Thèses : « Young cluster »

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Hußmann, Benjamin [Verfasser]. « The Quintuplet cluster : A young massive cluster study based on proper motion membership / Benjamin Hußmann ». Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/104762270X/34.

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Meyers-Rice, Barry Allan. « The dusty environment of the young galactic cluster NGC 2264 ». Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187282.

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This is a study of the young galactic cluster NGC 2264. In it 12-100 $\mu$m IRAS data are used to analyze emission from the cluster dust. This dust is warmed by the young point sources in the cluster. Images of the region were obtained in the V, R, and I bands, and the point source data extracted are combined with a pre-existing J-H-K database to produce a six-band photometric survey of the cluster. This 4900-entry catalogue and methods to eliminate spurious detections and non-cluster stars from it are discussed. The cluster is estimated to consist of 350-650 members. A device to produce polarimetric images was designed, built, and used to obtain data to explore star formation environments. The nature of one such region in NGC 2264 is discussed, and the sources responsible for illuminating this reflection nebula are identified. It is concluded that multiple scattering and a disk geometry can explain the features observed. Spectra of 361 stars in the cluster region were obtained and by extending the MK system to the red part of the spectrum their spectral types are determined. Many T Tauri stars are identified and aspects of their emission lines are analyzed. It is shown that the spectral lines of many cluster stars of types later than G9 are in emission while those of earlier-type stars show incipient emission diluted by stellar flux. An evolutionary sequence of stars based upon photometry and spectroscopy is proposed. Stars from this spectral survey are dereddened and the extinctions obtained are interpreted. Spectral energy distributions are produced for the dereddened stars, revealing infrared excesses in many. These excesses are modelled by disk-star systems, and it is shown that inner holes are required in the disks to explain the observed levels of short wavelength emission.

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Messa, M., A. Adamo, G. Östlin, D. Calzetti, K. Grasha, E. K. Grebel, F. Shabani et al. « The young star cluster population of M51 with LEGUS – I. A comprehensive study of cluster formation and evolution ». OXFORD UNIV PRESS, 2018. http://hdl.handle.net/10150/626277.

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Recently acquired WFC3 UV (F275W and F336W) imaging mosaics under the Legacy Extragalactic UV Survey (LEGUS), combined with archival ACS data of M51, are used to study the young star cluster (YSC) population of this interacting system. Our newly extracted source catalogue contains 2834 cluster candidates, morphologically classified to be compact and uniform in colour, for which ages, masses and extinction are derived. In this first work we study the main properties of the YSC population of the whole galaxy, considering a mass-limited sample. Both luminosity and mass functions follow a power-law shape with slope -2, but at high luminosities and masses a dearth of sources is observed. The analysis of the mass function suggests that it is best fitted by a Schechter function with slope -2 and a truncation mass at 1.00 +/- 0.12 x 10(5) M-circle dot . Through Monte Carlo simulations, we confirm this result and link the shape of the luminosity function to the presence of a truncation in the mass function. A mass limited age function analysis, between 10 and 200 Myr, suggests that the cluster population is undergoing only moderate disruption. We observe little variation in the shape of the mass function at masses above 1 x 10(4) M-circle dot over this age range. The fraction of star formation happening in the form of bound clusters in M51 is similar to 20 per cent in the age range 10-100 Myr and little variation is observed over the whole range from 1 to 200 Myr.

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Allen, Thomas S. « A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b ». University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1404697742.

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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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Dupree, A. K., A. Dotter, C. I. Johnson, A. F. Marino, A. P. Milone, J. I. Bailey, J. D. Crane, M. Mateo et E. W. Olszewski. « NGC 1866 : First Spectroscopic Detection of Fast-rotating Stars in a Young LMC Cluster ». IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625815.

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High-resolution spectroscopic observations were taken of 29 extended main-sequence turnoff (eMSTO) stars in the young (similar to 200 Myr) Large Magellanic Cloud (LMC) cluster, NGC 1866, using the Michigan/Magellan Fiber System and MSpec spectrograph on the Magellan-Clay 6.5 m telescope. These spectra reveal the first direct detection of rapidly rotating stars whose presence has only been inferred from photometric studies. The eMSTO stars exhibit Ha emission (indicative of Be-star decretion disks), others have shallow broad H alpha absorption (consistent with rotation. greater than or similar to 150 km s(-1)), or deep Ha core absorption signaling lower rotation velocities (less than or similar to 150 km s(-1)). The spectra appear consistent with two populations of stars-one rapidly rotating, and the other, younger and slowly rotating.

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DE, LUCA MASSIMO. « The Vela molecular ridge young population : from pre-stellar condensations to young clusters ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/472.

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Scopo di questa tesi e' la caratterizzazione della popolazione proto-stellare di una regione di formazione stellare (circa un grado quadro) nel complesso di nubi molecolari giganti denominato Vela Molecular Ridge, con particolare riguardo per la correlazione tra oggetti giovani e caratteristiche fisiche e morfologiche del mezzo interstellare. Le nubi molecolari giganti contengono piu' dell'80% del contenuto di idrogeno della Galassia e sono considerate responsabili della maggior parte della formazione stellare. Esse rappresentano quindi i siti maggiormente promettenti nell'ambito della ricerca sulla nascita delle stelle. Analizzando la strutura su larga scala della nube, vengono descritte le condensazioni di gas e polvere dentro le quali si originano le stelle. Segue uno studio dettagliato, sia dell'emissione infrarossa proveniente da tali condensazioni, che dei fenomeni di perdita di massa (jet e outflow) associati agli oggetti piu' giovani. Cio' permette di trarre interessanti conclusioni riguardo le modalita' della formazione stellare, tanto all'interno di ciascuna condensazione, quanto, piu' in generale, nella nube, consentendo altresi' un raffronto con altre nubi Galattiche. I dati analizzati spaziano dal vicino infrarosso alle lunghezze d'onda millimetriche e sono stati ottenuti per mezzo di osservazioni da Terra e dallo spazio (vengono presentati anche i primi risultati dello studio tutt'ora in corso di mappe acquisite dal telescopio spaziale Spitzer). Il contributo fornito dal presente lavoro all'attuale attivita' di ricerca in formazione stellare riguarda principalmente: (i) la relazione spaziale tra siti dove le stelle hanno origine e distribuzione del mezzo interstellare, (ii) il legame tra distribuzione in massa delle condensazioni e funzione iniziale di massa, (iii) la statistica dei differenti stadi evolutivi delle proto-stelle in connessione con dette condensazioni, (iv) l'identificazione di sorgenti che meritano di essere osservate mediante strumentazione di nuova generazione in via di completamento (e.g. ALMA ed Herschel). Questo lavoro e' stato svolto nell'ambito del gruppo di astronomia infrarossa presso l'Osservatorio Astronomico di Roma, sotto la guida della Dott. Teresa Giannini, del Prof. Dario Lorenzetti, e presso l'Universita' di Roma "Tor Vergata", sotto la supervisione del prof. Roberto Buonanno.
The aim of this thesis is the characterization of the proto-stellar population of a star forming region (about one square degree) of the Vela Giant Molecular Cloud Complex, paying particular attention on the correlation between young objects and physical and morphological characteristics of the cloud interstellar medium. As a by-product, observational targets for new generation instrumentation have been also identified. Giant Molecular Clouds contain over 80% of the molecular hydrogen content of the Galaxy and are now considered responsible for most of the star birth. They thus represent the most promising sites for the research activity on star formation. By analysing the large-scale cloud structure we describe the gas-dust condensations inside which collapse into new stars begins. It follows a detailed inspection of both the infrared emission arising from such condensations and of the mass-loss phenomena (jets and outflows) associated with the youngest objects. This allows us to draw interesting conclusions regarding the star-forming modalities, both within each condensation and, more in general, within the cloud, enabling a comparison with other Galactic clouds. The large analysed database covers the range from Near-Infrared to millimeter wavelengths and has been obtained by means of both ground based and space-born facilities (we present also the first results of the on-going study of maps acquired by the Spitzer Space Telescope). The contribution given by this study to the present-day research activity on star formation mostly concerns the debates regarding: (i) the spatial relation between sites of star birth and interstellar material distribution, (ii) the link between the mass distribution of the cloud condensations and the Initial Mass Function, (iii) the statistics of different evolutionary stages of young objects within dust and molecular cores, (iv) the identification of interesting sources for a future investigation by means of more powerful instrumentation (e.g. ALMA and Herschel). This work has been carried out within the Infrared group of the Astronomical Observatory of Rome (INAF-OAR) under the supervision of Dr. Teresa Giannini, Prof. Dario Lorenzetti (INAF-OAR), and on the behalf of the University "Tor Vergata" of Rome (supervisor Prof. Roberto Buonanno).

