Dissertations / Theses on the topic 'Magellanic Clouds'
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1
Ye, Taisheng. "Nebulae in the Magellanic clouds." Thesis, The University of Sydney, 1988. https://hdl.handle.net/2123/26240.
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In this thesis I am primarily concerned with radio observations of the nebulae in the Magellanic Clouds, with particular emphasis on the regions of ionised gas in the Small Magellanic Cloud (SMC).
Nebulae (Latin for ‘clouds’) are luminous fuzzy celestial objects with diverse size, shape and brightness. After several generations of observational and theoretical work, nebulae have been classified into four categories: external galaxies, H II regions, supernova remnants (SNRs) and planetary nebulae (PN). External galaxies are no longer regarded as true nebulae. H II regions are ionised hydrogen and are excited by the intense ultraviolet radiation of central or nearby hot stars. A planetary nebula is an extended, low density envelope which has expanded outward from a red giant star at a late stage in its evolution. SNRs are formed by the high velocity and high temperature material ejected when a star ends its life with a violent explosion.
The current matters of interest in nebulae research concentrate on their classification and evolution, and their relation to the interstellar medium and to nucleosynthesis in their parent galaxies. Specifically, many investigations are directed toward the measurements of physical parameters such as electron temperature, density and elemental abundances, the morphologies of individual nebulae, spatial distributions of each type of nebula in galaxies, the number counts of sources within different luminosity ranges (the luminosity functions) and within different diameter ranges (diameter functions), the global absorption, scattering or reflection by dust (extinction) inside or outside of a nebula and the extinction distribution over a nebula.
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Danforth, Charles Weston. "Interstellar matter kinematics in the magellanic clouds." Available to US Hopkins community, 2003. http://wwwlib.umi.com/dissertations/dlnow/3080648.
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Hatano, H., R. Kadowaki, D. Kato, S. Sato, and the IRSF/SIRIUS group. "IRSF/SIRIUS near-infrared survey of the Magellanic Clouds: triggered star formation in N11 in the Large Magellanic Cloud." Cambridge University Press, 2006. http://hdl.handle.net/2237/10293.
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Hunter, Ian Kennedy. "Evolution of massive stars in the Magellanic clouds." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492010.
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Rotation and the associated mixing has recently been included in massive star evolutionary models in an attempt to reconcile theory with observation, e.g surface abundance anomalies, such as nitrogen enrichments. However, despite the apparent importance of rotation there have been few observational tests, specifically in regard to fast rotating stars. This thesis presents the analysis of the Magellanic Cloud B-type stars from the 'The VLT-FLAMES survey of massive stars'. Atmospheric paramaters and rotational velocities have been estimated for rv400 objects, with chemical compositions being derived for over half this sample. This represents the largest homogenous survey undertaken to date. Comparison of the rotational velocity distributions in the SMC, LMC and our Galaxy reveals that objects at low metallicity typically rotate faster as predicted. Additionally the velocity distributions imply that the end of the core-hydrogen burning phase needs to be extended in current theoretical models. The present-day chemical compositions of the Magellanic Clouds have been derived, demonstrating that simply scaling the solar composition is not appropriate for all elements. Additionally chemical compositions have been estimated for a broad range of rotational velocities and hence are ideal for exploring the theory of rotational mixing. In the SMC and LMC both an excess of nitrogen enriched core hydrogen burning slowly rotating objects and highly enriched supergiants are observed. Additionally a group of LMC objects near the end of core-hydrogen burning with large rotational velocities and little enrichment has been identified. These observations are all incompatible with currently adopted rotational mixing theories. The work in this thesis highlights the need for examining entire populations of objects in order to make meaningful and robust comparisons with theory as well as providing a significant advance in our knowledge of massive star evolution.
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Nidever, David L., Knut Olsen, Alistair R. Walker, A. Katherina Vivas, Robert D. Blum, Catherine Kaleida, Yumi Choi, et al. "SMASH: Survey of the MAgellanic Stellar History." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626050.
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The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg2 (distributed over similar to 2400 square degrees at similar to 20% filling factor) to similar to 24th. mag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is similar to 15 mas and the accuracy is similar to 2 mas with respect to the Gaia reference frame. The photometric precision is similar to 0.5%-0.7% in griz and similar to 1% in u with a calibration accuracy of similar to 1.3% in all bands. The median 5s point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R. similar to. 18.4 kpc. SMASH DR1 contains measurements of similar to 100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.
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Bitsakis, Theodoros, R. A. González-Lópezlira, P. Bonfini, G. Bruzual, G. Maravelias, D. Zaritsky, S. Charlot, and V. H. Ramírez-Siordia. "The Distribution and Ages of Star Clusters in the Small Magellanic Cloud: Constraints on the Interaction History of the Magellanic Clouds." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626531.
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We present a new study of the spatial distribution and ages of the star clusters in the Small Magellanic Cloud (SMC). To detect and estimate the ages of the star clusters we rely on the new fully automated method developed by Bitsakis et al. Our code detects 1319 star clusters in the central 18 deg(2) of the SMC we surveyed (1108 of which have never been reported before). The age distribution of those clusters suggests enhanced cluster formation around 240 Myr ago. It also implies significant differences in the cluster distribution of the bar with respect to the rest of the galaxy, with the younger clusters being predominantly located in the bar. Having used the same setup, and data from the same surveys as for our previous study of the LMC, we are able to robustly compare the cluster properties between the two galaxies. Our results suggest that the bulk of the clusters in both galaxies were formed approximately 300 Myr ago, probably during a direct collision between the two galaxies. On the other hand, the locations of the young (<= 50 Myr) clusters in both Magellanic Clouds, found where their bars join the H I arms, suggest that cluster formation in those regions is a result of internal dynamical processes. Finally, we discuss the potential causes of the apparent outside-in quenching of cluster formation that we observe in the SMC. Our findings are consistent with an evolutionary scheme where the interactions between the Magellanic Clouds constitute the major mechanism driving their overall evolution.
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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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Amy, Shaun Wallace. "A Radio Study of Selected Regions in the Magellanic Clouds." Thesis, The University of Sydney, 2000. http://hdl.handle.net/2123/358.
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The Magellanic Clouds have long provided a rich celestial laboratory for many astrophysical research programmes. Their location relatively close to the Earth and away from the plane of our Galaxy has made them a natural target for Southern Hemisphere ground-based instrumentation. Likewise, the continuing quest for images of the Clouds with higher dynamic range and improved angular resolution has driven a continual improvement in instrumentation across a range of wavelength bands. The cornerstone of this thesis is a study of selected sources in the Magellanic Clouds. The sample was chosen from the 843MHz Molonglo Observatory Synthesis Telescope survey of the Clouds, based on the existing knowledge of each source, its flux density and angular extent. This sample was used to explore observational and analysis techniques with the Australia Telescope Compact Array in order to better determine the nature of these objects and to identify those sources worthy of further study. This work highlights many pertinent issues associated with the correct classification of sources when only a limited amount of data is available. These issues led directly to the development of a more systematic approach in the classification of the Large Magellanic Cloud source sample, detailed for the first time in this thesis. Two supernova remnants in the Small Magellanic Cloud were studied in detail. The Australia Telescope images of 1E0102.2-7219 revealed, for the first time, the radio structure of this young oxygen-rich supernova remnant, and allowed a detailed comparison with existing optical and X-ray data to be undertaken. The comparisons presented in this thesis and in an earlier publication have prompted exciting new X-ray observations at unprecedented angular resolution. The second, 0101-7226, studied as part of an international collaboration, has a shell morphology at radio wavelengths but no associated X-ray emission and is therefore something of an enigma.
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Amy, Shaun Wallace. "A Radio Study of Selected Regions in the Magellanic Clouds." University of Sydney. Physics, 2000. http://hdl.handle.net/2123/358.
