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Balog, Zoltan, Nick Siegler, G. H. Rieke, L. L. Kiss, James Muzerolle, R. A. Gutermuth, Cameron P. M. Bell, et al. "PROTOPLANETARY AND TRANSITIONAL DISKS IN THE OPEN STELLAR CLUSTER IC 2395." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622451.
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We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (similar to 6-10 Myr old), relatively nearby (800 pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope, covering the wavelength range from 3.6 to 24 mu m. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii from similar to 0.1 to similar to 10 au from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively, 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from similar to 1 to similar to 18 Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24 mu m excesses ([8] - [24]. 1.5) increases from (8.4. +/- 1.3)% at similar to 3 Myr to (46. +/- 5)% at similar to 10 Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend.
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Lim, Beomdu, Hwankyung Sung, Jinyoung S. Kim, Michael S. Bessell, Narae Hwang, and Byeong-Gon Park. "A CONSTRAINT ON THE FORMATION TIMESCALE OF THE YOUNG OPEN CLUSTER NGC 2264: LITHIUM ABUNDANCE OF PRE-MAIN SEQUENCE STARS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622162.
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The timescale of cluster formation is an essential parameter in order to understand the formation process of star clusters. Pre-main sequence (PMS) stars in nearby young open clusters reveal a large spread in brightness. If the spread were considered to be a result of a real spread in age, the corresponding cluster formation timescale would be about 5-20 Myr. Hence it could be interpreted that star formation in an open cluster is prolonged for up to a few tens of Myr. However, difficulties in reddening correction, observational errors, and systematic uncertainties introduced by imperfect evolutionary models for PMS stars can result in an artificial age spread. Alternatively, we can utilize Li abundance as a relative age indicator of PMS star to determine the cluster formation timescale. The optical spectra of 134 PMS stars in NGC 2264 have been obtained with MMT/Hectochelle. The equivalent widths have been measured for 86 PMS stars with a detectable Li line (3500 < T-eff [K] <= 6500). Li abundance under the condition of local thermodynamic equilibrium (LTE) was derived using the conventional curve of growth method. After correction for non-LTE effects, we find that the initial Li abundance of NGC 2264 is A(Li)= 3.2 +/- 0.2. From the distribution of the Li abundances, the underlying age spread of the visible PMS stars is estimated to be about 3-4 Myr and this, together with the presence of embedded populations in NGC 2264, suggests that the cluster formed on a timescale shorter than 5 Myr.
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Messina, Angela Elisa. "Chromospheric activity and lithium abundance in the NGC2516 and NGC3766 open clusters." Thesis, Università degli Studi di Catania, 2011. http://hdl.handle.net/10761/212.
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The aim of this thesis is the analysis of chromospheric activity and lithium abundance of late type stars in open clusters of different ages. The study of open cluster is very important for our understanding of stellar evolution and atmospheres, since all cluster members have almost the same age and chemical composition and this allows to infer their properties more
easily than individual stars. In this work two open clusters have been considered, NGC2516 and NGC3766, using spectra acquired by the ESO spectrograph FLAMES at VLT, in the LiI and CaII H and K region.
Most of our knowledge of young stars comes from the observations of general properties of open clusters, since they represents a good tool for testing the stellar evolution models, and the age measurement' methods. In fact, stellar ages can be determined only by comparison with theoretical models, and open clusters are widely used to calibrate methods of age
determination, since their observation allows to determine average properties of a group of
stars approximatly coeval.
One of the methods used to determine the age of young stars is the lithium depletion,
based on the determination of the lithium abundance of a cluster's star. This method has been used in this work to determine the age of both observed clusters. Their lithium depletion has been derived, confirming that, for the cluster NGC2516, the age is approximatly around 150Myr, as observed previously by other authors. Assuming solar metallicity for NGC3766, direct comparison of Li equivalent with other clusters indicates an age close to that of the Pleiades or even older, in disagreement with previous age determination. A metallicity higher
than solar may explain at least partially this disagreement.
Chromospheric activity in NGC2516 has also been studied using Ca II H & K lines
VLT/FLAMES-GIRAFFE observations. Since no VLT/FLAMES-GIRAFFE observations of Mt. Wilson standards are available, I applied the method of Linsky et al.,1979, ApJs,41,47, and Strassmeier et al., 2000,A&AS, 142, 275. A comparison with the standard Mt. Wilson method has been done using FEROS spectra. A study of astrophysical parameter determination using the spectral region between 3990 and 4040 A has also been performed.
This work is organised as follows: the problem of age determination in open clusters is briefly discussed in Chapter 1; Chapter 2 contains a review of chromospheric activity
indicators; Chapter 3 contains a description of the cluster studied; Chapter 4 describes the reduction of VLT/FLAMES-GIRAFFE data; Chapter 5 describes the method used to derive
stellar physical parameters. Finally, in Chapter 6 the chromospheric activity analysis for NGC2516 and the lithium abundance analysis in both NGC2516 and NGC3766 are presented.
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Da, Rio Nicola, Jonathan C. Tan, Kevin R. Covey, Michiel Cottaar, Jonathan B. Foster, Nicholas C. Cullen, John Tobin, et al. "IN-SYNC. V. Stellar Kinematics and Dynamics in the Orion A Molecular Cloud." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625776.
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The kinematics and dynamics of young stellar populations enable us to test theories of star formation. With this aim, we continue our analysis of the SDSS-III/APOGEE IN-SYNC survey, a high-resolution near-infrared spectroscopic survey of young clusters. We focus on the Orion A star-forming region, for which IN-SYNC obtained spectra of similar to 2700 stars. In Paper IV we used these data to study the young stellar population. Here we study the kinematic properties through radial velocities (vr). The young stellar population remains kinematically associated with the molecular gas, following a similar to 10 km s(-1) gradient along the filament. However, near the center of the region, the vr distribution is slightly blueshifted and asymmetric; we suggest that this population, which is older, is slightly in the foreground. We find evidence for kinematic subclustering, detecting statistically significant groupings of colocated stars with coherent motions. These are mostly in the lower-density regions of the cloud, while the ONC radial velocities are smoothly distributed, consistent with it being an older, more dynamically evolved cluster. The velocity dispersion sigma(v) varies along the filament. The ONC appears virialized, or just slightly supervirial, consistent with an old dynamical age. Here there is also some evidence for ongoing expansion, from a v(r)-extinction correlation. In the southern filament, sigma(v) is similar to 2-3 times larger than virial in the L1641N region, where we infer a superposition along the line of sight of stellar subpopulations, detached from the gas. In contrast, sv decreases toward L1641S, where the population is again in agreement with a virial state.
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Joner, Michael Deloss. "High-Quality Broadband BVRI Photometry of Benchmark Open Clusters." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2495.
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Photometric techniques are often used to observe stars and it can be demonstrated that fundamental stellar properties can be observationally determined using calibrated sets of photometric data. Many of the most powerful techniques utilized to calibrate stellar photometry employ the use of stars in clusters since the individual stars are believed to have many common properties such as age, composition, and approximate distance. Broadband photometric Johnson/Cousins BVRI observations are presented for several nearby open clusters. The new photometry has been tested for consistency relative to archival work and shown to be both accurate and precise. The careful use of a regular routine when making photometric observations, along with the monitoring of instrumental systems and the use of various quality control techniques when making observations or performing data reductions, will enhance an observer's ability to produce high-quality photometric measurements. This work contains a condensed review of the history of photometry, along with a brief description of several popular photometric systems that are often utilized in the field of stellar astrophysics. Publications written by Taylor or produced during the early Taylor and Joner collaboration are deemed especially relevant to the current work. A synopsis of seven archival publications is offered, along with a review of notable reports of VRI photometric observations for the nearby Hyades open star cluster. The body of this present work consists of four publications that appeared between the years 2005 and 2008, along with a soon to be submitted manuscript for a fifth publication. Each of these papers deals specifically with high-quality broadband photometry of open clusters with new data being presented for the Hyades, Coma, NGC 752, Praesepe, and M67. It is concluded that the VRI photometry produced during the Taylor and Joner collaborative investigations forms a high-quality data set that has been: 1) stable for a period of more than 25 years; 2) monitored and tested several times for consistency relative to the broadband Cousins system, and 3) shown to have well-understood transformations to other versions of broadband photometric systems. Further work is suggested for: 1) the transformation relationships for the reddest stars available for use as standards; 2) the standardization of more fields for use with CCD detectors; 3) a further investigation of transformations of blue color indices for observations done using CCD detectors with enhanced UV sensitivity, and 4) a continuation of work on methods to produce high-quality observations of assorted star clusters (both open and globular) with CCD-based instrumentation and intermediate-band photometric systems.