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Lyo, A.-Ran Physical Environmental &amp Mathematical Sciences Australian Defence Force Academy UNSW. « The nearby young [special character] Chamaeleontis cluster as a laboratory for star formation and evolution ». Awarded by:University of New South Wales - Australian Defence Force Academy. School of Physical, Environmental and Mathematical Sciences, 2004. http://handle.unsw.edu.au/1959.4/38707.

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[Special characters cannot be displayed. Please see the pdf version of the Abstract for an accurate reproduction.] We studied the circumstellar discs, the initial mass function (IMF), mass distribution, binarity and the fundamental properties of the [special character] 9 Myr-old pre-main sequence (PMS) [special character] Chamaeleontis cluster. Using JHKL colour-colour and colour-excess diagrams, we found the circumstellar disc fraction to be [special character] 0.60 among the late-type members. Four stars with [special character] (K - L) > 0.4 were identified as experiencing ongoing accretion which was later confirmed by high-resolution spectroscopic study. Quantitative analysis of the H[special character] profiles found accretion in these four stars at rates comparable to that of two members of the similarly-aged TW Hydrae Association (TWA); rates 1 - 3 orders of magnitude lower than in younger classical T Tauri stars. Together these results suggest that, while the mass accretion rate decreases with age, PMS stars can retain their inner discs for [special character] 10 Myr. An optical photometric survey spanning 1.3 ?? 1.3 pc added two low-mass stars to the cluster inventory. Together with other recent surveys the population is likely to be significantly complete for primaries with masses M > 0.15M[special character]. The cluster now consists of 18 primaries and 9 confirmed and candidate secondaries, with [special character] 2-4 times higher multiplicity than seen in field dwarfs. The cluster IMF is consistent with that of rich young clusters and field stars. By extending the IMF to lower masses, we predict 20-29 low-mass stars and brown dwarfs may remain undiscovered. From study of the cluster???s spatial and mass distribution, we find the [special character] Cha cluster has significant mass segregation, with > 50 per cent of the stellar mass residing within the central 0.17 pc. Lastly we classified members of the cluster with low-resolution spectra, providing information about the fundamental properties of the PMS stars by comparison to standard dwarfs. Broadband VRI colours and pseudocontinuum indices derived for the cluster stars are indistinguishable from dwarfs at visual and red wavelengths. This suggests the temperature sequence for the PMS [special character] Cha cluster is similar to that of the dwarf sequence. Narrow-band spectral indices for the [special character] Cha cluster possibly indicate higher metallicity and strongly indicate lower surface gravity than the dwarf indices.

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Yusuf, H. « Preventing obesity by reducing soft drinks consumption among young people attending dental practices : a feasibility cluster RCT ». Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1470597/.

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Background: In England, 70% of young people consume soft drinks on a regular basis which increases the likelihood of obesity and dental caries. Many young people often visit the dentist; however primary dental care has been an underutilised research setting for delivering and evaluating dietary interventions. Motivational Interviewing (MI) has been shown to be effective in behaviour change. Therefore, this study provides an opportunity to assess an obesity intervention to reduce soft drinks consumption among young people attending NHS dental practices. Aims: To conduct a feasibility trial of an MI intervention to reduce soft drinks consumption among young people attending primary dental care practices in North Central London (Camden, Islington, and Haringey). Methods: The initial developmental phase explored dental teams’ attitudes, behaviours and perceived barriers in delivering prevention, using a mixed methods approach (focus groups followed by a questionnaire survey). A purposive sample of 11 out of 22 dental practices was selected from the study area for the four focus groups (two with dentists and two with dental care professionals). A cross-sectional survey of all NHS dentists was also conducted using a self-complete questionnaire. Descriptive analysis of the questionnaire data was undertaken and differences by the age and sex of the sample were assessed. A cluster feasibility trial with embedded process evaluation was then undertaken in the second phase of the study. Participants: Ten randomly allocated NHS dental practices recruited 39 overweight or obese young people (11-16 years). Intervention: 3-4 MI sessions. The three main outcomes were: mean daily consumption of sugary soft drinks using a 24 hour dietary recall, body mass index (BMI) and waist circumference. Outcomes were measured at baseline and at 6 month follow-up. Process evaluation outcomes: Recruitment, retention, fidelity and acceptability of the intervention were assessed using mixed methods. MI Fidelity was assessed using the Motivational Interviewing Treatment Integrity Code (MITI). Thematic analysis was used to analyse the qualitative data and descriptive analysis for the quantitative data. The study was approved by the local Ethics Committee (10/H0722/2). Results: Of the 300 eligible respondents, 164 questionnaires were returned (response rate: 54.7%). In Phase I, there were broad similarities in the themes that emerged from the four focus groups and the questionnaire survey. The majority of respondents strongly agreed that NHS dentists had a role to play in smoking cessation counselling, diet and alcohol advice. For dentists, prevention was viewed to be part of their ethical obligation. A high proportion of respondents 95.7% delivered oral hygiene advice, 85.4% provided diet advice, and 76.7% offered smoking cessation advice always or frequently. Barriers to delivering prevention included organisational factors (lack of adequate remuneration, bureaucracy), patient-related factors (motivation and compliance), and clinician-related factors (lack of training and resources). There was significant variation in providing prevention by the age and sex of dentists with female and younger dentists more likely to provide certain aspects of preventive care. Phase II- 10 dental practices were recruited (5 control and 5 intervention). Out of 149 potential participants, 39 (26.2%) conformed to the eligibility criteria, 5 (12.8%) withdrew from the study, and 3 (7.6%) were lost to follow-up, resulting in a retention rate of 79.5%. Facilitators of study implementation included the use of a screening questionnaire, support from the research team and incentives for young people and dental teams. In terms of acceptability, participants reported that the study had a positive impact on their knowledge or behaviours. At follow-up, soft drinks consumption decreased. Dental teams valued being involved in research. They recognised the challenges in recruiting young people and employed varying mechanisms to overcome them. Intervention fidelity revealed the MI practitioners to be proficient in MI and there was little variation in proficiency among the practitioners. Conclusions: Dentists in the study area were actively involved and had a generally positive attitude towards delivering prevention in primary dental care. The intervention was acceptable and feasible among dental teams and young people. MI is a feasible tool for reducing sugary soft drinks consumption among overweight young people attending dental practices. Further research is required to assess its effectiveness in primary dental care.

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Arévalo, Aura de Las Estrellas Ramírez. « The Red Supergiants in the Supermassive Stellar Cluster Westerlund 1 ». Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-12092018-161841/.

