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Sample records for open cluster distance

  1. 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.

  2. 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).

  3. 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.

  4. The Distances to Open Clusters from Main-Sequence Fitting. IV. Galactic Cepheids, the LMC, and the Local Distance Scale

    NASA Astrophysics Data System (ADS)

    An, Deokkeun; Terndrup, Donald M.; Pinsonneault, Marc H.

    2007-12-01

    We derive the basic properties of seven Galactic open clusters containing Cepheids and construct their period-luminosity (P-L) relations. For our cluster main-sequence fitting we extend previous Hyades-based empirical color-temperature corrections to hotter stars using the Pleiades as a template. We use BVICJHKs data to test the reddening law and include metallicity effects to perform a more comprehensive study for our clusters than prior efforts. The ratio of total to selective extinction RV that we derive is consistent with expectations. Assuming the LMC P-L slopes, we find =-3.93+/-0.07 (statistical)+/-0.14 (systematic) for 10 day period Cepheids, which is generally fainter than those in previous studies. Our results are consistent with recent HST and Hipparcos parallax studies when using the Wesenheit magnitudes W(VI). Uncertainties in reddening and metallicity are the major remaining sources of error in the V-band P-L relation, but a higher precision could be obtained with deeper optical and near-infrared cluster photometry. We derive distances to NGC 4258, the LMC, and M33 of (m-M)0=29.28+/-0.10, 18.34+/-0.06, and 24.55+/-0.28, respectively, with an additional systematic error of 0.16 mag in the P-L relations. The distance to NGC 4258 is in good agreement with the geometric distance derived from water masers [Δ(m-M)0=0.01+/-0.24], our value for M33 is less consistent with the distance from an eclipsing binary [Δ(m-M)0=0.37+/-0.34], and our LMC distance is moderately shorter than the adopted distance in the HST Key Project, which formally implies an increase in the Hubble constant of 7%+/-8%.

  5. 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.

  6. 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).

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. Assessing Open and Distance Learners. Open and Distance Learning Series.

    ERIC Educational Resources Information Center

    Morgan, Chris; O'Reilly, Meg

    This book is designed to help readers reflect upon their personal approaches to open and distance learning (ODL) assessment and to adapt their techniques to benefit learners. Part A explores issues and themes in ODL assessment. It examines key terms in assessment; the important relationship between assessment and learning; unique issues of…

  13. 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.

  14. 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.

  15. 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.

  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. 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 Facade" (W. van der Schaaf);…

  18. An improved distance matrix computation algorithm for multicore clusters.

    PubMed

    Al-Neama, Mohammed W; Reda, Naglaa M; Ghaleb, Fayed F M

    2014-01-01

    Distance matrix has diverse usage in different research areas. Its computation is typically an essential task in most bioinformatics applications, especially in multiple sequence alignment. The gigantic explosion of biological sequence databases leads to an urgent need for accelerating these computations. DistVect algorithm was introduced in the paper of Al-Neama et al. (in press) to present a recent approach for vectorizing distance matrix computing. It showed an efficient performance in both sequential and parallel computing. However, the multicore cluster systems, which are available now, with their scalability and performance/cost ratio, meet the need for more powerful and efficient performance. This paper proposes DistVect1 as highly efficient parallel vectorized algorithm with high performance for computing distance matrix, addressed to multicore clusters. It reformulates DistVect1 vectorized algorithm in terms of clusters primitives. It deduces an efficient approach of partitioning and scheduling computations, convenient to this type of architecture. Implementations employ potential of both MPI and OpenMP libraries. Experimental results show that the proposed method performs improvement of around 3-fold speedup upon SSE2. Further it also achieves speedups more than 9 orders of magnitude compared to the publicly available parallel implementation utilized in ClustalW-MPI. PMID:25013779

  19. 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 and…

  20. Multi-relational Clustering Based on Relational Distance

    NASA Astrophysics Data System (ADS)

    Luan, Luan; Li, Yun; Yin, Jiang; Sheng, Yan

    When clustering the tuples in the target table which is in a relational database, the prior task is to exactly and effectively calculate the relational distance between tuples. A lot of methods are used today, such as the relational distance measuring based on RIBL2. However, all these methods fail to consider the differences of similarity between the objects in both non-target table and target table, which stopped them from getting a high clustering accuracy. Using canonical correlation analysis in this paper and setting a weight for each table in the relational database, the weight indicated its role in the calculation of the distance among target tables. In addition, when calculating the distance between the two clusters to find the center of each cluster, turn the calculation of the distance between clusters into a distance between center points. Experiments show that this method ensures clustering efficiency and improved clustering accuracy.

  1. 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.

  2. OCAAT: automated analysis of star cluster colour-magnitude diagrams for gauging the local distance scale

    NASA Astrophysics Data System (ADS)

    Perren, Gabriel I.; Vázquez, Ruben A.; Piatti, Andrés E.; Moitinho, André

    2014-05-01

    Star clusters are among the fundamental astrophysical objects used in setting the local distance scale. Despite its crucial importance, the accurate determination of the distances to the Magellanic Clouds (SMC/LMC) remains a fuzzy step in the cosmological distance ladder. The exquisite astrometry of the recently launched ESA Gaia mission is expected to deliver extremely accurate statistical parallaxes, and thus distances, to the SMC/LMC. However, an independent SMC/LMC distance determination via main sequence fitting of star clusters provides an important validation check point for the Gaia distances. This has been a valuable lesson learnt from the famous Hipparcos Pleiades distance discrepancy problem. Current observations will allow hundreds of LMC/SMC clusters to be analyzed in this light. Today, the most common approach for star cluster main sequence fitting is still by eye. The process is intrinsically subjective and affected by large uncertainties, especially when applied to poorly populated clusters. It is also, clearly, not an efficient route for addressing the analysis of hundreds, or thousands, of star clusters. These concerns, together with a new attitude towards advanced statistical techniques in astronomy and the availability of powerful computers, have led to the emergence of software packages designed for analyzing star cluster photometry. With a few rare exceptions, those packages are not publicly available. Here we present OCAAT (Open Cluster Automated Analysis Tool), a suite of publicly available open source tools that fully automatises cluster isochrone fitting. The code will be applied to a large set of hundreds of open clusters observed in the Washington system, located in the Milky Way and the Magellanic Clouds. This will allow us to generate an objective and homogeneous catalog of distances up to ~ 60 kpc along with its associated reddening, ages and metallicities and uncertainty estimates.

  3. 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.

  4. FUV imaging survey of Galactic open clusters

    NASA Astrophysics Data System (ADS)

    Maiz Apellaniz, Jesus

    2007-07-01

    We propose a WFPC2 FUV imaging survey of 6 Galactic open clusters with ages ranging from 1 Myr to 300 Myr complemented with NUV/optical imaging of the same fields. No such survey has ever been attempted before in the FUV at the resolution of WFPC2 {indeed, no WFPC2 FUV images of any Galactic open cluster exist in the HST archive} and, since WFPC2 will be retired in SM4 and none of the other HST instruments can do FUV imaging of bright objects, this is the last chance to do such a survey before another UV telescope is launched. This survey will provide a new perspective on young/intermediate age Galactic clusters and a key template for the study of star formation at high redshift, where the intensity peak we observe in the optical/NIR from Earth is located in the FUV in its rest frame. For clusters still associated with an H II region, UV imaging maps the continuum emission of the ionized gas and the radiation scattered by background dust and, combined with optical nebular images, can be used to determine the 3-D structure of the H II region. For all young clusters, FUV+NUV+optical photometry can be used to study the UV excesses of T-Tauri stars. For clusters older than 40 Myr, the same photometric combination is the easiest method to detect companion white dwarfs which are invisible using only the optical and NIR. WFPC2 is also an excellent instrument to discover close companions around bright stars and improve our knowledge of their multiplicity fraction. Finally, for all clusters, the combination of high-spatial-resolution UV and optical photometry can be used to simultaneously measure the temperature, extinction, extinction law, distance, and existence of companions {resolved and unresolved} and, thus, produce clean HR diagrams with resolved cluster membership and much-reduced systematic uncertainties.

  5. Fire safety distances for open pool fires

    NASA Astrophysics Data System (ADS)

    Sudheer, S.; Kumar, Lokendra; Manjunath, B. S.; Pasi, Amit; Meenakshi, G.; Prabhu, S. V.

    2013-11-01

    Fire accidents that carry huge loss with them have increased in the previous two decades than at any time in the history. Hence, there is a need for understanding the safety distances from different fires with different fuels. Fire safety distances are computed for different open pool fires. Diesel, gasoline and hexane are used as fuels for circular pool diameters of 0.5 m, 0.7 m and 1.0 m. A large square pool fire of 4 m × 4 m is also conducted with diesel as a fuel. All the prescribed distances in this study are purely based on the thermal analysis. IR camera is used to get the thermal images of pool fires and there by the irradiance at different locations is computed. The computed irradiance is presented with the threshold heat flux limits for human beings.

  6. 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 Age: From the School to…

  7. 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,…

  8. 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.

  9. 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.

  10. 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

  11. 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…

  12. 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…

  13. 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…

  14. 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 Distance Education" (Moore); "Creating the…

  15. 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)

  16. Towards a photometric metallicity scale for open clusters

    NASA Astrophysics Data System (ADS)

    Netopil, M.; Paunzen, E.

    2013-09-01

    Context. Open clusters are a useful tool when investigating several topics connected with stellar evolution; for example the age or distance can be more accurately determined than for field stars. However, one important parameter, the metallicity, is only known for a marginal percentage of open clusters. Aims: We aim at a consistent set of parameters for the open clusters investigated in our photometric Δa survey of chemically peculiar stars. Special attention is paid to expanding our knowledge of cluster metallicities and verifying their scale. Methods: Making use of a previously developed method based on normalised evolutionary grids and photometric data, the distance, age, reddening, and metallicity of open clusters were derived. To transform photometric measurements into effective temperatures to use as input for our method, a set of temperature calibrations for the most commonly used colour indices and photometric systems was compiled. Results: We analysed 58 open clusters in total. Our derived metallicity values were in excellent agreement with about 30 spectroscopically studied targets. The mean value of the absolute deviations was found to be 0.03 dex, with no noticeable offset or gradient. The method was also applied using recent evolutionary models based on the currently accepted lower solar abundance value Z ~ 0.014. No significant differences were found compared to grids using the former adopted solar value Z = 0.02. Furthermore, some divergent photometric datasets were identified and discussed. Conclusions: The method provides an accurate way of obtaining properly scaled metallicity values for open clusters. In light of present and future homogeneous photometric sky surveys, the sample of stellar clusters can be extended to the outskirts of the Milky Way, where spectroscopic studies are almost impossible. This will help for determining galactic metallicity gradients in more detail. Figure 7 is available in electronic form at http://www.aanda.org

  17. 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.

  18. Dynamics of very rich open clusters

    NASA Astrophysics Data System (ADS)

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

    The oldest open clusters in our Galaxy set the lower limit to the age of the Galactic Disk (9-10 Gyr). Although they appear to be very rich now, it is clear that their primordial populations were much larger. Often considered as transitional objects, these populous open clusters show structural differences with respect to globular clusters so their dynamics and characteristic evolutionary time scales can also be different. On the other hand, their large membership lead to different dynamical evolution as compared with average open clusters. In this paper, the differential features of the evolution of rich open clusters are studied using N-body simulations, including several of the largest (10^4 stars) published direct collisional N-body calculations so far, which were performed on a CRAY YMP. The disruption rate of rich open clusters is analysed in detail and the effect of the initial spatial distribution of the stars in the cluster on its dynamics is studied. The results show that cluster life-time depends on this initial distribution, decreasing when it is more concentrated. The effect of stellar evolution on the dynamical evolution of rich clusters is an important subject that also has been considered here. We demonstrate that the cluster's life-expectancy against evaporation increases because of mass loss by evolving high-mass stars.

  19. ZIRCONIUM, BARIUM, LANTHANUM, AND EUROPIUM ABUNDANCES IN OPEN CLUSTERS

    SciTech Connect

    Jacobson, Heather R.; Friel, Eileen D. E-mail: efriel@indiana.edu

    2013-04-15

    We present an analysis of the s-process elements Zr, Ba, and La and the r-process element Eu in a sample of 50 stars in 19 open clusters. Stellar abundances of each element are based on measures of a minimum of two lines per species via both equivalent width and spectrum synthesis techniques. We investigate cluster mean neutron-capture abundance trends as a function of cluster age and location in the Milky Way disk and compare them to results found in other studies in the literature. We find a statistically significant trend of increasing cluster [Ba/Fe] as a function of decreasing cluster age, in agreement with recent findings for other open cluster samples, supporting the increased importance of low-mass asymptotic giant branch stars to the generation of s-process elements. However, the other s-process elements, [La/Fe] and [Zr/Fe], do not show similar dependences, in contrast to theoretical expectations and the limited observational data from other studies. Conversely, cluster [Eu/Fe] ratios show a slight increase with increasing cluster age, although with marginal statistical significance. Ratios of [s/r]-process abundances, [Ba/Eu] and [La/Eu], however, show more clearly the increasing efficiency of s-process relative to r-process enrichment in open cluster chemical evolution, with significant increases among younger clusters. Last, cluster neutron-capture element abundances appear to be independent of Galactocentric distance. We conclude that a homogeneous analysis of a larger sample of open clusters is needed to resolve the apparent discrepant conclusions between different studies regarding s-process element abundance trends with age to better inform models of galactic chemical evolution.

  20. 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.

  1. A detailed study of the open cluster PISMIS 20.

    NASA Astrophysics Data System (ADS)

    Vazquez, R. A.; Will, J.-M.; Prado, P.; Feinstein, A.