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The Magellanic Clouds have long provided a rich celestial laboratory for many astrophysical research programmes. Their location relatively close to the Earth and away from the plane of our Galaxy has made them a natural target for Southern Hemisphere ground-based instrumentation. Likewise, the continuing quest for images of the Clouds with higher dynamic range and improved angular resolution has driven a continual improvement in instrumentation across a range of wavelength bands. The cornerstone of this thesis is a study of selected sources in the Magellanic Clouds. The sample was chosen from the 843MHz Molonglo Observatory Synthesis Telescope survey of the Clouds, based on the existing knowledge of each source, its flux density and angular extent. This sample was used to explore observational and analysis techniques with the Australia Telescope Compact Array in order to better determine the nature of these objects and to identify those sources worthy of further study. This work highlights many pertinent issues associated with the correct classification of sources when only a limited amount of data is available. These issues led directly to the development of a more systematic approach in the classification of the Large Magellanic Cloud source sample, detailed for the first time in this thesis. Two supernova remnants in the Small Magellanic Cloud were studied in detail. The Australia Telescope images of 1E0102.2-7219 revealed, for the first time, the radio structure of this young oxygen-rich supernova remnant, and allowed a detailed comparison with existing optical and X-ray data to be undertaken. The comparisons presented in this thesis and in an earlier publication have prompted exciting new X-ray observations at unprecedented angular resolution. The second, 0101-7226, studied as part of an international collaboration, has a shell morphology at radio wavelengths but no associated X-ray emission and is therefore something of an enigma.
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Stanimirović, Snežana. "The complex nature of the ISM in the SMC : an HI and infrared study /." View thesis, 1999. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20030826.143835/index.html.
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Thesis (PhD) -- University of Western Sydney, Nepean, 1999."A thesis submitted for the degree of Doctor of Philosophy at the University of Western Sydney Nepean" "July, 1999" Bibliography : p. 177-185.
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Pieres, A., B. X. Santiago, A. Drlica-Wagner, K. Bechtol, R. P. van der Marel, G. Besla, N. F. Martin, et al. "A stellar overdensity associated with the Small Magellanic Cloud." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/624062.
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We report the discovery of a stellar overdensity 8 degrees north of the centre of the Small Magellanic Cloud (SMC; Small Magellanic Cloud Northern Over-Density; SMCNOD), using data from the first 2 yr of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarily composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of similar to 6 degrees x 2 degrees. It has an absolute magnitude of M-V congruent to -7.7, r(h) = 2.1 kpc, and mu v(r < r(h)) = 31.2 mag arcsec(-2). We estimate a stellar mass of similar to 10(5) M-circle dot, following a Kroupa mass function. The SMCNOD was probably removed from the SMC disc by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent Large Magellanic Cloud-SMC encounters. This scenario is supported by the lack of significant H-1 gas. Other potential scenarios for the SMCNOD origin are a transient overdensity within the SMC tidal radius or a primordial SMC satellite in advanced stage of disruption.
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Nishiuchi, Mamiko. "X-ray study of Hot Plasmas in the Large Magellanic Cloud in the Magellanic Clouds - evolution from supernova remnants toward interstellar matter." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150823.
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Stroud, Larreal Vanessa Eva. "Massive binaries and be stars in galaxy & magellanic clouds." Thesis, Open University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534382.
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Mao, Sui Ann. "Magnetic Fields in the Milky Way and the Magellanic Clouds." Thesis, Harvard University, 2011. http://dissertations.umi.com/gsas.harvard:10017.
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This thesis is an observational investigation into the origin of large-scale coherent magnetic fields in the Milky Way and the Magellanic Clouds. I use Faraday rotation measure of both polarized extragalactic sources and that derived from diffuse polarized synchrotron emission as probes of interstellar magnetism. Rotation measure uniquely provides the magnetic field direction in the diffuse interstellar medium, which cannot be achieved using other observing techniques. Using extragalactic source rotation measures behind the Small Magellanic Cloud (SMC), I find a large-scale coherent magnetic field in this irregular galaxy, where the classic dynamo effect is expected to be weak. I suggest that the cosmic-ray driven dynamo, which relies heavily on cosmic ray pressure to generate poloidal fields could be in operation. By analyzing rotation measures derived from diffuse polarized emission from the Large Magellanic Cloud (LMC) simultaneously with rotation measures of 100 extragalactic sources behind it, I conclude that the LMC has a quadrupolar-type magnetic field structure, in accord with predictions from dynamo theories. However, the field amplification time scale of a classic dynamo is too long compared to frequent tidal-triggered star forming episodes experienced by the LMC which can prevent any large-scale coherent field from building up. I propose that the cosmic-ray driven dynamo, which has a much shorter amplification time scale than the classic dynamo, could be the origin of the observed coherent fields in the LMC. The dynamo theory predicts a symmetric vertical magnetic field across the galactic disk for Milky Way-type galaxies. However, based on rotation measures of 1,000 extragalactic sources toward the Galactic poles, I find a lack of vertical field symmetry across the Galactic mid-plane. I suggest that the observed RMs could be the superposition of a symmetric disk field and an anti-symmetric field produced by a separate dynamo effect in the Galactic halo. Furthermore, I demonstrate that existing Galactic halo magnetic field models cannot successfully reproduce extragalactic rotation measures at mid-Galactic latitudes in the second Galactic quadrant. I propose that halo fields consist of magnetic spirals could potentially account for the observed RM pattern.Astronomy
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Edge, William Raymond Tarratt. "Studies of Be X-ray binaries in the Magellanic Clouds." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420195.
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Monk, David James. "A spectroscopic study of Planetary Nebulae in the Magellanic Clouds." Thesis, University College London (University of London), 1986. http://discovery.ucl.ac.uk/10041868/.
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Spectroscopic data for 74 Planetary Nebulae (PN) in the Large and Small Magellanic Clouds (LMC and SMC) have been analysed. The optical line fluxes have been used to determine the nebular temperatures and densities, and the abundances of He, N, 0, Ne, and Ar, relative to H. In the sample the analogues of Galactic PN are found: there are 5 (and possibly 10) He- and N-rich nebulae resembling Peimbert's Type I PN, 6 objects with low oxygen abundance, analogous to the PN of the Galactic Halo, 5 very-low-excitation (VLE) nebulae, and 5 PN central stars with Wolf-Rayet WC class features. Mean abundances are calculated for each cloud, from the nebulae not in the Type I, 'low-oxygen', or VLE groups, and are compared with the average abundances for Galactic PN, and H II regions in the Galaxy, the LMC, and the SMC. The comparison shows a significant enhancement of He and N in the LMC and SMC PN, with respect to LMC and SMC H II regions, whilst oxygen, neon, and argon abundances are similar in PN and H II regions within each galaxy. The central star luminosities and HI Zanstra temperatures are derived for 19 objects within the survey, and are compared to the evolutionary tracks for PN central stars of Schonberner (1979,1983). The comparison shows good agreement between theory and observation for most objects, although the high luminosity of LMC N201 (27502 L0 )places it a long way above the tracks. Of the six MC PN with low oxygen abundances two, LMC N25 and LMC N199, also have very low ionic helium abundances, and central star temperatures at which only a small contribution from neutral helium would be expected (40000 - 45000 K). LMC N25 is studied in more detail through the analysis of recent IPCS spectra.
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Chevance, Mélanie. "Physical processes in the interstellar medium of the Magellanic Clouds." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC242/document.