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The purpose of this dissertation is to study the Red Supergiant stars (RSGs) in the supermassive young cluster Westerlund 1 through a photometric and spectral analysis. Due to its characteristics, Westerlund 1 is one of the most interesting young massive clusters in the Milky Way and has an impressive population of massive stars, with four RSGs among them. This represents a rare oportunity to study this type of stars in a cluster with well known distance and reddening. Apart from contributing to the general knowledge about RSGs, which parameters are poorly known due to their scarcity, an analysis of these four stars will contribute to solve the puzzle of the formation history of Westerlund 1. For the analysis presented here, photometric data of the four RSGs in Westerlund 1 were used, along with near infrared spectra covering the region from ~8400 Å to ~8900 Å, obtained at two different epochs with the 1.60 m telescope at Observatório do Pico dos Dias (OPD) and the Southern Astrophysical Research Telescope (SOAR). Magnitudes obtained with JHK band photometry were used to calculate effective temperatures and bolometric corrections at the K band through different methods involving the color indices (V-K)_0 and (J-K)_0, in order to determine the luminosities and locate the four RSGs in a Hertzsprung-Russell diagram (HRD). A spectral analysis was performed with the aim of estimating spectral types and the same stellar parameters calculated with the photomety. First, a visual comparison of the depth and strength of the main spectral features (TiO and VO bandheads, and CaT and Fe I lines) was carried out to classify the stars by spectral type. For this purpose, spectra of the four RSGs in the cluster were compared to a group of spectra from well studied reference stars, some of them also RSGs. Then, given their strong dependence on Teff, equivalent widths (EWs) of Fe I lines were measured in all the spectra available. By comparing the EWs measured on spectra of the four RSGs and the reference stars, the Teff\'s of the most similar reference stars were assigned to the RSGs in the cluster. With the Teff\'s obtained through the spectral analysis, new points were added to the initial HRD. The final objective of the present work was to estimate the initial masses and ages of the RSGs in Westerlund 1. This was accomplished by superimposing up to date evolutionary tracks and isochrones to the HRD. Masses and ages were determined for the cases with and without rotation, obtaining an average age for the RSGs of 8 Myr, thus doubling the age of the host cluster determined from the pre-main sequence (PMS). In the final part, it is presented a brief discussion about the discrepancy of the age of Westerlund 1 measured with the PMS isochrones and the age of the RSGs, as well as the uncertainties it raises regarding the formation history of the cluster.
O objetivo desta dissertação é estudar as estrelas Supergigantes Vermelhas (RSGs) no aglomerado jovem supermassivo Westerlund 1 através de uma análise fotométrica e espectral. Devido às suas características, Westerlund 1 é um dos aglomerados jovens mais interessantes da Via Láctea e tem uma população importante de estrelas massivas, com quatro RSGs entre elas. Isso representa uma oportunidade rara para estudar este tipo de estrelas em um aglomerado com a distância e avermelhamento bem conhecidos. Além de contribuir para o conhecimento geral sobre RSGs, cujos parâmetros são pouco conhecidos devido à sua escassez, uma análise dessas quatro estrelas contribuirá para resolver o enigma da história da formação de Westerlund 1. Para a análise apresentada aqui, foram utilizados dados fotométricos das quatro RSGs em Westerlund 1, juntamente com espectros no infravermelho próximo cobrindo a região de ~8400 Å a ~8900 Å, obtidos em duas épocas diferentes com o telescópio de 1.60 m do Observatório do Pico dos Dias (OPD) e o Southern Astrophysical Research Telescope (SOAR). Magnitudes obtidas com a fotometria nos filtros JHK foram usadas para calcular temperaturas efetivas e correções bolométricas na banda K através de diferentes métodos envolvendo os índices de cor (V-K)_0 e (J-K)_0, a fim de determinar as luminosidades e localizar as quatro RSGs em um diagrama de Hertzsprung-Russell (HRD). Uma análise espectral foi realizada com o objetivo de estimar os tipos espectrais e os mesmos parâmetros estelares calculados com a fotometria. Primeiramente, uma comparação visual da profundidade e força das principais características espectrais (as bandas moleculares de TiO e VO e as linhas de CaT e Fe I) foi realizada para classificar as estrelas por tipo espectral. Para este propósito, os espectros das quatro RSGs no aglomerado foram comparados com um grupo de espectros de estrelas de referência bem estudadas, algumas delas também RSGs. Depois, dada a sua forte dependência com a Teff, as larguras equivalentes (EWs) das linhas de Fe I foram medidas em todos os espectros disponíveis. Comparando as EWs medidas nos espectros das quatro RSGs e nos das estrelas de referência, as Teff das estrelas de referência mais similares foram atribuídas às RSGs do aglomerado. Com as Teff obtidas através da análise espectral, novos pontos foram adicionados ao HRD inicial. O objetivo final do presente trabalho foi estimar as massas iniciais e as idades das RSGs em Westerlund 1. Isto foi realizado através da sobreposição no HRD de caminhos evolutivos e de isócronas. Massas e idades foram determinadas para os casos com e sem rotação, obtendo-se uma média de idade para as RSGs de 8 milhões de anos, duplicando assim a idade do aglomerado ao que as RSGs pertencem, e que foi medida através de estrelas de pré-sequência principal (PMS). Na parte final, é apresentada uma breve discussão sobre a discrepância da idade de Westerlund 1 medida com as isócronas da PMS e a idade das RSGs, bem como as incertezas que isso suscita em relação à história da formação do aglomerado.

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Pang, Xiaoying [Verfasser], et Eva [Akademischer Betreuer] Grebel. « A comprehensive study of the young star cluster HD 97950 in NGC 3603 / Xiaoying Pang ; Betreuer : Eva Grebel ». Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1179784731/34.

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Lim, Beomdu, Hwankyung Sung, Jinyoung S. Kim, Michael S. Bessell, Narae Hwang et 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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West, Craig K. « Agency and Education : A Critical Discourse Analysis of the Rhetoric of Agency and Formal Education in Young Adult Literature ». University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1504798010232269.

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Zeidler, Peter [Verfasser], et Eva K. [Akademischer Betreuer] Grebel. « Revealing the secrets of Westerlund 2 - A young massive star cluster observed with the Hubble Space Telescope / Peter Zeidler ; Betreuer : Eva K. Grebel ». Heidelberg : Universitätsbibliothek Heidelberg, 2017. http://d-nb.info/1180739248/34.

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Stålnacke, Johanna. « Rough beginnings : Executive function in adolescents and young adults after preterm birth and repeat antenatal corticosteroid treatment ». Doctoral thesis, Stockholms universitet, Psykologiska institutionen, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-106798.

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This thesis investigates long-term cognitive outcome in two cohorts of adolescents and young adults exposed to stressors during the perinatal period: one group born preterm (<37 weeks of gestation and birth weight <1,500 g); one group exposed to two or more courses of antenatal corticosteroids (ACS), to stimulate lung maturation in the face of threatening preterm birth. In fetal life the brain undergoes dramatic growth, and a disruption to the early establishment of functional neural networks may interrupt development in ways that are difficult to predict. Executive function refers to a set of cognitive processes that are important for purposeful regulation of thought, emotion, and behavior, and even a subtle depreciation may influence overall functioning. Study I investigated the stability of executive function development after preterm birth. Executive functions were differentiated into working memory and cognitive flexibility. Both components were highly stable from preschool age to late adolescence. In Study II, we identified subgroups within the group of children born preterm with respect to cognitive profiles at 5½ and 18 years, and identified longitudinal streams. Outcome after preterm birth was diverse, and insufficiently predicted by perinatal and family factors. Individuals performing at low levels at 5½ years were unlikely to improve over time, while a group of individuals performing at or above norm at 5½ years had improved their performance relative to term-born peers by age 18. Studies I and II pointed to the need for developmental monitoring of those at risk, prior to formal schooling. Study III investigated long-term cognitive outcome after repeat ACS treatment. The study did not provide support for the concern that repeat ACS exposure will have an adverse impact on cognitive function later in life. In sum, exposure to perinatal stressors resulted in great variation in outcome. However, for many, their rough beginnings had not left a lasting mark.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 1: Submitted.