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An, Deokkeun. "Improving the Local Distance Scale from Empirically Calibrated Stellar Isochrones." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1218593380.
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Eisner, J. A., J. M. Bally, A. Ginsburg, and P. D. Sheehan. "PROTOPLANETARY DISKS IN THE ORION OMC1 REGION IMAGED WITH ALMA." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621374.
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We present ALMA observations of the Orion Nebula that cover the OMC1 outflow region. Our focus in this paper is on compact emission from protoplanetary disks. We mosaicked a field containing similar to 600 near-IR-identified young stars, around which we can search for sub-millimeter emission tracing dusty disks. Approximately 100 sources are known proplyds identified with the Hubble Space Telescope. We detect continuum emission at 1 mm wavelengths toward similar to 20% of the proplyd sample, and similar to 8% of the larger sample of near-IR objects. The noise in our maps allows 4 sigma detection of objects brighter than similar to 1.5 mJy, corresponding to protoplanetary disk masses larger than 1.5 M-J (using standard assumptions about dust opacities and gas-to-dust ratios). None of these disks are detected in contemporaneous CO(2-1) or (CO)-O-18(2-1) observations, suggesting that the gas-to-dust ratios may be substantially smaller than the canonical value of 100. Furthermore, since dust grains may already be sequestered in large bodies in Orion Nebula cluster (ONC) disks, the inferred masses of disk solids may be underestimated. Our results suggest that the distribution of disk masses in this region is compatible with the detection rate of massive planets around M dwarfs, which are the dominant stellar constituent in the ONC.
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Spitoni, Emanuele. "The effects of galactic fountains on the chemical evolution of galaxies." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3435.
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2008/2009In this thesis we study the effect of galactic fountains, namely gas and flows from the disk of galaxies produced by multiple supernova explosions, on the chemical evolution of galaxies. Sequential supernova explosions create a superbubble, whereas the swept up interstellar medium is concentrated in a supershell which can break out a stratified medium, producing bipolar outflows. The gas of the supershells can fragment into clouds which eventually fall toward the disk producing so-called galactic fountains. Many works in literature have dealt with superbubble expansion in stratified media. However, very few papers in the past have taken into account the chemical evolution of the superbubble and how the supershell get polluted from the metals produced by supernova explosions. With this thesis for the first time the effect of galactic fountains we consider in a detailed chemical evolution model for the Milky Way. In the first part of our work we study the expansion law and chemical enrichment of a supershell powered by the energetic feedback of a typical Galactic OB association at various galactocentric radii. We follow the orbits of the fragments created when the supershell breaks out and we compare their kinetic and chemical properties with the available observations of high - and intermediate - velocity clouds. We use the Kompaneets (1960) approximation for the evolution of the superbubble driven by sequential supernova explosions and we compute the abundances of oxygen and iron residing in the thin cold supershell. Due to Rayleigh-Taylor instabilities we assume that supershells are fragmented and we follow the orbit of the clouds either ballistically or by means of a hybrid model considering viscous interaction between the clouds and the extra-planar gas. We find that if the initial metallicity is solar, the pollution from the dying stars of the OB association has a negligible effect on the chemical composition of the clouds. The maximum height reached by the clouds above the plane seldom exceeds 2 kpc and when averaging over different throwing angles, the landing coordinate differs from the throwing coordinate by only 1 kpc. Therefore, it is unlikely that galactic fountains can affect abundance gradients on large scales. The range of heights and [O/Fe] ratios spanned by our clouds suggest that the high velocity clouds cannot have a Galactic origin, whereas intermediate velocity clouds have kinematic properties similar to our predicted clouds but have observed overabundances of the [O/Fe] ratios that can be reproduced only with initial metallicities which are too low compared to those of the Galaxy disk. Even if it is unlikely that galactic fountains can affect abundance gradients on large scales, they can still affect the chemical enrichment of the interstellar medium (ISM) because of the time-delay due to the non-negligible time taken by fountains to orbit around and fall back into the Galaxy. This implies a delay in the mixing of metals in ISM which conflicts with the instantaneous mixing approximation usually assumed in all models in literature. We test whether relaxing this approximation in a detailed chemical evolution model can improve or worsen the agreement with observations. To do that, we investigate two possible causes for relaxing of the instantaneous mixing: i) the ``galactic fountain time delay effect'' and ii) the ``metal cooling time delay effect''. We find that the effect of galactic fountains is negligible if an average time delay of 0.1 Gyr, as suggested by our model, is assumed. Longer time delays produce differences in the results but they are not realistic. The metal cooling time delays produce strong effects on the evolution of the chemical abundances only if we adopt stellar yields depending on metallicity. If, instead, the yields computed for the solar chemical composition are adopted, negligible effects are produced, as in the case of the galactic fountain delay. The relaxation of the IMA by means of the galactic fountain model, where the delay is considered only for massive stars and only in the disk, does not affect the chemical evolution results. The combination of metal dependent yields and time delay in the chemical enrichment from all stars starting from the halo phase, instead, produces results at variance with observations.
XXII Ciclo
1979
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Kiminki, Megan M., Nathan Smith, Megan Reiter, and John Bally. "Proper motions of five OB stars with candidate dusty bow shocks in the Carina Nebula." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/624060.
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We constrain the proper motions of five OB stars associated with candidate stellar wind bow shocks in the Carina Nebula using Hubble Space Telescope ACS imaging over 9-10 yr baselines. These proper motions allow us to directly compare each star's motion to the orientation of its candidate bow shock. Although these stars are saturated in our imaging, we assess their motion by the shifts required to minimize residuals in their airy rings. The results limit the direction of each star's motion to sectors less than 90 degrees wide. None of the five stars are moving away from the Carina Nebula's central clusters as runaway stars would be, confirming that a candidate bow shock is not necessarily indicative of a runaway star. Two of the five stars are moving tangentially relative to the orientation of their candidate bow shocks, both of which point at the OB cluster Trumpler 14. In these cases, the large-scale flow of the interstellar medium, powered by feedback from the cluster, appears to dominate over the motion of the star in producing the observed candidate bow shock. The remaining three stars all have some component of motion towards the central clusters, meaning that we cannot distinguish whether their candidate bow shocks are indicators of stellar motion, of the flow of ambient gas or of density gradients in their surroundings. In addition, these stars' lack of outward motion hints that the distributed massive-star population in Carina's South Pillars region formed in place, rather than migrating out from the association's central clusters.
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Bell, Cameron Pearce MacDonald. "A critical assessment of ages derived using pre-main-sequence isochrones in colour-magnitude diagrams." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/4017.
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In this thesis a critical assessment of the ages derived using theoretical pre-main-sequence (pre-MS) stellar evolutionary models is presented by comparing the predictions to the low-mass pre-MS population of 14 young star-forming regions (SFRs) in colour-magnitude diagrams (CMDs). Deriving pre-MS ages requires precise distances and estimates of the reddening. Therefore, the main-sequence (MS) members of the SFRs have been used to derive a self-consistent set of statistically robust ages, distances and reddenings with associated uncertainties using a maximum-likelihood fitting statistic and MS evolutionary models. A photometric method (known as the Q-method) for de-reddening individual stars in regions where the extinction is spatially variable has been updated and is presented. The effects of both the model dependency and the SFR composition on these derived parameters are also discussed. The problem of calibrating photometric observations of red pre-MS stars is examined and it is shown that using observations of MS stars to transform the data into a standard photometric system can introduce significant errors in the position of the pre-MS locus in CMD space. Hence, it is crucial that precise photometric studies (especially of pre- MS objects) be carried out in the natural photometric system of the observations. This therefore requires a robust model of the system responses for the instrument used, and thus the calculated responses for the Wide-Field Camera on the Isaac Newton Telescope are presented. These system responses have been tested using standard star observations and have been shown to be a good representation of the photometric system. A benchmark test for the pre-MS evolutionary models is performed by comparing them to a set of well-calibrated CMDs of the Pleiades in the wavelength regime 0.4−2.5 μm. The masses predicted by these models are also tested against dynamical masses using a sample of MS binaries by calculating the system magnitude in a given photometric band- pass. This analysis shows that for Teff ≤ 4000 K the models systematically overestimate the flux by a factor of 2 at 0.5 μm, though this decreases with wavelength, becoming negligible at 2.2 μm. Thus before the pre-MS models are used to derive ages, a recalibration of the models is performed by incorporating an empirical colour-Teff relation and bolometric corrections based on the Ks-band luminosity of Pleiades members, with theoretical corrections for the dependence on the surface gravity (log g). The recalibrated pre-MS model isochrones are used to derive ages from the pre-MS populations of the SFRs. These ages are then compared with the MS derivations, thus providing a powerful diagnostic tool with which to discriminate between the different pre- MS age scales that arise from a much stronger model dependency in the pre-MS regime. The revised ages assigned to each of the 14 SFRs are up to a factor two older than previous derivations, a result with wide-ranging implications, including that circumstellar discs survive longer and that the average Class II lifetime is greater than currently believed.