    1995-05-01

    The very young open cluster Pis 20 has been investigated using CCD UBVR photometry. New blue faint members were found down to V=19mag. With them we obtain a better definition of the lower cluster main sequence. Using the fitting method, we derive a cluster distance of d=3600pc (V_0_-M_V_=12.80). The mean color excess is =1.24mag. From the observed characteristics and spatial location of the bluest cluster stars we conclude that the star WR 67 has a good chance to be a cluster member. In that case, the mass of its progenitor should be greater than 50Msun_ according to evolutionary models. We obtain for Pis 20 an age of 5(+/-1)x10^6^yr from isochrone fitting. We discuss the cluster's mass spectrum whose slope, within the observational uncertainties, appears to be similar to the one in Salpeter's law. We notice that high WR/OB and WC/WN number ratios are present not only within the cluster itself but also in the association where Pis 20 is situated. Although the cluster distance derived here places Pis 20 nearer than the supernova remnant MSH 15-52, we cannot/rule out the possibility that they are spatially related. The presently observed cluster mass is around 600Msun_.

  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. 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.

  4. Two populations of open star clusters in the Galaxy

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

    Based on our compiled catalogue of fundamental astrophysical parameters for 593 open clusters, we analyze the relations between the chemical composition, spatial positions, Galactic orbital elements, age, and other physical parameters of open star clusters. We show that the population of open clusters is heterogeneous and is divided into two groups differing by their mean parameters, properties, and origin. One group includes the Galactic clusters formed mainly from the interstellar matter of the thin disk with nearly solarmetallicities ([Fe/H] > -0.2) and having almost circular orbits a short distance away from the Galactic plane, i.e., typical of the field stars of the Galactic thin disk. The second group includes the peculiar clusters formed through the interaction of extragalactic objects (such as high-velocity clouds, globular clusters, or dwarf galaxies) with the interstellar matter of the thin disk, which, as a result, derived abnormally low (for field thin-disk stars) metallicities and/or Galactic orbits typical of objects of the older Galactic subsystems. About 70% of the clusters older than 1Gyr have been found to be peculiar, suggesting a slower disruption of clusters with noncircular high orbits. Analysis of orbital elements has shown that the bulk of the clusters from both groups were formed within a Galactocentric radius of ≈10.5 kpc and closer than ≈180 pc from the Galactic plane, but owing to their high initial velocities, the peculiar clusters gradually took up the volumes occupied by the objects of the thick disk, the halo, and even the accreted halo of the Galaxy. Analysis of the relative abundances of magnesium (a representative of the α-elements) in clusters that, according to their kinematical parameters, belong to different Galactic subsystems has shown that all clusters are composed of matter incorporating the interstellar matter of a single protogalactic cloud in different proportions, i.e., reprocessed in genetically related stars of

  5. 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.

  6. Dynamical Evolution of Open Star Clusters

    NASA Astrophysics Data System (ADS)

    de La Fuente Marcos, Raúl

    1998-09-01

    Stars are not formed independently, but instead they form in clusters. The influence of the initial mass function (IMF) on the evolution of open star clusters is analyzed using numerical integrations of N-body systems by the code NBODY5 (S. J. Aarseth, in Multiple Time Scales, ed. J. U. Brackbill & B. I. Cohen [New York: Academic, 1985], p. 377), which include tidal effects, mass loss due to stellar evolution, the realistic fraction of primordial binaries, and the formation of multiple systems. Five different IMFs (E. E. Salpeter, ApJ, 121, 161 [1955]; L. G. Taff, AJ, 79, 11 [1974]; G. E. Miller & J. M. Scalo, ApJS, 41, 513 [1979]; P. Kroupa, C. A. Tout, & G. Gilmore, MNRAS, 262, 545 [1993]; J. M. Scalo, Fundam. Cosmic Phys., 11, 1 [1986]) are used for generating stellar masses. The results confirm significant differences with single-mass models and allow us to distinguish between the standard power-law models and modern ones. An approximate analytic expression for the escape rate is derived in order to fit the data obtained. When stellar evolution is included, the results show that for all the IMF's studied, the evolution of the cluster is slowed down and the initial core collapse loses importance because of an expansion of the inner regions of the cluster. We find that the total disruption time is very IMF dependent because of different numbers of massive stars and also depends on the richness of the cluster. A differential behavior is found between poor and rich systems with respect to mass loss. Poor systems disrupt earlier than homologous ones without mass loss; the opposite is found for rich systems. The transition population is about N = 300. The binary escape rate seems preferentially due to close encounters in poor clusters, but it seems mainly exponential for populated clusters. It suggests that ejection is the main mechanism for binary escape in poor clusters and evaporation is the dominant one for rich clusters. The formation and evolution of

  7. 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. PMID:14737161

  8. 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…

  9. 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.…

  10. 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.

  11. 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…

  12. Membership determination of Open Clusters with CLUSTERIX

    NASA Astrophysics Data System (ADS)

    Sezima, T.; Galadí-Enríquez, D.; Paunzen, E.; Jordi, C.; Balaguer-Núñez, L.; Jilkova, L.

    2015-05-01

    The web-based application Clusterix has been developed as a collaboration between the Masaryk University (Czech Republic) and the Universitat de Barcelona (Spain) to calculate the membership probability of open clusters on the WEBDA database using a completely non parametric method (Galadí-Enríquez et al., 1998; Balaguer-Núñez et al., 2004). WEBDA is a site devoted to observational data on stars in Galactic open clusters. Clusterix is an interactive tool where the user can define the default values to configure the membership estimation for the area of a cluster. Gaia's capabilities to study the kinematics of clusters of stars with great accuracy is one of the main motivations for the development of this tool. The applet first version can be found at: http://clusterix.cerit-sc.cz/

  13. 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.

  14. Open clusters in the Third Galactic Quadrant III. Alleged binary clusters

    NASA Astrophysics Data System (ADS)

    Vázquez, R. A.; Moitinho, A.; Carraro, G.; Dias, W. S.

    2010-02-01

    Aims: We aim to determine accurate distances and ages of eight open clusters in order to: (1) assess their possible binarity (2) provide probes to trace the structure of the Third Galactic Quadrant. Methods: Cluster reddenings, distances, ages and metallicities are derived from ZAMS and isochrone fits in UBVRI photometric diagrams. Field contamination is reduced by restricting analysis to stars within the cluster limits derived from star counts. Further membership control is done by requiring that stars have consistent positions in several diagrams and by using published spectral types. Results: The derived distances, ages and metallicities have shown that none of the analysed clusters compose binary/double systems. Of the four candidate pairs, only NGC 2383/NGC 2384 are close to each other, but have different metallicities and ages. Ruprecht 72 and Ruprecht 158 are not clusters but fluctuations of the field stellar density. Haffner 18 is found to be the superposition of two stellar groups at different distances: Haffner 18(1) at 4.5 kpc and Haffner 18(2) between 9.5 and 11.4 kpc from the Sun. The derived distances and ages have been used to situate the clusters in the Galactic context. In particular, young stellar groups trace spiral structure at large Galactocentric radii. At least two clusters formed during the last few 108 yr in an interstellar medium with less than solar abundances. Conclusions: In contrast with the LMC, double clusters are apparently rare, or even non existent, in the undisturbed environment of the Third Galactic Quadrant. This leaves open the question of whether binary clusters form more easily toward denser and more violent regions of the Milky Way such as the inner Galaxy. The original photometry is only available in electronic form at 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/511/A38on leave from Dipartimento di Astronomia, Università di Padova, Vicolo Osservatorio 2

  15. 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.

  16. 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.

  17. 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…

  18. 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.

  19. 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.

  20. Chemical Abundances of Solar-Type Dwarfs in Open Clusters

    NASA Astrophysics Data System (ADS)

    Schuler, S. C.

    2005-12-01

    Open clusters present homogeneous samples of stars that are of the same age, distance, and initial chemical composition, making open clusters valuable observational targets for studies of stellar evolution, stellar structure, exoplanetary systems, and Galactic chemical evolution. I present an overview of my graduate dissertation research on LTE abundances of solar-type dwarfs (4200 ≲ T eff ≲ 6400 ; {K}) in the open clusters Pleiades, M34, and Hyades, as well as in the Ursa Major moving group. For the dwarfs of intermediate T eff (5500 ≲ T eff ≲ 6100 ; {K}), intracluster metal abundances are in good agreement. Conversely, we have identified excitation/ionization-related abundance anomalies among the cool dwarfs (T eff ≤ 5500 ; {K}) of all three clusters and UMa; for example, O abundances derived from the high-excitation, near-IR \\ion{O}{1} triplet show a dramatic increase with decreasing T eff, a behavior that is not predicted by current non-LTE calculations. Intercluster comparisons are suggestive of an age-related diminution of the \\ion{O}{1} triplet abundance trend, and possible causes of these observed abundance anomalies, i.e., chromospheric activity, surface inhomogeneities, etc., are explored. Using multi-component ``toy model'' stellar atmospheres, we demonstrate that the \\ion{O}{1} triplet abundance trend may be due to inhomogeneous temperature structure, possibly resulting from spots or plages, in the photospheres of cool open cluster dwarfs. I gratefully acknowledge the following agencies that have provided support during this research: NSF (through grants AST 00-86576 and AST 02-39518 to Prof. J.R. King), South Carolina Space Grant Consortium (through the Graduate Student Research Fellowship program), and the Charles Curry Foundation (through a generous grant to Clemson University).

  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 That Never Shone"…

  2. Refining the true parameters of the open cluster NGC 4852

    NASA Astrophysics Data System (ADS)

    Solivella, Gladys; Giorg, Edgard; Vázquez, Rubén; Carraro, Giovanni

    2010-01-01

    NGC 4852 is a moderately compact cluster centered at α2000 = 13 : 00 : 09; δ = -59 : 36 : 48, located near the center of an Hα superring. This cluster forms part of an extended region including young stellar aggregates inside a circle with a radius of 3 degrees, where many show an abundance of emission line stars. In the field of this cluster, two stars of known type exist: Wray 15-1039 (emission-line object) and CD -58:4845 (emission-line star). We do not yet know whether the Be phase is transient or whether it is just what randomly happens in some hot stars. It appears that Be star may be found even in clusters as old as 70 Myr with a high occurrence rate in clusters of 25-27 Myr old. A recent photometric survey in NGC 4852 down to V = 22 - 23 mag established that NGC 4852 is about 200 - 250 Myr old, located at 1.1 kpc from the Sun and with a mean E(B - V) = 0.45 mag. Since the presence of potential Be-type stars in the cluster area suggests it may be a very young object instead of moderately old, we decided to carry out spectroscopy for 33 selected stars and CCD UBVI photometry for the bright objects in the cluster area. This way, we attempt to clarify their evolutionary state and include them in the framework of emission-line stars and open clusters. From our analysis, we agree with the cluster distance and reddening determined by earlier studies, but we derive that the age of NGC 4852 is younger than 40 Myr.

  3. 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.

  4. 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…

  5. 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…

  6. 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,…

  7. 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…

  8. 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…

  9. 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…

  10. 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…

  11. 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.

  12. Open-Cluster Population of Sh 2-109

    NASA Astrophysics Data System (ADS)

    LeMieux, Henri; Kaltcheva, Nadia

    2016-01-01

    The prominent nebulosity Sh 2-109 that dominates the Cygnus star-forming field is probably a complex of several overlapping H II regions. Since in this direction the line of sight is along the local Orion spiral arm, the isolation of individual stellar and interstellar structures is difficult. This study is focused on the massive stellar content of Sh 2-109 with the purpose of providing new insights on its structure. We use the catalog of optically visible open clusters and candidates (Dias et al. 2014) to study the properties of the open-cluster population within the boundaries of the Sh 2-109 star-forming region. We also utilize photometric uvbyβ data for the massive stars in Sh 2-109. This data set includes more than 10 young open clusters. Since the intermediate-band uvbyβ photometry allows the derivation of stellar physical parameters with high precision, we provide homogeneous distance and age estimates to the OB-associations identified toward Sh 2-109. Based on all the data we map the structure of the field in order to further study its morphology and energetics. Acknowledgments. This work was supported by NSF grant AST- 1516932.

  13. 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.

  14. 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 Learning for…

  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. 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.

  17. A new look at open cluster NGC 6520

    SciTech Connect

    Odell, Andrew P.

    2014-01-01

    We use CCD and photoelectric photometry with Strömgren filters along with medium resolution spectra to investigate NGC 6520, an open cluster very nearly in the direction of the galactic center. We find an age of 60 Myr, a distance of 2 kpc, and an average reddening E(b – y) = 0.295, which increases toward the south. The average heliocentric radial velocity of the B stars is –29 km s{sup –1}, while the velocity of the nearby Barnard 86 is about 0 (heliocentric; –11 km s{sup –1} compared to the LSR). This velocity difference amounts to about 1.8 kpc since the cluster formed, implying that it is extremely doubtful NGC 6520 is related to Barnard 86.

  18. 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.

  19. Long distance education for croatian nurses with open source software.

    PubMed

    Radenovic, Aleksandar; Kalauz, Sonja

    2006-01-01

    Croatian Nursing Informatics Association (CNIA) has been established as result of continuing work on promoting nursing informatics in Croatia. Main goals of CNIA are promoting nursing informatics and education of nurses about nursing informatics and using information technology in nursing process. CNIA in start of work is developed three courses from nursing informatics all designed with support of long distance education with open source software. Courses are: A - 'From Data to Wisdom', B - 'Introduction to Nursing Informatics' and C - 'Nursing Informatics I'. Courses A and B are obligatory for C course. Technology used to implement these online courses is based on the open source Learning Management System (LMS), Claroline, free online collaborative learning platform. Courses are divided in two modules/days. First module/day participants have classical approach to education and second day with E-learning from home. These courses represent first courses from nursing informatics' and first long distance education for nurses also. PMID:17102315

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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,…

  6. 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…

  7. 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…

  8. 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.

  9. 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.

