the largest gravitationally bound objects in the Universe. Finding such a large structure at this very early epoch can reveal important information about how the Universe evolved at this crucial stage. JKCS041 is found at the cusp of when scientists think galaxy clusters can exist in the early Universe based on how long it should take for them to assemble. Therefore, studying its characteristics - such as composition, mass, and temperature - will reveal more about how the Universe took shape. "This object is close to the distance limit expected for a galaxy cluster," said Stefano Andreon of the National Institute for Astrophysics (INAF) in Milan, Italy. "We don't think gravity can work fast enough to make galaxy clusters much earlier." Distant galaxy clusters are often detected first with optical and infrared observations that reveal their component galaxies dominated by old, red stars. JKCS041 was originally detected in 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT, the Canada-France-Hawaii telescope in Hawaii and NASA's Spitzer Space Telescope. Infrared observations are important because the optical light from the galaxies at large distances is shifted into infrared wavelengths because of the expansion of the universe. The Chandra data were the final - but crucial - piece of evidence as they showed that JKCS041 was, indeed, a genuine galaxy cluster. The extended X-ray emission seen by Chandra shows that hot gas has been detected

  1. The Distances to Open Clusters from Main-sequence Fitting. V. Extension of Color Calibration and Test Using Cool and Metal-rich Stars in NGC 6791

    NASA Astrophysics Data System (ADS)

    An, Deokkeun; Terndrup, Donald M.; Pinsonneault, Marc H.; Lee, Jae-Woo

    2015-09-01

    We extend our effort to calibrate stellar isochrones in the Johnson-Cousins ({{BVI}}C) and the 2MASS ({{JHK}}s) filter systems based on observations of well-studied open clusters. Using cool main-sequence (MS) stars in Praesepe, we define empirical corrections to the Lejeune et al. color-effective temperature ({T}{eff}) relations down to {T}{eff}˜ 3600 {{K}}, complementing our previous work based on the Hyades and the Pleiades. We apply empirically corrected isochrones to existing optical and near-infrared photometry of cool ({T}{eff}≲ 5500 {{K}}) and metal-rich ([{Fe}/{{H}}]= +0.37) MS stars in NGC 6791. The current methodology relies on an assumption that color-{T}{eff} corrections are independent of metallicity, but we find that estimates of color excess and distance from color-magnitude diagrams with different color indices converge on each other at the precisely known metallicity of the cluster. Along with a satisfactory agreement with eclipsing binary data in the cluster, we view the improved internal consistency as a validation of our calibrated isochrones at super-solar metallicities. For very cool stars ({T}{eff}≲ 4800 {{K}}), however, we find that B - V colors of our models are systematically redder than the cluster photometry by ˜0.02 mag. We use color-{T}{eff} transformations from the infrared flux method and alternative photometry to examine a potential color-scale error in the input cluster photometry. After excluding B - V photometry of these cool MS stars, we derive E(B\\-\\V)=0.105+/- 0.014, [M/H]\\=\\+0.42+/- 0.07, {(m\\-\\M)}0=13.04+/- 0.08, and the age of 9.5 ± 0.3 Gyr for NGC 6791.

  2. WIYN Open Cluster Study: UBVRI Photometry of NGC 2158

    NASA Astrophysics Data System (ADS)

    Taverne, Luke T.; Steinhauer, Aaron J.; Deliyannis, Constantine P.

    2015-01-01

    We present WIYN 0.9m HDI UBVRI photometry of NGC 2158, a very rich, intermediate-aged, open cluster located near the galactic anti-center. We report derived values for the cluster age, distance, reddening.

  3. Open clusters in Auriga OB2

    NASA Astrophysics Data System (ADS)

    Marco, Amparo; Negueruela, Ignacio

    2016-06-01

    We study the area around the H II region Sh 2-234, including the young open cluster Stock 8, to investigate the extent and definition of the association Aur OB2 and the possible role of triggering in massive cluster formation. We obtained Strömgren and J, H, KS photometry for Stock 8 and Strömgren photometry for two other cluster candidates in the area, which we confirm as young open clusters and name Alicante 11 and Alicante 12. We took spectroscopy of ˜33 early-type stars in the area, including the brightest cluster members. We calculate a common distance of 2.80^{+0.27}_{-0.24} kpc for the three open clusters and surrounding association. We derive an age 4-6 Ma for Stock 8, and do not find a significantly different age for the other clusters or the association. The star LS V +34°23, with spectral type O8 II(f), is likely the main source of ionization of Sh 2-234. We observe an important population of pre-main-sequence stars, some of them with discs, associated with the B-type members lying on the main sequence. We interpret the region as an area of recent star formation with some residual and very localized ongoing star formation. We do not find evidence for sequential star formation on a large scale. The classical definition of Aur OB2 has to be reconsidered, because its two main open clusters, Stock 8 and NGC 1893, are not at the same distance. Stock 8 is probably located in the Perseus arm, but other nearby H II regions whose distances also place them in this arm show quite different distances and radial velocities and, therefore, are not connected.

  4. Catalog of open clusters and associated interstellar matter

    NASA Technical Reports Server (NTRS)

    Leisawitz, David

    1988-01-01

    The Catalog of Open Clusters and Associated Interstellar Matter summarizes observations of 128 open clusters and their associated ionized, atomic, and molecular iinterstellar matter. Cluster sizes, distances, radial velocities, ages, and masses, and the radial velocities and masses of associated interstellar medium components, are given. The database contains information from approximately 400 references published in the scientific literature before 1988.

  5. Dossier: Open and Distance Learning.

    ERIC Educational Resources Information Center

    van Leeuwen, Fred, Ed.

    2002-01-01

    This magazine addresses diverse educational issues in different parts of the world. Articles in this issue are: "Education for All: Governments Must Do Much More to Make Schooling Accessible for All Children" (G. Machel and N. Mandela); "Afghanistan: Education Opens Up New Perspective"; "South Korea: Behind the…

  6. THE YOUNG OPEN CLUSTER BERKELEY 55

    SciTech Connect

    Negueruela, Ignacio; Marco, Amparo E-mail: amparo.marco@ua.es

    2012-02-15

    We present UBV photometry of the highly reddened and poorly studied open cluster Berkeley 55, revealing an important population of B-type stars and several evolved stars of high luminosity. Intermediate-resolution far-red spectra of several candidate members confirm the presence of one F-type supergiant and six late supergiants or bright giants. The brightest blue stars are mid-B giants. Spectroscopic and photometric analyses indicate an age 50 {+-} 10 Myr. The cluster is located at a distance d Almost-Equal-To 4 kpc, consistent with other tracers of the Perseus Arm in this direction. Berkeley 55 is thus a moderately young open cluster with a sizable population of candidate red (super)giant members, which can provide valuable information about the evolution of intermediate-mass stars.

  7. The Distances to Nearby Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Scodeggio, Marco

    1997-12-01

    The properties of the Fundamental Plane (FP) of E and S0 galaxies are analyzed using a sample of early-type galaxies in s nearby clusters of galaxies. I band CCD observations are presented for 631 galaxies in the A262, Cancer, A1367, Coma, Pegasus, and A2634 clusters, and in the NGC 383 and NGC 507 groups. Medium dispersion spectroscopic observations are presented for a sub-set composed of 212 galaxies. Combining this data-set with data taken from the literature, gives a FP sample of 294 galaxies. The clusters are chosen to span as large as possible a range of environmental conditions, from a rich, relaxed, X-ray luminous cluster like Coma, to rather poor groups of galaxies like the NGC 383 group. They are also chosen among the clusters that have the largest available samples of Tully-Fisher (TF) measurements, to allow an accurate comparison of the distance scales obtained using the FP and TF relations independently. Both selection criteria are aimed at quantifying the possible presence of environmental effects on the FP relation. The scatter observed around the FP template implies that the distance to a single galaxy can be obtained, using the FP, with a 22% uncertainty (a 0.48 mag uncertainty on the galaxy distance modulus). The peculiar velocity estimates for the 8 clusters in the sample are all small, consistent with the clusters being at rest in the Cosmic Microwave Background reference frame. Monte Carlo simulations are used to quantify the effects of sample selection and measurement uncertainties on the FP template, and correct the resulting biases. After these corrections are applied, it is found that the properties of the FP do not change significantly as a function of the cluster richness, or as a function of the galaxy position within the cluster. Moreover there is very good agreement between the distance measurements obtained using the FP relation, and those obtained using the TF relation. These results are used to derive an upper limit of 5% on

  8. Be Stars in Open Clusters

    NASA Astrophysics Data System (ADS)

    Tarasov, A. E.

    2017-06-01

    Based on high and medium resolution spectra, we analyze the population of Be stars in young open clusters. We have found a clear dependence of the relative content of early-type (B0-B3) stars on the cluster age. The relative concentration of Be stars of spectral types B0-B3 gradually increases with cluster age, reaching its maximum value 0.46 in clusters with ages of 12-20 Myr. Such a distribution of Be stars in clusters unequivocally points to the evolutionary status of the Be phenomenon. Two possibilities of Be stars' origin is discussed. The first one is for single B stars with rotational velocities increasing from moderate in the beginning of their life on Main Sequence (MS) to near critical in the end of MS. The second one includes evolution of close double systems, that are widely spreaded among early type stars.

  9. The Age and Distance of the Kepler Open Cluster NGC 6811 from an Eclipsing Binary, Turnoff Star Pulsation, and Giant Asteroseismology

    NASA Astrophysics Data System (ADS)

    Sandquist, Eric L.; Jessen-Hansen, J.; Shetrone, Matthew D.; Brogaard, Karsten; Meibom, Søren; Leitner, Marika; Stello, Dennis; Bruntt, Hans; Antoci, Victoria; Orosz, Jerome A.; Grundahl, Frank; Frandsen, Søren

    2016-11-01

    We present the analysis of an eccentric, partially eclipsing long-period (P = 19.23 days) binary system KIC 9777062 that contains main-sequence stars near the turnoff of the intermediate-age open cluster NGC 6811. The primary is a metal-lined Am star with a possible convective blueshift to its radial velocities, and one star (probably the secondary) is likely to be a γ Dor pulsator. The component masses are 1.603 ± 0.006(stat.) ± 0.016(sys.) and 1.419 ± 0.003 ± 0.008 {M}⊙ , and the radii are 1.744 ± 0.004 ± 0.002 and 1.544 ± 0.002 ± 0.002 {R}⊙ . The isochrone ages of the stars are mildly inconsistent: the age from the mass-radius combination for the primary (1.05 ± 0.05 ± 0.09 Gyr, where the last quote was systematic uncertainty from models and metallicity) is smaller than that from the secondary (1.21 ± 0.05 ± 0.15 Gyr) and is consistent with the inference from the color-magnitude diagram (1.00 ± 0.05 Gyr). We have improved the measurements of the asteroseismic parameters Δν and ν max for helium-burning stars in the cluster. The masses of the stars appear to be larger (or alternately, the radii appear to be smaller) than predicted from isochrones using the ages derived from the eclipsing stars. The majority of stars near the cluster turnoff are pulsating stars: we identify a sample of 28 δ Sct, 15 γ Dor, and 5 hybrid types. We used the period-luminosity relation for high-amplitude δ Sct stars to fit the ensemble of the strongest frequencies for the cluster members, finding {(m-M)}V=10.37+/- 0.03. This is larger than most previous determinations, but smaller than values derived from the eclipsing binary (10.47 ± 0.05). Based on observations made with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen, and with the Nordic Optical Telescope, operated by the Nordic

  10. Materials Production in Open and Distance Learning.

    ERIC Educational Resources Information Center

    Lockwood, Fred, Ed.

    This book contains 19 papers grouped in three sections that lead the reader through the process of planning, producing, and presenting materials in open and distance learning, based on experience in Great Britain. Following an overview by Roger Lewis, the Planning section contains the following six papers: "Resources and Constraints in Open…

  11. Studies on the corona of open clusters

    NASA Astrophysics Data System (ADS)

    Balaguer-Núñez, L.; Jordi, C.; Muiños, J. L.; Galadí-Enríquez, D.; Masana, E.

    2013-05-01

    High quality proper motions on an extended area of a selection of Open Clusters (OCs) will let us study their coronas with unprecedented accuracy. We are in the process of obtaining astrometry with the Meridian Circles of San Fernando CMASF at El Leoncito (Argentina) and the CTA at La Palma of an area few times the known radius (from Webda) of a selection of OCs. We will make use of Strömgren wide-field photometry to complement their characterization. We have already analysed the old open cluster M67, deriving properties for 2738 stars fainter and, in a wider area, than any previous precise survey in the cluster region. With new data from the CMASF we have covered an area of about 2°×1.4° and down to 17 magnitude in r^'. Proper motions are then used to determine the membership probabilities of stars in the region, applying parametric and non-parametric approaches to cluster/field segregation. Adding photometric criteria, we obtained a preliminary list of 665 probable member stars, up to a distance 0.96° from the cluster centre. These are preliminary results on our work that will lead us to the most complete study of its structure, dynamics and mass segregation up to date. We have already obtained proper motions for NGC 1817, NGC 2264 and NGC 2509 that are now being processed.

  12. Open Classroom: Distance Learning In and Out of Schools. Open and Distance Learning Series.

    ERIC Educational Resources Information Center

    Bradley, Jo, Ed.

    This collection of essays, which is separated into 4 sections, concerns open and distance learning at school level, or grades K-12. The first section, "The Knowledge Society," includes the following chapters: "Classroom Open Learning: A Case of Old Wine in New Bottles?" (Jenkins); "Living and Learning in the Information…

  13. Opening Education: Policies and Practices from Open and Distance Education. Routledge Studies in Distance Education Series.

    ERIC Educational Resources Information Center

    Evans, Terry, Ed.; Nation, Daryl, Ed.

    The overall theme of this book is the relationships between government and organizational policies and the work of practitioners in open and distance learning. The book explores a selection of international examples, many of which concern the use of new technologies for opening education. The contributors, many of whom are recognized experts,…

  14. Open Classroom: Distance Learning In and Out of Schools. Open and Distance Learning Series.

    ERIC Educational Resources Information Center

    Bradley, Jo, Ed.

    This collection of essays, which is separated into 4 sections, concerns open and distance learning at school level, or grades K-12. The first section, "The Knowledge Society," includes the following chapters: "Classroom Open Learning: A Case of Old Wine in New Bottles?" (Jenkins); "Living and Learning in the Information…

  15. Opening Education: Policies and Practices from Open and Distance Education. Routledge Studies in Distance Education Series.

    ERIC Educational Resources Information Center

    Evans, Terry, Ed.; Nation, Daryl, Ed.

    The overall theme of this book is the relationships between government and organizational policies and the work of practitioners in open and distance learning. The book explores a selection of international examples, many of which concern the use of new technologies for opening education. The contributors, many of whom are recognized experts,…

  16. Polygon cluster pattern recognition based on new visual distance

    NASA Astrophysics Data System (ADS)

    Shuai, Yun; Shuai, Haiyan; Ni, Lin

    2007-06-01

    The pattern recognition of polygon clusters is a most attention-getting problem in spatial data mining. The paper carries through a research on this problem, based on spatial cognition principle and visual recognition Gestalt principle combining with spatial clustering method, and creates two innovations: First, the paper carries through a great improvement to the concept---"visual distance". In the definition of this concept, not only are Euclid's Distance, orientation difference and dimension discrepancy comprehensively thought out, but also is "similarity degree of object shape" crucially considered. In the calculation of "visual distance", the distance calculation model is built using Delaunay Triangulation geometrical structure. Second, the research adopts spatial clustering analysis based on MST Tree. In the design of pruning algorithm, the study initiates data automatism delamination mechanism and introduces Simulated Annealing Optimization Algorithm. This study provides a new research thread for GIS development, namely, GIS is an intersection principle, whose research method should be open and diverse. Any mature technology of other relative principles can be introduced into the study of GIS, but, they need to be improved on technical measures according to the principles of GIS as "spatial cognition science". Only to do this, can GIS develop forward on a higher and stronger plane.

  17. Assessing the Quality of Open and Distance Learning Materials.

    ERIC Educational Resources Information Center

    Clarke, Alan

    This document is intended to help open learning and distance learning practitioners use, design, and select appropriate open and distance learning materials. The document begins with a brief overview of the following forms of open and distance learning materials: workbooks; structured materials; computer-based training materials; online materials;…

  18. Open and Distance Learning: Case Studies from Industry and Education. Open and Distance Learning Series.

    ERIC Educational Resources Information Center

    Brown, Stephen C., Ed.

    This book contains 14 case studies, written by those involved in the teaching and training initiatives, that illustrate the use of open and distance learning strategies. The case studies, drawn from many parts of the world (but mostly British based), feature efforts in large and small companies in a variety of industries. The first part of the…

  19. Supporting Students in Open and Distance Learning. Open and Distance Learning Series.

    ERIC Educational Resources Information Center

    Simpson, Ormond

    This book, which is intended for individuals involved in recruiting and teaching students in open and distance learning (ODL) situations, examines academic and nonacademic student support issues in ODL. The following are among the topics discussed in the book's 14 chapters: (1) models and definitions of ODL systems; (2) rationale for student…

  20. Open and Distance Learning: Case Studies from Industry and Education. Open and Distance Learning Series.

    ERIC Educational Resources Information Center

    Brown, Stephen C., Ed.

    This book contains 14 case studies, written by those involved in the teaching and training initiatives, that illustrate the use of open and distance learning strategies. The case studies, drawn from many parts of the world (but mostly British based), feature efforts in large and small companies in a variety of industries. The first part of the…

  1. Supporting Students in Open and Distance Learning. Open and Distance Learning Series.

    ERIC Educational Resources Information Center

    Simpson, Ormond

    This book, which is intended for individuals involved in recruiting and teaching students in open and distance learning (ODL) situations, examines academic and nonacademic student support issues in ODL. The following are among the topics discussed in the book's 14 chapters: (1) models and definitions of ODL systems; (2) rationale for student…

  2. VARIABLE STARS IN THE OPEN CLUSTER NGC 7142

    SciTech Connect

    Sandquist, Eric L.; Serio, Andrew W.; Shetrone, Matthew E-mail: aserio@gemini.edu

    2011-12-15

    We present new discoveries of variable stars near the turnoff of the old open cluster NGC 7142. Contrary to previous studies, we detect eight contact or near-contact eclipsing binaries (including three near the cluster turnoff), and most of these have good probability of being cluster members. We also identified one long-period variable that resides far to the red of the cluster giant branch, and four new detached eclipsing binaries. We have re-examined the question of distance and reddening for the cluster and find that the distance is larger and the reddening lower than in most previous studies. In turn this implies that NGC 7142 is probably slightly younger than M67, and is about 3 Gyr old. With an age of this size, NGC 7142 would be one of a small group of clusters with main-sequence turnoff stars at the transition between convective and radiative cores.

  3. Value, Cost, and Sharing: Open Issues in Constrained Clustering

    NASA Technical Reports Server (NTRS)

    Wagstaff, Kiri L.

    2006-01-01

    Clustering is an important tool for data mining, since it can identify major patterns or trends without any supervision (labeled data). Over the past five years, semi-supervised (constrained) clustering methods have become very popular. These methods began with incorporating pairwise constraints and have developed into more general methods that can learn appropriate distance metrics. However, several important open questions have arisen about which constraints are most useful, how they can be actively acquired, and when and how they should be propagated to neighboring points. This position paper describes these open questions and suggests future directions for constrained clustering research.

  4. Value, Cost, and Sharing: Open Issues in Constrained Clustering

    NASA Technical Reports Server (NTRS)

    Wagstaff, Kiri L.

    2006-01-01

    Clustering is an important tool for data mining, since it can identify major patterns or trends without any supervision (labeled data). Over the past five years, semi-supervised (constrained) clustering methods have become very popular. These methods began with incorporating pairwise constraints and have developed into more general methods that can learn appropriate distance metrics. However, several important open questions have arisen about which constraints are most useful, how they can be actively acquired, and when and how they should be propagated to neighboring points. This position paper describes these open questions and suggests future directions for constrained clustering research.

  5. On the metallicity of open clusters. III. Homogenised sample

    NASA Astrophysics Data System (ADS)

    Netopil, M.; Paunzen, E.; Heiter, U.; Soubiran, C.

    2016-01-01

    Context. Open clusters are known as excellent tools for various topics in Galactic research. For example, they allow accurately tracing the chemical structure of the Galactic disc. However, the metallicity is known only for a rather low percentage of the open cluster population, and these values are based on a variety of methods and data. Therefore, a large and homogeneous sample is highly desirable. Aims: In the third part of our series we compile a large sample of homogenised open cluster metallicities using a wide variety of different sources. These data and a sample of Cepheids are used to investigate the radial metallicity gradient, age effects, and to test current models. Methods: We used photometric and spectroscopic data to derive cluster metallicities. The different sources were checked and tested for possible offsets and correlations. Results: In total, metallicities for 172 open cluster were derived. We used the spectroscopic data of 100 objects for a study of the radial metallicity distribution and the age-metallicity relation. We found a possible increase of metallicity with age, which, if confirmed, would provide observational evidence for radial migration. Although a statistical significance is given, more studies are certainly needed to exclude selection effects, for example. The comparison of open clusters and Cepheids with recent Galactic models agrees well in general. However, the models do not reproduce the flat gradient of the open clusters in the outer disc. Thus, the effect of radial migration is either underestimated in the models, or an additional mechanism is at work. Conclusions: Apart from the Cepheids, open clusters are the best tracers for metallicity over large Galactocentric distances in the Milky Way. For a sound statistical analysis, a sufficiently large and homogeneous sample of cluster metallicities is needed. Our compilation is currently by far the largest and provides the basis for several basic studies such as the statistical

  6. Open and Distance Learning Today. Routledge Studies in Distance Education Series.

    ERIC Educational Resources Information Center

    Lockwood, Fred, Ed.

    This book contains the following papers on open and distance learning today: "Preface" (Daniel); "Big Bang Theory in Distance Education" (Hawkridge); "Practical Agenda for Theorists of Distance Education" (Perraton); "Trends, Directions and Needs: A View from Developing Countries" (Koul); "American…

  7. Open and Distance Learning Today. Routledge Studies in Distance Education Series.

    ERIC Educational Resources Information Center

    Lockwood, Fred, Ed.

    This book contains the following papers on open and distance learning today: "Preface" (Daniel); "Big Bang Theory in Distance Education" (Hawkridge); "Practical Agenda for Theorists of Distance Education" (Perraton); "Trends, Directions and Needs: A View from Developing Countries" (Koul); "American…

  8. Giant Planets in Open Clusters

    NASA Astrophysics Data System (ADS)

    Quinn, S. N.; White, R. J.; Latham, D. W.

    2015-10-01

    Two decades after the discovery of 51 Peg b, more than 200 hot Jupiters have now been confirmed, but the details of their inward migration remain uncertain. While it is widely accepted that short period giant planets could not have formed in situ, several different mechanisms (e.g., Type II migration, planet-planet scattering, Kozai-Lidov cycles) may contribute to shrinking planetary orbits, and the relative importance of each is not well-constrained. Migration through the gas disk is expected to preserve circular, coplanar orbits and must occur quickly (within ˜ 10 Myr), whereas multi-body processes should initially excite eccentricities and inclinations and may take hundreds of millions of years. Subsequent evolution of the system (e.g., orbital circularization and inclination damping via tidal interaction with the host star) may obscure these differences, so observing hot Jupiters soon after migration occurs can constrain the importance of each mechanism. Fortunately, the well-characterized stars in young and adolescent open clusters (with known ages and compositions) provide natural laboratories for such studies, and recent surveys have begun to take advantage of this opportunity. We present a review of the discoveries in this emerging realm of exoplanet science, discuss the constraints they provide for giant planet formation and migration, and reflect on the future direction of the field.

  9. OPEN CLUSTERS AS PROBES OF THE GALACTIC MAGNETIC FIELD. I. CLUSTER PROPERTIES

    SciTech Connect

    Hoq, Sadia; Clemens, D. P. E-mail: clemens@bu.edu

    2015-10-15

    Stars in open clusters are powerful probes of the intervening Galactic magnetic field via background starlight polarimetry because they provide constraints on the magnetic field distances. We use 2MASS photometric data for a sample of 31 clusters in the outer Galaxy for which near-IR polarimetric data were obtained to determine the cluster distances, ages, and reddenings via fitting theoretical isochrones to cluster color–magnitude diagrams. The fitting approach uses an objective χ{sup 2} minimization technique to derive the cluster properties and their uncertainties. We found the ages, distances, and reddenings for 24 of the clusters, and the distances and reddenings for 6 additional clusters that were either sparse or faint in the near-IR. The derived ranges of log(age), distance, and E(B−V) were 7.25–9.63, ∼670–6160 pc, and 0.02–1.46 mag, respectively. The distance uncertainties ranged from ∼8% to 20%. The derived parameters were compared to previous studies, and most cluster parameters agree within our uncertainties. To test the accuracy of the fitting technique, synthetic clusters with 50, 100, or 200 cluster members and a wide range of ages were fit. These tests recovered the input parameters within their uncertainties for more than 90% of the individual synthetic cluster parameters. These results indicate that the fitting technique likely provides reliable estimates of cluster properties. The distances derived will be used in an upcoming study of the Galactic magnetic field in the outer Galaxy.

  10. Problems and Prospects of Open and Distance Education in Nigeria

    ERIC Educational Resources Information Center

    Yusuf, Mudasiru Olalere

    2006-01-01

    Distance education as a mean of providing access to education, particularly tertiary level education, has gained great prominence in the world. Nigeria has taken giant steps of recent to introduce open and distance education programme. This paper explores the major terms inherent in open and distance education, its potentials, possible factors…

  11. A new distance measure for model-based sequence clustering.

    PubMed

    García-García, Darío; Parrado Hernández, Emilio; Díaz-de María, Fernando

    2009-07-01

    We review the existing alternatives for defining model-based distances for clustering sequences and propose a new one based on the Kullback-Leibler divergence. This distance is shown to be especially useful in combination with spectral clustering. For improved performance in real-world scenarios, a model selection scheme is also proposed.

  12. Map-based trigonometric parallaxes of open clusters: The Praesepe

    NASA Technical Reports Server (NTRS)

    Gatewood, George; De Jonge, Joost Kiewiet

    1994-01-01

    Trigonometric parallaxes for stars in the Praesepe open star cluster are deduced from data collected with the Multichannel Astrometric Photometer (MAP) at the Thaw Refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of five cluster members is +5.21 +/- 0.79 mas (0.00079 arcsec), corresponding to a distance modulus of 6.42 +/- 0.33 mag. We briefly compare this result with that derived earlier for the Hyades and note agreement with the distance found by main-sequence fitting. We also discuss briefly an improvement in the weighting scheme of the centroiding algorithm used in this series.

  13. Distance Teaching of Environmental Engineering Courses at the Open University.

    ERIC Educational Resources Information Center

    Porteous, Andrew; Nesaratnam, Suresh T.; Anderson, Judith

    1997-01-01

    Describes two integrated distance learning environmental engineering degree courses offered by the environmental engineering group of the Open University in Great Britain. Discusses admission requirements for courses, advantages offered by distance learning, professional accreditation, site visits, and tutors. (AIM)

  14. Distance Teaching of Environmental Engineering Courses at the Open University.

    ERIC Educational Resources Information Center

    Porteous, Andrew; Nesaratnam, Suresh T.; Anderson, Judith

    1997-01-01

    Describes two integrated distance learning environmental engineering degree courses offered by the environmental engineering group of the Open University in Great Britain. Discusses admission requirements for courses, advantages offered by distance learning, professional accreditation, site visits, and tutors. (AIM)

  15. Blue straggler stars: lessons from open clusters.

    NASA Astrophysics Data System (ADS)

    Geller, Aaron M.

    Open clusters enable a deep dive into blue straggler characteristics. Recent work shows that the binary properties (frequency, orbital elements and companion masses and evolutionary states) of the blue stragglers are the most important diagnostic for determining their origins. To date the multi-epoch radial-velocity observations necessary for characterizing these blue straggler binaries have only been carried out in open clusters. In this paper, I highlight recent results in the open clusters NGC 188, NGC 2682 (M67) and NGC 6819. The characteristics of many of the blue stragglers in these open clusters point directly to origins through mass transfer from an evolved donor star. Additionally, a handful of blue stragglers show clear signatures of past dynamical encounters. These comprehensive, diverse and detailed observations also reveal important challenges for blue straggler formation models (and particularly the mass-transfer channel), which we must overcome to fully understand the origins of blue straggler stars and other mass-transfer products.

  16. The open cluster NGC 2818 and its associated planetary nebula

    SciTech Connect

    Pedreros, M. )

    1989-12-01

    New CCD UBV photometry of the open cluster NGC 2818 central region indicates that previously derived values of distance and reddening for the cluster have been considerably overestimated, leading to erroneous values for the physical parameters of its associated planetary nebula (PK 261 + 8.1 deg). The analysis of the new data yields E(B-V) = 0.18 + or - 0.03 and V(0)-M(v) = 11.80 + or - 0.2 (2.3 + or - 0.2 kpc) for the cluster's color excess and distance modulus, respectively. If cluster membership is assumed for the planetary nebula, the above estimates result in physical parameters that compare better with those of a typical planetary nebula in the Galaxy and the Magellanic Clouds. 26 refs.

  17. Near-infrared Photometry of the Open Cluster NGC 2420

    NASA Astrophysics Data System (ADS)

    Hejazi, Neda; De Robertis, Michael M.; Dawson, Peter C.

    2016-01-01

    Open clusters have been used in numerous studies of stellar formation and evolution and have provided important constraints on theoretical stellar models. In this study, we carried out deep near-infrared imaging (I, J, H and Ks bands) with the 1024×1024 CFHT-IR camera at the Cassegrain focus of the Canada-France-Hawaii 3.6 m telescope of two fields in the relatively old open cluster, NGC 2420. This cluster was selected due to its relatively low metallicity, [Fe/H] ˜ -0.5, and rather high Galactic latitude (for an open cluster), b ≈ 20°, reducing the effects of reddening as well as reducing the extent of contamination by non-members of the cluster. The empirical data were calibrated using 2MASS and Stetson standards in the field. Non-cluster stars were removed using a field-cluster decontamination algorithm. By fitting available theoretical isochrones to the observed color-magnitude diagrams, we have been able to estimate the age, metallicity and distance of the cluster which are compared to previous studies.

  18. Search for variables in six Galactic open clusters

    NASA Astrophysics Data System (ADS)

    Paunzen, Ernst; Handler, Gerald; Lendl, Monika; Baumann, Bernhard; Rab, Christian; Meingast, Stefan; Rode-Paunzen, Monika; Netopil, Martin; Antoci, Victoria; Zhu, Liying; Zejda, Miloslav; Božić, Hrvoje

    2017-04-01

    Variables in open cluster (known distance, age, and metallicity) fields play an important role in stellar astrophysics because they allow to investigate the interior of stars. Therefore, six Galactic open clusters were selected to search for new variables and to complement data for already known variables. As five of these clusters are younger than 40 Myr, we aim at finding variable high-mass stars such as β Cephei and Slowly Pulsating B-type stars as well as classical pulsating stars within the instability strip. About 26 000 images (312 h) photometric images were taken at the 0.8 m (Vienna, Austria) and 1.0 m (Hvar, Croatia) telescope using V and I filters. The differential light curves were analyzed with standard time series analysis methods. In total, 11 variables were found in all investigated clusters. For nine of them, we were able to determine their nature and period. In addition, the membership probabilities from the literature were analyzed.

  19. Morphology of open clusters NGC 1857 and Czernik 20 using clustering algorithms

    NASA Astrophysics Data System (ADS)

    Bhattacharya, S.; Mahulkar, V.; Pandaokar, S.; Singh, P. K.

    2017-01-01

    The morphology and cluster membership of the Galactic open clusters-Czernik 20 and NGC 1857 were analyzed using two different clustering algorithms. We present the maiden use of density-based spatial clustering of applications with noise (DBSCAN) to determine open cluster morphology from spatial distribution. The region of analysis has also been spatially classified using a statistical membership determination algorithm. We utilized near infrared (NIR) data for a suitably large region around the clusters from the United Kingdom Infrared Deep Sky Survey Galactic Plane Survey star catalogue database, and also from the Two Micron All Sky Survey star catalogue database. The densest regions of the cluster morphologies (1 for Czernik 20 and 2 for NGC 1857) thus identified were analyzed with a K-band extinction map and color-magnitude diagrams (CMDs). To address significant discrepancy in known distance and reddening parameters, we carried out field decontamination of these CMDs and subsequent isochrone fitting of the cleaned CMDs to obtain reliable distance and reddening parameters for the clusters (Czernik 20: D = 2900 pc; E(J- K) = 0 . 33; NGC 1857: D = 2400 pc; E(J- K) =0.18-0.19). The isochrones were also used to convert the luminosity functions for the densest regions of Czernik 20 and NGC 1857 into mass function, to derive their slopes. Additionally, a previously unknown over-density consistent with that of a star cluster is identified in the region of analysis.

  20. Map-based trigonometric parallaxes of open clusters: Coma

    NASA Technical Reports Server (NTRS)

    Gatewood, George

    1995-01-01

    This is the fourth study in a series to determine the direct trigonometric parallaxes of four of the nearest open star clusters, the Hyades, the Pleiades, the Praesepe, and the nearby cluster in Coma (Gatewood et al. 1990; Gatewood et al. 1992); Gatewood & Kiewiet de Jonge 1994). The results for the open star cluster in Coma are compared with those of the other three clusters, and the members are found to be significantly subluminous. The trigonometric parallax of the cluster is estimated from that of three members studied with the Multichannel Astrometric Photometer (MAP) at the Thaw Refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of the cluster is +13.53 +/- 0.54 mass (0.00054 min), corresponding to a distance modulus of 4.34 +/- 0.09 mag. The U-B excess of the Coma cluster members may be used to adjust the observed absolute magnitudes and the B-V measurements as suggested by Sandage & Eggen (1959). The agreement obtained in this manner suggests that, like subdwarf stars, the stars of the Coma cluster appear subluminous because of line blanketing. One of the three members observed in this study was recognized as a member by its parallax and is the faintest known member of the cluster.

  1. Map-based trigonometric parallaxes of open clusters: Coma

    NASA Technical Reports Server (NTRS)

    Gatewood, George

    1995-01-01

    This is the fourth study in a series to determine the direct trigonometric parallaxes of four of the nearest open star clusters, the Hyades, the Pleiades, the Praesepe, and the nearby cluster in Coma (Gatewood et al. 1990; Gatewood et al. 1992); Gatewood & Kiewiet de Jonge 1994). The results for the open star cluster in Coma are compared with those of the other three clusters, and the members are found to be significantly subluminous. The trigonometric parallax of the cluster is estimated from that of three members studied with the Multichannel Astrometric Photometer (MAP) at the Thaw Refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of the cluster is +13.53 +/- 0.54 mass (0.00054 min), corresponding to a distance modulus of 4.34 +/- 0.09 mag. The U-B excess of the Coma cluster members may be used to adjust the observed absolute magnitudes and the B-V measurements as suggested by Sandage & Eggen (1959). The agreement obtained in this manner suggests that, like subdwarf stars, the stars of the Coma cluster appear subluminous because of line blanketing. One of the three members observed in this study was recognized as a member by its parallax and is the faintest known member of the cluster.

  2. A Framework for Developing Competencies in Open and Distance Learning

    ERIC Educational Resources Information Center

    Arinto, Patricia B.

    2013-01-01

    Many open universities and distance education institutions have shifted from a predominantly print-based mode of delivery to an online mode characterised by the use of virtual learning environments and various web technologies. This paper describes the impact of the shift to open and distance e-learning (ODeL), as this trend might be called, on…

  3. Quality Assurance, Open and Distance Learning, and Australian Universities

    ERIC Educational Resources Information Center

    Reid, Ian C.

    2005-01-01

    Open and distance education has integrated quality assurance processes since its inception. Recently, the increased use of distance teaching systems, technologies, and pedagogies by universities without a distance education heritage has enabled them to provide flexible learning opportunities. They have done this in addition to, or instead of,…

  4. Semi-automatic photo clustering with distance metric learning

    NASA Astrophysics Data System (ADS)

    Ji, Dinghuang; Wang, Meng; Tian, Qi; Hua, Xian-Sheng

    2010-07-01

    Photo clustering has been widely explored in many applications such as album management. But automatic clustering can hardly achieve satisfying performance due to the large variety of photos' content. This paper proposes a semi-automatic photo clustering scheme that attempts to improve clustering performance with users' interactions. Users can adjust the results of automatic clustering, and a set of constraints among photos are generated accordingly. A distance metric is then learned with these constraints and we can re-implement clustering with this metric. We conduct experiments on different photo albums, and experimental results have demonstrated that our approach is able to improve automatic photo clustering results, and it is better than pure manual adjustment approach by exploring distance metric learning.

  5. Properties of Open Clusters Containing Blue Stragglers

    NASA Astrophysics Data System (ADS)

    Lee, Hyun-Uk; Chang, Heon-Young

    2017-06-01

    The presence of blue stragglers pose challenges to standard stellar evolution theory, in the sense that explaining their presence demands a complex interplay between stellar evolution and cluster dynamics. In the meantime, mass transfer in binary systems and stellar collisions are widely studied as a blue straggler formation channel. We explore properties of the Galactic open clusters where blue stragglers are found, in attempting to estimate the relative importance of these two favored processes, by comparing them with those resulting from open clusters in which blue stragglers are absent as of now. Unlike previous studies which require a sophisticated process in understanding the implication of the results, this approach is straightforward and has resulted in a supplementary supporting evidence for the current view on the blue straggler formation mechanism. Our main findings are as follows: (1) Open clusters in which blue stragglers are present have a broader distribution with respect to the Z-axis pointing towards the North Galactic Pole than those in which blue stragglers are absent. The probability that two distributions with respect to the Z-axis are drawn from the same distribution is 0.2%. (2) Average values of log_{10}(t) of the clusters with blue stragglers and those without blue stragglers are 8.58 ± 0.232 and 7.52 ± 0.285, respectively. (3) The clusters with blue stragglers tend to be relatively redder than the others, and are distributed broader in colors. (4) The clusters with blue stragglers are likely brighter than those without blue stragglers. (5) Finally, blue stragglers seem to form in condensed clusters rather than simply dense clusters. Hence, we conclude that mass transfer in binaries seems to be a relatively important physical mechanism of the generation of blue stragglers in open clusters, provided they are sufficiently old.

  6. Study of Intermediate Age (~10-30 Myr) Open Clusters

    NASA Astrophysics Data System (ADS)

    Olguin, Lorenzo; Michel, Raul; Contreras, Maria; Hernandez, Jesus; Schuster, William; Chavarria-Kleinhenn, Carlos

    2013-07-01

    We present the study of a sample of intermediate age open clusters (age ~ 10-30 Myr) using optical (UBVRI) and infrared photometric data. Optical photometry was obtained as part of the San Pedro Martir Open Clusters Project (SPM-OCP, Schuster et al. 2007; Michel et al. 2013). Infrared photometry was retrieved from 2MASS public data archive and WISE database. Open clusters included in the SPM-OCP were selected from catalogues presented by Dias et al. (2002) and Froebrich, Scholz & Raftery (2007). One of the main goals of the SPM-OCP is to compile a self-consistent and homogeneous set of cluster fundamental parameters such as reddening, distance, age, and metallicity whenever possible. In this work, we have analyzed a set of 25 clusters from the SPM-OCP with estimated ages between 10 and 30 Myr. Derived fundamental parameters for each cluster in the sample as well as an example of typical color-color and color-magnitude diagrams are presented. Kinematic membership was established by using proper motion data taken from the literature. Based on infrared photometry, we have searched for candidate stars to posses a circumstellar disk within each clusters. For those selected candidates a follow-up spectroscpic study is being carried out. This work was partially supported by UNAM-PAPIIT grant IN-109311.

  7. Adaptive density trajectory cluster based on time and space distance

    NASA Astrophysics Data System (ADS)

    Liu, Fagui; Zhang, Zhijie

    2017-10-01

    There are some hotspot problems remaining in trajectory cluster for discovering mobile behavior regularity, such as the computation of distance between sub trajectories, the setting of parameter values in cluster algorithm and the uncertainty/boundary problem of data set. As a result, based on the time and space, this paper tries to define the calculation method of distance between sub trajectories. The significance of distance calculation for sub trajectories is to clearly reveal the differences in moving trajectories and to promote the accuracy of cluster algorithm. Besides, a novel adaptive density trajectory cluster algorithm is proposed, in which cluster radius is computed through using the density of data distribution. In addition, cluster centers and number are selected by a certain strategy automatically, and uncertainty/boundary problem of data set is solved by designed weighted rough c-means. Experimental results demonstrate that the proposed algorithm can perform the fuzzy trajectory cluster effectively on the basis of the time and space distance, and obtain the optimal cluster centers and rich cluster results information adaptably for excavating the features of mobile behavior in mobile and sociology network.

  8. White Dwarf Distance and Precision Age for Globular Clusters

    NASA Astrophysics Data System (ADS)

    Bragaglia, Angela

    1996-07-01

    This proposal is the natural complement of our Cycle 4 and 5 programs aimed at using the White Dwarf cooling sequence for the calibration of the globular cluster distance scale, the determination of accurate distances being a critical prerequisite for the estimate of reliable cluster ages. In Cycle 4 we obtained data on NGC6752, while in Cycle 5 we got images of 47Tuc. These two clusters will test whether there really exists a measurable age difference between the metal poor and the metal rich clusters, as has been inferred from some horizontal branch luminosity- metallicity calibration. While reducing our Cycle 4 data we have realized that a few short exposures would greatly help to accurately subtract the wings of the heavily saturated images in the field of view, hence to improve the accuracy of the faint star fotometry in the crowded field of the cluster. We therefore apply for one orbit for each of the two clusters in order to get shallow images of our Cycle 4 and 5 fields. The observed cooling sequences for the clusters {for DA and non-DA WDs} will then be fit to the corresponding FCSs to determine the cluster distance moduli. Moreover, directly fitting to each other the WD cooling sequences of the two clusters will provide very accurate relative distances {hence ages}.

  9. A Photometric Study of Five Open Clusters in the SDSS

    NASA Astrophysics Data System (ADS)

    Ryu, Jinhyuk; Lee, Myung Gyoon

    2011-10-01

    We present a photometric study of five open clusters (Czernik 5, Alessi 53, Berkeley 49, Berkeley 84, and Pfleiderer 3) in the Sloan Digital Sky Survey. The position and size of these clusters are determined using the radial number density profiles of the stars, and the member stars of the clusters are selected using the proper motion data in the literature. We estimate the reddening, distance and age of the clusters based on the isochrone fitting in the color-magnitude diagram. The foreground reddenings for these clusters are estimated to be E(B-V)=0.71-1.55 mag. The distances to these clusters are derived to be 2.0-4.4 kpc, and their distances from the Galactic center range from 7.57 kpc to 12.35 kpc. Their ages are in the range from 250 Myr to 1 Gyr. Berkeley 49 and Berkeley 84 are located in the Orion spur, Czernik 5 is in the Perseus arm, and Pfleiderer 3 and Alessi 53 are located beyond the Perseus arm.

  10. Planet host stars in open clusters

    NASA Astrophysics Data System (ADS)

    Yang, XiaoLing; Chen, YuQin; Zhao, Gang

    2015-03-01

    We have compiled a list of all planet host star candidates reported in the literature, which are likely to be cluster members, and we checked their memberships by the spatial location, radial velocity, proper motion and photometric criteria. We found that only six stars, BD-13 2130, HD 28305, Kepler-66, Kepler-67, Pr0201 and Pr0211, are planet orbiting stars in open clusters to date. Two stars, HD 70573 and HD 89744, belong to moving groups and one star, TYC 8975-2606-1, may not be a planet host star, while three stars, HD 16175, HD 46375 and HD 108874 are not members of open clusters. We note that all these six planetary systems in the stellar cluster environment are younger than ˜1 Gyr, which might indicate that the planetary system in open cluster can not survive for a long time, and we speculate that close stellar encounters between member stars in open cluster can potentially destroy, or at least strongly affect, the presence of planetary systems.

  11. Be Stars in Open Stellar Clusters

    NASA Astrophysics Data System (ADS)

    Tarasov, A. E.

    2017-06-01

    The current status of the problem of anomalous increases in the relative number of Be stars in young open stellar clusters is summarized in this article. The relative content of Be stars is shown to increase with the age of the clusters and reaches a maximum for stars in spectral classes B0-B3 when the age of the clusters is 12-20 Myr. In some clusters that are rich in B stars, the relative content exceeds 40%. It is shown that in young clusters with ages less than 9 Myr, Be stars are very rare or not observed at all. Models of the evolution of rotating massive stars indicates that the Be phenomenon may occur toward the end of the lifetime of B stars in the main sequence because of an increase in the ratio of the rotation velocity of a star to the critical velocity, but this cannot explain the presence of more than 40% Be stars in some young open stellar clusters. In this review, considerable attention is devoted to massive binary systems in different stages of the evolution of the binary system. The transfer of angular momentum during exchanges of mass in systems with different periods is a noteworthy alternative to the evolution of angular momentum in single stars. Some examples are shown of binary systems of different types which are or may be encountered in open stellar clusters.

  12. Do open clusters have distinguishable chemical signatures?

    NASA Astrophysics Data System (ADS)

    Blanco-Cuaresma, S.; Soubiran, C.; Heiter, U.

    2014-07-01

    Past studies have already shown that stars in open clusters are chemically homogeneous (e.g. De Silva et al. 2006, 2007 and 2009). These results support the idea that stars born from the same giant molecular cloud should have the same chemical composition. In this context, the chemical tagging technique was proposed by Freeman et al. (2002). The principle is to recover disrupted stellar clusters by looking only to the stellar chemical composition. In order to evaluate the feasibility of this approach, it is necessary to test if we can distinguish between stars born from different molecular clouds. For this purpose, we studied the chemical composition of stars in 32 old and intermediate-age open clusters, and we applied machine learning algorithms to recover the original cluster by only considering the chemical signatures.

  13. Emerging Open Online Distance Education Environment

    ERIC Educational Resources Information Center

    Schroeder, Raymond

    2012-01-01

    A revolution of sorts is underway in providing open access to rich resources, actual courses, and even entire degrees online. This revolution is fueled by the combination of a bubble in tuition rates, lingering effects of the recession, monumental student debt exceeding one trillion dollars in the United States, development of increasingly…

  14. CCD UBV photometry of the open cluster NGC 6819

    NASA Astrophysics Data System (ADS)

    Ak, T.; Bostancı, Z. F.; Yontan, T.; Bilir, S.; Güver, T.; Ak, S.; Ürgüp, H.; Paunzen, E.

    2016-04-01

    We present the results of CCD UBV observations of the open cluster NGC 6819. We calculated the stellar density profile in the cluster's field to determine the structural parameters of NGC 6819. Using the existing astrometric data, we calculated the probabilities of the stars being physical members of the cluster, and used these objects in the determination of the astrophysical parameters of NGC 6819. We inferred the reddening and metallicity of the cluster as E(B-V)=0.130±0.035 mag and [Fe/H]=+0.051± 0.020 dex, respectively, using the U-B vs B-V two-colour diagram and UV excesses of the F-G type main-sequence stars. We fit the colour-magnitude diagrams of NGC 6819 with the PARSEC isochrones and derived the distance modula, distance and age of the cluster as μV=12.22± 0.10 mag, d=2309±106 pc and t=2.4±0.2 Gyr, respectively. The parameters of the galactic orbit estimated for NGC 6819 indicate that the cluster is orbiting in a slightly eccentric orbit of e=0.06 with a period of P_{orb}= 142 Myr. The slope of the mass function estimated for the cluster is close to the one found for the stars in the solar neighbourhood.

  15. Spectroscopic and Photometric Study of Open Cluster Trumpler 27

    NASA Astrophysics Data System (ADS)

    Obonyo, W. O.; Baki, P.

    2016-12-01

    Open clusters are essential laboratories for understanding stellar evolution, as they allow constraints to be placed on stellar ages and luminosities. As distance indicators, they are important tracers of star formation in the Milky Way. One such cluster is Trumpler 27. Spectroscopic and photometric data of Trumpler 27 was used to estimate its distance, radial velocity, age, membership and reddening. The Spectroscopic data collected from SAAO's 1.9m telescope and photometric ones from catalogues were used to estimate reddening, identify cluster stars and approximate cluster distance. Classification of spectra was done by comparing them to spectral templates. The result from this work suggests that Trumpler 27 is made up of ∼55 stars which are at different stages of evolution. The stars include main sequence stars, blue supergiants, two cool supergiants and maybe the two WR stars. The cluster's age and distance were found to be 10Myrs old and 2.6 ± 0.2 kpc away from the Sun respectively suggesting that it is located on the outer part of Scutum Centaurus arm of the Galaxy. Its reddening, E(B - V) varies substantially across the field with the average value being 1.3±0.2. It has a radial velocity of -15.3±3km/s, as approximated from some of its cool supergiants. There is a likelihood of a younger population of OB stars located at 3.5 kpc away from the sun, that is right behind Trumpler 27 interpreted as either a cluster or background stars that mimic a cluster.

  16. Sustainable Assessment and Evaluation Strategies for Open and Distance Learning

    ERIC Educational Resources Information Center

    Okonkwo, Charity Akuadi

    2010-01-01

    This paper first presents an overview of the concepts of assessment and evaluation in Open and Distance Learning (ODL) environment. The large numbers of students and numerous courses make assessment and evaluation very difficult and administrative nightmare at Distance Learning (DL) institutions. These challenges informed exploring issues relating…

  17. The Role of ICT in Open and Distance Education

    ERIC Educational Resources Information Center

    Rahman, Habibur

    2014-01-01

    Open and distance learning is getting more dependent on information and communication technology (ICT) and has been playing an important role in the delivery strategies of distance learning. With the advancement in technology in the field education has introduces variety of new techniques for educators and learners to enhance knowledge.…

  18. Open clusters in the Kepler field. II. NGC 6866

    SciTech Connect

    Janes, Kenneth; Hoq, Sadia; Barnes, Sydney A.; Meibom, Søren

    2014-06-01

    We have developed a maximum-likelihood procedure to fit theoretical isochrones to the observed cluster color-magnitude diagrams of NGC 6866, an open cluster in the Kepler spacecraft field of view. The Markov chain Monte Carlo algorithm permits exploration of the entire parameter space of a set of isochrones to find both the best solution and the statistical uncertainties. For clusters in the age range of NGC 6866 with few, if any, red giant members, a purely photometric determination of the cluster properties is not well-constrained. Nevertheless, based on our UBVRI photometry alone, we have derived the distance, reddening, age, and metallicity of the cluster and established estimates for the binary nature and membership probability of individual stars. We derive the following values for the cluster properties: (m – M) {sub V} = 10.98 ± 0.24, E(B – V) = 0.16 ± 0.04 (so the distance = 1250 pc), age =705 ± 170 Myr, and Z = 0.014 ± 0.005.

  19. Dynamics of the coronas of open star clusters

    NASA Astrophysics Data System (ADS)

    Danilov, V. M.; Putkov, S. I.; Seleznev, A. F.

    2014-12-01

    A method for distinguishing coronas in models of open star clusters is proposed. The method uses trajectories of stars that do not leave the coronas over time intervals t comparable to the mean lifetime τ of the clusters. Corona models are constructed for six numerical cluster models, and the direction and character of the dynamical evolution of the coronas are determined. Retrograde stellar motions are dominant in the coronas. In spite of some signs of dynamical instability of the coronas (small densities compared to the critical density and accelerated expansion of the coronas), the formation of close-toequilibrium density and phase-density distributions at distances from one to three cluster tidal radii from the cluster center can be seen. Approximations are constructed for the corona and cluster phase density using distributions that depend on three parameters (the parameters of the stellar motion in the Lindblad rotating coordinate system). This temporary equilibrium of the corona is due to balance in the number of starsmoving from the central areas of the cluster to the corona, and from the corona to the corona periphery or beyond. Evidence that corona stars can be gravitationally bound at distances out to four tidal radii from the cluster center is found: the presence of nearly periodic retrograde mean motions of a large number of corona stars in the Galactic plane; 91-99% of corona stars satisfy the gravitational binding criterion of Ross, Mennim and Heggie over time intervals that are close to the mean cluster lifetime. The escape rate from the corona is estimated for t ≥ τ, and found to be from 0.03 to 0.23 of the number of corona stars per violent relaxation time.

  20. An improved Chebyshev distance metric for clustering medical images

    NASA Astrophysics Data System (ADS)

    Mousa, Aseel; Yusof, Yuhanis

    2015-12-01

    A metric or distance function is a function which defines a distance between elements of a set. In clustering, measuring the similarity between objects has become an important issue. In practice, there are various similarity measures used and this includes the Euclidean, Manhattan and Minkowski. In this paper, an improved Chebyshev similarity measure is introduced to replace existing metrics (such as Euclidean and standard Chebyshev) in clustering analysis. The proposed measure is later realized in analyzing blood cancer images. Results demonstrate that the proposed measure produces the smallest objective function value and converge at the lowest number of iteration. Hence, it can be concluded that the proposed distance metric contribute in producing better clusters.

  1. Photometry of the open cluster NGC 6996 in the North America nebula

    NASA Astrophysics Data System (ADS)

    Zdanavicius, K.; Straizys, V.

    1990-11-01

    Thirty stars in the direction of the open cluster NGC 6996 are measured in the Vilnius photometric system. Photometric spectral types, absolute magnitudes, interstellar reddenings, extinctions, and distances are determined for most of them. Fifteen stars are suspected to be cluster members. Their mean distance is 620 + or - 30 pc and mean extinction A(v) is 1.74 mag. The extinction within the cluster is variable. The age of the cluster is of the order of 100 million yr, and this excludes the possibility that it is evolutionary related with the North America and Pelican Nebulae complex. The distance of this complex 550 pc is confirmed.

  2. The Chemical Homogeneity of Open Clusters

    NASA Astrophysics Data System (ADS)

    Bovy, Jo

    2016-01-01

    Determining the level of chemical homogeneity in open clusters is of fundamental importance in the study of the evolution of star-forming clouds and that of the Galactic disk. Yet limiting the initial abundance spread in clusters has been hampered by difficulties in obtaining consistent spectroscopic abundances for different stellar types. Without reference to any specific model of stellar photospheres, a model for a homogeneous cluster is that it forms a one-dimensional sequence, with any differences between members due to variations in stellar mass and observational uncertainties. I present a novel method for investigating the abundance spread in open clusters that tests this one-dimensional hypothesis at the level of observed stellar spectra, rather than constraining homogeneity using derived abundances as is traditionally done. Using high-resolution APOGEE spectra for 49 giants in M67, NGC 6819, and NGC 2420 I demonstrate that these spectra form one-dimensional sequences for each cluster. With detailed forward modeling of the spectra and Approximate Bayesian Computation, I derive strong limits on the initial abundance spread of 15 elements: <0.01 (0.02) {dex} for C and Fe, ≲0.015 (0.03) {dex} for N, O, Mg, Si, and Ni, ≲0.02 (0.03) {dex} for Al, Ca, and Mn, and ≲0.03 (0.05) {dex} for Na, S, K, Ti, and V (at 68% and 95% confidence, respectively). The strong limits on C and O imply that no pollution by massive core-collapse supernovae occurred during star formation in open clusters, which, thus, need to form within ≲6 {Myr}. Further development of this and related techniques will bring the power of differential abundances to stars other than solar twins in large spectroscopic surveys and will help unravel the history of star formation and chemical enrichment in the Milky Way through chemical tagging.

  3. 2MASS analytical study of four open cluster candidates

    NASA Astrophysics Data System (ADS)

    Bisht, D.; Yadav, R. K. S.; Durgapal, A. K.

    2017-04-01

    The astrophysical parameters of four poorly studied open star clusters namely Teutsch 126, Teutsch 54, Teutsch 61 and Czernik 3, have been estimated using the Two Micron All Sky Survey (2MASS) database. The stellar density distributions and color-magnitude diagrams are used to determine their structural parameters (cluster center, cluster radius, core radius, tidal radius, Galactocenteric coordinates and the distance from the Galactic plane). We have also derived age, color excesses, total mass, relaxation time, luminosity and mass function for each clusters. The mass function slopes for these clusters are derived as 1.59 ± 0.62, 1.31 ± 0.60, 1.22 ± 0.75 and 1.62 ± 0.56 for Teutsch 126, Teutsch 54, Teutsch 61 and Czernik 3 respectively. These values are very close with the Salpeter value (x = 1.35) within the errors. The effect of mass-segregation are observed in the clusters Teutsch 126 and Teutsch 61. Estimated values of dynamical relaxation time are less than age of the clusters under study. This concludes that these objects are dynamically relaxed. The possible reason for relaxation may be due to the dynamical evolution or imprint of star formation or both.

  4. Planning and Developing Open and Distance Learning : A Quality Assurance Approach. Radiological Studies in Distance Education.

    ERIC Educational Resources Information Center

    Melton, Reginald F.

    This book presents a blueprint for using a quality assurance-based approach to planning and developing open and distance learning (ODL) courses in the United Kingdom. The following are among the specific topics discussed: (1) typical aims of ODL (opening access to education; responding to student needs; designing self-study materials; student…

  5. Planning and Developing Open and Distance Learning : A Quality Assurance Approach. Radiological Studies in Distance Education.

    ERIC Educational Resources Information Center

    Melton, Reginald F.

    This book presents a blueprint for using a quality assurance-based approach to planning and developing open and distance learning (ODL) courses in the United Kingdom. The following are among the specific topics discussed: (1) typical aims of ODL (opening access to education; responding to student needs; designing self-study materials; student…

  6. Tidal radius estimates for three open clusters

    NASA Astrophysics Data System (ADS)

    Danilov, V. M.; Loktin, A. V.

    2015-10-01

    A new method is developed for estimating tidal radii and masses of open star clusters (OCL) based on the sky-plane coordinates and proper motions and/or radial velocities of cluster member stars. To this end, we perform the correlation and spectral analysis of oscillations of absolute values of stellar velocity components relative to the cluster mass center along three coordinate planes and along each coordinate axis in five OCL models. Mutual correlation functions for fluctuations of absolute values of velocity field components are computed. The spatial Fourier transform of the mutual correlation functions in the case of zero time offset is used to compute wavenumber spectra of oscillations of absolute values of stellar velocity components. The oscillation spectra of these quantities contain series of local maxima at equidistant wavenumber k values. The ratio of the tidal radius of the cluster to the wavenumber difference Δ k of adjacent local maxima in the oscillation spectra of absolute values of velocity field components is found to be the same for all five OCL models. This ratio is used to estimate the tidal radii and masses of the Pleiades, Praesepe, and M67 based on the proper motions and sky-plane coordinates of the member stars of these clusters. The radial dependences of the absolute values of the tangential and radial projections of cluster star velocities computed using the proper motions relative to the cluster center are determined, along with the corresponding autocorrelation functions and wavenumber spectra of oscillations of absolute values of velocity field components. The Pleiades virial mass is estimated assuming that the cluster is either isolated or non-isolated. Also derived are the estimates of the Pleiades dynamical mass assuming that it is non-stationary and non-isolated. The inferred Pleiades tidal radii corresponding to these masses are reported.