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Bromfield, Pauline V. « 'Healthy schools' and childhood obesity : provision and perspectives within an extended services cluster on psychsocial outcomes for children and young people who are overweight or obese ». Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1115/.

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Research, policy and media discourses highlight risk of negative physical and non-physical outcomes for overweight/obese children compared with their non-overweight/obese peers. The study’s aim was to explore whether psychosocial correlates were being considered and informing policy and practice with regard to the ‘National Healthy Schools Programme’ (NHSP) within a cluster of schools, and with their community and strategic partners. Stakeholders’ perspectives including those of pupils were sought to illuminate whether, as a result of the NHSP, the potential risk of unintended harm was recognised and addressed. The research was conceptualized as an exploratory case study that primarily entailed the use of qualitative research methods for data collection and analysis. The findings of the study highlighted dominant socio-cultural practices that reinforce the ‘thin ideal’ and some of the risk potentiation and compensatory factors that could impact on outcomes for children. The dominance of the ‘physical’ themes of the NHSP reflected weakness in the operational delivery of a multidimensional rather than a fully integrated ‘holistic’ model of health and well-being. Recommendations for future research and practice include the future positioning of educational psychology practice and promoting meaningful consultation processes that ensure children’s perspectives are heard and listened to.

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Karnath, Nicole. « The Transition Points in Young Stars and Young Star Clusters ». University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564763305735395.

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Larsson, Therese. « Att falla för grupptrycket : Hur unga entreprenörer kan sälla sig till kluster för att hantera osäkerheter rörande företagande ». Thesis, Högskolan i Borås, Institutionen Textilhögskolan, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-20710.

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Tidigare forskning har visat att det finns ett stort intresse bland unga i Sverige att starta företag. Det har också uppenbarats att det finns brister i ungas kunskaper om företagande och entreprenörskap, och de vet inte heller hur de skall gå tillväga för få den kunskapen. De faktorerna påverkar ungas företagande negativt och hämmar dem i deras önskan om egenföretagande. Syftet med denna uppsats är att undersöka vilka specifika faktorer som hindrar unga från att starta företag, det vill säga vilka osäkerheter de upplever i den industriella omgivningen och hur de kan hanteras. I ett försök att finna metoder som hjälper unga att hantera de osäkerheter som upplevs har jag undersökt hur klusterteorin kan underlätta företagandet. Klusterteorin skapades av Michael Porter i slutet av nittonhundratalet och visar på hur företag kan erhålla konkurrensfördelar genom att samlas i industriella kluster. Till det empiriska materialet har jag använt mig av sekundärdata i form av en undersökning utförd av Nutek 2008. Jag har också genomfört en fallstudie med tre företag som opererar i klustret Textil- och Modefabriken.I analysen har jag kunnat identifiera att de osäkerheter som unga upplever är finansiella; hur verksamheten skall finansieras, operationella; hur effektivt företaget kan drivas, samt konkurrensmässiga; om förmågan att konkurrera med andra. Med hjälp av kluster kan de osäkerheterna hanteras då kluster gör unga till bättre företagare med större kunskap om branschen, minskar deras ekonomiska otrygghet och bidrar med en social miljö som främjar deras innovation och ökar den teknologiska utvecklingen.Previous research has shown that there is a great interest among young people in Sweden to start a business. It has also become apparent that there are gaps in young people’s knowledge about business venturing and entrepreneurship, as well as their ability to obtain that knowledge. These factors affect entrepreneurship among young people negatively and it inhibits them in their desire to start at business. The purpose of this paper is to examine the specific factors that prevent young people from starting a business, that is, the uncertainties they experience in the industrial environment and how they can be managed. In an attempt to find methods that can be used to help young people manage the perceived uncertainties I have researched how cluster theory can facilitate entrepreneurship. Cluster theory was created by Michael Porter in the late twentieth century as way to show how businesses can achieve a competitive advantage by congregating in industrial clusters. For my empirical material I have used secondary data in the form of a survey carried out by Nutek in 2008. I have also done a case study with three companies that operate in a cluster called Textil- och Modefabriken.I have identified that the nature of the uncertainties perceived by young people are financial; how the business will be financed, operational; how effectively they will be able to run the business, and competitive; the ability to compete with others. Through the use of clusters these uncertainties can be managed as clusters can turn the young people into better entrepreneurs with a greater knowledge of the industry, as well as reduce their financial insecurities and provide them with a social construct that increase innovation and technological advancements.
Program: Textilekonomutbildningen

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Foster, Duncan C. « Late-type stars in young open clusters ». Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263574.

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Allison, Richard James. « The dynamical evolution of young star clusters ». Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555711.

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Stars form in large clouds of cold, dense molecular gas. In these clouds the majority of stars do not form in isolation, but instead form in clusters. The formation of stars and their hos~ clusters are intrinsically linked, and thus to fully understand how stars form we must also understand the formation and early evolution of stellar clusters. The formation of stars is thought to be governed by the turbulent conditions inside these molecular clouds, and due to this the initial conditions of star formation are likely to be spatially complex and dynamically cool. In this Thesis we use fractal spatial distributions (D = 1.6,2.0,2.6 and 3.0) to mimic the complex initial conditions of star formation to investigate how the dynamical evolution of star clusters is affected by variations in the amount of primordial structure. We also use varying initial virial ratios (Q = 0.3, 0.4 and 0.5) to investigate what affect the initial kinematics have on a clusters dynamical evolution. I present a new method, based on the minimum spanning tree, which is able to determine and quantify the presence of mass segregation. The method is applied to observations of the ONe, ,vhich we find to be complexly mass segregated, with different levels of mass segregation depending on stellar mass. We find, contrary to common belief, that mass segregation can occur through purely dynamical processes on a short timescale (rv the initial cluster crossing time). We also find that the amount of dynamical mass segregation that occurs is dependant on both the initial structure and virial ratio, where cooler and more structured initial conditions tend to lead to more dramatic dynamical evolution. Additionally, we find that the clumpy and cool initial conditions also lead to the dynamical formation of high-mass multiple systems, which in turn can lead to the ejection of high-mass stars and the destruction of the host cluster itself.

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Christopher, Micol Huw Hillenbrand Lynne A. Scoville Nicholas Zabriskie. « Young, massive star clusters in the antennae / ». Diss., Pasadena, Calif. : California Institute of Technology, 2008. http://resolver.caltech.edu/CaltechETD:etd-05152008-141502.

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Ford, Alison. « Lithium in young open clusters and halo stars ». Thesis, Keele University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391218.

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Cabral, Ana Isabel Duarte. « Kinematics and physical properties of young proto-clusters ». Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/kinematics-and-physical-properties-of-young-protoclusters(8eb34d15-b343-4aab-b4b0-ede4bba903be).html.

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The formation of stars begins with the fragmentation of molecular clouds and the formation of dense cores. This fragmentation process can either be the result of classical gravitational instabilities or triggered by some external event. The gas and dust of young protoclusters often hold the imprints of the initial conditions and triggers of that specific star forming episode. In this context, my thesis work is a study of the gas properties of young protoclus- ters within the Gould Belt. The first part of my work consists of a detailed study of the young Serpens star forming region with CO isotopologues. This study has revealed a complex temperature, column density and velocity structure. I proposed a scenario where a collision between two filamentary clouds or flows is responsible for the observed complex structure and the most recent burst of star formation in Serpens. This hypothesis was tested with SPH simulations and provides a plausible scenario. I am currently extending this work to other regions with a variety of star formation efficiencies, in search of the particular physical properties and dynamics of a molecular cloud that allow or prevent clouds to be in the verge of forming stars. As such, I have included in this manuscript my study of the gas in the B59 star forming region, the only active clump in the Pipe Nebula. The results from this study have shown it to be very different from Serpens, even though further studies are needed to provide a complete picture of the region. B59 was taken as the starting point for a larger study of the entire Pipe Nebula, driven by the peculiarly low star formation efficiency in the cloud and a test to the physical properties of cores prior to star formation.