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Le milieu interstellaire (MIS) joue un rôle important dans l'évolution des galaxies. Les radiations et vents stellaires, ainsi que les supernovae par exemple, sont à l'origine de nombreux processus ayant un impact sur les propriétés globales des galaxies. Cependant, l'efficacité des ces processus est liée aux propriétés et à la structure des différentes phases du MIS, et est souvent incertaine. Grace à la sensibilité et résolution accrues des nouveaux télescopes observant dans l'infrarouge lointain (FIR) et le submillimetrique (comme par exemple le Herschel Space Observatory, SOFIA et ALMA), il est désormais possible d'étudier en détail les interactions réciproques entre la formation stellaire et les différentes phases du MIS environnant. Ce travail est axé sur les propriétés physiques du gaz dans les Nuages de Magellan. Le Grand Nuage de Magellan et le Petit Nuage de Magellan, nos plus proches voisins, tout deux à métallicité sub-solaire, sont de bons laboratoires pour étudier les interactions entre la formation stellaire et l'environnement. La région 30 Doradus, dans le Grand Nuage de Magellan, l'une des plus massives et des plus actives régions de formation stellaire connues dans notre voisinage, est étudiée en détail. Les observations des télescopes spatiaux Herschel et Spitzer sont utilisées pour contraindre la pression, le champ de radiation ainsi que la structure tri-dimensionnelle des régions de photo-dissociation (PDR), en combinaison avec le code PDR de Meudon. Cette modélisation permet également d'estimer la fraction de gaz moléculaire qui n'est pas détectée par le traceur généralement utilisé CO. Cette méthode est ensuite appliquée à d'autres régions de formation stellaire dans les Nuages de Magellan, présentant différents environnements. Cette étude permet d'évaluer les diagnostiques clés du chauffage et du refroidissement du gaz à faible métallicité dans des régions actives de formation stellaire, avec une bonne résolution spatiale. Ceci constitue une première étape pour mieux comprendre les observations non résolues de telles régions dans des galaxies lointainesThe interstellar medium (ISM) plays a major role in galaxy evolution. Feedback from stars, in particular, drives several processes responsible for the global properties of a galaxy. However, the efficiency of these processes is related to the properties and structure of the different gas and dust ISM phases and remains uncertain. Due to the increased sensitivity and resolution of the new far-infrared (FIR) and submillimeter facilities (such as the Herschel Space Observatory, SOFIA and ALMA, in particular), it now becomes possible to study in detail the interplay between star formation and the surrounding ISM phases. This work focuses on the physical properties of the gas in the Magellanic Clouds. The Large Magellanic Cloud and the Small Magellanic Cloud, our closest neighbors, both at subsolar metallicity, are good laboratories to study the interaction between star formation and environment.The 30 Doradus region, in the Large Magellanic Cloud, one of the most massive and active star forming region known in our neighborhood, is first studied in detail. We use the FIR and mid-infrared tracers, provided by the space telescopes Herschel and Spitzer, to bring constrains on the pressure, radiation field and 3D structure of the photo-dissociation regions (PDR) in this extreme region, using the Meudon PDR code. This modeling allows us to estimate the fraction of molecular gas not traced by CO, also known as the "CO-dark" molecular gas.We apply this method to other star forming regions of the Magellanic Clouds, which are characterized by different environmental conditions. This study allows us to evaluate key diagnostics of the gas heating and cooling of low metallicity resolved starburst regions. This is a first step toward understanding similar but unresolved regions, in high-redshift galaxies
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Woollands, Robyn. "Photometric Analysis of R Coronae Borealis stars in the Magellanic Clouds." Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/1876.
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This thesis presents the initiation of a multi-site photometric programme to examine the extraordinary behaviour displayed by 18 R Coronae Borealis (RCB) stars in the Magellanic Clouds (MCs). RCB stars exhibit a unique variability whereby they undergo rapid declines of up to several magnitudes. The decline may take several weeks, whereas the recovery to maximum light may take months or even years. The accepted wisdom for the cause of these enigmatic declines is a phenomenon whereby dust formed in the stellar environment reduces the brightness by as much as eight magnitudes (Clayton 1996). This is followed by the recovery phase during which the dust becomes homogeneously distributed in the stellar environment. The monitoring programme comprised the collection of UBVRI photometric data using five telescopes located at three different southern hemisphere longitudes (Las Campanas Observatory in Chile, Mount John University Observatory (MJUO) in New Zealand and the Southern African Large Telescope (SALT) in South Africa). The Optical Gravitational Lensing Experiment (OGLE), that operates at Las Campanas Observatory, provided the longest extent of data (December 1994 to February 2008). This was supplemented by data collected with telescopes at MJUO (September 2007 to January 2008) and SALTICAM on SALT (October 2007 to February 2008). Data calibration across the five instruments was a key element of the analysis, and entailed the use of F116 (an F region standard star) and other tertiary standards. Two important RCB characteristics, the enigmatic declines and the pulsational variability, form the bulk of the analysis presented in this thesis. Examination of the data acquired in the V and I filters resulted in the identification of a total of 18 RCB declines occurring in four stars (three stars in the Large Magellanic Cloud (LMC) and one in the Small Magellanic Cloud (SMC)). Construction of colour-magnitude diagrams (V −I vs V ), during the recovery to maximum light were undertaken in order to study the unique colour behaviour associated with the RCB declines. The combined recovery slope for the four stars was determined to be [(delta V)/(delta(V −I))] = 3.37 ± 0.24, which is similar to the value of [(delta V)/(delta(V −I))] = 3.1 ± 0.1 calculated for galactic RCB stars (Skuljan et al. 2003). In addition, the slopes calculated for the stars in the LMC ([(delta V)/(delta(V −I))]LMC = 3.34 ± 0.21) and SMC ([(delta V)/(delta((V −I))]SMC = 3.21 ± 0.22) alone, also agree to within their uncertainty. These results may imply that the nature of the dust (i.e. the particle size) is similar in both our Galaxy and the MCs. The pulsation analysis focused on the identification of pulsation periods in nine RCB stars in the MCs. Two different methods, Fourier analysis and dominant period subtraction, were employed for this purpose. Periodic variations are apparent in these stars, and for the majority, a period of around 40 days (common in RCB stars, Lawson et al. 1990, 1994) was detected using the second identification method. In the future, frequent data collection over several years, and more sophisticated pulsation identification techniques, will increase the probability of extracting individual periods from the complex RCB light curves.
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Olsen, Knut A. G. "The formation and evolution of the large magellanic cloud from selected clusters and star fields /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/5426.
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Sasaki, Manami. "X-rays tracing the star formation history of the Magellanic clouds." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=964798824.
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Sasaki, Manami. "X-rays tracing the star formation history of the Magellanic clouds." Diss., lmu, 2002. http://nbn-resolving.de/urn:nbn:de:bvb:19-4438.
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Iping, R. C., G. Sonneborn, D. L. Massa, D. Gies, and S. Williams. "Far-ultraviolet spectroscopy of O+O binaries in the Magellanic Clouds." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1789/.
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We report FUSE observations in 2005–2006 of three O-type, double-lined spectroscopic binaries in the Magellanic Clouds. The systems have very short periods (1.4–2.25 d), represent rare, young evolutionary stages of massive stars and binaries, and provide a unique glimpse at some of the most massive systems that form in dense clusters of massive stars. Improved orbit parameters, including revised masses, for LH54-425 are derived from new ctio spectroscopy. The systems are: LH54-425 in the LMC (O3V + O5V, P=2.25d, 62+37M⊙), J053441-693139 in the LMC (O2-3If+O6V, P=1.4 d, 41+27M⊙), and Hodge 53-47 in the SMC (O6V + O4-5IIIf, P=2.2 d, 24+14M⊙, where the O4 star appears to be less massive than the O6 star). Their short periods indicates that wind interaction and mass transfer are likely important factors in their evolution. The spectra provide quantitative and systematic studies of phase-dependent stellar wind properties, wind collision effects in O+O binaries at lower metallicities, improved radial velocity curves, and FUV spectro-photometric changes as a function of orbital phase.
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Hayashi, Ichizou. "Systematic X-ray Spectroscopy of Supernova Remnants in the Magellanic Clouds." 京都大学 (Kyoto University), 1997. http://hdl.handle.net/2433/202434.
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范改玲 and Gailing Fan. "Galaxy radio pulsar population modelling and magellanic clouds radio pulsar survey." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243058.
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Verdugo, Salgado Celia Anahi. "Submillimeter studies of cold gas and dust in the Magellanic Clouds." Tesis, Universidad de Chile, 2012. http://www.repositorio.uchile.cl/handle/2250/111317.