  7. Search for New Open Clusters in Huge Catalogues

    NASA Astrophysics Data System (ADS)

    Zolotukhin, I.; Koposov, S.; Glushkova, E.

    2006-07-01

    Current catalogues (lists indeed) of open clusters are simply heterogeneous and incomplete compilations. No attempts to search for open clusters through huge photometric catalogues using an homogeneous approach have been done so far. We have developed a method based on the analysis of star densities. Our algorithm finds star density peaks and then builds the color-magnitude diagram. We exploit the fact that only stars lying on the isochrone show a density peak whereas field stars show a flat distribution. An automatic procedure eliminates occasional density peaks and obtains the isochrone and the geometrical parameters of the survived candidates (coordinates, size, distance, age and color excess). A preliminary study of 150 sq. degrees in the Galaxy Anticentre region yielded 10 new clusters. The system will allow us to build, for the first time, an homogeneous catalogue of open clusters on an all-sky basis. Although we have started with 2MASS data, it will be possible to apply the automated pipeline on any multicolor catalogue provided that a VO-compliant way of access (e.g. ADQL + SkyNode) is implemented (SDSS, etc.).

  8. Course Evaluation in Open and Distance Learning: A Case Study from Indira Gandhi National Open University

    ERIC Educational Resources Information Center

    Gaba, Ashok K.; Dash, Nirod K.

    2004-01-01

    The success of any open and distance learning course depends on how well it is designed, executed, and evaluated. Evaluation of a course not only demonstrates its strengths, but also points out any inherent shortcomings in the course. This is why course evaluation constitutes an important function in an open and distance learning system. The…

  9. Course Evaluation in Open and Distance Learning: A Case Study from Indira Gandhi National Open University

    ERIC Educational Resources Information Center

    Gaba, Ashok K.; Dash, Nirod K.

    2004-01-01

    The success of any open and distance learning course depends on how well it is designed, executed, and evaluated. Evaluation of a course not only demonstrates its strengths, but also points out any inherent shortcomings in the course. This is why course evaluation constitutes an important function in an open and distance learning system. The…

  10. Prospecting for Chemical Tags among Open Clusters

    NASA Astrophysics Data System (ADS)

    Lambert, David L.; Reddy, Arumalla B. S.

    2016-11-01

    Determination of the chemical composition of red giants in a large sample of open clusters (OCs) shows that the abundances of the heavy elements La, Ce, Nd, and Sm, but not so obviously Y and Eu, vary from one cluster to another across a sample in which all the clusters have nearly solar metallicity. For La, Ce, Nd, and Sm the amplitudes of the variations at solar metallicity scale approximately with the main s-process contribution to solar system material. Consideration of published abundances of field stars suggests that such a spread in heavy-element abundances is present for the thin and thick disk stars of different metallicities. This new result provides an opportunity to chemically tag stars by their heavy elements and to reconstruct dissolved OCs from the field-star population.

  11. Astrometric and Photometric Study of the Open Cluster NGC 2323

    NASA Astrophysics Data System (ADS)

    Amin, M. Y.; Elsanhoury, W. H.

    2017-06-01

    We present a study of the open cluster NGC 2323 using astrometric and photometric data. In our study we used two methods that are able to separate open cluster's stars from those that belong to the stellar background. Our results of calculations by these two methods indicate that: 1) according to the membership probability, NGC 2323 should contain 497 stars, 2) the cluster center should be at 07h 02m 48.02s and -08° 20' 17" 74, 3) the limiting radius of NGC 2323 is 2.31 ± 0.04 pc, the surface number density at this radius is 98.16 stars pc^{-2}, 4) the magnitude function has a maximum at about m_{v} = 14 mag, 5) the total mass of NGC 2323 is estimated dynamically by using astrometric data to be 890 M_{⊙}, and statistically by using photometric data to be 900 M_{⊙}, and 6) the distance and age of the cluster are found to be equal to 900 ± 100 pc, and 140 ± 20 Myr, respectively. Finally the dynamical evolution parameter τ of the cluster is about 436.2.

  12. A Cepheid Distance to NGC 4603 in the Centaurus Cluster

    NASA Technical Reports Server (NTRS)

    Madore, B.; Newman, J.; Zepf, S.; Davis, M.; Freedman, W.; Madore, B.; Stetson, P.; Silbermann, N.; Phelps, R.

    1999-01-01

    In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling 6 orbits) in the F814W filter.

  13. A Cepheid Distance to NGC 4603 in the Centaurus Cluster

    NASA Technical Reports Server (NTRS)

    Madore, B.; Newman, J.; Zepf, S.; Davis, M.; Freedman, W.; Madore, B.; Stetson, P.; Silbermann, N.; Phelps, R.

    1999-01-01

    In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling 6 orbits) in the F814W filter.

  14. NGC 7789: An open cluster case study

    SciTech Connect

    Overbeek, Jamie C.; Friel, Eileen D.; Pilachowski, Catherine A.; Mészáros, Szabolcs; Jacobson, Heather R.; Johnson, Christian I.

    2015-01-01

    We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin–Indiana–Yale–NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed for the Gaia-ESO Survey (GES) compared to one based on Arcturus used in our previous work. [Fe/H] values decrease when using the GES linelist instead of the Arcturus-based linelist; these differences are probably driven by systematically lower (∼−0.1 dex) GES surface gravities. Using the GES linelist we determine abundances for 10 elements—Fe, Mg, Si, Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity [Fe/H] = 0.03 ± 0.07 dex, in good agreement with literature values, and a lower [Mg/Fe] abundance than has been reported before for this cluster (0.11 ± 0.05 dex). We also find the neutron-capture element barium to be highly enhanced—[Ba/Fe] = +0.48 ± 0.08—and disparate from cluster measurements of neutron-capture elements La and Zr (−0.08 ± 0.05 and 0.08 ± 0.08, respectively). This is in accordance with recent discoveries of supersolar Ba enhancement in young clusters along with more modest enhancement of other neutron-capture elements formed in similar environments.

  15. NGC 7789: an Open Cluster Case Study

    NASA Astrophysics Data System (ADS)

    Overbeek, Jamie C.; Friel, Eileen D.; Jacobson, Heather R.; Johnson, Christian I.; Pilachowski, Catherine A.; Mészáros, Szabolcs

    2015-01-01

    We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed for the Gaia-ESO Survey (GES) compared to one based on Arcturus used in our previous work. [Fe/H] values decrease when using the GES linelist instead of the Arcturus-based linelist; these differences are probably driven by systematically lower (˜-0.1 dex) GES surface gravities. Using the GES linelist we determine abundances for 10 elements—Fe, Mg, Si, Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity [Fe/H] = 0.03 ± 0.07 dex, in good agreement with literature values, and a lower [Mg/Fe] abundance than has been reported before for this cluster (0.11 ± 0.05 dex). We also find the neutron-capture element barium to be highly enhanced—[Ba/Fe] = +0.48 ± 0.08—and disparate from cluster measurements of neutron-capture elements La and Zr (-0.08 ± 0.05 and 0.08 ± 0.08, respectively). This is in accordance with recent discoveries of supersolar Ba enhancement in young clusters along with more modest enhancement of other neutron-capture elements formed in similar environments.

  16. Design Support System for Open Distance Learning Student Teamwork

    NASA Astrophysics Data System (ADS)

    Putranto, A.; Pradipto, Y. D.

    2017-01-01

    Open distance learning students in doing team assignment, they seldom face to some problems such as student fell unfair in numbers of workload contribution, instructors also do not know which students do more work than others. So there are some questions ie: how to connect between instructor, team members, and working documents. Methods will be used are first, analyzing current condition and last by designing systems to connect between instructor, team members, and document. The expected result is support systems for open distance learning student teamwork.

  17. The Hyades open cluster is chemically inhomogeneous

    NASA Astrophysics Data System (ADS)

    Liu, F.; Yong, D.; Asplund, M.; Ramírez, I.; Meléndez, J.

    2016-04-01

    We present a high-precision differential abundance analysis of 16 solar-type stars in the Hyades open cluster based on high-resolution, high signal-to-noise ratio (S/N ≈ 350-400) spectra obtained from the McDonald 2.7-m telescope. We derived stellar parameters and differential chemical abundances for 19 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ba) with uncertainties as low as ˜0.01-0.02 dex. Our main results include: (1) there is no clear chemical signature of planet formation detected among the sample stars, i.e. no correlations in abundances versus condensation temperature; (2) the observed abundance dispersions are a factor of ≈1.5-2 larger than the average measurement errors for most elements; (3) there are positive correlations, of high statistical significance, between the abundances of at least 90 per cent of pairs of elements. We demonstrate that none of these findings can be explained by errors due to the stellar parameters. Our results reveal that the Hyades is chemically inhomogeneous at the 0.02 dex level. Possible explanations for the abundance variations include (1) inhomogeneous chemical evolution in the proto-cluster environment, (2) supernova ejection in the proto-cluster cloud and (3) pollution of metal-poor gas before complete mixing of the proto-cluster cloud. Our results provide significant new constraints on the chemical composition of open clusters and a challenge to the current view of Galactic archaeology.

  18. The old, metal-poor, anticentre open cluster Trumpler 5

    NASA Astrophysics Data System (ADS)

    Donati, P.; Cocozza, G.; Bragaglia, A.; Pancino, E.; Cantat-Gaudin, T.; Carrera, R.; Tosi, M.

    2015-01-01

    As part of a long-term programme, we analyse the evolutionary status and properties of the old and populous open cluster Trumpler 5 (Tr 5), located in the Galactic anticentre direction, almost on the Galactic plane. Tr 5 was observed with Wide Field Imager@MPG/ESO Telescope using the Bessel U, B, and V filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram (CMD) method, i.e. the direct comparison of the observational CMD with a library of synthetic CMDs generated with different stellar evolution sets (Padova, FRANEC, and FST). Age, reddening, and distance are derived through the synthetic CMD method using stellar evolutionary models with subsolar metallicity (Z = 0.004 or Z = 0.006). Additional spectroscopic observations with Ultraviolet VLT Echelle Spectrograph@Very Large Telescope of three red clump stars of the cluster were used to determine more robustly the chemical properties of the cluster. Our analysis shows that Tr 5 has subsolar metallicity, with [Fe/H] = -0.403 ± 0.006 dex (derived from spectroscopy), age between 2.9 and 4 Gyr (the lower age is found using stellar models without core overshooting), reddening E(B - V) in the range 0.60-0.66 mag complicated by a differential pattern (of the order of ˜±0.1 mag), and distance modulus (m - M)0 = 12.4 ± 0.1 mag.

  19. Physical properties and membership in the open cluster NGC 6633 through uvby-β photoelectric photometry

    NASA Astrophysics Data System (ADS)

    Peña, J. H.; Robleto-Orús, A.; Piña, D. S.; Rentería, A.; Villarreal, C.; Chow-Martínez, M.; Trejo, O.

    2017-10-01

    uvby-β photoelectric photometry of stars in the direction of the open clusters NGC 6633 is presented. From the uvby-β photometry of the stars in this direction, we classify the spectral types which allow us to determine the reddening and, hence, their distance. Membership of the stars to the cluster and reddening were determined.

  20. Peculiarities of α-element abundances in Galactic open clusters

    NASA Astrophysics Data System (ADS)

    Marsakov, V. A.; Gozha, M. L.; Koval', V. V.; Shpigel', L. V.

    2016-01-01

    A catalog compiling the parameters of 346 open clusters, including their metallicities, positions, ages, and velocities has been composed. The elements of the Galactic orbits for 272 of the clusters have been calculated. Spectroscopic determinations of the relative abundances, [el/Fe], for 14 elements synthesized in various nuclear processes averaged over data from 109 publications are presented for 90 clusters. The compiled data indicate that the relative abundances of primary α elements (oxygen and magnesium) exhibit different dependences on metallicity, age, Galactocentric distance, and the elements of the Galactic orbits in clusters with high, elongated orbits satisfying the criterion ( Z max 2 + 4 e 2)1/2 > 0.40 and in field stars of the Galactic thin disk ( Z max is the maximum distance of the orbit from the Galactic plane in kiloparsec and e is the eccentricity of the Galactic orbit). Since no systematic effects distorting the relative abundances of the studied elements in these clusters have been found, these difference suggest real differences between clusters with high, elongated orbits and field stars. In particular, this supports the earlier conclusion, based on an analysis of the elements of the Galactic orbits, that some clusters formed as a result of interactions between high-velocity,metal-poor clouds and the interstellar mediumof theGalactic thin disk. On average, clusters with high, elongated orbits and metallicities [Fe/H] < -0.1 display lower relative abundances of the primary a elements than do field stars. The low [O, Mg/Fe] ratios of these clusters can be understood if the high-velocity clouds that gave rise to them were formed of interstellar material from regions where the star-formation rate and/or the masses of Type II supernovae were lower than near the Galactic plane. It is also shown that, on average, the relative abundances of the primary a elements are higher in relatively metal-rich clusters with high, elongated orbits than in

  1. Managing Information Technology in Open and Distance Higher Education.

    ERIC Educational Resources Information Center

    Holt, Dale M.; Thompson, Diane J.

    1998-01-01

    This paper uses the Massachusetts Institute of Technology (MIT) Management in the 1990s Research Framework as a basis for examining the challenges of managing information technology in higher education, with particular reference to open and distance education. Budgeting, technology trends, centralization, prototyping, staff, and competition versus…

  2. Online Tutorial Support in Open and Distance Learning: Students' Perceptions

    ERIC Educational Resources Information Center

    Zhang, Wei-yuan; Perris, Kirk; Yeung, Lesley

    2005-01-01

    The Open University of Hong Kong (OUHK) offers 199 courses with online features to enhance the distance learning environment. The university has arranged these courses to provide students with greater flexibility in interacting with tutors, classmates, and the content itself. Integral to learner flexibility online is access, valuing computers and…

  3. Musing on the Memes of Open and Distance Education

    ERIC Educational Resources Information Center

    Latchem, Colin

    2014-01-01

    Just as genes propagate themselves in the gene pool by leaping from body to body, so memes (ideas, behaviours, and actions) transmit cultural ideas or practices from one mind to another through writing, speech, or other imitable phenomena. This paper considers the memes that influence the evolution of open and distance education. If the…

  4. Attitudes toward Online Communications in Open and Distance Learning

    ERIC Educational Resources Information Center

    Erdem Aydin, Irem

    2012-01-01

    This article intended to reveal the results of a survey study in which the students' attitudes toward online communication in open and distance learning were investigated. In the study, affects of the students' gender and computer experience on their attitudes were also examined. A total of 626 subjects participated in the study and "Online…

  5. Globalisation, Post-Fordism and Open and Distance Education.

    ERIC Educational Resources Information Center

    Evans, Terry

    1995-01-01

    Post-Fordism and globalization are interrelated contemporary features of social and economic development. Individual, social, and educational issues concerned with globalization are discussed in relation to the emerging post-Fordism forms and practices of open and distance education, and to the cross-cultural contexts involved. (Author/AEF)

  6. Assuring Quality in Asian Open and Distance Learning

    ERIC Educational Resources Information Center

    Jung, Insung; Latchem, Colin

    2007-01-01

    Open and distance learning (ODL) is enjoying phenomenal growth in Asian higher education, new forms of provision are being developed, new institutions are being established and there is a surge in online export and import. However, there is still need to ensure that increasing access does not result in lowering standards and to prove that ODL is…

  7. Accreditation of Open and Distance Learning: A Framework for Turkey

    ERIC Educational Resources Information Center

    Kocdar, Serpil; Aydin, Cengiz Hakan

    2012-01-01

    The purpose of this study is to develop a framework for the accreditation of higher open and distance learning (ODL) programs in Turkey. The study was designed as a sequential monomethod multistrand mixed model including two strands which were both qualitative (QUAL[arrow right]QUAL). In the first strand, both quantitative and qualitative data…

  8. Assessment in Open and Distance Learning System (ODL): A Challenge

    ERIC Educational Resources Information Center

    Chaudhary, S. V. S.; Dey, Niradhar

    2013-01-01

    Assessment is an integral part of the learning process. The traditional practice of assessment has changed to meet the need of the contemporary society. In this paper assessment strategies used in Open and Distance Education are discussed and constructive suggestions are given to meet the challenges of assessment. Recently we experience a paradigm…

  9. Musing on the Memes of Open and Distance Education

    ERIC Educational Resources Information Center

    Latchem, Colin

    2014-01-01

    Just as genes propagate themselves in the gene pool by leaping from body to body, so memes (ideas, behaviours, and actions) transmit cultural ideas or practices from one mind to another through writing, speech, or other imitable phenomena. This paper considers the memes that influence the evolution of open and distance education. If the…

  10. Occasional Papers in Open and Distance Learning. Number 16.

    ERIC Educational Resources Information Center

    Donnan, Peter, Ed.; McDonald, Anne, Ed.

    Quality in distance education and open learning is the theme of this collection of five papers. The first is a compilation of outlines of Charles Sturt University (New South Wales, Australia) innovative teaching projects contributed by project leaders or team members. Quality initiatives are described in a range of disciplines. In seeking to…

  11. Delivery of Open, Distance, and E-Learning in Kenya

    ERIC Educational Resources Information Center

    Nyerere, Jackline Anyona; Gravenir, Frederick Q.; Mse, Godfrey S.

    2012-01-01

    The increased demand and need for continuous learning have led to the introduction of open, distance, and e-learning (ODeL) in Kenya. Provision of this mode of education has, however, been faced with various challenges, among them infrastructural ones. This study was a survey conducted in two public universities offering major components of ODeL,…

  12. The Costs and Economies of Open and Distance Learning.

    ERIC Educational Resources Information Center

    Rumble, Greville

    This book is designed to give planners of open and distance learning programs the technical information needed to determine the cost of programs and analyze the behavior of costs. The following are among the topics discussed: budgets; classification of resources (human resources, premises and accommodation, and equipment and furniture); a basic…

  13. The Costs and Economies of Open and Distance Learning.

    ERIC Educational Resources Information Center

    Rumble, Greville

    This book is designed to give planners of open and distance learning programs the technical information needed to determine the cost of programs and analyze the behavior of costs. The following are among the topics discussed: budgets; classification of resources (human resources, premises and accommodation, and equipment and furniture); a basic…

  14. Fundamental Parameters of the Open Cluster Kronberger 1

    NASA Astrophysics Data System (ADS)

    Sujatha, S.; Krishna Kumar, K.; Komala, S.

    2016-09-01

    In this paper, we present the fundamental physical parameters and the present-day mass function of the open cluster Kronberger 1. The cluster radius is estimated to be 3' and the interstellar extinction E(B-V) in the line-of-sight of the cluster is found to be 0.45±0.05 mag. This cluster is located in the direction of Auriga constellation at a distance of 2.5±0.2 kpc. From the appropriate theoretical isochrones, the log(age) of the cluster is found to be 7.65. The mass function slope for Kronberger 1 is derived for the first time and it is estimated to be α = 2.72±0.2 which is in agreement with the slope of α = 2.35 given by Salpeter. Similar results are obtained from a near infrared study performed using data from the Two Micron All Sky Survey thus substantiating the results obtained from the optical analysis. These results indicate that Kronberger 1 is a suitable object for mapping the spiral arm structure of our Galaxy and for understanding the behavior of mass function in the Galactic disk.

  15. Nine new open clusters within 500 pc from the Sun

    NASA Astrophysics Data System (ADS)

    Röser, Siegfried; Schilbach, Elena; Goldman, Bertrand

    2016-10-01

    Aims: One of the results of the Milky Way Star Clusters (MWSC) survey was the detection of a slight under-density of old (ca. 1 Gyr) clusters within the nearest kilo-parsec from the Sun. This under-density may be due to an ineffectiveness in the detection of larger structures with lower surface brightness. We report on our attempts to reveal such clusters. Methods: We derived proper motions from a combination of Tycho-2 with URAT1, and obtained a mean precision of about 1.4 mas/yr per co-ordinate for 1.3 million stars north of -20° declination. We cut the sky into narrow proper motion slices and searched for spatial over-densities of stars in each slice. We then examined stars from over-densities in optical and near-infrared colour-magnitude diagrams to determine if they are compatible with isochrones of a cluster. We estimated the field star contamination using our data and the Besançon Galactic model. Results: We detected nine hitherto unknown open clusters in the vicinity of the Sun with ages between 70 Myr and 1 Gyr, and distances between 200 and 500 pc.

  16. Towards a comprehensive knowledge of the open cluster Haffner 9

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.

    2017-03-01

    We turn our attention to Haffner 9, a Milky Way open cluster whose previous fundamental parameter estimates are far from being in agreement. In order to provide with accurate estimates, we present high-quality Washington CT1 and Johnson BVI photometry of the cluster field. We put particular care in statistically cleaning the colour-magnitude diagrams (CMDs) from field star contamination, which was found a common source in previous works for the discordant fundamental parameter estimates. The resulting cluster CMD fiducial features were confirmed from a proper motion membership analysis. Haffner 9 is a moderately young object (age ∼350 Myr), placed in the Perseus arm - at a heliocentric distance of ∼3.2 kpc - , with a lower limit for its present mass of ∼160 M⊙ and of nearly metal solar content. The combination of the cluster structural and fundamental parameters suggest that it is in an advanced stage of internal dynamical evolution, possibly in the phase typical of those with mass segregation in their core regions. However, the cluster still keeps its mass function close to that of the Salpeter's law.

  17. 2MASS photometry and kinematical studies of open cluster NGC 188

    NASA Astrophysics Data System (ADS)

    Elsanhoury, W. H.; Haroon, A. A.; Chupina, N. V.; Vereshchagin, S. V.; Sariya, Devesh P.; Yadav, R. K. S.; Jiang, Ing-Guey

    2016-11-01

    In this paper, we present our results for the photometric and kinematical studies of old open cluster NGC 188. We determined various astrophysical parameters like limited radius, core and tidal radii, distance, luminosity and mass functions, total mass, relaxation time etc. for the cluster using 2MASS catalog. We obtained the cluster's distance from the Sun as 1721 ± 41 pc and log (age)= 9.85 ± 0.05 at Solar metallicity. The relaxation time of the cluster is smaller than the estimated cluster age which suggests that the cluster is dynamically relaxed. Our results agree with the values mentioned in the literature. We also determined the clusters apex coordinates as (281°.88, -44∘ .76) using AD-diagram method. Other kinematical parameters like space velocity components, cluster center and elements of Solar motion etc. have also been computed.

  18. The Distance to the Galactic Globular Cluster, 47 Tuc

    NASA Astrophysics Data System (ADS)

    Woodley, Kristin; Goldsbury, R.; Kalirai, J.; Richer, H.; Tremblay, P.; Anderson, J.; Bergeron, P.; Dotter, A.; Esteves, L.; Fahlman, G.; Hansen, B.; Heyl, J.; Hurley, J.; Rich, R.; Shara, M.; Stetson, P.

    2012-01-01

    We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs to pure hydrogen atmosphere white dwarf models. Our photometric data set is obtained from a 121 orbit Hubble Space Telescope program using the Wide Field Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images. These images cover more than 60 arcmin2 and extend over a radial range of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Here, we present our best fitting distance modulus using a likelihood analysis. We also search the white dwarf photometry for infrared excess in the F160W filter, indicative of protoplanetary disks or low mass companions, and find no convincing cases within our sample.

  19. Two Intermediate Age Open Clusters - NGC752 and NGC3680

    NASA Astrophysics Data System (ADS)

    Carraro, G.; Bertelli, G.; Bressan, A.; Chiosi, C.

    1993-10-01

    In this paper, with the aid of synthetic color-magnitude diagram (CMD) technique we study two scarcely populated and slightly metal-poor intermediate age open clusters, namely NGC 752 and NGC 3680. The analysis is made using both standard and overshoot models calculated by the Padova group (Fagotto 1990; Alongi et al. 1991, 1993). The advantage with the synthetic CMD technique is that it allows for quantitative predictions for the star counts and luminosity functions. Adopting the metallicity indicated for each cluster by current determinations, we seek to determine the color excess, distance modulus, and age at the same time. Looking at the fit of the whole CMD, the behaviour of the main sequence stars LF, and two suitable ratios of star counts we try to discriminate between the two evolutionary schemes. We suggest that models with convective overshoot ought to be preferred to the classical ones.

  20. Open and Distance Learning in the Developing World. Routledge Studies in Distance Education.

    ERIC Educational Resources Information Center

    Perraton, Hilary

    This book contains 10 chapters that analyze and synthesize the progress of open and distance education (ODE) in the developing world. Most chapters include case studies of programs in a variety of countries. "Introduction: Golden Goose or Ugly Duckling" briefly delineates the history of the field. "Nonformal Education: The Light…

  1. Open and Distance Learning in the Developing World. Routledge Studies in Distance Education.

    ERIC Educational Resources Information Center

    Perraton, Hilary

    This book contains 10 chapters that analyze and synthesize the progress of open and distance education (ODE) in the developing world. Most chapters include case studies of programs in a variety of countries. "Introduction: Golden Goose or Ugly Duckling" briefly delineates the history of the field. "Nonformal Education: The Light…

  2. A populous intermediate-age open cluster and evidence of an embedded cluster among the FSR globular cluster candidates

    NASA Astrophysics Data System (ADS)

    Bica, E.; Bonatto, C.

    2008-03-01

    We study the nature of the globular cluster (GC) candidates FSR 1603 and FSR1755 selected from the catalogue of Froebrich, Scholz & Raftery. Their properties are investigated with Two-Micron All-Sky Survey field-star decontaminated photometry, which is used to build colour-magnitude diagrams (CMDs) and stellar radial density profiles. FSR1603 has the open cluster Ruprecht 101 as optical counterpart, and we show it to be a massive intermediate-age cluster. Relevant parameters of FSR1603 are the age ~1Gyr, distance from the Sun dsolar ~ 2.7kpc, Galactocentric distance RGC ~ 6.4kpc, core radius RC ~ 1.1pc, mass function slope χ ~ 1.8, observed stellar mass (for stars with mass in the range 1.27 <= m <= 2.03Msolar) Mobs ~ 500Msolar and a total (extrapolated to m = 0.08Msolar) stellar mass Mtot ~ 2300Msolar. FSR1755, on the other hand, is not a populous cluster. It may be a sparse young cluster embedded in the HII region Sh2-3, subject to an absorption AV ~ 4.1, located at dsolar ~ 1.3kpc. Important field-star contamination, spatially variable heavy dust obscuration, even in Ks, and gas emission characterize its field. A nearly vertical, sparse blue stellar sequence shows up in the CMDs.

  3. Investigation of the open star cluster NGC 6800

    NASA Astrophysics Data System (ADS)

    Ananjevskaja, Yu. K.; Frolov, V. N.; Polyakov, E. V.

    2015-07-01

    The results of a comprehensive study of the Galactic open cluster NGC 6800 are presented. The positions of stars to a limiting magnitude B ≃ 16{./ m }5 in an 80' × 80' field centered at the cluster were measured on eight plates from the Pulkovo normal astrograph with a maximum epoch difference of 57 years. The measurements were performed with the Pulkovo "Fantasy" automated measuring system. The corresponding field from the 2MASS catalogue was used as an additional plate. As a result, the relative proper motions of stars were obtained with a root-mean-square error of 3.0 mas yr-1. A catalogue of BV and JHK magnitudes for objects in the investigated region was compiled from available published resources. The astrometric selection of cluster members was made by the maximum likelihood method. An individual cluster membership probability of a star P ≥ 60% served as the first selection criterion. The position of a star on the photometric color-magnitude ( V ~ B - V, J ~ J - K s ) diagrams was considered as the second selection criterion. On the basis of these criteria, it was established that 109 stars are members of NGC 6800, These data were used to refine the physical parameters of the cluster: the mean reddening E( B - V) = 0 m . 40, the true distance modulus ( V - M V )0 = 10{./ m }05, and the cluster age ~250 Myr. The luminosity and mass functions were constructed. The position of the center of the cluster NGC 6800 was improved: α = 19h27m11{./s}2 and δ = +25°07'24〃(2000). The catalogue of relative proper motions for stars in the field is available in electronic form only.

  4. The Old, Super-Metal-Rich Open Cluster, NGC 6791

    NASA Astrophysics Data System (ADS)

    Boesgaard, Ann Merchant; Lum, Michael G. G.; Deliyannis, Constantine P.

    2015-08-01

    Stellar evolution and Galactic evolution have both been greatly advanced by the study of star clusters. In addition the elemental abundance results from clusters have revealed information about Galactic chemical evolution and nucleosynthesis. The cluster, NGC 6791, has a number of bizarre properties that make it especially interesting for comparative cluster studies. It is old (8.3 Gyr) yet metal-rich ([Fe/H] = +0.30). It has a heliocentric distance of 4 kpc and a galactic latitude of +11 degrees which makes it 1 kpc above the galactic plane. Its boxy orbit has a high eccentricity (~0.5) with a perigalactic distance of 3 kpc and an apogalactic distance of 10 kpc. The orbital period of ~130 Myr indicates that it has crossed the Galactic plane several times yet has remained as an intact cluster. We have determined abundances from high-resolution (R = 46,000) Keck/HIRES spectra of turn-off stars in this open cluster NGC 6791. We have a solid determination of [Fe/H] = +0.30 +/-0.02 from measurements of some 40 unblended, unsaturated lines of both Fe I and Fe II in eight turn-off stars. Our O abundances come from the O I triplet near 7774 Å and are corrected for small nLTE effects. We find consistent ratios of [O/Fe]n with a mean of -0.06 +/-0.02, indicating a single population of stars. Our results for the alpha elements [Mg/Fe], [Si/Fe], [Ca/Fe] and [Ti/Fe] are near solar and compare well with those of old, metal-rich field stars. The Fe-peak elements, Cr and Ni, have values of [Cr/Fe] = +0.05 +/-0.02 and [Ni/Fe] = +0.04 +/-0.01. Determinations of upper limits were found for Li by spectrum synthesis; this is consistent with the upper limits in this temperature range for turn-off/subgiant stars in the relatively old, super-metal-rich cluster NGC 6253. We speculate that no stars in NGC 6791 have retained the Li with which they formed.

  5. The open cluster King 1 in the second quadrant

    NASA Astrophysics Data System (ADS)

    Carrera, Ricardo; Rodríguez Espinosa, Loreto; Casamiquela, Laia; Balaguer Nuñez, Lola; Jordi, Carme; Allende Prieto, Carlos; Stetson, Peter B.

    2017-10-01

    We analyse the poorly studied open cluster King 1 in the second Galactic quadrant. From wide-field photometry, we have studied the spatial distribution of this cluster. We determined that the centre of King 1 is located at α2000 = 00h22m and δ2000 = +64°23΄. By parameterizing the stellar density with a King profile, we have obtained a central density of ρ0 = 6.5 ± 0.2 star arcmin-2 and a core radius of rcore = 1.9 ± 0.2 arcmin. By comparing the observed colour-magnitude diagram of King 1 with those of similar open clusters and with different sets of isochrones, we have estimated an age of 2.8 ± 0.3 Gyr, a distance modulus of (m - M)o = 10.6 ± 0.1 mag and a reddening of E(B - V) = 0.80 ± 0.05 mag. To complete our analysis, we acquired medium resolution spectra for 189 stars in the area of King 1. From their derived radial velocities, we determined an average velocity = -53.1 ± 3.1 km s-1. From the strength of the infrared Ca ii lines in red giants we have determined an average metallicity of <[M/H]> = +0.07 ± 0.08 dex. From spectral synthesis, we have also estimated an α-elements abundance of <[α/M]> = -0.10 ± 0.08 dex.

  6. X-Ray source populations in old open clusters: Collinder 261

    NASA Astrophysics Data System (ADS)

    Vats, Smriti; van den Berg, Maureen; Wijnands, Rudy

    2014-09-01

    We are carrying out an X-ray survey of old open clusters with the Chandra X-ray Observatory. Single old stars, being slow rotators, are very faint in X-rays (L_X < 1×10^27 erg/s). Hence, X-rays produced by mass transfer in cataclysmic variables (CVs) or by rapid rotation of the stars in tidally locked, detached binaries (active binaries; ABs) can be detected, without contamination from single stars. By comparing the properties of various types of interacting binaries in different environments (the Galactic field, old open clusters, globular clusters), we aim to study binary evolution and how it may be affected by dynamical encounters with other cluster stars. Stellar clusters are good targets to study binaries, as age, distance, chemical composition, are well constrained. Collinder (Cr) 261 is an old open cluster (age ~ 7 Gyr), with one of the richest populations inferred of close binaries and blue stragglers of all open clusters and is therefore an obvious target to study the products of close encounters in open clusters. We will present the first results of this study, detailing the low-luminosity X-ray population of Cr 261, in conjunction with other open clusters in our survey (NGC 188, Berkeley 17, NGC 6253, M67, NGC 6791) and in comparison with populations in globular clusters.

  7. TWO BARIUM STARS IN THE OPEN CLUSTER NGC 5822

    SciTech Connect

    Katime Santrich, O. J.; Pereira, C. B.; De Castro, D. B. E-mail: claudio@on.br

    2013-08-01

    Open clusters are very useful examples to explain the constraint of the nucleosynthesis process with the luminosities of stars because the distances of the clusters are better known than those of field stars. We carried out a detailed spectroscopic analysis to derive the chemical composition of two red giants in the young open cluster NGC 5822, NGC 5822-2, and NGC 5822-201. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. We found that NGC 5822-2 and -201 have, respectively, a mean overabundance of the elements created by the s-process, ''s'', with the notation [s/Fe] of 0.77 {+-} 0.12 and 0.83 {+-} 0.05. These values are higher than those for field giants of similar metallicity. We also found that NGC 5822-2 and -201 have, respectively, luminosities of 140 L{sub Sun} and 76 L{sub Sun }, which are much lower than the luminosity of an asymptotic giant branch star. We conclude that NGC 5822-2 and NGC 5822-201 are two new barium stars first identified in the open cluster NGC 5822. The mass transfer hypothesis is the best scenario to explain the observed overabundances.

  8. The Need for Participation in Open and Distance Education: The Open University Malaysia Experience

    ERIC Educational Resources Information Center

    Raghavan, Santhi; Kumar, P. Rajesh

    2007-01-01

    This paper provides an overview of adult learner participation in open and distance education by focusing participation needs based on selected socio-demographic variables such as age, years of working experience and monthly income. The related study involved a sample of 454 Open University Malaysia students from a number of learning centres…

  9. Challenges for Open and Distance Learning (ODL) Students: Experiences from Students of the Zimbabwe Open University

    ERIC Educational Resources Information Center

    Musingafi, Maxwell C. C.; Mapuranga, Barbra; Chiwanza, Kudzai; Zebron, Shupikai

    2015-01-01

    The purpose of this study was to investigate the challenges facing Open and Distance Learning students at the Zimbabwe Open University (ZOU). The study was conducted at ZOU Masvingo Regional Campus. The study employed both qualitative and quantitative approaches. The main data collection techniques were questionnaires and structured interviews,…

  10. Through the Open Door--Today's Revolution in Open Access and Distance Learning.

    ERIC Educational Resources Information Center

    Bennett, Roger, Ed.

    1986-01-01

    Consists of eight articles discussing the topic of open learning. Articles address (1) definitions, (2) corporate training, (3) further education programs, (4) university-based training, (5) distance learning, (6) learning to learn, (7) Britain's Open University, (8) the Business-Technical Education Council. (CH)

  11. The Role of Open Access and Open Educational Resources: A Distance Learning Perspective

    ERIC Educational Resources Information Center

    Hatzipanagos, Stylianos; Gregson, Jon

    2015-01-01

    The paper explores the role of Open Access (in licensing, publishing and sharing research data) and Open Educational Resources within Distance Education, with a focus on the context of the University of London International Programmes. We report on a case study where data were gathered from librarians and programme directors relating to existing…

  12. Gravitational interactions between globular and open clusters: an introduction

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, R.; de la Fuente Marcos, C.; Reilly, D.

    2014-01-01

    Historically, it has been assumed that globular and open clusters never interact. However, recent evidence suggests that: globular clusters passing through the disk may be able to perturb giant molecular clouds (GMCs) triggering formation of open clusters and some old open clusters may be linked to accreted globulars. Here, we further explore the existence of possible dynamical connections between globular and open clusters, and realize that the most obvious link must be in the form of gravitational interactions. If open clusters are born out of GMCs, they have to move in similar orbits. If we accept that globulars can interact with GMCs, triggering star formation, it follows that globular and open clusters must also interact. Consistently, theoretical arguments as well as observational evidence, show that globular and open clusters certainly are interacting populations and their interactions are far more common than usually thought, especially for objects part of the bulge/disk. Monte Carlo calculations confirm that conclusion. Globular clusters seem capable of not only inducing formation of open clusters but, more often, their demise. Relatively frequent high speed cluster encounters or cluster harassment may also cause, on the long-term, slow erosion and tidal truncation on the globulars involved. The disputed object FSR 1767 (2MASS-GC04) may be, statistically speaking, the best example of an ongoing interaction.

  13. Distances, Ages, and Epoch of Formation of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Carretta, Eugenio; Gratton, Raffaele G.; Clementini, Gisella; Fusi Pecci, Flavio

    2000-04-01

    We review the results on distances and absolute ages of Galactic globular clusters (GCs) obtained after the release of the Hipparcos catalog. Several methods aimed at the definition of the Population II local distance scale are discussed, and their results compared, exploiting new results for RR Lyraes in the Large Magellanic Cloud (LMC). We find that the so-called short distance and long distance scales may be reconciled whether or not a consistent reddening scale is adopted for Cepheids and RR Lyrae variables in the LMC. Emphasis is given in the paper to the discussion of distances and ages of GCs derived using Hipparcos parallaxes of local subdwarfs. We find that the selection criteria adopted to choose the local subdwarfs, as well as the size of the corrections applied to existing systematic biases, are the main culprit for the differences found among the various independent studies that first used Hipparcos parallaxes and the subdwarf fitting technique. We also caution that the absolute age of M92 (usually considered one of the oldest clusters) still remains uncertain due to the lack of subdwarfs of comparable metallicity with accurate parallaxes. Distances and ages for the nine clusters discussed in a previous paper by Gratton et al. are rederived using an enlarged sample of local subdwarfs, which includes about 90% of the metal-poor dwarfs with accurate parallaxes (Δπ/π<=0.12) in the whole Hipparcos catalog. On average, our revised distance moduli are decreased by 0.04 mag with respect to Gratton et al. The corresponding age of the GCs is t=11.5+/-2.6 Gyr, where the error bars refer to the 95% confidence range. The relation between the zero-age horizontal branch (ZAHB) absolute magnitude and metallicity for the nine program clusters turns out to be MV(ZAHB)=(0.18+/-0.09)([Fe/H]+1.5)+(0.53+/-0.12) Thanks to Hipparcos the major contribution to the total error budget associated with the subdwarf fitting technique has been moved from parallaxes to photometric

  14. CCD UBV(RI)C photometry of twenty open clusters

    NASA Astrophysics Data System (ADS)

    Oralhan, İnci Akkaya; Karataş, Yüksel; Schuster, William J.; Michel, Raúl; Chavarría, Carlos

    2015-01-01

    Fundamental astrophysical parameters have been derived for 20 open clusters (OCs) using CCD UBV(RI)C photometric data observed with the 84 cm telescope at the San Pedro Mártir National Astronomical Observatory, México. The interstellar reddenings, metallicities, distances, and ages have been compared to the literature values. Significant differences are usually due to the usage of diverse empirical calibrations and differing assumptions, such as concerning cluster metallicity, as well as distinct isochrones which correspond to differing element-abundance ratios, internal stellar physics, and photometric systems. Different interstellar reddenings, as well as varying reduction and cluster-membership techniques, are also responsible for these kinds of systematic differences and errors. The morphological ages, which are derived from the morphological indices (δV and δ1) in the CM diagrams, are in good agreement with the isochrone ages of 12 OCs, those with good red clump (RC) and red giant (RG) star candidates. No metal abundance gradient is detected for the range 6.82⩽RGC⩽15.37 kpc, nor any correlation between the cluster ages and metal abundances for these 20 OCs. Young, metal-poor OCs, observed here in the third Galactic quadrant, may be associated with stellar over-densities, such as that in Canis Major (Martin et al.) and the Monoceros Ring (Newberg et al.), or signatures of past accretion events, as discussed by Yong et al. and Carraro et al.

  15. The open cluster Havlen-Moffat No. 1 revisited

    NASA Astrophysics Data System (ADS)

    Vázquez, R. A.; Baume, G.

    2001-06-01

    A deep CCD UBVRI photometric survey combined with UBVRI polarimetric observations of 21 bright stars was carried out in the region of the open cluster Havlen-Moffat No. 1. Our data reveal that the extinction law in this cluster is variable and that six cluster stars show very high polarisation values (>4%), probably because of the presence of a nearby small dust cloud. The cluster is at a distance of d = 3300 pc, it is 2-4 Myr old and the initial mass function of its most massive stars (M > 3 Msun ) has a flat slope of x~ 0.7. As an additional result, it was possible to reconcile the absolute magnitudes of the two WN7-type members using the R-values valid in the regions where they are located. Based on observations collected at the University of Toronto Southern Observatory, Las Campanas, Chile, and the Complejo Astronómico El Leoncito, (CASLEO), Argentina, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan. Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/371/908.

  16. The OPD photometric survey of open clusters II. robust determination of the fundamental parameters of 24 open clusters

    NASA Astrophysics Data System (ADS)

    Monteiro, H.; Dias, W. S.; Hickel, G. R.; Caetano, T. C.

    2017-02-01

    In the second paper of the series we continue the investigation of open cluster fundamental parameters using a robust global optimization method to fit model isochrones to photometric data. We present optical UBVRI CCD photometry (Johnsons-Cousins system) observations for 24 neglected open clusters, of which 14 have high quality data in the visible obtained for the first time, as a part of our ongoing survey being carried out in the 0.6 m telescope of the Pico dos Dias Observatory in Brazil. All objects were then analyzed with a global optimization tool developed by our group which estimates the membership likelihood of the observed stars and fits an isochrone from which a distance, age, reddening, total to selective extinction ratio RV (included in this work as a new free parameter) and metallicity are estimated. Based on those estimates and their associated errors we analyzed the status of each object as real clusters or not, finding that two are likely to be asterisms. We also identify important discrepancies between our results and previous ones obtained in the literature which were determined using 2MASS photometry.

  17. NGC 6067: A young and populous open cluster

    NASA Astrophysics Data System (ADS)

    Alonso-Santiago, J.; Negueruela, I.; Marco, A.; Tabernero, H. M.; González-Fernández, C.; Castro, N.

    2017-03-01

    NGC 6067 is a young open cluster hosting the largest population of evolved stars among known Milky Way clusters in the 50 – 100 Ma age range. It thus represents the best laboratory in our Galaxy to constrain the evolutionary tracks of 5-7 M_{⊙} stars. We have used high-resolution spectra of a large sample of bright cluster members (45), combined with archival photometry, to obtain accurate parameters for the cluster as well as stellar atmospheric parameters. We derive a distance of 1.78±0.12 kpc, an age of 90±20 My and a tidal radius of 14.8^{6.8}_{3.2} arcmin. We estimate an initial mass above 5700 M_{⊙}, for a present-day evolved population of two Cepheids, two A supergiants and 12 red giants with masses ≈ 6 M_{⊙}. We also determine chemical abundances of Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the clump stars. We find a supersolar metallicity, [Fe/H]=+0.19±0.05, and a homogeneous chemical composition, consistent with the Galactic metallicity gradient. The presence of a Li-rich red giant, star 276, is also detected. An over-abundance of Ba is found, supporting the enhanced s-process. The mass of V340 Nor, a Cepheid that seems younger than the cluster itself, suggests that it has been a mass gainer in an interacting binary. The ratio of blue to red giants is smaller than one, in agreement with models with moderate overshooting, but the properties of the cluster Cepheids do not seem consistent with current Padova models for supersolar metallicity.

  18. First CCD UBVI photometric analysis of six open cluster candidates

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Clariá, J. J.; Ahumada, A. V.

    2011-04-01

    We have obtained CCD UBVIKC photometry down to V ˜ 22 for the open cluster candidates Haffner 3, Haffner 5, NGC 2368, Haffner 25, Hogg 3 and Hogg 4 and their surrounding fields. None of these objects have been photometrically studied so far. Our analysis shows that these stellar groups are not genuine open clusters since no clear main sequences or other meaningful features can be seen in their colour-magnitude and colour-colour diagrams. We checked for possible differential reddening across the studied fields that could be hiding the characteristics of real open clusters. However, the dust in the directions to these objects appears to be uniformly distributed. Moreover, star counts carried out within and outside the open cluster candidate fields do not support the hypothesis that these objects are real open clusters or even open cluster remnants.

  19. A distance of 133-137 parsecs to the Pleiades star cluster.

    PubMed

    Pan, Xiaopei; Shao, M; Kulkarni, S R

    2004-01-22

    Nearby 'open' clusters of stars (those that are not gravitationally bound) have played a crucial role in the development of stellar astronomy because, as a consequence of the stars having a common age, they provide excellent natural laboratories to test theoretical stellar models. Clusters also play a fundamental part in determining distance scales. The satellite Hipparcos surprisingly found that an extensively studied open cluster--the Pleiades (also known as the Seven Sisters)--had a distance of D = 118 +/- 4 pc (refs 2, 3), about ten per cent smaller than the accepted value. The discrepancy generated a spirited debate because the implication was that either current stellar models were incorrect by a surprising amount or Hipparcos was giving incorrect distances. Here we report the orbital parameters of the bright double star Atlas in the Pleiades, using long-baseline optical/infrared interferometry. From the data we derive a firm lower bound of D > 127 pc, with the most likely range being 133 < D < 137 pc. Our result reaffirms the fidelity of current stellar models.

  20. High-Quality Broadband BVRI Photometry of Benchmark Open Clusters

    NASA Astrophysics Data System (ADS)

    Joner, Michael D.

    Photometric techniques are often used to observe stars and it can be demonstrated that fundamental stellar properties can be observationally determined using calibrated sets of photometric data. Many of the most powerful techniques utilized to calibrate stellar photometry employ the use of stars in clusters since the individual stars are believed to have many common properties such as age, composition, and approximate distance. Broadband photometric Johnson/Cousins BVRI observations are presented for several nearby open clusters. The new photometry has been tested for consistency relative to archival work and shown to be both accurate and precise. The careful use of a regular routine when making photometric observations, along with the monitoring of instrumental systems and the use of various quality control techniques when making observations or performing data reductions, will enhance an observer's ability to produce high-quality photometric measurements. This work contains a condensed review of the history of photometry, along with a brief description of several popular photometric systems that are often utilized in the field of stellar astrophysics. Publications written by Taylor or produced during the early Taylor and Joner collaboration are deemed especially relevant to the current work. A synopsis of seven archival publications is offered, along with a review of notable reports of VRI photometric observations for the nearby Hyades open star cluster. The body of this present work consists of four publications that appeared between the years 2005 and 2008, along with a soon to be submitted manuscript for a fifth publication. Each of these papers deals specifically with high-quality broadband photometry of open clusters with new data being presented for the Hyades, Coma, NGC 752, Praesepe, and M67. It is concluded that the VRI photometry produced during the Taylor and Joner collaborative investigations forms a high-quality data set that has been: (1) stable for

  1. Interstellar Polarization and Extinction towards the Open Cluster NGC 457

    NASA Astrophysics Data System (ADS)

    Topasna, Gregory A.; Daman, Eryn A.; Kaltcheva, Nadia T.

    2017-10-01

    NGC 457 is a moderately reddened and relatively young open cluster very rich in variable stars, particularly Be stars, but not associated with any prominent star-forming field. We combine new multi-wavelength polarization measurements with existing UBV and uvby photometries to obtain precise estimates of the total-to-selective extinction in the field of the cluster and re-evaluate its distance and age. The polarization measurements show a tight alignment of the polarization vectors with the Galactic plane and yield an average value of the total-to-selective extinction of 3.05 ± 0.17 for the cluster’s field. Using this value and the confirmed color excess E(B-V)=0.500+/- 0.030 mag, we obtain a distance modulus of 12.20 ± 0.39, corresponding to 2.75 ± 0.49 kpc and, assuming slightly sub-solar metallicity, an age of 15.8 Myr.

  2. N-Body Numerical Simulations for Orbits of Old Open Clusters

    NASA Astrophysics Data System (ADS)

    Hsu, L.; Noriega-Crespo, A.; Friel, E. D.

    1996-12-01

    Analysis on age distributions of open clusters has shown that the average time it takes for a cluster to be completely disrupted is a few hundred million years. However, the ages of the old open clusters are on the order of one to ten billion years. The purpose of this project was to model the clusters as n-body systems and find relations between orbital kinematics and survivability. This work builds off of an earlier project which modeled the orbits using just a center of mass, or "one-body" model (1). Data were available for the complete orbital parameters of seven old open clusters. These seven, along with too purely theoretical open clusters were placed in the simulations. The clusters consisted of one hundred bodies (each of one solar mass) which were placed in a model galactic potential (2). Internal interactions were taken into account, but a relatively large softening parameter was used so that binary interactions would not dominate. The results show that there is a correlation between radial distance from the galactic center and survivability. For example, the cluster ngc6791 was found to contain approximately 55% of its original mass after one gyr. The closest radial approach for ngc6791 is 4.6 kpcs. However, ngc752, which has a distance of closest radial approach of 8.7 kpcs, retained 80% of its original mass. Model clusters were identical except for center of mass positions and velocities. These results support the observation that almost all old open clusters are found at large radial distances from the center of the galaxy (usually greater than 8kpcs). Currently, data analysis is still being carried out to find trends in mass loss verses time. [1] Finlay, Friel, Noriega-Crespo & Cudworth, 1995. [2] Allen & Santillan 1991, RevMxAA.

  3. TX Cnc AS A MEMBER OF THE PRAESEPE OPEN CLUSTER

    SciTech Connect

    Zhang, X. B.; Deng, L.; Lu, P.

    2009-08-15

    We present B-, V-, and I-band CCD photometry of the W UMa-type binary system TX Cnc, which is a member star of the Praesepe open cluster. Based on the observations, new ephemeris and a revised photometric solution of the binary system were derived. Combined with the results of the radial velocity solution contributed by Pribulla et al., the absolute parameters of the system were determined. The mass, radius, and luminosity of the primary component are derived to be 1.35 {+-} 0.02 M {sub sun}, 1.27 {+-} 0.04 R {sub sun}, and 2.13 {+-} 0.11 L {sub sun}. Those for the secondary star are computed as 0.61 {+-} 0.01 M {sub sun}, 0.89 {+-} 0.03 R {sub sun}, and 1.26 {+-} 0.07 L {sub sun}, respectively. Based on these results, a distance modulus of (m - M) {sub V} = 6.34 {+-} 0.05 is determined for the star. It confirms the membership of TX Cnc to the Praesepe open cluster. The evolutionary status and the physical nature of the binary system are discussed compared with the theoretical model.

  4. Study of globular cluster M53: new variables, distance, metallicity

    NASA Astrophysics Data System (ADS)

    Dékány, I.; Kovács, G.

    2009-11-01

    Aims: We study the variable star content of the globular cluster M53 to compute the physical parameters of the constituting stars and the distance of the cluster. Methods: Covering two adjacent seasons in 2007 and 2008, new photometric data are gathered for 3048 objects in the field of M53. By using the OIS (optimal image subtraction) method and subsequently TFA (trend filtering algorithm), we search for variables in the full sample by using discrete Fourier transformation and box-fitting least squares methods. We select variables based on the statistics related to these methods combined with visual inspection. Results: We identified 12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars - and 3 long-period variables). No eclipsing binaries were found in the present sample. Except for the 3 (hitherto unknown) Blazhko RR Lyrae (two RRab and an RRc) stars, no multiperiodic variables were found. We showed that after proper period shift, the PLC (period-luminosity-color) relation for the first overtone RR Lyrae sample tightly follows the one spanned by the fundamental stars. Furthermore, the slope is in agreement with that derived from other clusters. Based on the earlier Baade-Wesselink calibration of the PLC relations, the derived reddening-free distance modulus of M53 is 16.31±0.04 mag, corresponding to a distance modulus of 18.5 mag for the Large Magellanic Cloud. From the Fourier parameters of the RRab stars we obtained an average iron abundance of -1.58± 0.03 (error of the mean). This is ~0.5 dex higher than the overall abundance of the giants as given in the literature and derived in this paper from the three-color photometry of giants. We suspect that the source of this discrepancy (observable also in other, low-metallicity clusters) is the lack of a sufficient number of low-metallicity objects in the calibrating sample of the Fourier method. Table 1 is only available in electronic form at http://www.aanda.org Photometric data

  5. Investigation of open clusters based on IPHAS and APASS survey data

    NASA Astrophysics Data System (ADS)

    Dambis, A. K.; Glushkova, E. V.; Berdnikov, L. N.; Joshi, Y. C.; Pandey, A. K.

    2017-02-01

    We adapt the classical Q-method based on a reddening-free parameter constructed from three passband magnitudes to the filter set of Isaac Newton Telescope Photometric Hα Survey and combine it with the maximum-likelihood-based cluster parameter estimator by Naylor & Jeffries (2006) to determine the extinction, heliocentric distances, and ages of young open clusters using Hαri data. The method is also adapted for the case of significant variations of extinction across the cluster field. Our technique is validated by comparing the colour excesses, distances, and ages determined in this study with the most bona fide values reported for the 18 well-studied young open clusters in the past and a fairly good agreement is found between our extinction and distance estimates and earlier published results, although our age estimates are not very consistent with those published by other authors. We also show that individual extinction values can be determined rather accurately for stars with (r - i) > 0.1. Our results open up a prospect for determining a uniform set of parameters for northern clusters based on homogeneous photometric data, and for searching for new, hitherto undiscovered open clusters.

  6. On the Survival of High-altitude Open Clusters within the Milky Way Galaxy Tides

    NASA Astrophysics Data System (ADS)

    Martinez-Medina, L. A.; Pichardo, B.; Peimbert, A.; Moreno, E.

    2017-01-01

    It is a common assumption that high-altitude open clusters live longer compared to clusters moving close to the Galactic plane. This is because, at high altitudes, open clusters are far from the disruptive effects of in-plane substructures, such as spiral arms, molecular clouds, and the bar. However, an important aspect to consider in this scenario is that orbits of high-altitude open clusters will eventually cross the Galactic plane, where the vertical tidal field of the disk is strong. In this work, we simulate the interaction of open clusters with the tidal field of a detailed Milky Way Galactic model at different average altitudes and galactocentric radii. We find that the life expectancy of clusters decreases as the maximum orbital altitude increases and reaches a minimum at altitudes of approximately 600 pc. Clusters near the Galactic plane live longer because they do not experience strong vertical tidal shocks from the Galactic disk; then, for orbital altitudes higher than 600 pc, clusters again start to live longer due to the decrease in the number of encounters with the disk. With our study, we find that the compressive nature of the tides in the arms region and the bar play an important role in the survival of small clusters by protecting them from disruption: clusters inside the arms can live up to twice as long as those outside the arms at similar galactocentric distances.

  7. Higher Education through Open and Distance Learning. World Review of Distance Education and Open Learning, Volume 1. A Commonwealth of Learning Series.

    ERIC Educational Resources Information Center

    Harry, Keith, Ed.

    This book reports on the expansion of open and distance learning during the past decade, examining ways in which open and distance learning for higher education has responded to the needs of the new society, and summarizing the lessons of recent practice for policymakers and educators. After an introductory chapter, "Open and Distance…

  8. Higher Education through Open and Distance Learning. World Review of Distance Education and Open Learning, Volume 1. A Commonwealth of Learning Series.

    ERIC Educational Resources Information Center

    Harry, Keith, Ed.

    This book reports on the expansion of open and distance learning during the past decade, examining ways in which open and distance learning for higher education has responded to the needs of the new society, and summarizing the lessons of recent practice for policymakers and educators. After an introductory chapter, "Open and Distance…

  9. Absolute Spectrophotometry of 237 Open Cluster Stars

    NASA Astrophysics Data System (ADS)

    Clampitt, L.; Burstein, D.

    1994-12-01

    We present absolute spectrophotometry of 237 stars in 7 nearby open clusters: Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M 39. The observations were taken using the Wampler single-channel scanner (Wampler 1966) on the Crossley 0.9m telescope at Lick Observatory from July 1973 through December 1974. 21 bandpasses spanning the spectral range 3500 Angstroms to 7780 Angstroms were observed for each star, with bandwiths ranging from 32Angstroms to 64 Angstroms. Data are standardized to the Hayes--Latham (1975) system. Our measurements are compared to filter colors on the Johnson BV, Stromgren ubvy, and Geneva U V B_1 B_2 V_1 G systems, as well as to spectrophotometry of a few stars published by Gunn, Stryker & Tinsley and in the Spectrophotometric Standards Catalog (Adelman; as distributed by the NSSDC). Both internal and external comparisons to the filter systems indicate a formal statistical accuracy per bandpass of 0.01 to 0.02 mag, with apparent larger ( ~ 0.03 mag) differences in absolute calibration between this data set and existing spectrophotometry. These data will comprise part of the spectrophotometry that will be used to calibrate the Beijing-Arizona-Taipei-Connecticut Color Survey of the Sky (see separate paper by Burstein et al. at this meeting).

  10. A new open cluster binary system in the Milky Way

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Clariá, J. J.; Ahumada, A. V.

    2011-10-01

    We have obtained CCD UBVI_{KC} photometry for the open clusters (OCs) Hogg 12 and NGC 3590. Based on photometric and morphological criteria, as well as on the stellar density in the region, our evidence is sufficient to consider them a new open cluster binary system candidate.

  11. Radial velocities of stars in the globular cluster M4 and the cluster distance

    NASA Technical Reports Server (NTRS)

    Peterson, R. C.; Rees, Richard F.; Cudworth, Kyle M.