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Olivares, Romero Javier. "Modélisation hiérarchique bayésienne des amas stellaires jeunes." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY071/document.
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Il semble maintenant établi que la majorité des étoiles se forment dans des amas (Carpenter 2000; Porras et al. 2003; Lada & Lada 2003). Comprendre l'origine et l'évolution des populations stellaires est donc l'un des plus grands défis de l'astrophysique moderne. Malheureusement, moins d'un dixième de ces amas restent gravitationellement liés au delà de quelques centaines de millions d'années (Lada & Lada 2003). L’étude des amas stellaires doit donc se faire avant leur dissolution dans la galaxie.Le projet Dynamical Analysis of Nearby Clusters (DANCe, Bouy et al. 2013), dont le travail fait partie, fournit le cadre scientifique pour l'analyse des amas proches et jeunes (NYC) dans le voisinage solaire. Les observations de l'amas ouvert des Pléiades par le projet DANCe offrent une opportunité parfaite pour le développement d'outils statistiques visant à analyser les premières phases de l'évolution des amas.L'outil statistique développé ici est un système intelligent probabiliste qui effectue une inférence bayésienne des paramètres régissant les fonctions de densité de probabilité (PDF) de la population de l'amas (PDFCP). Il a été testé avec les données photométriques et astrométriques des Pléiades du relevé DANCe. Pour éviter la subjectivité de ces choix des priors, le système intelligent les établit en utilisant l'approche hiérarchique bayésienne (BHM). Dans ce cas, les paramètres de ces distributions, qui sont également déduits des données, proviennent d'autres distributions de manière hiérarchique.Dans ce système intelligent BHM, les vraies valeurs du PDFCP sont spécifiées par des relations stochastiques et déterministes représentatives de notre connaissance des paramètres physiques de l'amas. Pour effectuer l'inférence paramétrique, la vraisemblance (compte tenu de ces valeurs réelles), tient en compte des propriétés de l'ensemble de données, en particulier son hétéroscédasticité et des objects avec des valeurs manquantes.Le BHM obtient les PDF postérieures des paramètres dans les PDFCP, en particulier celles des distributions spatiales, de mouvements propres et de luminosité, qui sont les objectifs scientifiques finaux du projet DANCe. Dans le BHM, chaque étoile du catalogue contribue aux PDF des paramètres de l'amas proportionnellement à sa probabilité d'appartenance. Ainsi, les PDFCP sont exempts de biais d'échantillonnage résultant de sélections tronquées au-dessus d'un seuil de probabilité défini plus ou moins arbitrairement.Comme produit additionnel, le BHM fournit également les PDF de la probabilité d'appartenance à l'amas pour chaque étoile du catalogue d'entrée, qui permettent d'identifier les membres probables de l'amas, et les contaminants probables du champ. La méthode a été testée avec succès sur des ensembles de données synthétiques (avec une aire sous la courbe ROC de 0,99), ce qui a permis d'estimer un taux de contamination pour les PDFCP de seulement 5,8 %.Ces nouvelles méthodes permettent d'obtenir et/ou de confirmer des résultats importants sur les propriétés astrophysiques de l'amas des Pléiades. Tout d'abord, le BHM a découvert 200 nouveaux candidats membres, qui représentent 10% de la population totale de l'amas. Les résultats sont en excellent accord (99,6% des 100 000 objets dans l'ensemble de données) avec les résultats précédents trouvés dans la littérature, ce qui fournit une validation externe importante de la méthode. Enfin, la distribution de masse des systèmes actuelle (PDSMD) est en général en bon accord avec les résultats précédents de Bouy et al. 2015, mais présente l'avantage inestimable d'avoir des incertitudes beaucoup plus robustes que celles des méthodes précédentes.Ainsi, en améliorant la modélisation de l'ensemble de données et en éliminant les restrictions inutiles ou les hypothèses simplificatrices, le nouveau système intelligent, développé et testé dans le présent travail, représente l'état de l'art pour l'analyse statistique des populations de NYCThe origin and evolution of stellar populations is one of the greatest challenges in modern astrophysics. It is known that the majority of the stars has its origin in stellar clusters (Carpenter 2000; Porras et al. 2003; Lada & Lada 2003). However, only less than one tenth of these clusters remains bounded after the first few hundred million years (Lada & Lada 2003). Ergo, the understanding of the origin and evolution of stars demands meticulous analyses of stellar clusters in these crucial ages.The project Dynamical Analysis of Nearby Clusters (DANCe, Bouy et al. 2013), from which the present work is part of, provides the scientific framework for the analysis of Nearby Young Clusters (NYC) in the solar neighbourhood (< 500 pc). The DANCe carefully designed observations of the well known Pleiades cluster provide the perfect case study for the development and testing of statistical tools aiming at the analysis of the early phases of cluster evolution.The statistical tool developed here is a probabilistic intelligent system that performs Bayesian inference for the parameters governing the probability density functions (PDFs) of the cluster population (PDFCP). It has been benchmarked with the Pleiades photometric and astrometric data of the DANCe survey. As any Bayesian framework, it requires the setting up of priors. To avoid the subjectivity of these, the intelligent system establish them using the Bayesian Hierarchical Model (BHM) approach. In it, the parameters of prior distributions, which are also inferred from the data, are drawn from other distributions in a hierarchical way.In this BHM intelligent system, the true values of the PDFCP are specified by stochastic and deterministic relations representing the state of knowledge of the NYC. To perform the parametric inference, the likelihood of the data, given these true values, accounts for the properties of the data set, especially its heteroscedasticity and missing value objects. By properly accounting for these properties, the intelligent system: i) Increases the size of the data set, with respect to previous studies working exclusively on fully observed objects, and ii) Avoids biases associated to fully observed data sets, and restrictions to low-uncertainty objects (sigma-clipping procedures).The BHM returns the posterior PDFs of the parameters in the PDFCPs, particularly of the spatial, proper motions and luminosity distributions. In the BHM each object in the data set contributes to the PDFs of the parameters proportionally to its likelihood. Thus, the PDFCPs are free of biases resulting from typical high membership probability selections (sampling bias).As a by-product, the BHM also gives the PDFs of the cluster membership probability for each object in the data set. These PDFs together with an optimal probability classification threshold, which is obtained from synthetic data sets, allow the classification of objects into cluster and field populations. This by-product classifier shows excellent results when applied on synthetic data sets (with an area under the ROC curve of 0.99). From the analysis of synthetic data sets, the expected value of the contamination rate for the PDFCPs is 5.8 ± 0.2%.The following are the most important astrophysical results of the BHM applied tothe Pleiades cluster. First, used as a classifier, it finds ∼ 200 new candidate members, representing 10% new discoveries. Nevertheless, it shows outstanding agreement (99.6% of the 105 objects in the data set) with previous results from the literature. Second, the derived present day system mass distribution (PDSMD) is in general agreement with the previous results of Bouy et al. (2015).Thus, by better modelling the data set and eliminating unnecessary restrictions to it, the new intelligent system, developed and tested in the present work, represents the state of the art for the statistical analysis of NYC populations
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Manara, C. F., L. Testi, G. J. Herczeg, I. Pascucci, J. M. Alcalá, A. Natta, S. Antoniucci, et al. "X-shooter study of accretion in Chamaeleon I." EDP SCIENCES S A, 2017. http://hdl.handle.net/10150/625828.