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Williams, Douglas M. « The low mass IMF in young open clusters ». Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187410.

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We present the results of the investigation of the Initial Mass Function at the end of the Main Sequence in young open clusters. We find that over a large range in age and environment the IMFs are similar to each other, and to recent determinations of the field star IMF. We have obtained V, I, and K band photometry of fields in the three relatively unembedded open clusters. The photometry reaches down to various masses in ech cluster: 0.08Mʘ for Praesepe, 0.04Mʘ for the Pleiades, and 0.15Mʘ for NGC 7160. We compare the methods for estimating the masses of young, embedded stars developed by Comeron et al. (1993) and by Strom et al. (1995) and show them to be in good agreement. Spectra in the 2 11m region of six low mass objects from Comeron et al. (1993) are also in agreement with the mass estimates using these methods. The spectrum of a brown dwarf candidate is used to place an upper limit on its mass of 60% of the minimum required for hydrogen burning. The IMFs from these four clusters plus NGC 2024 (Cameron et al. (1995)) are shown to be in agreement with each other. The composite MF can be fitted with a power law between 0.04 and 0.5Mʘ with a slope of -0.75 ± 0.3. There is no evidence for a cutoff at the bottom of the main sequence (0.08Mʘ); brown dwarfs appear to be abundant in open clusters. However, the slope of the MF is well above the value of ≲ -2 required for very low mass stars and brown dwarfs to contribute a significant portion of the mass of open clusters. The composite cluster MF also is in agreement with recent determinations of the field star IMF for stellar masses. The field star data do not extend into the brown dwarf range; however, if we extrapolate in accordance with the cluster MF, we conclude that brown dwarfs probably do not contribute significantly to the dark matter.

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Stolte, Andrea. « Mass functions and mass segregation in young starburst clusters ». [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968318142.

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Goddard, Q. E. « The formation of young star clusters in extreme environments ». Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599453.

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Star clusters are fundamental building blocks of galaxies, and yet very little is known about young star clusters as they evolve unseen in the embedded phase. Using four band photometry of star clusters in NGC 3256 we are able to determine the chance of survival for star clusters over the course of the embedded phase, and combined with other data sets show a relationship between survivability and the star formation rate density. We also perform a detailed study of the XUV-disc phenomenon and their cluster population. Firstly we measure the broad properties of several XUV-disc galaxies in comparison to normal galaxies using surface photometry and individual object photometry. We reveal that these galaxies show a range of properties, some showing sharp edges in their Hα profiles whilst others do not, although all show a smoothly declining UV profile which extends beyond the optical edge of the disc. The HII regions in these outer discs appear to have luminosities consistent with single ionising O-type stars and have implied mass which suggest that the formation of the most massive stars is governed by stochastic processes. We also examine the spectra of HII regions in two XUV-disc galaxies, NGC 4625 and NGC 3621. Both galaxies show a shallower abundance gradient in the outer disc compared to the inner disc, yet NGC 4625 also shows a discontinuity close to the optical edge. This is of particular interest as NGC 3621 shows no sharp Hα and no discontinuity whilst NGC 4625 displays both of these features. The HII regions of both of these galaxies show properties different to bright inner disc HII regions, making abundance calculations less reliable.

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Rolleston, William Robert James. « Young stars in Galactic clusters and the Magellanic Clouds ». Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282334.

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Muench, August A. « Luminosity and mass functions of very young stellar clusters ». [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE0000578.

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Apai, Dániel. « Exploring the environment of young stars disks, companions and clusters / ». [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971655243.

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Henault-Brunet, Vincent. « Massive binary stars and the kinematics of Young Massive Clusters ». Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8047.

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Located in the Large Magellanic Cloud, R136 is a rare example of a nearby young and dense massive star cluster in which individual stars can be resolved. Often suggested as a globular cluster in formation, its study is of great interest and promises to provide insights into the early dynamical evolution of massive star clusters. This is crucial to understand more extreme and distant starburst clusters, which contribute to a significant fraction of all current star formation in the Local Universe, in particular in interacting galaxies. The majority of this thesis is based on multi-epoch spectroscopic observations in and around R136 obtained as part of the VLT-FLAMES Tarantula Survey (VFTS), an ambitious programme which targeted nearly 1 000 massive stars in the intricate 30 Doradus star-forming region. The motivations and observing strategy of this survey, designed to address key questions about the evolution of massive stars and clusters, are first introduced. The data reduction procedures applied to VFTS data are described, with an emphasis on the tasks accomplished in the context of this thesis. The VFTS data are first used to perform a detailed kinematic study of R136, determine its dynamical state, and evaluate the importance of gas expulsion in the early evolution of massive star clusters. Orbital motions of binary stars are found to dominate the line- of-sight velocity dispersion of the cluster, illustrating the risk of interpreting velocity dispersion measurements for unresolved extragalactic young massive clusters. However, once the detected binaries are rejected and the contribution of undetected binaries is accounted for through Monte Carlo simulations, the true velocity dispersion of the cluster is found to be low and consistent with it being in virial equilibrium. This suggests that gas expulsion has not had a dramatic effect on the early dynamical evolution of R136. Using the velocity measurements of R136 as a test case, a maximum likelihood method that fits the velocity dispersion of a cluster from a single epoch of radial velocity data is then tested. The method must be applied with care given the high binary fraction of massive stars and the large uncertainties in their binary orbital parameter distributions, but for typical velocity dispersions of young massive clusters (& 4 kms−1), it is shown that the velocity dispersion can be measured with an accuracy of 40% or better. This offers an efficient way of constraining the dynamics of these systems. The radial velocity measurements of apparently single stars in R136 are also used to investigate the internal rotation of the cluster, a potentially important but largely unexplored characteristic of young clusters. Evidence is found, at the 95% confidence level, for rotation of the cluster as a whole. A simple maximum likelihood method is presented to fit rotation curves to the data, from which a typical rotational velocity of 3 kms−1 is found. When compared to the low velocity dispersion of R136, this suggests that star clusters may form with as much as 20% of their kinetic energy in rotation. Finally, a smaller-scale survey of massive stars in the Wing of the Small Magellanic Cloud is introduced. As an example of the particularly interesting massive binaries that can be revealed by the synergy between large optical spectroscopic surveys of young clusters and observations at other wavelengths, the discovery of a new Be/X-ray pulsar binary and associated supernova remnant is reported. With a long spin period of over 1 000 seconds and a young age of 104 years constrained by its association with the supernova remnant, the pulsar in this system is quickly emerging as a unique object that challenges our understanding of the spin evolution of accreting neutron stars.

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McIntosh, Daniel Howard. « A search for young lenticular galaxies in nearby rich clusters ». Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/290434.

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We present a data base of U,V photometric and structural properties for 642 spectroscopically confirmed members, V-band selected to Mᵥ = -18 mag, from three local Abell clusters: A85 (z = 0.055), A496 (z = 0.033) and A754 (z = 0.055). From our (U - V) half-light aperture colors and total model V-band magnitudes we construct precise color-magnitude diagrams for member galaxies out to ≳1 h⁻¹ Mpc. We measure well-defined color-magnitude relations (CMR) with low intrinsic scatter (σCMR ∼ 0.06-0.09 mag) in the cluster cores ( < 0.5h⁻¹ Mpc). We define three galaxy populations based on the relative color difference Δ(U - V) between the galaxies color and the best-fit CMR: (1) red sequence galaxies with Δ( U - V) ≥ -2σ(CMR); (2) intermediately blue (≡ bS0) galaxies with -2σ(CMR) > Δ(U - V) > -0.425 mag; and (3) blue (Butcher-Oemler ≡ B-O) galaxies with Δ( U - V) ≤ -0.425 mag. These color-magnitude cuts provide a rough galaxy age segregation assuming blueward deviations from the CMR represent mean stellar age differences. Red sequence members are the traditional cluster old, early-types (E/S0) and B-O galaxies have spiral-like colors; therefore, the bS0 population are assumed to be intermediate in age. We find a significant (∼10% in numbers) population of bS0 members in two local clusters (A85 and A754) . This is the first evidence for a quantitatively classified population of bS0 galaxies in clusters at < 1 Gyr look-back time. The bS0 populations exhibit the following characteristics: (1) Bulge-to-total morphologies intermediate between red sequence and B-O members. (2) Less morphological structure associated with star formation compared to normal, field spirals. (3) bS0 members are not found near the cluster cores which suggests more recent infall. (4) Lack of a significant color gradient which is different from both the cluster red sequence and field spirals. The observed bS0 properties are consistent with these galaxies being present-day examples midway through the predicted evolution of infalling, field spiral to red, cluster S0 via galaxy harassment and/or ram-pressure stripping. Therefore, the existence of these galaxies provides clear observational evidence for the present-day whereabouts of the blue galaxies once prevalent in rich clusters (the B-O effect) and for environmental based evolution of the cluster galaxy membership.