    1995-01-01

    The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km/s and a rederivation of existing proper motions. The mean radial velocity of the cluster is 70.9 +/- 0.6 km/s. The velocity dispersion is 3.5 +/- 0.3 km/s at the core, dropping marginally towards the outskirts. Such a low internal dispersion is somewhat at odds with the cluster's orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruption is high; a tidal radius two-thirds the currently accepted value would eliminate the discrepancy. The cluster mass-to-light ratio is also small, M/L(sub V) = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a cluster of moderate and concentration with a mass-to-light ratio among the lowest known. The astrometric distance to the cluster is also smaller than expected, 1.72 +/- 0.14 kpc. This is only consistent with conventional estimates of the luminosity of horizontal branch stars provided an extinction law R = A(sub V)/E(B-V) approximately 4 is adopted, as has been suggested recently by several authors.

  12. Radial velocities of stars in the globular cluster M4 and the cluster distance

    NASA Technical Reports Server (NTRS)

    Peterson, R. C.; Rees, Richard F.; Cudworth, Kyle M.

    1995-01-01

    The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km/s and a rederivation of existing proper motions. The mean radial velocity of the cluster is 70.9 +/- 0.6 km/s. The velocity dispersion is 3.5 +/- 0.3 km/s at the core, dropping marginally towards the outskirts. Such a low internal dispersion is somewhat at odds with the cluster's orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruption is high; a tidal radius two-thirds the currently accepted value would eliminate the discrepancy. The cluster mass-to-light ratio is also small, M/L(sub V) = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a cluster of moderate and concentration with a mass-to-light ratio among the lowest known. The astrometric distance to the cluster is also smaller than expected, 1.72 +/- 0.14 kpc. This is only consistent with conventional estimates of the luminosity of horizontal branch stars provided an extinction law R = A(sub V)/E(B-V) approximately 4 is adopted, as has been suggested recently by several authors.

  13. Revisiting the region of the open cluster NGC 5606

    NASA Astrophysics Data System (ADS)

    Orsatti, A. M.; Feinstein, C.; Vega, E. I.; Vergne, M. M.

    2007-08-01

    We present polarimetric observations in the UBVRI bands corresponding to 54 stars located in the direction of NGC 5606. Our intention is to analyze the dust characteristics between the Sun and the cluster, as well as to confirm doubtful memberships using polarimetric tools. We also want to determine if a group of 11 B and A stars identified in the past by Vázquez & Feinstein (1991, A&AS, 87, 383) in front of NGC 5606 has any physical entity. From polarimetric data we have found at least two dust layers along the line of sight to the open cluster. The observations show that both dust layers have their local magnetic field with an orientation which is close to the direction of the Galactic Plane (θ = 70.0 °), but the direction of the polarimetric vector for the members of the cluster seems to be lower than this value. NGC 5606 can be polarimetrically characterized with P_max = 2.97% and θv = 63.5 °. The internal dispersion of the polarization values for the members of NGC 5606 seems to be compatible with intracluster dust. We were able to add four possible new members to the list of stars in NGC 5606, and to reject others accepted as members in past investigations; and we identified 17 (out of the 54 observed stars) with intrinsic polarization in their light. The group of late B- and A-type stars could be physically related, with characteristics of an open cluster of intermediate age (between 0.79 and 1. × 108 yr). For this group we obtained representative values of P = 2.12% and θv = 70.0 °. The new cluster, which we have provisionally named Anon (La Plata 1), extends from NE to SW across the face of NGC 5606 covering about 10'. The fitting procedure of Schmidt-Kaler's ZAMS (1982, in Landolt/Bornstein, Neue Series VI/2b) was used to derive the distance to the group, obtaining a distance modulus of Vo - Mv = 9.90 (649 pc from the Sun). The mean color excess associated with the small group is EB-V = 0.27 ± 0.08 mag and the dust distribution shows great

  14. Photometric study of the young open cluster NGC 3293

    NASA Astrophysics Data System (ADS)

    Baume, G.; Vázquez, R. A.; Carraro, G.; Feinstein, A.

    2003-05-01

    Deep and extensive CCD photometric observations at UBV(RI)_CHalpha were carried out in the area of the open cluster NGC 3293. The new data set allows to see the entire cluster sequence down to MV ~ +4.5, revealing that stars with MV < -2 are evolving off the main sequence; stars with -2 < MV < +2 are located on the main sequence and stars with MV > +2 are placed above it. According to our analysis, the cluster distance is d = 2750 +/- 250 pc (V0-MV = 12.2 +/- 0.2) and its nuclear age is 8 +/- 1 Myr. NGC 3293 contains an important fraction of pre-main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to 2.5 cal Msun and a mean contraction age of 10 Myr. This last value does not differ too much from the nuclear age estimate. If we take into account the many factors that may affect the PMS star positions on the colour-magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Using the Halpha data, we detected nineteen stars with signs of Halpha emission in the region of NGC 3293, another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope of x = 1.2 +/- 0.2, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters. Based on observations collected at UTSO, ESO (Dutch 0.9 m telescope) and CASLEO. The CCD and data acquisition system at CASLEO has been partly financed by R.M. Rich through U.S. NSF Grant AST-90-15827. Full Table 1 is only available in electronic form at the CDS via an anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/549

  15. OPEN CLUSTERS IN THE MILKY WAY OUTER DISK: NEWLY DISCOVERED AND UNSTUDIED CLUSTERS IN THE SPITZER GLIMPSE-360, CYG-X, AND SMOG SURVEYS

    SciTech Connect

    Zasowski, G.; Beaton, R. L.; Hamm, K. K.; Majewski, S. R.; Patterson, R. J.; Babler, B.; Churchwell, E.; Meade, M.; Whitney, B. A.; Benjamin, R. A.; Watson, C.

    2013-09-15

    Open stellar clusters are extremely valuable probes of Galactic structure, star formation, kinematics, and chemical abundance patterns. Near-infrared (NIR) data have enabled the detection of hundreds of clusters hidden from optical surveys, and mid-infrared (MIR) data are poised to offer an even clearer view into the most heavily obscured parts of the Milky Way. We use new MIR images from the Spitzer GLIMPSE-360, Cyg-X, and SMOG surveys to visually identify a large number of open cluster candidates in the outer disk of the Milky Way (65 Degree-Sign < l < 265 Degree-Sign ). Using NIR color-magnitude diagrams, stellar isochrones, and stellar reddening estimates, we derive cluster parameters (metallicity, distance, reddening) for those objects without previous identification and/or parameters in the literature. In total, we present coordinates and sizes of 20 previously unknown open cluster candidates; for 7 of these we also present metallicity, distance, and reddening values. In addition, we provide the first estimates of these values for nine clusters that had been previously cataloged. We compare our cluster sizes and other derived parameters to those in the open cluster catalog of Dias et al. and find strong similarities except for a higher mean reddening for our objects, which signifies our increased detection sensitivity in regions of high extinction. The results of this cluster search and analysis demonstrate the ability of MIR imaging and photometry to augment significantly the current census of open clusters in the Galaxy.

  16. Interstellar Extinction toward the Young Open Cluster NGC 1502

    NASA Astrophysics Data System (ADS)

    Topasna, Gregory A.; Kaltcheva, Nadia

    2017-01-01

    We present new multi-wavelength polarization measurements of 20 stars in the direction of the open cluster NGC 1502. Polarimetric results are combined with uvbyβ photometric data to obtain precise estimates of the total-to-selective extinction and distance for each star. NGC 1502 is located at the periphery of the Cam OB1 association and probably within the Orion Spur, with published distance estimates varying between 0.7 and 1.5 kpc. Our analysis suggests that the stars studied here form two concentrations along the line of sight. If a value of 3.2 for the total-to-selective extinction is assumed, the stars group at 0.8 ± 0.02 kpc and 1.1 ± 0.05 kpc. However, using the wavelength of maximum polarization to calculate the total-to-selective extinction for each star yields 0.9 ± 0.03 kpc and 1.3 ± 0.04 kpc, respectively. This approach indicates that combining polarimetric and uvbyβ data provides a more detailed stellar distribution of this region. Acknowledgments: Part of this work was supported by NSF grant AST-1516932.

  17. Gaia-ESO Survey: Properties of the intermediate age open cluster NGC 4815

    NASA Astrophysics Data System (ADS)

    Friel, E. D.; Donati, P.; Bragaglia, A.; Jacobson, H. R.; Magrini, L.; Prisinzano, L.; Randich, S.; Tosi, M.; Cantat-Gaudin, T.; Vallenari, A.; Smiljanic, R.; Carraro, G.; Sordo, R.; Maiorca, E.; Tautvaišienė, G.; Sestito, P.; Zaggia, S.; Jiménez-Esteban, F. M.; Gilmore, G.; Jeffries, R. D.; Alfaro, E.; Bensby, T.; Koposov, S. E.; Korn, A. J.; Pancino, E.; Recio-Blanco, A.; Franciosini, E.; Hill, V.; Jackson, R. J.; de Laverny, P.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Hourihane, A.; Costado, M. T.; Jofré, P.; Lind, K.

    2014-03-01

    Context. NGC 4815 is a populous ~500 Myr open cluster at Rgc ~ 7 kpc observed in the first six months of the Gaia-ESO Survey. Located in the inner Galactic disk, NGC 4815 is an important potential tracer of the abundance gradient, where relatively few intermediate age open clusters are found. Aims: The Gaia-ESO Survey data can provide an improved characterization of the cluster properties, such as age, distance, reddening, and abundance profile. Methods: We use the survey derived radial velocities, stellar atmospheric parameters, metallicity, and elemental abundances for stars targeted as potential members of this cluster to carry out an analysis of cluster properties. The radial velocity distribution of stars in the cluster field is used to define the cluster systemic velocity and derive likely cluster membership for stars observed by the Gaia-ESO Survey. We investigate the distributions of Fe and Fe-peak elements, alpha-elements, and the light elements Na and Al and characterize the cluster's internal chemical homogeneity comparing it to the properties of radial velocity non-member stars. Utilizing these cluster properties, the cluster color-magnitude diagram is analyzed and theoretical isochrones are fit to derive cluster reddening, distance, and age. Results: NGC 4815 is found to have a mean metallicity of [Fe/H] = +0.03 ± 0.05 dex (s.d.). Elemental abundances of cluster members show typically very small internal variation, with internal dispersions of ~0.05 dex. The alpha-elements [Ca/Fe] and [Si/Fe] show solar ratios, but [Mg/Fe] is moderately enhanced, while [Ti/Fe] appears slightly deficient. As with many open clusters, the light elements [Na/Fe] and [Al/Fe] are enhanced, [Na/Fe] significantly so, although the role of internal mixing and the assumption of local thermodynamical equilibrium in the analysis remain to be investigated. From isochrone fits to color-magnitude diagrams, we find a cluster age of 0.5 to 0.63 Gyr, a reddening of E(B - V) = 0.59 to 0

  18. STELLAR NUCLEOSYNTHESIS IN THE HYADES OPEN CLUSTER

    SciTech Connect

    Schuler, Simon C.; King, Jeremy R.; The, L.-S. E-mail: jking2@ces.clemson.edu

    2009-08-10

    We report a comprehensive light-element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. The abundances have been derived in a self-consistent fashion, and for each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Using the dwarfs to infer the initial composition of the giants, the combined abundance patterns confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived {sup 12}C/{sup 13}C ratio, but it fails to predict by a factor of 1.5 the observed level of {sup 12}C depletion. A similar discord appears to exist in previously reported observed and modeled C abundances of giants in the Galactic disk. Random uncertainties in the mean abundances and uncertainties related to possible systematic errors in the Hyades dwarf and giant parameter scales cannot account for the discrepancy in the observed and modeled abundances. Li abundances are derived to determine if noncanonical extra mixing, like that seen in low-mass metal-poor giants, has occurred in the Hyades giants. The Li abundance of the giant {gamma} Tau is in good accord with the predicted level of surface Li dilution, but a {approx}0.35 dex spread in the giant Li abundances is found and cannot be explained by the stellar model. Possible sources of the spread are discussed; however, it is apparent that the differential mechanism responsible for the Li dispersion must be unrelated to the uniformly low {sup 12}C abundances of the giants. Na, Mg, and Al

  19. Stellar Nucleosynthesis in the Hyades Open Cluster

    NASA Astrophysics Data System (ADS)

    Schuler, Simon C.; King, Jeremy R.; The, Lih-Sin

    2009-08-01

    We report a comprehensive light-element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. The abundances have been derived in a self-consistent fashion, and for each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Using the dwarfs to infer the initial composition of the giants, the combined abundance patterns confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived 12C/13C ratio, but it fails to predict by a factor of 1.5 the observed level of 12C depletion. A similar discord appears to exist in previously reported observed and modeled C abundances of giants in the Galactic disk. Random uncertainties in the mean abundances and uncertainties related to possible systematic errors in the Hyades dwarf and giant parameter scales cannot account for the discrepancy in the observed and modeled abundances. Li abundances are derived to determine if noncanonical extra mixing, like that seen in low-mass metal-poor giants, has occurred in the Hyades giants. The Li abundance of the giant γ Tau is in good accord with the predicted level of surface Li dilution, but a ~0.35 dex spread in the giant Li abundances is found and cannot be explained by the stellar model. Possible sources of the spread are discussed; however, it is apparent that the differential mechanism responsible for the Li dispersion must be unrelated to the uniformly low 12C abundances of the giants. Na, Mg, and Al abundances are derived as an additional

  20. An application of the KNND method for detecting nearby open clusters based on Gaia-DR1

    NASA Astrophysics Data System (ADS)

    Gao, Xin-Hua

    2017-05-01

    This paper presents a preliminary test of the k-th nearest neighbor distance (KNND) method for detecting nearby open clusters based on Gaia-DR1. We select 38 386 nearby stars (< 100 {pc}) from the Gaia-DR1 catalog, and then use the KNND method to detect overdense regions in three-dimensional space. We find two overdense regions (the Hyades and Coma Berenices (Coma Ber) open clusters), and obtain 57 reliable cluster members. Based on these cluster members, the distances to the Hyades and Coma Ber clusters are determined to be 46.0±0.2 and 83.5±0.3 pc, respectively. Our results demonstrate that the KNND method can be used to detect open clusters based on a large volume of astrometry data.

  1. Open clusters rich in red supergiants

    NASA Astrophysics Data System (ADS)

    Negueruela, Ignacio

    2015-08-01

    In the past few years, several clusters containing large numbers of red supergiants have been discovered. These clusters are amongst the most massive young clusters known in the Milky Way, with stellar masses reaching a few tens of thousands of solar masses. They have provided us, for the first time, with large homogeneous samples of red supergiants of a given age. These large populations make them, despite heavy extinction along their sightlines, powerful laboratories to understand the evolutionary status of red supergiants. While some of the clusters, such as the eponymous RSGC1, are so obscured that their members are only observable in the near-IR, at least van der Bergh-Hagen 222 is observable even in the U band, allowing for an excellent characterisation of cluster and stellar properties. The information gleaned so far from these clusters gives strong support to the idea that late-M type supergiants represent a separate class, characterised by very heavy mass loss. It also shows that the spectral-type distribution of red supergiants in the Milky Way is very strongly peaked towards M1, while providing strong hints about the possible evolutionary sequence of red supergiants. In addition, the clusters of red supergiants represent ideal tools to study metallicity in the inner regions of the Milky Way.

  2. Peakbagging in the open cluster NGC 6819: Opening a treasure chest or Pandora's box?

    NASA Astrophysics Data System (ADS)

    Handberg, R.; Miglio, A.; Brogaard, K.; Bossini, D.; Elsworth, Y. P.

    2016-09-01

    Here we report on an extensive peakbagging effort on the evolved red giant stars of the open cluster NGC 6819. This consists of around 50 stars spanning all the way up the red giant branch (RGB) and down to and including the red clump (RC). These stars represent a unique sample because of their common distance, metallicity and age. By employing sophisticated pre-processing of the time series and Markov Chain Monte Carlo (MCMC) techniques, we have extracted individual frequencies, heights, and line widths for hundreds of individual oscillation modes in the sample of stars. We show that average asteroseismic parameters derived from these can be used to distinguish the stellar evolutionary state between RGB and RC stars without having to measure the often difficult dipole modes. Furthermore, we show how the fitting of some of these dipole modes can improve the detectability of acoustic glitches arising from the helium II ionization zone and how this can potentially be used to constrain the helium content in the cluster. We also discuss some of the difficulties facing similar studies in the future, where it seems that detailed studies of star clusters are facing some difficult times ahead.

  3. CCD UBV photometry and kinematics of the open cluster NGC 225

    NASA Astrophysics Data System (ADS)

    Bilir, Selçuk; Bostancı, Z. Funda; Yontan, Talar; Güver, Tolga; Bakış, Volkan; Ak, Tansel; Ak, Serap; Paunzen, Ernst; Eker, Zeki

    2016-11-01

    We present the results of CCD UBV photometric and spectroscopic observations of the open cluster NGC 225. In order to determine the structural parameters of NGC 225, we calculated the stellar density profile in the cluster's field. We estimated the probabilities of the stars being physical members of the cluster using the existing astrometric data. The most likely members of the cluster were used in the determination of the astrophysical parameters of the cluster. We calculated the mean radial velocity of the cluster as Vr = - 8.3 ± 5.0 km s-1 from the optical spectra of eight stars in the cluster's field. Using the U - B vs B - V two-colour diagram and UV excesses of the F-G type main-sequence stars, the reddening and metallicity of NGC 225 were inferred as E (B - V) = 0.151 ± 0.047 mag and [Fe /H ] = - 0.11 ± 0.01 dex, respectively. We fitted the colour-magnitude diagrams of NGC 225 with the PARSEC isochrones and derived the distance modulus, distance and age of the cluster as μV = 9.3 ± 0.07 mag, d = 585 ± 20 pc and t = 900 ± 100 Myr, respectively. We also estimated the galactic orbital parameters and space velocity components of the cluster and found that the cluster has a slightly eccentric orbit of e = 0.07 ± 0.01 and an orbital period of Porb = 255 ± 5 Myr.

  4. Collaborative mission planning for UAV cluster to optimize relay distance

    NASA Astrophysics Data System (ADS)

    Tanil, Cagatay; Warty, Chirag; Obiedat, Esam

    Unmanned Aerial Vehicles (UAVs) coordinated path planning and intercommunication for visual exploration of a geographical region has recently become crucial. Multiple UAVs cover larger area than a single UAV and eliminate blind spots. To improve the surveillance, survivability and quality of the communication, we propose two algorithms for the route planning of UAV cluster operated in obstacle rich environment: (i) Multiple Population Genetic Algorithm (MPGA) (ii) Relay Selection Criteria (RSC). The main objective of MPGA is to minimize the total mission time while maintaining an optimal distance for communication between the neighboring nodes. MPGA utilizes evolutionary speciation techniques with a novel Feasible Population Creation Method (FPCM) and enhanced Inter-species Crossover Mechanism (ISCM) to obtain diversified routes in remarkably short time. In obtaining collision-free optimum paths, UAVs are subjected to constraints such as limited communication range, maximum maneuverability and fuel capacity. In addition to the path planning, RSC is developed for selection of UAVs relay nodes that is based on the location of the relay relative to source and destination. It is crucial since the Bit Error Rate (BER) performance of the link significantly depends on the location of the selected relay. In this paper, path planning and relay allocation algorithms are combined to have a seamless high quality monitoring of the region and to provide superior Quality of Service (QoS) for audio-video applications. Also, simulations in different operation zones with a cluster of up to six UAVs are performed to verify the feasibility of the proposed algorithms both in optimality and computation time.

  5. Open Clusters as Tracers of the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Cantat-Gaudin, Tristan

    2015-01-01

    Open clusters (OCs) are routinely used as reliable tracers of the properties and evolution of the galactic disk, as they can be found at all galactocentric distances and span a wide range of ages. More than 3000 OCs are listed in catalogues, although few have been studied in details. The goal of this work is to study the properties of open clusters. This work was conducted in the framework of the Gaia-ESO Survey (GES). GES is an observational campaign targeting more than 100,000 stars in all major components of the Milky Way, including stars in a hundred open clusters. It uses the FLAMES instrument at the VLT to produce high and medium-resolution spectra, which provide accurate radial velocities and individual elemental abundances. In this framework, the goals of the Thesis are: * to study the properties of OCs and of their stars from photometry and spectroscopy to derive their age, the extinction and the chemical composition of the stars, to begin to build a homogeneous data base. Looking at literature data it is clear that different authors derive substantially different chemical compositions, and in general OC parameters. * the study of OCs and their chemical homogeneity (or inhomogeneity) can cast light on what is still an open issue: the presence of multiple populations in clusters. While multiple generations of stars are now ubiquitously found in globular clusters in the Milky Way and in the Magellanic Clouds, they have not been yet detected in open clusters. What is the main driver of the self-pollution process? * to study the cluster formation process. All, or at least a significant fraction of stars form in clusters. Young clusters (a few Myr) can retain some of the properties of the molecular cloud they originate from and give us insight about the cluster assembly process. The first GES data release contains data for the young OC Gamma Velorum, in which two (dynamically different) subpopulations have been identified. This cluster can serve as a test case

  6. The search for delta Scuti stars in open clusters

    NASA Astrophysics Data System (ADS)

    Frandsen, S.; Arentoft, T.

    1998-05-01

    In order to improve the tests of models of stellar evolution, observations giving tighter constraints on the models were initiated by the formation of an informal group STACC (Frandsen, 1992). The purpose of the group is to search for and make observations of delta Scuti stars in open clusters. This paper presents some of the results of the search, mainly for distant open clusters with a rich population of variables. Included is an announcement of a target list (Frandsen & Arentoft 1998, The Book) and four examples of new Colour-Magnitude (CM) diagrams of open clusters considered to be interesting targets. Finally, we present the fruits of extensive searching: an open cluster that contains many delta Scuti stars. Based on observations made at the European Southern Observatory, La Silla, the Nordic Optical Telescope, ORM, La Palma and the IAC80, OT, Tenerife

  7. Looking for Interacting Binaries in Old Open Clusters

    NASA Technical Reports Server (NTRS)

    Grindley, Jonathan

    2005-01-01

    We requested a 12 ks observation of the old open cluster NGC7142 with the aim to investigate the population of interacting binaries, and compare the properties with those of interacting binaries in other old open clusters. Unfortunately, the observation suffered from long periods of background flaring, and as a result the effective exposure time was shortened to only approximately 25% of the planned exposure. The sensitivity to detect sources in the cluster was therefore much reduced, hampering a useful comparison with other clusters observed with Chandra and XMM. We detect 5 sources (all less than 300 counts) in the full field of view of the detectors; based on the large separations from the cluster center, we expect that at least 3-4 are not associated with the cluster. A brief paper that reports the results is in preparation.

  8. Hogg 12 and NGC 3590: A New Open Cluster Binary System Candidate

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Clariá, Juan J.; Ahumada, Andrea V.

    2010-05-01

    We have obtained CCD UBVIKC photometry down to V ∼ 22.0 for the open clusters Hogg 12 and NGC 3590 and the fields surrounding them. Based on photometric and morphological criteria, as well as on the stellar density in the region, our evidence is sufficient to confirm that Hogg 12 is a genuine open cluster. NGC 3590 was used as a control cluster. The color-magnitude diagrams of Hogg 12, cleaned from field star contamination, reveal that this is a solar metal content cluster, affected by E(B - V) = 0.40 ± 0.05, located at a heliocentric distance d = 2.0 ± 0.5 kpc, and of an age similar to that of NGC 3590 (t = 30 Myr). Both clusters are surprisingly small objects whose radii are barely ∼1 pc, andthey are separated in the sky by scarcely 3.6 pc. These facts, added to their similar ages, reddenings, and metallicities, allow us to consider them a new open cluster binary system candidate. Of the ∼180 open cluster binary systems estimated to exist in the Galaxy, of which 27 are actually well known, Hogg 12 and NGC 3590 appear to be one of the two closest pairs.

  9. WIYN OPEN CLUSTER STUDY LII: WIDE-FIELD CCD PHOTOMETRY OF THE OLD OPEN CLUSTER NGC 6819

    SciTech Connect

    Yang, Soung-Chul; Kim, Sang Chul; Kyeong, Jaemann; Sarajedini, Ata; Deliyannis, Constantine P.; Sarrazine, Angela R. E-mail: ata@astro.ufl.edu E-mail: asarrazi@bellsouth.net

    2013-01-01

    We present a comprehensive photometric study of the old open cluster, NGC 6819, using 1 Degree-Sign Multiplication-Sign 1 Degree-Sign field VI MOSAIC CCD imaging taken with the WIYN 0.9 m telescope. The resultant color-magnitude diagram (CMD) shows a well-developed main sequence (MS) extending from V {approx} 14.5 mag down to our photometric limit of V {approx} 21 mag. Fitting theoretical isochrones with the adopted values of the reddening and metallicity (E(B - V) = 0.14, [Fe/H] = +0.09 dex) to the observed CMD yields a distance modulus of (m - M){sub 0} = 11.93 {+-} 0.10 and an age of {approx}2.6 Gyr for NGC 6819. Our wide-field imaging reveals that NGC 6819 is larger in areal extent (R = 13') than previously thought. The wide field also benefits our estimate of the degree of field star contamination, and ultimately yields improved measurements of the structural parameters (r{sub c} = 2.'80, r{sub t} = 38.'2, and r{sub h} = 7') and tidal mass of the cluster (M {sub tid} = 3542.4 M {sub Sun }). The flattened luminosity and mass functions indicate that NGC 6819 has experienced mass segregation as a result of its dynamical evolution. Our variability study of the cluster blue straggler star (BSS) population using the Welch-Stetson variability index (I {sub WS}) has revealed a number of variable BSS candidates.

  10. New variable stars in open clusters. I. Methods and results for 20 open clusters

    NASA Astrophysics Data System (ADS)

    Paunzen, E.; Zwintz, K.; Maitzen, H. M.; Pintado, O. I.; Rode-Paunzen, M.

    2004-04-01

    We present high precision CCD photometry of 1791 objects in 20 open clusters with an age of 10 Myr to 1 Gyr. These observations were performed within the Δ a photometric system which is primarily used to detect chemically peculiar stars of the upper main sequence. Time bases range from 30 min up to 60 days with data from several nights. We describe the time series analysis reaching a detection limit of down to 0.006 mag for apparent variability. In total, we have detected 35 variable objects of which four are not members of their corresponding clusters. The variables cover the entire Hertzsprung-Russell diagram, hence they are interesting targets for follow-up observations. Based on observations obtained at Complejo Astronómico el Leoncito (CASLEO), operated under the agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba y San Juan; ESO-La Silla and UTSO-Las Campanas.

  11. Spin alignment of stars in old open clusters

    NASA Astrophysics Data System (ADS)

    Corsaro, Enrico; Lee, Yueh-Ning; García, Rafael A.; Hennebelle, Patrick; Mathur, Savita; Beck, Paul G.; Mathis, Stephane; Stello, Dennis; Bouvier, Jérôme

    2017-03-01

    Stellar clusters form by gravitational collapse of turbulent molecular clouds, with up to several thousand stars per cluster1. They are thought to be the birthplace of most stars and therefore play an important role in our understanding of star formation, a fundamental problem in astrophysics2,3. The initial conditions of the molecular cloud establish its dynamical history until the stellar cluster is born. However, the evolution of the cloud's angular momentum during cluster formation is not well understood4. Current observations have suggested that turbulence scrambles the angular momentum of the cluster-forming cloud, preventing spin alignment among stars within a cluster5. Here we use asteroseismology6-8 to measure the inclination angles of spin axes in 48 stars from the two old open clusters NGC 6791 and NGC 6819. The stars within each cluster show strong alignment. Three-dimensional hydrodynamical simulations of proto-cluster formation show that at least 50% of the initial proto-cluster kinetic energy has to be rotational in order to obtain strong stellar-spin alignment within a cluster. Our result indicates that the global angular momentum of the cluster-forming clouds was efficiently transferred to each star and that its imprint has survived several gigayears since the clusters formed.

  12. Distance Open Learning in the Developing Asian Countries: Problems and Possible Solutions. ZIFF Papiere 117.

    ERIC Educational Resources Information Center

    Ramanujam, P. R.

    Problems facing distance open learning in the developing Asian countries were examined, and possible solutions were proposed. The prominent features of distance and open learning in 10 developed nations were identified. Existing distance education (DE) systems in developing nations in Asia, Africa, and Latin America were reviewed and found to…

  13. First estimates of the fundamental parameters of the very small open cluster Ruprecht 1

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Clariá, J. J.; Parisi, M. C.; Ahumada, A. V.

    New CCD observations with the Washington C and T1 filters in the field of the open cluster Ruprecht 1 are presented. The cluster turned out to be very small, its linear radius being 2.6 +/- 0.2 pc. Ruprecht 1 is moderately reddened [E(B-V) = 0.25] and moderately young (~ 230 Myr). Heliocentric distances of 1.9 +/- 0.4 kpc and 1.5 +/- 0.3 kpc are determined for Z (metallicity) = 0.02 and 0.08, respectively, although evidence is presented favouring a solar metal content rather than a subsolar one. We compare the cluster properties with tose of known open clusters located within 1 kpc around it.

  14. The Palomar-Las Campanas Observatory-NOAO (PLCON) Open Cluster Survey

    NASA Astrophysics Data System (ADS)

    Phelps, R. L.; Tollefson, J.; Reafsnyder, S.; Frinchaboy, P.; Craig, Aidan; Postlethwaite, J.; Marshall, T.

    2000-12-01

    The Palomar-Las Campanas Observatory-NOAO (PLCON) Open Cluster Survey is a long-term survey intended to provide CCD derived, VI color-magnitude diagrams for the majority of the Milky Way's open clusters, most of which have been poorly studied in the past, or never studied at all. From these data, systematic estimates of cluster reddenings, distances and ages can be derived using a limited number of telescopes, CCDs and filter sets. These data will be useful for systematic studies of Galactic structure in the disk, the properties of unique/interesting stars within clusters, stellar evolution theory, and a host of other timely astrophysical questions. This paper will report on recent results from the Survey. This work is supported, in part, by grants from the National Science Foundation and the California State University, Sacramento Research and Creative Activity Awards Program.

  15. Open and Distance Learning Methodologies in Higher Education

    ERIC Educational Resources Information Center

    Cacheiro, Mariluz; Rodrigo, Covadonga; Laherran, Gorka; Olmo, Alicia

    2006-01-01

    The Spanish National Distance Education University (UNED) Model is presented in which traditional distance courses are complemented by CiberUNED services. The methodology used from the teacher's point of view is analysed and an overview of the strategies that has been emphasized using virtual courses are presented. Distance teaching guidelines has…

  16. Occasional Papers in Open and Distance Learning, Number 18.

    ERIC Educational Resources Information Center

    Donnan, Peter, Ed.

    Six papers examine innovations and trends in distance learning, frequently drawing upon empirical research or informal observations on distance learning students at Charles Sturt University (Australia). "On-Line Study Packages for Distance Education: Some Considerations of Conceptual Parameters" (Dirk M. R. Spennemann) discusses issues…

  17. Attitudes and Perceptions of Students to Open and Distance Learning in Nigeria

    ERIC Educational Resources Information Center

    Ojo, David Olugbenga; Olakulehin, Felix Kayode

    2006-01-01

    In the West African Region of Africa, the National Open University of Nigeria (NOUN) is the first full fledged university that operates in an exclusively open and distance learning (ODL) mode of education. NOUN focuses mainly on open and distance teaching and learning system, and delivers its courses materials via print in conjunction with…

  18. China's Radio and TV Universities: Reflections on Theory and Practice of Open and Distance Learning

    ERIC Educational Resources Information Center

    Wei, Runfang

    2010-01-01

    Distance education and open learning are western innovations, representing the educational concepts, cultures and societies of western countries. The introduction of distance education and the adoption of open learning in China's radio and TV universities are by no means an indication that they will and can be copied wholesale. Open and distance…

  19. On the physical reality of overlooked open clusters

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.

    2017-04-01

    We present UBVRI and CT1T2 photometry for 15 catalogued open clusters of relative high brightness and compact appearance. From these unprecedented photometric data sets, covering wavelengths from the blue up to the near-infrared, we performed a thorough assessment of their reality as stellar aggregates. We statistically assigned to each observed star within the object region a probability of being a fiducial feature of that field in terms of its local luminosity function, colour distribution and stellar density. Likewise, we used accurate parallaxes and proper motions measured by the Gaia satellite to help our decision on the open cluster reality. 10 catalogued aggregates did not show any hint of being real physical systems; three of them had been assumed to be open clusters in previous studies, though. On the other hand, we estimated reliable fundamental parameters for the remaining five studied objects, which were confirmed as real open clusters. They resulted to be clusters distributed in a wide age range, 8.0 ≤ log (t yr-1) ≤ 9.4, of solar metal content and placed between 2.0 and 5.5 kpc from the Sun. Their ages and metallicities are in agreement with the presently known picture of the spatial distribution of open clusters in the Galactic disc.

  20. On the physical reality of overlooked open clusters

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.

    2017-01-01

    We present UBVRI and CT1T2 photometry for fifteen catalogued open clusters of relative high brightness and compact appearance. From these unprecedented photometric data sets, covering wavelengths from the blue up to the near-infrared, we performed a thorough assessment of their reality as stellar aggregates. We statistically assigned to each observed star within the object region a probability of being a fiducial feature of that field in terms of its local luminosity function, colour distribution and stellar density. Likewise, we used accurate parallaxes and proper motions measured by the Gaia satellite to help our decision on the open cluster reality. Ten catalogued aggregates did not show any hint of being real physical systems; three of them had been assumed to be open clusters in previous studies, though. On the other hand, we estimated reliable fundamental parameters for the remaining five studied objects, which were confirmed as real open clusters. They resulted to be clusters distributed in a wide age range, 8.0 ≤ log (t yr-1) ≤ 9.4, of solar metal content and placed between 2.0 and 5.5 kpc from the Sun. Their ages and metallicities are in agreement with the presently known picture of the spatial distribution of open clusters in the Galactic disc.

  1. Membership determination of open cluster with parametric method: cross entropy

    NASA Astrophysics Data System (ADS)

    Khoirul Fitriana, Itsna; Ikbal Arifiyanto, M.

    2016-11-01

    Stellar open clusters are useful for studying the structure and evolution of Galaxy. Determination of the open cluster members can be viewed from their kinematics: proper motion and radial velocity. It is because the star cluster members will have a motion in the same direction, towards a convergent point. Parametric method with a double elliptic bivariate gaussian function which contains 11 parameters is used as a model of the proper motion distribution. The value of these parameters are determined numerically by cross entropy method. This method is a method of data fitting using the likelihood function whose value is maximized to get the proper parameters. This method solves the problem of determining the initial value that is often difficult to determine in other numerical methods. There are four open clusters which we have analysed: NGC 2244, ASCC 100, NGC 5168, and NGC 2169. The resulting of proper motion parameters of this method matches the parameters in the literature.

  2. Highly dynamically evolved intermediate-age open clusters

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Dias, Wilton S.; Sampedro, Laura M.

    2017-04-01

    We present a comprehensive UBVRI and Washington CT1T2 photometric analysis of seven catalogued open clusters, namely: Ruprecht 3, 9, 37, 74, 150, ESO 324-15 and 436-2. The multiband photometric data sets in combination with 2MASS photometry and Gaia astrometry for the brighter stars were used to estimate their structural parameters and fundamental astrophysical properties. We found that Ruprecht 3 and ESO 436-2 do not show self-consistent evidence of being physical systems. The remained studied objects are open clusters of intermediate age (9.0 ≤ log(t yr-1) ≤ 9.6), of relatively small size (rcls ∼ 0.4-1.3 pc) and placed between 0.6 and 2.9 kpc from the Sun. We analysed the relationships between core, half-mass, tidal and Jacoby radii as well as half-mass relaxation times to conclude that the studied clusters are in an evolved dynamical stage. The total cluster masses obtained by summing those of the observed cluster stars resulted to be ∼10-15 per cent of the masses of open clusters of similar age located closer than 2 kpc from the Sun. We found that cluster stars occupy volumes as large as those for tidally filled clusters.

  3. Deep Observations of the Open Cluster NGC 6253

    NASA Astrophysics Data System (ADS)

    Jeffery, E. J.

    2015-06-01

    We have obtained deep observations of the metal-rich open cluster NGC 6253 with GMOS on the Gemini-South telescope, with the goal of observing the cluster white dwarfs for the first time. These observations are an important piece and further test of the variously proposed scenarios to explain the formation of the strange white dwarfs in the metal rich open cluster NGC 6791. We will use the new observations of NGC 6253 to measure the cluster's white dwarf age and search for any anomalies in the white dwarf luminosity function. The high metallicity of this cluster will allow us to explore and better understand the formation of white dwarfs in such a high metallicity environment. These observations are an important piece in the continuing puzzle that has important implications on mass loss, white dwarf cooling, and stellar evolution as a whole.

  4. A SPITZER VIEW OF THE YOUNG OPEN CLUSTER NGC 2264

    SciTech Connect

    Sung, Hwankyung; Stauffer, John R.; Bessell, Michael S. E-mail: stauffer@ipac.caltech.edu

    2009-10-15

    We have performed mid-IR photometry of the young open cluster NGC 2264 using the images obtained with the Spitzer Space Telescope Infrared Array Camera and Multiband Imaging Photometer for Spitzer instruments and presented a normalized classification scheme of young stellar objects in various color-color diagrams to make full use of the information from multicolor photometry. These results are compared with the classification scheme based on the slope of the spectral energy distribution (SED). From the spatial distributions of Class I and II stars, we have identified two subclusterings of Class I objects in the CONE region of Sung et al. The disked stars in the other star-forming region S Mon are mostly Class II objects. These three regions show a distinct difference in the fractional distribution of SED slopes as well as the mean value of SED slopes. The fraction of stars with primordial disks is nearly flat between log m = 0.2 and -0.5 and that of transition disks is very high for solar mass stars. In addition, we have derived a somewhat higher value of the primordial disk fraction for NGC 2264 members located below the main pre-main-sequence locus (so-called BMS stars). This result supports the idea that BMS stars are young stars with nearly edge-on disks. We have also found that the fraction of primordial disks is very low near the most massive star S Mon and increases with distance from S Mon.

  5. CCD UBV(RI)C and 2MASS photometry of seven open clusters

    NASA Astrophysics Data System (ADS)

    Akkaya Oralhan, {İ.; Michel, R.

    Fundamental astrophysical parameters have been derived for Be 45, Be 55, Di 07, Feib 01, Ki 02, NGC 457 and NGC 1548 open clusters (OCs) using CCD U BV (RI)_C photometric data and PPMXL database. CCD U BV (RI)_C photometric data observed with the 84 cm telescope at the San Pedro Mártir National Astronomical Observatory (SPMO), México. The cluster members and field stars in the cluster regions have separated through their Proper Motion (PM) vector point diagrams. We have used JH{Ks} photometry of 2MASS data taken from PPMXL catalogue to have stellar Radial Density Profile (RDP) and determine limit radius of these seven clusters. Five different Color-Magnitude diagrams ane one color-color diagram have been used together with Padova isochrones and intrinsic-colour calibrations to obtain reddenings, metallicities, distance moduli, and ages for these seven clusters.

  6. An application of the k-th nearest neighbor method to open cluster membership determination

    NASA Astrophysics Data System (ADS)

    Gao, Xin-Hua

    2016-12-01

    We introduce a non-parametric method for open cluster membership determination in three-dimensional (3D) velocity space (proper motion and radial velocity). Clean 3D cluster members can be obtained by statistically analyzing the Euclidean distance between each star and its k-th nearest neighbor in 3D velocity space. We use 513 sample stars in the direction of open cluster M67 to construct a 3D velocity space and test our method; 291 3D cluster members are obtained. The color-magnitude diagram, proper motions, radial velocities and spatial distribution of these 3D cluster members demonstrate the effectiveness of our method. From the 291 3D cluster members, the mean radial velocity and absolute proper motion of M67 are Vr = +33.46 ± 0.05 km s-1 and (PMRA, PMDEC) = (-7.64 ± 0.07, -5.98 ± 0.07) mas yr-1, respectively. In addition, we use 640 sample stars with precise proper motions and radial velocities in the direction of open cluster NGC 188 to test our method. The test results also show that our method is effective.

  7. Chemical abundance gradients from open clusters in the Milky Way disk: Results from the APOGEE survey

    NASA Astrophysics Data System (ADS)

    Cunha, K.; Frinchaboy, P. M.; Souto, D.; Thompson, B.; Zasowski, G.; Allende Prieto, C.; Carrera, R.; Chiappini, C.; Donor, J.; García-Hernández, D. A.; García Pérez, A. E.; Hayden, M. R.; Holtzman, J.; Jackson, K. M.; Johnson, J. A.; Majewski, S. R.; Mészáros, S.; Meyer, B.; Nidever, D. L.; O'Connell, J.; Schiavon, R. P.; Schultheis, M.; Shetrone, M.; Simmons, A.; Smith, V. V.; et al.

    2016-09-01

    Metallicity gradients provide strong constraints for understanding the chemical evolution of the Galaxy. We report on radial abundance gradients of Fe, Ni, Ca, Si, and Mg obtained from a sample of 304 red-giant members of 29 disk open clusters, mostly concentrated at galactocentric distances between ˜ 8-15 kpc, but including two open clusters in the outer disk. The observations are from the APOGEE survey. The chemical abundances were derived automatically by the ASPCAP pipeline and these are part of the SDSS III Data Release 12. The gradients, obtained from least squares fits to the data, are relatively flat, with slopes ranging from -0.026 to -0.033 dex kpc-1 for the α-elements [O/H], [Ca/H], [Si/H], and [Mg/H], and -0.035 dex kpc-1 and -0.040 dex kpc-1 for [Fe/H] and [Ni/H], respectively. Our results are not at odds with the possibility that metallicity ([Fe/H]) gradients are steeper in the inner disk ({R_GC˜ 7}-12 kpc) and flatter towards the outer disk. The open cluster sample studied spans a significant range in age. When breaking the sample into age bins, there is some indication that the younger open cluster population in our sample (log age < 8.7) has a flatter metallicity gradient when compared with the gradients obtained from older open clusters.

  8. The Distance to the Massive Galactic Cluster Westerlund 2 from a Spectroscopic and HST Photometric Study

    NASA Astrophysics Data System (ADS)

    Vargas Álvarez, Carlos A.; Kobulnicky, Henry A.; Bradley, David R.; Kannappan, Sheila J.; Norris, Mark A.; Cool, Richard J.; Miller, Brendan P.

    2013-05-01

    We present a spectroscopic and photometric determination of the distance to the young Galactic open cluster Westerlund 2 using WFPC2 imaging from the Hubble Space Telescope (HST) and ground-based optical spectroscopy. HST imaging in the F336W, F439W, F555W, and F814W filters resolved many sources previously undetected in ground-based observations and yielded photometry for 1136 stars. We identified 15 new O-type stars, along with two probable binary systems, including MSP 188 (O3 + O5.5). We fit reddened spectral energy distributions based on the Padova isochrones to the photometric data to determine individual reddening parameters RV and AV for O-type stars in Wd2. We find average values langRV rang = 3.77 ± 0.09 and langAV rang = 6.51 ± 0.38 mag, which result in a smaller distance than most other spectroscopic and photometric studies. After a statistical distance correction accounting for close unresolved binaries (factor of 1.08), our spectroscopic and photometric data on 29 O-type stars yield that Westerlund 2 has a distance langdrang = 4.16 ± 0.07 (random) +0.26 (systematic) kpc. The cluster's age remains poorly constrained, with an upper limit of 3 Myr. Finally, we report evidence of a faint mid-IR polycyclic aromatic hydrocarbon ring surrounding the well-known binary candidate MSP 18, which appears to lie at the center of a secondary stellar grouping within Westerlund 2. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  9. THE DISTANCE TO THE MASSIVE GALACTIC CLUSTER WESTERLUND 2 FROM A SPECTROSCOPIC AND HST PHOTOMETRIC STUDY

    SciTech Connect

    Vargas Alvarez, Carlos A.; Kobulnicky, Henry A.; Bradley, David R.; Kannappan, Sheila J.; Norris, Mark A.; Cool, Richard J.; Miller, Brendan P. E-mail: chipk@uwyo.edu E-mail: sheila@physics.unc.edu E-mail: rcool@obs.carnegiescience.edu

    2013-05-15

    We present a spectroscopic and photometric determination of the distance to the young Galactic open cluster Westerlund 2 using WFPC2 imaging from the Hubble Space Telescope (HST) and ground-based optical spectroscopy. HST imaging in the F336W, F439W, F555W, and F814W filters resolved many sources previously undetected in ground-based observations and yielded photometry for 1136 stars. We identified 15 new O-type stars, along with two probable binary systems, including MSP 188 (O3 + O5.5). We fit reddened spectral energy distributions based on the Padova isochrones to the photometric data to determine individual reddening parameters R{sub V} and A{sub V} for O-type stars in Wd2. We find average values (R{sub V} ) = 3.77 {+-} 0.09 and (A{sub V} ) = 6.51 {+-} 0.38 mag, which result in a smaller distance than most other spectroscopic and photometric studies. After a statistical distance correction accounting for close unresolved binaries (factor of 1.08), our spectroscopic and photometric data on 29 O-type stars yield that Westerlund 2 has a distance (d) = 4.16 {+-} 0.07 (random) +0.26 (systematic) kpc. The cluster's age remains poorly constrained, with an upper limit of 3 Myr. Finally, we report evidence of a faint mid-IR polycyclic aromatic hydrocarbon ring surrounding the well-known binary candidate MSP 18, which appears to lie at the center of a secondary stellar grouping within Westerlund 2.

  10. Integrated spectral properties of 7 galactic open clusters

    NASA Astrophysics Data System (ADS)

    Ahumada, A. V.; Clariá, J. J.; Bica, E.; Piatti, A. E.

    2000-01-01

    This paper presents flux-calibrated integrated spectra in the range 3600-9000 Ä for 7 concentrated, relatively populous Galactic open clusters. We perform simultaneous estimates of age and foreground interstellar reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of template cluster spectra with known parameters. For five clusters these two parameters have been determined for the first time (Ruprecht 144, BH 132, Pismis 21, Lyng\\aa 11 and BH 217), while the results here derived for the remaining two clusters (Hogg 15 and Melotte 105) show very good agreement with previous studies based mainly on colour-magnitude diagrams. We also provide metallicity estimates for six clusters from the equivalent widths of CaII triplet and TiO features. The present cluster sample improves the age resolution around solar metal content in the cluster spectral library for population synthesis. We compare the properties of the present sample with those of clusters in similar directions. Hogg 15 and Pismis 21 are among the most reddened clusters in sectors centered at l = 270o and l = 0o, respectively. Besides, the present results would favour an important dissolution rate of star clusters in these zones. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

  11. Photometric and spectroscopic study of the intermediate-age open cluster NGC 2355

    NASA Astrophysics Data System (ADS)

    Donati, P.; Bragaglia, A.; Carretta, E.; D'Orazi, V.; Tosi, M.; Cusano, F.; Carini, R.

    2015-11-01

    In this paper we analyse the evolutionary status and properties of the old open cluster NGC 2355, located in the Galactic anticentre direction, as a part of the long-term programme Bologna Open Clusters Chemical Evolution. NGC 2355 was observed with the Large Binocular Camera at the Large Binocular Telescope using the Bessel B, V, and Ic filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram method, as done in other papers of this series. Additional spectroscopic observations with the Fibre-fed Echelle Spectrograph at the Nordic Optical Telescope of three giant stars were used to determine the chemical properties of the cluster. Our analysis shows that NGC 2355 has metallicity slightly less than solar, with [Fe/H]= -0.06 dex, age between 0.8 and 1 Gyr, reddening E(B - V) in the range 0.14-0.19 mag, and distance modulus (m - M)0 of about 11 mag. We also investigate the abundances of O, Na, Al, α, iron-peak, and neutron capture elements, showing that NGC 2355 falls within the abundance distribution of similar clusters (same age and metallicity). The Galactocentric distance of NGC 2355 places it at the border between two regimes of metallicity distribution; this makes it an important cluster for the study of the chemical properties and evolution of the disc.

  12. Angular cross-relations of Abell clusters in different distance classes

    NASA Technical Reports Server (NTRS)

    Szalay, A. S.; Hollosi, J.; Toth, G.

    1989-01-01

    The angular autocorrelation and cross-correlation functions of the D = 1 ... 4, D = 5, and D = 6 distance class Abell clusters are estimated. There is a strong anticorrelation between the most distant D = 6 and the closest D = 1 ... 4 subsamples. It is suggested that an artifact of the cluster identification process presumably due to the finite angular size of the cluster. This anticorrelation seems to contradict some recent estimations of projection contaminations in the Abell catalog. The angular proximity of a foreground cluster may have caused a background cluster not to be counted as it was thought to be a subcluster or it was erroneously assigned to a nearer distance class.

  13. The Membership and Distance of the Open Cluster Collinder 419

    DTIC Science & Technology

    2010-09-01

    Univ. Obs.) Indebetouw, R., et al. 2005, ApJ, 619, 931 Kharchenko, N . V., Piskunov , A. E., Röser, S., Schilbach, E., & Scholz, R.-D. 2005, A&A, 438...primary of the system, Aa1, has a spectral type of O9 V:(( n )) (Walborn 1972), with the suffix indicating slightly broadened lines. McKibben et al...comparison between the target stars and the template spectra. Our spectra for the combined flux of Aa1, Aa2, and Ab agree with the O9 V:(( n

  14. Singlet-paired coupled cluster theory for open shells.

    PubMed

    Gomez, John A; Henderson, Thomas M; Scuseria, Gustavo E

    2016-06-28

    Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior for strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.

  15. Radial Velocities, Metallicities, and Improved Fundamental Parameters of Outer Disk Open Clusters

    NASA Astrophysics Data System (ADS)

    Zasowski, Gail; Hamm, K.; Beaton, R.; Damke, G.; Carlberg, J. K.; Majewski, S. R.; Frinchaboy, P. M.

    2014-01-01

    Open stellar clusters have proven to be powerful tools for understanding the structure and stellar evolution of our Galaxy. Using photometry from 2MASS and the new Spitzer-IRAC GLIMPSE-360 surveys, Zasowski et al. (2013) identified and characterized more than a dozen new or poorly studied, heavily reddened open clusters in the outer Galactic disk. Here, we present follow-up spectroscopy for 11 of the clusters. Low resolution optical spectra were obtained with the DIS spectrograph on the Apache Point Observatory 3.5-meter telescope (R˜1200) for candidate members of seven clusters (GLM-CYGX 16, GLM-G360 18, GLM-G360 105, SAI 24, Berkeley 14, Berkeley 14a, and Czernik 20), and with the B&C spectrograph on the Las Campanas Observatory duPont telescope (R˜5400) for three clusters (GLM-G360 50, GLM-G360 75, and GLM-G360 79). High resolution (R˜22,500) infrared (H-band) spectra were also obtained for one cluster (GLM-G360 90) as part of an ancillary program for the SDSS-III/APOGEE survey. We use the mean chemical abundances and radial velocities (RVs) to identify likely cluster members and then revisit our previous isochrone fits. With reddening constrained by the Rayleigh-Jeans Color Excess method and mean metallicities by spectroscopy, the cluster distances and ages are estimated from improved isochrone fits to the stellar overdensity, weighted by confirmed RV and/or abundance members.

  16. Costing Distance Education and Open Learning in Sub-Saharan Africa: Working Group on Distance Education and Open Learning-- A Survey of Policy and Practice. Final Report

    ERIC Educational Resources Information Center

    Commonwealth of Learning, 2004

    2004-01-01

    Ideological arguments are made for open learning, economic ones for distance education. If it can produce similar results to those of conventional education at a lower cost, then distance education has a powerful appeal. With increasing demand for access to educational opportunities at all levels, and often decreasing budgets in real terms for…

  17. Costing Distance Education and Open Learning in Sub-Saharan Africa: Working Group on Distance Education and Open Learning-- A Survey of Policy and Practice. Final Report

    ERIC Educational Resources Information Center

    Commonwealth of Learning, 2004

    2004-01-01

    Ideological arguments are made for open learning, economic ones for distance education. If it can produce similar results to those of conventional education at a lower cost, then distance education has a powerful appeal. With increasing demand for access to educational opportunities at all levels, and often decreasing budgets in real terms for…

  18. Why the Information Highway? Lessons from Open & Distance Learning.

    ERIC Educational Resources Information Center

    Roberts, Judith M., Ed.; Keough, Erin M., Ed.

    Containing practical applications supported by pertinent theory and analysis, this book is designed for educators navigating the information highway. The 13 chapters are divided into three sections--emerging issues, case studies, and analysis--and are as follows: (1) "Distinctions in Distance: Is Distance Education an Obsolete Term?" (M.…

  19. Virtual Proctoring in Distance Education: An Open-Source Solution

    ERIC Educational Resources Information Center

    Rose, Chris

    2009-01-01

    Students will cheat during exams, that is nothing new, but now that the Higher Education Act requires the proctoring of exams, distance education institutions now find that both they and their students have a major problem. Exams have to be proctored, but requiring distance education students to search out a reliable proctor and travel to a…

  20. BVI Photometric Study of the Old Open Cluster Ruprecht 6

    NASA Astrophysics Data System (ADS)

    Kim, Sang Chul; Kyeong, Jaemann; Park, Hong Soo; Han, Ilseung; Lee, Joon Hyeop; Moon, Dae-Sik; Lee, Youngdae; Kim, Seongjae

    2017-06-01

    We present a BVI optical photometric study of the old open cluster Ruprecht 6 using the data obtained with the SMARTS 1.0 m telescope at the CTIO, Chile. Its color-magnitude diagrams show the clear existence of the main-sequence stars, whose turn-off point is located around V ≈ 18.45 mag and B-V ≈ 0.85 mag. Three red clump (RC) stars are identified at V = 16.00 mag, I = 14.41 mag and B-V = 1.35 mag. From the mean K_s-band magnitude of RC stars (K_s=12.39 ± 0.21 mag) in Ruprecht 6 from 2MASS photometry and the known absolute magnitudes of the RC stars (M_{K_S} = -1.595 ± 0.025 mag), we obtain the distance modulus to Ruprecht 6 of (m-M)_0 = 13.84 ± 0.21 mag (d=5.86 ± 0.60 kpc). From the (J-K_s) and (B-V) colors of the RC stars, comparison of the (B-V) and (V-I) colors of the bright stars in Ruprecht 6 with those of the intrinsic colors of dwarf and giant stars, and the PARSEC isochrone fittings, we derive the reddening values of E(B-V) = 0.42 mag and E(V-I) = 0.60 mag. Using the PARSEC isochrone fittings onto the color-magnitude diagrams, we estimate the age and metallicity to be: log(t)=9.50 ± 0.10 (t=3.16 ± 0.82 Gyr) and [Fe/H] = -0.42 ± 0.04 dex. We present the Galactocentric radial metallicity gradient analysis for old (age > 1 Gyr) open clusters of the Dias et al. catalog, which likely follow a single relation of [Fe/H] =(-0.034±0.007) R_{GC} + (0.190±0.080) (rms = 0.201) for the whole radial range or a dual relation of [Fe/H] =(-0.077±0.017) R_{GC} + (0.609±0.161) (rms = 0.152) and constant ([Fe/H] ˜ -0.3 dex) value, inside and outside of R_{GC} ˜ 12 kpc, respectively. The metallicity and Galactocentric radius (13.28± 0.54 kpc) of Ruprecht 6 obtained in this study seem to be consistent with both of the relations.

  1. Occasional Papers in Open and Distance Learning, Number 13.

    ERIC Educational Resources Information Center

    Donnan, Peter, Ed.

    Each of the four papers in this collection is concerned with open learning in one form or another. "Open Learning: Some Current Perspectives" (Ian Barnard) addresses the topic of open learning in general, commenting on contemporary views and developments, and defining the term as a collective for approaches and practices that focus on…

  2. Stellar Multiplicity of the Open Cluster ASCC 113

    NASA Astrophysics Data System (ADS)

    Guerrero, C. A.; Orlov, V. G.

    2015-10-01

    We present a high angular resolution survey of binary stars and multiple systems in the galactic open cluster ASCC 113. Combining our speckle-interferometric observations with data taken from the literature, we estimated a ratio of 27:7 (single to binaries) for the the most probable members, so the multiplicity fraction for this cluster is 20.6% ± 3%. For field stars, we estimated a ratio of multiplicities to be 125:27:4:1:0:0:0:1 (between one and eight companions), which is equivalent to a multiplicity fraction of 20.9% ± 1%. We concluded that the multiplicity fraction in the cluster and in the field are statistically indistinguishable from each other; we also concluded that the multiplicity frequency in this open cluster is rather small, ˜ 20%, in agreement with high angular resolution surveys in the Pleiades, Hyades, alpha \\ Per and Praesepe.

  3. Toward open-shell nuclei with coupled-cluster theory

    SciTech Connect

    Jansen, G. R.; Hjorth-Jensen, M.; Hagen, G.; Papenbrock, T.

    2011-05-15

    We develop a method based on equation-of-motion coupled-cluster theory to describe properties of open-shell nuclei with A{+-}2 nucleons outside a closed shell. We perform proof-of-principle calculations for the ground states of the helium isotopes {sup 3-6}He and the first excited 2{sup +} state in {sup 6}He. The comparison with exact results from matrix diagonalization in small model spaces demonstrates the accuracy of the coupled-cluster methods. Three-particle-one-hole excitations of {sup 4}He play an important role for the accurate description of {sup 6}He. For the open-shell nucleus {sup 6}He, the computational cost of the method is comparable with the coupled-cluster singles-and-doubles approximation while its accuracy is similar to the coupled-cluster with singles, doubles, and triples excitations.

  4. Open clusters and associations in the Gaia era

    NASA Astrophysics Data System (ADS)

    Moraux, E.

    2016-11-01

    Open clusters and associations are groups of young stars, respectively bound and unbound, that share the same origin and disperse over time into the galactic field. As such, their formation and evolution are the key to understand the origin and properties of galactic stellar populations. Moreover, since their members have about the same age, they are ideal laboratories to study the properties of young stars and constrain stellar evolution theories. In this contribution, I present our current knowledge on open clusters and associations. I focus on the methods used to derive the statistical properties (IMF, spatial distribution, IMF) of young stars and briefly discuss how they depend on the environment. I then describe how open clusters can be used as probes to investigate the structure, dynamics and chemical composition of the Milky Way. I conclude by presenting the Gaia mission and discuss how it will revolutionize this field of research.