  10. Abundance analysis of an extended sample of open clusters: A search for chemical inhomogeneities

    NASA Astrophysics Data System (ADS)

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

    We have initiated a program to explore the presence of chemical inhomogeneities in the Galactic disk using the open clusters as ideal probes. We have analyzed high-dispersion echelle spectra (R ≥ 55,000) of red giant members for eleven open clusters to derive abundances for many elements. The membership to the cluster has been confirmed through their radial velocities and proper motions. The spread in temperatures and gravities being very small among the red giants, nearly the same stellar lines were employed thereby reducing the random errors. The errors of average abundance for the cluster were generally in 0.02 to 0.07 dex range. Our present sample covers galactocentric distances of 8.3 to 11.3 kpc and an age range of 0.2 to 4.3 Gyrs. Our earlier analysis of four open clusters (Reddy A.B.S. et al., 2012, MNRAS, 419,1350) indicate that abundances relative to Fe for elements from Na to Eu are equal within measurement uncertainties to published abundances for thin disk giants in the field. This supports the view that field stars come from disrupted open clusters. In the enlarged sample of eleven open clusters we find cluster to cluster abundance variations for some s- and r- process elements, with certain elements such as Zr and Ba showing large variation. These differences mark the signatures that these clusters had formed under different environmental conditions (Type II SN, Type Ia SN, AGB stars or a mixture of any of these) unique to the time and site of formation. These eleven clusters support the widely held impression that there is an abundance gradient such that the metallicity [Fe/H] at the solar galactocentric distance decreases outwards at about -0.1 dex per kpc.

  11. 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.

  12. 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.

  13. A multiwavelength polarimetric study towards the open cluster NGC 1893

    NASA Astrophysics Data System (ADS)

    Eswaraiah, C.; Pandey, A. K.; Maheswar, G.; Medhi, Biman J.; Pandey, J. C.; Ojha, D. K.; Chen, W. P.

    2011-03-01

    We present multiwavelength linear polarimetric observations for 44 stars of the NGC 1893 young open cluster region along with V-band polarimetric observations of stars of four other open clusters located between l˜ 160° and 175°. We found evidence for the presence of two dust layers located at a distance of ˜170 and ˜360 pc. The dust layers produce a polarization PV˜ 2.2 per cent. It is evident from the clusters studied in this work that, in the Galactic longitude range from l˜ 160° to 175° and within the Galactic plane (|b| < 2°), the polarization angles remain almost constant, with a mean of ˜163° and a dispersion of 6°. The small dispersion in polarization angle could be due to the presence of a uniform dust layer beyond 1 kpc. Present observations reveal that in the case of NGC 1893, the foreground two dust layers, in addition to the intracluster medium, seem to be responsible for the polarization effects. It is also found that towards the direction of NGC 1893, the dust layer that exists between 2 and 3 kpc has a negligible contribution towards the total observed polarization. The weighted mean for percentage of polarization (Pmax) and the wavelength at maximum polarization (λmax) are found to be 2.59 ± 0.02 per cent and 0.55 ± 0.01 μm, respectively. The estimated mean value of λmax indicates that the average size of the dust grains within the cluster is similar to that in the general interstellar medium. The spatial variation of the polarization is found to decrease towards the outer region of the cluster. In this work, we support the notion, as has already been shown in previous studies, that polarimetry, in combination with the (U-B)-(B-V) colour-colour diagram, is a useful tool for identifying non-members in a cluster.

  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. Distance duality relation from x-ray and Sunyaev-Zel'dovich observations of clusters

    SciTech Connect

    Uzan, Jean-Philippe; Aghanim, Nabila; Mellier, Yannick

    2004-10-15

    X-ray and Sunyaev-Zel'dovich data of clusters of galaxies enable to construct a test of the distance duality relation between the angular and luminosity distances. We argue that such a test on large cluster samples maybe of importance, as a consistency check, while trying to distinguish between various models accounting for the acceleration of the universe. The analysis of a data set of 18 clusters shows no significant violation of this relation for a {lambda}-Cold Dark Matter (CDM) model. The origin and amplitude of systematic effects and the possibility to increase the precision of this method are discussed.

  16. Dolidze-35: Results for a Possible Open Cluster

    NASA Astrophysics Data System (ADS)

    Gulledge, Deborah J.; Borges, Richard A.; Juelfs, Elizabeth; Allyn Smith, J.; Olive, Mary E.; McDonald, Christopher P.; Williams, Sarah M.; Cohen, Eden M.; Gawel, Jason D.; McCole, Bambi A.; Robertson, Jacob M.; Wilson, Tyler; Young, William J.; Buckner, Spencer L.; Allen, Nic R.; Head, H. Hope

    2016-01-01

    Dolidze-35 is an under-observed northern hemisphere open cluster. It is noted in WEBDA as "No data available for this cluster". As such, we chose this cluster as an undergraduate class project to investigate its existence. We present SDSS-ugriz magnitudes for the possible cluster and cross these with existing JHK data obtained from 2MASS. Selection of possible members is aided by the proper motion study of Krone-Martins (2010).

  17. 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

  18. Open University and Distance Education Coordination: Strategies Used to Consolidate Distance Education at the National Autonomous University of Mexico

    ERIC Educational Resources Information Center

    Berruecos, Citlalli

    2004-01-01

    This case study describes three main strategies used from March 2002 to November 2003 at the Open University and Distance Education Coordination (CUAED) of the National Autonomous University of Mexico (UNAM) to consolidate distance education at the University. The author explains how, in just 18 months, these three main strategies enabled the UNAM…

  19. The San Pedro Mártir Open Cluster Survey: Progress, Techniques, Preliminary Results

    NASA Astrophysics Data System (ADS)

    Schuster, W.; Michel, R.; Dias, W.; Tapia-Peralta, T.; Vázquez, R.; Macfarland, J.; Chavarría, C.; Santos, C.; Moitinho, A.

    2007-05-01

    A CCD UBVRI survey of northern open clusters is being undertaken at San Pedro Mártir, Mexico, and performed using always the same instrumental setup (telescope, CCD, filters), reduction methods, and system of standards (Landolt). To date more than 300 clusters (mostly unstudied previously) have been observed, and about half the data reduced using aperture-photometry and PSF techniques. Our analysis procedures are being refined by studying in detail a small subset of these clusters. For example, the heavily reddened clusters Be80 and Be95 are being examined in the color-color diagrams: (B-V,U-B) and (B-V,R-I) to better understand the problems of curvature and variable reddening. For clusters for which our U data reaches the F-type stars, such as NGC2192 and NGC7296, techniques are being examined for estimating both the reddening E(B-V) and metallicity [Fe/H] via the use of the (U-B) excess. If the clusters also have "red clump" stars, such as NGC1798 and Do02, these procedures can be iterated between the clump and main sequence stars to establish even better the values of E(B-V) and [Fe/H]. Finally, color-magnitude diagrams, such as (B-V,V) and (V-I,V), are being employed together with the Schmidt-Kaler colors and Padova isochrones to obtain distances and ages for these clusters. A java-based computer program is being developed to help in the visualization and analysis of these photometric data. This system is capable of displaying each cluster simultaneously in different color-color and color-magnitude diagrams and has an interactive way to identify a star, or group of stars, in one diagram and to see were it falls in the other diagrams, facilitating the elimination of field stars and the apperception of cluster features. This program is capable of displaying up to 16 different diagrams for one cluster and processing up to 20 clusters at the same time. Our aims are the following: (1) a common UBVRI photometric scale for open clusters, (2) an atlas of color

  20. WIYN OPEN CLUSTER STUDY. XXXVIII. STELLAR RADIAL VELOCITIES IN THE YOUNG OPEN CLUSTER M35 (NGC 2168)

    SciTech Connect

    Geller, Aaron M.; Mathieu, Robert D.; Braden, Ella K.; Meibom, Soeren; Dolan, Christopher J.; Platais, Imants E-mail: mathieu@astro.wisc.edu E-mail: smeibom@cfa.harvard.edu E-mail: imants@pha.jhu.edu

    2010-04-15

    We present 5201 radial-velocity (RV) measurements of 1144 stars as part of an ongoing study of the young (150 Myr) open cluster M35 (NGC 2168). We have observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN 3.5 m telescope. Our stellar sample covers main-sequence stars over a magnitude range of 13.0 {<=} V {<=} 16.5 (1.6-0.8 M {sub sun}) and extends spatially to a radius of 30 arcmin (7 pc in projection at a distance of 805 pc or {approx}4 core radii). Due to its youth, M35 provides a sample of late-type stars with a range of rotation periods. Therefore, we analyze the RV measurement precision as a function of the projected rotational velocity. For narrow-lined stars (vsin i{<=} 10 km s{sup -1}), the RVs have a precision of 0.5 km s{sup -1}, which degrades to 1.0 km s{sup -1} for stars with vsin i = 50 km s{sup -1}. The RV distribution shows a well-defined cluster peak with a central velocity of -8.16 {+-} 0.05 km s{sup -1}, permitting a clean separation of the cluster and field stars. For stars with {>=}3 measurements, we derive RV membership probabilities and identify RV variables, finding 360 cluster members, 55 of which show significant RV variability. Using these cluster members, we construct a color-magnitude diagram for our stellar sample cleaned of field star contamination. We also compare the spatial distribution of the single and binary cluster members, finding no evidence for mass segregation in our stellar sample. Accounting for measurement precision, we place an upper limit on the RV dispersion of the cluster of 0.81 {+-} 0.08 km s{sup -1}. After correction for undetected binaries, we derive a true RV dispersion of 0.65 {+-} 0.10 km s{sup -1}.

  1. 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.

  2. 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.

  3. 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).

  4. 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…

  5. Ranked Adjusted Rand: integrating distance and partition information in a measure of clustering agreement

    PubMed Central

    Pinto, Francisco R; Carriço, João A; Ramirez, Mário; Almeida, Jonas S

    2007-01-01

    Background Biological information is commonly used to cluster or classify entities of interest such as genes, conditions, species or samples. However, different sources of data can be used to classify the same set of entities and methods allowing the comparison of the performance of two data sources or the determination of how well a given classification agrees with another are frequently needed, especially in the absence of a universally accepted "gold standard" classification. Results Here, we describe a novel measure – the Ranked Adjusted Rand (RAR) index. RAR differs from existing methods by evaluating the extent of agreement between any two groupings, taking into account the intercluster distances. This characteristic is relevant to evaluate cases of pairs of entities grouped in the same cluster by one method and separated by another. The latter method may assign them to close neighbour clusters or, on the contrary, to clusters that are far apart from each other. RAR is applicable even when intercluster distance information is absent for both or one of the groupings. In the first case, RAR is equal to its predecessor, Adjusted Rand (HA) index. Artificially designed clusterings were used to demonstrate situations in which only RAR was able to detect differences in the grouping patterns. A study with larger simulated clusterings ensured that in realistic conditions, RAR is effectively integrating distance and partition information. The new method was applied to biological examples to compare 1) two microbial typing methods, 2) two gene regulatory network distances and 3) microarray gene expression data with pathway information. In the first application, one of the methods does not provide intercluster distances while the other originated a hierarchical clustering. RAR proved to be more sensitive than HA in the choice of a threshold for defining clusters in the hierarchical method that maximizes agreement between the results of both methods. Conclusion RAR has

  6. An observational asteroseismic study of the pulsating B-type stars in the open cluster NGC 884

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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 asteroseismic study based on the discovery of numerous multi-periodic and mono-periodic B-type stars in the open cluster NGC 884 (χ Persei). Our study illustrates the current status of ensemble asteroseismology of this young open cluster.

  7. Basic parameters of open star clusters DOLIDZE 14 and NGC 110 in infrared bands

    NASA Astrophysics Data System (ADS)

    Joshi, Gireesh C.; Joshi, Y. C.; Joshi, S.; Tyagi, R. K.

    2015-10-01

    The basic physical parameters of a poorly studied open cluster NGC 110 and an unstudied open cluster DOLIDZE 14 are estimated in the present study using the archival PPMXL and WISE catalogues. The radius of both the clusters are estimated by fitting the modified King's empirical model on their stellar density profiles. The other basic parameters of the clusters such as distance, reddening, and age are obtained by visual fitting of the Marigo's solar metallicity isochrone on their IR colour-magnitude diagrams (CMDs). The mean-proper motion of the clusters are estimated through the individual proper motion of probable members identified through the dynamical and statistical methods. The archival catalogues (JHKW1W2) are constructed for both the clusters by compiling the extracted data from the PPMXL and WISE catalogues. The various colour-excesses, such as E (J - H), E (H - K) and E (W1 -W2) , are estimated using the best fit theoretical isochrone on the (J - H) - H, (H - K) - H and (W1 -W2) - H CMDs, respectively. The ratios of various infrared colours of the clusters are obtained through their two-colour diagrams. We also identify the most probable members in these clusters by estimating spatial, kinematic and spatio-kinematic probabilities of stars within the cluster. A correlation between the E (H - K) and E (W1 -W2) is also established.