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Perina, Sibilla <1970&gt. « Young and old star clusters in M31 : an HST view ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2851/1/perina_sibilla_tesi.pdf.

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Perina, Sibilla <1970&gt. « Young and old star clusters in M31 : an HST view ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2851/.

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Oh, Seungkyung [Verfasser]. « The Dynamical Ejections of Massive Stars from Young Star Clusters / Seungkyung Oh ». Bonn : Universitäts- und Landesbibliothek Bonn, 2017. http://d-nb.info/1139048805/34.

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Moll, Sarah Lorraine. « Properties of young massive clusters in nearby galaxies from high-resolution spectroscopy ». Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500160.

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Luhman, Kevin Lee 1971. « Low-mass star formation and the initial mass function in young clusters ». Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/288884.

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I have used optical and near-infrared spectroscopy and imaging to measure spectral types and luminosities for young (τ < 10 Myr), embedded (Aᵥ = 0-50), low-mass (0.1-1 M(⊙)) stars in three nearby (d < 300 pc) clusters: L1495E, IC 348, and ρ Ophiuchi. In conjunction with theoretical evolutionary tracks, I have derived the star formation history and initial mass function for each stellar population. A large number of brown dwarf candidates have been identified in the photometry, several of which are confirmed through spectroscopy. Finally, I have measured the frequency and survival times of circumstellar disks and investigated the photometric and spectroscopic properties of protostars. In § 2, I apply observational tests to the available sets of evolutionary models for low-mass stars, concluding that the calculations of D'Antona & Mazzitelli are preferred for the range of masses and ages considered here. In § 3 and § 4, I examine in detail the spectroscopic characteristics and substellar nature of two brown dwarf candidates. The study then expands to include the populations within the clusters L1495E (§ 5), IC 348 (§ 6), and ρ Ophiuchi (§ 7). In § 8, I briefly discuss the past, present, and future of scientific research related to this thesis.

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Fletcher, André B. (André Basil) 1965. « The nature and evolution of I. extragalactic radio sources, and II. young stellar clusters ». Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50332.

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Greissl, Julia. « Constraints on the Low-Mass IMF in Young Super-Star Clusters in Starburst Galaxies ». Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195926.

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As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions.Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way.We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. One cluster is young (< 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr - 18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. While the superposition of clusters does not allow us to place stringent constraints on the IMF there is no evidence of a low-mass cutoff in the cluster and the IMF is consistent with a Chabrier and Kroupa IMF typical of the field.The cluster in NGC 253 shows the same signs of youth as the cluster in NGC 4038/39 and sits in front of a background population of older stars. The background population has an age of $approx$ 12 Myr and thus contains red supergiants. After carefully subtracting this background we model the spectrum of the young cluster. We find that its IMF is consistent with a Chabrier and Kroupa IMF with a best-fit power-law slope of 1.0 in linear units. Slopes of 0.0 - 1.5 are also formally consistent with the cluster spectrum. We conclude that there is no strong evidence for an unusual IMF or a lack of low-mass stars (< 1 Msun) in either of these galaxies.

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Morales, Häfelin Esteban [Verfasser]. « Young stellar clusters throughout the Galaxy and the interaction with their molecular environment / Esteban Morales Häfelin ». Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1048616088/34.

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Evanko, Liberty Rae. « Development of an H alpha index for the detection of PMS candidates in young open clusters / ». Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1715.pdf.

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Randriamanakoto, Rojovola Zara-Nomena. « Formation of young massive star clusters : a high-resolution multi-wavelength study of intensely star-formation galaxies ». Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15766.

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Super star clusters (SSCs) represent the youngest and most massive form of known gravitationally bound star clusters in the Universe. They are born abundantly in environments that trigger strong and violent star formation (SF) such as in galaxy mergers and interacting systems. SSCs are thus used as fundamental tools to understand the context of massive SF and galaxy evolution in general. This thesis investigates properties of these young, massive and dense star clusters in a sample of 42 nearby starbursts and luminous infrared galaxies (LIRGs) ...

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Pooley, David Aaron 1976. « Very old and very young compact objects : X-ray studies of galactic globular clusters and recent core-collapse supernovae ». Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29309.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2003.
Includes bibliographical references.
This thesis comprises the results of two distinct areas of research, namely, X-ray studies of Galactic globular clusters and X-ray studies of recent core collapse supernovae. My analyses of the Chandra X-ray Observatory observations of the globular clusters NGC 6752 and NGC 6440 revealed as many low-luminosity X-ray sources as was in the entire census of globular cluster sources with the previous best X-ray imaging instrument, Rontgensatellit. In the observation of NGC 6752, I detect 6 X-ray sources within the 10':5 core radius and 13 more within the 115" half-mass radius down to a limiting luminosity of Lx = 1030 ergs s-l for cluster sources. Based on a reanalysis of archival data from the Hubble Space Telescope and the Australia Telescope Compact Array, I make 12 optical identifications and one radio identification. Based on X-ray and optical properties of the identifications, I find 10 likely cataclysmic variables (CVs), 1-3 likely RS CVn or BY Dra systems, and 1 or 2 possible background objects. Of the 7 sources for which no optical identifications were made, one was detected in the archival radio data, and another was found to be a millisecond pulsar. Of the remaining sources, I expect that 2-4 are background objects and that the rest are either CVs or millisecond pulsars whose radio emission has not been detected. These and other Chandra results on globular clusters indicate that the dozens of CVs per cluster expected by theoretical arguments are being found. The findings to date also suggest that the ratio of CVs to other types of X-ray sources is remarkably similar in clusters of very different structural parameters.
(cont.) In the observation of NGC 6440, I detect 24 sources to a limiting luminosity of 2 x 1031 ergs s-1 (0.5-2.5 keV) inside the cluster's half-mass radius, all of which lie within 2 core radii of the cluster center. I also find excess emission in and around the core which could be due to unresolved point sources. Based upon X-ray luminosities and colors, I conclude that there are 4-5 likely quiescent low-mass X-ray binaries and that most of the other sources are cataclysmic variables. I compare these results to Chandra results from other globular clusters and find the X-ray luminosity functions differ among the clusters. Observations of the Type II-P (plateau) Supernova (SN) 1999em and Type IIn (narrow emission line) SN 1998S have enabled estimation of the profile of the SN ejecta, the structure of the circumstellar medium (CSM) established by the pre-SN stellar wind, and the nature of the shock interaction. SN 1999em is the first Type II-P detected at both X-ray and radio wavelengths. It is the least radio luminous and one of the least X-ray luminous SNe ever detected (except for the unusual and very close SN 1987A). My analysis of the Chandra X-ray data indicate non-radiative interaction of SN ejecta with a power-law density profile ... for a pre-SN wind with a low mass-loss rate of ... for a wind velocity of 10 km s-1, in agreement with radio mass-loss rate estimates. The Chandra data show an unexpected, temporary rise in the 0.4-2.0 keV X-ray flux at 100 days after explosion. My analysis of SN 1998S yielded the first X-ray spectrum of a supernova in which numerous heavy element emission features (Ne, Al, Si, S, Ar, Fe) were present ...
by David Aaron Pooley.
Ph.D.