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The dependence of the mass accretion rate on the stellar properties is a key constraint for star formation and disk evolution studies. Here we present a study of a sample of stars in the Chamaeleon I star-forming region carried out using spectra taken with the ESO VLT/X-shooter spectrograph. The sample is nearly complete down to stellar masses (M-star) similar to 0.1 M-circle dot for the young stars still harboring a disk in this region. We derive the stellar and accretion parameters using a self-consistent method to fit the broadband flux-calibrated medium resolution spectrum. The correlation between accretion luminosity to stellar luminosity, and of mass accretion rate to stellar mass in the logarithmic plane yields slopes of 1.9 +/- 0.1 and 2.3 +/- 0.3, respectively. These slopes and the accretion rates are consistent with previous results in various star-forming regions and with different theoretical frameworks. However, we find that a broken power-law fit, with a steeper slope for stellar luminosity lower than similar to 0.45 L-circle dot and for stellar masses lower than similar to 0.3 M-circle dot is slightly preferred according to different statistical tests, but the single power-law model is not excluded. The steeper relation for lower mass stars can be interpreted as a faster evolution in the past for accretion in disks around these objects, or as different accretion regimes in different stellar mass ranges. Finally, we find two regions on the mass accretion versus stellar mass plane that are empty of objects: one region at high mass accretion rates and low stellar masses, which is related to the steeper dependence of the two parameters we derived. The second region is located just above the observational limits imposed by chromospheric emission, at M-star similar to 0.3-0.4 M-circle dot. These are typical masses where photoevaporation is known to be effective. The mass accretion rates of this region are similar to 10(-10) M-circle dot/yr, which is compatible with the value expected for photoevaporation to rapidly dissipate the inner disk.
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Burgess, Andrew. "Exploration de la fonction de faible masse initiale dans les amas jeunes et les r ´egions de formation stellaire." Phd thesis, Université de Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00576460.
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La détermination de l'extrémité inférieure de la fonction de masse initiale (FMI) prévoit de fortes contraintes sur les théories de la formation des étoiles. IC4665 est un amas d'´étoile jeune (30Myr) et il a situe 356pc de la Terre. L'extinction est Av~ 0.59 ± 0.15 mag. WIRCam Y, J, H et K observations ont été faites par le CFHT et a comprise 10 champs (de 1.1sq.deg totale) et deux zones de contrle de 20'x20' chacun. Diagrammes couleur/magnitude et couleur/couleur ont été utilisées pour comparer les candidats sélectionnées par les modèles BT-SETTL 30 et 50Myr. Les images CH4off et CH4on ont été obtenus avec CFHT/WIRCam plus 0.11 sq.deg. dans IC348. Naines-T ont ensuite été identifiés à partir de leur couleur de 1.69μm d'absorption du méthane et trois candidats nain-T ont été trouvée avec CH4on−CH4 >0.4 mag. Extinction a été estimée à Av~ 5 − 12 mag. Les comparaisons avec les naines-T modèles, et des diagrammes couleur/couleur et magnitude, rejeter 2 entre 3 candidats en raison de leur extrême z′ − J coleur. L'objet reste n'est pas considéré comme un nain avant l'amas en raison d'un argument de densité en nombre ou l'extinction forte Av~ 12 mag, ni d'être un champ de fond nain-T qui serait devrait être beaucoup plus faible. Les modèles et les schémas de donner cet objet un type T6 préliminaires spectrale. Avec un peu de la masse de Jupiter, ce jeune candidat nain-T est potentiellement parmi les plus jeunes, des objets de masse plus faible détectée dans une région de formation d'´étoiles `a ce jour. Sa fréquence est conforme à l'extrapolation du courant lognormal FMI estime `a au domaine de masse planétaire.
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Miret, Roig Núria. "COSMIC-DANCE : A comprehensive census of nearby star forming regions." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0327.
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Comprendre comment se forment les étoiles est l’une des questions fondamentales auxquelles l’astronomie entend répondre. Malheureusement, nous ne pouvons pas étudier la formation stellaire en temps réel et différentes méthodes indirectes doivent être utilisées pour faire la lumière sur ce sujet. L’objectif principal de cette thèse est de déterminer la fonction de masse initiale, la distribution de masse des étoiles à leur naissance, dans différentes associations et régions de formation d’étoiles. La fonction de masse est le produit direct de la formation stellaire et constitue donc un paramètre d’observation fondamental pour contraindre les théories de formation stellaire et sous-estellaire. Nous nous sommes concentrés sur l’amas ouvert de 30 Ma IC 4665 et la région de formation d’étoiles de 1 - 10 Ma de Upper Scorpius (USC) et r Ophiuchi (r Oph). Nous avons combiné l’astrométrie et la photométrie de Gaia Data Release 2 avec nos observations au sol pour préparer un catalogue profond et étendu de chaque région. Ensuite, nous avons calculé les probabilités d’appartenance en utilisanttoute l’astrométrie et la photométrie disponibles et identifié les membres à haute probabilité. Nous avons utilisé la liste finale des membres pour estimer la distribution de magnitude, et les fonctions de luminosité et masse de ces associations. Alors que la première a l’avantage d’être indépendante des modèles d’évolution, tandis que les fonctions de luminosité et de masse peuvent être utilisées pour contraindre les mécanismes de formation d’étoiles. L’étude d’IC 4556 nous a permis d’identifier des objets sous-stellaires, sans pour autant pouvoir fournir un recensement complet dans ce domaine de masse. Dans USC et r Oph, nous avons identifié une population très riche d’objets sous-stellaires, significativement plus nombreux que les prédictions des modèles de formation par effondrement de coeurs moléculaires, suggérant que la formation de naines brunes et d’objets de masses planétaires isolés par des phénomènes d’éjection dans des systèmes planétaires a une contribution importante et du même ordre que l’effondrement des coeurs moléculaires à la population finale d’objets dans un amas. L’âge est un paramètre fondamental pour étudier la formation et l’évolution des étoiles pour plusieurs raisons: premièrement puisqu’il établit une échelle de temps sur laquelle placer les observations. Deuxièmement car il est essentiel pour convertir les luminosités en masses, avec l’aide de modèles d’évolution stellaire. Les incertitudes sur l’age de USC et r Oph se traduisant en erreurs importantes dans notre estimation de la fonction de masse, j’ai développé une stratégie d’étude de "l’âge dynamique" au moyen d’une analyse orbitale de traçage des mouvements des membres d’associations jeunes. J’ai ainsi mis au point une stratégie incluant i) les observations et la recherche de données dans les archives publiques, ii) la réduction et l’analyse des spectres échelles obtenus; iii) et l’analyse dynamique, pour déterminer l’âge d’une association. La méthodologie, développée avec l’association b Pictoris (b Pic), est prête à être appliquée à d’autres régions et en particulier à USC et r Oph. Les membres que nous avons identifiés sont par ailleurs d’excellentes cibles pour des études complémentaires telles que la recherche de disques (produit également fondamental de la formation stellaire), d’exoplanètes, de système multiples, mais aussi pour la caractérisation des atmosphères et propriétés physiques des naines brunes et des planètes errantes. [...]Understanding how stars form is one of the fundamental questions which astronomy aims to answer. Currently, it is well accepted that the majority of stars form in groups and that their predominant mechanism of formation is the core-collapse. However, several mechanisms have been suggested to explain the formation of substellar objects, and their contribution is still under debate. The main goal of this thesis is to determine the initial mass function, the mass distribution of stars at birth time, in different associations and star-forming regions. The mass function constitutes a fundamental observational parameter to constrain stellar and substellar formation theories since different formation mechanisms predict different fraction of stellar and substellar objects. We used the Gaia Data Release 2 catalogue together with ground-based observations from the COSMIC-DANCe project to look for high probability members via a probabilistic model of the distribution of the observable quantities in both the cluster and background populations. We applied this method to the 30 Myr open cluster IC 4665 and the 1 - 10 Myr star-forming region Upper Scorpius (USC) and r Ophiuchi (r Oph). We found very rich populations of substellar objects which largely exceed the numbers predicted by core-collapse models. In USC, where our sensitivity is best, we found a large number of free-floating planets and we suggest that ejection from planetary systems must have a similar contribution than core-collapse in their formation. The age is a fundamental parameter to study the formation and evolution of stars and is essential to accurately convert luminosities to masses. For that, we also presented a strategy to study the dynamical traceback age of young local associations through an orbital traceback analysis. We applied this method to determine the age of the b Pictoris moving group and in the future, we plan to apply it to other regions such as USC. The members we identified with the membership analysis are excellent targets for follow-up studies such as a search for discs, exoplanets, characterisation of brown dwarfs and free-floating planets. I this thesis, we presented a search for discs hosted by members of IC 4665 and we found six excellent candidates to be imaged with ALMA or the JWST. The tools we developed, are ready to be used in other regions such as USC and r Oph, where we expect to find a larger number of disc-host stars
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Chappelle, R. J. "Brown dwarfs in the Praesepe open cluster." Thesis, Liverpool John Moores University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431263.