  8. 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…

  9. BATC 15 Band Photometry of the Open Cluster NGC 188

    NASA Astrophysics Data System (ADS)

    Wang, Jiaxin; Ma, Jun; Wu, Zhenyu; Wang, Song; Zhou, Xu

    2015-08-01

    This paper presents CCD multicolor photometry for the old open cluster NGC 188. The observations were carried out as part of the Beijing-Arizona-Taiwan-Connecticut Multicolor Sky Survey from 1995 February to 2008 March, using 15 intermediate-band filters covering 3000-10000 Å. By fitting the Padova theoretical isochrones to our data, the fundamental parameters of this cluster are derived: an age of t=7.5+/- 0.5 Gyr, a distance modulus of {(m-M)}0=11.17+/- 0.08, and a reddening of E(B-V)=0.036+/- 0.010. The radial surface density profile of NGC 188 is obtained using the star count. By fitting the King model, the structural parameters of NGC 188 are derived: a core radius of {R}c=3\\buildrel{ \\prime}\\over{.} 80, a tidal radius of {R}t=44\\buildrel{ \\prime}\\over{.} 78, and a concentration parameter of {C}0={log}({R}t/{R}c)=1.07. Fitting the mass function (MF) to a power-law function φ (m)\\propto {m}α , the slopes of the MFs for different spatial regions are derived. We find that NGC 188 presents a slope break in the MF. The break mass is {m}{break}=0.885 {M}⊙ . In the mass range above {m}{break}, the slope of the overall region is α =-0.76. The slope of the core region is α =1.09, and the slopes of the external regions are α =-0.86 and α =-2.15, respectively. In the mass range below {m}{break}, these slopes are α =0.12, α =4.91, α =1.33, and α =-1.09, respectively. The mass segregation in NGC 188 is reflected in the obvious variation of the slopes in different spatial regions of this cluster.

  10. 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

  11. 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.

  12. Photometry and Spectroscopy of Short-Period Binary Stars in Four Old Open Clusters

    NASA Astrophysics Data System (ADS)

    Blake, R. M.; Rucinski, S. M.

    2004-12-01

    We have performed a spectroscopic and photometric study of six contact binary stars in four old open clusters, M67, Praesepe, NGC 6791 and NGC 752, in order to evaluate their suitability for measuring the distance to their respective clusters. The technique being tested uses the cosine Fourier coefficients of the light curves of the binary stars, and the mass ratios obtained spectroscopically, to provide distances to the binaries. The contact binary TX Cnc was used to obtain the distance to Praesepe, which we find to be (V - MV}){o = 6.30 ± 0.08, which is in good agreement with the values of V - MV = 6.20 - 6.35 found in color-magnitude diagram (CMD) studies. Our spectroscopic study of QX And in NGC 752 provided a distance modulus of (V - MV}){o = 8.30± 0.07 for this cluster. This compares to a value of (V - MV}){o = 7.9 ± 0.1 obtained by Milone et al. (1995) using the same star, but is in good agreement with V - MV = 8.25 ± 0.10 obtained by Daniel et al. (1994) from the CMD. We obtained a distance modulus of (V - MV}){o = 12.71 ± 0.44 for V7 in NGC 6791, the oldest cluster in our survey. This agrees within ˜ 1σ the values of 13.3 ≤ (V - MV) ≤ 13.42 obtained by isochrone fitting of the cluster CMD. EV Cnc in M67 did not yield a distance to the cluster from our procedure because of faintness of the system resulting in poor spectroscopic data. The distances to the clusters as determined from the contact binaries using our procedure do not seem to give systematically smaller or larger distances as compared to CMD fitting. However, we have measured the distances to only three clusters, and only one object per cluster, and so establishing any systematic differences may require a larger survey. R. M. Blake acknowledges the support of the Natural Science and Engineering Research Council of Canada through grants to S. M. Rucinski and C. T. Bolton.

  13. 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

  14. A Swift/UVOT Study of Open Clusters

    NASA Astrophysics Data System (ADS)

    LaPorte, Samuel; Siegel, Michael

    2016-01-01

    Star clusters, due to being coeval populations of similar stars, provide a convenient snapshot of a stellar population to study and compare to theoretical models of stellar evolution. They also serve as the empirical baseline for studies of distant unresolved stellar populations. However, few studies have been performed of detailed color-magnitude diagrams (CMDs) of young open clusters in the near ultraviolet. We present a sample of 92 open clusters compiled using Swift's Ultra-Violet and Optical Telescope (UVOT). We construct CMDs and perform isochrone fitting for the most luminous clusters to determine how well the theoretical models reproduce the salient features of the CMDs. We find that the isochrones provide excellent fits to the primary color-magnitude loci, lending confidence to models of unresolved stellar populations and providing, in the future, an opportunity to use open clusters to probe the UV properties of foreground dust.

  15. NGC 2309: A Relatively Young Open Cluster Projected onto a Random Stellar Concentration

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    We have obtained CCD UBVIKC photometry down to V ~ 22.0 for the open cluster NGC 2309 and its surrounding field. Twenty three probable cluster members have been identified for the first time on the basis of sound photometric criteria. Because NGC 2309 is a relatively poor cluster projected onto a rich star field showing density fluctuations, the frequently used membership criteria based on stellar density profiles or proper motion measurements would not be enough to assess the star membership status if employed independently. We estimated a cluster radius of 7.9' and a radius at half the maximum of the cluster density profile of 1.7'. Based on the best fits of isochrones computed by the Geneva group to the cluster color-magnitude and color-color diagrams, previously shifted by the cluster reddening (E(B - V) = 0.32) and distance (d = 2.5 kpc), we derived the cluster age (250 Myr) and metallicity ([Fe/H] sime 0.0). If an 8.5 kpc distance from the Sun to the center of the Galaxy is assumed, then NGC 2309 is found to be located just in front of the Perseus spiral arm.

  16. 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.

  17. Sejong Open Cluster Survey (SOS) - III. The young open cluster NGC 1893 in the H II region W8

    NASA Astrophysics Data System (ADS)

    Lim, Beomdu; Sung, Hwankyung; Kim, Jinyoung S.; Bessell, Michael S.; Park, Byeong-Gon

    2014-09-01

    We present a UBVI and Hα photometric study of the young open cluster NGC 1893 in the H II region W8 (IC 410 or Sh 2-236). A total of 65 early-type members are selected from photometric diagrams. A mean reddening of the stars is = 0.563 ± 0.083 mag. The published photometric data in the near- and mid-infrared passbands are used to test the reddening law towards the cluster, and we confirm that the reddening law is normal (RV = 3.1). Zero-age main-sequence fitting gives a distance modulus of V0 - MV = 12.7 ± 0.2 mag, equivalent to 3.5 ± 0.3 kpc. From Hα photometry, 125 Hα emission stars and candidates are identified as pre-main-sequence (PMS). The lists of young stellar objects and X-ray sources published by previous studies allow us to select a large number of PMS members down to 1 M⊙. Isochrone fitting in the Hertzsprung-Russell diagram gives a turn-off age of 1.5 Myr and the median age of 1.9 Myr from the PMS members with a spread of ˜5 Myr. We derive the initial mass function (IMF) for stars with mass larger than 1 M⊙. The slope of the IMF (Γ = -1.3 ± 0.1) is well consistent with the Salpeter/Kroupa IMF. A total mass of the cluster appears to be in excess of 1300 M⊙. Finally, we estimate the mass accretion rate of 82 PMS members in the mass range of 0.6-5 M⊙.

  18. Photometry of the young open cluster Trumpler 37

    SciTech Connect

    Marschall, L.A.; Karshner, G.B.; Comins, N.F. Main, Univ., Orono )

    1990-05-01

    Photoelectric UBV observations of 120 stars in the young open cluster Trumpler 37 are presented, primarily in the magnitude range 10.0 - 13.5. An analysis of the color-magnitude diagram of the cluster yields an age of 6.7 million yr and reveals the presence of a number of possible pre-main-sequence stars in the cluster. 24 refs.

  19. 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.

  20. Bayesian Inference of Kinematics and Memberships of Open Cluster

    NASA Astrophysics Data System (ADS)

    Shao, Z. Y.; Chen, L.; Zhong, J.; Hou, J. L.

    2014-07-01

    Based on the Bayesian Inference (BI) method, the Multiple-modelling approach is improved to combine coordinative positions, proper motions (PM) and radial velocities (RV), to separate the motion of the open cluster from field stars, as well as to describe the intrinsic kinematic status of the cluster.

  1. 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 in the…

  2. The WIYN Open Cluster Study: A 15-Year Report

    NASA Astrophysics Data System (ADS)

    Mathieu, Robert D.; WOCS Collaboration

    2013-06-01

    The WIYN 3.5m telescope combines large aperture, wide field of view and superb image quality. The WIYN consortium includes investigators in numerous areas of open cluster research. The combination spawned the WIYN Open Cluster Study (WOCS) over a decade ago, with the goals of producing 1) comprehensive photometric, astrometric and spectroscopic data for new fundamental open clusters and 2) addressing key astrophysical problems with these data. The set of core WOCS open clusters spans age and metallicity. Low reddening, solar proximity and richness were also desirable features in selecting core open clusters. More than 50 WIYN Open Cluster Study papers have been published in refereed journals. Highlights include: deep and wide-field photometry of NGC 188, NGC 2168 (M35), and NGC 6819 (WOCS I, II, XI and LII); deep and wide-field proper-motion studies of the old open clusters NGC 188, NGC 2682 (M67) and NGC 6791 (WOCS XVII, XXXIII and XLVI); comprehensive radial-velocity surveys of NGC 188, NGC 2168 and NGC 6819 (WOCS XXXII, XXIV, and XXXVIII); metallicity and lithium abundances in NGC 2168 (WOCS V); comprehensive definition of the hard-binary populations of NGC 188 and NGC 2168 (WOCS XXII and XLVIII); rotation period distributions in NGC 1039 (M34) and NGC 2168 (WOCS XXXV, XLIII, and XLV); study of chromospheric activity in NGC 2682 (WOCS XVIII); photometric variability surveys in NGC 188 and NGC 2682 (IX and XV); new Bayesian techniques for determination of cluster parameters (WOCS XXIII); a new infrared age-diagnostic for open clusters (WOCS XL); theoretical studies of stellar rotation (WOCS XIII and XIV); sophisticated N-body simulations of NGC 188 (WOCS LI); and the discovery of a high binary frequency and white dwarf companions among NGC 188 blue stragglers. While the WIYN 3.5m telescope remains at its heart, today the WIYN Open Cluster Study collaboration extends beyond both the WIYN observatory and consortium, and continues as a vital and productive

  3. 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

  4. 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…

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

    NASA Astrophysics Data System (ADS)

    Santos-da-Costa, Simony; Busti, Vinicius C.; Holanda, Rodrigo F. L.

    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.

  6. Differentiating between distance/open education systems-parameters for comparison

    NASA Astrophysics Data System (ADS)

    Guri-Rozenblit, Sarah

    1993-07-01

    A wide range of institutions all over the world utilize various forms of distance and/or open learning. This paper suggests eight parameters for categorizing distance/open education systems: (1) target population; (2) dimensions of openness; (3) organizational structure; (4) design and development of learning materials; (5) use of advanced technology; (6) teaching/tutoring system; (7) student-support system; and (8) inter-institutional collaboration. These parameters provide criteria for comparing a broad spectrum of distance/open learning institutions, and assist in depicting the unique characteristics of each distance/open education system. The discussion is preceded by a conceptual examination of the relations and interrelations between the distance education and open learning terms.

  7. Clustering of Local Group Distances: Publication Bias or Correlated Measurements? III. The Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    de Grijs, Richard; Bono, Giuseppe

    2015-06-01

    Aiming at providing a firm mean distance estimate to the SMC, and thus to place it within the internally consistent Local Group distance framework we recently established, we compiled the current largest database of published distance estimates to the galaxy. Based on careful statistical analysis, we derive mean distance estimates to the SMC using eclipsing binary systems, variable stars, stellar population tracers, and star cluster properties. Their weighted mean leads to a final recommendation for the mean SMC distance of (m-M)0SMC=18.96+/- 0.02 mag, where the uncertainty represents the formal error. Systematic effects related to lingering uncertainties in extinction corrections, our physical understanding of the stellar tracers used, and the SMC's complex geometry—including its significant line of sight depth, its irregular appearance which renders definition of the galaxy's center uncertain, as well as its high inclination and possibly warped disk—may contribute additional uncertainties possibly exceeding 0.15-0.20 mag.

  8. 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…

  9. X-ray sources in Galactic old Open Star Clusters

    NASA Astrophysics Data System (ADS)

    van den Berg, M.

    2013-01-01

    I review the current status of studies of the X-ray sources in Galactic old open clusters. Cataclysmic variables (CVs), magnetically-active binaries (ABs), and sub-subgiants (SSGs) dominate the X-ray emission of old open clusters. Surprisingly, the number of ABs detected inside the half-mass radius with LX ≥ 1 × 1030 erg s-1 (0.3-7 keV) does not appear to scale with cluster mass. Comparison of the numbers of CVs, ABs, and SSGs per unit mass in old open and globular clusters shows that each of these classes is under-abundant in globulars. This suggests that dense environments suppress the frequency of even some of the hardest binaries.

  10. 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.

  11. 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.

  12. 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,…

  13. 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…

  14. 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 the…

  15. 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 and Research"…

  16. 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…

  17. Distributed Open and Distance Learning: How Does E-Learning Fit? LSDA Reports.

    ERIC Educational Resources Information Center

    Fletcher, Mick

    The distinctions between types of open and distance learning broadly equate to the concept of learning at a time, place, and pace that best suits the learner. Distance learning refers to geography, whereas open learning refers to time. Flexible learning is a generic term referring either to geography or time. Combining these distinctions allows…

  18. 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…

  19. 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.

    2016-09-01

    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, multi-band photometric data sets were used to trace the cluster stellar density radial profiles and to build colour-magnitude diagrams (CMDs) and colour-colour (CC) 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 - 380M$⊙$), with higher concentration parameter values (c ˜ 0.75-1.15) and dynamically evolved ones.

  2. 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…

  3. 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…

  4. 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.

  5. 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…

  6. 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 the needs of…

  7. 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. PMID:27369507

  8. Open Cluster Neutron Capture Element Abundances and Milky Way Disk Evolution

    NASA Astrophysics Data System (ADS)

    Jacobson, Heather R.; Friel, E. D.