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Laugalys, Vygandas. « Young stars and interstellar extinction in the North America and Pelican nebulae ». Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2009~D_20100401_123143-10518.

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A Milky Way region in the direction of the North America and Pelican Nebulae is investigated using CCD photometry of 2600 stars in the Vilnius seven-color system. Its central part was covered with a CCD camera on the Maksutov wide-field telescope of the Moletai Observatory. Deeper CCD exposures for most interesting selected targets were taken with the 1 m telescope of the USNO Flagstaff Station. The author developed a new method for CCD data processing trying to reduce systematic errors and to increase photometric accuracy. This allowed us to measure M67 stars with high precision and use it as a CCD standard region in all our subsequent observations. To investigate interstellar extinction law in the area we obtained spectra for 33 B-type stars with the 2.3 m telescope of Steward Observatory at Kitt Peak. We also used near-infrared 2MASS data and other data sources when they were available. From photometric results in the Vilnius system we determined two-dimensional spectral types, color excesses, interstellar extinctions and distances of ~1300 stars. For more accurate determination of open cluster ages we recalibrated the zero-age main sequence in absolute magnitude vs. color diagram of the Vilnius system. We also investigated the possible connection between two open clusters in the area and surrounding star-forming region. Young stellar objects and possible ionizing sources of the NAP gas clouds were identified.
Naudojant CCD fotometriją, ištirta Paukščių Tako sritis Šiaurės Amerikos ir Pelikano ūkų kryptimi. Vilniaus fotometrinėje sistemoje išmatuota 2600 žvaigždžių. Didesnė sritis, apimanti abu ūkus ir tarp jų esantį dulkių debesį L935 buvo eksponuojama Molėtų observatorijos plataus lauko Maksutovo sistemos teleskopu. Mažesnės sritys, turinčios svarbių objektų, buvo eksponuojamos JAV laivyno observatorijos Flagstafo stoties 1 m. teleskopu. Autorius sukūrė metodiką. kaip ženkiai sumažinti sistematines redukcijos paklaidas ir padidinti CCD fotometrijos tikslumą. Tiksliai išmatuoti CCD fotometriniai standartai padrikąjame spiečiuje M67 bus naudojami tolimesniuose stebėjimuose. Ekstinkcijos dėsnio tyrimui buvo gauti 33 O-B žvaigždžių spektrai Stiuarto observatorijos 2.3 m teleskopu. Taip pat buvo panaudota 2MASS infraraudonosios fotometrijos katalogas ir kiti duomenys. Iš CCD ekspozicijų Vilniaus sistemoje fotometrijos daugumai fotometruotų žvaigždžių nustatyta: spektrinė ir šviesio klasė (MK sistemoje), spalvos ekscesas, tarpžvaigždinė ekstinkcija ir nuotolis. Tikslesniam padrikųjų spiečių amžiaus nustatymui iš naujo sukalibruota nulinio amžiaus pagrindinė seka Vilniaus fotometrinėje sistemoje. Ištirti du padrikieji žvaigždžių spiečiai esantys Šiaurės Amerikos ūko kryptimi ir patikrintas jų ryšys su aplinkine žvaigždėdaros sritimi. Aptikta apie 30 jaunų emisinių žvaigždžių ir 4 ar 5 žvaigždės, kurios galėtų būti ūkų jonizacijos šaltiniai.

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44

jackson, Richard. « Observing the effects of rotation, magnetic activity and starspots on the structure of low mass stars in young open clusters ». Thesis, Keele University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.530777.

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45

O'Dell, Mark Anthony. « Rotation-activity-age in young solar-mass stars from a study of the open clusters surrounding #alpha# Persei and #xi# Sculptoris ». Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260906.

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46

Kaczmarek, Thomas [Verfasser], Susanne [Akademischer Betreuer] Pfalzner et Joachim [Akademischer Betreuer] Krug. « The Evolution of Binary Populations in Young Star Clusters : From the ONC to OB associations / Thomas Kaczmarek. Gutachter : Susanne Pfalzner ; Joachim Krug ». Köln : Universitäts- und Stadtbibliothek Köln, 2012. http://d-nb.info/1038380618/34.

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47

King, Robert R. « Low-mass stars and brown dwarfs : optical/infrared photometry and spectroscopy of low-mass stars and brown dwarfs in the Field and Young Clusters ». Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/97095.

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In this thesis I will present optical and near-infrared photometric and spectroscopic observations of an evolved field brown dwarf binary pair and of populations of low-mass stars in high-mass young stellar clusters and will compare them to stellar and substellar theoretical model predictions. Epsilon Indi Ba and Bb are the closest known brown dwarfs to the Earth, and, as such, make possible a concerted observational campaign to obtain a complete characterisation of two intermediate-age T dwarfs. Although some recent observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, there have been few conclusive tests to date. I will present high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R~5000) spectroscopy of these two T dwarfs. Using these data I have derived luminosities of log L/Lsun = -4.699 +/- 0.017 and -5.232 +/- 0.020 for Epsilon Indi Ba, Bb, respectively, and I will show that the predictions of substellar evolutionary models using luminosity and mass constraints are inconsistent with the effective temperatures and surface gravities derived from fitting atmospheric models to observed spectra. Furthermore, I will show that, even where estimates of the effective temperature, surface gravity, and luminosity are available, estimates of the mass of cool brown dwarfs can be up to a factor of two lower than the measured dynamical mass. Considering the difficulty in assigning accurate ages to any system and the mass-luminosity-age degeneracy of brown dwarfs, I would caution against the over-analysis of predicted brown dwarf masses at this time. I have also used Chandra X-ray observations to identify near-complete and relatively unbiased samples of pre-main-sequence stars in the young stellar clusters NGC 2244 and Trumpler 14. Using optical photometric and spectroscopic observations, I will characterise the apparent age spreads seen in the cluster pre-main-sequences. Mass estimates will then be derived for their stellar populations and used to construct the initial mass function for each cluster. It is found that NGC 2244 appears to have a Salpeter-like IMF for stars in the mass range 0.5--2.0 Msun if a likely age of 2 Myr is adopted, while Tr 14 may have a top-heavy IMF at a similar age. However, I will show that because the observed slopes of the cluster pre-main-sequences are not well-matched by the predicted slope in colour-magnitude space, such determinations are heavily dependent on the assumed age of the cluster and complicated due to the large spreads in isochronal ages.

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48

Laugalys, Vygandas. « Jaunos žvaigždės ir tarpžvaigždinė ekstinkcija Šiaurės Amerikos ir Pelikano debesyse ». Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2009~D_20100401_123158-02686.