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Albers, Cory David. "Hydraulics of a three obstacle cluster in open channels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq21149.pdf.
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Christensen, Kirsten Elvira. "Open-Framework Germanates : Crystallography, structures and cluster building units." Doctoral thesis, Stockholm : Department of Physical, Inorganic and Structural Chemistry, Stockholm university, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7501.
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Afonso, Mário João da Costa. "Clopencl (opencl para ambiente cluster)." Master's thesis, Instituto Politécnico de Bragança, Escola Superior de Tecnologia e Gestão, 2012. http://hdl.handle.net/10198/8066.
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Nos dias correntes, as pessoas estão cada vez mais familiarizadas com a necessidade de um aumento dos recursos computacionais. Com isto, torna-se evidente a junção de dispositivos, como CPUs e GPUs de fabricantes diferentes, com a finalidade de preencher o mesmo propósito. Este nível de heterogeneidade é trazida pela tecnologia OpenCL.
O trabalho aqui desenvolvido abrange o High-Performance Computing e o OpenCL, com o resultado do clOpenCL. O objetivo do clOpenCL é suportar o conjunto de dispositivos OpenCL num ambiente cluster. O clOpenCL foi construído sobre duas vertentes, estando estas inteiramente ligadas ao tipo de tecnologia utilizada no processo de comunicação entre a biblioteca e o daemon. A primeira vertente da API foi construída sobre a tecnologia de comunicação socket TCP/IP e a segunda foi desenvolvida sobre o Open-MX. Ambos os modelos do clOpenCL estão ligados à tecnologia de comunicação e à forma como é suportada a comunicação ao nível de programação.
No decorrer do trabalho serão apresentadas todas as caraterísticas integradas pelo clOpenCL e todos os seus recursos abrangidos. Irá também ser analisada a performance obtida para cada vertente do clOpenCL, em termos de utilização de largura de banda e com a leitura e escrita em buffers remotos.
In the current days, people are increasingly acquainted with the need for an increase computing resources. It becomes evident the combination of devices such as CPUs and GPUs from different vendors, with the task of fulfill the same purpose. This level of heterogeneity, is brought by OpenCL technology.
This work covers the High-Performance Computing and OpenCL, with the result of clOpenCL. The main goal of clOpenCL is to support a set of OpenCL devices in a cluster environment. The clOpenCL was built in two branches, fully connected with the type of technology used in the comunication process, between the library and the daemon.
The first version of the API was built on socket TCP/IP communication technology, and the second one was developed on the Open-MX tecnology. Both clOpenCL models are connected to the communication technology and the way that communication is supported at programming level.
Throughout this work, we will present all the clOpenCL integrated features and all its covered resources. We will also analyze the performance obtained for each side of clOpenCL in terms of bandwidth usage, through the reading and writing of remote buffers.
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Paolucci, Cristian. "Prototyping a scalable Aggregate Computing cluster with open-source solutions." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15716/.
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L'Internet of Things è un concetto che è stato ora adottato in modo pervasivo per descrivere un vasto insieme di dispositivi connessi attraverso Internet. Comunemente, i sistemi IoT vengono creati con un approccio bottom-up e si concentrano principalmente sul singolo dispositivo, il quale è visto come la basilare unità programmabile. Da questo metodo può emergere un comportamento comune trovato in molti sistemi esistenti che deriva dall'interazione di singoli dispositivi. Tuttavia, questo crea un'applicazione distribuita spesso dove i componenti sono strettamente legati tra di loro. Quando tali applicazioni crescono in complessità, tendono a soffrire di problemi di progettazione, mancanza di modularità e riusabilità, difficoltà di implementazione e problemi di test e manutenzione.
L'Aggregate Programming fornisce un approccio top-down a questi sistemi, in cui l'unità di calcolo di base è un'aggregazione anziché un singolo dispositivo.
Questa tesi consiste nella progettazione e nella distribuzione di una piattaforma, basata su tecnologie open-source, per supportare l'Aggregate Computing nel cloud, in cui i dispositivi saranno in grado di scegliere dinamicamente se il calcolo si trova su se stessi o nel cloud. Anche se Aggregate Computing è intrinsecamente progettato per un calcolo distribuito, il Cloud Computing introduce un'alternativa scalabile, affidabile e altamente disponibile come strategia di esecuzione. Quest'opera descrive come sfruttare una Reactive Platform per creare un'applicazione scalabile nel cloud.
Dopo che la struttura, l'interazione e il comportamento dell'applicazione sono stati progettati, viene descritto come la distribuzione dei suoi componenti viene effettuata attraverso un approccio di containerizzazione con Kubernetes come orchestratore per gestire lo stato desiderato del sistema con una strategia di Continuous Delivery.
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van, den Brink Nemo. "Chemical abundances in main-sequence stars in open cluster M67." Thesis, Uppsala universitet, Teoretisk astrofysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-169017.
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The discovery of a solar twin in the open star cluster M67 (Önehag et al. 2011) implies a near-solar chemical composition for the cluster. This study uses high-resolution spectroscopic data of five main-sequence stars in M67 to analyze their abundance of a few key elements and compare results to the solar-twin composition and the composition of field twins (Melendez et al. 2009). The derived composition was also compared to predictions of stellar-structure models including the effects of element diffusion. (Richard, private communication). It is found that all analyzed elements are, to varying degree, less abundant in the five main sequence stars than in the solar twin. With the possible exception of iron, all derived abundances also fall clearly below the diffusion predictions.
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Simbi, Nadia, and Koukouvinou Panagiota. "Managing Open Digital Technology in the Cluster Environment : A case study of the Cluster of Forest Technology." Thesis, Umeå universitet, Institutionen för informatik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-160771.
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The role of open innovation is becoming increasingly important for organizational competitiveness, while digital technologies provide new opportunities for organizational innovativeness. Regardless of domain and industry, digital technologies have reshaped structure, business logic and organizational dynamics. In that spirit, the forestry industry moves from the traditional model to the open paradigm, embracing the significance of purposive external exploration and internal exploitation of knowledge and technologies. Although the importance of digital technologies has been highlighted by academia, their enabling role in the open innovation process is insufficiently explored. Moreover, little research showcases the systematic way to organize for open innovation in the digital world. This process towards openness creates new opportunities as well as challenges. In order to investigate these emerging challenges and opportunities for open innovation in a digital world, we conducted a qualitative exploratory case study in the Cluster of Forest Technology in northern Sweden. Our results illustrate that challenges such as trust, power asymmetries, knowledge flow and coopetitive activities need to be managed. This study contributes to the existing literature by providing a way to address these challenges, seize more opportunities and bridge the gap between open innovation and digital technologies.
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Yau, Anthony. "A parallel direct open-shell Coupled-Cluster Singles and Doubles algorithm." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006633.
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Conrad, Claudia [Verfasser], and Ralf-Dieter [Akademischer Betreuer] Scholz. "Open cluster groups and complexes / Claudia Conrad ; Betreuer: Ralf-Dieter Scholz." Potsdam : Universität Potsdam, 2015. http://d-nb.info/1218399260/34.
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Bramich, Daniel Martyn. "Transiting extra-solar planets in the field of open cluster NGC 7789." Thesis, University of St Andrews, 2005. http://hdl.handle.net/10023/12944.
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We present results from 30 nights of observations of the intermediate-age Solar-metallicity open cluster NGC 7789 with the WFC camera on the INT telescope in La Palma. From ~900 epochs, we obtained lightcurves and Sloan r' - i' colours for ~33000 stars, with ~2400 stars with better than 1% precision. We find 24 transit candidates, 14 of which we can assign a period. We rule out the transiting planet model for 21 of these candidates using various robust arguments. For 2 candidates we are unable to decide on their nature, although it seems most likely that they are eclipsing binaries as well. We have one candidate exhibiting a single eclipse for which we derive a radius of 1.81+/0.09- Three candidates remain that require follow-up observations in order to determine their nature. Monte Carlo simulations reveal that we expected to detect ~2 transiting 3d to 5d hot Jupiter planets from all the stars in our sample if 1% of stars host such a companion and that a typical hot Jupiter radius is similar to that of HD 209458b. Our failure to find good transiting hot Jupiter candidates allows us to place an upper limit on the 3d to 5d hot Jupiter fraction of 2.6% for all stars at the 1% significance level, and similar useful limits on the hot Jupiter fraction of the different star types in our sample.