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Magíster en Ciencias, Mención AstronomíaPresentamos datos a 870 mu obtenidos con el telescopio APEX en la SMC, LMC y puente Magallanico, obteniendo imagenes con 22 .4'' de resolucion para 9 nubes moleculares gigantes. Usamos estos datos en combinacion con observaciones de Spitzer (SAGE) y Herschel (HERITAGE) para construir distribuciones de energia espectral (SEDs) y ajustar una ley de cuerpo negro modificada simple, a fin de determinar temperaturas de polvo, indices de emisividad espectral y opacidades de polvo. Encontramos valores promedios de temperaturas de polvo de 22, 24 y 19 K para la LMC, SMC y puente Magallanico respectivamente, y para los indices de emisividad espectral estos resultados fueron 1.7, 1.6 y 1.7. Encontramos opacidades de polvo promedio a 870 mu de 9, 4 y 2 x10^5 para la LMC, SMC y puente Magallanico respectivamente. De las SEDs encontramos un claro exceso de emision a 870 mu con respecto a la ley de cuerpo negro modificada. Para la LMC, estos excesos variaron de 0.3 a 3 veces lo que habia sido predicho por la ley de cuerpo negro modificada a 870 mu, y de 1.3 a 2.5 veces para la SMC. El puente Magallanico reporto el exceso mas alto con un factor de 9. Con el proposito de entender este exceso de emision a 870 mu, realizamos un analisis de tres partes con los resultados que se obtienen a partir de la emision a 870 mu: la emisividad del polvo, la masa de gas y la razon de gas-a-polvo. Usando datos complementarios de CO determinamos densidades de columna de hidrogeno a partir de masas viriales, y junto con las opacidades de polvo obtenidas de los ajustes, calculamos emisividades de polvo por columna de gas, permitiendonos determinar masas de gas y polvo a partir de la emision milimetrica a 870 mu. Estas emisividades de polvo resultaron mayores que el valor Galactico de Boulanger et al. (1996), indicando una mayor emisividad del polvo o que la aproximacion virial estaria equivocada. Adicionalmente, calculamos masas de gas a partir de la emision milimetrica usando el valor de emisividad de Bot et al. (2010), el cual es un valor Galactico correguido por metalicidad, y las comparamos con las masas viriales obtenidas a partir de los datos complementarios de CO. Obtuvimos masas milimetricas de gas mayores que las masas viriales en un factor de 2-14 en la LMC, 2-6 en la SMC y 100 en el puente Magallanico. Esto nuevamente indica que la aproximacion virial estaria equivocada, por lo tanto no estaria trazando toda la masa de gas, o que la emisividad a 870 mu es mas alta, produciendo una sobrestimacion de la masa de gas a partir de la emision milimetrica. Finalmente, usamos masas de polvo obtenidas a partir de la emision milimetrica usando el resultado de emisividad de Bot et al. (2010), y las masas de gas a partir de los datos de CO y la aproximacion virial para determinar razones de gas-a-polvo. Obtuvimos valores mas altos que el Galactico (~100), indicando menores cantidades de polvo en relacion al gas que en nuestra Galaxia. Esto muestra la dificultad en explicar el exceso de emision a 870 mu como una componente en masa en estos sistemas de bajo contenido de polvo, y tal vez seria la emisividad del polvo que es distinta a 870 mu y que produce este exceso de emision.
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Rajoelimanana, Andry Fitiavana. "Long-term properties of X-ray binaries in the magellanic clouds." Doctoral thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/4405.
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Includes abstractIncludes bibliographical references.
Long-term variability in all types of X-ray binaries is a well established characteristic, but due to observation limitations and lack of long-term monitoring capability these variations have not been studied before in a systematic way. In this thesis, we exploit the ~ 16 yr optical light curves from the MACHO and OGLE databases, and combine these with archival XMM-Newton X-ray observations to study the long-term properties of Be/X-ray binaries and Supersoft X-ray Sources in the Magellanic Clouds.
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Richter, Philipp. "FUV absorption spectroscopy of interstellar molecular hydrogen towards the Magellanic clouds /." Aachen : Shaker, 1999. http://catalogue.bnf.fr/ark:/12148/cb37739235j.
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Dissertation--Mathematisch-Naturwissenschaftliche Fakultät--Bonn--Rheinische Friedrich-Wilhelms-Universität, 1999. Titre de soutenance : FUV spectroscopy of interstellar molecular hydrogen towards the Magellanic clouds.FUV = far ultraviolet. Bibliogr. p. 83-85.
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Fan, Gailing. "Galaxy radio pulsar population modelling and magellanic clouds radio pulsar survey /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25059294.
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Bagheri, Gemma Louise. "The tidal features of the Magellanic Cloud System." Thesis, University of Hertfordshire, 2014. http://hdl.handle.net/2299/13890.
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The Magellanic System at a distance of 50 kpc from the Milky Way (MW), is a prime target in the study of stellar populations, star formation histories and galactic dynamics in low metallicity environments. The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) have been observed in great depth, however there has been somewhat less interest in the Magellanic Bridge connecting the two and only more recently has the interest surged in the Magellanic Stream, which trails the Clouds between them and the MW. The Magellanic Bridge has a known younger stellar population dating back to Irwin’s observations (Irwin et al., 1990), only more recently has an older population been confirmed in the Bridge by Bagheri et al. (2013) and No¨el et al. (2013), while the Magellanic Stream is known to contain gas only with no stellar component. The estimated ages of the Bridge and Stream are 200 Myr (Bekki, 2007) and 2 Gyr (Diaz and Bekki, 2012) respectively, with the postulated Bridge formation from a tidal interaction between the Clouds. The formation of the Stream is less well understood with different models using varying assumptions and parameters such as Besla et al. (2012) and Nidever et al. (2010), including possibilities that the Clouds were historically bound or un-bound, and that the MW may or may not have been involved in the Stream formation. The work in this thesis makes use of different methods of removing the Galactic foreground population in the direction of the Magellanic Bridge and Stream to create cleaned catalogues of these regions. Various methods of analysis are applied to the cleaned catalogues in this work to identify stellar populations in the Bridge and Stream and density variations in the Bridge, including the production of CMDs and two-colour diagrams, fitting isochrones to the observational data, creating stellar density maps and studying spatial variations. This work contains the first published confirmation that the Bridge contains an older population of stars from public catalogues, which is supported with observations of the older population in recent deeper surveys, and confirmed with spectroscopic follow up observations. The young population has ages within the age of the Bridge ( 200 − 500 Myr) and are likely to have formed in-situ, in regions of high density gas closest to the SMC. The number of young blue objects in the Bridge tiles is greater towards the SMC and decreases towards the LMC. Populations identified here reach ages up to 3 Gyr are likely to have been drawn into the Bridge from the Clouds at formation. The key results from this work are that an older Bridge stellar population has been identified and confirmed, indicating that stars as well as gas were drawn into the Bridge at its creation. The fact that the younger population has the highest density away from the main concentration of hydrogen show that the gas within the Bridge has been displaced by ram pressure, most likely due to the Clouds moving through the Galactic halo. Less concrete results in this work reveal a puzzling populetion of objects within the Magellanic Stream, which could be stellar in nature and with follow up work, could be the first observation of Stream objects. This work contributes to our understanding of the interaction between the LMC and SMC via the Stellar populations between them.
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曾梓豪 and Tsz-ho Tsang. "Survey of supersoft and quasisoft X-ray sources in the Magellanic Clouds with XMM-Newton and Chandra." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hdl.handle.net/10722/193077.
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Supersoft and quasisoft X-ray sources are collectively known as Very Soft X-ray Sources (VSSs) characterized by their considerably lower effective temperatures than normal X-ray emitting objects and the lack of significant emission above 1 keV, with measured temperatures ranging from about tens to less than about 300 eV, respectively. They are defined observationally and believed to be associated with a wide variety of astrophysical systems such as white dwarfs, neutron stars, and black holes.
VSSs have been identified in our own Galaxy, the Magellanic Clouds, and other external galaxies. Due to the vicinity of the Magellanic Clouds and the low associated absorption of soft X-ray photons, they are unique in the studies of VSSs. However, no attempt has been made to search for VSSs and investigate the source population in the Magellanic Clouds using all the available archival data. A systematic survey of VSSs in the Magellanic Clouds was therefore performed using data from both XMM-Newton and Chandra. VSSs were identified by selection algorithim based on X-ray hardness ratio after the background galaxies and foreground stars were filtered. A total of 47 new supersoft and 75 new quasisoft candidates were identified. Six of them were strong enough for spectral analysis with derived temperatures of 15 – 250 eV and luminosities of of 3.5 ×?10?^34– 5.4 ×?10?^36 erg s^(-1). The softest and brightest candidate represents a promising supersoft candidate with a possible UV counterpart identified with XMM-Newton Optical Monitor having an estimated UV luminosity of ~2.7 ×?10?^35 erg s^(-1). The large dataset also allows the long-term studies of some of the previously identified supersoft X-ray sources. Through the comprehensive survey with multi-epoch data, an X-ray/UV stellar flare was discovered and its analysis is also reported.published_or_final_version
Physics
Master
Master of Philosophy
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Stevens, James Bernard. "The circumstellar environments of Be stars in X-ray binaries." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327609.
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Crawford, T. M., R. Chown, G. P. Holder, K. A. Aird, B. A. Benson, L. E. Bleem, J. E. Carlstrom, et al. "MAPS OF THE MAGELLANIC CLOUDS FROM COMBINED SOUTH POLE TELESCOPE AND PLANCK DATA." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622699.