    2012-01-01

    Open clusters, whose ages and distances can be precisely determined, are useful probes of the chemical evolution of the Milky Way disk. The sample sizes of clusters subject to homogeneous analysis of high resolution spectra have grown in recent years, and increased attention has turned to measuring the abundances of neutron capture elements. The relative abundances of r-process elements (e.g., europium) to s-process elements (e.g., barium, lanthanum and zirconium) in cluster stars reveal the relative contributions of Type II supernovae and low-mass AGB stars to the chemical evolution of the galactic disk. A recent study of cluster s-process element abundances has revealed a surprising trend of increasing s-process element abundance ([s/Fe]) with decreasing cluster age, at odds with current s-process yield predictions (D'Orazi et al. 2009, Maiorca et al. 2011). We have undertaken an analysis of Zr, Ba, La, and Eu abundances in 17 open clusters based on high resolution optical spectra. The sample spans 700 Myr to 10 Gyr in age and Rgc 7-22 kpc in galactocentric distance, allowing for the exploration of neutron capture [x/Fe] ratios as a function of age and location in the disk. Preliminary results confirm the trend of enhanced [s/Fe] with decreasing cluster age found by other studies, though with a weaker correlation. Here we present the latest results of this analysis, including newly-determined abundances for the r-process element Eu for an expanded cluster sample that includes outer disk objects. This research is supported by a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship to HRJ under award AST-0901919.

  9. Primordial binary populations in low-density star clusters as seen by Chandra: globular clusters versus old open clusters

    NASA Astrophysics Data System (ADS)

    van den Berg, Maureen C.

    2015-08-01

    The binaries in the core of a star cluster are the energy source that prevents the cluster from experiencing core collapse. To model the dynamical evolution of a cluster, it is important to have constraints on the primordial binary content. X-ray observations of old star clusters are very efficient in detecting the close interacting binaries among the cluster members. The X-ray sources in star clusters are a mix of binaries that were dynamically formed and primordial binaries. In massive, dense star clusters, dynamical encounters play an important role in shaping the properties and numbers of the binaries. In contrast, in the low-density clusters the impact of dynamical encounters is presumed to be very small, and the close binaries detected in X-rays represent a primordial population. The lowest density globular clusters have current masses and central densities similar to those of the oldest open clusters in our Milky Way. I will discuss the results of studies with the Chandra X-ray Observatory that have nevertheless revealed a clear dichotomy: far fewer (if any at all) X-ray sources are detected in the central regions of the low-density globular clusters compared to the number of secure cluster members that have been detected in old open clusters (above a limiting X-ray luminosity of typically 4e30 erg/s). The low stellar encounter rates imply that dynamical destruction of binaries can be ignored at present, therefore an explanation must be sought elsewhere. I will discuss several factors that can shed light on the implied differences between the primordial close binary populations in the two types of star clusters.

  10. Testing the gas mass density profile of galaxy clusters with distance duality relation

    NASA Astrophysics Data System (ADS)

    Cao, Shuo; Biesiada, Marek; Zheng, Xiaogang; Zhu, Zong-Hong

    2016-03-01

    In this paper, assuming the validity of distance duality relation, η = DL(z)(1 + z)-2/DA(z) = 1, where DA(z) and DL(z) are the angular and the luminosity distance, respectively, we explore two kinds of gas mass density profiles of clusters: the isothermal β model and the non-isothermal double-β model. In our analysis, performed on 38 massive galaxy clusters observed by Chandra (within the redshift range of 0.14 < z < 0.89), we use two types of cluster gas mass fraction data corresponding to different mass density profiles fitted to the X-ray data. Using two general parameterizations of η(z) (phenomenologically allowing for distance duality violation), we find that the non-isothermal double-β model agrees better with the distance duality relation, while the isothermal β model tends to be marginally incompatible with the Etherington theorem at 68.3 per cent confidence level (CL). However, current accuracy of the data does not allow to distinguish between the two models for the gas-density distribution at a significant level.

  11. Properties of the Old Open Cluster Czernik 30

    NASA Astrophysics Data System (ADS)

    Hayes, Christian R.; Friel, Eileen D.; Slack, Taleah J.; Boberg, Owen M.

    2015-12-01

    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-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)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 Rgc ˜ 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.

  12. Radial velocity membership for the open cluster IC4756

    NASA Astrophysics Data System (ADS)

    Weingrill, Joerg; Geller, Aaron; Strassmeier, Klaus; Barnes, Sydney; Meibom, Soeren; Granzer, Thomas; Spada, Federico

    2013-08-01

    IC 4756 is an ~800 Myr-old nearby (500 pc) open cluster that conveniently splits the difference in age between the well-studied Hyades (625 Myr) and NGC 6811 (1 Gyr) clusters. As a result, measuring IC 4756 rotation periods offers us the chance to test the universality of the intermediate-age rotational evolution of stars independent of any theoretical models. Therefore we have performed precision time-series photometry of the IC 4756 field with the CoRoT satellite, and derived 111 main sequence rotation periods in the cluster region. We have also acquired new multicolor Stromgren photometry of the cluster. However, heavy differential reddening and imprecise membership information do not yet allow a satisfactory determination of the cluster parameters and membership, far less interpretation of the rotation periods. We propose here to use WIYN+Hydra to securely identify the cluster members, determine the cluster parameters, and to fully interpret the corresponding color-period diagram. This work will provide a new benchmark open cluster for the community, and help to develop the associated study of stellar rotation and gyrochronology.

  13. The old, massive, metal rich open cluster NGC 6791

    NASA Astrophysics Data System (ADS)

    Carraro, Giovanni

    2015-08-01

    NGC~6791 is a rich open cluster that attracted a lot of attention in the last decade. Recent estimates indicate that the mass is even larger, around 5000\\,$\\mathrm{M}_{\\odot}$. This is quite remarkable: the cluster is in fact 8\\,Gyr old, while the typical dissolution time for Galactic open clusters is a few Myr only. This might imply that the cluster managed to survive so long either because its original mass was much larger, or because it moved along a preferential orbit. In any case, such combination of old age and large mass is unique among Galactic open clusters, especially for clusters located in the inner regions of the Galactic disk. This is not the only special property of NGC 6791. Its abundance in iron is [Fe/H] $\\sim$ +0.40. again unique among Galactic star clusters of the same age range. Significant dispersions in various elements have been detected, that are not routinely found in Galactic open clusters. The combined UV flux of the few hot HB stars makes the cluster the closest proxy of an elliptical galaxy. This surprising result might indeed indicate that NGC 6791 was massive enough at origin to experience a strong burst of star formation and a fast enrichment.This pletora of unique properties renders NGC 6791 an extremely important object to study and understand.How and where could such a stellar system have formed? Is NGC 6791 just an open cluster? Did it form close to the bulge? How could have survived in the adverse, high-density, environment of the inner Galactic disk?These are difficult questions to answer to, of course. One of the still missing key observational evidence is whether the cluster suffered from tidal interaction, that could have significantly decreased its mass. We find such evidences, and use them as an argument to support a scenario in which the cluster formed as a massive object. We also estimate, using approximate analytic description based on available $N$-body models, how much mass NGC~6791 lost, and which was its

  14. Radial velocities of three poorly studied clusters and the kinematics of open clusters

    SciTech Connect

    Hayes, Christian R.; Friel, Eileen D. E-mail: efriel@indiana.edu

    2014-04-01

    We present radial velocities for stars in the field of the open star clusters Berkeley 44, Berkeley 81, and NGC 6802 from spectra obtained using the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5 m telescope. These clusters are of intermediate age (1-3 Gyr), located within the solar Galactocentric radius, and have no previous radial velocity measurements. We find mean radial velocities of –9.6 ± 3.0 km s{sup –1}, 48.1 ± 2.0 km s{sup –1}, and 12.4 ± 2.8 km s{sup –1} for Be 44, Be 81, and NGC 6802, respectively. We present an analysis of radial velocities of 134 open clusters of a wide range of ages using data obtained in this study and the literature. Assuming the system of clusters rotates about the Galactic center with a constant velocity, we find older clusters exhibit a slower rotation and larger line-of-sight (LOS) velocity dispersion than younger clusters. The gradual decrease in rotational velocity of the cluster system with age is accompanied by a smooth increase in LOS velocity dispersion, which we interpret as the effect of heating on the open cluster system over time.

  15. 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.

  16. Using Hamming Distance as Information for SNP-Sets Clustering and Testing in Disease Association Studies

    PubMed Central

    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. PMID:26302001

  17. 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.

  18. A search for white dwarfs in the Galactic plane: the field and the open cluster population

    NASA Astrophysics Data System (ADS)

    Raddi, R.; Catalán, S.; Gänsicke, B. T.; Hermes, J. J.; Napiwotzki, R.; Koester, D.; Tremblay, P.-E.; Barentsen, G.; Farnhill, H. J.; Mohr-Smith, M.; Drew, J. E.; Groot, P. J.; Guzman-Ramirez, L.; Parker, Q. A.; Steeghs, D.; Zijlstra, A.

    2016-04-01

    We investigated the prospects for systematic searches of white dwarfs at low Galactic latitudes, using the VLT Survey Telescope H α Photometric Survey of the Galactic plane and Bulge (VPHAS+). We targeted 17 white dwarf candidates along sightlines of known open clusters, aiming to identify potential cluster members. We confirmed all the 17 white dwarf candidates from blue/optical spectroscopy, and we suggest five of them to be likely cluster members. We estimated progenitor ages and masses for the candidate cluster members, and compare our findings to those for other cluster white dwarfs. A white dwarf in NGC 3532 is the most massive known cluster member (1.13 M⊙), likely with an oxygen-neon core, for which we estimate an 8.8_{-4.3}^{+1.2} M⊙ progenitor, close to the mass-divide between white dwarf and neutron star progenitors. A cluster member in Ruprecht 131 is a magnetic white dwarf, whose progenitor mass exceeded 2-3 M⊙. We stress that wider searches, and improved cluster distances and ages derived from data of the ESA Gaia mission, will advance the understanding of the mass-loss processes for low- to intermediate-mass stars.

  19. 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. PMID:26569618

  20. 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

  1. 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.

  2. Pulsating B-type Stars in the Open Cluster NGC 884: Frequencies, Mode Identification, and Asteroseismology

    NASA Astrophysics Data System (ADS)

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

    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.

  3. 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.

  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. 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.

  6. Mass-losing red giants in open clusters

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1987-01-01

    Mass-losing stars in open clusters with main-sequence turn-offs at intermediate mass have been searched for by using the IRAS data base. The absence of many strong 60 micron sources in open clusters implies that intermediate-mass stars lose much of their mass during an intense wind phase of rather short duration. For stars of about seven solar masses, this phase, if it exists at all, lasts for not much more than 100,000 yr. For stars of about four solar masses, the intense wind phase appears to last considerably less than 10 million yr; it may well last for less than a million yr.

  7. Commentary on interstellar matter associated with 18 open clusters

    NASA Technical Reports Server (NTRS)

    Leisawitz, David

    1989-01-01

    Information supplementary to that contained in Section 4 of an article entitled, A CO Survey of Regions Around 34 Open Clusters, (Leisawitz, Bash, and Thaddeus) published in the Astrophysical Journal Supplement Series, Volume 70, Number 4, August 1989 is summarized. The information presented here, which describes the interstellar environments of young clusters and some cluster physical characteristics, comes from observations published in the astronomical literature and the author's carbon monoxide (CO) emission line survey, and may help clarify our understanding of the interaction of massive stars with the interstellar medium.

  8. 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.

  9. Application of the Direct Distance Estimation procedure to eclipsing binaries in star clusters

    NASA Astrophysics Data System (ADS)

    Milone, E. F.; Schiller, S. J.

    2013-02-01

    We alert the community to a paradigm method to calibrate a range of standard candles by means of well-calibrated photometry of eclipsing binaries in star clusters. In particular, we re-examine systems studied as part of our Binaries-in-Clusters program, and previously analyzed with earlier versions of the Wilson-Devinney light-curve modeling program. We make use of the 2010 version of this program, which incorporates a procedure to estimate the distance to an eclipsing system directly, as a system parameter, and is thus dependent on the data and analysis model alone. As such, the derived distance is accorded a standard error, independent of any additional assumptions or approximations that such analyses conventionally require.

  10. 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.

  11. 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}.

  12. 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.

  13. 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.

  14. 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…

  15. Commute time distance transformation applied to spectral imagery and its utilization in material clustering

    NASA Astrophysics Data System (ADS)

    Albano, James A.; Messinger, David W.; Rotman, Stanley R.

    2012-07-01

    Spectral image analysis problems often begin by applying a transformation that generates an alternative representation of the spectral data with the intention of exposing hidden features not discernable in the original space. We introduce and demonstrate a transformation based on a Markov-chain model of a random walk on a graph via application to spectral image clustering. The random walk is quantified by a measure known as the average commute time distance (CTD), which is the average length that a random walker takes, when starting at one node, to transition to another and return to the starting node. This distance metric has the important characteristic of increasing when the number of paths between two nodes decreases and/or the lengths of those paths increase. Once a similarity graph is built on the spectral data, a transformation based on an eigendecomposition of the graph Laplacian matrix is applied that embeds the nodes of the graph into a Euclidean space with the separation between nodes equal to the square-root of the average commute time distance. This is referred to as the Commute Time Distance transformation. As an example of the utility of this data transformation, results are shown for standard clustering algorithms applied to hyperspectral data sets.