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Tobin, Ryan Wesley. "Photometric variability of Sun-like stars in the old open cluster M67." [Ames, Iowa : Iowa State University], 2008.
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Thurston, Mark Robert. "X-ray and optical observations of the young open cluster NGC 2516." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366165.
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Ahlvind, Julia. "Isochrone and chemical ages of stars in the old open cluster M67." Thesis, Uppsala universitet, Observationell astrofysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-434634.
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The open cluster Messier 67 is known to have chemical composition, metallicity and age (~ 4 Gyr) close to the Sun. Therefore, it is advantageous for stellar physical studies and of stellar evolution, in particular for solar like stars within the cluster. This work considers three such stars, the formerly studied solar twin M67-1194 and two more recently suggested solar twins M67-1787 & 2018. Most solar twins show a ratio of volatile to refractory elements that systematically depart from the Sun’s. Our targets do not follow this trend as closely. Their composition is closer to the Sun and they are, therefore, exquisite targets for studies of stellar evolution within the cluster. However, their solar likeness also provides studies regarding the origin and evolution of the Solar system. The stellar ages of the solar twins are established through a chemical clock [Y/Mg] and via stellar isochrones from BaSTI. The latter age assessment of the solar twins is supplemented with the analysis of two subgiant stars M67-1442 & 1844. We approach the isochrone-based method using spectroscopically, astrometrically and photometrically derived parameters. The different ages of the stars and methods thus estimate the age of the cluster itself. The chemical ages of the stars suggest a cluster age of 4.56 ±0.44 Gyr and the isochrone-based estimates suggests a cluster age within the range 3.30-5.51 Gyr. Our results thus affirm and imply a near solar age of the cluster.
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Christie, Morgan B. "EXAMINING THE ASSOCIATIONS BETWEEN RACIAL IDENTITY AND RACIAL ATTITUDES FOR WHITE AMERICANS USING CLUSTER ANALYSIS." OpenSIUC, 2021. https://opensiuc.lib.siu.edu/dissertations/1954.
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Few researchers have examined the contributing factors to racial identity development for White Americans. In order to better understand White racial identity development, the current study was designed to use Helms’s (1990) theory of White racial identity development to examine the associations between racial attitudes and status profiles of White racial identity, with particular interest in color-blind racial attitudes (i.e., the belief that race is a non-issue in modern society) and belief in a just world (i.e., the view that the world is fair and just). To gain further insight into profiles of White racial identity, additional social attitudes were included in the analyses, including social dominance orientation and internal and external motivation to avoid prejudice, as well as demographic variables. A sample of 350 White American adults recruited from Amazon’s MTurk completed measures of racial identity, racial attitudes, social desirability, and demographic information. K means cluster analyses were conducted to create five status profiles of White identity. Among all study variables, cluster group membership was primarily defined by color-blind racial attitudes, social dominance orientation, and age. Results revealed color-blind racial attitudes were the strongest variables across all five clusters, even those in which the primary racial identity status was autonomy. Belief in a just world, on the other hand, did not appear to be a prominent factor in determining cluster membership in the current study. These results pointed to implications for both research and theory on White racial identity statuses, given that participants who were autonomous were also high in color-blind racial attitudes, which is inconsistent with current conceptualizations of the autonomy ego status. The results indicated the possibility of an ego status prior to autonomy and hold implications for identifying additional statuses of White racial identity within Helms’s (1990) model. The study results hold further implications for future research in the exploration of connections between White racial identity and multicultural counseling competence.
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Ware, Jennifer J. "Exploring associations between the nicotinic acetylcholine receptor gene cluster CHRNA5-A3-B4 and smoking-related behaviours." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/46871/.
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Tobacco use is the leading preventable cause of death worldwide. In order to address this epidemic, it is important that we have a thorough understanding of the aetiology of tobacco use and dependence. Twin and adoption studies have consistently demonstrated the importance of genetic factors in smoking behaviours. The advent of genome-wide technologies has greatly facilitated the search to determine which specific genetic factors contribute to tobacco use phenotypes. A locus within the nicotinic acetylcholine receptor gene cluster CHRNA5-A3-B4 has generated particular interest – that marked by variants rs16969968 in CHRNA5 and rs1051730 in CHRNA3. The primary aim of this thesis was to determine the role played by this locus in smoking-related behaviours, with an emphasis on phenotype refinement. A number of different approaches were utilised to address this objective, namely systematic review and meta-analysis, genetic epidemiology (including detailed phenotyping of smoking behaviour in adolescence), laboratory-based techniques, and genome-wide meta-analysis. Compelling evidence for a small, robust association was observed between the rs1051730/rs16966968 variants and daily cigarette consumption, equivalent to a per allele effect of approximately one cigarette per day. This effect was consistent across population sub-groups. Compelling evidence for an association between this locus and level of tobacco exposure was further illustrated through genome-wide meta-analysis of cotinine levels in current smokers. No association was observed between this locus and smoking initiation however, as examined in a prospectively assessed cohort using precisely defined phenotypes. An association between rs1051730/rs16969968 and smoking topography has yet to be explored. However, a full protocol was developed and piloted to investigate this. In addition, this research has also illustrated the importance of precise, objective, phenotype definition, an observation which has important implications for the fields of molecular genetics and epidemiology.
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Slack, Rebecca A. "Open space preservation in rural residential development." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-12172008-063233/.
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Szigeti, László, Szabolcs Mészáros, Verne V. Smith, Katia Cunha, Nadège Lagarde, Corinne Charbonnel, D. A. García-Hernández, et al. "12C/13C isotopic ratios in red-giant stars of the open cluster NGC 6791." OXFORD UNIV PRESS, 2018. http://hdl.handle.net/10150/627135.
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Carbon isotope ratios, along with carbon and nitrogen abundances, are derived in a sample of 11 red-giant members of one of the most metal-rich clusters in the Milky Way, NGC 6791. The selected red-giants have a mean metallicity and standard deviation of [Fe/H] = +0.39 +/- 0.06 (Cunha et al. 2015). We used high-resolution H-band spectra obtained by the SDSS-IV Apache Point Observatory Galactic Evolution Experiment. The advantage of using high-resolution spectra in the H band is that lines of CO are well represented and their line profiles are sensitive to the variation of C-12/C-13. Values of the C-12/C-13 ratio were obtained from a spectrum synthesis analysis. The derived C-12/C-13 ratios varied between 6.3 and 10.6 in NGC 6791, in agreement with the final isotopic ratios from thermohaline-induced mixing models. The ratios derived here are combined with those obtained for more metal poor red-giants from the literature to examine the correlation between C-12/C-13, mass, metallicity, and evolutionary status.
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Fernández, Ortega Carlos. "A differential spectroscopic study of a faint solar twin in the open cluster M67." Thesis, Uppsala universitet, Observationell astrofysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302601.
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A solar twin is a star with characteristics very similar to those of the Sun. This is, a Sun-like star. Earlier studies show that M67-1194 is one of the best solar twins found to date. But this star is not exactly like the Sun. There exist differences between them, in terms of chemical composition, that were defined as well. The goal of this study is to apply a new method to study the similarities of the mentioned star with the Sun. Hopefully a method that provides more precise results. The method uses difference spectra, result of subtracting the spectrum of the star from the solar spectrum, instead of the regular spectra. Then the question is: can this method cast more precise results than those obtained by Önehag et al. in 2011? The answer is that it does. The earlier study gave an uncertainty of ±0.02 dex and ours gave uncertainties between ±0.01 dex and ±0.02 dex. Nevertheless, this conclusion must be taken with caution as the study is not as conclusive as the one out carried by Önehag et al..En soltvilling är en stjärna som liknar solen väldigt mycket. Tidigare studier visar att M67-1194 är en av de bästa upptäckta soltvillingarna hittills. Men stjärnan är inte exakt som solen. Det finns skillnader mellan dem angående deras kemiska sammansättningar vilket har också visats i tidigare studier. Den här studiens syfte är att tillämpa en ny metod för att granska likheterna mellan den nämnda stjärnan och solen. En metod som förhoppningsvis ger noggrannare resultat. Metoden använder differensspektra som erhålls genom att subtrahera stjärnans spektrum från solens spektrum, i stället för att använda de vanliga spektra. Frågan är om den här nya metoden kan ge noggrannare resultat än dem som Önehag et al. fick 2011. Svaret är ja. Den tidigare studien visade en osäkerhet på ±0,02 dex medan vår gav osäkerheter mellan ±0,01 dex och ±0,02 dex. Icke desto mindre måste våra slutsatser tas försiktigt ty vår studie är inte lika säker som Önehags et al..