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We present maps of the Large and Small Magellanic Clouds from combined South Pole Telescope (SPT) and Planck data. The Planck satellite observes in nine bands, while the SPT data used in this work were taken with the three-band SPT-SZ camera, The SPT-SZ bands correspond closely to three of the nine Planck bands, namely those centered at 1.4, 2.1, and 3.0 mm. The angular resolution of the Planck data ranges from 5 to 10 arcmin, while the SPT resolution ranges from 1.0 to 1.7 arcmin. The combined maps take advantage of the high resolution of the SPT data and the long-timescale stability of the space-based Planck observations to deliver robust brightness measurements on scales from the size of the maps down to similar to 1 arcmin. In each band, we first calibrate and color-correct the SPT data to match the Planck data, then we use noise estimates from each instrument and knowledge of each instrument's beam to make the inverse-variance-weighted combination of the two instruments' data as a function of angular scale. We create maps assuming a range of underlying emission spectra and at a range of final resolutions. We perform several consistency tests on the combined maps and estimate the expected noise in measurements of features in them. We compare maps from this work to those from the Herschel HERITAGE survey, finding general consistency between the data sets. All data products described in this paper are available for download from the NASA Legacy Archive for Microwave Background Data Analysis server.
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Connors, Timothy W. "High resolution simulations of galactic cannibalism." Swinburne Research Bank, 2008. http://hdl.handle.net/1959.3/44962.
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Thesis (PhD) - Swinburne University of Technology, 2008.A dissertation presented in fulfillment of the requirements for the degree of Doctor of Philosophy, Swinburne University of Technology - 2008. Typescript. Bibliography: p. 133-145.
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Ferreira, Elisa Merkel. "Star formation in the Magellanic Clouds based on 1.2 mm continuum observations." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972090940.
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Bond, Ian Anthony. "Study of the magellanic clouds and other southern objects at TeV energies." Thesis, University of Auckland, 1991. http://hdl.handle.net/2292/2447.
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The results of observational studies of very high energy (VHE) and ultra high energy (UHE) gamma ray emission, by various astrophysical objects, made from 1988 to 1990 with the JANZOS Cerenkov facility are presented. The active galaxy Cen A and the Galactic X-ray binary systems Vela X-1, Cen X-3, and Cir X-1 were monitored for VHE gamma ray emission above 1 TeV. No evidence was found for persistent or episodic emission from any of these objects. Upper limits on the VHE fluxes above 1 TeV of 2.1×10-11, 2.7×10-11, 3.6×10-11 and 3.5×10-11 cm-2 s-1 respectively were obtained for these objects. These limits are consistent with previous observations made by other groups. Various objects in the Magellanic Clouds were monitored for UHE gamma ray emission using the Cerenkov technique at large zenith angles. This technique has been found to be more sensitive at UHE energies -100 TeV than the conventional air shower technique. During 1990 the equipment was modified to allow a sky coverage of 7°×23° at large zenith angles. This enabled most of the extent of the Large Magellanic Cloud to be surveyed at UHE energies. An examination of the UHE database yielded no evidence for persistent emission from SN1987A and selected X-ray pulsars in the Magellanic Clouds. Upper limits on the UHE fluxes (in cm-2s-1) above the given threshold energies were obtained as follows: SMC X-1, 2.4×10-13 (>30 TeV); SN1987A, 2.3×10-13 (>65 TeV); PSR0540-693, 2.3×10-13(>65 TeV); LMC Trans, 1.5×10-13(>130 TeV); LMC X-4, 1.3×l0-l3 (>140 TeV). Evidence was found for two episodes of pulsed gamma ray emission above 65 TeV from SN1987A. On the nights of May 28 and June 23, 1990, a periodicity search using the Rayleigh test showed significant power at 18.356 ms. This is near a periodicity reported at optical wavelengths in September, 1990. The chance probability for the individual period was about 10-6 on each of the two nights. Excess events of the order of 1σ were also seen on these nights. The overall chance probability, allowing for all degrees of freedom, was found to be 0.1%. Evidence was also found for a single episode of gamma ray emission above 140 TeV from LMC X-4 on May 27, 1990. Excess events were seen with a statistical significance of 2.4 σ. A periodicity test showed maximum Rayleigh power at 13.488 s on this night. The chance probability for the individual period was 8×10-3 and the overall chance probability was found to be 0.5%. Adopting a recent estimate of the pulsar population in the Large Magellanic Cloud, an upper bound of 3×1034 erg s-1 on the luminosity of an average pulsar, at energies >65 TeV, was obtained.
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Dias, Bruno Moreira de Souza. "Formation and evolution of globular clusters in the Galaxy and Magellanic Clouds." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-26082014-090039/.
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Globular clusters are tracers of the formation and evolution of their host galaxies. Kinematics, chemical abundances, age and position of the clusters allows tracing interactions between Milky Way and surrounding galaxies and outlines their chemical enrichment history. In this thesis we analyse mid-resolution spectra of about 800 red giant stars in 51 Galactic globular clusters. It is the first time that [Fe/H] and [Mg/Fe] derived in a consistent way are published for such a huge sample of globular clusters, almost 1/3 of the total number of catalogued clusters. Our metallicities are showed to be more precise than previous works based on mid-resolution spectroscopy. A turnover at [Fe/H] ~ -1.0 is found in the plot [Fe/H] vs. [Mg/Fe] for bulge and halo, although bulge seems to have a more metal-rich turnover, i.e, bulge has more efficient formation than the halo. Comparing the abundances with age the timescale for SNIa to start to become important is 1Gyr. [Fe/H] vs. age corroborates the different star formation efficiency of bulge and halo while [Mg/Fe] does not follow that. Halo was formed in mini halos or dwarf galaxies, and two multiple population clusters had their origin analysed to check it. M 22 seems to have been formed in the Milky Way while NGC 5824 possibly was originated in a dwarf galaxy, although our results are inconclusive for NGC 5824. The Galactic bulge seems to have been formed fast i.e., probably the oldest globular cluster is there. In fact HP 1 has a bluer horizontal branch than expected for its metallicity and we interpret that as an age effect. We determine its distance using light curves of variable stars in order to constrain future age determinations via colour-magnitude diagram. Finally, we investigate interaction between Milky Way and its neighbour galaxy SMC. We find that some star clusters are being stripped out of the SMC main body, which is consistent with tidal stripping scenario for the interaction between the galaxies, instead of ram pressure that would only affect gas.Aglomerados globulares são traçadores da formação e evolução de suas galáxias. Cinemática, abundâncias químicas, idades e posições dos aglomerados permitem traçar interações entre Via Láctea e galáxias vizinhas e suas histórias de enriquecimento químico. Nesta tese analisamos espectros de média resolução de mais de 800 estrelas gigantes vermelhas em 51 aglomerados globulares Galácticos. É a primeira vez que [Fe/H] and [Mg/Fe] determinados de modo consistente são publicados para uma amostra desse porte, ~1/3 dos objetos catalogados. Nossas metalicidades são mais precisas que trabalhos anteriores similares. Uma quebra em [Fe/H] ~ -1.0 é encontrada no gráfico [Fe/H] vs. [Mg/Fe] para o bojo e halo, embora bojo parece ter uma quebra em [Fe/H] maior, i.e, bojo tem formaçãao mais eficiente que o halo. Comparando abundâncias com idade, a escala de tempo para SNIa ficar importante é 1Gano. [Fe/H] vs. idade corrobora diferentes eficiências de formação do bojo e halo, mas [Mg/Fe] vs. idade não mostra isso. O halo foi formado em mini halos ou galáxias anãs, e dois aglomerados com dispersão em [Fe/H] tiveram suas origens analisadas. M 22 parece ter sido formado na Via Láctea e NGC 5824 possivelmente foi originado em uma galáxia anã, embora os resultados são inconclusivos para NGC 5824. O bojo parece ter sido formado rapidamente e deve possuir o aglomerado mais velho. De fato, HP 1 tem um ramo horizontal mais azul que o esperado para sua metalicidade e vemos isso como um efeito da idade. Determinamos sua distância usando curvas de luz de RR Lyrae de maneira a restringir futuras determinações de idade via diagrama cor-magnitude. Finalmente, investigamos a interação entre Via Láctea e sua galáxia vizinha SMC. Encontramos aglomerados sendo removidos do corpo central da SMC, consistente com cenário de remoção por força de maré para a interação entre as galáxias, em vez de ``ram pressure\'\' que afeta só gás.
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Ward, Jacob L. "High-resolution studies of massive young stellar objects in the Magellanic Clouds." Thesis, Keele University, 2017. http://eprints.keele.ac.uk/3562/.