  5. Sunyaev-Zeldovich Effect-Derived Distances to the High-Redshift Clusters

    NASA Technical Reports Server (NTRS)

    Reese, Erik D.; Mohr, Joseph J.; Carlstrom, John E.; Joy, Marshall; Grego, Laura; Holder, Gilbert P.; Holzapfel, William L.; Hughes, John P.; Patel, Sandeep K.; Donahue, Megan

    2000-01-01

    We determine the distances to the z approximately equals 0.55 galaxy clusters MS 0451.6 - 0305 and Cl 0016 + 16 from a maximum-likelihood joint fit to interferometric Sunyaev-Zeldovich effect (SZE) and X-ray observations. We model the intracluster medium (ICM) using a spherical isothermal beta model. We quantify the statistical and systematic uncertainties inherent to these direct distance measurements, and we determine constraints on the Hubble parameter for three different cosmologies. For an Omega(sub M) = 0.3, Omega(sub lambda) = 0.7 cosmology, these distances imply a Hubble constant of 63(sup +12) (sub -9) (sup + 21) (sub -21) km/s Mp/c, where the uncertainties correspond to statistical followed by systematic at 68% confidence. The best-fit H(sub 0) is 57 km/s Mp/c for an open (Omega(sub M) = 0.3) universe and 52 km/s Mp/c for a flat (Omega(sub M) = 1) universe.

  6. NGC 1252: a high altitude, metal poor open cluster remnant

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, R.; de la Fuente Marcos, C.; Moni Bidin, C.; Carraro, G.; Costa, E.

    2013-09-01

    If stars form in clusters but most stars belong to the field, understanding the details of the transition from the former to the latter is imperative to explain the observational properties of the field. Aging open clusters are one of the sources of field stars. The disruption rate of open clusters slows down with age but, as an object gets older, the distinction between the remaining cluster or open cluster remnant (OCR) and the surrounding field becomes less and less obvious. As a result, finding good OCR candidates or confirming the OCR nature of some of the best candidates still remain elusive. One of these objects is NGC 1252, a scattered group of about 20 stars in Horologium. Here we use new wide-field photometry in the UBVI passbands, proper motions from the Yale/San Juan SPM 4.0 catalogue and high-resolution spectroscopy concurrently with results from N-body simulations to decipher NGC 1252's enigmatic character. Spectroscopy shows that most of the brightest stars in the studied area are chemically, kinematically and spatially unrelated to each other. However, after analysing proper motions, we find one relevant kinematic group. This sparse object is relatively close (˜1 kpc), metal poor and is probably not only one of the oldest clusters (3 Gyr) within 1.5 kpc from the Sun but also one of the clusters located farthest from the disc, at an altitude of nearly -900 pc. That makes NGC 1252 the first open cluster that can be truly considered a high Galactic altitude OCR: an unusual object that may hint at a star formation event induced on a high Galactic altitude gas cloud. We also conclude that the variable TW Horologii and the blue straggler candidate HD 20286 are unlikely to be part of NGC 1252. NGC 1252 17 is identified as an unrelated, Population II cannonball star moving at about 400 km s-1.

  7. Sejong Open Cluster Survey (SOS). 0. Target Selection and Data Analysis

    NASA Astrophysics Data System (ADS)

    Sung, Hwankyung; Lim, Beomdu; Bessell, Michael S.; Kim, Jinyoung S.; Hur, Hyeonoh; Chun, Moo-Young; Park, Byeong-Gon

    2013-06-01

    Star clusters are superb astrophysical laboratories containing cospatial and coeval samples of stars with similar chemical composition. We initiate the Sejong Open cluster Survey (SOS) - a project dedicated to providing homogeneous photometry of a large number of open clusters in the SAAO Johnson-Cousins' UBVI system. To achieve our main goal, we pay much attention to the observation of standard stars in order to reproduce the SAAO standard system. Many of our targets are relatively small sparse clusters that escaped previous observations. As clusters are considered building blocks of the Galactic disk, their physical properties such as the initial mass function, the pattern of mass segregation, etc. give valuable information on the formation and evolution of the Galactic disk. The spatial distribution of young open clusters will be used to revise the local spiral arm structure of the Galaxy. In addition, the homogeneous data can also be used to test stellar evolutionary theory, especially concerning rare massive stars. In this paper we present the target selection criteria, the observational strategy for accurate photometry, and the adopted calibrations for data analysis such as color-color relations, zero-age main sequence relations, Sp - M_V relations, Sp - T_{eff} relations, Sp - color relations, and T_{eff} - BC relations. Finally we provide some data analysis such as the determination of the reddening law, the membership selection criteria, and distance determination.

  8. Extended Stromgren Photometry in the Intermediate-age Open Cluster, NGC 5822

    NASA Astrophysics Data System (ADS)

    Anthony-Twarog, Barbara; Twarog, Bruce A.

    2010-02-01

    Open clusters remain invaluable objects for probing evolution on a galactic scale and testing the finer details of stellar evolution. In recent years we have focused on the study of open clusters as markers of Galactic disk evolution, evaluating the cluster parameters to test the reality and significance of detailed structure within the disk abundance gradient, confirming the apparent change in the slope of the gradient beyond the solar circle, evidence for an apparent inside-out development of the disk (Twarog et al. 1997). The current proposal is built around a comprehensive photometric study of the Hyades-age open cluster NGC 5822 as a prelude to high-dispersion spectroscopic analysis of the Li abundance for stars from the rich giant branch to the main sequence well below the so-called Li-dip. Our proposed CCD study on the extended Stromgren system, the first CCD study of this cluster on any photometric system, will supply reddening, metallicity, distance, and cluster age, while allowing us to identify and eliminate probable non- members and binaries, thereby optimizing the sample for spectroscopic followup.

  9. Multicolor CCD Photometry of the Open Cluster IC361

    DTIC Science & Technology

    2010-01-01

    journal Volume 19 Numbers 1/2 2010 Contents V. Straizys, A. Kazlauskas. Young stars in the Camelopardalis dust and molecular clouds. VI. YSOs...Vilnius + I system for 7250 stars down to 1= 19.6 mag has been obtained in the 20’ x 26’ field of the open cluster IC 361 in Camelopardalis . The catalog...1= 19.6 mag has been obtained in the 20’ x 26’ field of the open cluster IC 361 in Camelopardalis . The catalog of 1420 stars down to V ~ 18.5 mag

  10. The Enigma of the Open Cluster M29 (NGC 6913) Solved

    NASA Astrophysics Data System (ADS)

    Straižys, V.; Milašius, K.; Boyle, R. P.; Vrba, F. J.; Munari, U.; Walborn, N. R.; Černis, K.; Kazlauskas, A.; Zdanavičius, K.; Janusz, R.; Zdanavičius, J.; Laugalys, V.

    2014-11-01

    Determining the distance to the open cluster M29 (NGC 6913) has proven difficult, with distances determined by various authors differing by a factor of two or more. To solve this problem, we have initiated a new photometric investigation of the cluster in the Vilnius seven-color photometric system, supplementing it with available data in the BV and JHK s photometric systems and spectra of the nine brightest stars of spectral classes O and B. Photometric spectral classes and luminosities of 260 stars in a 15' × 15' area down to V = 19 mag are used to investigate the interstellar extinction run with distance and to estimate the distance of the Great Cygnus Rift, ~ 800 pc. The interstellar reddening law in the optical and near-infrared regions is found to be close to normal, with the ratio of extinction to color excess RBV = 2.87. The extinction AV of cluster members is between 2.5 and 3.8 mag, with a mean value of 2.97 mag, or E B - V = 1.03. The average distance of eight stars of spectral types O9-B2 is 1.54 ± 0.15 kpc. Two stars from the seven brightest stars are field stars: HDE 229238 is a background B0.5 supergiant and HD 194378 is a foreground F star. In the intrinsic color-magnitude diagram, seven fainter stars of spectral classes B3-B8 are identified as possible members of the cluster. The 15 selected members of the cluster of spectral classes O9-B8 plotted on the log L/L ⊙ versus log T eff diagram, together with the isochrones from the Padova database, give the age of the cluster as 5 ± 1 Myr.

  11. The enigma of the open cluster M29 (NGC 6913) solved

    SciTech Connect

    Straižys, V.; Milašius, K.; Černis, K.; Kazlauskas, A.; Zdanavičius, K.; Zdanavičius, J.; Laugalys, V.; Boyle, R. P.; Vrba, F. J.; Munari, U.; Walborn, N. R.; Janusz, R.

    2014-11-01

    Determining the distance to the open cluster M29 (NGC 6913) has proven difficult, with distances determined by various authors differing by a factor of two or more. To solve this problem, we have initiated a new photometric investigation of the cluster in the Vilnius seven-color photometric system, supplementing it with available data in the BV and JHK {sub s} photometric systems and spectra of the nine brightest stars of spectral classes O and B. Photometric spectral classes and luminosities of 260 stars in a 15' × 15' area down to V = 19 mag are used to investigate the interstellar extinction run with distance and to estimate the distance of the Great Cygnus Rift, ∼ 800 pc. The interstellar reddening law in the optical and near-infrared regions is found to be close to normal, with the ratio of extinction to color excess R{sub BV} = 2.87. The extinction A{sub V} of cluster members is between 2.5 and 3.8 mag, with a mean value of 2.97 mag, or E {sub B–V} = 1.03. The average distance of eight stars of spectral types O9-B2 is 1.54 ± 0.15 kpc. Two stars from the seven brightest stars are field stars: HDE 229238 is a background B0.5 supergiant and HD 194378 is a foreground F star. In the intrinsic color-magnitude diagram, seven fainter stars of spectral classes B3-B8 are identified as possible members of the cluster. The 15 selected members of the cluster of spectral classes O9-B8 plotted on the log L/L {sub ☉} versus log T {sub eff} diagram, together with the isochrones from the Padova database, give the age of the cluster as 5 ± 1 Myr.

  12. A comprehensive photometric study of dynamically evolved small van den Bergh-Hagen open clusters

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.

    2016-12-01

    We present results from Johnson UBV, Kron-Cousins RI and Washington CT1T2 photometries for seven van den Bergh-Hagen (vdBH) open clusters, namely, vdBH 1, 10, 31, 72, 87, 92, and 118. The high-quality, multiband photometric data sets were used to trace the cluster stellar density radial profiles and to build colour-magnitude diagrams and colour-colour diagrams from which we estimated their structural parameters and fundamental astrophysical properties. The clusters in our sample cover a wide age range, from ˜60 Myr up to 2.8 Gyr, are of relatively small size (˜1-6 pc) and are placed at distances from the Sun which vary between 1.8 and 6.3 kpc, respectively. We also estimated lower limits for the cluster present-day masses as well as half-mass relaxation times (tr). The resulting values in combination with the structural parameter values suggest that the studied clusters are in advanced stages of their internal dynamical evolution (age/tr ˜ 20-320), possibly in the typical phase of those tidally filled with mass segregation in their core regions. Compared to open clusters in the solar neighbourhood, the seven vdBH clusters are within more massive (˜80-380 M⊙), with higher concentration parameter values (c ˜ 0.75-1.15) and dynamically evolved ones.

  13. Integrated spectral study of small angular diameter galactic open clusters

    NASA Astrophysics Data System (ADS)

    Clariá, J. J.; Ahumada, A. V.; Bica, E.; Pavani, D. B.; Parisi, M. C.

    2017-10-01

    This paper presents flux-calibrated integrated spectra obtained at Complejo Astronómico El Leoncito (CASLEO, Argentina) for a sample of 9 Galactic open clusters of small angular diameter. The spectra cover the optical range (3800-6800 Å), with a resolution of ∼14 Å. With one exception (Ruprecht 158), the selected clusters are projected into the fourth Galactic quadrant (282o < l < 345o) near the Galactic plane (∣b∣ ≤ 9o). We performed simultaneous estimates of foreground interstellar reddening and age by comparing the continuum distribution and line strenghts of the cluster spectra with those of template cluster spectra with known parameters. We thus provide spectroscopic information independent from that derived through color-magnitude diagram studies. We found three clusters (Collinder 249, NGC 4463 and Ruprecht 122) younger than ∼40 Myr, four moderately young ones (BH 92, Harvard 5, Hogg 14 and Pismis 23) with ages within 200-400 Myr, and two intermediate-age ones (Ruprecht 158 and ESO 065-SC07) with ages within 1.0-2.2 Gyr. The derived foreground E(B - V) color excesses vary from around 0.0 in Ruprecht 158 to ∼1.1 in Pismis 23. In general terms, the results obtained show good agreement with previous photometric results. In Ruprecht 158 and BH 92, however, some differences are found between the parameters here obtained and previous values in the literature. Individual spectra of some comparatively bright stars located in the fields of 5 out of the 9 clusters here studied, allowed us to evaluate their membership status. The current cluster sample complements that of 46 open clusters previously studied by our group in an effort to gather a spectral library with several clusters per age bin. The cluster spectral library that we have been building is an important tool to tie studies of resolved and unresolved stellar content.

  14. Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting Delta Scuti Stars

    NASA Astrophysics Data System (ADS)

    Majaess, D. J.; Turner, D. G.; Lane, D. J.; Krajci, T.

    2011-09-01

    This research aims to secure precise distances for cluster δ Scuti stars in order to investigate their properties via a VI Wesenheit framework. Deep JHKs color-color and zero-age main sequence (ZAMS) relations derived from ~700 unreddened stars featuring 2MASS photometry and precise Hipparcos parallaxes (d≤25 pc) are applied to establish distances to several benchmark open clusters that host δ Scuti stars: Hyades, Pleiades, Praesepe, α Persei, and M67 (d = 47 ± 2, 138 ± 6, 183 ± 8, 171 ± 8, 815 ± 40 pc). That analysis provided constraints on the Δ Sct sample's absolute Wesenheit magnitudes (W_VI,0), evolutionary status, and pulsation modes (order, n). The reliability of JHKs established cluster parameters is demonstrated via a comparison with van Leeuwen (2009a) revised Hipparcos results. Distances for seven of nine nearby (d≤250 pc) clusters agree, and the discrepant cases (Pleiades and Blanco 1) are unrelated to (insignificant) Te-(J-Ks) variations with cluster age or iron abundance. JHKs photometry is tabulated for ~3x10^3 probable cluster members on the basis of proper motions (NOMAD). The deep JHKs photometry extends into the low mass regime (~0.4 M_sun) and ensures precise (≤5%) ZAMS fits. Pulsation modes inferred for the cluster δ Scuti stars from VI Wesenheit and independent analyses are comparable (±n), and the methods are consistent in identifying higher order pulsators. Most small-amplitude cluster δ Scuti stars lie on VI Wesenheit loci characterizing n≥1 pulsators. A distance established to NGC 1817 from δ Scuti stars (d~1.7 kpc) via a universal VI Wesenheit template agrees with estimates in the literature, assuming the variables delineate the n≥1 boundary. Small statistics in tandem with other factors presently encumber the use of mmag Δ Scuti stars as viable distance indicators to intermediate-age open clusters, yet a VI Wesenheit approach is a pertinent means for studying δ Scuti stars in harmony with other methods.

  15. Global survey of star clusters in the Milky Way. IV. 63 new open clusters detected by proper motions

    NASA Astrophysics Data System (ADS)

    Scholz, R.-D.; Kharchenko, N. V.; Piskunov, A. E.; Röser, S.; Schilbach, E.

    2015-09-01

    candidates are 63 new open clusters confirmed by the MWSC pipeline. They predominantly occupy the two inner Galactic quadrants and have apparent sizes and numbers of highly probable members slightly larger than those of the typically small MWSC clusters, whereas their other parameters (ages, distances, tidal radii) fall in the typical ranges. As we searched for compact clusters, we did not find new very nearby (extended) clusters, and the mean total proper motion of the new 63 clusters is with 6.3 mas/yr similar to the MWSC average (5.5 mas/yr). Only four new clusters have mean proper motions between 10 mas/yr and our observed maximum of about 13 mas/yr. The full tables with all determined cluster parameters are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A39

  16. Increasing Access to Higher Education through Open and Distance Learning: Empirical Findings from Mzuzu University, Malawi

    ERIC Educational Resources Information Center

    Chawinga, Winner Dominic; Zozie, Paxton Andrew

    2016-01-01

    Slowly but surely, open and distance learning (ODL) programmes are being regarded as one of the most practical ways that universities across the world are increasingly adopting in order to increase access to university education. Likewise, Mzuzu University (MZUNI) set up the Centre for Open and Distance Learning (CODL) to oversee the running of…

  17. Distance Education Regulatory Frameworks: Readiness for Openness in Southwest Pacific/South East Asia Region Nations

    ERIC Educational Resources Information Center

    Tynan, Belinda; James, Rosalind

    2013-01-01

    This paper reports in brief the pilot study, Distance Education Regulatory Frameworks, undertaken by the International Council for Open and Distance Education (ICDE) in 2010-2012 and the implications for openness for higher education in Southwest Pacific/South East Asia region nations. The project developed a methodological approach to…

  18. Examining Digital Literacy Competences and Learning Habits of Open and Distance Learners

    ERIC Educational Resources Information Center

    Ozdamar-Keskin, Nilgun; Ozata, Fatma Zeynep; Banar, Kerim; Royle, Karl

    2015-01-01

    The purpose of the study is to examine digital literacy competences and learning habits of learners enrolled in the open and distance education system of Anadolu University in Turkey. Data were gathered from 20.172 open and distance learners through a survey which included four parts: demographic information, abilities to use digital technologies,…

  19. Open and Distance Learning and the Professionalisation of Trainers. TTnet Dossier No. 4. CEDEFOP Reference.

    ERIC Educational Resources Information Center

    Brugia, Mara; Gerard, Francoise; Tetart, Michel; Battezzati, Luciano; Mallet, Jeanne; Pellerey, Michele; Walker, Simon

    This document contains five papers from a 1999 workshop in Rome on enhancing the professional skills and qualifications of trainers in open and distance learning organized by the TTnet network (Training of Trainers network). "The Different Types of Open and Distance Training and Their Impact on Trainers' Skills" (Michel Tetart) examines…

  20. Innovation in Open & Distance Learning: Successful Development of Online and Web-Based Learning.

    ERIC Educational Resources Information Center

    Lockwood, Fred, Ed.; Gooley, Anne, Ed.

    This book contains 19 papers examining innovation in open and distance learning through development of online and World Wide Web-based learning. The following papers are included: "Innovation in Distributed Learning: Creating the Environment" (Fred Lockwood); "Innovation in Open and Distance Learning: Some Lessons from Experience…

  1. Issues and Challenges in Open and Distance e-Learning: Perspectives from the Philippines

    ERIC Educational Resources Information Center

    Arinto, Patricia Brazil

    2016-01-01

    Rapid advances in information and communications technology in the digital age have brought about significant changes in the practice of distance education (DE) worldwide. DE practitioners in the Philippines' open university have coined the term "open and distance e-learning" (ODeL) to refer to the new forms of DE, which are…

  2. Different Discourses, Discourses of Difference: Globalisation, Distance Education and Open Learning.

    ERIC Educational Resources Information Center

    Edwards, Richard

    1995-01-01

    Drawing on Foucault's notion of discourse, it is suggested that post-Fordism and globalization trends can be found in changing theories of distance education and open learning. Argues that notions of distance education are part of a trend towards uniformity under conditions of globalization, while those of open learning are part of a trend to…

  3. Innovation in Open & Distance Learning: Successful Development of Online and Web-Based Learning.

    ERIC Educational Resources Information Center

    Lockwood, Fred, Ed.; Gooley, Anne, Ed.

    This book contains 19 papers examining innovation in open and distance learning through development of online and World Wide Web-based learning. The following papers are included: "Innovation in Distributed Learning: Creating the Environment" (Fred Lockwood); "Innovation in Open and Distance Learning: Some Lessons from Experience…

  4. Connecting Multiple Intelligences through Open and Distance Learning: Going towards a Collective Intelligence?

    ERIC Educational Resources Information Center

    Medeiros Vieira, Leandro Mauricio; Ferasso, Marcos; Schröeder, Christine da Silva

    2014-01-01

    This theoretical essay is a learning approach reflexion on Howard Gardner's Theory of Multiple Intelligences and the possibilities provided by the education model known as open and distance learning. Open and distance learning can revolutionize traditional pedagogical practice, meeting the needs of those who have different forms of cognitive…

  5. The wide variety of evolutionary stages among 34 unstudied Teutsch open clusters

    NASA Astrophysics Data System (ADS)

    Bonatto, C.; Bica, E.

    2010-10-01

    Context. Close investigations of unstudied open-cluster candidates may improve the statistics of objects undergoing the dissolution phase. Aims: We plan to settle the nature and derive astrophysical (fundamental, structural, and stellar mass content) parameters for 34 unstudied open cluster candidates from the near-infrared Teutsch list. Methods: The analysis employs 2MASS photometry, field-star decontamination (to enhance the intrinsic colour-magnitude diagram morphology), and colour-magnitude filters (for high contrast in stellar radial density profiles). Results: We find 8 clusters younger than ~30 Myr, 21 with ages within 100-900 Myr, 3 older than 1 Gyr, and possibly 1 as old as ~7 Gyr. Part of the sample is affected by reddening as high as AV ~ 9, and about half is located more than d_⊙ ~ 3 kpc away from the Sun, with a few reaching d_⊙ = 6-9 kpc. The sample contains essentially low-luminosity clusters in the optical, with < M_V> ≈ -3±3. These properties are consistent with their near-infrared origin. Cluster size increases both with Galactocentric distance and height over the plane, which is consistent with the low level of tidal stress (and field contamination) associated with these regions. The average mass density falls off with cluster radius as ρ ~ R-3, which in clusters younger than ~20 Myr and more massive than ~103 M_⊙ has been interpreted as diffusion-related cluster expansion. Conclusions: Besides the derivation of astrophysical parameters for a sample of unstudied open clusters, in this paper we identify a set of clusters older than several 102 Myr, with 4 of them having survived a few Gyr. Surveys of open cluster candidates should be further explored to fill in the gap between the detected and predicted number of clusters. An improved statistic, especially on the population of clusters in highly evolved phases, can be used to investigate cluster formation rates and constrain the dissolution-time scale in the Galaxy. Appendix A is only

  6. Variable stars in the field of the open cluster NGC 6939

    NASA Astrophysics Data System (ADS)

    Maciejewski, G.; Georgiev, Ts.; Niedzielski, A.

    2008-05-01

    The results of CCD photometric survey performed with the 90/180 cm Schmidt-Cassegrain Telescope of the Nicolaus Copernicus University Astronomical Observatory in Piwnice (Poland) and the 70/172 cm Schmidt Telescope of the National Astronomical Observatory (NAO) at Rozhen (Bulgaria) of the field of the 1 Gyr old open cluster NGC 6939 are presented. Twenty two variable stars were detected, four of them previously known. Four eclipsing systems (3 detached and 1 contact binary) were found to be members of the cluster. Analysis of the brightness of the contact binary V20 strongly supports the distance to the cluster of 1.74 ± 0.20 kpc. The small population of contact binaries in NGC 6939 confirms also the relatively young age of the cluster.

  7. Universities, the Information Technology Challenge, and Open and Distance Learning in Central and Eastern Europe.

    ERIC Educational Resources Information Center

    Lajos, Tamas; Szucs, Andras

    1998-01-01

    The educational needs of Eastern and Central Europe can be met by distance education. Since the 1990 founding of the European Distance Education Network, proponents of open and distance education have expanded the scope of their activities. Governments and institutions must find the best ways to use technology to integrate traditional and distance…

  8. Meeting the Needs of Distance Learners of M.Ed Program: Bangladesh Open University Perspective

    ERIC Educational Resources Information Center

    Islam, Amirul; Ferdowsi, Sakiba

    2014-01-01

    This study draws on the experience of a cohort of 22 students from 09 tutorial centers enrolled in a Master of Education (M Ed) distance learning program administered by the Bangladesh Open University (BOU). It's purpose is to locate the aims and philosophies of distance learning within the experiences of actual distance learners in order to see…

  9. Finding Semirigid Domains in Biomolecules by Clustering Pair-Distance Variations

    PubMed Central

    Schreiner, Wolfgang

    2014-01-01

    Dynamic variations in the distances between pairs of atoms are used for clustering subdomains of biomolecules. We draw on a well-known target function for clustering and first show mathematically that the assignment of atoms to clusters has to be crisp, not fuzzy, as hitherto assumed. This reduces the computational load of clustering drastically, and we demonstrate results for several biomolecules relevant in immunoinformatics. Results are evaluated regarding the number of clusters, cluster size, cluster stability, and the evolution of clusters over time. Crisp clustering lends itself as an efficient tool to locate semirigid domains in the simulation of biomolecules. Such domains seem crucial for an optimum performance of subsequent statistical analyses, aiming at detecting minute motional patterns related to antigen recognition and signal transduction. PMID:24959586

  10. Finding semirigid domains in biomolecules by clustering pair-distance variations.

    PubMed

    Kenn, Michael; Ribarics, Reiner; Ilieva, Nevena; Schreiner, Wolfgang

    2014-01-01

    Dynamic variations in the distances between pairs of atoms are used for clustering subdomains of biomolecules. We draw on a well-known target function for clustering and first show mathematically that the assignment of atoms to clusters has to be crisp, not fuzzy, as hitherto assumed. This reduces the computational load of clustering drastically, and we demonstrate results for several biomolecules relevant in immunoinformatics. Results are evaluated regarding the number of clusters, cluster size, cluster stability, and the evolution of clusters over time. Crisp clustering lends itself as an efficient tool to locate semirigid domains in the simulation of biomolecules. Such domains seem crucial for an optimum performance of subsequent statistical analyses, aiming at detecting minute motional patterns related to antigen recognition and signal transduction.

  11. Search for variables in the open cluster King 12

    NASA Astrophysics Data System (ADS)

    Paunzen, E.; Netopil, M.; Rode-Paunzen, M.; Bozic, H.

    2015-06-01

    We present the time series analysis of CCD photometry from the 1 m telescope at the Hvar Observatory (Croatia) for 54 stars in the area of the young open clusters King 12. We found no new variable but list upper detection limits.

  12. First photometric analysis of six open cluster candidates

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Clariá, J. J.; Ahumada, A. V.

    2011-10-01

    In this study we try to clarify the nature of six catalogued open cluster (OC) candidates using CCD UBVI_{KC} photometry down to V = 22. The objects are Haffner 3, Haffner 5, NGC 2368, Haffner 25, Hogg 3 and Hogg 4. None of them was found to be a real OC.

  13. A Multisite Cluster Randomized Field Trial of Open Court Reading

    ERIC Educational Resources Information Center

    Borman, Geoffrey D.; Dowling, N. Maritza; Schneck, Carrie

    2008-01-01

    In this article, the authors report achievement outcomes of a multisite cluster randomized field trial of Open Court Reading 2005 (OCR), a K-6 literacy curriculum published by SRA/McGraw-Hill. The participants are 49 first-grade through fifth-grade classrooms from predominantly minority and poor contexts across the nation. Blocking by grade level…

  14. Open and Distance Learning: Cultural Practices in Nepal

    ERIC Educational Resources Information Center

    Pangeni, Shesha Kanta

    2016-01-01

    Nepali education culture is dominated by face-to-face tutoring. It has a long history starting from the Gurukul culture to the present formal schooling. Emerging practices of using technology in education have been promoting online learning as a form of distance education and gaining popularity. This paper focuses on digging out the contextual…

  15. Educational Triage in Open Distance Learning: Walking a Moral Tightrope

    ERIC Educational Resources Information Center

    Prinsloo, Paul; Slade, Sharon

    2014-01-01

    Higher education, and more specifically, distance education, is in the midst of a rapidly changing environment. Higher education institutions increasingly rely on the harvesting and analyses of student data to inform key strategic decisions across a wide range of issues, including marketing, enrolment, curriculum development, the appointment of…

  16. Assessment in Open and Distance Learning. Teeode Project.

    ERIC Educational Resources Information Center

    Steffens, Karl; Underwood, Jean; Bartolome, Antonio; Grave, Lidia

    The aim of the TEEODE project was to develop a representative survey of the models of assessment and evaluation used by institutions supporting distance learning in the 15 member states of the European Union. This paper focuses on issues of course development and assessment, and, in particular, on how effective learning outcomes are achieved and…

  17. The Substellar Mass Function in the Central Region of the Open Cluster Praesepe from Deep LBT Observations

    NASA Astrophysics Data System (ADS)

    Wang, W.; Boudreault, S.; Goldman, B.; Henning, Th.; Caballero, J. A.; Bailer-Jones, C. A. L.

    2011-12-01

    Studies of the mass function (MF) of open clusters of different ages allow us to probe the efficiency with which brown dwarfs (BDs) are evaporated from clusters to populate the field. Surveys in old clusters (age gtrsim 100 Myr) do not suffer so severely from several problems encountered in young clusters, such as intra-cluster extinction and large uncertainties in BD models. Here we present the results of a deep photometric survey to study the MF of the old open cluster Praesepe (age 590+150-120 Myr and distance 190+6.0-5.8 pc), down to a 5σ detection limit at i˜25.6 mag (˜40 MJup). We identify 62 cluster member candidates, of which 40 are substellar, from comparison with predictions from a dusty atmosphere model. The MF rises from the substellar boundary until ˜60 MJup and then declines. This is quite different from the form inferred for other open clusters older than 50 Myr, but seems to be similar to those found in very young open cluster, whose MFs peak at ˜10 MJup. Either Praesepe really does have a different MF from other clusters or they had similar initial MFs but have differed in their dynamical evolution. We further have identified six foreground T dwarf candidates towards Praesepe, which require follow-up spectroscopy to confirm their nature.

  18. First CCD UBVI photometric analysis of four moderately young open clusters in the third galactic quadrant

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Clariá, Juan J.; Ahumada, Andrea V.

    2010-10-01

    We present CCD photometry in the Johnson UBV and Kron-Cousins I systems down to V ~ 22.0 for the open clusters NGC2311, Trumpler6, NGC2432 and BH54 and their surrounding fields. Trumpler6 and BH54 have never been studied before and so we provide, for the first time, estimates of their fundamental parameters. We obtained colour-magnitude diagrams (CMDs) and colour-colour diagrams cleaned from field star contamination by statistically subtracting stars in terms of spatial density, magnitude and colour distributions. Cluster angular radii were estimated from star counts in appropriate-sized boxes distributed throughout the entire observed fields. Using the cleaned CMDs and colour-colour diagrams, we applied sound photometric membership criteria to discriminate cluster members from interloper field stars. The interstellar extinction across the cluster fields derived from the 100-μm dust emission full-sky maps can be considered uniform within the quoted uncertainties. The E(B - V) and E(V - I) colour excesses and the apparent distance moduli of the clusters were estimated from the fit of the zero-age main-sequence to the colour-colour diagrams and CMDs, respectively. Cluster ages were determined from the comparison of the four clusters' CMDs with solar metallicity theoretical isochrones of the Geneva group. All the clusters were found to be moderately young objects, their ages ranging between 60 and 250Myr.

  19. Direct Distance Estimation applied to Eclipsing Binaries in Star Clusters:Case Study of DS Andromedae in NGC 752

    NASA Astrophysics Data System (ADS)

    Milone, Eugene F.; Schiller, Stephen Joseph

    2015-08-01

    Eclipsing binaries (EB) with well-calibrated photometry and precisely measured double-lined radial velocities are candidate standard candles when analyzed with a version of the Wilson-Devinney (WD) light curve modeling program that includes the direct distance estimation (DDE) algorithm. In the DDE procedure, distance is determined as a system parameter, thus avoiding the assumption of stellar sphericity and yielding a well-determined standard error for distance. The method therefore provides a powerful way to calibrate the distances of other objects in any aggregate that contains suitable EB's. DDE has been successfully applied to nearby systems and to a small number of EB's in open clusters. Previously we reported on one of the systems in our Binaries-in-Clusters program, HD27130 = V818 Tau, that had been analyzed with earlier versions of the WD program (see 1987 AJ 93, 1471; 1988 AJ 95, 1466; and 1995 AJ 109, 359 for examples). Results from those early solutions were entered as starting parameters in the current work with the WD 2013 version.Here we report several series of ongoing modeling experiments on a 1.01-d period, early type EB in the intermediate age cluster NGC 752. In one series, ranges of interstellar extinction and hotter star temperature were assumed, and in another series both component temperatures were adjusted. Consistent parameter sets, including distance, confirm DDE's advantages, essentially limited only by knowledge of interstellar extinction, which is small for DS And. Uncertainties in the bandpass calibration constants (flux in standard units from a zero magnitude star) are much less important because derived distance scales (inversely) only with the calibration's square root. This work was enabled by the unstinting help of Bob Wilson. We acknowledge earlier support for the Binaries-in-Clusters program from NSERC of Canada, and the Research Grants Committee and Department of Physics & Astronomy of the University of Calgary.

  20. PULSATING B-TYPE STARS IN THE OPEN CLUSTER NGC 884: FREQUENCIES, MODE IDENTIFICATION, AND ASTEROSEISMOLOGY

    SciTech Connect

    Saesen, S.; Briquet, M.; Aerts, C.; Carrier, F.; Miglio, A.

    2013-10-01

    Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physical description in the stellar structure and evolution model computations of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance, and chemical composition. We present an observational asteroseismology study based on the discovery of numerous multi-periodic and mono-periodic B stars in the open cluster NGC 884. We describe a thorough investigation of the pulsational properties of all B-type stars in the cluster. Overall, our detailed frequency analysis resulted in 115 detected frequencies in 65 stars. We found 36 mono-periodic, 16 bi-periodic, 10 tri-periodic, and 2 quadru-periodic stars and one star with nine independent frequencies. We also derived the amplitudes and phases of all detected frequencies in the U, B, V, and I filter, if available. We achieved unambiguous identifications of the mode degree for 12 of the detected frequencies in nine of the pulsators. Imposing the identified degrees and measured frequencies of the radial, dipole, and quadrupole modes of five pulsators led to a seismic cluster age estimate of log (age/yr) = 7.12-7.28 from a comparison with stellar models. Our study is a proof-of-concept for and illustrates the current status of ensemble asteroseismology of a young open cluster.

  1. Old open clusters in the outer Galactic disk

    NASA Astrophysics Data System (ADS)

    Carraro, G.; Geisler, D.; Villanova, S.; Frinchaboy, P. M.; Majewski, S. R.

    2007-12-01

    Context: The outer parts of the Milky Way disk are believed to be one of the main arenas where the accretion of external material in the form of dwarf galaxies and subsequent formation of streams is taking place. The Monoceros stream and the Canis Major and Argo over-densities are notorious examples. Understanding whether what we detect is the signature of accretion or, more conservatively, simply the intrinsic nature of the disk, represents one of the major goals of modern Galactic astronomy. Aims: We try to shed more light on the properties of the outer disk by exploring the properties of distant anti-center old open clusters. We want to verify whether distant clusters follow the chemical and dynamical behavior of the solar vicinity disk, or whether their properties can be better explained in terms of an extra-galactic population. Methods: VLT high resolution spectra have been acquired for five distant open clusters: Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73 and Berkeley 75. We derive accurate radial velocities to distinguish field interlopers and cluster members. For the latter we perform a detailed abundance analysis and derive the iron abundance [Fe/H] and the abundance ratios of several α elements. Results: Our analysis confirms previous indications that the radial abundance gradient in the outer Galactic disk does not follow the expectations extrapolated from the solar vicinity, but exhibits a shallower slope. By combining the metallicity of the five program clusters with eight more clusters for which high resolution spectroscopy is available, we find that the mean metallicity in the outer disk between 12 and 21 kpc from the Galactic center is [Fe/H] ≈ -0.35, with only marginal indications for a radial variation. In addition, all the program clusters exhibit solar scaled or slightly enhanced α elements, similar to open clusters in the solar vicinity and thin disk stars. Conclusions: We investigate whether this outer disk cluster sample might

  2. Training Teachers at a Distance: Perceptions and Challenges of Open and Distance Learning (ODL) in Teacher Education: The Zimbabwean Experience

    ERIC Educational Resources Information Center

    Samkange, Wellington

    2013-01-01

    Zimbabwe like most developing countries continues to experience shortages in skills. One such area that has experienced skills shortages is education. This has resulted in governments and education institutions coming up with innovative ways to improve the training of of teachers. Such innovative models include the Open & Distance Learning…

  3. Discovery of Variable Stars in the Field of the Galactic Open Cluster NGC 7039

    NASA Astrophysics Data System (ADS)

    Hu, Juei-Hwa; Chen, Hui-Chen; Chen, Ying-Tung; Chang, Ding-Cheng; Lin, Hsing-Wen; Ngeow, Chow-Choong; Chen, W. P.; Ip, Wing-Huen

    2011-06-01

    We report variable stars identified in the field of the Galactic open cluster, NGC 7039. In the fall/winter of 2009, imaging photometry has been acquired, mainly in the R band, for eight open clusters using the 81 cm Tenagra telescope in Arizona. We present the results for our first target, NGC 7039. We have found 42 new variable stars and six suspected variable stars. Among the variable stars, there are 14 eclipsing binaries, including one RS Canum Venaticorum-type system, one RR Lyrae, two Cepheid, one β Cephei, three δ Scuti, eight pulsatinglike stars, five variable stars with periods longer than the observation window of 41 days, and eight irregular variable stars. Two contact binary systems could be members of NGC 7039 because of their loci in the color-magnitude diagram and their distance moduli close to that of the open cluster. One of the contact binary systems shows infrared excess in the (J - H) and (H - Ks) diagrams. It could have circumstellar dust. None of the pulsating stars belong to the open cluster.

  4. OCCASO - II. Physical parameters and Fe abundances of red clump stars in 18 open clusters

    NASA Astrophysics Data System (ADS)

    Casamiquela, L.; Carrera, R.; Blanco-Cuaresma, S.; Jordi, C.; Balaguer-Núñez, L.; Pancino, E.; Anders, F.; Chiappini, C.; Díaz-Pérez, L.; Aguado, D. S.; Aparicio, A.; Garcia-Dias, R.; Heiter, U.; Martínez-Vázquez, C. E.; Murabito, S.; del Pino, A.

    2017-10-01

    Open clusters have long been used to study the chemodynamical evolution of the Galactic disc. This requires a homogeneously analysed sample covering a wide range of ages and distances. In this paper, we present the Open Clusters Chemical Abundances from Spanish Observatories (OCCASO) second data release. This comprises a sample of high-resolution (R > 65 000) and high signal-to-noise spectra of 115 red clump stars in 18 open clusters. We derive atmospheric parameters (Teff, log g, ξ), and [Fe/H] abundances using two analysis techniques: equivalent widths and spectral synthesis. A detailed comparison and a critical review of the results of the two methods are made. Both methods are carefully tested between them, with the Gaia FGK benchmark stars, and with an extensive sample of literature values. We perform a membership study using radial velocities and the resulting abundances. Finally, we compare our results with a chemodynamical model of the Milky Way thin disc concluding that the oldest open clusters are consistent with the models only when dynamical effects are taken into account.

  5. International Trade Modelling Using Open Flow Networks: A Flow-Distance Based Analysis.

    PubMed

    Shen, Bin; Zhang, Jiang; Li, Yixiao; Zheng, Qiuhua; Li, Xingsen

    2015-01-01

    This paper models and analyzes international trade flows using open flow networks (OFNs) with the approaches of flow distances, which provide a novel perspective and effective tools for the study of international trade. We discuss the establishment of OFNs of international trade from two coupled viewpoints: the viewpoint of trading commodity flow and that of money flow. Based on the novel model with flow distance approaches, meaningful insights are gained. First, by introducing the concepts of trade trophic levels and niches, countries' roles and positions in the global supply chains (or value-added chains) can be evaluated quantitatively. We find that the distributions of trading "trophic levels" have the similar clustering pattern for different types of commodities, and summarize some regularities between money flow and commodity flow viewpoints. Second, we find that active and competitive countries trade a wide spectrum of products, while inactive and underdeveloped countries trade a limited variety of products. Besides, some abnormal countries import many types of goods, which the vast majority of countries do not need to import. Third, harmonic node centrality is proposed and we find the phenomenon of centrality stratification. All the results illustrate the usefulness of the model of OFNs with its network approaches for investigating international trade flows.

  6. International Trade Modelling Using Open Flow Networks: A Flow-Distance Based Analysis

    PubMed Central

    Shen, Bin; Zhang, Jiang; Li, Yixiao; Zheng, Qiuhua; Li, Xingsen

    2015-01-01

    This paper models and analyzes international trade flows using open flow networks (OFNs) with the approaches of flow distances, which provide a novel perspective and effective tools for the study of international trade. We discuss the establishment of OFNs of international trade from two coupled viewpoints: the viewpoint of trading commodity flow and that of money flow. Based on the novel model with flow distance approaches, meaningful insights are gained. First, by introducing the concepts of trade trophic levels and niches, countries’ roles and positions in the global supply chains (or value-added chains) can be evaluated quantitatively. We find that the distributions of trading “trophic levels” have the similar clustering pattern for different types of commodities, and summarize some regularities between money flow and commodity flow viewpoints. Second, we find that active and competitive countries trade a wide spectrum of products, while inactive and underdeveloped countries trade a limited variety of products. Besides, some abnormal countries import many types of goods, which the vast majority of countries do not need to import. Third, harmonic node centrality is proposed and we find the phenomenon of centrality stratification. All the results illustrate the usefulness of the model of OFNs with its network approaches for investigating international trade flows. PMID:26569618

  7. The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three-dimensional Structure of the Virgo Cluster

    NASA Astrophysics Data System (ADS)

    Mei, Simona; Blakeslee, John P.; Côté, Patrick; Tonry, John L.; West, Michael J.; Ferrarese, Laura; Jordán, Andrés; Peng, Eric W.; Anthony, André; Merritt, David

    2007-01-01

    The ACS Virgo Cluster Survey consists of HST ACS imaging for 100 early-type galaxies in the Virgo Cluster, observed in the F475W (~SDSS g) and F850LP (~SDSS z) filters. We derive distances for 84 of these galaxies using the method of surface brightness fluctuations (SBFs), present the SBF distance catalog, and use this database to examine the three-dimensional distribution of early-type galaxies in the Virgo Cluster. The SBF distance moduli have a mean (random) measurement error of 0.07 mag (0.5 Mpc), or roughly 3 times better than previous SBF measurements for Virgo Cluster galaxies. Five galaxies lie at a distance of d~23 Mpc and are members of the W' cloud. The remaining 79 galaxies have a narrow distribution around our adopted distance of =16.5+/-0.1 (random mean error) +/-1.1 Mpc (systematic). The rms distance scatter of this sample is σ(d)=0.6+/-0.1 Mpc, with little or no dependence on morphological type or luminosity class (i.e., 0.7+/-0.1 and 0.5+/-0.1 Mpc for the giants and dwarfs, respectively). The back-to-front depth of the cluster measured from our sample of early-type galaxies is 2.4+/-0.4 Mpc (i.e., +/-2 σ of the intrinsic distance distribution). The M87 (cluster A) and M49 (cluster B) subclusters are found to lie at distances of 16.7+/-0.2 and 16.4+/-0.2 Mpc, respectively. There may be a third subcluster associated with M86. A weak correlation between velocity and line-of-sight distance may be a faint echo of the cluster velocity distribution not having yet completely virialized. In three dimensions, Virgo's early-type galaxies appear to define a slightly triaxial distribution, with axis ratios of (1:0.7:0.5). The principal axis of the best-fit ellipsoid is inclined ~20°-40° from the line of sight, while the galaxies belonging to the W' cloud lie on an axis inclined by ~10°-15°. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the association of

  8. PROPERTIES OF THE OLD OPEN CLUSTER CZERNIK 30

    SciTech Connect

    Hayes, Christian R.; Friel, Eileen D.; Slack, Taleah J.; Boberg, Owen M. E-mail: efriel@indiana.edu

    2015-12-15

    We present new photometric and spectroscopic data of the old open cluster Czernik 30. Wide field BVI photometry allows us to correct for the high field contamination by statistical subtraction to produce a color–magnitude diagram (CMD) that clearly reveals the cluster sequence. From spectra of stars in the cluster field obtained with the Hydra spectrograph on the Wisconsin-Indiana-Yale-NOAO 3.5 m telescope we determine a mean cluster velocity of +79.9 ± 1.5 km s{sup −1} and provide membership information that helps further define the cluster giant branch and red clump. Stellar abundances for the brighter giants in the cluster indicate a mean metallicity of [Fe/H] = −0.2 ± 0.15. Fitting theoretical isochrones to the CMD we determine the following properties of Czernik 30: age = 2.8 ± 0.3 Gyr, (m − M){sub v} = 14.8 ± 0.1, E(B − V) = 0.24 ± 0.06, and E(V − I) = 0.36 ± 0.04. Czernik 30 is an old, sub-solar metallicity cluster located at a Galactocentric radius of R{sub gc}  ∼ 13.3 kpc. Given its age and position just beyond the transition to a flat abundance gradient seen in the open cluster population, Czernik 30 provides an interesting target for future observations.

  9. Photometric Determination of Binary Mass Ratios in the WIYN Open Cluster Study (WOCS) Using Theoretical Isochrones

    NASA Astrophysics Data System (ADS)

    Cai, K.; Durisen, R. H.; Deliyannis, C. P.

    2003-05-01

    Binary stars in Galactic open clusters are difficult to detect without spectroscopic observations. However, from theoretical isochrones, we find that binary stars with different primary masses M1 and mass ratios q = M2/M1 have measurably different behaviors in various UBVRI color-magnitude and color-color diagrams. By using appropriate Yonsei-Yale Isochrones, in the best cases we can evaluate M1 and q to within about +/- 0.1Msun and +/- 0.1, respectively, for individual proper-motion members that have multiple WOCS UBVRI measurements of high quality. The cluster metallicity, reddening, and distance modulus and best-fit isochrones are determined self-consistently from the same WOCS data. This technique allows us to detect binaries and determine their mass ratios in open clusters without time-consuming spectrocopy, which is only sensitive to a limited range of binary separations. We will report results from this photometric technique for WOCS cluster M35 for M1 in the range of 1 to 4 Msun. For the lower main sequence, we used the empirical colors to reduce the error introduced by the problematic color transformations of Y2 Isochrones. In addition to other sources of uncertainty, we have considered effects of rapid rotation and pulsational instability. We plan to apply our method to other WOCS clusters in the future and explore differences in binary fractions and/or mass ratio distributions as a function of cluster age, metallicity, and other parameters.

  10. An open-population hierarchical distance sampling model

    USGS Publications Warehouse

    Sollmann, Rachel; Beth Gardner,; Richard B Chandler,; Royle, J. Andrew; T Scott Sillett,

    2015-01-01

    Modeling population dynamics while accounting for imperfect detection is essential to monitoring programs. Distance sampling allows estimating population size while accounting for imperfect detection, but existing methods do not allow for direct estimation of demographic parameters. We develop a model that uses temporal correlation in abundance arising from underlying population dynamics to estimate demographic parameters from repeated distance sampling surveys. Using a simulation study motivated by designing a monitoring program for island scrub-jays (Aphelocoma insularis), we investigated the power of this model to detect population trends. We generated temporally autocorrelated abundance and distance sampling data over six surveys, using population rates of change of 0.95 and 0.90. We fit the data generating Markovian model and a mis-specified model with a log-linear time effect on abundance, and derived post hoc trend estimates from a model estimating abundance for each survey separately. We performed these analyses for varying number of survey points. Power to detect population changes was consistently greater under the Markov model than under the alternatives, particularly for reduced numbers of survey points. The model can readily be extended to more complex demographic processes than considered in our simulations. This novel framework can be widely adopted for wildlife population monitoring.

  11. Role of Radio and TV Programmes in Distance and Open Learning System: A Case of Bangladesh Open University.

    ERIC Educational Resources Information Center

    Karim, Salma; Kama, Mustafa Azad; Islam, Md. Mayenul

    2001-01-01

    Examines the role and effectiveness of radio and television programs in distance and open learning systems based on a survey of students at Bangladesh Open University. Offers recommendations for improvements, including extending the time span, ensuring the quality of presentations, teacher involvement, and audio and video cassette…

  12. Role of Radio and TV Programmes in Distance and Open Learning System: A Case of Bangladesh Open University.

    ERIC Educational Resources Information Center

    Karim, Salma; Kama, Mustafa Azad; Islam, Md. Mayenul

    2001-01-01

    Examines the role and effectiveness of radio and television programs in distance and open learning systems based on a survey of students at Bangladesh Open University. Offers recommendations for improvements, including extending the time span, ensuring the quality of presentations, teacher involvement, and audio and video cassette…

  13. Assuring Quality Evaluation Practices in Open and Distance Learning System: The Case of National Open University of Nigeria

    ERIC Educational Resources Information Center

    Ofoha, D.

    2012-01-01

    The success of any open and distance learning (ODL) programme depends on how well it is evaluated. In the National Open University of Nigeria (NOUN), students are assessed and evaluated through continuous assessment as well as end of semester examinations. This paper focuses on Tutor Marked Assignment (TMA), which forms part of continuous…

  14. The distance to the Large Magellanic Cloud - Constraints from Cepheids in Large Magellanic Cloud star clusters

    NASA Technical Reports Server (NTRS)

    Bertelli, Gianpaolo; Bressan, Alessandro; Chiosi, Cesare; Mateo, Mario; Wood, Peter R.

    1993-01-01

    We have used recent observational data for the Cepheids in the rich, young LMC clusters NGC 1866 and NGC 2031 to constrain the cluster distances with the mass-equivalency (ME) method. The basis of this approach is to fix the cluster distances by requiring the Cepheid evolutionary and pulsational masses to be equal. Using evolutionary models incorporating a mild amount of core and envelope overshooting along with recent pulsational models, we derive distance moduli of 18.51 +/- 0.21 and 18.32 +/- 0.20 for NGC 1866 and NGC 2031, respectively. The quoted errors are dominated by the uncertainties in the heavy element abundances of the clusters (assumed to be 0.3 dex for both clusters), with a smaller contribution due to the apparently intrinsic spread in the masses of the Cepheids in each cluster. For the ME method, we find that Delta(m-M)(0)/Delta sub Z(1) = 0.69, where Z(1) = log (Z/0.016). This result implies that the cluster distances can be determined to better than +/- 5 percent if the cluster abundances can be measured to better than about +/- 0.15 dex.

  15. NGC2587: a sparse open cluster projected on to a populous star field

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Clariá, Juan J.; Ahumada, Andrea V.

    2009-08-01

    We present CCD photometry in the Johnson U, B and V and Kron-Cousins I passbands for the open cluster NGC2587. The sample consists of 4406 stars reaching down to V ~ 21.0. We developed a new method to clean statistically the colour-magnitude diagrams. NGC2587 appears to be a sparse, relatively bright open cluster, with a few tens of members projected on to a populous star field. The comparatively bright F7/8 II type star HD70927, located close to the cluster centre, seems not to be a member. Our analysis suggests that NGC2587 is slightly younger than the Hyades and probably of solar metallicity. A cluster radius of roughly 8 arcmin was estimated from the radial stellar density profile. From 18 probable cluster members with measured proper motions, we derive the following mean values for NGC2587: μα = -4.3 +/- 3.6masyr-1 and μδ = -2.5 +/- 3.4masyr-1. Adopting the theoretical metal content Z = 0.02, which provides the best global fit, we derive a cluster age of 500+60-50. Simultaneously, colour excesses E(B - V) = 0.10 and E(V - I) = 0.15 and an apparent distance modulus of V - MV = 12.50 are obtained. The interstellar extinction in the cluster direction is found to follow the normal law. NGC2587 is located at a distance of (2.70 +/- 0.70) kpc from the Sun and ~9.8 kpc from the Galactic centre.

  16. The Internal Proper Motions of Stars in the Open Cluster M35

    NASA Astrophysics Data System (ADS)

    McNamara, Bernard J.; Harrison, Thomas E.; McArthur, Barbara E.; Benedict, G. Fritz

    2011-08-01

    Relative proper motions, based on 108 orbits of Hubble Space Telescope Fine Guidance Sensor data extending from 1992 to 2006, are reported for 74 stars in the open cluster M35 (NGC 2168). A subset of 22 of these objects are then used to compute the cluster's internal proper motion dispersions in both right ascension and declination. We find that these dispersions are equal to within their measurement errors. The average one-dimensional dispersion is 0.018 ± 0.002 arcsec century-1. When combined with the M35 radial velocity dispersion of 0.65 ± 0.10 km s-1 found by Geller et al., this produces a cluster distance of 762 ± 145 pc. Using isochrone fits to the cluster main sequence, this distance suggests that M35 has an age of about 133 Myr. Although this age is consistent with that typically found for M35, the formal error in the dynamical distance of ±19% can accommodate ages between 65 Myr and 201 Myr.

  17. THE INTERNAL PROPER MOTIONS OF STARS IN THE OPEN CLUSTER M35

    SciTech Connect

    McNamara, Bernard J.; Harrison, Thomas E.; McArthur, Barbara E.; Fritz Benedict, G.

    2011-08-15

    Relative proper motions, based on 108 orbits of Hubble Space Telescope Fine Guidance Sensor data extending from 1992 to 2006, are reported for 74 stars in the open cluster M35 (NGC 2168). A subset of 22 of these objects are then used to compute the cluster's internal proper motion dispersions in both right ascension and declination. We find that these dispersions are equal to within their measurement errors. The average one-dimensional dispersion is 0.018 {+-} 0.002 arcsec century{sup -1}. When combined with the M35 radial velocity dispersion of 0.65 {+-} 0.10 km s{sup -1} found by Geller et al., this produces a cluster distance of 762 {+-} 145 pc. Using isochrone fits to the cluster main sequence, this distance suggests that M35 has an age of about 133 Myr. Although this age is consistent with that typically found for M35, the formal error in the dynamical distance of {+-}19% can accommodate ages between 65 Myr and 201 Myr.

  18. Cepheids in Galactic Open Clusters: An All-sky Census

    NASA Astrophysics Data System (ADS)

    Anderson, Richard I.; Eyer, Laurent; Mowlavi, Nami

    2012-04-01

    We perform an all-sky search for classical (type I) Cepheids that are members of Galactic Open Clusters. Our approach is multi-dimensional, using all available spatial and kinematic parameters. The quantification of errors is crucial for this analysis, so care is taken to find adequate and realistic representations of parameter uncertainties. The data employed in the calculation are taken from published catalogues and the literature, supplemented by specific radial-velocity observations. Our work in progress is outlined here, and issues related to the inhomogeneity of cluster radii in the literature are discussed in some detail.

  19. Generalized chemical distance distribution in all-sided critical percolation clusters

    NASA Astrophysics Data System (ADS)

    Katunin, Andrzej

    2016-12-01

    The algorithm of evaluation of chemical distance distribution in 2D and 3D critical percolation clusters is presented in the following study. The algorithm is enriched by numerous examples of 2D and 3D critical percolation clusters related to the currently investigated problem of electrical percolation in a mixture of conducting/dielectric polymers. The introduced measure of the chemical distance distribution can be a useful tool for characterization of percolation clusters, and in problems of percolation theory and graphs theory in general.

  20. A clustering algorithm based on two distance functions for MEC model.

    PubMed

    Wang, Ying; Feng, Enmin; Wang, Ruisheng

    2007-04-01

    Haplotype reconstruction, based on aligned single nucleotide polymorphism (SNP) fragments, is to infer a pair of haplotypes from localized polymorphism data gathered through short genome fragment assembly. This paper first presents two distance functions, which are used to measure the difference degree and similarity degree between SNP fragments. Based on the two distance functions, a clustering algorithm is proposed in order to solve MEC model. The algorithm involves two sections. One is to determine the initial haplotype pair, the other concerns with inferring true haplotype pair by re-clustering. The comparison results prove that our algorithm utilizing two distance functions is effective and feasible.

  1. A Survey of Open Clusters in the u'g'r'i'z' Filter System. 3. Results for the Cluster NGC 188

    SciTech Connect

    Fornal, Bartosz; Tucker, Douglas L.; Smith, J.Allyn; Allam, Sahar S.; Rider, Cristin J.; Sung, Hwankyung; /Jagiellonian U. /Fermilab /Austin Peay State U. /Wyoming U. /Johns Hopkins U. /Sejong U.

    2006-11-01

    The authors continue the series of papers describing the results of a photometric survey of open star clusters, primarily in the southern hemisphere, taken in the u'g'r'i'z' filter system. The entire observed sample covered more than 100 clusters, but here they present data only on NGC 188, which is one of the oldest open clusters known in the Milky Way. They fit the Padova theoretical isochrones to the data. Assuming a solar metallicity for NGC 188, they find a distance of 1700 {+-} 100 pc, an age of 7.5 {+-} 0.7 Gyr, and a reddening E(B-V) of 0.025 {+-} 0.005. This yields a distance modulus of 11.23 {+-} 0.14.

  2. Study of open clusters within 1.8 kpc and understanding the Galactic structure

    NASA Astrophysics Data System (ADS)

    Joshi, Y. C.; Dambis, A. K.; Pandey, A. K.; Joshi, S.