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Wynn, James Joshi. "Open Space Cluster Developments to Conservation Subdivisions: Standards and Management Plans Influencing Conservation Goals." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1219345472.
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Wynn, James Joshi. "Open space cluster developments to conservation subdivisions standards and managment plans influencing conservation goals /." Ohio : Ohio University, 2008. http://www.ohiolink.edu/etd/view.cgi?ohiou1219345472.
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Luque, N. E. "Cluster dynamics in the Basque region of Spain." Thesis, Coventry University, 2011. http://curve.coventry.ac.uk/open/items/4f4161ca-11db-4d70-9954-aea64f4fbaa4/1.
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Developing and retaining competitive advantage was a major concern for all companies; it fundamentally relied on being aware of the external environment and customer satisfaction. Modifications of the environment conditions and unexpected economic events could cause of a loss of the level of organisational adjustment and subsequent loss in competitiveness, only those organisations able to rapidly adjust to these dynamics would be able to remain. In some instances, companies decided to geographically co-locate seeking economies of scale and benefiting from complementarities. Literature review revealed the strong support that clusters had from Government and Local Authorities, but it also highlighted the limited practical research in the field. The aim of this research was to measure the dynamism of the cluster formed by the geographical concentration of diverse manufacturers within the Mondragon Cooperativa Group in the Basque region of Spain, and compared it to the individual dynamism of these organisations in order to have a better understanding the actual complementarities and synergies of this industrial colocation. Literature review identified dynamic capabilities as the core enablers of organisation when competing in dynamic environments; based on these capabilities, a model was formulated. This model combined with the primary data collected via questionnaire and interviews helped measure the dynamism of the individual cluster members and the cluster as whole as well as provided an insight on the complementarities and synergies of this type of alliance. The findings of the research concluded that the cluster as a whole was more dynamic than the individual members; nevertheless, the model suggested that there were considerable differences in speed among the cluster members. These differences on speed were determined by the size of the company and their performance in dimensions such as marketing, culture and management. The research also suggested that despite of the clear differences in the level of dynamism among cluster members, all companies benefited in some way from being part of the cluster; these benefits were different in nature depending on each specific members.
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Street, Rachel. "A search for extra-solar planetary transits in the field of open cluster NGC 6819." Thesis, University of St Andrews, 2002. http://hdl.handle.net/10023/12939.
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The technique of searching for extra-solar planetary transits is investigated. This technique, which relies on detecting the brief, shallow eclipses caused by planets passing across the line of sight to the primary star, requires high-precision time-series photometry of large numbers of stars in order to detect these statistically rare events. Observations of ~ 18000 stars in the field including the intermediate-age open cluster NGC 6819 are presented. This target field contrasts with the stellar environment surveyed by the radial velocity technique, which concentrates on the Solar neighbourhood. I present the data-reduction techniques used to obtain high-precision photometry in a semi-automated fashion for tens of thousands of stars at a time, together with an algorithm designed to search the resulting lightcurves for the transit signatures of hot Jupiter type planets. I describe simulations designed to test the detection efficiency of this algorithm and, for comparison, predict the number of transits expected from this data, assuming that hot Jupiter planets similar to HD 209458 are as common in the field of NGC 6819 as they are in the Solar neighbourhood. While no planetary transits have yet been identified, the detection of several very low amplitude eclipses by stellar companions demonstrates the effectiveness of the method. This study also indicates that stellar activity and particularly blending are significant causes of false detections. A useful additional consequence of studying this time-series photometry is the census it provides of some of the variable stars in the field. I report on the discovery of a variety of newly-discovered variables, including Algol-type detached eclipsing binaries which are likely to consist of M-dwarf stars. Further study of these stars is strongly recommended in order to help constrain models of stellar structure at the very low mass end. I conclude with a summary of this work in the context of other efforts being made in this field and recommend promising avenues of further study.
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Elçi, E. "Algorithmic and geometric aspects of the random-cluster model." Thesis, Coventry University, 2015. http://curve.coventry.ac.uk/open/items/b59dab0c-fef8-4c06-b251-2f5416727431/1.
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In this thesis we investigate the geometric and algorithmic aspects of the random-cluster model, a correlated bond percolation model of great importance in the field of mathematics and statistical mechanics. We focus on the computational and statistical efficiency of the single-bond or heat-bath Markov chain for the random-cluster model and develop algorithmic techniques that allow for an improvement from a previously known polynomial to a poly-logarithmic runtime scaling of updates for general graphs. The interplay between the (critical) cluster structure of the random-cluster model and algorithmic, as well as statistical, efficiencies is considered, leading to new exact identities. A complementary analysis of certain fragility properties of the Fortuin-Kasteleyn clusters provides new insights into fragmentation phenomena, culminating in a revised scaling relation for a related fragmentation power law exponent, previously only shown for the marginal bond percolation case. By utilising the established structural results, a dynamic fragmentation process is studied that allows for an extraction of characteristics of the equilibrium cluster structure by a careful analysis of the limiting fragments, as well as the entire evolution of the fragmentation process. Besides focussing on structural and computational aspects, in this dissertation we also analyse the efficiency of the coupling from the past perfect sampling algorithm for the random-cluster model via large-scale numerical simulations. Two key results are the particular, close to optimal, efficiency in the off-critical setting and the intriguing observation of its superiority compared to the alternative Chayes-Machta-Swendsen-Wang approach in three dimensions. Governed by a random runtime, the efficiency of the coupling from the past algorithm depends crucially on the fluctuations of the runtime. In this connection a compelling appearance of universal Gumbel fluctuations in the distribution of the runtime of the coupling from the past algorithm is established, both at and off criticality. Fluctuations at a tricritical point and at a discontinuous phase transition are shown to deviate from this Gumbel law. The above findings in two and three dimensions are supported by a rigorous analysis of certain aspects of the algorithm in one dimension, including a proof of the limiting Gumbel law.
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Morrison, Heather. "Professional library & information associations should rise to the challenge of promoting open access and lead by example." Emerald, 2004. http://hdl.handle.net/2429/956.
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Reinhardt, Mirko. "Optimizing Point-to-Point Ethernet Cluster Communication." Master's thesis, Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200600257.
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This work covers the implementation of a raw Ethernet communication module
for the Open MPI message passing library. Thereby it focuses on both the reduction of the
communication latency for small messages and maximum possible compatibility.
Especially the need for particular network devices, adapted network device drivers or
kernel patches is avoided. The work is divided into three major parts: First, the
networking subsystem of the version 2.6 Linux kernel is analyzed. Second, an Ethernet
protocol family is implemented as a loadable kernel module, consisting of a basic
datagram protocol (EDP), providing connection-less and unreliable datagram transport,
and a streaming protocol (ESP), providing connection-oriented, sequenced and reliable
byte streams. The protocols use the standard device driver interface of the Linux kernel
for data transmission and reception. Their services are made available to user-space
applications through the standard socket interface. Last, the existing Open MPI TCP
communication module is ported atop the ESP. With bare EDP/ESP sockets a message
latency of about 30 us could be achieved for small messages, which compared to the
TCP latency of about 40 us is a reduction of 25 %.
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Irwin, J. M. "Observational constraints on pre-main sequence stellar evolution from time-series analysis of open cluster stars." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604961.