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This thesis presents sub-arcsecond resolution observations of massive Young Stellar Objects (YSOs) in two satellite galaxies of the Milky Way, the Magellanic Clouds. With metallicities of »0.5 and »0.2 Z¯ for the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), respectively the Magellanic Clouds present a unique opportunity to study star formation in environments which differ significantly from those of our own Galaxy. 19 targets in the SMC and 3 targets in the Hii region LHA 120-N113 in the LMC were observed with the near-infrared integral field spectrograph SINFONI at the VLT. Archival SINFONI data towards 7 targets in the Tarantula nebula in the LMC were also obtained. These observations reveal a wide variety of spatially extended emission line morphologies, indicative of outflows and compact Hii regions. Additionally, the most direct indications to date for the presence of discs in massive YSOs in the Magellanic Clouds are presented. Previously obtained optical spectra towards massive YSOs in the SMC have been analysed, as well as newly obtained spectra using the Robert Stobie Spectrograph (RSS) at the Southern African Large Telescope (SALT). Fabry-Perot interferometric observations obtained with RSS at SALT towards two star forming Hii regions in the Magellanic Clouds, are also presented, along with a new Fabry-Perot data reduction pipeline. Through analysis of the optical spectra in the context of the SINFONI data the massive YSOs in the SMC appear to reside in a porous ISM, allowing a large mean-free-path for energetic photons. Through a comparison of massive YSOs in the Magellanic Clouds and a previously obtained Galactic sample, evidence of significantly enhanced accretion rates towards the YSOs in the Magellanic Clouds is detected. Whilst the underlying mechanism of this enhancement is uncertain, there appears to be a convincing correlation between metallicity and accretion rates in massive YSOs.
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Minelli, Alice <1994>. "Chemical composition of Milky Way satellites: Magellanic Clouds and Sagittarius dwarf galaxy." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10313/1/PhDThesis_AliceMinelli.pdf.
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This PhD project is aimed at investigating the chemical composition of the stellar populations in the closest satellites of the Milky Way (MW), namely the Large and Small Magellanic Cloud (LMC and SMC, respectively) and the remnant of the Sagittarius (Sgr) dwarf spheroidal galaxy. Their proximity allows us to resolve their individual stars both with spectroscopy and photometry, studying in detail the characteristics of their stellar populations. All these objects are interacting galaxies: LMC and SMC are in an early stage of a minor merger event, and Sgr is being disrupted by the tidal field of the MW. There is a plenty of literature regarding the chemical composition of these systems, however, the extension of these galaxies prevents a complete and homogeneous analysis.
Therefore, we homogeneously analysed stellar spectra belonging to MW and its
satellites galaxies and we derived their chemical compositions. We highlighted the importance of a homogeneous analysis in the comparison among different galaxies or different samples, to avoid systematics due to different methods or physical assumptions.
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Loon, Jacobus Theodorus van. "Mass loss and evolution of asymptotic giant branch stars in the Magellanic Clouds." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 1999. http://dare.uva.nl/document/91817.
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Rubele, Stefano. "The Star Formation History of the Magellanic Clouds from HST and VISTA data." Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3422855.
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This thesis presents a study of the Star Formation History on the Magellanic
Clouds using HST and VISTA data.
Chapter 2 introduces the VMC survey and then describes the observing strategy and first observations, the data reduction steps for producing images and catalogs for individual observations. Than present a description of the subsequent stages of reduction for deep and linked observations and presents the archival procedures.
In chapter 3 as part of the preparation for the VMC survey, we aim to access the accuracy in the Star Formation History (SFH) that can be expected from VMC data, in particular for the Large Magellanic Cloud (LMC). We first simulate VMC images containing LMC stellar populations and the foreground Milky Way (MW) stars and background galaxies. We then evaluate the expected errors in the recovered star formation rate as a function of stellar age, SFR(t), starting from models with a known Age–Metallicity Relation (AMR).
In chapter 4 we applied to the NGC 419 SMC star cluster data the classical
method of star formation history (SFH) recovery via CMD reconstruction, deriving for the first time this function for a star cluster with multiple turn-offs. The values for the cluster metallicity, reddening, distance and binary fraction, were varied within the limits allowed by present observations. Star formation is found to last for at least 700 Myr, and to have a marked peak at the middle of this interval, for an age of 1.5 Gyr. Our findings argue in favour of multiple star formation episodes (or continued star formation) being at the origin of the multiple main sequence turn-offs in Magellanic Cloud clusters with ages around 1 Gyr.
In chapter 5 we studied the HST/ACS colour–magnitude diagrams (CMD) of the populous LMC star cluster NGC 1751 that present both a broad main sequence turn-off and a dual clump of red giants. We show that the latter feature is real and corresponds to the first appearance of electron-degeneracy in the H-exhausted cores of the cluster stars. We then apply to the NGC 1751 data the classical method of star formation history (SFH) recovery via CMD reconstruction.
After considering the random and systematic errors in the analysis, star formation in the cluster centre is found to last for a time span of 460 Myr.
In chapter 6 we present the preliminary results on the recovery of the SFH
with VISTA data of 3 LMC VMC (Cioni et al. 2010) fields located around the
LMC main body. Following the method described in Kerber et al. (2009a), Harris & Zaritsky (2004), Gallart et al. (1999) we evaluated the SFH deriving at the same time the Age Metallicity Relation AMR, the distance modulus (m− M)0 and the extinction AV . The comparison of ours results on the AV and (m− M)0 with Zaritsky et al. (2004) (for the AV ), Nikolaev et al. (2004), van der Marel & Cioni (2001b) and van der Marel et al. (2002) (for the (m− M)0 ) to the VMC field 8 3 show an agreement with this authors in all subregions analyzed.
Chapter 7 summarizes and comments the results obtained in this work.Questa tesi presenta uno studio sulla storia della formazione stellare delle nubi di Magellano usando dati osservati con i telescopi HST e VISTA. Il capitolo 2 introduce il programma osservativo VMC e ne descrive la strategia osservativa e i primi risultati, la riduzione dati e i passi fatti per produrre le immagini scientifiche finali e i relativi cataloghi. Il capitolo 3 presenta il lavoro di preparazine al programma VMC al fine di valutare l’accuratezza sulla ricostruzione della storia della formazione stellare (SFH) che ci si aspetta dai dati ottenuti con il telescopio VISTA nel caso della grande nube di Magellano (LMC). In questa parte della tesi sono state simulate le immagini del programma VMC nel caso della LMC contenenti tipiche popolazioni stellari osservate nella LMC, stelle appartenenti alla Via Lattea (MW) piu le galassie. In seguito sono stati analizzati gli errori dovuti al recupero della SFH in funzione dell’ eta , partendo da modelli con conosciuta relazione eta –metallicita (AMR). Nel capitolo 4 e stato applicato il metodo per il recupero della SFH attraverso il diagramma colore magnitudine all’ammasso NGC 419 nella SMC. E stato possibile derivare per la prima volta la SFH per un ammasso che presenta un turn-offs multiplo. Si sono potuti derivare inoltre la metallicit` , l’estinzione, il modulo di distanza e la frazione di binarie nei limiti degli errori stocastici e sistematici. Abbiamo valutato per questo ammasso un periodo prolungato di formazione stellare con ampiezza pari a 700 Myr, e con un picco di et` a 1.5 Gyr. I nostri risultati favoriscono l’idea che all’origine del turn-offs multiplo di sequenza principale in ammassi delle nubi di Magellano con eta vicine a 1 Gyr ci siano episodi di formazione stellari multipli. Nel capitolo 5 abbiamo studiato il diagramma colore–magnitudine (CMD) ottenuto utilizzando i dati HST/ACS dell’ammasso stellare NGC 1751 nella LMC, il quale presenta un turn-off di sequenza principale allargato ed un doppio clump per le giganti rosse. Abbiamo dimostrato che queste caratteristiche nel CMD si spiegano allo stesso modo di quanto fatto per l’ammasso NGC419 nel capitolo precedente. Applicando anche a questo ammasso il metodo per la ricostruzione della SFH via CMD abbimo valutato il tasso di formazione stellare in funzione del tempo trovando un’ampiezza pari a 460 Myr. Il capitolo 6 presnta i primi risultati sul recupero della SFH con dati VMC (Cioni et al. 2010) per 3 campi della LMC localizzati attorno alla parte centrale della galassia. Seguendo il metodo descritto nel capitolo 3, Harris & Zaritsky (2004), Gallart et al. (1999) abbiamo misurato la SFH e derivato contemporaneamente la relazione eta metallicita AMR, il modulo di distanza (m− M)0 e l’estinzione AV . Infine abbiamo confrontato i nostri risultati per AV e (m− M)0 con quelli ottenuti in Zaritsky et al. (2004) (per AV ), Nikolaev et al. (2004), van der Marel & Cioni (2001b) e van der Marel et al. (2002) (per (m− M)0 ). Per il campo 8 3 il confronto mostra un buon accordo nella gran parte delle aree considerate. In fine il capitolo 7 riassume e commenta tutte le parti affrontate in questo lavoro.