  16. A search for open cluster Cepheids in the Galactic plane

    NASA Astrophysics Data System (ADS)

    Chen, Xiaodian; de Grijs, Richard; Deng, Licai

    2015-01-01

    We analyse all potential combinations of Galactic Cepheids and open clusters (OCs) in the most up-to-date catalogues available. Isochrone fitting and proper-motion calculation are applied to all potential OC-Cepheid combinations. Five selection criteria are used to select possible OC Cepheids: (i) the Cepheid of interest must be located within 60 arcmin of the OC's centre; (ii) the Cepheid's proper motion is located within the 1σ distribution of that of its host OC; (iii) the Cepheid is located in the instability strip of its postulated host OC; (iv) the Cepheid and OC distance moduli should differ by less than 1 mag; and (v) the Cepheid and OC ages (and, where available, their metallicities) should be comparable: Δlog (t yr-1) < 0.3. 19 possible OC Cepheids are found based on our near-infrared (NIR) analysis; eight additional OC-Cepheid associations may be genuine pairs for which we lack NIR data. Six of the Cepheids analysed at NIR wavelengths are new, high-probability OC Cepheids, since they lie on the NIR period (P)-luminosity relation (PLR). These objects include TY Sct and CN Sct in Dolidze 34, XX Sgr in Dolidze 52, CK Sct in NGC 6683, VY Car in ASCC 61 and U Car in Feinstein 1. Two additional new OC Cepheids lack NIR data: V0520 Cyg in NGC 6991 and CS Mon in Juchert 18. The NIR PLR for our confirmed sample of OC Cepheids is MJ = (-3.12 ± 0.29)log (Pd-1) - (2.17 ± 0.29) mag, which is in good agreement with the best NIR PLR available for all Galactic Cepheids.

  17. 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.

  18. Stellar open clusters' membership probabilities: an N-dimensional geometrical approach

    NASA Astrophysics Data System (ADS)

    Sampedro, Laura; Alfaro, Emilio J.

    2016-04-01

    We present a new geometrical method aimed at determining the members of open clusters. The methodology estimates, in an N-dimensional space, the membership probabilities by means of the distances between every star and the cluster central overdensity. It can handle different sets of variables, which have to satisfy the simple condition of being more densely distributed for the cluster members than for the field stars (as positions, proper motions, radial velocities and/or parallaxes are). Unlike other existing techniques, this fact makes the method more flexible and so can be easily applied to different data sets. To quantify how the method identifies the cluster members, we design series of realistic simulations recreating sky regions in both position and proper motion subspaces populated by clusters and field stars. The results, using different simulated data sets (N = 1, 2 and 4 variables), show that the method properly recovers a very high fraction of simulated cluster members, with a low number of misclassified stars. To compare the goodness of our methodology, we also run other existing algorithms on the same simulated data. The results show that our method has a similar or even better performance than the other techniques. We study the robustness of the new methodology from different subsamplings of the initial sample, showing a progressive deterioration of the capability of our method as the fraction of missing objects increases. Finally, we apply all the methodologies to the real cluster NGC 2682, indicating that our methodology is again in good agreement with preceding studies.

  19. VizieR Online Data Catalog: Star clusters distances and extinctions. II. (Buckner+, 2014)

    NASA Astrophysics Data System (ADS)

    Buckner, A. S. M.; Froebrich, D.

    2015-04-01

    Until now, it has been impossible to observationally measure how star cluster scaleheight evolves beyond 1Gyr as only small samples have been available. Here, we establish a novel method to determine the scaleheight of a cluster sample using modelled distributions and Kolmogorov-Smirnov tests. This allows us to determine the scaleheight with a 25% accuracy for samples of 38 clusters or more. We apply our method to investigate the temporal evolution of cluster scaleheight, using homogeneously selected sub-samples of Kharchenko et al. (MWSC, 2012, Cat. J/A+A/543/A156, 2013, J/A+A/558/A53 ), Dias et al. (DAML02, 2002A&A...389..871D, Cat. B/ocl), WEBDA, and Froebrich et al. (FSR, 2007MNRAS.374..399F, Cat. J/MNRAS/374/399). We identify a linear relationship between scaleheight and log(age/yr) of clusters, considerably different from field stars. The scaleheight increases from about 40pc at 1Myr to 75pc at 1Gyr, most likely due to internal evolution and external scattering events. After 1Gyr, there is a marked change of the behaviour, with the scaleheight linearly increasing with log(age/yr) to about 550pc at 3.5Gyr. The most likely interpretation is that the surviving clusters are only observable because they have been scattered away from the mid-plane in their past. A detailed understanding of this observational evidence can only be achieved with numerical simulations of the evolution of cluster samples in the Galactic disc. Furthermore, we find a weak trend of an age-independent increase in scaleheight with Galactocentric distance. There are no significant temporal or spatial variations of the cluster distribution zero-point. We determine the Sun's vertical displacement from the Galactic plane as Z⊙=18.5+/-1.2pc. (1 data file).

  20. WIYN Open Cluster Study. LXVI. Spectroscopic Binary Orbits in the Young Open Cluster M35 (NGC 2168)

    NASA Astrophysics Data System (ADS)

    Leiner, E. M.; Mathieu, R. D.; Gosnell, N. M.; Geller, A. M.

    2015-07-01

    The young (150 Myr) open cluster M35 (NGC 2168) has been one of the core clusters of the WIYN Open Cluster Study since 1997. Over these 17 years we have obtained approximately 8000 radial-velocity (RV) measurements of stars in the M35 field, which we provide here. Our target sample consists of 1355 photometrically selected stars in the field of M35 within the main sequence and binary sequence of the cluster and within 13≤slant V≤slant 16.5 and (B-V)≥slant 0.6. Using our RV measurements we cleanly separate likely cluster members from field stars. We calculate RV membership probabilities for over 1200 stars in our sample. 418 are probable cluster members, of which 64 are velocity-variable (binary) systems. Here we present 52 orbital solutions for binary members of M35. This sample defines the hard binary population of M35 that dynamically powers the cluster. We also present XMM-Newton X-ray detections within the cluster. We use our large binary sample to search for interacting binaries among the X-ray sources, investigate M35's period-eccentricity distribution, and determine binary frequency. We find a circularization period of 9.9 ± 1.2 days and a binary frequency of 24% ± 3% for main-sequence binaries with P\\lt {10}4 days. Determining these properties in a young cluster like M35 is key to defining the initial conditions used in models of cluster dynamical evolution.

  1. The Blue Stragglers of the Old Open Cluster NGC 188

    NASA Astrophysics Data System (ADS)

    Mathieu, Robert D.; Geller, Aaron M.

    The old (7 Gyr) open cluster NGC 188 has yielded a wealth of astrophysical insight into its rich blue straggler population. Specifically, the NGC 188 blue stragglers are characterised by: A binary frequency of 80 % for orbital periods less than 104 days;

  2. 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…

  3. 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.

  4. Distance Learning: From Correspondence Institute to Open University via Distance Education Centre.

    ERIC Educational Resources Information Center

    Singh, Abhimanyu

    Asserting that the traditional system of higher education is not capable of meeting the ever-increasing demands of a developing country such as India, this paper suggests possible alternative methods of higher education. In addition to in-depth descriptions of the United Kingdom's Open University at Walton Hall, Milton Keynes, and the Regional…

  5. 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.

  6. 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.

  7. ELEMENTAL ABUNDANCE RATIOS IN STARS OF THE OUTER GALACTIC DISK. IV. A NEW SAMPLE OF OPEN CLUSTERS

    SciTech Connect

    Yong, David; Carney, Bruce W.; Friel, Eileen D. E-mail: bruce@physics.unc.edu

    2012-10-01

    We present radial velocities and chemical abundances for nine stars in the old, distant open clusters Be18, Be21, Be22, Be32, and PWM4. For Be18 and PWM4, these are the first chemical abundance measurements. Combining our data with literature results produces a compilation of some 68 chemical abundance measurements in 49 unique clusters. For this combined sample, we study the chemical abundances of open clusters as a function of distance, age, and metallicity. We confirm that the metallicity gradient in the outer disk is flatter than the gradient in the vicinity of the solar neighborhood. We also confirm that the open clusters in the outer disk are metal-poor with enhancements in the ratios [{alpha}/Fe] and perhaps [Eu/Fe]. All elements show negligible or small trends between [X/Fe] and distance (<0.02 dex kpc{sup -1}), but for some elements, there is a hint that the local (R{sub GC} < 13 kpc) and distant (R{sub GC} > 13 kpc) samples may have different trends with distance. There is no evidence for significant abundance trends versus age (<0.04 dex Gyr{sup -1}). We measure the linear relation between [X/Fe] and metallicity, [Fe/H], and find that the scatter about the mean trend is comparable to the measurement uncertainties. Comparison with solar neighborhood field giants shows that the open clusters share similar abundance ratios [X/Fe] at a given metallicity. While the flattening of the metallicity gradient and enhanced [{alpha}/Fe] ratios in the outer disk suggest a chemical enrichment history different from that of the solar neighborhood, we echo the sentiments expressed by Friel et al. that definitive conclusions await homogeneous analyses of larger samples of stars in larger numbers of clusters. Arguably, our understanding of the evolution of the outer disk from open clusters is currently limited by systematic abundance differences between various studies.

  8. Map-based trigonometric parallaxes of open clusters - The Pleiades

    NASA Technical Reports Server (NTRS)

    Gatewood, George; Castelaz, Michael; Han, Inwoo; Persinger, Timothy; Stein, John

    1990-01-01

    The multichannel astrometric photometer and Thaw refractor of the University of Pittsburgh's Allegheny Observatory have been used to determine the trigonometric parallax of the Pleiades star cluster. The distance determined, 150 with a standard error of 18 parsecs, places the cluster slightly farther away than generally accepted. This suggests that the basis of many estimations of the cosmic distance scale is approximately 20 percent short. The accuracy of the determination is limited by the number and choice of reference stars. With careful attention to the selection of reference stars in several Pleiades regions, it should be possible to examine differences in the photometric and trigonometric modulus at a precision of 0.1 magnitudes.

  9. 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 aim of the…

  10. 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…

  11. The Quality and Reputation of Open, Distance and E-Learning: What Are the Challenges?

    ERIC Educational Resources Information Center

    Gaskell, Anne; Mills, Roger

    2014-01-01

    Distance education institutions, students and staff have often had to overcome negative perceptions about the overall quality of their programmes and qualifications. In this paper, we identify four of the major challenges cited as undermining the credibility and effectiveness of open, distance and e-learning (ODeL): the quality of teaching,…

  12. 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,…

  13. 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…

  14. 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…

  15. CCD Washington photometry of three highly field star contaminated open clusters in the third Galactic quadrant

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

    We present CCD photometry in the Washington system C and T1 passbands down to T1 ˜ 19.5 magnitudes in the fields of Czernik 26, Czernik 30, and Haffner 11, three poorly studied open clusters located in the third Galactic quadrant. We measured T1 magnitudes and C - T1 colors for a total of 6472 stars distributed throughout cluster areas of 13.6' × 13.6' each. Cluster radii were estimated from star counts in appropriate-sized boxes distributed throughout the entire observed fields. Based on the best fits of isochrones computed by the Padova group to the ( C - T1, T1) color-magnitude diagrams (CMDs), we derived color excesses, heliocentric distances and ages for the three clusters. These are characterized by a relatively small angular size and by a high field star contamination. We performed a firm analysis of the field star contamination of the CMDs and examined different relationships between the position in the Galaxy of known open clusters located within 1 kpc around the three studied ones, their age and their interstellar visual absorption. We confirm previous results in the sense that the closer the cluster birthplace to the Galactic plane, the higher the interstellar visual absorption. We also found that the space velocity dispersion perpendicular to the Galactic plane diminishes as the clusters are younger. The positions, interstellar visual absorptions, ages, and metallicities of the three studied clusters favor the hypothesis that they were not born in the recently discovered Canis major (CMa) dwarf galaxy before it was accreted by the Milky Way.

  16. THE SPECTRAL ENERGY DISTRIBUTIONS OF WHITE DWARFS IN 47 Tucanae: THE DISTANCE TO THE CLUSTER

    SciTech Connect

    Woodley, K. A.; Goldsbury, R.; Richer, H. B.; Heyl, J. E-mail: rgoldsb@phas.ubc.ca E-mail: heyl@phas.ubc.ca; and others

    2012-02-15

    We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs (WDs) to pure hydrogen atmosphere WD 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 arcmin{sup 2} and extend over a radial range of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Using a likelihood analysis, we obtain a best-fitting unreddened distance modulus of (m - M){sub o} = 13.36 {+-} 0.02 {+-} 0.06 corresponding to a distance of 4.69 {+-} 0.04 {+-} 0.13 kpc, where the first error is random and the second is systematic. We also search the WD photometry for infrared excess in the F160W filter, indicative of low-mass companions, and find no convincing cases within our sample.

  17. Bayesian inference of mass segregation of open clusters

    NASA Astrophysics Data System (ADS)

    Shao, Zhengyi; Chen, Li; Lin, Chien-Cheng; Zhong, Jing; Hou, Jinliang

    2015-08-01

    Based on the Bayesian inference (BI) method, the mixture-modeling approach is improved to combine all kinematic data, including the coordinative position, proper motion (PM) and radial velocity (RV), to separate the motion of the cluster from field stars in its area, as well as to describe the intrinsic kinematic status. Meanwhile, the membership probabilities of individual stars are determined as by product results. This method has been testified by simulation of toy models and it was found that the joint usage of multiple kinematic data can significantly reduce the missing rate of membership determination, say from ~15% for single data type to 1% for using all position, proper motion and radial velocity data.By combining kinematic data from multiple sources of photometric and redshift surveys, such as WIYN and APOGEE, M67 and NGC188 are revisited. Mass segregation is identified clearly for both of these two old open clusters, either in position or in PM spaces, since the Bayesian evidence (BE) of the model, which includes the segregation parameters, is much larger than that without it. The ongoing work is applying this method to the LAMOST released data which contains a large amount of RVs cover ~200 nearby open clusters. If the coming GAIA data can be used, the accuracy of tangential velocity will be largely improved and the intrinsic kinematics of open clusters can be well investigated, though they are usually less than 1 km/s.

  18. Accurate age determinations of several nearby open clusters containing magnetic Ap stars

    NASA Astrophysics Data System (ADS)

    Silaj, J.; Landstreet, J. D.