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Observational constraints on evolutionary models of low-mass stars (≲ 1.0 M⊙) are presently extremely scarce on the pre-main sequence. Recent observational evidence has indicated substantial discrepancies between the predictions of these models and observations made in binary star systems, where the masses can be measured dynamically. It is clear that in order to resolve these issues, a larger sample of precise measurements will be needed to anchor the theory. This work pursues two avenues to do this, using time-series photometric measurements in young open clusters (ages 1 – 200 Myr) obtained as part of the Monitor project, a large-scale survey using 2 – 4 m class telescopes. Stellar rotation periods are readily measured using photometry alone, and yet probe directly a fundamental stellar property: the angular velocity. These measurements place direct constraints on models of rotational evolution, had hence on the stellar models themselves. By examining rotation periods in six of the Monitor open clusters, I show that simple rotational evolution models can partially describe the data, with rapid rotators better-described by a model assuming rotation as a solid body, and slower rotators by a model including differential rotation between the radiative core and convective envelope in stars with masses ≳ 0.4 M⊙, but that more theoretical work is clearly needed to resolve discrepancies between the models and the data. Eclipsing binary systems provide some of the most precise and accurate determination of stellar masses and radii available, from combined analysis of radial velocity and light curves. Searching for these systems is one of the primary science goals of Monitor. Dynamical solutions are presented for four of these systems, and two found to be on the pre-main sequence are compared to the predictions of the models, finding reasonable agreement in the mass-radius plane, but that there may be significant discrepancies in the effective temperatures, as found by several other authors.
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Bubnick, Benjamin Frank. "Massive Stellar Clusters in the Disk of the Milky Way Galaxy." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288378106.
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Wilking, B. A., C. J. Lada, and E. R. Young. "IRAS Observations of the Rho Ophiuchi Infrared Cluster: Spectral Energy Distributions and Luminosity Function." Steward Observatory, The University of Arizona (Tucson, Arizona), 1988. http://hdl.handle.net/10150/623919.
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Burke, Christopher J. "Survey for transiting extrasolar planets in stellar systems stellar and planetary content of the Open Cluster NGC 1245 /." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1132168623.
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Effelsberg, Martin [Verfasser]. "Innovation durch Kooperation in einem Cluster : Eine empirische Analyse von Open Innovation in der deutschen Biotechnologie / Martin Effelsberg." Aachen : Shaker, 2013. http://d-nb.info/1051573378/34.
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David, David [Verfasser], and Bernhard [Akademischer Betreuer] Dick. "Development of local Coupled Cluster response methods for high-spin open-shell molecules / David David ; Betreuer: Bernhard Dick." Regensburg : Universitätsbibliothek Regensburg, 2020. http://d-nb.info/1204635846/34.
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Anacker, Tony. "Incremental Scheme for Open-Shell Systems." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-197726.
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In this thesis, the implementation of the incremental scheme for open-shell systems with unrestricted Hartree-Fock reference wave functions is described. The implemented scheme is tested within robustness and performance with respect to the accuracy in the energy and the computation times.
New approaches are discussed to implement a fully automated incremental scheme in combination with the domain-specific basis set approximation. The alpha Domain Partitioning and Template Equalization are presented to handle unrestricted wave functions for the local correlation treatment. Both orbital schemes are analyzed with a test set of structures and reactions. As a further goal, the DSBSenv orbital basis sets and auxiliary basis sets are optimized to be used as environmental basis in the domain-specific basis set approach. The performance with respect to the accuracy and computation times is analyzed with a test set of structures and reactions. In another project, a scheme for the optimization of auxiliary basis sets for uranium is presented. This scheme was used to optimize the MP2Fit auxiliary basis sets for uranium. These auxiliary basis enable density fitting in quantum chemical methods and the application of the incremental scheme for systems containing uranium. Another project was the systematical analysis of the binding energies of four water dodecamers. The incremental scheme in combination with the CCSD(T) and CCSD(T)(F12*) method were used to calculate benchmark energies for these large clusters.
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Walk, Rachel Suzanne. "Associations Involving Open Court Reading in Kindergarten and Student Performance on Standardized Assessments in Reading in a Tennessee School System." Digital Commons @ East Tennessee State University, 2005. https://dc.etsu.edu/etd/1036.
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The purpose of this study was to determine what, if any, associations existed between the implementation of the Open Court Reading® program in kindergarten and students’ reading achievement on the Terra Nova standardized achievement test in the first grade. The study involved first-grade students who attended kindergarten in one school system in East Tennessee. Using a quantitative design, this study included the first-grade Terra Nova scores from 2001, 2002, 2003, and 2004. Scores obtained by first-grade students who did not receive Open Court Reading® in kindergarten (2001 and 2002) were compared with first-grade scores obtained by students who did receive Open Court Reading® in kindergarten (2003 and 2004). The study factored in gender, ethnicity, students receiving special education services, and Title I and nonTitle I status of the school attended. Reading Normal Curve Equivalent (NCE), vocabulary NCE, reading composite NCE, language NCE, and word analysis NCE scores from four years of Terra Nova scores were used in the analysis. t-tests for independent means and two-way analysis of variance (ANOVA) were employed to examine the information. The data were analyzed using the Statistical Program for the Social Sciences.
Based on the findings, implementing the Open Court Reading® program in kindergarten appears to have reduced learning gaps that often emerge in early grades when children are learning to read. The findings indicated that a positive relationship exists between participation in Open Court Reading® in kindergarten and test performance in first grade. From the two years of test data analyzed after the implementation of Open Court Reading® in kindergarten, learning gaps between females and males diminished; in some cases the males surpassed the females. Implementation of Open Court Reading® in kindergarten does not appear to reduce differences in test performance between non-minority and minority students. Students with special needs who are exposed to Open Court Reading® in kindergarten appear to perform higher on reading subtests in the first grade. According to the results of the reading, reading composite, and word analysis subtests, Title I students reduced the gap with nonTitle I students after they participated in the Open Court Reading® program in kindergarten.
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Shoop, Stephen Scott. "The Texas Bandmasters Association a historical study of activities, contributions, and leadership (1920-1997) /." Thesis, view full-text document, 2000. http://www.library.unt.edu/theses/open/20012/shoop%5Fstephen/index.htm.
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Christlmaier, Evelin Martine. "CC2 response method using local correlation and density fitting approximations for the calculation of the electronic g-tensor of extended open-shell molecules." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22835.
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In dieser Arbeit wird eine unrestricted Coupled-Cluster CC2 Response-Methode für die Berechnung von Eigenschaften erster und zweiter Ordnung, mit dem elektronischen g-Tensor als Schwerpunkt, präsentiert. Lokale Korrelations- und Dichtefittingnäherungen wurden verwendet. Die fundamentalen Konzepte notwendig für das Verständnis von Coupled-Cluster-Theorie, Dichtefitting, lokaler Korrelation, allgemeinen Coupled-Cluster Eigenschaften
und dem elektronischen g-Tensor werden diskutiert. Die berechneten g-Tensoren werden mit denen durch Coupled-Cluster Singles and Doubles, Dichtefunktionaltheorie und Experiment erhaltenen verglichen. Effizienz und Genauigkeit der Näherung wird untersucht. Ein detailierter Anhang beschreibt die diagrammatische Coupled-Cluster-Theorie sowie ihre Anwendung zur Herleitung der verwendeten Arbeitsgleichungen. Die in dieser Arbeit entwickelte Methode ermöglicht es, den elektronischen g-Tensor von ausgedehnten Systemen mit einer Methode, die nicht auf Dichtefunktionaltheorie basiert, quantitativ vorherzusagen.
Damit ist sie ein wichtiger Schritt hin zur Entwicklung von niedrig skalierenden Coupled-Cluster-Methoden höherer Ordnung für diese Art von Problem.This work presents an unrestricted coupled-cluster CC2 response method using local correlation and density fitting approximations for the calculation of first and second order properties with particular focus on the electronic g-tensor. The fundamental concepts related to coupled-cluster theory, density fitting, local correlation, general coupled-cluster properties and the electronic g-tensor are discussed. The calculated g-tensors are benchmarked against those obtained from coupled-cluster singles and doubles, density functional theory and experiment. Efficiency and accuracy of the approximations is investigated. A detailed appendix covers the fundamentals of diagrammatic coupled-cluster and its application to the derivation of the working equations. The method presented in this thesis enables the quantitative prediction of the electronic g-tensor of extended systems with a method other than density functional theory. It represents an important step towards the development of low-scaling higher order coupled-cluster methods for this type of problem.
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Bertelli, Motta Clio [Verfasser], and Eva K. [Akademischer Betreuer] Grebel. "The footprints of stellar evolution on the chemical composition of the Galactic old open cluster M67 / Clio Bertelli Motta ; Betreuer: Eva K. Grebel." Heidelberg : Universitätsbibliothek Heidelberg, 2018. http://d-nb.info/1177384574/34.
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