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Dunstall, Paul Robert. "Binarity and the B[e] phenomenon : investigating massive star populations in the Magellanic clouds." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601443.
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The body of this thesis looks at two large observational programmes: The VLT-FLAMES Survey of Massive Stars (VFSMS) and The VLT-FLAMES Tarantula Survey. The VFSMS aimed to advance the current understanding of massive star evolution by pressing the issue of rotational mixing for a sample of over 700 early type stars in the Galaxy and Magellanic Clouds. The YFTS is an extension of the VFSMS to study, in detail , the comparison of binary and single massive stars. A detailed investigation into several different massive star populations is given, from both the VFSMS and the VFTS. The work of the VFSMS is focused on a sample of 64 Be-type stars within the Magellanic Clouds . Atmospheric parameters and photospheric abundances have been used to show the Be-type star sample is inconsistent with stars rotating close to critical velocity. The VFTS investigates the number of B-type binary systems within the 30 Doradus region of the LMC, by using a cross correlations analysis technique. A binary fraction of 29% is determined from over 500 B-type stars, further refined to a true binary fraction of 66% by modelling the sample incompleteness. From the binary search, investigations are presented into three high radial velocity variable stellar objects. Firstly a study highlights the B[e] phenomenon through the analysis of the supergiant B[e ]-like binary, VFTS698. Secondly a detailed analysis of two Tare blue supergiant binary systems, VFTS450 and VFTS652 is undertaken. Finally consideration is given to the remaining B-type star samples of the VFTS that require further investigation, viz. the projected rotational velocity distribution of binaries, and the potential short-period binary systems.
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Bayne, Glenn. "Detection and CCD photometry of eclipsing binaries in the Large and Small Magellanic Clouds." Thesis, University of Canterbury. Physics and Astronomy, 2003. http://hdl.handle.net/10092/5577.
Full textAbstract:
Eclipsing binary stars allow the physics of the component stars to be studied. These systems can provide a wealth of knowledge ranging from fundamental parameters such as mass, radius, and luminosity through to tests of stellar evolution and distances to the systems.
A search for eclipsing binaries in the SMC using the MOA photometric time series database yielded 169 detections. These detections were cross-referenced with the OGLE catalogue of eclipsing binaries in the SMC. A total of 35 systems were new detections with most of these lying in the outer, less dense regions of the SMC, and some outside the OGLE fields. The remainder were within the overlap region of the fields of the two surveys. In the overlap region of the two MOA survey fields, 21 systems were detected but only 2 detections were common to both fields. This implies the MOA survey is far from complete. Additionally, 14 systems (~10%) were not detected by OGLE in the MOA-OGLE overlap region implying the OGLE survey is also not complete, though to a lesser extent. The unequivocal determination of whether all systems were real eclipsing binaries was not able to be made based on the photometric light curves alone. Objects for which there was some uncertainty concerning their true nature were indicated as such.
Two of the new detections in the MOA SMC catalogue were selected for follow-up photometry, MOA J005018.4-723855 and MOA J005623.5-722123. An LMC target was selected from the MACHO LMC catalogue, MACHO*05:36:48.7-69:17:00. Observations were made from MJUO in Strömgren u, Johnson VJ and Cousins IC filters between 1999 April and 2002 July. The McLellan 1-m telescope and CCD photometer head were used. Differential fluxes for the target stars were extracted using the ISIS-2.1 difference imaging package. To obtain flux changes with respect to a level of zero flux, DAOPHOT II was used to establish the targets' flux levels in the reference images relative to which ISIS-2.1 works.
The light curves were analysed using the Wilson synthetic light-curve code. It was not possible to make a definitive analysis of the physical nature of the three targets based on differential photometry alone. Nevertheless, it was possible to make rough estimates of the systems' apparent magnitudes and hence, via the known distance moduli and reddenings to the Magellanic Clouds, their absolute magnitudes. Coupled with additional constraints derived from Geneva models of stellar evolution for stars of reduced metallicity, it was possible to obtain astrophysically plausible parameters for the component stars comprising each target.
The LMC target MACHO*05:36:48.7-69:17:00 is located near the Tarantula nebula and very close to SN1987A. It is a well-detached, eccentric system, (e = 0.2) with a sidereal period of 3.853529 ± 0.000005d and an apsidal period of 100 ± 5 years. The difference in mean epochs for the VJ and u/IC observations resulted in an averaging of the solution parameters.
The most astrophysically plausible solution was obtained by matching the derived components to a pair of Geneva LMC models of identical age. This solution indicates a primary of ~20 Mסּ and secondary of ~14 Mסּ with a common age of 5 x 106 yr. Other parameters are mean effective temperatures Teff,1=33500K, Teff,2=29500K, semi-major axis a=33.3Rסּ , mean radii R1 /a = 0.21, R2/a = 0.15 and inclination i = 85.8º.
MOA J005018.4-723855 is a semi-detached system, period 1.839870 ± 0.000005d, with the secondary filling its Roche lobe and with the O'Connell effect evident in the light curve. Of the three systems, this is the most affected by blending. Third light was necessary to obtain satisfactory light-curve fits in all bandpasses. Light-curve solutions fix the mass ratio and suggest the system is undergoing case A mass transfer from the present secondary. Since the mass receptor in such a system may mimic a normal main-sequence star to within a factor of two in luminosity for a given mass and temperature, an estimate of the physical nature of this system was found by requiring the parameters to match those of a Geneva evolutionary model. This yielded M1 =13.5Mסּ), Teff,1=29000K, R1=5.9Rסּ), M2 =20.5 Mסּ), Teff,2=20000K, R2=8.5Rסּ), a=20.5 Rסּ) and i=77.6°.
MOA J005623.5-722123 is a detached system, period 2.32005 ± 0.00002d. Third light was necessary in the analysis of this star. Analysis of the derived solutions and comparison to the Geneva evolutionary models indicates a system 10 x 106 yr old. The most astrophysically plausible parameters for this system are M1 = 13.5 Mסּ), Teff,1 = 29 000K, R1 = 5.8 Rסּ), M2 = 15.5 Mסּ),
Teff,2=29350K, R1 =7.8 Rסּ), a=22.65 Rסּ) and i=87.8°. The preferred light curve solution gives a secondary marginally hotter than the primary, yet with shallower eclipse depths. The high inclination as well as the gravity brightening in B-stars are the cause of this. During the secondary eclipse, the primary's path passes across the cooler central region the secondary, thereby leaving the hotter poles exposed. This accounts for the higher hemisphere-averaged temperature in the solution.
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Pritchard, J. D. "CCD photometry of eclipsing binary star systems in the Large and Small Magellanic Clouds." Thesis, University of Canterbury. Physics and Astronomy, 1997. http://hdl.handle.net/10092/7938.
Full textAbstract:
Double lined, eclipsing binaries are an important probe of stellar structure and evolution. Their study provides the most accurate data on the defining fundamental properties of stars, namely stellar masses, radii and luminosities.
Observations made at the Mount John University Observatory (MJUO) have yielded high precision, six colour CCD light curves and calibrated standard system Strömgren uvby and Cousins VI photometry for three Magellanic Cloud eclipsing binaries; HV982 and HV2241 in the Large Magellanic Cloud (LMC) and HV 1620 in the Small Magellanic Cloud (SMC). The masses, radii and luminosities for HV 1620 and HV 2241 have been determined by analysis of the light curves and standard system photometry in conjunction with IUE ultraviolet spectrophotometry and spectroscopic radial velocity curves obtained by other investigators. The masses, radii and luminosities for HV 982 have been estimated in conjunction with IUE ultraviolet spectrophotometry by adopting a distance for the system. No spectroscopic radial-velocity curves are available for HV 982 at this time.