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Naudojant CCD fotometriją, ištirta Paukščių Tako sritis Šiaurės Amerikos ir Pelikano ūkų kryptimi. Vilniaus fotometrinėje sistemoje išmatuota 2600 žvaigždžių. Didesnė sritis, apimanti abu ūkus ir tarp jų esantį dulkių debesį L935 buvo eksponuojama Molėtų observatorijos plataus lauko Maksutovo sistemos teleskopu. Mažesnės sritys, turinčios svarbių objektų, buvo eksponuojamos JAV laivyno observatorijos Flagstafo stoties 1 m. teleskopu. Autorius sukūrė metodiką. kaip ženkiai sumažinti sistematines redukcijos paklaidas ir padidinti CCD fotometrijos tikslumą. Tiksliai išmatuoti CCD fotometriniai standartai padrikąjame spiečiuje M67 bus naudojami tolimesniuose stebėjimuose. Ekstinkcijos dėsnio tyrimui buvo gauti 33 O-B žvaigždžių spektrai Stiuarto observatorijos 2.3 m teleskopu. Taip pat buvo panaudota 2MASS infraraudonosios fotometrijos katalogas ir kiti duomenys. Iš CCD ekspozicijų Vilniaus sistemoje fotometrijos daugumai fotometruotų žvaigždžių nustatyta: spektrinė ir šviesio klasė (MK sistemoje), spalvos ekscesas, tarpžvaigždinė ekstinkcija ir nuotolis. Tikslesniam padrikųjų spiečių amžiaus nustatymui iš naujo sukalibruota nulinio amžiaus pagrindinė seka Vilniaus fotometrinėje sistemoje. Ištirti du padrikieji žvaigždžių spiečiai esantys Šiaurės Amerikos ūko kryptimi ir patikrintas jų ryšys su aplinkine žvaigždėdaros sritimi. Aptikta apie 30 jaunų emisinių žvaigždžių ir 4 ar 5 žvaigždės, kurios galėtų būti ūkų jonizacijos šaltiniai.
A Milky Way region in the direction of the North America and Pelican Nebulae is investigated using CCD photometry of 2600 stars in the Vilnius seven-color system. Its central part was covered with a CCD camera on the Maksutov wide-field telescope of the Moletai Observatory. Deeper CCD exposures for most interesting selected targets were taken with the 1 m telescope of the USNO Flagstaff Station. The author developed a new method for CCD data processing trying to reduce systematic errors and to increase photometric accuracy. This allowed us to measure M67 stars with high precision and use it as a CCD standard region in all our subsequent observations. To investigate interstellar extinction law in the area we obtained spectra for 33 B-type stars with the 2.3 m telescope of Steward Observatory at Kitt Peak. We also used near-infrared 2MASS data and other data sources when they were available. From photometric results in the Vilnius system we determined two-dimensional spectral types, color excesses, interstellar extinctions and distances of ~1300 stars. For more accurate determination of open cluster ages we recalibrated the zero-age main sequence in absolute magnitude vs. color diagram of the Vilnius system. We also investigated the possible connection between two open clusters in the area and surrounding star-forming region. Young stellar objects and possible ionizing sources of the NAP gas clouds were identified.

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49

Ohlendorf, Henrike [Verfasser], et Thomas [Akademischer Betreuer] Preibisch. « Young stars in the Carina Nebula Complex : Clusters, jets and indications for triggered star formation observed in the mid-infrared with the Spitzer Space Telescope / Henrike Ohlendorf. Betreuer : Thomas Preibisch ». München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1050647858/34.

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50

Wittwer, Rico. « Zwangsmobilität und Verkehrsmittelorientierung junger Erwachsener ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-158952.

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In der Mobilitätsforschung entstand in den vergangenen Jahrzehnten eine breite Wissensbasis für das Verständnis von Verkehrsursachen und Zusammenhängen, die das Verkehrsverhalten determinieren. Mit der Entwicklung von Verkehrsmodellen lag das Forschungsinteresse zunächst primär bei Ökonomen und Ökonometrikern sowie Verkehrsingenieuren. Bald kamen andere Wissenschaftsbereiche wie die Psychologie oder die Geowissenschaften hinzu, welche sich in der Folge zunehmend mit dem Thema Mobilität befassten und die zur Erklärung des menschlichen Verhaltens ganz unterschiedliche Methoden und Maßstäbe nutzten. Heute versuchen zumeist handlungsorientierte Ansätze, auf Individualebene, Faktoren zu bestimmen, die Aufschluss über die Verhaltensvariabilität in der Bevölkerung geben und damit einen möglichst großen Beitrag zur Varianzaufklärung leisten. Werden Einflussfaktoren in geeigneter Weise identifiziert und quantifiziert, können Defizite und Chancen erkannt und das Verhalten steuernde Maßnahmen entworfen werden. Mit deren Hilfe wird ungewollten Entwicklungen entgegengesteuert. Junge Erwachsene stellen aufgrund ihrer sehr unterschiedlichen Phasen im Lebenszyklus, z. B. gerade anstehender oder abgeschlossener Ausbildung, Umzug in eine eigene Wohnung, Familiengründung, Neuorientierung in Arbeitsroutinen oder das Einleben in ein anderes Lebensumfeld einer fremden Stadt, intuitiv eine sehr heterogene Gruppe dar. Die Modellierung des Verhaltens ist für diese Altersgruppe besonders schwierig. Aus der Komplexität dieser Problemstellung heraus ist ersichtlich, dass fundierte Analysen zur Mobilität junger Erwachsener notwendig sind, um verkehrsplanerische Defizite aufzudecken und Chancen zu erkennen. Der methodische Schwerpunkt des Beitrages liegt auf der Bildung einer Typologie des Verkehrsverhaltens junger Erwachsener. Die verwendete Datengrundlage ist das „Deutsche Mobilitätspanel – MOP“. Dabei wird der Versuch unternommen, zunächst Variablen aller relevanten Dimensionen des handlungsorientierten, aktivitätsbasierten Verkehrsverhaltens zusammenzustellen und für eine entsprechende Analyse aufzubereiten. Im Anschluss werden geeignete und in den Sozialwissenschaften erprobte Verfahren zur Ähnlichkeitsmessung eingesetzt, um möglichst verhaltensähnliche Personen zu typologisieren. Im Weiteren finden konfirmatorische Analysetechniken Anwendung, mit deren Hilfe Verhaltenshintergründe erklärt und inferenzstatistisch geprüft werden. Als Ergebnis wird eine clusteranalytische Typologisierung vorgestellt, die im Anschluss anhand soziodemografischer Indikatoren und raumstruktureller Kriterien der Lagegunst beschrieben wird. Aufgrund der gewonnenen Erkenntnisse können objektive und im Idealfall quantifizierbare, d. h. prognosefähige Merkmale zur Bildung verkehrssoziologischer und weitgehend verhaltensähnlicher Personengruppen genutzt werden
Over the last few decades of mobility research, a wide base of knowledge for understanding travel determinants and causal relationships in mobility behavior has been established. The development of travel models was at first of interest primarily to economists and econometricians as well as transportation engineers. They were soon joined by other scientific areas such as psychology or the geosciences, which as a result increasingly addressed the theme of mobility and used quite different methodologies and criteria for explaining human behavior. Today, activity-oriented approaches generally attempt to determine individual-level factors that provide information on behavioral variability within the population, thereby contributing greatly to explaining variances. If explanatory factors can be properly identified and quantified, then deficiencies and opportunities can be recognized and measures for influencing behavior can be conceptualized. With their help, undesirable developments can be avoided. Because of their highly differing stages in life, e.g. upcoming or recently completed education, moving into their own apartment, starting a family, becoming oriented in a work routine or adapting to a new environment in a different city, young adults are intuitively a very heterogeneous group. Modeling the behavior of this age group is particularly difficult. This problem makes it clear that founded analysis of the mobility of young adults is necessary in order to recognize deficiencies and opportunities in transportation planning. The methodological focus of this work is on creating a typology of young adults’ travel behavior. The base data is from the “Deutsches Mobilitätspanel – MOP” (German Mobility Panel). An attempt is made to gather and prepare all relevant dimensions of decision-oriented, activity-based travel behavior for a corresponding analysis. Afterward, appropriate and proven methods from the social sciences are used to test for similarity in order to identify groups of persons which are as behaviorally homogeneous as possible. In addition, confirmatory data analysis is utilized which helps explain and test, through inferential statistics, determinants of behavior. The resulting typology from the cluster analysis is presented and followed by a description using sociodemographic indicators and spatial criteria of accessibility. The findings make it possible to use objective and, ideally, quantifiable and therefore forecastable characteristics for identifying sociological population groups within which similar travel behavior is displayed

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