    2016-10-01

    Context. Significant progress has been made in recent years to understand the formation and evolution of our Galaxy, but we still lack a complete understanding of the Galaxy and its structure. Aims: Using an almost complete sample of Galactic open star clusters within 1.8 kpc, we aim to understand the general properties of the open cluster system in the Galaxy and probe the Galactic structure. Methods: We first extracted 1241 open clusters within 1.8 kpc of the Sun from the Milky Way Star Clusters (MWSC) catalog. Considering it an almost complete sample of clusters within this distance, we performed a comprehensive statistical analysis of various cluster parameters such as spatial position, age, size, mass, and extinction. Results: We find an average cluster scale height of zh = 60 ± 2 pc for clusters younger than 700 Myr, which increases to 64 ± 2 pc when we include all the clusters. The zh is found to be strongly dependent on RGC and age, and on an average, zh is more than twice as large as in the outer region than in the inner region of the solar circle, except for the youngest population of clusters. The solar offset is found to be 6.2 ± 1.1 pc above the formal Galactic plane. We derive a local mass density of ρ0 = 0.090 ± 0.005 M⊙/ pc3 and estimate a negligibly small amount of dark matter in the solar neighborhood. The reddening in the direction of clusters suggests a strong correlation with their vertical distance from the Galactic plane with a respective slope of dE(B-V) / dz = 0.40 ± 0.04 and 0.42 ± 0.05 mag/kpc below and above the Galactic plane. We observe a linear mass-radius and mass-age relations in the open clusters and derive the slopes of dR/ d(log M) = 2.08 ± 0.10 and d(log M) / d(log T) = -0.36 ± 0.05, respectively. Conclusions: The dependence of the spatial distribution of clusters on their age points to a complex interplay between cluster formation and survivability within the Galaxy. The geometrical characteristics of a significant

  3. PHR 1315-6555: a bipolar planetary nebula in the compact Hyades-age open cluster ESO 96-SC04

    NASA Astrophysics Data System (ADS)

    Parker, Quentin A.; Frew, David J.; Miszalski, Brent; Kovacevic, Anna V.; Frinchaboy, Peter M.; Dobbie, Paul D.; Köppen, Joachim

    2011-05-01

    We present a detailed study of a bipolar, possible Type I planetary nebula (PN), PHR 1315-6555 (PN G305.3-03.1), which was discovered as part of the Macquarie/AAO/Strasbourg Hα planetary nebula project (MASH), and that we considered at the time was an excellent candidate for membership of the distant, compact, intermediate-age open cluster, ESO 96-SC04. The strong evidence for this association is presented here, making this the only known example of a PN physically associated with a Galactic open cluster. Cluster membership is extremely important as it allows for very precise estimates of the fundamental properties of the PN as the cluster is at a known distance. The PN was discovered by one of us (QAP) during systematic MASH searches for new Galactic PNe of the AAO United Kingdom Schmidt Telescope (UKST) Hα survey and had been missed in earlier broad-band surveys, including specific CCD studies of the host cluster. We present original discovery images and Cerro Tololo Inter-American Observatory (CTIO) 4-m MOSAIC-II camera follow-up narrow-band images that reveal its bipolar morphology. We also present (i) low-resolution optical spectra that spectroscopically confirm the PN, (ii) accurate radial velocities of PN and cluster stars from high-resolution spectroscopy which show they are consistent and (iii) a reliable, independent distance estimate to the PN using a robust PN distance indicator which agrees with the published cluster distance to within the errors. We also provide preliminary estimates of basic PN properties and abundance estimates from deeper spectra that show it to be of possible Type I chemistry. This is also consistent with its estimated turn-off mass. Taken together, these findings present a powerful case for clear physical association between the PN and host cluster. Results for this association will be of considerable interest to specialists across differing astrophysical disciplines, including PNe, white dwarfs and open clusters.

  4. Optical and Near Infrared Study of the Open Cluster Czernik 17

    NASA Astrophysics Data System (ADS)

    Sujatha, S.; Krishna, K. K.; Komala, S.; Babu, G. S. D.

    2015-09-01

    In this paper we present the fundamental physical parameters of the poorly studied open cluster Czernik 17. The parameters have been derived from the UBVRI CCD photometric observations obtained with the 2-m Himalayan Chandra Telescope as well as using data taken from the Two-Micron All Sky Survey. This cluster is located in the direction of Camelopardalis constellation with a radial extent of 4' and is estimated to be at a distance of 7 ± 0.5 kpc. The interstellar extinction in the line of sight of the cluster is found to be E(B-V) = 0.72 ± 0.05 mag. Based on the evolutionary stage of the evolved stars the log(age) of the cluster is found to be 8.05 to 8.1 making it a relatively young cluster which can be considered as a spiral arm tracer of the outer arm. We have constructed the luminosity function for the stars within the adopted cluster radius which shows the common trend of the number of stars increasing toward the fainter magnitudes. We also find the presence of Böhm-Vitense gaps in the main-sequence branch of the color-magnitude diagrams of this cluster which may be attributed to surface convection which has the effect of making the stars redder although the luminosity remains unchanged.

  5. Tidal disruption of open clusters in their parent molecular clouds

    NASA Technical Reports Server (NTRS)

    Long, Kevin

    1989-01-01

    A simple model of tidal encounters has been applied to the problem of an open cluster in a clumpy molecular cloud. The parameters of the clumps are taken from the Blitz, Stark, and Long (1988) catalog of clumps in the Rosette molecular cloud. Encounters are modeled as impulsive, rectilinear collisions between Plummer spheres, but the tidal approximation is not invoked. Mass and binding energy changes during an encounter are computed by considering the velocity impulses given to individual stars in a random realization of a Plummer sphere. Mean rates of mass and binding energy loss are then computed by integrating over many encounters. Self-similar evolutionary calculations using these rates indicate that the disruption process is most sensitive to the cluster radius and relatively insensitive to cluster mass. The calculations indicate that clusters which are born in a cloud similar to the Rosette with a cluster radius greater than about 2.5 pc will not survive long enough to leave the cloud. The majority of clusters, however, have smaller radii and will survive the passage through their parent cloud.

  6. Google Classroom and Open Clusters: An Authentic Science Research Project for High School Students

    NASA Astrophysics Data System (ADS)

    Johnson, Chelen H.; Linahan, Marcella; Cuba, Allison Frances; Dickmann, Samantha Rose; Hogan, Eleanor B.; Karos, Demetra N.; Kozikowski, Kendall G.; Kozikowski, Lauren Paige; Nelson, Samantha Brooks; O'Hara, Kevin Thomas; Ropinski, Brandi Lucia; Scarpa, Gabriella; Garmany, Catharine D.

    2016-01-01

    STEM education is about offering unique opportunities to our students. For the past three years, students from two high schools (Breck School in Minneapolis, MN, and Carmel Catholic High School in Mundelein, IL) have collaborated on authentic astronomy research projects. This past year they surveyed archival data of open clusters to determine if a clear turnoff point could be unequivocally determined. Age and distance to each open cluster were calculated. Additionally, students requested time on several telescopes to obtain original data to compare to the archival data. Students from each school worked in collaborative teams, sharing and verifying results through regular online hangouts and chats. Work papers were stored in a shared drive and on a student-designed Google site to facilitate dissemination of documents between the two schools.

  7. Clustering of local group distances: publication bias or correlated measurements? I. The large Magellanic cloud

    SciTech Connect

    De Grijs, Richard; Wicker, James E.; Bono, Giuseppe

    2014-05-01

    The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder yet the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly—and with a small spread—around the 'canonical' distance modulus, (m – M){sub 0} = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available to date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading to the tightly clustered distances is based on highly non-independent tracer samples and analysis methods, hence leading to significant correlations among the LMC distances reported in subsequent articles. Based on a careful, weighted combination, in a statistical sense, of the main stellar population tracers, we recommend that a slightly adjusted canonical distance modulus of (m – M){sub 0} = 18.49 ± 0.09 mag be used for all practical purposes that require a general distance scale without the need for accuracies of better than a few percent.

  8. Clustering of Local Group Distances: Publication Bias or Correlated Measurements? I. The Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    de Grijs, Richard; Wicker, James E.; Bono, Giuseppe

    2014-05-01

    The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder yet the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly—and with a small spread—around the "canonical" distance modulus, (m - M)0 = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available to date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading to the tightly clustered distances is based on highly non-independent tracer samples and analysis methods, hence leading to significant correlations among the LMC distances reported in subsequent articles. Based on a careful, weighted combination, in a statistical sense, of the main stellar population tracers, we recommend that a slightly adjusted canonical distance modulus of (m - M)0 = 18.49 ± 0.09 mag be used for all practical purposes that require a general distance scale without the need for accuracies of better than a few percent.

  9. Setting Stellar Chronometers: The PTF(+) Open Cluster Survey

    NASA Astrophysics Data System (ADS)

    Agüeros, M. A.

    2017-07-01

    While we have known for 45 years that a solar-type star's rotation rate and magnetic activity depend on its age (Skumanich 1972), many details still elude us. We cannot yet fully describe the evolution of rotation or activity for stars of a given mass, nor can we use rotation or activity measurements to estimate accurately the ages of isolated field stars. Fortunately, recent technological advances have transformed our ability to observe open clusters, the best laboratories for testing age-dependent stellar properties. We are currently surveying low-mass stars in six open clusters ranging in age from 35 Myr to 3.5 Gyr; here, I focus on our results for the Hyades and Praesepe. These data will allow us to improve our understanding of the age-rotation-activity relation for ≲1M⊙ stars.

  10. Rotation periods of open-cluster stars, 3

    NASA Technical Reports Server (NTRS)

    Prosser, Charles F.; Shetrone, Matthew D.; Dasgupta, Amil; Backman, Dana E.; Laaksonen, Bentley D.; Baker, Shawn W.; Marschall, Laurence A.; Whitney, Barbara A.; Kuijken, Konrad; Stauffer, John R.

    1995-01-01

    We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several show rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using all available Pleiades stars with photometric periods together with current X-ray flux measurements, we illustrate the X-ray activity/rotation relation among Pleiades late-G/K dwarfs. The data show a clear break in the rotation-activity relation around P approximately 6-7 days -- in general accordance with previous results using more heterogeneous samples of G/K stars.

  11. Chemical abundances of solar-type dwarfs in open clusters

    NASA Astrophysics Data System (ADS)

    Schuler, Simon C.

    Open clusters have proven continuously to be invaluable tools to the studies of stellar physics and Galactic evolution. Until recently, however, the chemical abundances of the populous and astrophysically important late-F, G, and K open cluster dwarfs have gone largely unanalyzed. In this thesis I report on the study of the chemical abundances derived from high-resolution, moderate-to-high signal-to-noise echelle spectra obtained with the 10-m Keck I, 9.2-m Hobby- Eberly, 8.2-m VLT, 4.0-m KPNO, 2.7-m Harlan J. Smith, and the 2.1-m Otto Struve telescopes of cool dwarfs in the Pleiades, Hyades, and M34 open clusters. The main result of the study is the identification of excitation-related abundance trends found among cool open cluster dwarfs ( T eff <= 5500 K), as well as an overionization of Fe- abundances derived from singly ionized lines are greater than those derived from neutral lines- among the cool Hyades dwarfs; the trends are such that abundances derived from high-excitation (h >= 4.0 eV) spectral lines and using atmospheric models assuming local thermodynamic equilibrium (LTE) increase with decreasing T eff . Particular attention is given to the high-excitation (h = 9.15 eV) near-IR ll7774 O I triplet, a line used often in the derivation of stellar O abundances and known to be susceptible to non-LTE (NLTE) effects. The O I triplet-based abundances show a dramatic increase with decreasing T eff in all three clusters, behavior that is in stark contrast to expectations from canonical NLTE calculations. Other elements with lines of various excitation potentials are also analyzed and are found to exhibit abundance trends that are qualitatively similar to those of the O I triplet. Possible explanations for the observed cool open cluster dwarf abundance anomalies are investigated, and photospheric surface temperature inhomogeneities possibly due to spots, faculae, and/or plages are found to be a plausible culprit. Indeed, multi-component LTE model atmospheres are

  12. AMPLITUDES OF SOLAR-LIKE OSCILLATIONS: CONSTRAINTS FROM RED GIANTS IN OPEN CLUSTERS OBSERVED BY KEPLER

    SciTech Connect

    Stello, Dennis; Huber, Daniel; Bedding, Timothy R.; Benomar, Othman; Kallinger, Thomas; Basu, Sarbani; Mosser, BenoIt; Hekker, Saskia; Mathur, Savita; GarcIa, Rafael A.; Gilliland, Ronald L.; Verner, Graham A.; Chaplin, William J.; Elsworth, Yvonne P.; Meibom, Soeren; Molenda-Zakowicz, Joanna; Szabo, Robert

    2011-08-10

    Scaling relations that link asteroseismic quantities to global stellar properties are important for gaining understanding of the intricate physics that underpins stellar pulsations. The common notion that all stars in an open cluster have essentially the same distance, age, and initial composition implies that the stellar parameters can be measured to much higher precision than what is usually achievable for single stars. This makes clusters ideal for exploring the relation between the mode amplitude of solar-like oscillations and the global stellar properties. We have analyzed data obtained with NASA's Kepler space telescope to study solar-like oscillations in 100 red giant stars located in either of the three open clusters, NGC 6791, NGC 6819, and NGC 6811. By fitting the measured amplitudes to predictions from simple scaling relations that depend on luminosity, mass, and effective temperature, we find that the data cannot be described by any power of the luminosity-to-mass ratio as previously assumed. As a result we provide a new improved empirical relation which treats luminosity and mass separately. This relation turns out to also work remarkably well for main-sequence and subgiant stars. In addition, the measured amplitudes reveal the potential presence of a number of previously unknown unresolved binaries in the red clump in NGC 6791 and NGC 6819, pointing to an interesting new application for asteroseismology as a probe into the formation history of open clusters.

  13. Numerical experiments on galaxy clustering in open universes

    NASA Technical Reports Server (NTRS)

    Miller, R. H.

    1984-01-01

    Numerical studies were performed on the dynamical effects on the evolution of clumps, filaments, voids, and galaxy clusters by various final Omega values. The final Omega values examined ranged from 0.03-1, and attention was given to defining observations of superclusters which would aid in determining an actual value for Omega. The numerical trials consisted of n-body integration programs governed by the total expansion and final Omega value and included comparisons between results for open and closed universes. All runs started from the same initial conditions. The dispersion trajectories of particles and the final galactic cluster forms were found to be equivalent, regardless of the final Omega value. The possibility of deriving a value for Omega from velocity data on galaxies which have not yet joined clusters is discussed.

  14. Rotation periods of open-cluster stars, 2

    NASA Technical Reports Server (NTRS)

    Prosser, Charles F.; Shetrone, Matthew D.; Marilli, Ettore; Catalano, Santo; Williams, Scott D.; Backman, Dana E.; Laaksonen, Bentley D.; Adige, Vikram; Marschall, Laurence A.; Stauffer, John R.

    1993-01-01

    We present the results from a photometric monitoring program of 21 stars observed during 1992 in the Pleiades and Alpha Persei open clusters. Period determinations for 16 stars are given, 13 of which are the first periods reported for these stars. Brightness variations for an additional five cluster stars are also given. One K dwarf member of the alpha Per cluster is observed to have a period of rotation of only 4.39 hr. perhaps the shortest period currently known among BY Draconis variables. The individual photometric measurements have been deposited with the NSSDC. Combining current X-ray flux determinations with known photometric periods, we illustrate the X-ray activity/rotation relation among Pleiades K dwarfs based on available data.

  15. Disintegration of the Aged Open Cluster Berkeley 17

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Souradeep; Mishra, Ishan; Vaidya, Kaushar; Chen, W. P.

    2017-10-01

    We present the analysis of the morphological shape of Berkeley 17, the oldest known open cluster (∼10 Gyr), using the probabilistic star counting of Pan-STARRS point sources, and confirm its core-tail shape, plus an antitail, previously detected with the 2MASS data. The stellar population, as diagnosed by the color–magnitude diagram and theoretical isochrones, shows many massive members in the clusters core, whereas there is a paucity of such members in both of the tails. This manifests mass segregation in this aged star cluster with the low-mass members being stripped away from the system. It has been claimed that Berkeley 17 is associated with an excessive number of blue straggler candidates. A comparison of nearby reference fields indicates that about half of these may be field contamination.

  16. Clustering WHO-ART Terms Using Semantic Distance and Machine Learning Algorithms

    PubMed Central

    Iavindrasana, Jimison; Bousquet, Cedric; Degoulet, Patrice; Jaulent, Marie-Christine

    2006-01-01

    WHO-ART was developed by the WHO collaborating centre for international drug monitoring in order to code adverse drug reactions. We assume that computation of semantic distance between WHO-ART terms may be an efficient way to group related medical conditions in the WHO database in order to improve signal detection. Our objective was to develop a method for clustering WHO-ART terms according to some proximity of their meanings. Our material comprises 758 WHO-ART terms. A formal definition was acquired for each term as a list of elementary concepts belonging to SNOMED international axes and characterized by modifier terms in some cases. Clustering was implemented as a terminology service on a J2EE server. Two different unsupervised machine learning algorithms (KMeans, Pvclust) clustered WHO-ART terms according to a semantic distance operator previously described. Pvclust grouped 51% of WHO-ART terms. K-Means grouped 100% of WHO-ART terms but 25% clusters were heterogeneous with k = 180 clusters and 6% clusters were heterogeneous with k = 32 clusters. Clustering algorithms associated to semantic distance could suggest potential groupings of WHO-ART terms that need validation according to the user’s requirements. PMID:17238365

  17. Clustering WHO-ART terms using semantic distance and machine learning algorithms.

    PubMed

    Iavindrasana, Jimison; Bousquet, Cedric; Degoulet, Patrice; Jaulent, Marie-Christine

    2006-01-01

    WHO-ART was developed by the WHO collaborating centre for international drug monitoring in order to code adverse drug reactions. We assume that computation of semantic distance between WHO-ART terms may be an efficient way to group related medical conditions in the WHO database in order to improve signal detection. Our objective was to develop a method for clustering WHO-ART terms according to some proximity of their meanings. Our material comprises 758 WHO-ART terms. A formal definition was acquired for each term as a list of elementary concepts belonging to SNOMED international axes and characterized by modifier terms in some cases. Clustering was implemented as a terminology service on a J2EE server. Two different unsupervised machine learning algorithms (KMeans, Pvclust) clustered WHO-ART terms according to a semantic distance operator previously described. Pvclust grouped 51% of WHO-ART terms. K-Means grouped 100% of WHO-ART terms but 25% clusters were heterogeneous with k = 180 clusters and 6% clusters were heterogeneous with k = 32 clusters. Clustering algorithms associated to semantic distance could suggest potential groupings of WHO-ART terms that need validation according to the user's requirements.

  18. Managing the Changing Nature of Distance and Open Education at Institutional Level.

    ERIC Educational Resources Information Center

    King, Bruce

    2001-01-01

    Discusses changes that distance and open learning are facing, partly because the context of higher education generally is being transformed. Topics include globalization; massification; increasing government intervention; technological developments; resistance from teachers; individualization; institutional change; and the need for management…

  19. Managing the Changing Nature of Distance and Open Education at Institutional Level.

    ERIC Educational Resources Information Center

    King, Bruce

    2001-01-01

    Discusses changes that distance and open learning are facing, partly because the context of higher education generally is being transformed. Topics include globalization; massification; increasing government intervention; technological developments; resistance from teachers; individualization; institutional change; and the need for management…

  20. A CHEMICAL ABUNDANCE STUDY OF RED GIANTS IN OPEN CLUSTERS NGC 2204 AND NGC 2243

    SciTech Connect

    Jacobson, Heather R.; Friel, Eileen D.; Pilachowski, Catherine A. E-mail: edfriel@mac.com

    2011-02-15

    Detailed element abundances have been determined for 10-13 stars each in the open clusters (OCs) NGC 2204 and NGC 2243 based on Hydra multi-object echelle spectra obtained with the CTIO 4 m telescope. We have found average cluster metallicities of [Fe/H] = -0.23 {+-} 0.04 and -0.42 {+-} 0.05 for NGC 2204 and NGC 2243, respectively, from an equivalent width analysis. NGC 2243 is the most metal-poor cluster at its Galactocentric radius and is one of the most metal-poor OCs currently known. These two clusters lie {approx}1 kpc below the Galactic plane; it is therefore worthwhile to compare their abundance patterns to those of clusters both closer to and further from the plane. To that end, we combined the results of the current study with those of clusters from our previous work as well as from the literature. To minimize systematic differences between different studies, element abundances of many outer disk OCs as well as thin and thick disk field stars have been placed on our abundance scale. Plots of [X/Fe] versus [Fe/H] for NGC 2204, NGC 2243, other clusters from the literature, and thin and thick disk field stars show NGC 2204 and NGC 2243 to have element abundance patterns comparable to those of other clusters regardless of distance from the plane or center of the Galaxy. Similarly, no individual cluster or group of clusters far from the Galactic mid-plane can be identified as belonging to the thick disk based on their abundance patterns.

  1. The Gaia-ESO Survey: the inner disk, intermediate-age open cluster Trumpler 23

    NASA Astrophysics Data System (ADS)

    Overbeek, J. C.; Friel, E. D.; Donati, P.; Smiljanic, R.; Jacobson, H. R.; Hatzidimitriou, D.; Held, E. V.; Magrini, L.; Bragaglia, A.; Randich, S.; Vallenari, A.; Cantat-Gaudin, T.; Tautvaišienė, G.; Jiménez-Esteban, F.; Frasca, A.; Geisler, D.; Villanova, S.; Tang, B.; Muñoz, C.; Marconi, G.; Carraro, G.; San Roman, I.; Drazdauskas, A.; Ženovienė, R.; Gilmore, G.; Jeffries, R. D.; Flaccomio, E.; Pancino, E.; Bayo, A.; Costado, M. T.; Damiani, F.; Jofré, P.; Monaco, L.; Prisinzano, L.; Sousa, S. G.; Zaggia, S.

    2017-02-01

    Context. Trumpler 23 is a moderately populated, intermediate-age open cluster within the solar circle at a RGC 6 kpc. It is in a crowded field very close to the Galactic plane and the color-magnitude diagram shows significant field contamination and possible differential reddening; it is a relatively understudied cluster for these reasons, but its location makes it a key object for determining Galactic abundance distributions. Aims: New data from the Gaia-ESO Survey enable the first ever radial velocity and spectroscopic metallicity measurements for this cluster. We aim to use velocities to isolate cluster members, providing more leverage for determining cluster parameters. Methods: Gaia-ESO Survey data for 167 potential members have yielded radial velocity measurements, which were used to determine the systemic velocity of the cluster and membership of individual stars. Atmospheric parameters were also used as a check on membership when available. Literature photometry was used to re-determine cluster parameters based on radial velocity member stars only; theoretical isochrones are fit in the V, V-I diagram. Cluster abundance measurements of ten radial-velocity member stars with high-resolution spectroscopy are presented for 24 elements. These abundances have been compared to local disk stars, and where possible placed within the context of literature gradient studies. Results: We find Trumpler 23 to have an age of 0.80 ± 0.10 Gyr, significant differential reddening with an estimated mean cluster E(V-I) of 1.02, and an apparent distance modulus of 14.15 ± 0.20. We find an average cluster metallicity of [Fe/H] = 0.14 ± 0.03 dex, a solar [α/Fe] abundance, and notably subsolar [s-process/Fe] abundances.

  2. Strategic Developments in Open and Distance Learning in Central and Eastern Europe.

    ERIC Educational Resources Information Center

    Williams, Ruth

    2000-01-01

    Based on work by the European Union's PHARE Multi-Country Programme in Distance Education, explores: (1) contextual issues related to the development of open and distance learning and the changing nature of higher education; (2) developments across Europe and associated problems; and (3) possible solutions in Central and Eastern Europe related to…

  3. Transactional Distance among Open University Students: How Does it Affect the Learning Process?

    ERIC Educational Resources Information Center

    Kassandrinou, Amanda; Angelaki, Christina; Mavroidis, Ilias

    2014-01-01

    This study examines the presence of transactional distance among students, the factors affecting it, as well as the way it influences the learning process of students in a blended distance learning setting in Greece. The present study involved 12 postgraduate students of the Hellenic Open University (HOU). A qualitative research was conducted,…

  4. Application of the Classification Tree Model in Predicting Learner Dropout Behaviour in Open and Distance Learning

    ERIC Educational Resources Information Center

    Yasmin, Dr.

    2013-01-01

    This paper demonstrates the meaningful application of learning analytics for determining dropout predictors in the context of open and distance learning in a large developing country. The study was conducted at the Directorate of Distance Education at the University of North Bengal, West Bengal, India. This study employed a quantitative research…

  5. Burnout Syndrome in Students of a Distance Learning Program: The Open University of Cyprus Experience

    ERIC Educational Resources Information Center

    Pavlakis, Andreas; Kaitelidou, Dafni

    2012-01-01

    Introduction: Distance learning seems to have a crucial impact on the social and emotional life of students. Within the framework of distance learning at the Open University of Cyprus, the "Healthcare Management" department conducted a study regarding the levels of stress, anxiety and depression reported by the student population. The…

  6. Characteristics of Distance Learners at the Universitas Terbuka (Open University) Indonesia.

    ERIC Educational Resources Information Center

    Hiola, Yahya; Moss, Dennis

    1990-01-01

    Describes survey of distance education students at the Universitas Terbuka, the Open University of Indonesia, that was conducted to determine characteristics of the students and their attitudes toward distance learning. Findings related to gender, status, age, occupation, and previous qualifications are reported, and implications for third world…

  7. Student Access to and Skills in Using Technology in an Open and Distance Learning Context

    ERIC Educational Resources Information Center

    Liebenberg, Hanlie; Chetty, Yuraisha; Prinsloo, Paul

    2012-01-01

    Amidst the different challenges facing higher education, and particularly distance education (DE) and open distance learning (ODL), access to information and communication technology (ICT) and students' abilities to use ICTs are highly contested issues in the South African higher education landscape. While there are various opinions about the…

  8. A spectroscopic study of the open cluster NGC 6250

    NASA Astrophysics Data System (ADS)

    Martin, A. J.; Stift, M. J.; Fossati, L.; Bagnulo, S.; Scalia, C.; Leone, F.; Smalley, B.

    2017-04-01

    We present the chemical abundance analysis of 19 upper main-sequence stars of the young open cluster NGC 6250 (log t ∼ 7.42 yr). This work is part of a project aimed at setting observational constraints on the theory of atomic diffusion in stellar photospheres, by means of a systematic study of the abundances of the chemical elements of early F-, A- and late B-type stars of well-determined age. Our data set consists of low-, medium- and high-resolution spectra obtained with the Fibre Large Array Multi Element Spectrograph (FLAMES) instrument of the ESO Very Large Telescope (VLT). To perform our analysis, we have developed a new suite of software tools for the chemical abundance analysis of stellar photospheres in local thermodynamical equilibrium. Together with the chemical composition of the stellar photospheres, we have provided new estimates of the cluster mean radial velocity, proper motion, refined the cluster membership, and we have given the stellar parameters including masses and fractional age. We find no evidence of statistically significant correlation between any of the parameters, including abundance and cluster age, except perhaps for an increase in Ba abundance with cluster age. We have proven that our new software tool may be successfully used for the chemical abundance analysis of large data sets of stellar spectra.

  9. Roche volume filling and the dissolution of open star clusters

    NASA Astrophysics Data System (ADS)

    Ernst, A.; Berczik, P.; Just, A.; Noel, T.

    2015-08-01

    From direct N-body simulations we find that the dynamical evolution of star clusters is strongly influenced by the Roche volume filling factor. We present a parameter study of the dissolution of open star clusters with different Roche volume filling factors and different particle numbers. We study both Roche volume underfilling and overfilling models and compare with the Roche volume filling case. We find that in the Roche volume overfilling limit of our simulations two-body relaxation is no longer the dominant dissolution mechanism but the changing cluster potential. We call this mechanism ``mass-loss driven dissolution'' in contrast to ``two-body relaxation driven dissolution'' which occurs in the Roche volume underfilling regime. We have measured scaling exponents of the dissolution time with the two-body relaxation time. In this experimental study we find a decreasing scaling exponent with increasing Roche volume filling factor. The evolution of the escaper number in the Roche volume overfilling limit can be described by a log-logistic differential equation. We report the finding of a resonance condition which may play a role for the evolution of star clusters and may be calibrated by the main periodic orbit in the large island of retrograde quasiperiodic orbits in the Poincaré surfaces of section. We also report on the existence of a stability curve which may be of relevance with respect to the structure of star clusters.

  10. A Bayesian Analysis of the Ages of Four Open Clusters

    NASA Astrophysics Data System (ADS)

    Jeffery, Elizabeth J.; von Hippel, Ted; van Dyk, David A.; Stenning, David C.; Robinson, Elliot; Stein, Nathan; Jefferys, William H.

    2016-09-01

    In this paper we apply a Bayesian technique to determine the best fit of stellar evolution models to find the main sequence turn-off age and other cluster parameters of four intermediate-age open clusters: NGC 2360, NGC 2477, NGC 2660, and NGC 3960. Our algorithm utilizes a Markov chain Monte Carlo technique to fit these various parameters, objectively finding the best-fit isochrone for each cluster. The result is a high-precision isochrone fit. We compare these results with the those of traditional “by-eye” isochrone fitting methods. By applying this Bayesian technique to NGC 2360, NGC 2477, NGC 2660, and NGC 3960, we determine the ages of these clusters to be 1.35 ± 0.05, 1.02 ± 0.02, 1.64 ± 0.04, and 0.860 ± 0.04 Gyr, respectively. The results of this paper continue our effort to determine cluster ages to a higher precision than that offered by these traditional methods of isochrone fitting.

  11. Photometry and spectroscopy in the open cluster alpha Persei, 2.

    NASA Technical Reports Server (NTRS)

    Prosser, Charles F.

    1994-01-01

    Results from a combination of new spectroscopic and photometric observations in the lower main sequence and pre-main sequence of the open cluster alpha Persei are presented. New echelle spectroscopy has provided radial and rotational velocity information for thirteen candidate members, three of which are nonmembers based on radial velocity, absence of a Li 6707 A feature, and absence of H alpha emission. A set of revised rotational velocity estimates for several slowly rotating candidates identified earlier is given, yielding rotational velocities as low as 7 km/s for two apparent cluster members. VI photometry for several pre-main-sequence members is given; the new (V, V-I(sub K) photometry yields a more clearly defined pre-main sequence. A list of approximately 30 new faint candidate members based on the (V, V-I(sub K)), charge coupled device (CCD) photometry is presented in an effort to identify additional cluster members at very low masses. Low-dispersion spectra obtained for several of these candidates provide in some cases supporting evidence for cluster membership. The single brown dwarf candidate in this cluster is for the first time placed in a color-magnitude diagram with other cluster members, providing a better means for establishing its true status. Stars from among the list of new photometric candidates may provide the means for establishing a sequence of cluster members down to very faint magnitudes (V approximately 21) and consequently very low masses. New coordinate determinations for previous candidate members and finding charts for the new photometric candidates are provided in Appendices.

  12. Photometry and spectroscopy in the open cluster Alpha Persei, 2

    NASA Technical Reports Server (NTRS)

    Prosser, Charles F.

    1993-01-01

    Results from a combination of new spectroscopic and photometric observations in the lower main-sequence and pre-main sequence of the open cluster alpha Persei are presented. New echelle spectroscopy has provided radial and rotational velocity information for thirteen candidate members, three of which are nonmembers based on radial velocity, absence of a Li 6707A feature, and absence of H-alpha emission. A set of revised rotational velocity estimates for several slowly rotating candidates identified earlier is given, yielding rotational velocities as low as 7 km/s for two apparent cluster members. VRI photometry for several pre-main sequence members is given; the new (V,V-I(sub K)) photometry yields a more clearly defined pre-main sequence. A list of approximately 43 new faint candidate members based on the (V,V-I(sub K)) CCD photometry is presented in an effort to identify additional cluster members at very low masses. Low-dispersion spectra obtained for several of these candidates provide in some cases supporting evidence for cluster membership. The single brown dwarf candidate in this cluster is for the first time placed in a color-magnitude diagram with other cluster members, providing a better means for establishing its true status. Stars from among the list of new photometric candidates may provide the means for establishing a sequence of cluster members down to very faint magnitudes (V approximately 21) and consequently very low masses. New coordinate determinations for previous candidate members and finding charts for the new photometric candidates are provided in appendices.

  13. Photometry and spectroscopy in the open cluster alpha Persei, 2.

    NASA Technical Reports Server (NTRS)

    Prosser, Charles F.

    1994-01-01

    Results from a combination of new spectroscopic and photometric observations in the lower main sequence and pre-main sequence of the open cluster alpha Persei are presented. New echelle spectroscopy has provided radial and rotational velocity information for thirteen candidate members, three of which are nonmembers based on radial velocity, absence of a Li 6707 A feature, and absence of H alpha emission. A set of revised rotational velocity estimates for several slowly rotating candidates identified earlier is given, yielding rotational velocities as low as 7 km/s for two apparent cluster members. VI photometry for several pre-main-sequence members is given; the new (V, V-I(sub K) photometry yields a more clearly defined pre-main sequence. A list of approximately 30 new faint candidate members based on the (V, V-I(sub K)), charge coupled device (CCD) photometry is presented in an effort to identify additional cluster members at very low masses. Low-dispersion spectra obtained for several of these candidates provide in some cases supporting evidence for cluster membership. The single brown dwarf candidate in this cluster is for the first time placed in a color-magnitude diagram with other cluster members, providing a better means for establishing its true status. Stars from among the list of new photometric candidates may provide the means for establishing a sequence of cluster members down to very faint magnitudes (V approximately 21) and consequently very low masses. New coordinate determinations for previous candidate members and finding charts for the new photometric candidates are provided in Appendices.

  14. A Hubble Space Telescope Photometric Study of the Galactic Open Cluster Westerlund 2

    NASA Astrophysics Data System (ADS)

    Vargas Alvarez, Carlos; Kobulnicky, H.

    2012-01-01

    The young and massive Galactic open cluster Westerlund 2 has been a source of controversy because of the widely varying and inconsistent estimates for its distance. In this study we use Hubble Space Telescope multi-band photometry to make improved photometric measurements in the crowded cluster core where many of the most luminous members are now resolved into multiple stars. Using new stellar spectroscopy, we provide a more reliable distance measurement based on the mean spectroscopic parallax of 20 O-type member stars. The new spectrophotometric distance, after correction for reddening, is 7.38 ± 0.02 (random) ± 0.08 (systematic) kpc. We also use the HST optical photometry along with mid-infrared photometry to correct for reddening on a star-by-star basis. Differential reddening causes AV to vary from 1.11 mag to as much as 39.25 mag across the cluster. The best solar metallicity isochrone fit to the de-reddened color-magnitude diagram corresponds to an age of 1 - 3 Myr.

  15. A New Distance Measurement to NGC 4874 in the Coma Cluster

    NASA Astrophysics Data System (ADS)

    Bartier, Crystal-Lynn; Jensen, Joseph; Blakeslee, John

    2017-01-01

    By measuring distances to remote galaxies we can determine the size, expansion rate, and age of the Universe. One of the best ways to measure distance is known as surface brightness fluctuations (SBF). The purpose of this research is to improve the current distance to the Coma Cluster by making accurate SBF distance measurements to two galaxies, NGC 4874 and NGC 4921. We analyzed HST WFC3 images in the F110W and F160W bands for NGC 4874 and ACS F814W and F606W for NGC 4921. Although NGC 4921 has a Cepheid distance measurement, we were unable to make an SBF measurement to NGC 4921 due to the presence of dust and young stars. The results of the distance measurement to NGC 4874 will be compared with previous distance measurements for the Coma Cluster. We also present a comparison of the globular cluster luminosity function for NGC 4874 measured using Source Extractor and a modified version of Dophot to help determine the photometric accuracy of our measurements in the presence of the bright galaxy background.

  16. Abundances and kinematics for ten anticentre open clusters

    NASA Astrophysics Data System (ADS)

    Cantat-Gaudin, T.; Donati, P.; Vallenari, A.; Sordo, R.; Bragaglia, A.; Magrini, L.

    2016-04-01

    Context. Open clusters are distributed all across the Galactic disk and are convenient tracers of its properties. In particular, outer disk clusters bear a key role in the investigation of the chemical evolution of the Galactic disk. Aims: The goal of this study is to derive homogeneous elemental abundances for a sample of ten outer disk open clusters, and investigate possible links with disk structures such as the Galactic anticentre stellar structure. Methods: We analysed high-resolution spectra of red giants, obtained from the Keck-HIRES and VLT-UVES archives. We derived elemental abundances and stellar atmosphere parameters by means of the classical equivalent width method. We also performed orbit integrations using proper motions. Results: The Fe abundances we derive trace a shallow negative radial metallicity gradient of slope -0.027 ± 0.007 dex kpc-1 in the outer 12 kpc of the disk. The [α/Fe] gradient appears flat, with a slope of 0.006 ± 0.007 dex kpc-1. The two outermost clusters (Be 29 and Sau 1) appear to follow elliptical orbits. The cluster Be 20 also exhibits a peculiar orbit with a large excursion above the plane. Conclusions: The irregular orbits of the three most metal poor clusters (two of which are located at the edge of the Galactic disk), are compatible with an inside-out formation scenario for the Milky Way in which extragalactic material is accreted onto the outer disk. This is the case if the irregular orbits of these clusters are confirmed by more robust astrometric measurements such as those of the Gaia mission. We cannot determine whether Be 20, Be 29, and Sau 1 are of extragalactic origin, as they may be old, genuine Galactic clusters whose orbits were perturbed by accretion events or minor mergers in the past 5 Gyr, or they may be representants of the thick disk population. The nature of these objects is intriguing and deserves further investigation in the near future. The measured equivalent widths are only available at the CDS via

  17. The young open cluster NGC 7067 using Strömgren photometry

    NASA Astrophysics Data System (ADS)

    Monguió, M.; Negueruela, I.; Marco, A.; González-Fernández, C.; Alonso-Santiago, J.; Costado, M. T.; Casamiquela, L.; López-Corredoira, M.; Molgó, J.; Vilardell, F.; Alfaro, E. J.; Antoja, T.; Figueras, F.; Garcia, M.; Jordi, C.; Romero-Gómez, M.

    2017-04-01

    NGC 7067 is a young open cluster located in the direction between the first and the second Galactic quadrants and close to the Perseus spiral arm. This makes it useful for studies of the nature of the Milky Way spiral arms. Strömgren photometry taken with the Wide Field Camera at the Isaac Newton Telescope allowed us to compute individual physical parameters for the observed stars and hence to derive the cluster's physical parameters. Spectra from the 1.93-m telescope at the Observatoire de Haute-Provence helped to check and improve the results. We obtained photometry for 1233 stars, individual physical parameters for 515 and spectra for 9 of them. The 139 selected cluster members lead to a cluster distance of 4.4 ± 0.4 kpc, with an age below log10(t(yr)) = 7.3 and a present mass of 1260 ± 160 M⊙. The morphology of the data reveals that the centre of the cluster is at (α, δ) = (21: 24: 13.69, +48: 00: 39.2) J2000, with a radius of 6.1 arcmin. Strömgren and spectroscopic data allowed us to improve the previous parameters available for the cluster in the literature.

  18. DETECTION OF SOLAR-LIKE OSCILLATIONS FROM KEPLER PHOTOMETRY OF THE OPEN CLUSTER NGC 6819

    SciTech Connect

    Stello, Dennis; Bedding, Timothy R.; Huber, Daniel; Basu, Sarbani; Bruntt, Hans; Mosser, BenoIt; Barban, Caroline; Goupil, Marie-Jo; Stevens, Ian R.; Chaplin, William J.; Elsworth, Yvonne P.; Hekker, Saskia; Brown, Timothy M.; Christensen-Dalsgaard, Joergen; Kjeldsen, Hans; Arentoft, Torben; Gilliland, Ronald L.; Ballot, Jerome; GarcIa, Rafael A.

    2010-04-20

    Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance, and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819-one of the four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation, {delta}{nu}, and the frequency of maximum oscillation power, {nu}{sub max}. We find that the asteroseismic parameters allow us to test cluster membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about 2 orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler.

  19. Testing the chemical tagging technique with open clusters

    NASA Astrophysics Data System (ADS)

    Blanco-Cuaresma, S.; Soubiran, C.; Heiter, U.; Asplund, M.; Carraro, G.; Costado, M. T.; Feltzing, S.; González-Hernández, J. I.; Jiménez-Esteban, F.; Korn, A. J.; Marino, A. F.; Montes, D.; San Roman, I.; Tabernero, H. M.; Tautvaišienė, G.

    2015-05-01

    Context. Stars are born together from giant molecular clouds and, if we assume that the priors were chemically homogeneous and well-mixed, we expect them to share the same chemical composition. Most of the stellar aggregates are disrupted while orbiting the Galaxy and most of the dynamic information is lost, thus the only possibility of reconstructing the stellar formation history is to analyze the chemical abundances that we observe today. Aims: The chemical tagging technique aims to recover disrupted stellar clusters based merely on their chemical composition. We evaluate the viability of this technique to recover co-natal stars that are no longer gravitationally bound. Methods: Open clusters are co-natal aggregates that have managed to survive together. We compiled stellar spectra from 31 old and intermediate-age open clusters, homogeneously derived atmospheric parameters, and 17 abundance species, and applied machine learning algorithms to group the stars based on their chemical composition. This approach allows us to evaluate the viability and efficiency of the chemical tagging technique. Results: We found that stars at different evolutionary stages have distinct chemical patterns that may be due to NLTE effects, atomic diffusion, mixing, and biases. When separating stars into dwarfs and giants, we observed that a few open clusters show distinct chemical signatures while the majority show a high degree of overlap. This limits the recovery of co-natal aggregates by applying the chemical tagging technique. Nevertheless, there is room for improvement if more elements are included and models are improved. Based on observations obtained at the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique of France, and on public data obtained from the ESO Science Archive Facility under requests number 81252 and 81618.

  20. Time-Series Monitoring of Open Star Clusters

    NASA Astrophysics Data System (ADS)

    Hojaev, A. S.; Semakov, D. G.

    2006-08-01

    Star clusters especially a compact ones (with diameter of few to ten arcmin) are suitable targets to search of light variability for orchestera of stars by means of ordinary Casegrain telescope plus CCD system. A special patroling with short time-fixed exposures and mmag accuracy could be used also to study of stellar oscillation for group of stars simultaneously. The last can be carried out both separately from one site and within international campaigns. Detection and study of optical variability of X-ray sources including X-ray binaries with compact objects might be as a result of a long-term monitoring of such clusters as well. We present the program of open star clusters monitoring with Zeiss 1 meter RCC telescope of Maidanak observatory has been recently automated. In combination with quite good seeing at this observatory (see, e.g., Sarazin, M. 1999, URL http://www.eso.org/gen-fac/pubs/astclim/) the automatic telescope equipped with large-format (2KX2K) CCD camera AP-10 available will allow to collect homogenious time-series for analysis. We already started this program in 2001 and had a set of patrol observations with Zeiss 0.6 meter telescope and AP-10 camera in 2003. 7 compact open clusters in the Milky Way (NGC 7801, King1, King 13, King18, King20, Berkeley 55, IC 4996) have been monitored for stellar variability and some results of photometry will be presented. A few interesting variables were discovered and dozens were suspected for variability to the moment in these clusters for the first time. We have made steps to join the Whole-Earth Telescope effort in its future campaigns.

  1. Globalization, Information and Communication Technologies (ICTs) and Open/Distance Learning in Nigeria: Trends, Issues and Solution

    ERIC Educational Resources Information Center

    Olusola, Akande Joshua; Alaba, Sofowora Olaniyi

    2011-01-01

    The main thrust of this paper is to discuss the development of open and distance education in Nigeria and the major manifestations of the use of information and communication technologies (ICTs) in education in open and distance learning. This study further discusses the importance and use of ICTs in open and distance learning in making education…

  2. THE IMPACT OF CONTAMINATED RR LYRAE/GLOBULAR CLUSTER PHOTOMETRY ON THE DISTANCE SCALE

    SciTech Connect

    Majaess, D.; Turner, D.; Lane, D.; Gieren, W.

    2012-06-10

    RR Lyrae variables and the stellar constituents of globular clusters are employed to establish the cosmic distance scale and age of the universe. However, photometry for RR Lyrae variables in the globular clusters M3, M15, M54, M92, NGC 2419, and NGC 6441 exhibit a dependence on the clustercentric distance. For example, variables and stars positioned near the crowded high-surface brightness cores of the clusters may suffer from photometric contamination, which invariably affects a suite of inferred parameters (e.g., distance, color excess, absolute magnitude, etc.). The impetus for this study is to mitigate the propagation of systematic uncertainties by increasing awareness of the pernicious impact of contaminated and radial-dependent photometry.

  3. Integrated Teacher Education Programme for Open Distance Learning: A Model for Development and Implementation

    ERIC Educational Resources Information Center

    Bose, Sutapa

    2013-01-01

    Teacher education in India, including that offered by the open distance learning (ODL) system to thousands every year, imparts mainly pedagogic knowledge, although the need for integrated teacher education programmes has been underscored. As the Indira Gandhi National Open University (IGNOU), an ODL institution, will develop an integrated Bachelor…

  4. Recasting Distance Learning with Network-Enabled Open Education: An Interview with Vijay Kumar

    ERIC Educational Resources Information Center

    Morrison, James L.; Kumar, Vijay

    2008-01-01

    In an interview with James Morrison, "Innovate's" editor-in-chief, Vijay Kumar describes how rethinking distance learning as network-enabled open education can catalyze a whole new set of learning opportunities. The growing open-education movement has made an increasing number and variety of resources freely available online, including everything…

  5. Integrated Teacher Education Programme for Open Distance Learning: A Model for Development and Implementation

    ERIC Educational Resources Information Center

    Bose, Sutapa

    2013-01-01

    Teacher education in India, including that offered by the open distance learning (ODL) system to thousands every year, imparts mainly pedagogic knowledge, although the need for integrated teacher education programmes has been underscored. As the Indira Gandhi National Open University (IGNOU), an ODL institution, will develop an integrated Bachelor…

  6. Exploring Open Distance Learning at a Jordanian University: A Case Study

    ERIC Educational Resources Information Center

    Dirani, Khalil M.; Yoon, Seung Won

    2009-01-01

    This case study explores an open distance learning program offered by the Information Technology and Computing (ITC) department at AOUJ, a major university in Jordan. It provides an overview of e-learning in the Arab region and explores factors that affect ODL quality in the Arab Open University in Jordan (AOUJ). The research utilized a…

  7. Effects of Mathematics Innovation and Technology on Students Performance in Open and Distance Learning

    ERIC Educational Resources Information Center

    Israel, Oginni 'Niyi

    2016-01-01

    This study investigated the effect of mathematics innovation and technology on students' academic performance in open and distance learning. Quasi -- experimental research design was adopted for the study. The population for the study consisted of all the 200 level primary education students at the National Open University of Nigeria (Ekiti and…

  8. Recasting Distance Learning with Network-Enabled Open Education: An Interview with Vijay Kumar

    ERIC Educational Resources Information Center

    Morrison, James L.; Kumar, Vijay

    2008-01-01

    In an interview with James Morrison, "Innovate's" editor-in-chief, Vijay Kumar describes how rethinking distance learning as network-enabled open education can catalyze a whole new set of learning opportunities. The growing open-education movement has made an increasing number and variety of resources freely available online, including everything…

  9. The Origin of Gamma-Rays from Young Open Clusters

    NASA Astrophysics Data System (ADS)

    Fujita, Yutaka; Muller, Erik; Saito, Masao; Kobayashi, Naoto; Yasui, Chikako

    2012-04-01

    Young massive open clusters are often believed to be sites of cosmic-ray (CR) acceleration. In such clusters, OB stars explode for short intervals of time, and CRs may be accelerated to higher energies than those in a single supernova remnant. Thus, with MOPRA we propose to observe two young massive open clusters, Westerlund 1 and RSGC 1, from which gamma-rays have been detected. We observe them in order to reveal the origin of the gamma-rays and acceleration mechanism of the CRs from which gamma-rays originate. We plan to observe recombination line emission of H73a and CO to find the kinematics and distribution of interstellar matter (ISM). From the velocity fields of the ISM, we will find the position of the energy source. From the ratio of the ISM kinetic energy to the total CR energy, we can find the efficiency of CR acceleration, which gives us a clue to the acceleration mechanism of the CRs. From the correlation between ISM maps and gamma-ray maps, we can conclude whether ISM is working as the targets of the CR.

  10. Clustering of Local Group Distances: Publication Bias or Correlated Measurements? V. Galactic Rotation Constants

    NASA Astrophysics Data System (ADS)

    de Grijs, Richard; Bono, Giuseppe

    2017-10-01

    As part of an extensive data mining effort, we have compiled a database of 162 Galactic rotation speed measurements at R 0 (the solar Galactocentric distance), {{{\\Theta }}}0. Published between 1927 and 2017 June, this represents the most comprehensive set of {{{\\Theta }}}0 values since the 1985 meta-analysis that led to the last revision of the International Astronomical Union’s recommended Galactic rotation constants. Although we do not find any compelling evidence for the presence of “publication bias” in recent decades, we find clear differences among the {{{\\Theta }}}0 values and the {{{\\Theta }}}0/{R}0 ratios resulting from the use of different tracer populations. Specifically, young tracers (including OB and supergiant stars, masers, Cepheid variables, H ii regions, and young open clusters), as well as kinematic measurements of Sgr A* near the Galactic Center, imply a significantly larger Galactic rotation speed at the solar circle and a higher {{{\\Theta }}}0/{R}0 ratio (i.e., {{{\\Theta }}}0=247+/- 3 km s‑1 and {{{\\Theta }}}0/{R}0=29.81+/- 0.32 km s‑1 kpc‑1 statistical uncertainties only) than any of the tracers dominating the Galaxy’s mass budget (i.e., field stars and the H i/CO distributions). Using the latter to be most representative of the bulk of the Galaxy’s matter distribution, we arrive at an updated set of Galactic rotation constants,

  11. A Dynamical Evolution Study of 40 2MASS Open Clusters

    NASA Astrophysics Data System (ADS)

    Güneş, Orhan; Karataş, Yüksel; Bonatto, Charles

    2017-05-01

    We investigate the dynamical evolution of 40 open clusters (OCs) by means of their astrophysical parameters derived from field-decontaminated 2MASS photometry. We find a bifurcation in the planes core radius vs. age and cluster radius vs. age, in which part of the clusters appear to expand with time probably due to the presence of stellar black holes while others seem to shrink due to dynamical relaxation. Mass functions (MFs) are built for 3/4 of the sample (31 OCs), which are used to search for indications of mass segregation and external dynamical processes by means of relations among astrophysical, structural and evolutionary parameters. We detect a flattening of MF slopes ocurring at the evolutionary parameters τ_{core}≤ 32 and τ_{overall}≤ 30, respectively. Within the uncertainties involved, the overall MF slopes of 14 out of 31 OCs with m_{overall} > 500 M_{⊙} are consistent with Kroupa's initial mass function, implying little or no dynamical evolution for these clusters. The remaining 17 OCs with MF slopes departing from that of Kroupa show mild/large scale mass segregation due to dynamical evolution.

  12. Chemical composition of the old open clusters melotte 66 and NGC 2243

    SciTech Connect

    Gratton, R.G.

    1982-06-15

    The chemical composition of the old open cluster Melotte 66 and NGC 2243 is determined by means of high-dispersion spectra of some red giants and a model atmosphere analysis. The two clusters are found to be quite metal poor ((Fe/H) = -0.7 +- 0.1 for Melotte 66 and (Fe/H) = -1.2 +- 0.1 for NGC 2243), with oxygen perhaps enhanced in NGC 2243. A reanalysis is made of the color-magnitude diagrams of the four old open clusters which have been studied with high dispersion (M67, NGC 2420, NGC 2243, and Melotte 66), and new values for the distance moduli of M67 and Melotte 66 are determined. Age estimates are 4 x 10/sup 9/ years for M67 and NGC 2420 and 6 x 10/sup 9/ years for NGC 2243 and Melotte 66. The helium content = 0.25 +- 0.03 is estimated from the magnitude of the horizontal branch and the ratio of the horizontal branch stars to red giants, and seems remarkably constant within this sample of clusters. The results suggest that the time scale of the galactic halo collapse is long (5--10 x 10/sup 9/ years), in agreement with recent models.

  13. Fundamental parameters of the highly reddened young open clusters Westerlund 1 and 2

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Bica, E.; Claria, J. J.

    1998-02-01

    We study the compact open clusters Westerlund1 (BH197) and Westerlund2. We present CCD integrated spectroscopy for both clusters, and CCD imaging in the V and I bands for the former one. So far, Westerlund1 is possibly the most reddened open cluster studied in detail (Av ~ 13.0). It has an age of 8 +/- 3 Myr and a distance from the Sun of d_sun ~ 1.0 +/- 0.4 kpc. For Westerlund2 we derive a visual absorption AV~ 5.0 mag, an age of 2-3 Myr, and d_sun=5.7+/- 0.3 kpc. From luminosity and structural arguments we conclude that Westerlund1, although young and compact, it is a massive cluster, in contrast to Westerlund2. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina and the Universities of La Plata, Cordoba and San Juan, Argentina, and at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile. The photometric observations are available at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

  14. Water quality assessment with hierarchical cluster analysis based on Mahalanobis distance.

    PubMed

    Du, Xiangjun; Shao, Fengjing; Wu, Shunyao; Zhang, Hanlin; Xu, Si

    2017-07-01

    Water quality assessment is crucial for assessment of marine eutrophication, prediction of harmful algal blooms, and environment protection. Previous studies have developed many numeric modeling methods and data driven approaches for water quality assessment. The cluster analysis, an approach widely used for grouping data, has also been employed. However, there are complex correlations between water quality variables, which play important roles in water quality assessment but have always been overlooked. In this paper, we analyze correlations between water quality variables and propose an alternative method for water quality assessment with hierarchical cluster analysis based on Mahalanobis distance. Further, we cluster water quality data collected form coastal water of Bohai Sea and North Yellow Sea of China, and apply clustering results to evaluate its water quality. To evaluate the validity, we also cluster the water quality data with cluster analysis based on Euclidean distance, which are widely adopted by previous studies. The results show that our method is more suitable for water quality assessment with many correlated water quality variables. To our knowledge, it is the first attempt to apply Mahalanobis distance for coastal water quality assessment.

  15. WIYN open cluster study. LIX. Radial velocity membership of the evolved population of the old open cluster NGC 6791

    SciTech Connect

    Tofflemire, Benjamin M.; Gosnell, Natalie M.; Mathieu, Robert D.; Platais, Imants E-mail: imants@pha.jhu.edu

    2014-10-01

    The open cluster NGC 6791 has been the focus of much recent study due to its intriguing combination of old age and high metallicity (∼8 Gyr, [Fe/H] = +0.30), as well as its location within the Kepler field. As part of the WIYN Open Cluster Study, we present precise (σ = 0.38 km s{sup –1}) radial velocities for proper motion candidate members of NGC 6791 from Platais et al. Our survey, extending down to g' ∼ 16.8, is comprised of the evolved cluster population, including blue stragglers, giants, and horizontal branch stars. Of the 280 proper-motion-selected stars above our magnitude limit, 93% have at least one radial velocity measurement and 79% have three measurements over the course of at least 200 days, sufficient for secure radial-velocity-determined membership of non-velocity-variable stars. The Platais et al. proper motion catalog includes 12 anomalous horizontal branch candidates blueward of the red clump, of which we find only 4 to be cluster members. Three fall slightly blueward of the red clump and the fourth is consistent with being a blue straggler. The cleaned color-magnitude diagram shows a richly populated red giant branch and a blue straggler population. Half of the blue stragglers are in binaries. From our radial velocity measurement distribution, we find the cluster's radial velocity dispersion to be σ {sub c} = 0.62 ± 0.10 km s{sup –1}. This corresponds to a dynamical mass of ∼4600 M {sub ☉}.

  16. The Galactic open cluster system: evidence of enhanced formation episodes

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.

    The exciting debate about the existence of signs of enhanced formation of Galactic open clusters (OCs) is revisited here on the basis of a revised age distribution. By using the recently updated 2009 version of the Dias et al. catalogue of 1787 OCs, we found that the present OC's age distribution presents two primary excesses at t ~ 10-15 Myr and 1.5 Gyr. We interpret both excesses as signs of enhanced formation episodes similar to those that occurred in other galaxies (e.g., M 51, NGC 1705). When restricting the OC sample to those located in the solar neighbourhood, with the aim of avoiding incompleteness effects, we also find that these clusters are engraved with clear signs of enhanced formation at both ages.

  17. Blue stragglers in open clusters. III. NGC 7789

    NASA Astrophysics Data System (ADS)

    Schönberner, D.; Andrievsky, S. M.; Drilling, J. S.

    2001-02-01

    We performed for the first time a detailed LTE spectroscopic study of a sample of blue straggler stars in the moderately old open cluster NGC 7789. For eight stars the parameters and abundances of several elements were determined. The cluster members show a remarkable surface magnesium deficiency which is quite unusual for late B - early A stars. Iron and titanium abundances are in agreement with other photometric and spectroscopic estimates of the NGC 7789 metallicity. All the confirmed blue stragglers have rather low projected rotational velocities (with one exception for K88, vsin i = 80 km s-1). Based on the spectra collected at Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation, and at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Plank Institute for Astronomy, Heidelberg, jointly with the Spanish National Commission for Astronomy.}

  18. Late-Type Membership of the Open Cluster NGC 2232

    NASA Technical Reports Server (NTRS)

    Orban, Chris; Patten, Brian

    2004-01-01

    NGC 2232 is one of the nearest open clusters (approx.360 pc) with an age of approx.25 Myr. This places it in the unique position to study the transition from T Tauri activity to the Zero Age Main Sequence. In order for those studies to begin, late-type members must be identified for the cluster. X-ray observations combined with ground-based photometry and spectroscopy offers the best way to accomplish this goal. We present photometry in the VRI bands, 2MASS near-infrared measurements in the J, H , Ks bands and spectra for the suspected optical counterparts to the X-ray sources in the field of NGC 2232. 46 candidate members were identified through these efforts ranging from F5 to M5.

  19. Pushing up the size limit of chalcogenide supertetrahedral clusters: two- and three-dimensional photoluminescent open frameworks from (Cu(5)In(30)S(54))(13-) clusters.

    PubMed

    Bu, Xianhui; Zheng, Nanfeng; Li, Yuqi; Feng, Pingyun

    2002-10-30

    Direct band gap copper indium chalcogenides are of great technological importance in part because of their high photovoltaic conversion efficiency. Covalent superlattices constructed from copper indium chalcogenide clusters are of particular interest because they may combine open framework architecture with semiconducting properties. Here two photoluminescent covalent superlattices built from core-shell type copper indium sulfide supertetrahedral clusters are reported. Each cluster consists of 35 metal cations and is so far the largest known supertetrahedral cluster with a metal-to-metal distance of 1.6 nm. In addition, this is the first example of supertetrahedral clusters in heterometallic copper indium chalcogenides. The preparation of these large clusters has narrowed down the size gap between colloidal nanoclusters and small supertetrahedral clusters and revealed new possibilities in the construction of nanoporous semiconducting superlattices with tunable pore size. Through the combination of metal ions with different oxidation states to provide both overall and local charge neutrality, an effective approach has been demonstrated in the rational synthesis of chalcogenide open framework materials with large and unprecedented supertetrahedral clusters.