    2014-06-01

    Context. To study the time evolution of magnetic fields, chemical abundance peculiarities, and other characteristics of magnetic Ap and Bp stars during their main sequence lives, a sample of these stars in open clusters has been obtained, as such stars can be assumed to have the same ages as the clusters to which they belong. However, in exploring age determinations in the literature, we find a large dispersion among different age determinations, even for bright, nearby clusters. Aims: Our aim is to obtain ages that are as accurate as possible for the seven nearby open clusters α Per, Coma Ber, IC 2602, NGC 2232, NGC 2451A, NGC 2516, and NGC 6475, each of which contains at least one magnetic Ap or Bp star. Simultaneously, we test the current calibrations of Te and luminosity for the Ap/Bp star members, and identify clearly blue stragglers in the clusters studied. Methods: We explore the possibility that isochrone fitting in the theoretical Hertzsprung-Russell diagram (i.e. log (L/L⊙) vs. log Te), rather than in the conventional colour-magnitude diagram, can provide more precise and accurate cluster ages, with well-defined uncertainties. Results: Well-defined ages are found for all the clusters studied. For the nearby clusters studied, the derived ages are not very sensitive to the small uncertainties in distance, reddening, membership, metallicity, or choice of isochrones. Our age determinations are all within the range of previously determined values, but the associated uncertainties are considerably smaller than the spread in recent age determinations from the literature. Furthermore, examination of proper motions and HR diagrams confirms that the Ap stars identified in these clusters are members, and that the presently accepted temperature scale and bolometric corrections for Ap stars are approximately correct. We show that in these theoretical HR diagrams blue stragglers are particularly easy to identify. Conclusions: Constructing the theoretical HR diagram

  19. Stellar multiplicity of the open cluster ASCC 113

    SciTech Connect

    Guerrero, C. A.; Orlov, V. G.; Monroy-Rodríguez, M. A.; Voitsekhovich, V. V. E-mail: orlov@astro.unam.mx E-mail: voisteko@astro.unam.mx

    2014-02-01

    We present a high angular resolution survey for binary and multiple stars in the Galactic open cluster ASCC 113. Our observations were conducted on the 2.1 m telescope of the Observatorio Astronómico Nacional, Sierra San Pedro Mártir, México. Combining our results with data taken from the literature, we found a ratio of the number of single to binary stars to be 27:7 for the most probable members, so the multiplicity fraction for this cluster is 20.6% ± 3%. We also observed field stars in the vicinity of the cluster and estimated a ratio of multiplicities to be 125:27:4:1:0:0:0:1 (between one and eight companions), equivalent to a multiplicity fraction of 20.9% ± 1%. We estimated the number of undetected companions in our sample to be very small. Comparing the multiplicity frequency of the cluster with the frequency of the field, we concluded that they are statistically indistinguishable from each other. We provide a brief review on the topic of stellar multiplicity in open clusters.

  20. Stellar Multiplicity of the Open Cluster ASCC 113

    NASA Astrophysics Data System (ADS)

    Guerrero, C. A.; Orlov, V. G.; Monroy-Rodríguez, M. A.; Voitsekhovich, V. V.

    2014-02-01

    We present a high angular resolution survey for binary and multiple stars in the Galactic open cluster ASCC 113. Our observations were conducted on the 2.1 m telescope of the Observatorio Astronómico Nacional, Sierra San Pedro Mártir, México. Combining our results with data taken from the literature, we found a ratio of the number of single to binary stars to be 27:7 for the most probable members, so the multiplicity fraction for this cluster is 20.6% ± 3%. We also observed field stars in the vicinity of the cluster and estimated a ratio of multiplicities to be 125:27:4:1:0:0:0:1 (between one and eight companions), equivalent to a multiplicity fraction of 20.9% ± 1%. We estimated the number of undetected companions in our sample to be very small. Comparing the multiplicity frequency of the cluster with the frequency of the field, we concluded that they are statistically indistinguishable from each other. We provide a brief review on the topic of stellar multiplicity in open clusters.

  1. Open cluster membership probability based on K-means clustering algorithm

    NASA Astrophysics Data System (ADS)

    El Aziz, Mohamed Abd; Selim, I. M.; Essam, A.

    2016-05-01

    In the field of galaxies images, the relative coordinate positions of each star with respect to all the other stars are adapted. Therefore the membership of star cluster will be adapted by two basic criterions, one for geometric membership and other for physical (photometric) membership. So in this paper, we presented a new method for the determination of open cluster membership based on K-means clustering algorithm. This algorithm allows us to efficiently discriminate the cluster membership from the field stars. To validate the method we applied it on NGC 188 and NGC 2266, membership stars in these clusters have been obtained. The color-magnitude diagram of the membership stars is significantly clearer and shows a well-defined main sequence and a red giant branch in NGC 188, which allows us to better constrain the cluster members and estimate their physical parameters. The membership probabilities have been calculated and compared to those obtained by the other methods. The results show that the K-means clustering algorithm can effectively select probable member stars in space without any assumption about the spatial distribution of stars in cluster or field. The similarity of our results is in a good agreement with results derived by previous works.

  2. VizieR Online Data Catalog: Open clusters in Auriga OB2 (Marco+, 2016)

    NASA Astrophysics Data System (ADS)

    Marco, A.; Negueruela, I.

    2016-05-01

    We present tables with coordinates in J2000, near IR photometry and Stromgren photometry for stars in the open cluster Stock 8 and in the two new open clusters: Alicante 11 and Alicante 12 (7 data files).

  3. 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…

  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. A search for new open clusters hosting cepheids

    NASA Astrophysics Data System (ADS)

    Glushkova, E. V.; Zabolotskikh, M. V.; Rastorguev, A. S.; Grudskaya, A. V.; Koposov, S. E.

    We analyze yet-unknown genetic links between open star clusters (OSC) and galactic Cepheids and report the results of the new search for Cepheids -- probable OSC members. A sample of 25% of the stars from a new catalog by Berdnikov (published in Melnik et al. 2015) which lists 674 Cepheids with reliable parameters was investigated. Based on photometric and kinematic data, we selected 17 Cepheids that are likely to be related to star clusters, four of which being new OSCs discovered by us.

  7. Studies of Open Clusters using 50BiN

    NASA Astrophysics Data System (ADS)

    Deng, Licai; Xin, Yu; Zhang, Xiaobin; Wang, Kun; Luo, Changqing

    2015-08-01

    50BiN (50cm Binocular Network) is a sub-program of SONG, funded by Chinese participating universities. The Science goals is to do simulteneous two-color widep-field photometry of Galactic open clusters in time-domain, and to study the fundamental properties of the clusters and to search variable objects in a systematic manner. The proto-type node, located in West-China, is now in operation. The science plan of the program and some preliminary results will be presented.

  8. Characterizing the Stellar Content of the Young Open Cluster Blanco 1

    NASA Astrophysics Data System (ADS)

    King, Piera Andrea Soto; James, David

    2015-01-01

    In this work we seek to derive the age of the nearby and young open cluster Blanco 1. This solar metallicity cluster, is located far from the Galactic plane making it quite unusual and astrophysically interesting. The methods that we used to determinate the age of Blanco 1 employed color magnitude diagrams and various flavors of stellar evolution models.Initially, the data that we used are a suite of F- and G-star spectra, which were acquired using the low-resolution cassegrain spectrograph installed on the 1.9m Radcliffe telescope located at the South African Astronomical Observatory. Comparing optical photometry with spectral types, we hoped to derive reddening vectors to help us with the isochrone fitting of Blanco 1. However, magnetic activity on our target stars prevented us from completing this analysis. We instead used hot, higher-mass, early-spectral type stars in thecluster to derive its reddening vectors.To fit the distance we tried with the HIPPARCOS (209 pc) distance, that have no a good fit in the main sequence. On the other hand we found that the best fit is 240 pc by isochrones D'Antona & Mazzitelli (1997).Finally, isochrones generated from theoretical stellar models were compared to the cluster's color magnitude diagrams, allowing us to estimate the distance-dependent age of Blanco 1. We find that its photometric age is ˜150 Myr, comparable to its lithium and gyrochronology age.

  9. Chemical analysis of giant stars in the young open cluster NGC 3114

    NASA Astrophysics Data System (ADS)

    Santrich, O. J. Katime; Pereira, C. B.; Drake, N. A.

    2013-06-01

    Context. Open clusters are very useful targets for examining possible trends in galactocentric distance and age, especially when young and old open clusters are compared. Aims: We carried out a detailed spectroscopic analysis to derive the chemical composition of seven red giants in the young open cluster NGC 3114. Abundances of C, N, O, Li, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd were obtained, as well as the carbon isotopic ratio. Methods: 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. Results: We found that NGC 3114 has a mean metallicity of [Fe/H] = -0.01 ± 0.03. The isochrone fit yielded a turn-off mass of 4.2 M⊙. The [N/C] ratio is in good agreement with the models predicted by first dredge-up. We found that two stars, HD 87479 and HD 304864, have high rotational velocities of 15.0 km s-1 and 11.0 km s-1; HD 87526 is a halo star and is not a member of NGC 3114. Conclusions: The carbon and nitrogen abundance in NGC 3114 agree with the field and cluster giants. The oxygen abundance in NGC 3114 is lower compared to the field giants. The [O/Fe] ratio is similar to the giants in young clusters. We detected sodium enrichment in the analyzed cluster giants. As far as the other elements are concerned, their [X/Fe] ratios follow the same trend seen in giants with the same metallicity. Based on observations made with the 2.2 m telescope at the European Southern Observatory (La Silla, Chile).Tables 2 and 5 are available in electronic form at http://www.aanda.org

  10. 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.

  11. SOUNDING OPEN CLUSTERS: ASTEROSEISMIC CONSTRAINTS FROM KEPLER ON THE PROPERTIES OF NGC 6791 AND NGC 6819

    SciTech Connect

    Basu, Sarbani; Esch, Lisa; Grundahl, Frank; Brogaard, Karsten; Bruntt, Hans; Stello, Dennis; Bedding, Timothy R.; Huber, Daniel; Kallinger, Thomas; Hekker, Saskia; Chaplin, William J.; Elsworth, Yvonne; Mosser, Benoit; GarcIa, Rafael A.; Gai, Ning; Ballot, Jerome; Gruberbauer, Michael; Miglio, Andrea; Yildiz, Mutlu

    2011-03-01

    We present initial results on some of the properties of open clusters NGC 6791 and NGC 6819 derived from asteroseismic data obtained by NASA's Kepler mission. In addition to estimating the mass, radius, and log g of stars on the red giant branch (RGB) of these clusters, we estimate the distance to the clusters and their ages. Our model-independent estimate of the distance modulus of NGC 6791 is (m - M){sub 0} = 13.11 {+-} 0.06. We find (m - M){sub 0} = 11.85 {+-} 0.05 for NGC 6819. The average mass of stars on the RGB of NGC 6791 is 1.20 {+-} 0.01 M{sub sun}, while that of NGC 6819 is 1.68 {+-} 0.03 M{sub sun}. It should be noted that we do not have data that cover the entire RGB and the actual mass will be somewhat lower. We have determined model-dependent estimates of ages of these clusters. We find ages between 6.8 and 8.6 Gyr for NGC 6791, however, most sets of models give ages around 7 Gyr. We obtain ages between 2 and 2.4 Gyr for NGC 6819.

  12. 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.

  13. UBV Photometry of the young open cluster Berkely 87

    NASA Astrophysics Data System (ADS)

    Akinyemi, Abolaji; Eskridge, Paul B.

    2015-01-01

    We obtained UBV imaging of a field in the young open cluster Berkeley 87. From these images, we measured the brightness of ~180 stars in the cluster. Our photometry was calibrated using published photometry (Turner & Forbes 1982 PASP 94, 789) of a subset of stars in our field. The cluster is in a region of the sky with strongly varying extinction. Therefore we made a (U-B)-(B-V) color-color diagram of the field and used this to de-redden the stars on a case by case basis. We de-reddened the stars using the unreddened supergiant and main sequence colors from Astrophysical Quantities (Cox 2000).The color-magnitude diagrams of the de-reddened stars are compared to the Padova isochrones(Marigo et al 2008 A&A 482 883). The isochrones are generated for a range of ages, with solar metalicity and no α enhancement. The best fit for the isochrones was the main sequence de-reddened stars from which the age of the cluster is estimated to be 20 million years. This is older than previous age estimates (1-5 million years) from earlier studies of the cluster. This may indicate age variation in the cluster.We acknowledge the support of the Physics and Astronomy department, and the College of Science and Engineering, Minnesota State University, Mankato.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. Photometrically determined membership of the young, open cluster IC 2391

    NASA Astrophysics Data System (ADS)

    Rolleston, W. R. J.; Byrne, P. B.

    1997-12-01

    New 4-colour BV(RI)KC CCD photometry to a limiting magnitude of V ~19 is presented for 1428 objects observed towards the direction of the young, open cluster IC 2391. We observed 36 (2' X 3') fields within 17 arcmin of the nominal cluster core. By fitting the theoretical isochrones of \\cite[D'Antona & Mazzitelli (1994]{Dan94}) to a combination of colour-magnitude and colour-colour diagrams, we have identified 17 stars as probable cluster members with a further 85 stars as possible members. The brightness distribution of low-mass members is compared with the luminosity function observed for the Pleiades and we estimate that the contamination due to background giants should be small. Figure 4 is only available in electronic form via http://www.ed-phys.fr

  19. 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.

  20. 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.