  20. LITHIUM IN THE INTERMEDIATE-AGE OPEN CLUSTER, NGC 3680

    SciTech Connect

    Anthony-Twarog, Barbara J.; Twarog, Bruce A.; Deliyannis, Constantine P.; Croxall, Kevin V.; Cummings, Jeffrey D. E-mail: btwarog@ku.edu E-mail: kcroxall@indiana.edu

    2009-10-15

    High-dispersion spectra centered on the Li 6708 A line have been obtained for 70 potential members of the intermediate-age open cluster NGC 3680, with an emphasis on stars in the turnoff region of the cluster color-magnitude diagram (CMD). A measurable Li abundance has been derived for 53 stars, 39 of which have radial velocities and proper motions consistent with cluster membership. After being transferred to common temperature and abundance scales, previous Li estimates have been combined to generate a sample of 49 members, 40 of which bracket the cluster Li-dip. Spectroscopic elemental analysis of eight giants and five 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 {sup 2} isochrone comparisons lead to an age of 1.75 {+-} 0.1 Gyr and an apparent modulus of (m - M) = 10.30 {+-} 0.15 for the cluster, placing the center of the Li-dip at 1.35 {+-} 0.03 M {sub sun}. Among the giants, five of the nine cluster members are now known to have measurable Li with A(Li) near 1.0. A combined sample of dwarfs in the Hyades and Praesepe is used to delineate the Li-dip profile at 0.7 Gyr and [Fe/H] = +0.15, establishing its center at 1.42 {+-} 0.02 M {sub sun} and noting the possible existence of a secondary dip on its red boundary. When evolved to the typical age of the clusters NGC 752 (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 the observed morphology of the combined Li-dip within the CMDs of the intermediate-age clusters while implying a metallicity dependence for the central mass of the Li-dip given by M/M {sub sun} = 1.38 {+-} 0.04 + 0.4 {+-} 0.2 [Fe/H]. The implications of the similarity of the Li-dichotomy among giants in NGC 752 and IC 4651 and the disagreement with the pattern among NGC

  1. Be Stars and Physical Properties of the Young Open Cluster NGC 6834

    NASA Astrophysics Data System (ADS)

    Miller, G. J.; Grebel, E. K.; Yoss, K. M.

    1996-12-01

    We present initial results for the young open cluster NGC 6834 obtained with the 1-m telescope at Mount Laguna Observatory. We observed this cluster as part of a CCD-photometric survey for Be stars using B,V filters and two narrow-band interference filters at Hα and Hα continuum. Through a census of Be stars in clusters, where stars are coeval, equidistant, have the same metallicities, and share a common origin, we hope to gain a better understanding of the properties and origins of the still enigmatic Be phenomenon. Our B,V color-magnitude diagram of NGC 6834 shows an extended blue main sequence widened at fainter magnitudes by field star contamination. Fitting Geneva isochrones with solar metallicity to the cluster population, we find an age of ~ 50 Myr, a mean reddening of E(B-V)~ 0.7 mag, and a distance modulus of 12.2 mag (i.e. a distance of ~ 2750 pc). Our data reach roughly 4 magnitudes fainter in V than previous photographic or photoelectric studies. For the detection of Be stars, we use a two-color diagram. The most prominent feature distinguishing Be stars from B stars is their Balmer emission. The (Hα \\ continuum - Hα ) index allows us to find stars bright in Hα . The (B-V) color index serves to distinguish blue stars from red giants and red supergiants, which also may exhibit Hα emission. We find six Be star candidates in NGC 6834, that stand out clearly through their enhanced Balmer emission. Only one was known previously in this cluster. The brightness in Hα is well-correlated with reddened (B-V) colors. The relatively small number of Be stars in NGC 6834 is consistent with the young age of the cluster and the spectral type (B5) at the main-sequence turnoff.

  2. On the physical nature of six galactic open cluster candidates

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Clariá, J. J.; Ahumada, A. V.

    We present CCD UBVI_(KC) photometry in the fields of the unstudied open cluster (OC) candidates Haffner 3, Haffner 5, NGC 2368, Haffner 25, Hogg 3 and Hogg 4. Our analysis shows that none of these objects are genuine OCs since no clear main sequences or other typical features can be seen in their colour-magnitude and colour-colour diagrams. Star counts performed within and outside the OC candidate fields not only support these results but also suggest that these objects are not OC remnants. A detailed version of this work can be seen in New Astronomy, 16, 161 (2011).

  3. Two new tests to the distance duality relation with galaxy clusters

    SciTech Connect

    Santos-da-Costa, Simony; Busti, Vinicius C.; Holanda, Rodrigo F.L. E-mail: vcbusti@astro.iag.usp.br

    2015-10-01

    The cosmic distance duality relation is a milestone of cosmology involving the luminosity and angular diameter distances. Any departure of the relation points to new physics or systematic errors in the observations, therefore tests of the relation are extremely important to build a consistent cosmological framework. Here, two new tests are proposed based on galaxy clusters observations (angular diameter distance and gas mass fraction) and H(z) measurements. By applying Gaussian Processes, a non-parametric method, we are able to derive constraints on departures of the relation where no evidence of deviation is found in both methods, reinforcing the cosmological and astrophysical hypotheses adopted so far.

  4. Combining Photometric and Astrometric Data to Identify Stellar Clustering at KPC-Distances

    NASA Astrophysics Data System (ADS)

    Teixeira, R.; Medina-Tanco, G.; Corti, M.; Ducourant, C.

    2005-01-01

    A field of 0.5° × 0.5° , at l ˜ 265° and b ˜ -2° , is used as a test bed for stellar structure identification. Spectroscopic and photometric observations were used to estimate distances to the early-type stars inside in the field. Positions, distances and proper motions were combined in a series of statistical analysis to identify clustering. In this way we are able to characterize stellar structures up to distances of approximately 8 kpc, probably as far as the outer spiral arm.

  5. Searching for the birthplaces of open clusters with ages of several billion years

    NASA Astrophysics Data System (ADS)

    Acharova, I. A.; Shevtsova, E. S.

    2016-01-01

    We discuss the possibility of finding the birthplaces of open clusters (OC) with ages of several billion years. The proposed method is based on the comparison of the results of the chemical evolution modeling of the Galactic disk with the parameters of the cluster. Five OCs older than 7 Gyr are known: NGC6791, BH176, Collinder 261, Berkeley 17, and Berkeley 39. The oxygen and iron abundances in NGC6791 and the oxygen abundance in BH176 are twice the solar level, the heavy-element abundances in other clusters are close to the corresponding solar values. According to chemical evolution models, at the time of the formation of the objects considered the regions where the oxygen and iron abundances reached the corresponding levels extended out to 5 kpc from the Galactic center.At present time theOCs considered are located several kpc from the Galactic center. Some of these clusters are located extremely high, about 1 kpc above the disk midplane, i.e., they have been subject to some mechanism that has carried them into orbits uncharacteristic of this type of objects. It follows from a comparison with the results of chemical evolution that younger clusters with ages of 4-5 Gyr, e.g., NGC1193,M67, and others, may have formed in a broad range of Galactocentric distances. Their large heights above the disk midplane is sufficient to suggest that these clusters have moved away from their likely birthplaces. Clusters are carried far away from the Galactic disk until the present time: about 40 clusters with ages from 0 to 2 Gyr are observed at heights ranging from 300 to 750 pc.

  6. UBVI photometric study of open star clusters Ruprecht 25 and Czernik 6

    NASA Astrophysics Data System (ADS)

    Bisht, D.; Yadav, R. K. S.; Durgapal, A. K.

    2016-11-01

    We present a UBVI CCD photometric study of two open star clusters Ruprecht 25 and Czernik 6 using the data taken with 104-cm Sampurnanand telescope, ARIES, Nainital, India. The optical CCD data for these clusters are obtained for the first time. The clusters radii are found to be 2‧.4 and 1‧.5. Using two colour (U - B) versus (B - V) diagram we have estimated the reddening as E(B - V) = 0.55 ± 0.05 mag for Ruprecht 25 and 0.48 ± 0.05 mag for Czernik 6, while the corresponding distances are 5.8 ± 0.5 and 5.0 ± 0.3 kpc. Ages of 800 ± 80 Myr for Ruprecht 25 and 40 ± 10 Myr for Czernik 6 are determined using the stellar isochrones of metallicity Z = 0.019 . We have also determined the relaxation time for the clusters Ruprecht 25 and Czernik 6. Our analysis indicates that both clusters are dynamically relaxed. This may be due to the dynamical evolution or imprint of star formation itself or both.

  7. Radial Velocities, Binarity, and Kinematic Membership in the Open Cluster NGC 2516

    NASA Astrophysics Data System (ADS)

    González, Jorge Federico; Lapasset, Emilio

    2000-05-01

    We present echelle spectroscopic observations for 36 bright (V<9.6) stars in the open cluster NGC 2516, including several blue straggler candidates and four red giants. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. From 22 cluster members a mean cluster velocity of +22.0+/-0.2 km s-1 was derived. Membership probabilities of the observed stars are computed on the basis of their distance to the cluster center and kinematic criteria. We report the discovery of three double-lined spectroscopic binaries and several probable binaries among main-sequence stars. A binary frequency of more than 26% is found among the high-mass main-sequence stars. The blue straggler HD 66341 is a slowly rotating cluster member with constant velocity, while HD 66194 is a fast-rotating Be star with probable variations in radial velocity. Other blue straggler candidates, such as HD 65663, 65950, 66066, and 65987, must be considered turnoff stars. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the national universities of La Plata, Córdoba, and San Juan.

  8. A CHEMICAL ABUNDANCE STUDY OF 10 OPEN CLUSTERS BASED ON WIYN -HYDRA SPECTROSCOPY

    SciTech Connect

    Jacobson, Heather R.; Pilachowski, Catherine A.; Friel, Eileen D. E-mail: catyp@astro.indiana.edu

    2011-08-15

    We present a detailed chemical abundance study of evolved stars in 10 open clusters based on Hydra multi-object echelle spectra obtained with the WIYN 3.5 m telescope. From an analysis of both equivalent widths and spectrum synthesis, abundances have been determined for the elements Fe, Na, O, Mg, Si, Ca, Ti, Ni, Zr, and for two of the 10 clusters, Al and Cr. To our knowledge, this is the first detailed abundance analysis for clusters NGC 1245, NGC 2194, NGC 2355, and NGC 2425. These 10 clusters were selected for analysis because they span a Galactocentric distance range R{sub gc} {approx} 9-13 kpc, the approximate location of the transition between the inner and outer disks. Combined with cluster samples from our previous work and those of other studies in the literature, we explore abundance trends as a function of cluster R{sub gc}, age, and [Fe/H]. As found previously by us and other studies, the [Fe/H] distribution appears to decrease with increasing R{sub gc} to a distance of {approx}12 kpc and then flattens to a roughly constant value in the outer disk. Cluster average element [X/Fe] ratios appear to be independent of R{sub gc}, although the picture for [O/Fe] is more complicated with a clear trend of [O/Fe] with [Fe/H] and sample incompleteness. Other than oxygen, no other element [X/Fe] exhibits a clear trend with [Fe/H]; likewise, there does not appear to be any strong correlation between abundance and cluster age. We divided clusters into different age bins to explore temporal variations in the radial element distributions. The radial metallicity gradient appears to have flattened slightly as a function of time, as found by other studies. There is also some indication that the transition from the inner disk metallicity gradient to the {approx}constant [Fe/H] distribution of the outer disk occurs at different Galactocentric radii for different age bins. However, interpretation of the time evolution of radial abundance distributions is complicated by the

  9. Is the Hogg 12-NGC 3590 pair a new open cluster binary system?

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Clariá, J. J.; Ahumada, A. V.

    Based on CCD UBVI_(KC) images obtained at Cerro Tololo Inter-American Observatory (CTIO, Chile) and on morphological criteria, as well as on the stellar density in the region, we confirm that Hogg 12 is a genuine open cluster (OC) separated in the sky from NGC 3590 by scarcely 3.6 pc. The colour-magnitude diagrams of Hogg 12, cleaned from field star contamina- tion, reveal that this is a solar metal content cluster, affected by E(B-V) = 0.40 ± 0.05, located at a heliocentric distance d = 2.0 ± 0.5 kpc, and of an age similar to that of NGC 3590. Evidence that these two objects form an OC binary system is presented. A detailed version of this work can be seen in PASP, 122, 516 (2010).

  10. Interpreting the colour-magnitude diagrams of open star clusters through numerical simulations

    NASA Astrophysics Data System (ADS)

    Kalirai, Jasonjot Singh; Tosi, Monica

    2004-06-01

    We present detailed comparisons between high quality observational colour-magnitude diagrams (CMDs) of open star clusters and synthetic CMDs based on Monte Carlo numerical simulations. The comparisons account for all of the main parameters which determine the shape of the CMD for a stellar population. For the four clusters studied, NGC 6819, 2099 (M37), 2168 (M35) and 2323 (M50), we derive reddening, distance, age, binary fraction, star formation rate and indicative metallicity by comparing the locations and density of points in the observed CMDs to the simulated CMDs. We estimate the uncertainties related to stellar evolution theories by adopting various sets of stellar models for all of the synthetic CMDs and discuss which stellar models provide the theoretical CMDs that best reproduce the observations.

  11. CONFIGURATIONS OF BOUNDED AND FREE-FLOATING PLANETS IN VERY YOUNG OPEN CLUSTERS

    SciTech Connect

    Liu Huigen; Zhang Hui; Zhou Jilin

    2013-08-01

    Open clusters (OCs) are usually young and suitable for studying the formation and evolution of planetary systems. So far, only four planets have been found with radial velocity measurements in OCs. Meanwhile, a lot of free-floating planets (FFPs) have been detected. We utilize N-body simulations to investigate the evolution and final configurations of multi-planetary systems in very young open clusters with an age <10 Myr. After an evolution of 10 Myr, 61%-72% of the planets remain bounded and more than 55% of the planetary systems will maintain their initial orbital configurations. For systems with one planet ejected, more than 25% of them have the surviving planets in misaligned orbits. In the clusters, the fraction of planetary systems with misalignment is >6%, and only 1% have planets in retrograde orbits. We also obtain a positive correlation between the survival planet number and the distance from the cluster center r: planetary systems with a larger r tend to be more stable. Moreover, stars with a mass >2.5 M{sub Sun} are likely unstable and lose their planets. These results are roughly consistent with current observations. Planetary systems in binaries are less stable and we achieve a rough criterion: most of the binary systems with a{sub b}(1-e{sub b}{sup 2})>100 AU can retain all the initial planets. Finally, 80% of the FFPs are ejected out of the clusters, while the rest ({approx}20%) still stay in host clusters and most of them are concentrated in the center (<2 pc)

  12. Are CRIS Cluster Patterns Differentially Associated with African American Enculturation and Social Distance?

    ERIC Educational Resources Information Center

    Chavez-Korell, Shannon; Vandiver, Beverly J.

    2012-01-01

    The authors examined whether Black racial identity cluster patterns, using Cross Racial Identity Scale (CRIS) scores, were differentially associated with preference for African American culture and social distance from various cultural groups. African American college students (N = 351) completed the CRIS, an enculturation scale, and a social…

  13. Polarimetry of an intermediate-age open cluster: NGC 5617

    NASA Astrophysics Data System (ADS)

    Orsatti, A. M.; Feinstein, C.; Vergne, M. M.; Martínez, R. E.; Vega, E. I.

    2010-04-01

    Aims: We present polarimetric observations in the UBVRI bands of 72 stars located in the direction of the medium age open cluster NGC 5617. Our intention is to use polarimetry as a tool in membership identification, by building on previous investigations intended mainly to determine the cluster's general characteristics rather than provide membership suitable for studies such as stellar content and metallicity, as well as study the characteristics of the dust lying between the Sun and the cluster. Methods: The obsevations were carried out using the five-channel photopolarimeter of the Torino Astronomical Observatory attached to the 2.15 m telescope at the Complejo Astronómico El Leoncito (CASLEO; Argentina). Results: We are able to add 32 stars to the list of members of NGC 5617, and review the situation for others listed in the literature. In particular, we find that five blue straggler stars in the region of the cluster are located behind the same dust as the member stars are and we confirm the membership of two red giants. The proposed polarimetric memberships are compared with those derived by photometric and kinematical methods, with excellent results. Among the observed stars, we identify 10 with intrinsic polarization in their light. NGC 5617 can be polarimetrically characterized with Pmax = 4.40 % and θv = 73.1 deg. The spread in polarization values for the stars observed in the direction of the cluster seems to be caused by the uneven distribution of dust in front of the cluster's face. Finally, we find that in the direction of the cluster, the interstellar medium is apparently free of dust, from the Sun's position up to the Carina-Sagittarius arm, where NGC 5617 seems to be located at its farthest border. Based on observations obtained at Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Universities of La Plata, Córdoba, and San Juan.

  14. Efficient open-shell coupled-cluster and perturbation theories

    SciTech Connect

    Lee, T.J.; Jayatilaka, D.

    1993-12-31

    A new spin orbital basis is employed in the development of efficient open-shell coupled-cluster and perturbation theories that are based on a restricted Hartree-Fock (RHF) reference function. The spin orbital basis is different from the standard one in the spin functions that are associated with the singly occupied spatial orbital. The occupied orbital (in the spin orbital basis) is assigned the {sigma}{sup +} = 1/{radical}2({alpha} + {beta}) spin function while the unoccupied orbital is assigned the {sigma}{sup {minus}} = 1/{radical}2({alpha} {minus} {beta}) spin function. The doubly occupied and unoccupied orbitals (in the reference function) are assigned the standard {alpha} and {beta} spin orbitals. The coupled-cluster and perturbation theory wave functions based on this set of {open_quotes}symmetric spin orbitals{close_quotes} exhibit much more symmetry than those based on the standard spin orbital basis. This, together with interacting space arguments, leads to a dramatic reduction in the computational cost.

  15. DEBRIS DISKS OF MEMBERS OF THE BLANCO 1 OPEN CLUSTER

    SciTech Connect

    Stauffer, John R.; Noriega-Crespo, Alberto; Rebull, Luisa M.; James, David; Strom, Steven; Wolk, Scott; Carpenter, John M.; Barrado y Navascues, David; Backman, Dana; Cargile, P. A.

    2010-08-20

    We have used the Spitzer Space Telescope to obtain Multiband Imaging Photometer for Spitzer (MIPS) 24 {mu}m photometry for 37 members of the {approx}100 Myr old open cluster Blanco 1. For the brightest 25 of these stars (where we have 3{sigma} uncertainties less than 15%), we find significant mid-IR excesses for eight stars, corresponding to a debris disk detection frequency of about 32%. The stars with excesses include two A stars, four F dwarfs, and two G dwarfs. The most significant linkage between 24 {mu}m excess and any other stellar property for our Blanco 1 sample of stars is with binarity. Blanco 1 members that are photometric binaries show few or no detected 24 {mu}m excesses whereas a quarter of the apparently single Blanco 1 members do have excesses. We have examined the MIPS data for two other clusters of similar age to Blanco 1-NGC 2547 and the Pleiades. The AFGK photometric binary star members of both of these clusters also show a much lower frequency of 24 {mu}m excesses compared to stars that lie near the single-star main sequence. We provide a new determination of the relation between the V - K {sub s} color and K {sub s} - [24] color for main sequence photospheres based on Hyades members observed with MIPS. As a result of our analysis of the Hyades data, we identify three low mass Hyades members as candidates for having debris disks near the MIPS detection limit.

  16. Stellar rotational periods in the planet hosting open cluster Praesepe

    NASA Astrophysics Data System (ADS)

    Kovács, Géza; Hartman, Joel D.; Bakos, Gáspár Á.; Quinn, Samuel N.; Penev, Kaloyan; Latham, David W.; Bhatti, Waqas; Csubry, Zoltán; de Val-Borro, Miguel

    2014-08-01

    By using the dense coverage of the extrasolar planet survey project HATNet (Hungarian-made Automated Telescope Network), we Fourier analyse 381 high-probability members of the nearby open cluster Praesepe (Beehive/M44/NGC 2632). In addition to the detection of 10 variables (of δ Scuti and other types), we identify 180 rotational variables (including the two known planet hosts). This sample increases the number of known rotational variables in this cluster for spectral classes earlier than M by more than a factor of 3. These stars closely follow a colour/magnitude-period relation from early F to late K stars. We approximate this relation by polynomials for an easier reference to the rotational characteristics in different colours. The total (peak-to-peak) amplitudes of the large majority (94 per cent) of these variables span the range of 0.005-0.04 mag. The periods cover a range from 2.5 to 15 d. These data strongly confirm that Praesepe and the Hyades have the same gyrochronological ages. Regarding the two planet hosts, Pr0211 (the one with the shorter orbital period) has a rotational period that is ˜2 d shorter than the one expected from the main rotational pattern in this cluster. This, together with other examples discussed in the paper, may hint that star-planet interaction via tidal dissipation can be significant in some cases in the rotational evolution of stars hosting hot Jupiters.

  17. A spectroscopic investigation of early-type stars in the young open cluster Westerlund 2

    NASA Astrophysics Data System (ADS)

    Rauw, G.; Sana, H.; Nazé, Y.

    2011-11-01

    Context. The distance of the very young open cluster Westerlund 2, which contains the very massive binary system WR 20a and is likely associated with a TeV source, has been the subject of much debate. Aims: We attempt a joint analysis of spectroscopic and photometric data of eclipsing binaries in the cluster to constrain its distance. Methods: A sample of 15 stars, including three eclipsing binaries (MSP 44, MSP 96, and MSP 223) was monitored with the FLAMES multi-object spectrograph. The spectroscopic data are analysed together with existing B V photometry. Results: The analysis of the three eclipsing binaries clearly supports the larger values of the distance, around 8 kpc, and rules out values of about 2.4 - 2.8 kpc that have been suggested in the literature. Furthermore, our spectroscopic monitoring reveals no clear signature of binarity with periods shorter than 50 days in either the WN6ha star WR 20b, the early O-type stars MSP 18, MSP 171, MSP 182, MSP 183, MSP 199, and MSP 203, or three previously unknown mid O-type stars. The only newly identified candidate binary system is MSP 167. The absence of a binary signature is especially surprising for WR 20b and MSP 18, which were previously found to be bright X-ray sources. Conclusions: The distance of Westerlund 2 is confirmed to be around 8 kpc as previously suggested based on the spectrophotometry of its population of O-type stars and the analysis of the light curve of WR 20a. Our results suggest that short-period binary systems are not likely to be common, at least not among the population of O-type stars in the cluster. Based on observations collected at the European Southern Observatory (Cerro Paranal, Chile).Appendix A is available in electronic form at http://www.aanda.org

  18. Lithium in Open Cluster Red Giants Hosting Substellar Companions

    NASA Technical Reports Server (NTRS)

    Carlberg, Joleen K.; Smith, Verne V.; Cunha, Katia; Carpenter, Kenneth G.

    2016-01-01

    We have measured stellar parameters, [Fe/H], lithium abundances, rotation, and (12)C/13C in a small sample of red giants (RGs) in three open clusters that are each home to a RG star that hosts a substellar companion (SSC) (NGC 2423 3, NGC 4349 127, and BD+12 1917 in M67). Our goal is to explore whether the presence of SSCs influences the Li content. Both (12)C/13C and stellar rotation are measured as additional tracers of stellar mixing. One of the companion hosts, NGC 2423?3, is found to be Li-rich with A(Li)(sub NLTE) = 1.56 dex, and this abundance is significantly higher than the A(Li) of the two comparison stars in NGC 2423. All three SSC hosts have the highest A(Li) and (12)C/13C when compared to the control RGs in their respective clusters; however, except for NGC 2423?3, at least one control star has similarly high abundances within the uncertainties. Higher A(Li) could suggest that the formation or presence of planets plays a role in the degree of internal mixing on or before the RG branch. However, a multitude of factors affect A(Li) during the RG phase, and when the abundances of our sample are compared with the abundances of RGs in other open clusters available in the literature, we find that they all fall well within a much larger distribution of A(Li) and (12)C/13C. Thus, even the high Li in NGC 2423 3 cannot be concretely tied to the presence of the SSC.

  19. Lithium in Open Cluster Red Giants Hosting Substellar Companions

    NASA Technical Reports Server (NTRS)

    Carlberg, Joleen K.; Smith, Verne V.; Cunha, Katia; Carpenter, Kenneth G.

    2016-01-01

    We have measured stellar parameters, [Fe/H], lithium abundances, rotation, and (12)C/13C in a small sample of red giants (RGs) in three open clusters that are each home to a RG star that hosts a substellar companion (SSC) (NGC 2423 3, NGC 4349 127, and BD+12 1917 in M67). Our goal is to explore whether the presence of SSCs influences the Li content. Both (12)C/13C and stellar rotation are measured as additional tracers of stellar mixing. One of the companion hosts, NGC 2423?3, is found to be Li-rich with A(Li)(sub NLTE) = 1.56 dex, and this abundance is significantly higher than the A(Li) of the two comparison stars in NGC 2423. All three SSC hosts have the highest A(Li) and (12)C/13C when compared to the control RGs in their respective clusters; however, except for NGC 2423?3, at least one control star has similarly high abundances within the uncertainties. Higher A(Li) could suggest that the formation or presence of planets plays a role in the degree of internal mixing on or before the RG branch. However, a multitude of factors affect A(Li) during the RG phase, and when the abundances of our sample are compared with the abundances of RGs in other open clusters available in the literature, we find that they all fall well within a much larger distribution of A(Li) and (12)C/13C. Thus, even the high Li in NGC 2423 3 cannot be concretely tied to the presence of the SSC.

  20. Lithium in Open Cluster Red Giants Hosting Substellar Companions

    NASA Astrophysics Data System (ADS)

    Carlberg, Joleen K.; Smith, Verne V.; Cunha, Katia; Carpenter, Kenneth G.

    2016-02-01

    We have measured stellar parameters, [Fe/H], lithium abundances, rotation, and 12C/13C in a small sample of red giants (RGs) in three open clusters that are each home to a RG star that hosts a substellar companion (SSC) (NGC 2423 3, NGC 4349 127, and BD+12 1917 in M67). Our goal is to explore whether the presence of SSCs influences the Li content. Both 12C/13C and stellar rotation are measured as additional tracers of stellar mixing. One of the companion hosts, NGC 2423 3, is found to be Li-rich with A(Li){}{{NLTE}} = 1.56 dex, and this abundance is significantly higher than the A(Li) of the two comparison stars in NGC 2423. All three SSC hosts have the highest A(Li) and 12C/13C when compared to the control RGs in their respective clusters; however, except for NGC 2423 3, at least one control star has similarly high abundances within the uncertainties. Higher A(Li) could suggest that the formation or presence of planets plays a role in the degree of internal mixing on or before the RG branch. However, a multitude of factors affect A(Li) during the RG phase, and when the abundances of our sample are compared with the abundances of RGs in other open clusters available in the literature, we find that they all fall well within a much larger distribution of A(Li) and 12C/13C. Thus, even the high Li in NGC 2423 3 cannot be concretely tied to the presence of the SSC.

  1. The Gaia-ESO Survey: Insights into the inner-disc evolution from open clusters

    NASA Astrophysics Data System (ADS)

    Magrini, L.; Randich, S.; Donati, P.; Bragaglia, A.; Adibekyan, V.; Romano, D.; Smiljanic, R.; Blanco-Cuaresma, S.; Tautvaišienė, G.; Friel, E.; Overbeek, J.; Jacobson, H.; Cantat-Gaudin, T.; Vallenari, A.; Sordo, R.; Pancino, E.; Geisler, D.; San Roman, I.; Villanova, S.; Casey, A.; Hourihane, A.; Worley, C. C.; Francois, P.; Gilmore, G.; Bensby, T.; Flaccomio, E.; Korn, A. J.; Recio-Blanco, A.; Carraro, G.; Costado, M. T.; Franciosini, E.; Heiter, U.; Jofré, P.; Lardo, C.; de Laverny, P.; Monaco, L.; Morbidelli, L.; Sacco, G.; Sousa, S. G.; Zaggia, S.

    2015-08-01

    Context. The inner disc, which links the thin disc with the bulge, has been somewhat neglected in the past because of the intrinsic difficulties in its study, among which crowding and high extinction. Open clusters located in the inner disc are among thebest tracers of its chemistry at different ages and distances. Aims: We analyse the chemical patterns of four open clusters located within 7 kpc of the Galactic centre and of field stars to infer the properties of the inner disc with the Gaia-ESO survey idr2/3 data release. Methods: We derive the parameters of the newly observed cluster, Berkeley 81, finding an age of about 1 Gyr and a Galactocentric distance of ~5.4 kpc. We construct the chemical patterns of clusters and we compare them with those of field stars in the solar neighbourhood and in the inner-disc samples. Results: Comparing the three populations we observe that inner-disc clusters and field stars are both, on average, enhanced in [O/Fe], [Mg/Fe], and [Si/Fe]. Using the idr2/3 results of M67, we estimate the non-local thermodynamic equilibrium (NLTE) effect on the abundances of Mg and Si in giant stars. After empirically correcting for NLTE effects, we note that NGC 6705 and Be 81 still have a high [α/Fe]. Conclusions: The location of the four open clusters and of the field population reveals that the evolution of the metallicity [Fe/H] and of [α/Fe] can be explained within the framework of a simple chemical evolution model: both [Fe/H] and [α/Fe] of Trumpler 20 and of NGC 4815 are in agreement with expectations from a simple chemical evolution model. On the other hand, NGC 6705, and to a lesser degree Berkeley 81, have higher [α/Fe] than expected for their ages, location in the disc, and metallicity. These differences might originate from local enrichment processes as explained in the inhomogeneous evolution framework. Based on observations collected with the FLAMES spectrograph at VLT/UT2 telescope (Paranal Observatory, ESO, Chile), for the Gaia

  2. Contractivity of the Hilbert-Schmidt distance under open-system dynamics

    SciTech Connect

    Wang Xiaoting; Schirmer, S. G.

    2009-05-15

    It is shown that the Hilbert-Schmidt (HS) norm and distance, unlike the trace norm and distance, are generally not contractive for open quantum systems under Lindblad dynamics. Necessary and sufficient conditions for contractivity of the HS norm and distance are given, and explicit criteria in terms of the Lindblad operators are derived. It is also shown that the requirements for contractivity of the HS distance are strictly weaker than those for the HS norm, although simulations suggest that noncontractivity is a typical case, i.e., that systems for which the HS distance between quantum states is monotonically decreasing are exceptional for N>2, in contrast to the N=2 case where it is always monotonically decreasing.

  3. X-Ray Activity in the Open Cluster IC 4665

    NASA Technical Reports Server (NTRS)

    Giamapapa, Mark S.; Prosser, Charles F.; Fleming, Thomas A.

    1997-01-01

    We present the results of a joint ROSAT High Resolution Imager (HRI) and optical investigation of the open cluster IC 4665. The ROSAT data contains detections for 28 stellar sources in the field, including 22 cluster members and candidate members spanning the color range -0.18 less than or equal to (B - V(sub o)) less than or equal to +1.63 (approx. B3 - M3). Upper limits are given for the remaining members (or candidate members) in the HRI field. Keck HIRES spectra have been obtained that yield radial and rotational velocity measures, respectively, for faint, low mass candidate members located within the field of the ROSAT HRI observation. In addition, photometry of possible optical counterparts to previously uncatalogued X-ray sources in the HRI field is presented. The trends in X-ray properties with (B - V) color in IC 4665 are found to be quite similar to that for other, more nearby young clusters such as the Pleiades and alpha Persei. In particular, a maximum in normalized X-ray luminosity of log (L(sub x)/L(sub bol)) approx. equal 3 is observed, beginning in the color range of (B - V)(sub o) = 0.7 - 0.8. This is similar to the corresponding color range among Pleiades members, in agreement with the earlier estimate, that the age of IC 4665 is similar to the age of the Pleiades. The correlation of rotation and X-ray emission levels is consistent with that in other young clusters. Among the high mass stars in IC 4665, five B stars are detected as X-ray sources. Of these, one is a spectroscopic binary while the remaining objects are apparently single staxs. The level of intrinsic X-ray emission observed in the rapidly rotating (v sini greater than 200 km/ s), single B stars is consistent with an origin due to shock heating of the ambient medium by radiatively driven, rotationally enhanced winds. On the basis of these observations and the results for other clusters, we argue that observed levels of X-ray emission in high mass stars of log (L(sub x)/L(sub bol

  4. The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters

    NASA Astrophysics Data System (ADS)

    McSwain, M. Virginia; Gies, Douglas R.

    2005-11-01

    Be stars are a class of rapidly rotating B stars with circumstellar disks that cause Balmer and other line emission. There are three possible reasons for the rapid rotation of Be stars: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence (MS) evolution of B stars. To test the various formation scenarios, we have conducted a photometric survey of 55 open clusters in the southern sky. Of these, five clusters are probably not physically associated groups and our results for two other clusters are not reliable, but we identify 52 definite Be stars and an additional 129 Be candidates in the remaining clusters. We use our results to examine the age and evolutionary dependence of the Be phenomenon. We find an overall increase in the fraction of Be stars with age until 100 Myr, and Be stars are most common among the brightest, most massive B-type stars above the zero-age main sequence (ZAMS). We show that a spin-up phase at the terminal-age main sequence (TAMS) cannot produce the observed distribution of Be stars, but up to 73% of the Be stars detected may have been spun-up by binary mass transfer. Most of the remaining Be stars were likely rapid rotators at birth. Previous studies have suggested that low metallicity and high cluster density may also favor Be star formation. Our results indicate a possible increase in the fraction of Be stars with increasing cluster distance from the Galactic center (in environments of decreasing metallicity). However, the trend is not significant and could be ruled out due to the intrinsic scatter in our data. We also find no relationship between the fraction of Be stars and cluster density.

  5. Toward the Detection of Transiting Hot Earths and Hot Neptunes in Open Clusters

    NASA Astrophysics Data System (ADS)

    Pepper, J.; Gaudi, B. S.

    2006-06-01

    Radial velocity searches for extrasolar planets have recently detected several very low mass (7-20 M_oplus) planets in close orbits with periods less than 10 days. We consider the prospects for detecting the analogs of these planets in Galactic open clusters via transits. We outline the requirements for constructing a transit survey that would allow one to probe such ``Hot Earths'' and ``Hot Neptunes.'' Specifically, we present a simple criterion for detection that defines the minimum aperture required to detect planets of a given radius in a cluster at a given distance. Adopting photometric precisions that have been demonstrated in state-of-the-art variability surveys, we then predict the number of planets one could potentially detect with ambitious transit surveys toward several open clusters. Dedicated surveys lasting more than 20 nights with Pan-STARRS toward the Hyades and Praesepe could detect a handful of Hot Earths, if the majority of stars host such planets. Similar surveys with larger aperture telescopes (eg CFHT, MMT), toward M67, M35, M50, and M37 could detect Hot Neptunes, provided that their frequency is greater than 1%. The majority of planets will be detected around M dwarfs; detecting Hot Neptunes around such primaries requires photometric precisions of approx 1%, whereas Hot Earths require approx 0.1 %. We discuss potential hurdles in detecting and confirming small planets in ground-based surveys, including correlated noise, false positives, and intrinsic stellar variability.

  6. CCD Washington photometry of four poorly studied open clusters in the two inner quadrants of the galactic plane

    NASA Astrophysics Data System (ADS)

    Marcionni, N.; Clariá, J. J.; Parisi, M. C.; Palma, T.; Oddone, M.; Ahumada, A. V.

    2014-11-01

    Complementing our Washington photometric studies on Galactic open clusters (OCs), we now focus on four poorly studied OCs located in the first and fourth Galactic quadrants, namely BH 84, NGC 5381, BH 211 and Czernik 37. We have obtained CCD photometry in the Washington system C and T1 passbands down to T1 ∼ 8.5 mag for these four clusters. Their positions and sizes were determined using the stellar density radial profiles. We derived reddening, distance, age and metallicity of the clusters from extracted (C-T1,T1) color-magnitude diagrams (CMDs), using theoretical isochrones computed for the Washington system. There are no previous photometric data in the optical band for BH 84, NGC 5381 and BH 211. The CMDs of the observed clusters show relatively well defined main sequences, except for Czernik 37, wherein significant differential reddening seems to be present. The red giant clump is clearly seen only in BH 211. For this cluster, we estimated the age in (1000-200+260) Myr, assuming a metallicity of Z = 0.019. BH 84 was found to be much older than it was previously believed, while NGC 5381 happened to be much younger than previously reported. The heliocentric distances to these clusters are found to range between 1.4 and 3.4 kpc. BH 84 appears to be located at the solar galactocentric distance, while NGC 5381, BH 211 and Czernik 37 are situated inside the solar ring.

  7. A study of the two northern open clusters NGC 1582 and NGC 1663

    NASA Astrophysics Data System (ADS)

    Baume, G.; Villanova, S.; Carraro, G.

    2003-08-01

    We present CCD UBV(I)C observations obtained in the field of the previously unstudied northern open clusters NGC 1582 and NGC 1663. For the former, we also provide high-resolution spectra of the brightest stars and complement our data with Two-Micron All-Sky-Survey (2MASS) near-infrared photometry and with astrometric data from the Tycho-2 catalog. From the analysis of all these data, we argue that NGC 1582 is a very poor, quite large and heavily contaminated open cluster. It turns out to have a reddening EB-V = 0.35 +/- 0.03, to be situated 1100 +/- 100 pc from the Sun and to have an age of 300 +/- 100 Myr. On the other hand, we were not able to unambiguously clarify the nature of NGC 1663. By assuming it is a real cluster and from the analysis of its photometric diagrams, we found a color excess value EB-V = 0.20, an intermediate age value ( ~ 2000 Myr) and a distance of about 700 pc. The distribution of the stars in the region however suggests we are probably facing an open cluster remnant. As an additional result, we obtained aperture photometry of three previously unclassified galaxies placed in the field of NGC 1663 and performed a preliminary morphological classification of them. Based on observations carried out at Mt Ekar, Asiago, Italy. Data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/527

  8. CORS BAADE-WESSELINK DISTANCE TO THE LMC NGC 1866 BLUE POPULOUS CLUSTER

    SciTech Connect

    Molinaro, R.; Ripepi, V.; Marconi, M.; Musella, I.; Brocato, E.; Mucciarelli, A.; Stetson, P. B.; Storm, J.; Walker, A. R.

    2012-03-20

    We used optical, near-infrared photometry, and radial velocity data for a sample of 11 Cepheids belonging to the young LMC blue populous cluster NGC 1866 to estimate their radii and distances on the basis of the CORS Baade-Wesselink method. This technique, based on an accurate calibration of surface brightness as a function of (U - B), (V - K) colors, allows us to estimate, simultaneously, the linear radius and the angular diameter of Cepheid variables, and consequently to derive their distance. A rigorous error estimate on radii and distances was derived by using Monte Carlo simulations. Our analysis gives a distance modulus for NGC 1866 of 18.51 {+-} 0.03 mag, which is in agreement with several independent results.

  9. Variability Survey in the Open Cluster Stock 14 and the Surrounding Fields

    NASA Astrophysics Data System (ADS)

    Drobek, D.; Pigulski, A.; Shobbrook, R. R.; Narwid, A.

    2013-09-01

    We present the results of a photometric variability survey in the young open cluster Stock 14 and the surrounding fields. In total, we detected 103 variable stars of which 88 are new discoveries. We confirm short-period, low-amplitude light variations in two eclipsing members of the cluster, HD 101838 and HD 101794. In addition, we find two new β Cep stars of which one, HD 101993, is also a member. The sample of pulsating cluster members is supplemented by one multimode slowly pulsating B-type star and several single-mode candidates of this type. The other pulsating stars in our sample are mostly field stars. In particular, we found fourteen δ Sct stars including one γ Dor/δ Sct hybrid pulsator. From our UBV photometry we derived new parameters of Stock 14: the mean reddening E(B-V)=0.21±0.02 mag, the true distance modulus, 11.90±0.05 mag, and the age, 20±10 Myr. Finally, we use the new photometry to analyze changes of the 6.322-d orbital period of the bright eclipsing binary and the member of the cluster, V346 Cen. In addition to the known apsidal motion, we find that another effect, possibly light-time effect in a hierarchical system of a very long orbital period, affects these changes. The updated value of the period of apsidal motion for this system amounts to 306±4 yr. The open cluster Stock 14 was found to be a fairly good candidate for successful ensemble asteroseismology.

  10. Potentiality of Disaster Management Education through Open and Distance Learning System in Bangladesh Open University

    ERIC Educational Resources Information Center

    Ahmad, Saima; Numan, Sharker Md.

    2015-01-01

    Bangladesh Open University (BOU) is the only public educational institution in Bangladesh, where, a dual-mode method of learning system has been introduced. Established in 21st October, 1992, the University now accommodates 174,459 learners in 2012. The wide range networking of this university provides it a great prospect to execute a broad…

  11. Detailed studies om three open clusters from Gaia ESO Survey (GES)

    NASA Astrophysics Data System (ADS)

    Balaguer-Núnez, L.; Casamiquela, L.; Jordana, N.; Massana, P.; Jordi, C.; Masana, E.

    2017-03-01

    We present results for the intermediate-age and old open clusters NGC 6633, NGC 6705 (M 11) and NGC 2682 (M 67). We have used new Str ̈omgren-Crawford photometry, proper motions from ROA observations and spectral information from Gaia-ESO Survey (GES), to study the physical parameters of the stars in the three cluster's areas. The astrometric studies cover an area of about 1°x2° and down to r' ˜ 17 while our INT-WFC CCD intermediate-band photometry covers an area of about 40'x40' down to V ˜ 19. The stars of those areas selected as cluster members from their proper motions, are classified into photometric regions and their physical parameters determined, using uvbyHβ photometry and standard relations among colour indices for each of the photometric regions of the HR diagram. That allows us to determine reddening, distances, absolute magnitudes, spectral types, effective temperatures, gravities and metallicities, thus providing an astrophysical characterization of the clusters. These results are compared with the physical parameters obtained from GES spectral data as well as radial velocities to confirm membership. All these data lead us to a comparison of photometric and spectroscopic physical parameters.

  12. A study of variable stars in the open cluster NGC 1582 and its surrounding field

    NASA Astrophysics Data System (ADS)

    Song, Fang-Fang; Esamdin, Ali; Ma, Lu; Liu, Jin-Zhong; Zhang, Yu; Niu, Hu-Biao; Yang, Tao-Zhi

    2016-10-01

    This paper presents Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B, V and R filters by using the Nanshan 1 m telescope administered by Xinjiang Astronomical Observatory. 19 variable stars and three variable candidates were detected in a 45‧ × 48.75‧ field around the cluster. 12 of the variable stars are newly-discovered variable objects. The physical properties, classifications and memberships of these 22 objects are studied through their light curves, their positions on the color-magnitude diagram and with archival data from the Naval Observatory Merged Astrometric Dataset. Among these objects, five are eclipsing binary systems, six are pulsating variable stars including one known δ Scuti star and one newly-discovered RR Lyrae star. The distance to the RR Lyrae star is estimated to be 7.9 ± 0.3 kpc, indicating that the star is located far behind the cluster. Four variable stars are probable members of the cluster, and 13 of the 22 objects are confirmed to be field stars.

  13. UBVI CCD Photometry of the Open Clusters NGC 4609 and Hogg 15

    NASA Astrophysics Data System (ADS)

    Kook, Seung-Hwa; Sung, Hwankyung; Bessell, M. S.

    2010-10-01

    {UBVI CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V) = 0.37 ± 0.03, V_0 - M_V = 10.60 ± 0.08, log τ= 7.7 ± 0.1; Hogg 15 : E(B-V) = 1.13 ± 0.11, V_0 - M_V = 12.50 ± 0.15, log τ ≲ 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We also determine the mass function of these clusters and obtain a slope Γ = -1.2 (± 0.3) for NGC 4609 which is normal and a somewhat shallow slope (Γ = -0.95 ± 0.5) for Hogg 15.

  14. Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald J. (Technical Monitor); Patten, Brian M.

    2004-01-01

    Making use of eight archival ROSAT HRI images in the regions of the NGC 2232 and Cr 140, this project's primary focus is to identify X-ray sources and to extract net source counts for these sources in these two open clusters. These X-ray data would be combined with ground-based photometry and spectroscopy in order to identify G, K, and early-M type cluster members. Such membership data are important because, at present, no members later than spectral type approx. F5 are currently known for either cluster. With ages estimated to be approx. 25 Myr and at distances of just approx. 350 pc, the combined late-type membership of the NGC 2232 and Cr 140 clusters would yield an almost unique sample of solar-type stars in the post-T Tauri/pre-main sequence phase of evolution. These stars could be used to assess the level and dispersion of coronal activity levels, as a part of a probe of the importance of magnetic braking and the level of magnetic dynamo activity, for solar-type stars just before they reach the zero-age main sequence.

  15. Characterization of a young open cluster G144.9+0.4 in Cam OB1

    NASA Astrophysics Data System (ADS)

    Lin, Chien-Cheng; Chen, Wen-Ping; Panwar, Neelam

    2013-06-01

    Open clusters are good laboratories to study stellar evolution and dynamical interaction among member stars. We are carrying out a program to identify uncharted clusters using sky-survey data. Our preliminary result is finding stellar density enhancement using the 2MASS Point Source Catalog in Galactic latitude |b| < 50 deg. One such density peak (G144.9+0.4), located in the Cam OB1 association, is a young star cluster centered at (ℓ,b) = (144.904,+0.434), first recognized but not well characterized, by Glushkova et al. [8]. We used the PPMXL proper motions to constrain the membership. Our analysis yields a distance of 1.0 kpc. G144.9+0.4 is hence physically related to the Cam OB1 association. Based on the 2MASS and WISE colors, seven classical T-Tauri Star candidates are found within the cluster, though, three of these have proper motions inconsistent with members. One of the kinematic members has been confirmed by spectroscopy to be a CTTS.

  16. CURious Variables Experiment (CURVE). CCD Photometry and Variable Stars in the Field of Open Cluster NGC637

    NASA Astrophysics Data System (ADS)

    Pietrukowicz, P.; Olech, A.; Wisniewski, M.; Kedzierski, P.; Mularczyk, K.; Zloczewski, K.; Starczewski, S.; Szaruga, K.

    2006-09-01

    We present VI photometry for the open cluster NGC 637 which is located in the Cassiopeia region. Morphology of cluster color-magnitude diagram indicates that it is a young object with age of a few million years. The apparent distance modulus of the cluster is 13.9<(m-M)_V<14.3 mag, while reddening is 0.69distance as 2.6

  17. Using Hamming Distance as Information for SNP-Sets Clustering and Testing in Disease Association Studies.

    PubMed

    Wang, Charlotte; Kao, Wen-Hsin; Hsiao, Chuhsing Kate

    2015-01-01

    The availability of high-throughput genomic data has led to several challenges in recent genetic association studies, including the large number of genetic variants that must be considered and the computational complexity in statistical analyses. Tackling these problems with a marker-set study such as SNP-set analysis can be an efficient solution. To construct SNP-sets, we first propose a clustering algorithm, which employs Hamming distance to measure the similarity between strings of SNP genotypes and evaluates whether the given SNPs or SNP-sets should be clustered. A dendrogram can then be constructed based on such distance measure, and the number of clusters can be determined. With the resulting SNP-sets, we next develop an association test HDAT to examine susceptibility to the disease of interest. This proposed test assesses, based on Hamming distance, whether the similarity between a diseased and a normal individual differs from the similarity between two individuals of the same disease status. In our proposed methodology, only genotype information is needed. No inference of haplotypes is required, and SNPs under consideration do not need to locate in nearby regions. The proposed clustering algorithm and association test are illustrated with applications and simulation studies. As compared with other existing methods, the clustering algorithm is faster and better at identifying sets containing SNPs exerting a similar effect. In addition, the simulation studies demonstrated that the proposed test works well for SNP-sets containing a large proportion of neutral SNPs. Furthermore, employing the clustering algorithm before testing a large set of data improves the knowledge in confining the genetic regions for susceptible genetic markers.

  18. E-Learning and Technologies for Open Distance Learning in Management Accounting

    ERIC Educational Resources Information Center

    Kashora, Trust; van der Poll, Huibrecht M.; van der Poll, John A.

    2016-01-01

    This research develops a knowledge acquisition and construction framework for e-learning for Management Accounting students at the University of South Africa, an Open Distance Learning institution which utilises e-learning. E-learning refers to the use of electronic applications and processes for learning, including the transfer of skills and…

  19. Instance-Based Ontology Matching for Open and Distance Learning Materials

    ERIC Educational Resources Information Center

    Cerón-Figueroa, Sergio; López-Yáñez, Itzamá; Villuendas-Rey, Yenny; Camacho-Nieto, Oscar; Aldape-Pérez, Mario; Yáñez-Márquez, Cornelio

    2017-01-01

    The present work describes an original associative model of pattern classification and its application to align different ontologies containing Learning Objects (LOs), which are in turn related to Open and Distance Learning (ODL) educative content. The problem of aligning ontologies is known as Ontology Matching Problem (OMP), whose solution is…

  20. The End of Innocence: Critical Approaches to Open and Distance Learning.

    ERIC Educational Resources Information Center

    Tait, Alan

    1994-01-01

    Presents critical approaches to open and distance learning (ODL) and its role in modern societies based on experiences in the United Kingdom. Topics discussed include a history of correspondence education; industrial and Post-Fordist analysis of ODL; late modernity, the market, and consumerism; feminist approaches; and media and cultural studies.…

  1. Open-Distance Education as a Mechanism for Sustainable Development: Reflections on the Nigerian Experience

    ERIC Educational Resources Information Center

    Aderinoye, Rashid; Ojokheta, Kester

    2004-01-01

    This article examines open-distance learning in Nigeria and the role it plays in personal, community, and national development. Following consultation with existing literature, a qualitative survey was conducted using questionnaires, interviews, and participatory experience. Although particular emphasis was paid to the Nigerian context, the…

  2. Drivers of Learning Management System Use in a South African Open and Distance Learning Institution

    ERIC Educational Resources Information Center

    Venter, Peet; van Rensburg, Mari Jansen; Davis, Annemarie

    2012-01-01

    The study on which this article reports examined the determinants of usage of an online learning management system (LMS) by fourth level business students at a South African open and distance learning university using an extension of the widely used technology acceptance model (TAM) as a theoretical basis. A survey was conducted among students at…

  3. Psychosocial Well-Being of Israeli Students and Attitudes toward Open and Distance Learning

    ERIC Educational Resources Information Center

    Kurtz, Gila; Amichai-Hamburger, Yair; Kantor, Jeffrey

    2009-01-01

    This article reports on a study conducted in Israel at an academic institution. The study investigates the correlation between students' attitudes toward open and distance learning (ODL) and their perceived self-esteem and loneliness at the last stage of their online learning experience. For this study, 120 students were asked to complete a…

  4. E-Readiness of Open and Distance Learning (ODL) Facilitators: Implications for Effective Mediation

    ERIC Educational Resources Information Center

    Nyoni, Jabulani

    2014-01-01

    This article is a narrative report of the findings from the analysis of multicultural facilitators' discourses on their e-readiness in the use of information and communication technologies (ICTs) affordances in open and distance learning (ODL) mediation experiences. First, the findings revealed by qualitative deconstructive discourse analysis…

  5. Libraries' Services at Distance: A Survey of Allama Iqbal Open University Tutors in Pakistan

    ERIC Educational Resources Information Center

    Arif, Muhammad; Mahmood, Khalid

    2009-01-01

    A survey was conducted to determine the satisfaction level of distance education tutors with the location and physical setup, collection, resources and services being offered at thirty-four regional campuses and centers' libraries network of Allama Iqbal Open University (AIOU) in Pakistan including Azad Jummu and Kashmir territory. A semi…

  6. Prediction and Assessment of Student Behaviour in Open and Distance Education in Computers Using Bayesian Networks

    ERIC Educational Resources Information Center

    Xenos, Michalis

    2004-01-01

    This paper presents a methodological approach based on Bayesian Networks for modelling the behaviour of the students of a bachelor course in computers in an Open University that deploys distance educational methods. It describes the structure of the model, its application for modelling the behaviour of student groups in the Informatics Course of…

  7. Teaching Gender Studies via Open and Distance Learning in South Africa

    ERIC Educational Resources Information Center

    Murray, Jessica; Byrne, Deirdre; Koenig-Visagie, Leandra

    2013-01-01

    The University of South Africa (UNISA) has recently redesigned its honors degree in Gender Studies. The course design team members have been mindful of three key factors while redesigning this degree. First, we are aligning our course design with the demands of open and distance learning (ODL) and UNISA's institutional move to online delivery of…

  8. Challenges of Virtual and Open Distance Science Teacher Education in Zimbabwe

    ERIC Educational Resources Information Center

    Mpofu, Vongai; Samukange, Tendai; Kusure, Lovemore M.; Zinyandu, Tinoidzwa M.; Denhere, Clever; Huggins, Nyakotyo; Wiseman, Chingombe; Ndlovu, Shakespear; Chiveya, Renias; Matavire, Monica; Mukavhi, Leckson; Gwizangwe, Isaac; Magombe, Elliot; Magomelo, Munyaradzi; Sithole, Fungai; Bindura University of Science Education (BUSE),

    2012-01-01

    This paper reports on a study of the implementation of science teacher education through virtual and open distance learning in the Mashonaland Central Province, Zimbabwe. The study provides insight into challenges faced by students and lecturers on inception of the program at four centres. Data was collected from completed evaluation survey forms…

  9. Administering Examinations for Quality Control in Distance Education: The National Open University of Nigeria Perspective

    ERIC Educational Resources Information Center

    Ibara, E. C.

    2008-01-01

    Examination is an important tool for evaluating students learning outcome and require proper planning to meet high standards. This paper therefore examines the processes leading to administration of face-to-face examination in distance education with focus on the National Open University of Nigeria. It highlighted some procedures such as test…

  10. Cost Effectiveness of Open and Distance Learning in Nigeria: Responses from Focus Group Discussions

    ERIC Educational Resources Information Center

    Ojo, David Olugbenga; Rotimi, Ogidan; Kayode, Olakulehin Felix

    2006-01-01

    This study reports the out come of a primary qualitative investigation of open and distance learning system of education as a panacea to the problem of socially induced constraints on the acquisition of education, that may lead to the inability to attend higher institutions of learning, acquire certificates, become a qualified skilled worker by…

  11. Teaching Mathematics in Open Distance Learning (ODL): A Challenge to Quality Instruction?

    ERIC Educational Resources Information Center

    Kaino, L. M.

    2012-01-01

    Teaching mathematics through Open Distance Learning (ODL) has been a challenge to educators due to the nature of communication with learners and material delivery during instruction. In this paper, as a case study, we look at one mathematics module offered through ODL and the performance in the course for the past four years. A sample of 50…

  12. Implementing Randomised Control Trials in Open and Distance Learning: A Feasibility Study

    ERIC Educational Resources Information Center

    Herodotou, Christothea; Heiser, Sarah; Rienties, Bart

    2017-01-01

    Randomised control trials (RCTs) are an evidence-based research approach which has not yet been adopted and widely used in open and distance education to inform educational policy and practice. Despite the challenges entailed in their application, RCTs hold the power to robustly evaluate the effects of educational interventions in distance…

  13. The Production and Distribution of Knowledge through Open and Distance Learning.

    ERIC Educational Resources Information Center

    Fox, Stephen

    1989-01-01

    Addresses socio-political implications of open and distance learning (ODL) technology, which is viewed as a new form of marketing for the distribution of knowledge. The influence of information technology is discussed, the nature and the purpose of post-modern knowledge is described, and challenges to humanistic education are discussed. (36…

  14. A Conceptual Framework for Achieving Good Governance at Open and Distance Learning Institutions

    ERIC Educational Resources Information Center

    Khanna, Pankaj

    2017-01-01

    This paper describes a good governance architecture framework that would bring significant improvements in the overall working of open and distance learning institutions in a well-structured and systematic way. The good governance framework is articulated with seven basic principles which are performance, transparency, accountability,…

  15. The Impact of Web Based Resource Material on Learning Outcome in Open Distance Higher Education

    ERIC Educational Resources Information Center

    Masrur, Rehana

    2010-01-01

    One of the most powerful educational option in open and distance education is web-based learning. A blended (hybrid) course combines traditional face to face and web-based learning approaches in an educational environment that is nonspecific as to time and place. The study reported here investigated the impact of web based resource material…

  16. Will E-Business Shape the Future of Open and Distance Learning?

    ERIC Educational Resources Information Center

    Oblinger, Diana

    2001-01-01

    Explores the impact that electronic business is likely to have on the growth of open and distance learning. Discusses global consortia and global virtual universities; technological developments, including Web qualities; value chains; pricing models; the importance of scale; operating efficiencies; and increasing competition. (Author/LRW)

  17. Teaching Gender Studies via Open and Distance Learning in South Africa

    ERIC Educational Resources Information Center

    Murray, Jessica; Byrne, Deirdre; Koenig-Visagie, Leandra

    2013-01-01

    The University of South Africa (UNISA) has recently redesigned its honors degree in Gender Studies. The course design team members have been mindful of three key factors while redesigning this degree. First, we are aligning our course design with the demands of open and distance learning (ODL) and UNISA's institutional move to online delivery of…

  18. Continuity Education in Emergency and Conflict Situations: The Case for Using Open, Distance and Flexible Learning

    ERIC Educational Resources Information Center

    Creed, Charlotte; Morpeth, Roslyn Louise

    2014-01-01

    Emergency and conflict in countries such as Syria, the Philippines, Sri Lanka and Afghanistan have made us more aware of the long-term serial disruption and psychosocial damage faced by people caught up in emergency and conflict areas. Open, distance and flexible learning (ODFL) has sometimes been employed in these regions to maintain a degree of…

  19. E-Learning and Technologies for Open Distance Learning in Management Accounting

    ERIC Educational Resources Information Center

    Kashora, Trust; van der Poll, Huibrecht M.; van der Poll, John A.

    2016-01-01

    This research develops a knowledge acquisition and construction framework for e-learning for Management Accounting students at the University of South Africa, an Open Distance Learning institution which utilises e-learning. E-learning refers to the use of electronic applications and processes for learning, including the transfer of skills and…

  20. The Organization of the Distance Teaching Sub-System in an Open University.

    ERIC Educational Resources Information Center

    Chacon, Fabio J.