  1. Peculiarities of the abundances of neutron-capture elements in Galactic open clusters

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    The properties of the relative abundances of rapid and slow neutron-capture elements are studied using a catalog containing spectroscopic abundance determinations for 14 elements produced in various nuclear-synthesis processes for 90 open clusters. The catalog also contains the positions, ages, velocities, and elements of the Galactic orbits of the clusters. The relative abundances of both r-elements (Eu) and s-elements (Y, Ba, La, and Ce) in clusters with high, elongated orbits and in field stars of the Galactic thin disk display different dependences on metallicity, age, Galactocentric distance, and the elements of the Galactic orbits, supporting the view that these objects have different natures. In young clusters, not only barium, but also the three other studied s-elements display significantly higher relative abundances than field stars of the same metallicity. The relative abundances of Eu are lower in highmetallicity clusters ([Fe/H] > -0.1) with high, elongated orbits than in field giants, on average, while the [Eu/Fe] ratios in lower-metallicity clusters are the same as those in field stars, on average, although with a large scatter. The metallicity dependence of the [O, Mg/Eu] ratios in clusters with high, elongated orbits and in field stars are substantially different. These and other described properties of the Eu abundances, together with the properties of the abundances of primary a-elements, can be understood in a natural way if clusters with high, elongated orbits with different metallicities formed as a result of interactions of two types of high-velocity clouds with the interstellar medium of the Galactic disk: low-metallicity highvelocity clouds that formed from "primordial" gas, and high-metallicity clouds with intermediate velocities that formed in "Galactic fountains."

  2. 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.

  3. Photometric study of open star clusters in II quadrant: Teutsch 1 and Riddle 4

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    We present the broad band UBVI CCD photometry in the region of two open star clusters Teutsch 1 and Riddle 4 located in the second Galactic quadrant. The optical CCD data for these clusters are obtained for the first time. Radii of the clusters are estimated as 3‧.5 for both the clusters. Using two color (U - B) versus (B - V) diagram we determined the reddening as E(B - V) = 0.40 ± 0.05 mag for Teutsch 1 and 1.10 ± 0.05 mag for Riddle 4. Using 2MASS JHK and optical data, we estimated E(J - K) = 0.24 ± 0.05 mag and E(V - K) = 1.40 ± 0.05 mag for Teutsch 1 and E(J - K) = 0.47 ± 0.06 mag and E(V - K) = 2.80 ± 0.06 mag for Riddle 4. Color-excess ratio indicates normal interstellar extinction law in the direction of both the clusters. We estimated distance as 4.3 ± 0.5 Kpc for Teutsch 1 and 2.8 ± 0.2 Kpc for Riddle 4 by comparing the color-magnitude diagram of the clusters with theoretical isochrones. The age of the clusters has been estimated as 200 ± 20 Myr for Teutsch 1 and 40 ± 10 Myr for Riddle 4 using the stellar isochrones of metallicity Z = 0.02 . The Mass function slope has been derived 1.89 ± 0.43 and 1.41 ± 0.70 for Teutsch 1 and Riddle 4 respectively. Our analysis indicates that both the clusters are dynamically relaxed. A slight bend of Galactic disc towards the southern latitude is found in the longitude range l = 130-180°.

  4. 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.

  5. Distance perception in an open water environment: Analysis of individual differences.

    PubMed

    Button, Chris; Schofield, Matthew; Croft, James

    2016-04-01

    We investigated whether distance estimation accuracy over open water is influenced by the viewing direction of the observer. Twenty-two healthy students (9 male, 13 female) made 10 distance estimates ranging between 50 and 950 m actual distance in 2 viewing conditions: (1) from shore to boat and (2) from boat to shore. There were no consistent differences in estimation accuracy between viewing directions. The group data revealed a general tendency to underestimate actual distances (74%), but there was considerable interindividual variance (mean error of 74% ± 27%, range = 31% to 145%). A multilevel regression model of estimate accuracy suggests there were three subgroups of participants. One subgroup (N = 4, 18%) were consistent underestimaters, regardless of distance, whereas another subgroup (N = 5, 23%) consistently overestimated. However, the majority (N = 13, 59%) tended to underestimate at shorter distances (less than 400 m) and then overestimate at longer distances. These findings have important implications in survival situations in open water where an individual may need to judge an estimated distance against their perceived swimming capacity in order to self-rescue. PMID:26715515

  6. 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

  7. Spectroscopic Abundances in the Open Cluster NGC 6819

    NASA Astrophysics Data System (ADS)

    Lee-Brown, Donald B.; Anthony-Twarog, Barbara J.; Deliyannis, Constantine P.; Rich, Evan; Twarog, Bruce A.

    2015-04-01

    High-dispersion spectra of 333 stars in the open cluster NGC 6819, obtained using the HYDRA spectrograph on the WIYN 3.5 m telescope, have been analyzed to determine the abundances of iron and other metals from lines in the 400 Å region surrounding the Li 6708 Å line. Our spectra, with signal-to-noise per pixel ranging from 60 to 300, span the luminosity range from the tip of the red giant branch to a point two magnitudes below the top of the cluster turnoff. We derive radial and rotational velocities for all stars, as well as [Fe/H] based on 17 iron lines, [Ca/H], [Si/H], and [Ni/H] in the 247 most probable, single members of the cluster. Input Teff estimates for model atmosphere analysis are provided by (B-V) colors merged from several sources, with individual reddening corrections applied to each star relative to a cluster mean of E(B-V) = 0.16. Extensive use is made of ROBOSPECT, an automatic equivalent width measurement program; its effectiveness on large spectroscopic samples is discussed. From the sample of likely single members, [Fe/H] = -0.03 ± 0.06, where the error describes the median absolute deviation about the sample median value, leading to internal precision for the cluster below 0.01 dex. The final uncertainty in the cluster abundance is therefore dominated by external systematics due to the temperature scale, surface gravity, and microturbulent velocity, leading to [Fe/H] = -0.02 ± 0.02 for a sub-sample restricted to main sequence and turnoff stars. This result is consistent with our recent intermediate-band photometric determination of a slightly subsolar abundance for this cluster. [Ca/Fe], [Si/Fe], and [Ni/Fe] are determined to be solar within the uncertainties. NGC 6819 has an abundance distribution typical of solar metallicity thin disk stars in the solar neighborhood. WIYN Open Cluster study LXV.

  8. 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)

  9. 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.

  10. HR Diagrams of Open Clusters: A Virtual Observational Exercise from Project CLEA

    NASA Astrophysics Data System (ADS)

    Snyder, Glenn; Marschall, L. A.; Cooper, P. R.

    2007-12-01

    Project CLEA announces a new laboratory exercise on the analysis of HR Diagrams of Open Clusters. The new software allows students to examine plots of V vs B-V for any of 14 open clusters for which high quality data has been published in the literature. (E.g., NGC 752, Alpha Persei, M45, and M67) The clusters range in distance from about 50 to 2000 pc, and in age from 2 x 106 to 4.5 x 109 years. Students can overlay theoretical isochrones and ZAMS lines to these plots using sliders on an interactive tool to determine the distance, age, and even the metallicity of the cluster. Files of magnitudes and colors can be loaded directly into the plotting program, or students can carry out their own photometry using a simulated optical telescope and photometer or a simulated CCD camera that produces FITS files. A student manual provides information on the software and alternative exercises for in-class use and independent study. This exercise is the first that utilizes CLEA's new Virtual Educational Observatory, VIREO. VIREO is a simulated multi-wavelength observatory including optical, radio, infrared, and x-ray instrumentation very large-all-sky database, and access to catalog resources on the Web. The VIREO software provides an environment under which a wide variety of astronomical exercises can be carried out, from observations of asteroids, to searches for high-redshift quasars using a multi-slit spectrograph. The website of Project CLEA is http://public.gettysburg.edu/~marschal/clea/CLEAhome.html This research was sponsored by the National Science Foundation and Gettysburg College.

  11. HR Diagrams of Open Clusters: A Virtual Observational Exercise from Project CLEA

    NASA Astrophysics Data System (ADS)

    Snyder, Glenn; Marschall, L. A.; Cooper, P. R.

    2007-05-01

    Project CLEA announces a new laboratory exercise on the analysis of HR Diagrams of Open Clusters. The new software allows students to examine plots of V vs B-V for any of 14 open clusters for which high quality data has been published in the literature. (E.g., NGC 752, Alpha Persei, M45, and M67) The clusters range in distance from about 50 to 2000 pc, and in age from 2 x 106 to 4.5 x 109 years. Students can overlay theoretical isochrones and ZAMS lines to these plots using sliders on an interactive tool to determine the distance, age, and even the metallicity of the cluster. Files of magnitudes and colors can be loaded directly into the plotting program, or students can carry out their own photometry using a simulated optical telescope and photometer or a simulated CCD camera that produces FITS files. A student manual provides information on the software and alternative exercises for in-class use and independent study. This exercise is the first that utilizes CLEA’s new Virtual Educational Observatory, VIREO. VIREO is a simulated multi-wavelength observatory including optical, radio, infrared, and x-ray instrumentation very large-all-sky database, and access to catalog resources on the Web. The VIREO software provides an environment under which a wide variety of astronomical exercises can be carried out, from observations of asteroids, to searches for high-redshift quasars using a multi-slit spectrograph. The website of Project CLEA is http://www.gettysburg.edu/ marschal/clea/CLEAhome.html This research was sponsored by the National Science Foundation and Gettysburg College.

  12. Open cluster detection in extensive sky regions using astrometric parameters

    NASA Astrophysics Data System (ADS)

    Paíz, L. G.; De Biasi, M. S.; Orellana, R. B.

    2014-10-01

    We developed a non-parametric method for identifying open clusters in large areas of the sky using stellar position and proper motions. Two binary codes were established from the analysis of the empirical probability density functions in position and proper motion, after eliminating field stars contamination. For each star, these codes provided a parameter indicating the star belongingness to spatial and proper motion overdensities. The method was tested in a region of 4°×5° where Collinder 140 and Collinder 132 are located. 1300 stars up to the magnitude R=11 were obtained from UCAC2 and its supplement UCAC2 BSS catalogue. We detected six stellar groups having spatial and proper motion overdensities. A detailed analysis revealed that three of them could be open clusters. We confirmed that one of them is Collinder 140, for which mean coordinates (mathaccent α,mathaccent δ)=(110.8°,-32.0°), a radius of about 12' and mean proper motion components (mathaccent μ_{α} cosδ,mathaccent μ_{δ})=(9,4) mas/yr were obtained, in good agreement with the literature. The other two possible clusters have members fainter than magnitude 10.0 and they are not found in the literature. Related to Collinder 132, the low density of the data used in the area did not allow to detect it.

  13. 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

  14. 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 ☉}.

  15. Global survey of star clusters in the Milky Way. III. 139 new open clusters at high Galactic latitudes.

    NASA Astrophysics Data System (ADS)

    Schmeja, S.; Kharchenko, N. V.; Piskunov, A. E.; Roeser, S.; Schilbach, E.; Froebrich, D.; Scholz, R.-D.

    We were looking for stellar density enhancements using a star count algorithm in the 2MASS point source catalogue (II/246). In total we discovered 714 density enhancements (regarded as cluster candidates). The candidates were cross-identified with known objects. Unidentified objects were passed through the standard MWSC pipeline for verification, cluster membership construction and structure, kinematic and astrophysical parameter determination. The basic stellar data were taken from the all-sky catalogue 2MAst (2MASS with Astrometry), that was extracted from the all-sky catalogues PPMXL (Roeser et al. 2010, Cat. I/317) and 2MASS (Cutri et al. 2003, Cat. II/246). We found that 359 candidates coincide with known objects, other 355 candidates are non identified, and 139 of them we classified as real star clusters and determined their basic cluster parameters. Around each confirmed object from our target list we defined a circular area with a radius of ra=r2+radd where r2 is initial estimate of cluster radius, and radd=0.3°. In these areas we selected in 2MAst only those stars with flags Rflg (the 2nd triple of the flags in 2MASS) set to 1, 2, or 3 in each band, i.e. the stars with the best quality detections in photometric and astrometric data. The 139 sky areas with confirmed clusters contain about 0.52 mln 2MAst stars with best quality detections in photometric and astrometric data. We selected most probable members and determined - with a homogeneous method/pipeline - angular sizes of the main morphological parts, heliocentric distances, colour-excesses, mean proper motions, ages, tidal parameters. This work extends MWSC project having input list of 3784 targets by 714 new candidates. We have adopted for them that MWSC numbering starts with 5001. Since the search was performed for Northern and Shouthern hemispheres separately the candidate numbering is discontinuous: the numbers 5001<=MWSC<5499 are assigned at b>18.5, and 5500<=MWSC<5999 designate candidates at b

  16. 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.

  17. 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.

  18. 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.

  19. Assembly of open clusters of colloidal dumbbells via droplet evaporation

    NASA Astrophysics Data System (ADS)

    Pham Van, Hai; Fortini, Andrea; Schmidt, Matthias

    2016-05-01

    We investigate the behavior of a mixture of asymmetric colloidal dumbbells and emulsion droplets by means of kinetic Monte Carlo simulations. The evaporation of the droplets and the competition between droplet-colloid attraction and colloid-colloid interactions lead to the formation of clusters built up of colloid aggregates with both closed and open structures. We find that stable packings and hence complex colloidal structures can be obtained by changing the relative size of the colloidal spheres and/or their interfacial tension with the droplets.

  20. 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…

  1. 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…

  2. 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)

  3. 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…

  4. 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…

  5. An Inquiry into Benefits of Reflective Practice in Open and Distance Learning

    ERIC Educational Resources Information Center

    Athar Hussain, Muhammad; Mehmood, Azhar; Sultana, Munazza

    2011-01-01

    Innovations in learning with conscious thinking result in conceptual and effective learning. New strategies and techniques of learning aim at bringing about change in behavior that might help in solving problems of the individual at local and global level. This paper inquires into benefits of Reflective Practice in Open and Distance Learning in…

  6. 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…

  7. 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…

  8. 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…

  9. 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…

  10. 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…