    The problem of finding an adequate organization for the distance teaching subsystem in the Open University of Venezuela (Universidad Nacional Abierta) is analyzed. Problems facing this subsystem concern: communications with the headquarters and within the learning centers network, interaction with the environment in order to create a favorable…

  1. Will E-Business Shape the Future of Open and Distance Learning?

    ERIC Educational Resources Information Center

    Oblinger, Diana

    2001-01-01

    Explores the impact that electronic business is likely to have on the growth of open and distance learning. Discusses global consortia and global virtual universities; technological developments, including Web qualities; value chains; pricing models; the importance of scale; operating efficiencies; and increasing competition. (Author/LRW)

  2. Open and Distance Learning: An Emerging System for Alternative Higher Education in Nigeria

    ERIC Educational Resources Information Center

    Ibara, Emmanuel Chisa

    2008-01-01

    Nigeria no doubt is at the threshold of transformation in information and communication technology (ICT), a development that should be utilized to meet the demand of time, especially in the education sector. One area in which ICT has made enormous impact is in open and distance learning. Undoubtedly, the demand on the conventional higher education…

  3. Seamless Support: Technology Enhanced Learning in Open Distance Learning at NWU

    ERIC Educational Resources Information Center

    Esterhuizen, Hennie

    2015-01-01

    Frantic attempts of investing in technology to demonstrate willingness to educate for the knowledge society may result in failure to address the real requirements. This paper presents the main features of a framework for integrating Technology Enhanced Learning in Open Distance Learning at North-West University, South Africa. Support towards…

  4. Developing Open and Distance Learning Resources for Continuing Professional Development: Experiences in a Scottish University.

    ERIC Educational Resources Information Center

    Bagnall, Gellisse

    1997-01-01

    Discusses the provision of continuing professional development (CPD) for health professionals by open and distance learning, focusing on the experience of the Faculty of Medicine at the University of Edinburgh (Scotland). Describes the needs-analysis and pilot evaluation of a primarily text-based resource, reporting high satisfaction with content…

  5. Student Teachers' Experiences of Teaching Practice at Open and Distance Learning Institution in South Africa

    ERIC Educational Resources Information Center

    Mokoena, Sello

    2017-01-01

    This small-scale study focused on the experiences of student teachers towards teaching practice in an open and distance learning (ODL) institution in South Africa. The sample consisted of 65 fourth year students enrolled for Bachelor of Education, specializing in secondary school teaching. The mixed-method research design consisting of…

  6. Chemistry Post-Graduate Student Training from an Open Distance Learning Perspective

    ERIC Educational Resources Information Center

    Mphahlele, M. J.; Tafesse, F.

    2015-01-01

    The University of South Africa's (UNISA) College of Science, Engineering and Technology (CSET) stands unique in the world by offering laboratory-based disciplines through Open Distance Learning (ODL) at both undergraduate and postgraduate levels. Lack of postgraduate programmes in chemistry at the very few ODL institutions offering undergraduate…

  7. A Conceptual Framework for Achieving Good Governance at Open and Distance Learning Institutions

    ERIC Educational Resources Information Center

    Khanna, Pankaj

    2017-01-01

    This paper describes a good governance architecture framework that would bring significant improvements in the overall working of open and distance learning institutions in a well-structured and systematic way. The good governance framework is articulated with seven basic principles which are performance, transparency, accountability,…

  8. Chemistry Post-Graduate Student Training from an Open Distance Learning Perspective

    ERIC Educational Resources Information Center

    Mphahlele, M. J.; Tafesse, F.

    2015-01-01

    The University of South Africa's (UNISA) College of Science, Engineering and Technology (CSET) stands unique in the world by offering laboratory-based disciplines through Open Distance Learning (ODL) at both undergraduate and postgraduate levels. Lack of postgraduate programmes in chemistry at the very few ODL institutions offering undergraduate…

  9. Combating AIDS in South Africa and Mozambique: The Role of Open, Distance, and Flexible Learning

    ERIC Educational Resources Information Center

    Pridmore, Pat; Yates, Chris

    2005-01-01

    This article examines the potential for open, distance, and flexible learning (ODFL) to mitigate the impact of HIV and AIDS on young people. Based on experience from a field study in Mozambique and South Africa, the authors show how ODFL can support and extend the work of existing infrastructures supporting vulnerable youth. As neighboring…

  10. The Education of Refugees in Africa: The Role of Distance and Open Learning.

    ERIC Educational Resources Information Center

    Dodds, Tony

    1988-01-01

    Description of education services to refugees in Africa focuses on three case studies: Institute of In-Service Teacher Training (IITT) in Somalia; Sudan Extension Unit (SEU); and Namibian Extension Unit (NEU) in Angola and Zambia. Highlights include refugee problems, the relevance of distance and open learning approaches, and international…

  11. Open and Distance Learning for Health: Supporting Health Workers through Education and Training

    ERIC Educational Resources Information Center

    Dodds, Tony

    2011-01-01

    This case study surveys the growing use of open and distance learning approaches to the provision of support, education and training to health workers over the past few decades. It classifies such uses under four headings, providing brief descriptions from the literature of a few examples of each group. In conclusion, it identifies key lessons…

  12. Comparative Analysis of Pedagogical Strategies across Disciplines in Open Distance Learning at Unisa

    ERIC Educational Resources Information Center

    Ramdass, Kemlall; Masithulela, Fulufhelo

    2016-01-01

    Re-engineering technological strategies in teaching and learning in an open distance learning (ODL) environment is paramount as the demand for access to quality higher education escalates drastically on a year to year basis. The organisational framework requires change in order to accommodate the increasing number of students. In view of the…

  13. Mechanism of F2F Student Support in Open and Distance Learning System: Indian Experience

    ERIC Educational Resources Information Center

    Dimri, Anil K.

    2015-01-01

    Present paper seeks to analyse the system of face to face programme delivery adopted by Indira Gandhi National Open University (IGNOU) for its distance learners over a period of two and half decades. The paper also analysed that with the growth in student enrolment, new schemes of face to face programme delivery was developed and implemented and…

  14. Using Random Parameter Logit in Open and Distance Learning (ODL) Institutions in Malaysia

    ERIC Educational Resources Information Center

    Chiam, Chooi Chea; Loo, SzeWei

    2015-01-01

    Attention has been drawn to Open Distance Learning (ODL) as a mode for teaching and learning with the advancement in communication via the Internet. Education today has expanded the role of ICT in learning and knowledge generation, leveraging on Internet technology to transmit education across the country. Due to the advancement of technology and…

  15. Challenges for Successful Planning of Open and Distance Learning (ODL) : A Template Analysis

    ERIC Educational Resources Information Center

    Minnaar, Ansie

    2013-01-01

    How to plan an open and distance learning (ODL) unit in higher education is not clearly described in the literature. A number of ODL facilities at residential universities have not been successful because of a lack of planning or because of failure to ensure that all the different systems for ODL delivery were in place and functioning. This paper…

  16. The Growing Impact of Open Access Distance Education Journals: A Bibliometric Analysis

    ERIC Educational Resources Information Center

    Zawacki-Richter, Olaf; Anderson, Terry; Tuncay, Nazime

    2010-01-01

    Open access dissemination resonates with many distance education researchers and practitioners because it aligns with their fundamental mission of extending access to learning opportunity. However, there remains lingering doubt whether this increase in access comes at a cost of reducing prestige, value (often determined in promotion and tenure…

  17. The Education of Refugees in Africa: The Role of Distance and Open Learning.

    ERIC Educational Resources Information Center

    Dodds, Tony

    1988-01-01

    Description of education services to refugees in Africa focuses on three case studies: Institute of In-Service Teacher Training (IITT) in Somalia; Sudan Extension Unit (SEU); and Namibian Extension Unit (NEU) in Angola and Zambia. Highlights include refugee problems, the relevance of distance and open learning approaches, and international…

  18. The Growing Impact of Open Access Distance Education Journals: A Bibliometric Analysis

    ERIC Educational Resources Information Center

    Zawacki-Richter, Olaf; Anderson, Terry; Tuncay, Nazime

    2010-01-01

    Open access dissemination resonates with many distance education researchers and practitioners because it aligns with their fundamental mission of extending access to learning opportunity. However, there remains lingering doubt whether this increase in access comes at a cost of reducing prestige, value (often determined in promotion and tenure…

  19. Quality Assurance in Asian Open and Distance Learning: Policies and Implementation

    ERIC Educational Resources Information Center

    Darojat, Ojat; Nilson, Michelle; Kaufman, David

    2015-01-01

    Open universities have emerged as an innovative pillar in the expansion of access to higher education participation, with single-mode distance education providers broadening access in many countries through economies of scale supported by large enrolments. These models raise questions about the quality of education provided. This paper reports on…

  20. Forms, Factors and Consequences of Cheating in University Examinations: Insight from Open and Distance Learning Students

    ERIC Educational Resources Information Center

    Mokula, Lebeloane Lazarus Donald; Lovemore, Nyaumwe

    2014-01-01

    The present study narrated the forms, factors and consequences of cheating in university examinations by UNISA Open and Distance learning students from anecdotal data. The results showed that the perpetrators mostly used crib materials on paper, ruler and calculator cover. The factors that influenced examination cheating were gender, age range and…

  1. Open and Distance Education Accreditation Standards Scale: Validity and Reliability Studies

    ERIC Educational Resources Information Center

    Can, Ertug

    2016-01-01

    The purpose of this study is to develop, and test the validity and reliability of a scale for the use of researchers to determine the accreditation standards of open and distance education based on the views of administrators, teachers, staff and students. This research was designed according to the general descriptive survey model since it aims…

  2. Nearest hyperplane distance neighbor clustering algorithm applied to gene co-expression analysis in Alzheimer's disease.

    PubMed

    Pasluosta, Cristian F; Dua, Prerna; Lukiw, Walter J

    2011-01-01

    Microarray analysis can contribute considerably to the understanding of biologically significant cellular mechanisms that yield novel information regarding co-regulated sets of gene patterns. Clustering is one of the most popular tools for analyzing DNA microarray data. In this paper, we present an unsupervised clustering algorithm based on the K-local hyperplane distance nearest-neighbor classifier (HKNN). We adapted the well-known nearest neighbor clustering algorithm for use with hyperplane distance. The result is a simple and computationally inexpensive unsupervised clustering algorithm that can be applied to high-dimensional data. It has been reported that the NFkB1 gene is progressively over-expressed in moderate-to-severe Alzheimer's disease (AD) cases, and that the NF-kB complex plays a key role in neuroinflammatory responses in AD pathogenesis. In this study, we apply the proposed clustering algorithm to identify co-expression patterns with the NFkB1 in gene expression data from hippocampal tissue samples. Finally, we validate our experiments with biomedical literature search.

  3. Red giants in the vicinity of open clusters. Field stars

    NASA Astrophysics Data System (ADS)

    Pakhomov, Yu. V.; Antipova, L. I.; Boyarchuk, A. A.; Zhao, G.; Liang, Ya.

    2009-08-01

    We present a comparative analysis of the atmospheric abundances of red giants in the vicinity of open clusters. The atmospheric parameters, atmospheric abundances, masses, ages, Galactic velocities, and elements of the Galactic orbits are derived for all the studied stars. We have discovered high metal abundances (close to 0.3dex) for five stars, which we classify as super-metal-rich stars. Several stars have lower [Na/Fe] than normal red giants with similar atmospheric parameters. The kinematic characteristics of these stars are somewhat different from those for objects in the Galactic thin disk. We suggest that the observed effect can be explained by inhomogeneity of the chemical composition of gas-dust clouds, which could be due to different rates of SNe II supernovae in different regions of the Galaxy.

  4. A new estimate of the Hubble constant using the Virgo cluster distance

    NASA Astrophysics Data System (ADS)

    Visvanathan, N.

    The Hubble constant, which defines the size and age of the universe, remains substantially uncertain. Attention is presently given to an improved distance to the Virgo Cluster obtained by means of the 1.05-micron luminosity-H I width relation of spirals. In order to improve the absolute calibration of the relation, accurate distances to the nearby SMC, LMC, N6822, SEX A and N300 galaxies have also been obtained, on the basis of the near-IR P-L relation of the Cepheids. A value for the global Hubble constant of 67 + or 4 km/sec per Mpc is obtained.

  5. The OCCASO Survey: Open Clusters Chemical Abundances from Spanish Observatories

    NASA Astrophysics Data System (ADS)

    Casamiquela, L.; Carrera, R.; Jordi, C.; Balaguer-Núñez, L.

    2014-07-01

    Stellar clusters are crucial in the study of a variety of topics including the star formation process, stellar nucleosynthesis and evolution, dynamical interaction among stars, or the assembly and evolution of galaxies. In particular, Open Clusters (OCs) have been widely used to constrain the formation and evolution of the Milky Way disc. They provide information about the chemical patterns and the existence of radial and vertical gradients or an age-metallicity relation. However, all these investigations are hampered by the fact that only a small fraction of clusters have been studied homogeneously. Galactic surveys performed from the ground such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE), the Gaia-ESO Survey (GES), or the GALactic Archaeology with HERMES (GALAH) include OCs among their targets. OCs are also sampled from the space by the Gaia and Kepler missions. The OCCASO goal is to derive abundances for more than 20 chemical species in at least 6 Red Clump stars in ˜30 Northern hemisphere OCs. In order to ensure the reliability of the derived chemical abundances, these are derived using different analysis techniques similar to what is being performed by GES. One of the OCCASO requirements is the homogeneity between instruments, methods and model atmospheres used, and in the same scale than the GES-UVES abundances. For this reason we are performing different tests checking internal and external consistency. Derived stellar atmosphere parameters and Fe abundances will be published in the first data release scheduled for the first semester of 2015. The online pdf of the poster with first results is available at https://gaia.ub.edu/Twiki/pub/GREATITNFC/ProgramFinalconference/poster_OCCASO.pdf.

  6. Searching for Be stars in the open cluster NGC 663

    SciTech Connect

    Yu, P. C.; Lin, C. C.; Chen, W. P.; Lee, C. D.; Ip, W. H.; Ngeow, C. C.; Laher, Russ; Surace, Jason

    2015-02-01

    We present Be star candidates in the open cluster NGC 663, identified by Hα imaging photometry with the Palomar Transient Factory Survey, as a pilot program to investigate how the Be star phenomena, the emission spectra, extended circumstellar envelopes, and fast rotation, correlate with massive stellar evolution. Stellar membership of the candidates was verified by 2MASS magnitudes and colors and by proper motions (PMs). We discover four new Be stars and exclude one known Be star from being a member due to its inconsistent PMs. The fraction of Be stars to member stars [N(Be)/N(members)] in NGC 663 is 3.5%. The spectral type of the 34 Be stars in NGC 663 shows bimodal peaks at B0–B2 and B5–B7, which is consistent with the statistics in most star clusters. Additionally, we also discover 23 emission-line stars of different types, including non-member Be stars, dwarfs, and giants.

  7. Open clusters. I. Fundamental parameters of B stars in NGC 3766 and NGC 4755

    NASA Astrophysics Data System (ADS)

    Aidelman, Y.; Cidale, L. S.; Zorec, J.; Arias, M. L.

    2012-08-01

    Context. Spectroscopic investigations of galactic open clusters are scarce and limited to a reduced sample of cluster members. Aims: We intend to perform a complete study of the physical parameters of two galactic clusters as well as of their individual members. Methods: To carry out this study, we used the BCD (Barbier-Chalonge-Divan) spectrophotometric system, which is based on the study of the Balmer discontinuity and is independent of interstellar and circumstellar extinction. Additional physical properties were derived from the line profiles (FWHM) and stellar evolution models. We analyzed low-resolution spectra around the Balmer discontinuity for normal B-type and Be stars in two open clusters: NGC 3766 and NGC 4755. We determined the stellar fundamental parameters, such as effective temperatures, surface gravities, spectral types, luminosity classes, absolute and bolometric magnitudes, and color gradient excesses. The stellar rotation velocity was also determined. Complementary information, mainly stellar mass, age, and radius of the star population were calculated using stellar evolution models. In some cases, the stellar fundamental parameters were derived for the first time. The obtained results allowed us also to determine the reddening, age, and distance to the clusters. Results: The cluster parameters obtained through the BCD method agree very well with those derived from classical methods based on photometric data. The BCD system also provides physical properties of the star members. This study enables us to test the good behavior of Mbol(λ1,D)-calibrations and detect systematic discrepancies between log g estimates from model atmospheres and those derived from stellar evolution models. To improve our knowledge on the formation and evolution of the clusters, more statistical studies on the initial mass luminosity and angular momentum distributions should be addressed. Therefore, the BCD spectrophotometric system could be a powerful tool for studying

  8. Radial Velocities and Kinematic Membership in the Open Cluster NGC 3114

    NASA Astrophysics Data System (ADS)

    González, Jorge Federico; Lapasset, Emilio

    2001-05-01

    Echelle spectroscopic observations for 30 bright stars in the field of the sparse open cluster NGC 3114 are presented. The sample includes main-sequence stars, yellow and red giants, and blue straggler candidates. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. The cluster mean velocity is well defined from eight giants and several main-sequence stars whose average is =-3.52+/-0.25 km s-1. The membership probabilities of the observed stars are computed on the basis of the velocity distributions of the cluster and field stars, and the expected percentage of contamination at each position. We classified 19 cluster members and 10 nonmembers; the remaining star is a known spectroscopic binary for which no membership probability was assigned. Among the members, there is a bright yellow giant, seven red giants, and four blue straggler candidates, although they should be considered as turn-off stars. The location of two of them in the color-magnitude diagram (slightly blueward of the turn-off) can be explained by their low rotational velocities. No velocity variations were detected in the 16 stars measured more than once, which indicates that NGC 3114 possess an abnormally low binary frequency. From spectral types of cluster members, a distance modulus (V-Mv)=9.8+/-0.2 mag and a reddening E(B-V)=0.07+/-0.01 mag are derived. The cluster age is estimated to be 1.6×108 yr. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the National Universities of La Plata, Córdoba and San Juan.

  9. Angular-diameter distance estimates from the Sunyaev-Zeldovich effect in hydrodynamical cluster simulations

    NASA Astrophysics Data System (ADS)

    Ameglio, S.; Borgani, S.; Diaferio, A.; Dolag, K.

    2006-07-01

    The angular-diameter distance DA of a galaxy cluster can be measured by combining its X-ray emission with the cosmic microwave background fluctuation due to the Sunyaev-Zeldovich (SZ) effect. The application of this distance indicator usually assumes that the cluster is spherically symmetric, the gas is distributed according to the isothermal β-model, and the X-ray temperature is an unbiased measure of the electron temperature. We test these assumptions with galaxy clusters extracted from an extended set of cosmological N-body/hydrodynamical simulations of a Λ cold dark matter concordance cosmology, which include the effect of radiative cooling, star formation and energy feedback from supernovae. We find that, due to the temperature gradients which are present in the central regions of simulated clusters, the assumption of isothermal gas leads to a significant underestimate of DA. This bias is efficiently corrected by using the polytropic version of the β-model to account for the presence of temperature gradients. In this case, once irregular clusters are removed, the correct value of DA is recovered with a ~5 per cent accuracy on average, with a ~20 per cent intrinsic scatter due to cluster asphericity. This result is valid when using either the electron temperature or a spectroscopic-like temperature. Instead When using the emission-weighted definition for the temperature of the simulated clusters, DA is biased low by ~20 per cent. We discuss the implications of our results for an accurate determination of the Hubble constant H0 and of the density parameter Ωm. We find that, at least in the case of ideal (i.e. noiseless) X-ray and SZ observations extended out to r500, H0 can be potentially recovered with exquisite precision, while the resulting estimate of Ωm, which is unbiased, has typical errors ΔΩm ~= 0.05.

  10. The distance duality relation test from the ACT cluster and type Ia supernova data

    NASA Astrophysics Data System (ADS)

    Hu, Lin-Hai; Wu, Pu-Xun; Yu, Hong-Wei

    2016-05-01

    The validity of the cosmic distance-duality (DD) relation is investigated by using 91 measurements of the gas mass fraction of galaxy clusters recently reported by the Atacama Cosmology Telescope (ACT) and the luminosity distance from the Union2.1 type Ia supernova (SNIa) sample independent of any cosmological models and the value of the Hubble constant. We consider four different approaches to derive the gas mass function and two different parameterizations of the DD relation, and find that they have very slight influences on the DD relation test and the relation is valid at the 1σ confidence level. We also discuss the constraints on α and β, which represent the effects of the shapes and colors of the light curves of SNIa, respectively. Our results on α and β are different from those obtained from the ΛCDM model and the galaxy cluster plus SNIa data.

  11. Spectral Clustering of Polarimetric SAR Data with the Wishart-Derived Distance Measures

    NASA Astrophysics Data System (ADS)

    Anfinsen, S. N.; Jenssen, R.; Eltoft, T.

    2007-03-01

    This paper presents a new spectral clustering algorithm, which is specially tailored for segmentation of polari- metric SAR images. This is accomplished by use of certain pairwise distance measures between pixels. The measures are derived from the complex Wishart distribu- tion, and capture the statistical information contained in the coherency matrix. We demonstrate how the pairwise distances are transformed into an affinity matrix, whose eigendecomposition determines the optimal partitioning of pixels. We further show that the obtained clustering provides an improved initialization of the classical unsu- pervised Wishart classifier, and that the entire classifica- tion can also be performed in a kernel induced feature space. The algorithms are tested on crop classification with promising results.

  12. BVI photometry and integrated spectroscopy of the very young open clusters Ruprecht 119, NGC 6318 and BH 245

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Bica, E.; Clariá, J. J.

    2000-10-01

    We present CCD BVI observations obtained for stars in the fields of the unstudied or poorly studied open clusters Ruprecht 119, NGC 6318, and BH 245 projected close to the direction towards the Galactic centre. We measured V magnitude and B-V and V-I colours for about 600 stars reaching down to V ~ 19 mag. From the analysis of the colour magnitude diagrams, we confirmed the physical reality of the clusters and derived their reddening, distance and age for the first time. In addition, we obtained flux-calibrated integrated spectra in the range 3500-9200 Å for the cluster sample. Using the equivalent widths of the Balmer lines and comparing the cluster spectra with template spectra we derive both foreground reddening and age. The photometric and spectroscopic results reveal that the three studied objects are very young open clusters with ages ranging between 10 and 15 Myr, which have already undergone the HII region evolutionary phase and are dominated by the upper MS stars. The clusters, located between 1.1 kpc and 3.3 kpc from the Sun, are affected by different amounts of interstellar visual absorption (2.4 <= A_v <= 7.0). In particular, BH 245 turned out to be a highly reddened open cluster located at a distance of scarcely 1.1 kpc. Based on observations made at the University of Toronto (David Dunlap Observatory) 24inch telescope, Las Campanas, Chile, and at the Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnics de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan, Argentina.

  13. Anchoring the Distance Scale via X-Ray/Infrared Data for Cepheid Clusters: SU Cas

    NASA Astrophysics Data System (ADS)

    Majaess, D.; Turner, D. G.; Gallo, L.; Gieren, W.; Bonatto, C.; Lane, D. J.; Balam, D.; Berdnikov, L.

    2012-07-01

    New X-ray (XMM-Newton) and JHKs (Observatoire du Mont-Mégantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J - H) = 0.08 ± 0.02 and d = 405 ± 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d=414+/- 5(\\sigma _{\\bar{x}}) +/- 10 (\\sigma) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (δ Cep, ζ Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H 0.

  14. ANCHORING THE DISTANCE SCALE VIA X-RAY/INFRARED DATA FOR CEPHEID CLUSTERS: SU Cas

    SciTech Connect

    Majaess, D.; Turner, D. G.; Gallo, L.; Lane, D. J.; Gieren, W.; Bonatto, C.; Balam, D.; Berdnikov, L.

    2012-07-10

    New X-ray (XMM-Newton) and JHK{sub s} (Observatoire du Mont-Megantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J - H) = 0.08 {+-} 0.02 and d = 405 {+-} 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d=414{+-}5({sigma}{sub x}-bar){+-}10 ({sigma}) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators ({delta} Cep, {zeta} Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H{sub 0}.

  15. Determining Distance, Age, and Activity in a New Benchmark Cluster: Ruprecht 147

    NASA Astrophysics Data System (ADS)

    Wright, Jason T.

    2009-08-01

    This proposal seeks 0.7 night of time on Hectochelle to observe the F, G, and K dwarfs of Ruprecht 147, recently identified as the closest old stellar cluster. At only ~ 200 pc and at an age of ~ 1-2 Gyr, this will be an important benchmark in stellar astrophysics, providing the only sample of spectroscopically accessible old, late-type stars of determinable age. Hectochelle is the ideal instrument to study this cluster, with a FOV, fiber count, and telescope aperture well matched to the cluster's diameter (~ 1°), richness (~ 100 identified members), and distance modulus (6.5-7 mag., putting the G and K dwarfs at B=11-15). Hectochelle will measure the Ca II line strengths of members to establish, for the first time, the chromospheric activity levels of a statistically significant sample of single, G and K dwarfs of this modest age. Hectochelle will also vet background stars for suitability as astrometric reference stars for a forthcoming HST FGS proposal to robustly measure the cluster's distance.

  16. Distance Estimates for High Redshift Clusters SZ and X-Ray Measurements

    NASA Technical Reports Server (NTRS)

    Joy, Marshall K.

    1999-01-01

    I present interferometric images of the Sunyaev-Zel'dovich effect for the high redshift (z $ greater than $ 0.5) galaxy clusters in the \\emph(Einstein) Medium Sensitivity Survey: MS0451.5-0305 (z = 0.54), MS0015.9+1609 (z = 0.55), MS2053.7-0449 (z = 0.58), MS1 137.5+6625 (z = 0.78), and MS 1054.5-0321 (z = 0.83). Isothermal $\\beta$ models are applied to the data to determine the magnitude of the Sunyaev-Zel'dovich (S-Z) decrement in each cluster. Complementary ROSAT PSPC and HRI x-ray data are also analyzed, and are combined with the S-Z data to generate an independent estimate of the cluster distance. Since the Sunyaev-Zel'dovich Effect is invariant with redshift, sensitive S-Z imaging can provide an independent determination of the size, shape, density, and distance of high redshift galaxy clusters; we will discuss current systematic uncertainties with this approach, as well as future observations which will yield stronger constraints.

  17. Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters

    NASA Technical Reports Server (NTRS)

    Patten, Brian M.; Oliversen, Ronald J. (Technical Monitor)

    2001-01-01

    This is the second annual performance report for our grant "Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters." We propose to identify X-ray sources and extract net source counts in 8 archival ROSAT HRI images in the regions of the NGC 2232 and Cr 140 open clusters. These X-ray data will be combined with ground-based photometry and spectroscopy in order to identify G, K, and early-M type cluster members. At present, no members later than approximately F5 are currently known for either cluster. With ages of approximately 25 Myr and at a distance of just 320 - 360 pc, the combined late-type membership of the NGC 2232 and Cr 140 clusters will yield an almost unique sample of solar-type stars in the post-T Tauri/pre-main sequence phase of evolution. These stars will be used to assess the level and dispersion in coronal activity levels, as part of a probe of the importance of magnetic braking and the level of magnetic dynamo activity, for solar-type stars just before they reach the ZAMS. Over the past year we have successfully acquired all of the ground-based data necessary to support the analysis of the archival ROSAT X-ray data in the regions around both of these clusters. By the end of 2001 we expect to have completed the reduction and analysis of the ground-based photometry and spectroscopy and will begin the integration of these data with the ROSAT X-ray data. A certain amount of pressure to complete the work on NGC 2232 is coming from the SIRTF project, as this cluster may be a key component to a circumstellar disk evolution GTO program. We are only too happy to try to help and have worked to speed the analysis as much as possible. The primary activity to be undertaken in the next few months is the integration of the groundbased photometry and spectroscopy with the archival ROSAT X-ray data and then writing the paper summarizing our results. The most time consuming portion of this next phase is, of course, seeing the paper through

  18. jClustering, an open framework for the development of 4D clustering algorithms.

    PubMed

    Mateos-Pérez, José María; García-Villalba, Carmen; Pascau, Javier; Desco, Manuel; Vaquero, Juan J

    2013-01-01

    We present jClustering, an open framework for the design of clustering algorithms in dynamic medical imaging. We developed this tool because of the difficulty involved in manually segmenting dynamic PET images and the lack of availability of source code for published segmentation algorithms. Providing an easily extensible open tool encourages publication of source code to facilitate the process of comparing algorithms and provide interested third parties with the opportunity to review code. The internal structure of the framework allows an external developer to implement new algorithms easily and quickly, focusing only on the particulars of the method being implemented and not on image data handling and preprocessing. This tool has been coded in Java and is presented as an ImageJ plugin in order to take advantage of all the functionalities offered by this imaging analysis platform. Both binary packages and source code have been published, the latter under a free software license (GNU General Public License) to allow modification if necessary.

  19. jClustering, an Open Framework for the Development of 4D Clustering Algorithms

    PubMed Central

    Mateos-Pérez, José María; García-Villalba, Carmen; Pascau, Javier; Desco, Manuel; Vaquero, Juan J.

    2013-01-01

    We present jClustering, an open framework for the design of clustering algorithms in dynamic medical imaging. We developed this tool because of the difficulty involved in manually segmenting dynamic PET images and the lack of availability of source code for published segmentation algorithms. Providing an easily extensible open tool encourages publication of source code to facilitate the process of comparing algorithms and provide interested third parties with the opportunity to review code. The internal structure of the framework allows an external developer to implement new algorithms easily and quickly, focusing only on the particulars of the method being implemented and not on image data handling and preprocessing. This tool has been coded in Java and is presented as an ImageJ plugin in order to take advantage of all the functionalities offered by this imaging analysis platform. Both binary packages and source code have been published, the latter under a free software license (GNU General Public License) to allow modification if necessary. PMID:23990913

  20. Open and Distance Language Learning at the Shantou Radio and TV University, China, and the Open University, United Kingdom: A Cross-Cultural Perspective

    ERIC Educational Resources Information Center

    Hurd, Stella; Xiao, Junhong

    2006-01-01

    Open and distance learning is experiencing rapid growth throughout the world. China in particular is undergoing a massive expansion of its distance EFL programmes. This global phenomenon challenges all those involved in delivering distance learning materials to examine current practice and the assumptions and expectations that underlie it, with…

  1. ACCRETION RATES ON PRE-MAIN-SEQUENCE STARS IN THE YOUNG OPEN CLUSTER NGC 6530

    SciTech Connect

    Gallardo, Jose; Del Valle, Luciano; Ruiz, Maria Teresa E-mail: ldelvall@das.uchile.cl

    2012-01-15

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first {approx}1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the H{sub {alpha}} emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad H{sub {alpha}} emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR.

  2. Massive open star clusters using the VVV survey. IV. WR 62-2, a new very massive star in the core of the VVV CL041 cluster

    NASA Astrophysics Data System (ADS)

    Chené, A.-N.; Ramírez Alegría, S.; Borissova, J.; O'Leary, E.; Martins, F.; Hervé, A.; Kuhn, M.; Kurtev, R.; Consuelo Amigo Fuentes, P.; Bonatto, C.; Minniti, D.

    2015-12-01

    Context. The ESO Public Survey VISTA Variables in the Vía Láctea (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. deg of the Galactic bulge and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims: We present the fourth article in a series of papers focussed on young and massive clusters discovered in the VVV survey. This article is dedicated to the cluster VVV CL041, which contains a new very massive star candidate, WR 62-2. Methods: Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters (distance, reddening, mass, age) of VVV CL041. Results: We confirm that the cluster VVV CL041 is a young (less than 4 Myr) and massive (3 ± 2 × 103 M⊙) cluster, and not a simple asterism. It is located at a distance of 4.2 ± 0.9 kpc, and its reddening is AV = 8.0 ± 0.2 mag, which is slightly lower than the average for the young clusters towards the centre of the Galaxy. Spectral analysis shows that the most luminous star of the cluster, of the WN8h spectral type, is a candidate to have an initial mass larger than 100 M⊙. Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002, and on observations with VLT/ISAAC at ESO (programme 087.D.0341A) and Flamingos-2 at Gemini (programme GS-2014A-Q-72).The photometric catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A31

  3. Spectrophotometry of 237 Stars in 7 Open Clusters

    NASA Astrophysics Data System (ADS)

    Clampitt, Lori; Burstein, David

    1997-08-01

    Spectrophotometry is presented for 237 stars in 7 nearby open clusters: Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M39. The observations were taken by Lee McDonald and David Burstein using the Wampler single-channel scanner on the Crossley 0.9m telescope at Lick Observatory from July 1973 through December 1974. Sixteen bandpasses spanning the spectral range 3500 Angstroms to 7780 Angstroms were observed for each star, with bandwidths 32Angstroms, 48 Angstroms or 64 Angstroms. Data are standardized to the Hayes-Latham system to mutual accuracy of 0.016 mag per passband. The accuracy of the spectrophotometry is assessed in three ways on a star-by-star basis. First, comparisons are made with previously published spectrophotometry for 19 stars observed in common. Second, (B-V) colors and uvby colors are compared for 236 stars and 221 stars, respectively. Finally, comparsions are made for 200 main sequence stars to the spectral synthesis models of Kurucz, fixing log g = 4.0 and [Fe/H] = 0.0, and only varying effective temperature. The accuracy of tests using uvby colors and the Kurucz models are shown to track each other closely, yielding an accuracy estimate (1 sigma ) of 0.01 mag for the 13 colors formed from bandpasses longward of the Balmer jump, and 0.02 mag for the 3 colors formed from the three bandpasses below the Balmer jump. In contrast, larger scatter is found relative to the previously published spectrophotometry of Bohm-Vitense & Johnson (16 stars in common) and Gunn & Stryker (3 stars). We also show that the scatter in the fits of the spectrophotometric colors and the uvby filter colors is a reasonable way to identify the observations of which specific stars are accurate to 1 sigma , 2 sigma , .... As such, the residuals from both the filter color fits and the Kurucz model fits are tabulated for each star where it was possible to make a comparison, so users of these data can choose stars according to the accuracy of the data

  4. Staff Development Practices of Open and Distance Learning Institutions in Ghana: The Case of the Distance Education Programme of University of Education, Winneba, Ghana

    ERIC Educational Resources Information Center

    Owusu-Mensah, Francis; Anyan, Jerry Addison; Denkyi, Charles

    2015-01-01

    Staff development plays a crucial role in Open and Distance learning programmes because most of the staff working on these programmes are products of the conventional face to face system. Lack of proper training of staff in ODL can lead to high dropout rate among distance learners. The purpose of this study was to investigate staff development…

  5. Spectroscopic Binaries and Kinematic Membership in the Open Cluster NGC 3532

    NASA Astrophysics Data System (ADS)

    González, Jorge Federico; Lapasset, Emilio

    2002-06-01

    We report spectroscopic observations for bright stars in the open cluster NGC 3532 up to 1 mag below the turnoff point. We compute radial velocities by cross-correlations and determine spectral types and rotational velocities. Using 21 stars identified as certain members, we derive a mean cluster velocity of +3.4+/-0.3 km s-1. From radial velocities and angular distances to the cluster center, we compute membership probabilities for all but two stars that are radial velocity variables. Only one out of 34 program stars is a clear kinematic nonmember. Three spectroscopic binaries and three additional possible radial velocity variables are detected among the 23 stars measured more than once. We report the star HD 96609 as a double-lined spectroscopic binary. Using the two-dimensional cross-correlation technique TODCOR developed by Zucker & Mazeh, we derive the radial velocity curves for both components and obtain the orbital parameters with errors of 0.3% and 0.7% for the projected orbital semiaxis and masses, respectively. This system is composed of two main-sequence stars in a circular orbit, with a period of 8.19 days. The observations presented here were obtained at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) and the National Universities of La Plata, Córdoba, and San Juan.

  6. Photometric and Proper Motion Study of the Neglected Open Cluster NGC 2215

    NASA Astrophysics Data System (ADS)

    Fitzgerald, M. T.; Inwood, L.; McKinnon, D. H.; Dias, W. S.; Sacchi, M.; Scott, B.; Zolinski, M.; Danaia, L.; Edwards, R.

    2015-06-01

    Optical UBVRI photometric measurements using the Faulkes Telescope North were taken in early 2011 and combined with 2MASS JHKs and WISE infrared photometry as well as UCAC4 proper motion data in order to estimate the main parameters of the galactic open cluster NGC 2215 of which large uncertainty exists in the current literature. Fitting a King model we estimate a core radius of 1.‧12 ± 0.‧04 (0.24 ± 0.01 pc) and a limiting radius of 4.‧3 ± 0.‧5 (0.94 ± 0.11 pc) for the cluster. The results of isochrone fits indicates an age of log (t)=8.85+/- 0.10 with a distance of d=790+/- 90 pc, a metallicity of [Fe/H]=-0.40+/- 0.10 dex, and a reddening of E(B-V)=0.26+/- 0.04. A proportion of the work in this study was undertaken by Australian and Canadian upper secondary school students involved in the Space to Grow astronomy education project, and is the first scientific publication to have utilized our star cluster photometry curriculum materials.

  7. License plate detection in an open environment by density-based boundary clustering

    NASA Astrophysics Data System (ADS)

    Tian, Jiangmin; Wang, Guoyou; Liu, Jianguo; Xia, Yuanchun

    2017-05-01

    Due to the variation of background, illumination, and view point, license plate detection in an open environment is challenging. We propose a detection method by boundary clustering. To start with, a boundary map is obtained through Canny edge detector and removal of unwanted horizontal background edges. Second, boundaries are classified into different clusters by a density-based approach. In the approach, the density of each boundary is defined by the total gradient intensity of its neighboring and reachable boundaries. Also, the cluster centers and the number of them are determined automatically according to a minimum-distance principle. At last, a set of horizontal candidate regions with accurately located borders are extracted for classification. The classifier is trained on the histogram of oriented gradient feature by a linear support vector machine model. Experiments on three public datasets including images captured under different scenarios demonstrate that the proposed method outperforms several state-of-the-art methods in detection accuracy and its performance in efficiency is also comparable.

  8. The galactic open cluster NGC 7419 and its five red supergiants

    NASA Astrophysics Data System (ADS)

    Beauchamp, Alain; Moffat, Anthony F. J.; Drissen, Laurent

    1994-07-01

    UBV CCD photometry has been carried out on the heavily reddened (Av = 6.7) Cepheus open cluster NGC 7419. An age of 14 +/- 2 million yr and a distance of 2.3 kpc have been derived using the isochrones of Maeder. The mass function of the cluster satisfies the Salpeter form N(M) is approximately M(-gamma) with gamma = 2.25. The cluster is dynamically relaxed. Radial velocities of the five red supergiants and the six brightest blue stars (mean approximately equals -74 km/s) confirm their membership. However, the radial velocity of the nearby carbon star (MZ Cep) is a factor of 2 too low for it to be a member. There is at most one blue supergiant member; this is much less than the number of red supergiants, in contrast with theoretical predictions. The red supergiants range in type from M2Iab to M7.5I, the coolest (MY Cep) -- an OH/IR source -- being strongly variable in the visible, but not in the IR. The two supergiants cooler than M2 do not fit the theoretical isochrones.

  9. Evidence of tidal distortions and mass-loss from the old open cluster NGC 6791

    NASA Astrophysics Data System (ADS)

    Dalessandro, E.; Miocchi, P.; Carraro, G.; Jílková, L.; Moitinho, A.

    2015-05-01

    We present the first evidence of clear signatures of tidal distortions in the density distribution of the fascinating open cluster NGC 6791. We used deep and wide-field data obtained with the Canada-France-Hawaii Telescope covering a 2° × 2° area around the cluster. The 2D density map obtained with the optimal matched filter technique shows a clear elongation and an irregular distribution starting from ˜300 arcsec from the cluster centre. At larger distances, two tails extending in opposite directions beyond the tidal radius are also visible. These features are aligned to both the absolute proper motion and to the Galactic Centre directions. Moreover, other overdensities appear to be stretched in a direction perpendicular to the Galactic plane. Accordingly to the behaviour observed in the density map, we find that both the surface brightness and the star count density profiles reveal a departure from a King model starting from ˜600 arcsec from the centre. These observational evidence suggest that NGC 6791 is currently experiencing mass-loss likely due to gravitational shocking and interactions with the tidal field. We use this evidence to argue that NGC 6791 should have lost a significant fraction of its original mass. A larger initial mass would in fact explain why the cluster survived so long. Using available recipes based on analytic studies and N-body simulations, we derived the expected mass-loss due to stellar evolution and tidal interactions and estimated the initial cluster mass to be Mini = (1.5-4) × 105 M⊙.

  10. NGC 6067: a young and massive open cluster with high metallicity

    NASA Astrophysics Data System (ADS)

    Alonso-Santiago, J.; Negueruela, I.; Marco, A.; Tabernero, H. M.; González-Fernández, C.; Castro, N.

    2017-08-01

    NGC 6067 is a young open cluster hosting the largest population of evolved stars among known Milky Way clusters in the 50-150 Ma age range. It thus represents the best laboratory in our Galaxy to constrain the evolutionary tracks of 5-7 M⊙ stars. We have used high-resolution spectra of a large sample of bright cluster members (45), combined with archival photometry, to obtain accurate parameters for the cluster as well as stellar atmospheric parameters. We derive a distance of 1.78 ± 0.12 kpc, an age of 90 ± 20 Ma and a tidal radius of 14.8^{+6.8}_{-3.2} arcmin. We estimate an initial mass above 5700 M⊙, for a present-day evolved population of two Cepheids, two A supergiants and 12 red giants with masses ≈6 M⊙. We also determine chemical abundances of Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y and Ba for the red clump stars. We find a supersolar metallicity, [Fe/H] = +0.19 ± 0.05, and a homogeneous chemical composition, consistent with the Galactic metallicity gradient. The presence of a Li-rich red giant, star 276 with A(Li) = 2.41, is also detected. An overabundance of Ba is found, supporting the enhanced s-process. The ratio of yellow to red giants is much smaller than 1, in agreement with models with moderate overshooting, but the properties of the cluster Cepheids do not seem consistent with current Padova models for supersolar metallicity.

  11. A homogeneous photometric and spectroscopic survey of open clusters in the Perseus Arm

    NASA Astrophysics Data System (ADS)

    Marco, Amparo; Negueruela, Ignacio; Monguió, Maria

    2015-08-01

    We are carrying out a homogeneous photometric survey of all young (< 100 Ma) open clusters in the Perseus Arm between Galactic longitudes 90º and 140º, using Strömgren filters at the Isaac Newton Telescope in La Palma. We intend to derive relative ages and distances with typical accuracies of 5 Ma and 200 pc. Our data will allow us to test the predictions of different models for the main mechanism producing the spiral structure of the Milky Way. In addition, we will enormously improve our knowledge of stellar evolution for stars in the 6-15 Msolar range. Moreover, the huge dataset of homogeneous photometry for thousands of stars (including ~2000 B-type stars) will have an enormous legacy value

  12. Increasing the object recognition distance of compact open air on board vision system

    NASA Astrophysics Data System (ADS)

    Kirillov, Sergey; Kostkin, Ivan; Strotov, Valery; Dmitriev, Vladimir; Berdnikov, Vadim; Akopov, Eduard; Elyutin, Aleksey

    2016-10-01

    The aim of this work was developing an algorithm eliminating the atmospheric distortion and improves image quality. The proposed algorithm is entirely software without using additional hardware photographic equipment. . This algorithm does not required preliminary calibration. It can work equally effectively with the images obtained at a distances from 1 to 500 meters. An algorithm for the open air images improve designed for Raspberry Pi model B on-board vision systems is proposed. The results of experimental examination are given.

  13. Do open star clusters evolve towards energy equipartition?

    NASA Astrophysics Data System (ADS)

    Spera, Mario; Mapelli, Michela; Jeffries, Robin D.

    2016-07-01

    We investigate whether open clusters (OCs) tend to energy equipartition, by means of direct N-body simulations with a broken power-law mass function. We find that the simulated OCs become strongly mass segregated, but the local velocity dispersion does not depend on the stellar mass for most of the mass range: the curve of the velocity dispersion as a function of mass is nearly flat even after several half-mass relaxation times, regardless of the adopted stellar evolution recipes and Galactic tidal field model. This result holds both if we start from virialized King models and if we use clumpy sub-virial initial conditions. The velocity dispersion of the most massive stars and stellar remnants tends to be higher than the velocity dispersion of the lighter stars. This trend is particularly evident in simulations without stellar evolution. We interpret this result as a consequence of the strong mass segregation, which leads to Spitzer's instability. Stellar winds delay the onset of the instability. Our simulations strongly support the result that OCs do not attain equipartition, for a wide range of initial conditions.

  14. Sub-subgiants in Old Open Cluster NGC 6791

    NASA Astrophysics Data System (ADS)

    Milliman, Katelyn E.; Leiner, Emily; Mathieu, Robert D.; Tofflemire, Benjamin M.; Platais, Imants

    2016-01-01

    In an optical color-magnitude diagram sub-subgiants (SSGs) lie red of the main-sequence and fainter than the red giant branch in a region not easily populated by standard stellar evolution theory. We present radial-velocity follow-up to five SSG candidates in the old open cluster NGC 6791 (8 Gyr, [Fe/H]= +0.3). Our observations began in 2014 July with the Hydra multi-object spectrograph on the WIYN 3.5 m telescope. We find four SSGs to be three-dimensional kinematic members of NGC 6791, with three also being short-period binary systems. The existence of these newly discovered SSGs in NGC 6791 strengthens the case that SSGs are a new class of non-standard stellar products, and that a physical mechanism must be found that explains the unusual evolutionary path of these stars. We gratefully acknowledge funding from the National Science Foundation under grant AST- 0908082 and the Wisconsin Space Grant Consortium.

  15. Exploring Differences between Self-Regulated Learning Strategies of High and Low Achievers in Open Distance Learning

    ERIC Educational Resources Information Center

    Geduld, Bernadette

    2016-01-01

    Open distance students differ in their preparedness for higher education studies. Students who are less self-regulated risk failure and drop out in the challenging milieu of open distance learning. In this study, the differences between the application of self-regulated learning strategies by low and high achievers were explored. A multi-method…

  16. LOL--Limitations of Online Learning--Are We Selling the Open and Distance Education Message Short?

    ERIC Educational Resources Information Center

    Todhunter, Barrie

    2013-01-01

    The thesis of this paper is that the open and distance education sector is based on a framework of terminology that is typologically inconsistent and which lacks clarity, and open and distance education teaching and learning models are examined to explore these concerns. The findings of this analysis are then used to assist in the articulation of…

  17. Science Practical Work Instructional Technologies and Open Distance Learning in Science Teacher Training: A Case Study in Zimbabwe

    ERIC Educational Resources Information Center

    Bhukuvhani, Crispen; Mupa, Mathew; Mhishi, Misheck; Dziva, Daimond

    2012-01-01

    The practical work component offers unique challenges for university science courses. This is even more pertinent in an Open and Distance Learning (ODL) environment like the Bindura University of Science Education's Virtual and Open Distance Learning (VODL) programme. Effective ODL education should be flexible enough to accommodate science…

  18. LOL--Limitations of Online Learning--Are We Selling the Open and Distance Education Message Short?

    ERIC Educational Resources Information Center

    Todhunter, Barrie

    2013-01-01

    The thesis of this paper is that the open and distance education sector is based on a framework of terminology that is typologically inconsistent and which lacks clarity, and open and distance education teaching and learning models are examined to explore these concerns. The findings of this analysis are then used to assist in the articulation of…

  19. Exploring Differences between Self-Regulated Learning Strategies of High and Low Achievers in Open Distance Learning

    ERIC Educational Resources Information Center

    Geduld, Bernadette

    2016-01-01

    Open distance students differ in their preparedness for higher education studies. Students who are less self-regulated risk failure and drop out in the challenging milieu of open distance learning. In this study, the differences between the application of self-regulated learning strategies by low and high achievers were explored. A multi-method…

  20. Building Capacity for Open and Distance Learning (ODL) in West Africa Sub-Region: The Pivotal Role of RETRIDAL

    ERIC Educational Resources Information Center

    Amini, Clifford; Oluyide, Oluwaseun

    2016-01-01

    The paper posits the Regional Training and Research Institute for Distance and Open Learning (RETRIDAL) as an institution established for the purpose of enhancing Open and Distance Learning in the West African sub-region. The institute has pursued this mandate with an unparalleled vigour since its establishment in 2003--a partnership of the…

  1. VizieR Online Data Catalog: Shape parameters for 154 Galactic open clusters (Zhai+, 2017)

    NASA Astrophysics Data System (ADS)

    Zhai, M.; Abt, H.; Zhao, G.; Li, C.

    2017-06-01

    The data used are from database WEBDA (http://www.univie.ac.at/webda/). We have found 946 open clusters with equatorial coordinates for each cluster member. Since cluster members are easily contaminated by field stars, we have only adopted stars with membership probabilities higher than 70% as cluster members. It is rarely possible to determine a cluster's shape with a small number of members, so we have only considered relatively richer clusters, which host more than 20 of the most probable member stars. After these selections, there are 154 clusters left. (1 data file).

  2. Review and Content Analysis of the "International Review of Research in Open and Distance/Distributed Learning" (2000-2015)

    ERIC Educational Resources Information Center

    Zawacki-Richter, Olaf; Alturki, Uthman; Aldraiweesh, Ahmed

    2017-01-01

    This paper presents a review of distance education literature published in the "International Review of Research in Open and Distance/Distributed Learning" (IRRODL) to describe the status thereof and to identify gaps and priority areas in distance education research based on a validated classification of research areas. All articles (N =…

  3. Access and Success in Learning: Technologies for Scaling Up Open and Distance Learning Programme in the Institute of Distance Learning, KNUST, Kumasi, Ghana

    ERIC Educational Resources Information Center

    Essel, Rebecca; Owusu-Boateng, William

    2011-01-01

    ODL (Open and Distance Learning) has come to stay. In recent years, there has been some extra-ordinary increasing international interest in it and Ghana is no exception. Currently, new ways of providing education are inevitable and ODL provides an effective alternate way. It represents approaches that focus on opening access to education and…

  4. CCD Photometry of the Old Open Clusters ESO 093-SC08 and VandenBerg-Hagen 176

    NASA Astrophysics Data System (ADS)

    Phelps, R. L.

    2002-05-01

    Faint-magnitude CCD photometry has been obtained for the clusters ESO 093-SC08 and VandenBerg-Hagen 176. These data reveal ESO 093-SC08 to be an old open cluster, with a derived age of 5.5 +/- 1.0 Gyr, a heliocentric distance of 14.00 +/- 0.75 kpc, an inferred metallicity between -0.60 < [Fe/H] < -0.20 dex, and Galactocentric positions Rgc = 13.0 +/- 0.7 kpc and Z = -1000 +/- 50 pc. For VandenBerg-Hagen 176, a derived age of 7.0 +/- 1.5 Gyr, a heliocentric distance of 18.00 +/- 1.00 kpc, an inferred metallicity between -0.20 < [Fe/H] < 0.20 dex, and Galactocentric positions Rgc = 12.0 +/- 0.9 kpc and Z = +1350 +/- 100 pc are found. The current results for ESO 093-SC08 are in good agreement with a study by Bica et al. VandenBerg-Hagen 176 appears to be a massive metal-rich old open cluster, similar to NGC 6791, or a young, metal-rich globular cluster. This research was supported by NSF grant AST-9800216, an Oberlin College Grant-In-Aid award, and grants from the California State University, Sacramento Research and Creative Activities program. An allocation of telescope time from the Carnegie Observatories, that made this research possible, is also gratefully acknowledged.

  5. Stellar rotation, binarity, and lithium in the open cluster IC 4756

    NASA Astrophysics Data System (ADS)

    Strassmeier, K. G.; Weingrill, J.; Granzer, T.; Bihain, G.; Weber, M.; Barnes, S. A.

    2015-08-01

    Context. An important aspect in the evolutionary scenario of cool stars is their rotation and the rotationally induced magnetic activity and interior mixing. Stars in open clusters are particularly useful tracers for these aspects because of their known ages. Aims: We aim to characterize the open cluster IC 4756 and measure stellar rotation periods and surface differential rotation for a sample of its member stars. Methods: Thirty-seven cluster stars were observed continuously with the CoRoT satellite for 78 days in 2010. Follow-up high-resolution spectroscopy of the CoRoT targets and deep Strömgren uvbyβ and Hα photometry of the entire cluster were obtained with our robotic STELLA facility and its echelle spectrograph and wide-field imager, respectively. Results: We determined high-precision photometric periods for 27 of the 37 CoRoT targets and found values between 0.155 and 11.4 days. Twenty of these are rotation periods. Twelve targets are spectroscopic binaries of which 11 were previously unknown; orbits are given for six of them. Six targets were found that show evidence of differential rotation with ΔΩ/Ω in the range 0.04-0.15. Five stars are non-radially pulsating stars with fundamental periods of below 1 d, two stars are semi-contact binaries, and one target is a micro-flaring star that also shows rotational modulation. Nine stars in total were not considered members because of much redder color(s) and deviant radial velocities with respect to the cluster mean. Hα photometry indicates that the cluster ensemble does not contain magnetically over-active stars. The cluster average metallicity is -0.08 ± 0.06 (rms) and its logarithmic lithium abundance for 12 G-dwarf stars is 2.39 ± 0.17 (rms). Conclusions: The cluster is 890 ± 70 Myrs old with an average turn-off mass of 1.8 M⊙ and a solar or slightly subsolar metallicity. The distance modulus is 8m.02 and the average reddening E(b - y) = 0m.16.. The cluster is masked by a very inhomogeneous

  6. Intermediate and old age Open Clusters science case for high resolution spectroscopy

    NASA Astrophysics Data System (ADS)

    Jordi, C.; Carrera, R.; Balaguer-Núnez, L.; Casamiquela, L.

    2017-03-01

    Open Clusters are dynamically-bound groups of stars that formed from the same giant molecular cloud, having a similar age and bulk chemical composition. Open Clusters are key objects for studying the formation and evolution of the Galactic disk. They are targets in on-going large spectroscopic surveys like Gaia-ESO and OCCASO surveys. We discuss the science case of the intermediate age and old Open Clusters for WEAVE, the upcoming multifiber spectroscopic facility in the WHT. In particular we do an overview of the target selection and the survey strategy. Additionally, the impact of the discovery of new clusters by Gaia space mission is discussed.

  7. A revision of the fundamental parameters of the open cluster Hogg 15 and the projected star WR 47

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.; Bica, E.; Santos, J. F. C., Jr.; Clariá, J. J.

    2002-05-01

    We revise the fundamental parameters of the faint open cluster Hogg 15, for which two recent colour-magnitude diagram (CMD) studies have obtained significantly different ages. In the present study, we combine a series of methods trying to constrain age, together with other fundamental parameters. We employ spatial extractions to construct the CMDs, and the cluster integrated spectrum to compare it with those of templates of known age. We derive fundamental parameters, in particular, distance, of the closely projected Wolf-Rayet star HDE 311884 (WR 47) - often proposed to be physically related to Hogg 15. Based on the WR 47 spectrum and available photometry, we conclude that the short distance implied by the Hipparcos parallax (216 pc) is affected by binary motion. From the WR 47 spectrum we estimate a reddening E(B-V) and a distance of 1.10 +/- 0.05 and 5.2 +/- 0.9 kpc, respectively. For Hogg 15 we derive an age of 20 +/- 10 Myr, a reddening of 1.10 +/- 0.05, and a distance of 3.1 +/- 0.5 kpc. We conclude that Hogg 15 is not related to WR 47 from the point of view of origin, since the cluster and the star do not belong to the same formation event.

  8. Open cluster evolutions in binary system: How they dissolved

    NASA Astrophysics Data System (ADS)

    Priyatikanto, R.; Arifyanto, M. I.; Wulandari, H. R. T.

    2014-03-01

    Binarity among stellar clusters in galaxy is such a reality which has been realized for a long time, but still hides several questions and problems to be solved. Some of binary star clusters are formed by close encounter, but the others are formed together from similar womb. Some of them undergo separation process, while the others are in the middle of merger toward common future. The products of merger binary star cluster have typical characteristics which differ from solo clusters, especially in their spatial distribution and their stellar members kinematics. On the other hand, these merger products still have to face dissolving processes triggered by both internal and external factors. In this study, we performed N-body simulations of merger binary clusters with different initial conditions. After merging, these clusters dissolve with greater mass-loss rate because of their angular momentum. These rotating clusters also experience more deceleration caused by external tidal field.

  9. Measuring the distance-redshift relation with the baryon acoustic oscillations of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Veropalumbo, A.; Marulli, F.; Moscardini, L.; Moresco, M.; Cimatti, A.

    2016-05-01

    We analyse the largest spectroscopic samples of galaxy clusters to date, and provide observational constraints on the distance-redshift relation from baryon acoustic oscillations. The cluster samples considered in this work have been extracted from the Sloan Digital Sky Survey at three median redshifts, z = 0.2, 0.3 and 0.5. The number of objects is 12 910, 42 215 and 11 816, respectively. We detect the peak of baryon acoustic oscillations for all the three samples. The derived distance constraints are rs/DV(z = 0.2) = 0.18 ± 0.01, rs/DV(z = 0.3) = 0.124 ± 0.004 and rs/DV(z = 0.5) = 0.080 ± 0.002. Combining these measurements with the sound horizon scale measured from the cosmic microwave background, we obtain robust constraints on cosmological parameters. Our results are in agreement with the standard Λ cold dark matter (ΛCDM) model. Specifically, we constrain the Hubble constant in a ΛCDM model, H_0 = 64_{-8}^{+17} km s^{-1} Mpc^{-1} , the density of curvature energy, in the oΛCDM context, Ω _K = -0.01_{-0.33}^{+0.34}, and finally the parameter of the dark energy equation of state in the wCDM case, w = -1.06_{-0.52}^{+0.49}. This is the first time the distance-redshift relation has been constrained using only the peak of baryon acoustic oscillations of galaxy clusters.

  10. VizieR Online Data Catalog: Abundances in Galactic open clusters (Marsakov+, 2016)

    NASA Astrophysics Data System (ADS)

    Marsakov, V. A.; Gozha, M. L.; Koval', V. V.; Shpigel', L. V.

    2016-07-01

    Spectroscopic determinations of the relative abundances of alpha-elements (O, Mg, Si, Ca, and Ti), slow neutron capture elements (Y, Ba, La, Ce, Nd, and Zr), rapid neutron capture element (Eu), and elements with an odd number of protons (Na, Al) are collected for 90 open clusters of the Galaxy. Metallicities are presented for 346 clusters. In addition catalog contains positions, ages, velocities, elements of Galactic orbits for open clusters. (2 data files).

  11. Hubble constant from Pritchet and von den Bergh's nova distance to the Virgo cluster

    SciTech Connect

    Sandage, A.; Tammann, G.A.

    1988-05-01

    Two reasons are offered why the value for H(0) of 69 + or - 14 km/s/Mpc of Pritchet and van den Bergh (1987) is likely to be too high by about 20 percent even when their value of 6.8 + or - 0.4 for the M31-Virgo modulus difference is adopted. One reason concerns the free expansion velocity of the Virgo cluster core and the other concerns the apparent distance modulus of M31. Reasons for adopting a global H(0) value of 56 + or - 12 km/s/Mpc are discussed. 25 references.

  12. Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample

    NASA Astrophysics Data System (ADS)

    Bernardi, M.; Alonso, M. V.; da Costa, L. N.; Willmer, C. N. A.; Wegner, G.; Pellegrini, P. S.; Rité, C.; Maia, M. A. G.

    2002-06-01

    This paper presents data on the ENEARc subsample of the larger ENEAR survey of nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a Dn-σ template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg2, and the angular diameter dn), as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies, and new photometry is presented for 348 objects. Repeat and overlap observations with external data sets are used to construct a final merged catalog consisting of 640 early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to assign galaxies to clusters. In a companion paper, these data are used to construct the template Dn-σ distance relation for early-type galaxies, which has been used to estimate galaxy distances and derive peculiar velocities for the ENEAR all-sky sample. Based on observations at Complejo Astronomico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan; Cerro Tololo Inter-American Observatory, National Optical Astronomical Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation; the European Southern Observatory (ESO), partially under the ESO-ON agreement; the Fred Lawrence Whipple Observatory; the Observatório do Pico dos Dias, operated by the Laboratório Nacional de Astrofísica and the MDM Observatory at Kitt Peak.

  13. TESTING THE DISTANCE-DUALITY RELATION WITH GALAXY CLUSTERS AND TYPE Ia SUPERNOVAE

    SciTech Connect

    Holanda, R. F. L.; Lima, J. A. S.; Ribeiro, M. B.

    2010-10-20

    In this Letter, we propose a new and model-independent cosmological test for the distance-duality (DD) relation, {eta} = D{sub L} (z)(1 + z){sup -2}/D{sub A} (z) = 1, where D{sub L} and D{sub A} are, respectively, the luminosity and angular diameter distances. For D{sub L} we consider two sub-samples of Type Ia supernovae (SNe Ia) taken from Constitution data whereas D{sub A} distances are provided by two samples of galaxy clusters compiled by De Filippis et al. and Bonamente et al. by combining Sunyaev-Zeldovich effect and X-ray surface brightness. The SNe Ia redshifts of each sub-sample were carefully chosen to coincide with the ones of the associated galaxy cluster sample ({Delta}z < 0.005), thereby allowing a direct test of the DD relation. Since for very low redshifts, D{sub A} (z) ape D{sub L} (z), we have tested the DD relation by assuming that {eta} is a function of the redshift parameterized by two different expressions: {eta}(z) = 1 + {eta}{sub 0} z and {eta}(z) = 1 + {eta}{sub 0} z/(1 + z), where {eta}{sub 0} is a constant parameter quantifying a possible departure from the strict validity of the reciprocity relation ({eta}{sub 0} = 0). In the best scenario (linear parameterization), we obtain {eta}{sub 0} = -0.28{sup +0.44} {sub -0.44} (2{sigma}, statistical + systematic errors) for the De Filippis et al. sample (elliptical geometry), a result only marginally compatible with the DD relation. However, for the Bonamente et al. sample (spherical geometry) the constraint is {eta}{sub 0} = -0.42{sup +0.34} {sub -0.34} (3{sigma}, statistical + systematic errors), which is clearly incompatible with the duality-distance relation.

  14. ANALYSIS OF DETACHED ECLIPSING BINARIES NEAR THE TURNOFF OF THE OPEN CLUSTER NGC 7142

    SciTech Connect

    Sandquist, Eric L.; Serio, Andrew W.; Orosz, Jerome; Shetrone, Matthew E-mail: aserio@gemini.edu E-mail: shetrone@astro.as.utexas.edu

    2013-08-01

    We analyze extensive BVR{sub C}I{sub C} photometry and radial velocity measurements for three double-lined deeply eclipsing binary stars in the field of the old open cluster NGC 7142. The short period (P = 1.9096825 days) detached binary V375 Cep is a high probability cluster member, and has a total eclipse of the secondary star. The characteristics of the primary star (M = 1.288 {+-} 0.017 M{sub Sun }) at the cluster turnoff indicate an age of 3.6 Gyr (with a random uncertainty of 0.25 Gyr), consistent with earlier analysis of the color-magnitude diagram. The secondary star (M = 0.871 {+-} 0.008 M{sub Sun }) is not expected to have evolved significantly, but its radius is more than 10% larger than predicted by models. Because this binary system has a known age, it is useful for testing the idea that radius inflation can occur in short period binaries for stars with significant convective envelopes due to the inhibition of energy transport by magnetic fields. The brighter star in the binary also produces a precision estimate of the distance modulus, independent of reddening estimates: (m - M){sub V} = 12.86 {+-} 0.07. The other two eclipsing binary systems are not cluster members, although one of the systems (V2) could only be conclusively ruled out as a present or former member once the stellar characteristics were determined. That binary is within 0. Degree-Sign 5 of edge-on, is in a fairly long-period eccentric binary, and contains two almost indistinguishable stars. The other binary (V1) has a small but nonzero eccentricity (e = 0.038) in spite of having an orbital period under 5 days.

  15. NEWS ON THE s PROCESS FROM YOUNG OPEN CLUSTERS

    SciTech Connect

    Maiorca, Enrico; Busso, Maurizio; Palmerini, Sara; Trippella, Oscar; Magrini, Laura; Randich, Sofia

    2012-03-01

    Recent spectroscopic measurements in open clusters younger than the Sun with [Fe/H] {approx}> 0 showed that the abundances of neutron-rich elements have continued to increase in the Galaxy after the formation of the Sun, roughly maintaining a solar-like distribution. This growth requires neutron fluences larger than those so far assumed, as these would have too few neutrons per iron seed. We suggest that the observed enhancements can be produced by nucleosynthesis in asymptotic giant branch (AGB) stars of low mass (M < 1.5 M{sub Sun }) if they release neutrons from the {sup 13}C({alpha},n){sup 16}O reaction in reservoirs larger by a factor of four than assumed in more massive AGB stars (M > 1.5 M{sub Sun }). Adopting such a stronger neutron source as a contributor to the abundances at the time of formation of the Sun, we show that this also affects the solar s-process distribution, so that its main component is well reproduced, without the need to assume ad hoc primary sources for the synthesis of s elements up to A {approx} 130, contrary to suggestions from other works. The changes in the expected abundances that we find are primarily due to the following reasons. (1) Enhancing the neutron source increases the efficiency of the s process, so that the ensuing stellar yields now mimic the solar distribution at a metallicity higher than before ([Fe/H ] {approx}> -0.1). (2) The age-metallicity relation is rather flat for several Gyr in that metallicity regime, so that those conditions remain stable and the enhanced nuclear yields, which are necessary to maintain a solar-like abundance pattern, can dominate the composition of the interstellar medium from which subsequent stars are formed.

  16. Nucleophilic ring opening of bridging thietanes in open triosmium cluster complexes

    SciTech Connect

    Adams, R.D.; Belinski, J.A.

    1992-07-01

    The complexes Os{sub 3}(CO){sub 9}({mu}{sub 3}-S)[{mu}-SCH{sub 2}CMe{sub 2}CMe{sub 2}CH{sub 2}] (1) and Os{sub 3}(CO){sub 9}({mu}{sub 3}-S)[{mu}-SCH{sub 2}CH{sub 2}CH{sub 2}] (2) were obtained from the reactions of Os{sub 3}(CO){sub 10}({mu}{sub 3}-S) with 3,3-dimethylthietane (DMT) and thietane, respectively, at -42 {degree}C in the presence of Me{sub 3}NO. Compound 1 was characterized by a single-crystal X-ray diffraction analysis and was found to contain a DMT group bridging two of the nonbonded metal atoms in the open cluster of three metal atoms by using both lone pairs of electrons on the sulfur atom. Compound 1 reacted with bis(triphenylphosphine)nitrogen(1+) chloride ([PPN]Cl) at 25 {degrees}C to yield the salt [PPN][Os{sub 3}-(CO){sub 9}({mu}-SCH{sub 2}CMe{sub 2}CH{sub 2}Cl)({mu}{sub 3}-S)] (3; 76%), in which the chloride ion was added to one of the methylene groups of the DMT ring in a process that caused the ring to open by cleavage of one of the carbon-sulfur bonds. A 4-chloro-3,3-dimethylpropanethiolate ligand bridges the open edge of the anionic triosmium cluster. Compound 3 was converted to the neutral complex Os{sub 3}(CO){sub 9}[{mu}-SCH{sub 2}CMe{sub 2}CMe{sub 2}CH{sub 2}Cl]({mu}{sub 3}-S)({mu}-H) (4) by reaction with HCl at 25 {degrees}C. Compound 4 is structurally similar to 3, except that is contains a hydride ligand bridging one of the two metal-metal bonds. Compounds 1 and 2 react with HCl in CH{sub 2}Cl{sub 2} solvent to yield the neutral compounds 4 and Os{sub 3}(CO){sub 9}[{mu}-SCH{sub 2}CH{sub 2}CH{sub 2}Cl]({mu}{sub 3}-S)({mu}-H) (5) in 89% and 90% yields, respectively, in one step. 11 refs., 3 figs., 10 tabs.

  17. VizieR Online Data Catalog: UBVR photometry of the open cluster King 2 (Aparicio+ 1990)

    NASA Astrophysics Data System (ADS)

    Aparicio, A.; Bertelli, G.; Chiosi, C.; Garcia-Pelayo, J. M.

    2003-06-01

    In this paper we present the Johnson-Cousins UBVR CCD photometry of the stars in King 2, an old open cluster towards the galactic anticenter. We have obtained the colour-magnitude diagram, the colour excess, the reddening, an estimate of the metallicity, and the distance modulus. The comparison of the observational colour-magnitude diagram with the theoretical simulations based on stellar models with convective overshoot shows that a major revision of the model structure is required. To this aim, we explore the possibility that the formulation of convective overshoot for stars in the mass range 1 to 2M{sun} ought to be different from the one currently in use. The point of major uncertainty that we see to affect the stars in this domain is whether or not convective overshoot may erode the gradient in molecular weight in the regions surrounding the convective core. We find that models, in which this is not allowed to occur, better fit the overall morphology of the colour-magnitude diagram of King 2. In addition to this, analyzing the width of the main sequence band we suggest that a significant fraction of the stars are members of binary systems, and evaluate the range spanned by their mass ratios. Finally, we derive the luminosity function and the mass function for the main sequence stars of the cluster. (1 data file).

  18. Basic physical properties of the close binary V497 Cep in the open cluster NGC 7160

    NASA Astrophysics Data System (ADS)

    Yakut, K.; Tarasov, A. E.; İbanoğlu, C.; Harmanec, P.; Kalomeni, B.; Holmgren, D. E.; Božić, H.; Eenens, P.

    2003-07-01

    New light and radial-velocity curves of V497 Cep , a binary in the open cluster NGC 7160, were obtained and the linear ephemeris of the system was refined to HJD (Min I) = (2 446 299.1596 +/- 0.0064) + (1.2028287d +/- 0.0000015d ) x E. The first light and radial-velocity curve solutions allowed us to derive the basic physical properties of this astrophysically important binary. It was found that the observed light variation of V497 Cep consists of a strong ellipticity effect and a small contribution from grazing eclipses. A comparison of masses and radii of V497 Cep with theoretical evolutionary tracks indicates that both binary components are very close to the zero-age main sequence. A comparison of disentangled line profiles of the He I 6678 line with synthetic, rotationally broadened line profiles indicates that the rotation of both stars is synchronized with the orbital revolution as expected. This finding increases the credibility of our solutions. We find E(B-V)=0fm39 . The distance to the cluster NGC 7160 was found to be about 760 (+/- 100) pc which agrees well with other available estimates. Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/1087

  19. VizieR Online Data Catalog: Optically visible open clusters and Candidates (Dias+ 2002-2010)

    NASA Astrophysics Data System (ADS)

    Dias, W. S.; Alessi, B. S.; Moitinho, A.; Lepine, J. R. D.

    2010-04-01

    We have compiled a new catalogue of open clusters in the Galaxy which updates the previous catalogues of Lynga (1987, Cat. ) and of Mermilliod (1995, in Information and On-Line Data in Astronomy, ed. D. Egret & M. A. Albrecht (Dordrecht: Kluwer), 127) (included in the WEBDA database, http://obswww.unige.ch/webda). New objects and new data, in particular, data on kinematics (proper motions) that were not present in the old catalogues, have been included. Virtually all the clusters (1629) presently known were included, which represents an increment of about 476 objects relative to the Lynga (1987, Cat. ) catalogue. The catalogue is presented in a single table containing all the important data, which makes it easy to use. In total, 99% of the objects have estimates of their apparent diameters, and 38% have distance, E(B-V) and age determinations. Concerning the data on kinematics, 22% have their mean proper motions listed, 14% their mean radial velocities, and 11% have both information simultaneously. (5 data files).

  20. VizieR Online Data Catalog: Optically visible open clusters and Candidates (Dias+ 2002-2015)

    NASA Astrophysics Data System (ADS)

    Dias, W. S.; Alessi, B. S.; Moitinho, A.; Lepine, J. R. D.

    2014-10-01

    We have compiled a new catalogue of open clusters in the Galaxy which updates the previous catalogues of Lynga (1987, Cat. VII/92) and of Mermilliod (1995, in Information and On-Line Data in Astronomy, ed. D. Egret & M. A. Albrecht (Dordrecht: Kluwer), 127) (included in the WEBDA database, http://obswww.unige.ch/webda). New objects and new data, in particular, data on kinematics (proper motions) that were not present in the old catalogues, have been included. Virtually all the clusters (2167) presently known were included, which represents an increment of about 986 objects relative to the Lynga (1987, VII/92) catalogue. The catalogue is presented in a single table containing all the important data, which makes it easy to use. In total, 99.7% of the objects have estimates of their apparent diameters, and 74.5% have distance, E(B-V) and age determinations. Concerning the data on kinematics, 54.7% have their mean proper motions listed, 25% their mean radial velocities, and 24.2% have both information simultaneously. (6 data files).

  1. VizieR Online Data Catalog: Optically visible open clusters and Candidates (Dias+ 2002-2013)

    NASA Astrophysics Data System (ADS)

    Dias, W. S.; Alessi, B. S.; Moitinho, A.; Lepine, J. R. D.

    2012-01-01

    We have compiled a new catalogue of open clusters in the Galaxy which updates the previous catalogues of Lynga (1987, Cat. ) and of Mermilliod (1995, in Information and On-Line Data in Astronomy, ed. D. Egret & M. A. Albrecht (Dordrecht: Kluwer), 127) (included in the WEBDA database, http://obswww.unige.ch/webda). New objects and new data, in particular, data on kinematics (proper motions) that were not present in the old catalogues, have been included. Virtually all the clusters (1629) presently known were included, which represents an increment of about 476 objects relative to the Lynga (1987, Cat. ) catalogue. The catalogue is presented in a single table containing all the important data, which makes it easy to use. In total, 99% of the objects have estimates of their apparent diameters, and 38% have distance, E(B-V) and age determinations. Concerning the data on kinematics, 22% have their mean proper motions listed, 14% their mean radial velocities, and 11% have both information simultaneously. (6 data files).

  2. VizieR Online Data Catalog: Optically visible open clusters and Candidates (Dias+ 2002-2007)

    NASA Astrophysics Data System (ADS)

    Dias, W. S.; Alessi, B. S.; Moitinho, A.; Lepine, J. R. D.

    2007-09-01

    We have compiled a new catalogue of open clusters in the Galaxy which updates the previous catalogues of Lynga (1987, Cat. ) and of Mermilliod (1995, in Information and On-Line Data in Astronomy, ed. D. Egret & M. A. Albrecht (Dordrecht: Kluwer), 127) (included in the WEBDA database, http://obswww.unige.ch/webda). New objects and new data, in particular, data on kinematics (proper motions) that were not present in the old catalogues, have been included. Virtually all the clusters (1629) presently known were included, which represents an increment of about 476 objects relative to the Lynga (1987, Cat. ) catalogue. The catalogue is presented in a single table containing all the important data, which makes it easy to use. In total, 99% of the objects have estimates of their apparent diameters, and 38% have distance, E(B-V) and age determinations. Concerning the data on kinematics, 22% have their mean proper motions listed, 14% their mean radial velocities, and 11% have both information simultaneously. (5 data files).

  3. Modified distance in average linkage based on M-estimator and MADn criteria in hierarchical cluster analysis

    NASA Astrophysics Data System (ADS)

    Muda, Nora; Othman, Abdul Rahman

    2015-10-01

    The process of grouping a set of objects into classes of similar objects is called clustering. It divides a large group of observations into smaller groups so that the observations within each group are relatively similar and the observations in different groups are relatively dissimilar. In this study, an agglomerative method in hierarchical cluster analysis is chosen and clusters were constructed by using an average linkage technique. An average linkage technique requires distance between clusters, which is calculated based on the average distance between all pairs of points, one group with another group. In calculating the average distance, the distance will not be robust when there is an outlier. Therefore, the average distance in average linkage needs to be modified in order to overcome the problem of outlier. Therefore, the criteria of outlier detection based on MADn criteria is used and the average distance is recalculated without the outlier. Next, the distance in average linkage is calculated based on a modified one step M-estimator (MOM). The groups of cluster are presented in dendrogram graph. To evaluate the goodness of a modified distance in the average linkage clustering, the bootstrap analysis is conducted on the dendrogram graph and the bootstrap value (BP) are assessed for each branch in dendrogram that formed the group, to ensure the reliability of the branches constructed. This study found that the average linkage technique with modified distance is significantly superior than the usual average linkage technique, if there is an outlier. Both of these techniques are said to be similar if there is no outlier.

  4. Open Clusters as Laboratories: The Angular Momentum Evolution of Young Stars

    NASA Technical Reports Server (NTRS)

    Stauffer, John R.

    1998-01-01

    The core group concentrated on three primary research topics: (1) ROSAT observation of the coronal activity of low mass stars in young open clusters; (2) the determination of stellar ages and the determination of the timescale for dissipation of circumstellar disks around young stars; and (3) the determination of rotation velocities of low mass stars in young open cluster and the inferred angular momentum evolution of low mass stars. With accurate ages for the clusters, we can then derive an independent estimate of the timescale for debris disks to dissipate. As the second half of that project, we are using the Caltech/UC/NASA Keck telescopes to obtain spectra of brown dwarf candidates in a number of nearby, young open clusters, from which we can determine new and accurate cluster ages. The final primary program that we have addressed was the determination of rotational velocities for low mass stars in our target open clusters. Our group has obtained rotational velocities for a large number of stars in several open clusters during this LTSA program, and we have published the results in several papers. One particularly time-consuming aspect of our program was the development of a database of the photometry and rotational velocities for nearby open clusters, which we have made available to the community.

  5. Open Clusters as Laboratories: The Angular Momentum Evolution of Young Stars

    NASA Technical Reports Server (NTRS)

    Stauffer, John R.

    1998-01-01

    The core group concentrated on three primary research topics: (1) ROSAT observation of the coronal activity of low mass stars in young open clusters; (2) the determination of stellar ages and the determination of the timescale for dissipation of circumstellar disks around young stars; and (3) the determination of rotation velocities of low mass stars in young open cluster and the inferred angular momentum evolution of low mass stars. With accurate ages for the clusters, we can then derive an independent estimate of the timescale for debris disks to dissipate. As the second half of that project, we are using the Caltech/UC/NASA Keck telescopes to obtain spectra of brown dwarf candidates in a number of nearby, young open clusters, from which we can determine new and accurate cluster ages. The final primary program that we have addressed was the determination of rotational velocities for low mass stars in our target open clusters. Our group has obtained rotational velocities for a large number of stars in several open clusters during this LTSA program, and we have published the results in several papers. One particularly time-consuming aspect of our program was the development of a database of the photometry and rotational velocities for nearby open clusters, which we have made available to the community.

  6. The OPD photometric survey of open clusters I. Techniques, program details and first results of robust determination of the fundamental parameters

    NASA Astrophysics Data System (ADS)

    Caetano, T. C.; Dias, W. S.; Lépine, J. R. D.; Monteiro, H. S.; Moitinho, A.; Hickel, G. R.; Oliveira, A. F.

    2015-07-01

    Open clusters are considered valuable objects for the investigation of galactic structure and dynamics since their distances, ages and velocities can be determined with good precision. According to the New Catalog of Optically Visible Open Clusters and Candidates (Dias et al., 2002) about 10% of the optically revealed open clusters remain unstudied. However, previous analysis (Moitinho, 2010) has indicated that not considering this unstudied population introduces significant biases in the study of the structure and evolution of the Milky Way. In addition, a systematic revision of the data contained in the catalog, collected from the literature, is needed, due to its inhomogeneity. In this first paper of a series, we present the observational strategy, data reduction and analysis procedures of a UBRVI photometric survey of southern open star clusters carried out at Pico dos Dias Observatory (Brazil). The aim of the program is to contribute to an unbiased, homogenous collection of cluster fundamental parameters. We show that the implementation of a sequence of systematic procedures considerably improves the quality of the results. To illustrate the methods we present the first results based on one night of observations. The parameters, reddening, distance, age and metallicity, were obtained by fitting theoretical isochrones to cluster color-color and multidimensional color-magnitude diagrams, applying a cross-entropy optimization algorithm developed by our group, which takes into account UBVRI photometric data weighted using a membership-likelihood estimation.

  7. Bayesian investigation of isochrone consistency using the old open cluster NGC 188

    SciTech Connect

    Hills, Shane; Courteau, Stéphane; Von Hippel, Ted; Geller, Aaron M. E-mail: courteau@astro.queensu.ca E-mail: a-geller@northwestern.edu

    2015-03-01

    This paper provides a detailed comparison of the differences in parameters derived for a star cluster from its color–magnitude diagrams (CMDs) depending on the filters and models used. We examine the consistency and reliability of fitting three widely used stellar evolution models to 15 combinations of optical and near-IR photometry for the old open cluster NGC 188. The optical filter response curves match those of theoretical systems and are thus not the source of fit inconsistencies. NGC 188 is ideally suited to this study thanks to a wide variety of high-quality photometry and available proper motions and radial velocities that enable us to remove non-cluster members and many binaries. Our Bayesian fitting technique yields inferred values of age, metallicity, distance modulus, and absorption as a function of the photometric band combinations and stellar models. We show that the historically favored three-band combinations of UBV and VRI can be meaningfully inconsistent with each other and with longer baseline data sets such as UBVRIJHK{sub S}. Differences among model sets can also be substantial. For instance, fitting Yi et al. (2001) and Dotter et al. (2008) models to UBVRIJHK{sub S} photometry for NGC 188 yields the following cluster parameters: age = (5.78 ± 0.03, 6.45 ± 0.04) Gyr, [Fe/H] = (+0.125 ± 0.003, −0.077 ± 0.003) dex, (m−M){sub V} = (11.441 ± 0.007, 11.525 ± 0.005) mag, and A{sub V} = (0.162 ± 0.003, 0.236 ± 0.003) mag, respectively. Within the formal fitting errors, these two fits are substantially and statistically different. Such differences among fits using different filters and models are a cautionary tale regarding our current ability to fit star cluster CMDs. Additional modeling of this kind, with more models and star clusters, and future Gaia parallaxes are critical for isolating and quantifying the most relevant uncertainties in stellar evolutionary models.

  8. Distance-Learning, ADHD Quality Improvement in Primary Care: A Cluster-Randomized Trial.

    PubMed

    Fiks, Alexander G; Mayne, Stephanie L; Michel, Jeremy J; Miller, Jeffrey; Abraham, Manju; Suh, Andrew; Jawad, Abbas F; Guevara, James P; Grundmeier, Robert W; Blum, Nathan J; Power, Thomas J

    2017-10-01

    To evaluate a distance-learning, quality improvement intervention to improve pediatric primary care provider use of attention-deficit/hyperactivity disorder (ADHD) rating scales. Primary care practices were cluster randomized to a 3-part distance-learning, quality improvement intervention (web-based education, collaborative consultation with ADHD experts, and performance feedback reports/calls), qualifying for Maintenance of Certification (MOC) Part IV credit, or wait-list control. We compared changes relative to a baseline period in rating scale use by study arm using logistic regression clustered by practice (primary analysis) and examined effect modification by level of clinician participation. An electronic health record-linked system for gathering ADHD rating scales from parents and teachers was implemented before the intervention period at all sites. Rating scale use was ascertained by manual chart review. One hundred five clinicians at 19 sites participated. Differences between arms were not significant. From the baseline to intervention period and after implementation of the electronic system, clinicians in both study arms were significantly more likely to administer and receive parent and teacher rating scales. Among intervention clinicians, those who participated in at least 1 feedback call or qualified for MOC credit were more likely to give parents rating scales with differences of 14.2 (95% confidence interval [CI], 0.6-27.7) and 18.8 (95% CI, 1.9-35.7) percentage points, respectively. A 3-part clinician-focused distance-learning, quality improvement intervention did not improve rating scale use. Complementary strategies that support workflows and more fully engage clinicians may be needed to bolster care. Electronic systems that gather rating scales may help achieve this goal. Index terms: ADHD, primary care, quality improvement, clinical decision support.

  9. Open cluster Dolidze 25: Stellar parameters and the metallicity in the Galactic anticentre

    NASA Astrophysics Data System (ADS)

    Negueruela, I.; Simón-Díaz, S.; Lorenzo, J.; Castro, N.; Herrero, A.

    2015-12-01

    Context. The young open cluster Dolidze 25, in the direction of the Galactic anticentre, has been attributed a very low metallicity, with typical abundances between -0.5 and -0.7 dex below solar. Aims: We intend to derive accurate cluster parameters and accurate stellar abundances for some of its members. Methods: We have obtained a large sample of intermediate- and high-resolution spectra for stars in and around Dolidze 25. We used the fastwind code to generate stellar atmosphere models to fit the observed spectra. We derive stellar parameters for a large number of OB stars in the area, and abundances of oxygen and silicon for a number of stars with spectral types around B0. Results: We measure low abundances in stars of Dolidze 25. For the three stars with spectral types around B0, we find 0.3 dex (Si) and 0.5 dex (O) below the values typical in the solar neighbourhood. These values, even though not as low as those given previously, confirm Dolidze 25 and the surrounding H ii region Sh2-284 as the most metal-poor star-forming environment known in the Milky Way. We derive a distance 4.5 ± 0.3 kpc to the cluster (rG ≈ 12.3 kpc). The cluster cannot be older than ~3 Myr, and likely is not much younger. One star in its immediate vicinity, sharing the same distance, has Si and O abundances at most 0.15 dex below solar. Conclusions: The low abundances measured in Dolidze 25 are compatible with currently accepted values for the slope of the Galactic metallicity gradient, if we take into account that variations of at least ±0.15 dex are observed at a given radius. The area traditionally identified as Dolidze 25 is only a small part of a much larger star-forming region that comprises the whole dust shell associated with Sh2-284 and very likely several other smaller H ii regions in its vicinity. Based on observations made with the Nordic Optical Telescope, the Mercator Telescope, and the telescopes of the Isaac Newton Group.

  10. A comparison of open and closed loop applications of the minimum distance guidance technique

    NASA Technical Reports Server (NTRS)

    Lattimore, J. P., Jr.

    1972-01-01

    A comparison is made of open and closed loop applications of a second order guidance algorithm, using the minimum distance strategy. A nonlinear reoptimization procedure is used as the ideal guidance history. The system model used for the comparison is a low-thrust vehicle performing a minimum time, three-dimensional, heliocentric Earth-Mars transfer. For the example problem considered, closed loop guidance proves to be much more accurate on satisfaction of the final state than the open loop procedure. On the other hand, closed loop guidance proves to be much more vulnerable to perturbation by highly nonlinear regions in the trajectory. Finally, the results indicate that for this problem the best loop closure interval is at each integration step, about one day, or more often, if possible.

  11. Learning at a Distance through Mobile Devices: A Global Choice of Learners in the Open and Distance Learning (ODL) System

    ERIC Educational Resources Information Center

    Sethy, Satya

    2011-01-01

    In the techno-driven world, mobile learning is an indispensable element of teaching-learning activities. It helps distance learners in many ways by providing their required facilities. The paper discusses about these facilities in an eclectic and summary manner. Thus, by implication, it is popularized among distance learners across the globe.…

  12. Stay Here, Go Further: The Status of Open and Distance Education in Bangladesh Open University (BOU) in Comparison to Two Other South Asian Countries

    ERIC Educational Resources Information Center

    Jahan, Monira; Akhter, Selina; Habib, Rakib

    2012-01-01

    Distance education has emerged out of social compulsion, the dynamics of change and new cultures. It was the failure of traditional systems to be able to meet the demand in countries, where the resources available for tertiary education are limited, which basically gave birth to the new trend of education known as open and distance education. This…

  13. Distance Education and Open Learning in Sub-Saharan Africa: Criteria and Conditions for Quality and Critical Success Factor-- Working Group on Distance Education and Open Learning. A Survey of Policy and Practice. Final Report

    ERIC Educational Resources Information Center

    Commonwealth of Learning, 2004

    2004-01-01

    Both of these "Surveys of policy and practice" were conducted on behalf of COL by the South African Institute for Distance Education (SAIDE) as part of COL's partnership agreement with the Association for the Development of Education in Africa (ADEA) Working Group on Distance Education and Open Learning. The first report identifies…

  14. Massive open star clusters using the VVV survey. II. Discovery of six clusters with Wolf-Rayet stars

    NASA Astrophysics Data System (ADS)

    Chené, A.-N.; Borissova, J.; Bonatto, C.; Majaess, D. J.; Baume, G.; Clarke, J. R. A.; Kurtev, R.; Schnurr, O.; Bouret, J.-C.; Catelan, M.; Emerson, J. P.; Feinstein, C.; Geisler, D.; de Grijs, R.; Hervé, A.; Ivanov, V. D.; Kumar, M. S. N.; Lucas, P.; Mahy, L.; Martins, F.; Mauro, F.; Minniti, D.; Moni Bidin, C.

    2013-01-01

    Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims: This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods: Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results: We find that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 × 103 M⊙) clusters. They are highly obscured (AV ~ 5-24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ~30-50 M⊙ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters. Based on observations with ISAAC, VLT, ESO (programme 087.D-0341A), New Technology Telescope at ESO's La Silla Observatory (programme 087.D-0490A) and with the Clay telescope at the Las Campanas Observatory (programme CN2011A-086). Also based on data from the VVV survey (programme 172.B-2002).

  15. Photometric investigation of two contact binaries in the young open cluster NGC 957

    NASA Astrophysics Data System (ADS)

    Luo, ChangQing; Zhang, XiaoBin; Deng, Licai; Wang, Kun; Luo, Yangping; Fang, Xiangsong

    2017-04-01

    We present V- and R- band time-series CCD photometry of two contact binaries in the region of the young open cluster NGC 957. The two eclipsing binaries were discovered by Bukowiecki et al., 2009. OEJV 112, 1 and named as V4 and V5, respectively. In the present paper, the first detailed studies of the two contact binary systems are carried out. Firstly, based on the light curves, 28 times of minimum light were detected for V4 and 21 times of minimum light for V5, respectively. Secondly, the orbital periods of V4 and V5 were redetermined as PV4 = 0.40032(5) days and PV5 = 0.30752 (4)days, respectively. The photometric solutions were analyzed by using Wilson Decinny Code. The results reveal that both V4 and V5 are W UMa-type contact binaries with a degree of fV4 = 31(± 1)% and fV5 = 65(± 1)%. The mass ratios were determined to be qV4 = 0.30 and qV5 = 0.19. For V5, the well known O'Connell effect was detected in the dataset, which effect can be explained by employing a dark spot placed on the more massive primary component. Finally, based on the distances of the two contact binaries, which were calculated by using an relation given by Gettel et al., the two contact binaries are judged to be foreground stars in the open cluster NGC 957.

  16. Accretion Rates on Pre-main-sequence Stars in the Young Open Cluster NGC 6530

    NASA Astrophysics Data System (ADS)

    Gallardo, José; del Valle, Luciano; Ruiz, María Teresa

    2012-01-01

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first ~1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the Hα emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad Hα emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciencia e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva

  17. The same frequency of planets inside and outside open clusters of stars.

    PubMed

    Meibom, Søren; Torres, Guillermo; Fressin, Francois; Latham, David W; Rowe, Jason F; Ciardi, David R; Bryson, Steven T; Rogers, Leslie A; Henze, Christopher E; Janes, Kenneth; Barnes, Sydney A; Marcy, Geoffrey W; Isaacson, Howard; Fischer, Debra A; Howell, Steve B; Horch, Elliott P; Jenkins, Jon M; Schuler, Simon C; Crepp, Justin

    2013-07-04

    Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years. Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field. The field planets are usually the size of Neptune or smaller. In contrast, only four planets have been found orbiting stars in open clusters, all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.

  18. OpenCluster: A Flexible Distributed Computing Framework for Astronomical Data Processing

    NASA Astrophysics Data System (ADS)

    Wei, Shoulin; Wang, Feng; Deng, Hui; Liu, Cuiyin; Dai, Wei; Liang, Bo; Mei, Ying; Shi, Congming; Liu, Yingbo; Wu, Jingping

    2017-02-01

    The volume of data generated by modern astronomical telescopes is extremely large and rapidly growing. However, current high-performance data processing architectures/frameworks are not well suited for astronomers because of their limitations and programming difficulties. In this paper, we therefore present OpenCluster, an open-source distributed computing framework to support rapidly developing high-performance processing pipelines of astronomical big data. We first detail the OpenCluster design principles and implementations and present the APIs facilitated by the framework. We then demonstrate a case in which OpenCluster is used to resolve complex data processing problems for developing a pipeline for the Mingantu Ultrawide Spectral Radioheliograph. Finally, we present our OpenCluster performance evaluation. Overall, OpenCluster provides not only high fault tolerance and simple programming interfaces, but also a flexible means of scaling up the number of interacting entities. OpenCluster thereby provides an easily integrated distributed computing framework for quickly developing a high-performance data processing system of astronomical telescopes and for significantly reducing software development expenses.

  19. GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle

    NASA Astrophysics Data System (ADS)

    Santos, João F. C., Jr.; Roman-Lopes, Alexandre; Carrasco, Eleazar R.; Maia, Francisco F. S.; Neichel, Benoit

    2016-02-01

    Physical properties were derived for the candidate open cluster La Serena 94, recently unveiled by the VISTA Variables in the Vía Láctea (VVV) survey. Thanks to the exquisite angular resolution provided by Gemini South multiconjugate adaptive optics system/Gemini South Adaptive Optics Imager (GeMS/GSAOI), we could characterize this system in detail, for the first time, with deep photometry in JHKs bands. Decontaminated JHKs diagrams reach about 5 mag below the cluster turnoff in H. The locus of red clump giants in the colour-colour diagram, together with an extinction law, was used to obtain an average extinction of AV = 14.18 ± 0.71. The same stars were considered as standard candles to derive the cluster distance, 8.5 ± 1.0 kpc. Isochrones were matched to the cluster colour-magnitude diagrams to determine its age, log t(yr) = 9.12 ± 0.06, and metallicity, Z = 0.02 ± 0.01. A core radius of rc = 0.51 ± 0.04 pc was found by fitting King models to the radial density profile. By adding up the visible stellar mass to an extrapolated mass function, the cluster mass was estimated as M=(2.65± 0.57)× 10^3 M⊙, consistent with an integrated magnitude of M_{K_s}=-5.82± 0.16 and a tidal radius of rt = 17.2 ± 2.1 pc. The overall characteristics of La Serena 94 confirm that it is an old open cluster located in the Crux spiral arm towards the fourth Galactic quadrant and distant 7.30 ± 0.49 kpc from the Galactic Centre. The cluster distorted structure, mass segregation and age indicate that it is a dynamically evolved stellar system.

  20. Distance-Based and Low Energy Adaptive Clustering Protocol for Wireless Sensor Networks

    PubMed Central

    Gani, Abdullah; Anisi, Mohammad Hossein; Ab Hamid, Siti Hafizah; Akhunzada, Adnan; Khan, Muhammad Khurram

    2016-01-01

    A wireless sensor network (WSN) comprises small sensor nodes with limited energy capabilities. The power constraints of WSNs necessitate efficient energy utilization to extend the overall network lifetime of these networks. We propose a distance-based and low-energy adaptive clustering (DISCPLN) protocol to streamline the green issue of efficient energy utilization in WSNs. We also enhance our proposed protocol into the multi-hop-DISCPLN protocol to increase the lifetime of the network in terms of high throughput with minimum delay time and packet loss. We also propose the mobile-DISCPLN protocol to maintain the stability of the network. The modelling and comparison of these protocols with their corresponding benchmarks exhibit promising results. PMID:27658194

  1. Distance-Based and Low Energy Adaptive Clustering Protocol for Wireless Sensor Networks.

    PubMed

    Liaqat, Misbah; Gani, Abdullah; Anisi, Mohammad Hossein; Ab Hamid, Siti Hafizah; Akhunzada, Adnan; Khan, Muhammad Khurram; Ali, Rana Liaqat

    A wireless sensor network (WSN) comprises small sensor nodes with limited energy capabilities. The power constraints of WSNs necessitate efficient energy utilization to extend the overall network lifetime of these networks. We propose a distance-based and low-energy adaptive clustering (DISCPLN) protocol to streamline the green issue of efficient energy utilization in WSNs. We also enhance our proposed protocol into the multi-hop-DISCPLN protocol to increase the lifetime of the network in terms of high throughput with minimum delay time and packet loss. We also propose the mobile-DISCPLN protocol to maintain the stability of the network. The modelling and comparison of these protocols with their corresponding benchmarks exhibit promising results.

  2. HIPPARCOS subdwarfs and globular cluster ages: the distance and age of M 92

    NASA Astrophysics Data System (ADS)

    Pont, F.; Mayor, M.; Turon, C.; Vandenberg, D. A.

    1998-01-01

    A new determination of the distance and age of the old globular cluster M 92 (NGC 6341) is obtained from a consideration of a set of more than 500 subdwarf candidates with Hipparcos parallaxes. Precise [Fe/H] values are derived for most stars using the equivalent width of the Coravel cross-correlation function. We examine at some length the biases affecting the determination of the mean luminosity of a set of subdwarfs selected by metallicity and sigma_ pi /pi distance of M 92 is (m-M)_V=14.67+/- 0.08 mag, from a fit of the cluster main sequence to the 17 subdwarfs in our set with [Fe/H]<-1.8 and sigma_ pi /pi <15%. Bias and binarity corrections are included. The adoption of an alternative [Fe/H] scale causes only minor differences in this result. A more classic treatment of binaries (i.e., simply excluding the detected binaries from the sample) leads to (m-M)_V=14.74 mag. The location of the evolved field subdwarfs (along the subgiant branch) provides a strong indication that M 92 and the most metal-poor subdwarfs are coeval. The M 92 C-M diagram is confronted with up-to-date stellar evolutionary models (recent opacities and nuclear reaction rates, non-ideal equation of state, alpha -element enhancement). The agreement between theory and observations is excellent, including the position of the horizontal branch, if the models are shifted by delta (B-V)= +0.012 mag. An age of 14 Gyr is derived from the luminosities of the cluster turnoff and subgiant branch stars. A similar colour shift is found from an examination of an independent set

  3. Asteroseismic study on cluster distance moduli for red giant branch stars in NGC 6791 and NGC 6819

    SciTech Connect

    Wu, T.; Li, Y.; Hekker, S. E-mail: ly@ynao.ac.cn

    2014-05-01

    Stellar distance is an important basic parameter in stellar astrophysics. Stars in a cluster are thought to be formed coevally from the same interstellar cloud of gas and dust; therefore, they are expected to have common properties. These common properties strengthen our ability to constrain theoretical models and/or to determine fundamental parameters, such as stellar mass, metal fraction, and distance, when tested against an ensemble of cluster stars. Here we derive a new relation based on solar-like oscillations, photometric observations, and the theory of stellar structure and evolution of red giant branch stars to determine cluster distance moduli through the global oscillation parameters Δν and ν{sub max} and photometric data V. The values of Δν and ν{sub max} are derived from Kepler observations. At the same time, it is used to interpret the trends between V and Δν. From the analyses of this newly derived relation and observational data of NGC 6791 and NGC 6819, we devise a method in which all stars in a cluster are regarded as one entity to determine the cluster distance modulus. This approach fully reflects the characteristic of member stars in a cluster as a natural sample. From this method we derive true distance moduli of 13.09 ± 0.10 mag for NGC 6791 and 11.88 ± 0.14 mag for NGC 6819. Additionally, we find that the distance modulus only slightly depends on the metallicity [Fe/H] in the new relation. A change of 0.1 dex in [Fe/H] will lead to a change of 0.06 mag in the distance modulus.

  4. Quality Assurance in Open and Distance Learning. Knowledge Series. A Topical, Start-Up Guide to Distance Education Practice and Delivery

    ERIC Educational Resources Information Center

    Kirkpatrick, Denise

    2005-01-01

    Assuring the quality of education provision is a fundamental aspect of gaining and maintaining credibility for programmes, institutions and national systems of higher education worldwide. Despite a long and generally successful track record, open and distance learning (ODL) is still required to prove that the quality of student learning is at…

  5. Quality Assurance in Open and Distance Learning. Knowledge Series. A Topical, Start-Up Guide to Distance Education Practice and Delivery

    ERIC Educational Resources Information Center

    Kirkpatrick, Denise

    2005-01-01

    Assuring the quality of education provision is a fundamental aspect of gaining and maintaining credibility for programmes, institutions and national systems of higher education worldwide. Despite a long and generally successful track record, open and distance learning (ODL) is still required to prove that the quality of student learning is at…

  6. The Impact of ICT in Learning through Distance Education Programmes at Zimbabwe Open University (ZOU): Roles of ICT in Learning through Distance Education Programmes

    ERIC Educational Resources Information Center

    Mpofu, John; Chimhenga, Sylod; Mafa, Onias

    2013-01-01

    Zimbabwe Distance Open University is enrols students from both urban and rural settings. The majority of students living and working in rural areas have limited or no access to computers and electricity as a result the use of information and communication technology (ICT) in the learning process is very limited. Though government has realized the…

  7. The Shape Evolution of Galactic Open Clusters from Observations Under Galactic External Forces

    NASA Astrophysics Data System (ADS)

    Zhai, Meng; Abt, Helmut; Zhao, Gang; Li, Chengdong

    2017-02-01

    We present the Galactic characteristics of 154 open clusters using the stellar statistics method with data from the WEBDA database. We find that all clusters in our sample are elongated in shape, which indicates that the spherical clusters are stretched out to be ellipsoid as a function of age ({log}({age}/{year})=6.64{--}9.7). By dividing a cluster into a central core and an outer part, we have computed the apparent ellipticities of these two parts respectively. The scale relations between ellipticities and age indicate that the outer parts of open clusters become more elliptical while the central cores remain circular. We suppose that the outer parts become more elliptical because they are more subjected to the external forces, e.g., Galactic differential rotation, while the central cores form a circular shape under the domination of stellar dynamics. We have also performed an analysis of the crucial influence of cluster mass and location on its shape.

  8. Open clusters as laboratories: The angular momentum evolution of young stars

    NASA Technical Reports Server (NTRS)

    Stauffer, John R.

    1994-01-01

    This is the annual status report for the third year of our LTSA grant 'Open Clusters as Laboratories.' Because we have now had a few years to work on the project, we have started to produce and publish a large number of papers. We have been extremely successful in obtaining ROSAT observations of open clusters. With the demise of the PSPC on ROSAT, our main data source has come to an end and we will be able to concentrate on analyzing those data.

  9. Anchoring the Population II Distance Scale: Accurate Ages for Globular Clusters

    NASA Technical Reports Server (NTRS)

    Chaboyer, Brian C.; Chaboyer, Brian C.; Carney, Bruce W.; Latham, David W.; Dunca, Douglas; Grand, Terry; Layden, Andy; Sarajedini, Ataollah; McWilliam, Andrew; Shao, Michael

    2004-01-01

    The metal-poor stars in the halo of the Milky Way galaxy were among the first objects formed in our Galaxy. These Population II stars are the oldest objects in the universe whose ages can be accurately determined. Age determinations for these stars allow us to set a firm lower limit, to the age of the universe and to probe the early formation history of the Milky Way. The age of the universe determined from studies of Population II stars may be compared to the expansion age of the universe and used to constrain cosmological models. The largest uncertainty in estimates for the ages of stars in our halo is due to the uncertainty in the distance scale to Population II objects. We propose to obtain accurate parallaxes to a number of Population II objects (globular clusters and field stars in the halo) resulting in a significant improvement in the Population II distance scale and greatly reducing the uncertainty in the estimated ages of the oldest stars in our galaxy. At the present time, the oldest stars are estimated to be 12.8 Gyr old, with an uncertainty of approx. 15%. The SIM observations obtained by this key project, combined with the supporting theoretical research and ground based observations outlined in this proposal will reduce the estimated uncertainty in the age estimates to 5%).

  10. Swimming performances in long distance open-water events with and without wetsuit

    PubMed Central

    2014-01-01

    Background Existing literature showed improved swimming performances for swimmers wearing wetsuits competing under standardized conditions in races held in pools on short to middle distances. Data about the influence of wetsuits on swimming performances in long and ultra-long open-water swimming races are missing. It is unknown whether the benefit of wearing wetsuits is comparable in men and women. The aim of this study was to investigate the influence of wearing a wetsuit on open-water swimming performances at the 26.4 km ‘Marathon Swim in Lake Zurich’ in Lake Zurich, Switzerland, and the 3.8 km Lake Ontario Swim Team-Race (LOST-Race) in Lake Ontario, Canada. Methods Race times of the fastest female and male swimmers competing with and without wetsuit were compared using multi-level regression analyses and analysis of variance. Results In the ‘Marathon Swim’ in Lake Zurich, wearing a wetsuit had no effect on race time regarding the gender where athletes wearing a wetsuit were not faster than athletes without wetsuit. However, the ten fastest men wearing a wetsuit (410.6 ± 26.7 min) were faster (32.7%, p < 0.01) than the ten fastest women without wetsuit (544.9 ± 81.3 min). In the ‘LOST-Race’, the top ten men wearing a wetsuit (51.7 ± 2.5 min) were faster (13.2%, p < 0.01) than the top ten women wearing a wetsuit (58.5 ± 3.2 min). Additionally, the top ten men without wetsuit (52.1 ± 2.4 min) were faster (19.6%, p < 0.01) than the top ten women without wetsuit (62.3 ± 2.5 min). The top ten women wearing a wetsuit (58.5 ± 3.2 min) were faster (6.5%, p < 0.01) than top ten women without a wetsuit (62.3 ± 25 min). Conclusions These results suggest that wearing a wetsuit had a positive influence on swimming speed for both women and men but the benefit of the use of wetsuits seemed to depend on additional factors (i.e. race distance). Women seemed to benefit more from wearing wetsuits than men in longer

  11. Functional classification of genes using semantic distance and fuzzy clustering approach: evaluation with reference sets and overlap analysis.

    PubMed

    Devignes, Marie-Dominique; Benabderrahmane, Sidahmed; Smaïl-Tabbone, Malika; Napoli, Amedeo; Poch, Olivier

    2012-01-01

    Functional classification aims at grouping genes according to their molecular function or the biological process they participate in. Evaluating the validity of such unsupervised gene classification remains a challenge given the variety of distance measures and classification algorithms that can be used. We evaluate here functional classification of genes with the help of reference sets: KEGG (Kyoto Encyclopaedia of Genes and Genomes) pathways and Pfam clans. These sets represent ground truth for any distance based on GO (Gene Ontology) biological process and molecular function annotations respectively. Overlaps between clusters and reference sets are estimated by the F-score method. We test our previously described IntelliGO semantic distance with hierarchical and fuzzy C-means clustering and we compare results with the state-of-the-art DAVID (Database for Annotation Visualisation and Integrated Discovery) functional classification method. Finally, study of best matching clusters to reference sets leads us to propose a set-difference method for discovering missing information.

  12. Virtual Attendance: Analysis of an Audiovisual over IP System for Distance Learning in the Spanish Open University (UNED)

    ERIC Educational Resources Information Center

    Vazquez-Cano, Esteban; Fombona, Javier; Fernandez, Alberto

    2013-01-01

    This article analyzes a system of virtual attendance, called "AVIP" (AudioVisual over Internet Protocol), at the Spanish Open University (UNED) in Spain. UNED, the largest open university in Europe, is the pioneer in distance education in Spain. It currently has more than 300,000 students, 1,300 teachers, and 6,000 tutors all over the…

  13. Open clusters. II. Fundamental parameters of B stars in Collinder 223, Hogg 16, NGC 2645, NGC 3114, and NGC 6025

    NASA Astrophysics Data System (ADS)

    Aidelman, Y.; Cidale, L. S.; Zorec, J.; Panei, J. A.

    2015-05-01

    Context. The knowledge of accurate values of effective temperature, surface gravity, and luminosity of stars in open clusters is very important not only to derive cluster distances and ages but also to discuss the stellar structure and evolution. Unfortunately, stellar parameters are still very scarce. Aims: Our goal is to study five open clusters to derive stellar parameters of the B and Be star population and discuss the cluster properties. In a near future, we intend to gather a statistically relevant samples of Be stars to discuss their origin and evolution. Methods: We use the Barbier-Chalonge-Divan spectrophotometric system, based on the study of low-resolution spectra around the Balmer discontinuity, since it is independent of the interstellar and circumstellar extinction and provides accurate Hertzsprung-Russell diagrams and stellar parameters. Results: We determine stellar fundamental parameters, such as effective temperatures, surface gravities, spectral types, luminosity classes, absolute and bolometric magnitudes and colour gradient excesses of the stars in the field of Collinder 223, Hogg 16, NGC 2645, NGC 3114, and NGC 6025. Additional information, mainly masses and ages of cluster stellar populations, is obtained using stellar evolution models. In most cases, stellar fundamental parameters have been derived for the first time. We also discuss the derived cluster properties of reddening, age and distance. Conclusions: Collinder 223 cluster parameters are overline{E(B-V) = 0.25 ± 0.03} mag and overline{(mv - M_v)0 = 11.21 ± 0.25} mag. In Hogg 16, we clearly distinguish two groups of stars (Hogg 16a and Hogg 16b) with very different mean true distance moduli (8.91 ± 0.26 mag and 12.51 ± 0.38 mag), mean colour excesses (0.26 ± 0.03 mag and 0.63 ± 0.08 mag), and spectral types (B early-type and B late-/A-type stars, respectively). The farthest group could be merged with Collinder 272. NGC 2645 is a young cluster (<14 Myr) with overline{E(B-V) = 0

  14. Investigation of Galactic open cluster remnants: the case of NGC 7193

    NASA Astrophysics Data System (ADS)

    de Souza Angelo, Mateus; Francisco Coelho dos Santos, João, Jr.; Barbosa Corradi, Wagner José; Ferreira de Souza Maia, Francisco; Piatti, Andrés Eduardo

    2017-01-01

    Galactic open clusters (OCs) that survive the early gas-expulsion phase are gradually destroyed over time by the action of disruptive dynamical processes. Their final evolutionary stages are characterized by a poorly populated concentration of stars called an open cluster remnant (OCR). This study is devoted to assessing the real physical nature of the OCR candidate NGC 7193. GMOS/Gemini spectroscopy of 53 stars in the inner target region were obtained to derive radial velocities and atmospheric parameters. We also employed photometric and proper motion data. The analysis method consists of the following steps: (i) analysis of the statistical resemblance between the cluster and a set of field samples with respect to the sequences defined in color-magnitude diagrams (CMDs); (ii) a 5-dimensional iterative exclusion routine was employed to identify outliers from kinematical and positional data; (iii) isochrone fitting to the Ks×(J-Ks) CMD of the remaining stars and the dispersion of spectral types along empirical sequences in the (J-H)×(H-Ks) diagram were checked. A group of stars was identified for which the mean heliocentric distance is compatible with that obtained via isochrone fitting and whose metallicities are compatible with each other. Fifteen of the member stars observed spectroscopically were identified together with another 19 probable members. Our results indicate that NGC 7193 is a genuine OCR, of a once very populous OC, for which the following parameters were derived: d = 501±46 pc, t=2.5+/-1.2 Gyr, < [Fe/H] >=-0.17+/-0.23 and E(B-V)=0.05+/-0.05. Its luminosity and mass functions show depletion of low mass stars, confirming the OCR is in a dynamically evolved state. Based on observations obtained at the Gemini Observatory, which is operated by the AURA under a cooperative agreement with the NSF on behalf of the Gemini partnership: NSF (United States), STFC (United Kingdom), NRC (Canada), CONICYT (Chile), ARC (Australia), CNPq (Brazil) and CONICET

  15. On the stellar X-ray content of the Open Cluster Remnant NGC 1901

    NASA Astrophysics Data System (ADS)

    Lopes de Oliveira, Raimundo

    2009-10-01

    Open Cluster Remnants (OCRs) are poorly populated groups of stars in an advanced stage of the evolution of open clusters. They are especially rich in late-type stars and binary systems of stars, of which a fraction is expected to be interacting binaries (RS CVn, cataclysmic variables, and low-mass X-ray binaries). We propose to investigate the X-ray content of the OCR NGC 1901, looking for signatures of accreting/interacting binary systems and active stars in order to put constraints on the evolutionary models describing the final stages of star clusters.

  16. The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Overview and Membership Methods

    NASA Astrophysics Data System (ADS)

    Donor, John; Frinchaboy, Peter M.; O'Connell, Julia; Cunha, Katia M. L.; Thompson, Benjamin A.; Melendez, Matthew; Shetrone, Matthew D.; Majewski, Steven R.; Zasowski, Gail; Allende-Prieto, Carlos; Pinsonneault, Marc H.; Roman-Lopes, Alexandre; Schultheis, Mathias; Stassun, Keivan G.; Apogee Team

    2017-01-01

    The Open Cluster Chemical Analysis and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based data set for hundreds of open clusters, and constrain key Galactic dynamical and chemical parameters using the SDSS/APOGEE survey. We present the sample and methods being used by the survey to determine membership for the few-star sampling for most clusters as observed by the SDSS/APOGEE. We present verification of the membership method using the DR13 sample, and show an extension of the method by incorporation of proper motion and parallax data from the ESA Gaia mission.This work is supported by an NSF AAG grant AST-1311835.

  17. piRNA clusters and open chromatin structure

    PubMed Central

    2014-01-01

    Transposable elements (TEs) are major structural components of eukaryotic genomes; however, mobilization of TEs generally has negative effects on the host genome. To counteract this threat, host cells have evolved genetic and epigenetic mechanisms that keep TEs silenced. One such mechanism involves the Piwi-piRNA complex, which represses TEs in animal gonads either by cleaving TE transcripts in the cytoplasm or by directing specific chromatin modifications at TE loci in the nucleus. Most Piwi-interacting RNAs (piRNAs) are derived from genomic piRNA clusters. There has been remarkable progress in our understanding of the mechanisms underlying piRNA biogenesis. However, little is known about how a specific locus in the genome is converted into a piRNA-producing site. In this review, we will discuss a possible link between chromatin boundaries and piRNA cluster formation. PMID:25126116

  18. Lithium Abundances in the Young Open Cluster IC 2602

    NASA Technical Reports Server (NTRS)

    Randich, S.; Aharpour, N.; Pallavicini, R.; Prosser, C. F.; Stauffer, J. R.

    1997-01-01

    We have obtained high-resolution spectra for 28 candidate late-type stars in the 30 Myr old cluster IC 2602. NLTE Li abundances have been derived from measured equivalent widths. The log n(Li) - T(sub eff) and log n(Li) - mass distributions for our sample stars have been compared with those of the Pleiades and alpha Persei. Our data show that F stars in the three clusters have the same lithium content, which corresponds to the initial content for Pop. I stars. G and early-K IC 2602 stars are, on average, somewhat more Li-rich than their counterparts in the two slightly older clusters. Finally, the latest-type IC 2602 stars are heavily Li depleted, with their Li content being as low as the lowest measured among the Pleiades. As in the Pleiades and alpha Per, a star-to-star scatter in lithium is observed among 30 Myr old late-K/early-K dwarfs in IC 2602, indicating that this spread develops in the pre-main sequence phases.

  19. Reddening and age for 13 southern Galactic open clusters determined from integrated spectra

    NASA Astrophysics Data System (ADS)

    Ahumada, A. V.; Clariá, J. J.; Bica, E.; Dutra, C. M.; Torres, M. C.

    2001-10-01

    In this study we present flux-calibrated integrated spectra in the range 3800-6800 Å for 13 concentrated open clusters with Galactic longitudes between 219deg and 316deg, nine of which have not been previously studied. Using the equivalent widths of the Balmer lines and comparing the cluster spectra with template spectra of Magellanic Clouds and Galactic star clusters with known parameters, we derive both foreground interstellar reddening values and age. For nine clusters these two parameters have been determined for the first time, while for the rest of the sample the results show good agreement with previous studies. The present analysis indicates four very young (Hogg 11, NGC 5606, vdB-RN 80 and Pismis 17), seven moderately young (ESO 429-SC13, Hogg 3, Hogg 12, Haffner 7, BH 87, NGC 2368 and Bochum 12) and two intermediate-age (Berkeley 75 and NGC 2635) open clusters. The derived foreground interstellar reddening values are in the range 0.00 <= E(B-V) <= 0.38. The age and reddening distributions of the present sample of relatively faint open clusters match those of open clusters with known parameters in a 90deg sector centered at l = 270deg. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

  20. ON THE ORIGIN OF HIGH-ALTITUDE OPEN CLUSTERS IN THE MILKY WAY

    SciTech Connect

    Martinez-Medina, L. A.; Pichardo, B.; Moreno, E.; Peimbert, A.; Velazquez, H.

    2016-01-20

    We present a dynamical study of the effect of the bar and spiral arms on the simulated orbits of open clusters in the Galaxy. Specifically, this work is devoted to the puzzling presence of high-altitude open clusters in the Galaxy. For this purpose we employ a very detailed observationally motivated potential model for the Milky Way and a careful set of initial conditions representing the newly born open clusters in the thin disk. We find that the spiral arms are able to raise an important percentage of open clusters (about one-sixth of the total employed in our simulations, depending on the structural parameters of the arms) above the Galactic plane to heights beyond 200 pc, producing a bulge-shaped structure toward the center of the Galaxy. Contrary to what was expected, the spiral arms produce a much greater vertical effect on the clusters than the bar, both in quantity and height; this is due to the sharper concentration of the mass on the spiral arms, when compared to the bar. When a bar and spiral arms are included, spiral arms are still capable of raising an important percentage of the simulated open clusters through chaotic diffusion (as tested from classification analysis of the resultant high-z orbits), but the bar seems to restrain them, diminishing the elevation above the plane by a factor of about two.