Analysis of the calibrated standard system photometry, light curves and IUE spectrophotometry for the well-detached, 5.55335 d period HV 982 permits the determination of the effective temperatures of the two components of HV 982; Teff,₁= 24 000 ± 5 000 K and 23 400 ± 5 000 K. The large uncertainties result from the poorly defined reddening which in turn is primarily due to large uncertainty in the (b-y) photometry resulting from observations obtained on only two nights, both of questionable quality. The fact that no spectroscopic radial-velocity curves are available means that neither the mass ratio nor the physical size of the system can be determined directly. The derived temperatures are nonetheless insensitive to reasonable ranges of the mass ratio (as deduced from the the form of the light curve) and of the physical size of the system (in order to be consistent with the distance to the LMC). Adopting a value of unity for the mass ratio and a distance modulus of (m- M)₀ = 18.35 ± 0.2mag allows the estimation of masses, radii and thus luminosities of the individual components of HV982. They are M₁ = M₂ = 9.1 ± 3.2M⊙, R₁ = R₂ = 7.0 ± 1.1 R⊙ and log[L₂/ L⊙] = 4.2±0.5, log[L₂/ L⊙ = 4.1±0.5. These properties correspond well to the expected properties of normal single stars as predicted by modern theoretical stellar evolution models. Moreover the position of the components of HV 982 in the Hertzsprung-Russell Diagram (HRD) implies the components are main sequence stars, although not far from the Terminal Age Main Sequence (TAMS), i.e. HV 982 is still relatively young, which is consistent with the fact that HV 982 is an eccentric orbit system. Apsidal motion with a period of 206±6 yr has also been discovered and an improved ephemeris, including the effects of the apsidal motion has been derived.
Combined analysis of the MJUO photometry and light curves, the IUE spectrophotometry and the published spectroscopic radial-velocity curves permits a complete analysis and direct determination of the properties of the 3.62642d period HV 1620. The analysis yields the following properties for the components of HV 1620: Teff,₁ = 33 000±4 500 K, M₁ = 20.9±0.4 M⊙, R₁ = 6.27±0.10 R⊙ and log[L₁/ L⊙] 4.62±0.25; Teff,₂ = 24 400±3 500 M₂ = 14.3±0. 7 ⊙, R₂ = 11.3±0.2 R₂ and log[L₂/ L⊙] 4.53±0.25. The system is found to be in a semi-detached configuration, with the cooler component filling its Roche lobe, while the hotter component is well-detached from its Roche lobe. Despite this evolved binary state, the properties of both components correspond well to those of normal single stars, implying that any mass transfer currently in progress is occuring at a rate slow enough that both components can retain at least the appearance of normal single stars. Comparison of the the observed spectral flux distribution with model flux distributions also yields the distance modulus, (m M)₀ = 18.6±0.3 mag, which is in agreement with other measurements of the distance modulus for the SMC. An improved ephemeris has been determined.
Similarly, the combined analysis of the MJUO photometry and light curves, the IUE spectrophotometry and the published spectroscopic radial-velocity curves permits a complete analysis and direct determination of the properties of the 4.3426241 d period HV 2241. The effective temperatures, masses, radii and luminosities of the components of HV 2241 are Teff,₁ = 27 000±3 000 K, M₁ = 36.82±0.10 M⊙, R₁ 16.1±0.2 R⊙ and log[L₁/L⊙] = 5.10±0.20 and Teff,₂ = 20200±1500K, M₂ = 19.4±0.6M⊙, :R₂ 13.9±0.1 R⊙ and log[L₂/ L⊙] = 4.49±0.13. The distance modulus is 18.50±0.16 mag, likewise in good agreement with other measurements of the distance modulus for the LMC. Like HV 1620, this system is found to be in a semi-detached configuration with the cooler component filling its Roche lobe. However the hotter component of HV 2241 is very close to filling its Roche lobe also. The above properties give stars that are somewhat under-luminous in comparison to normal single-star models and are not consistent with binary-star evolution models for very massive, short period systems. The derived properties can however be brought into agreement with current theory if there is a large (~12 percent) systematic error in the radial velocity data for this star. (If there is a systematic error in one of the data sets, it seems most probable that it would be in the radial velocities since this data was obtained photographically on a 1-m telescope and a Mv = 13.5mag star like HV2241 must surely be close to the practical limit of such a system.) If on the other hand the properties derived here are accurate then it would appear that HV 2241 has been caught in an unprecedented evolutionary phase.
A new analysis procedure has been employed in order to investigate the nature of a selection of eight stars from the recently published EROS catalogue of eclipsing binary stars in the bar of the Large Magellanic Cloud. All eight stars are well-detached systems with obviously eccentric orbits. The results of the analysis show seven of the eight to be composed of young (i.e. main sequence), coeval components, in accord with theoretical models for binary star formation and evolution. Consideration of the position of the components of eighth system, EROS 1061, in the HRD leads to the suggestion that this system is composed of two pre-main sequence stars in the final stages of contraction down onto the zero-age main sequence.
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Tatton, Benjamin. "The structure of the Magellanic Clouds traced by red clump stars at near-infrared wavelengths." Thesis, Keele University, 2018. http://eprints.keele.ac.uk/5587/.
Full textAbstract:
This thesis is about the Red Clump (RC) star population within the Magellanic Clouds. These are observed in the near-infrared Y JKs wavelengths using data obtained by the ESO public VMC survey. These were studied to shed more light on the internal structure and past and current evolution of this interacting system of dwarf irregular galaxies. RC stars were selected from the colour magnitude diagram (CMD) using a contour method to assign the selection box and reddening vector. The J − Ks vs Ks CMD of the central 30 Doradus region of the Large Magellanic Cloud (LMC) region was analysed to determine the extinction content there, producing a reddening map. This was compared with other works including an optical reddening map which also used RC stars. The reddening map also proved to be a useful tool as a tracer of ISM features including the identification of molecular clouds. The extinction maps were made in the Y − Ks colours for the whole LMC and whole SMC. These were then used to deredden the populations. These populations had their distribution examined in a number of ways including line of sight depth and residuals derived from least-squares plane fitting. The distorted structures found appear to be the product of interactions between the LMC and SMC. RC content was also studied in the Magellanic Bridge region (lying between the LMC and SMC) where a RC population was found throughout the Bridge, mainly at LMC distance and mostly towards the LMC and SMC showing evidence of a tidally stripped SMC population. Maps were created showing this. This thesis thus presents an unprecedented, global view of the stellar and interstellar structure of the interacting Magellanic Cloud, using an intermediate-age stellar tracer, piercing through and using dust.
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Johanson, Adam. "Radio Emission Toward Regions of Massive Star Formation in the Large Magellanic Cloud." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/4419.
Full textAbstract:
Four regions of massive star formation in the Large Magellanic Cloud (LMC) were observed for water and methanol maser emission and radio continuum emission. A total of 42 radio detections were made including 27 new radio sources, four water masers, and eight compact HII regions. The lobes of a radio galaxy were resolved for the first time, and the host galaxy identified. Seven sources were associated with known massive young stellar objects (YSOs). A multi-wavelength analysis using both the infrared and radio spectrum was used to characterize the sources. Mid-infrared color-magnitude selection criteria for ultracompact HII (UCHII) regions in the LMC are presented, yielding 136 UCHII region candidates throughout that galaxy. New maser detections identified two previously unknown massive YSOs. No methanol masers were detected, consistent with previous studies and supporting the hypothesis that the LMC may be deficient in these molecules. These discoveries contribute to the history of star formation in the LMC, which will lead to a better understanding of star formation in the Milky Way and throughout the universe.
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Gomes, Aiara Lobo. "A estrutura do campo magnético na Pequena Nuvem de Magalhães." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-18062012-061001/.
Full textAbstract:
A Pequena Nuvem de Magalhães (PNM) é uma galáxia irregular e rica em gás, que juntamente com a Grande Nuvem de Magalhães (GNM) orbita a Via Láctea (VL). Elas formam um sistema triplo em constante interação. A PNM possui metalicidade baixa, e consequentemente seu meio interestelar (MI) apresenta propriedades particularmente diferentes das observadas para o MI da Galáxia. Mais do que isso, a importância do campo magnético em escalas galácticas vem sendo evidenciada cada vez mais. Então, o objetivo desta dissertação foi estudar a estrutura do campo magnético na PNM, e sua relação com componentes do MI desta galáxia. Para este fim, utilizamos dados de polarimetria no óptico, obtidos no Cerro Tololo Inter American Observatory. Construímos um catálogo polarimétrico que contém 7.207 estrelas em 28 campos distribuídos nas secções Nordeste e da Asa da PNM. Os mapas de polarização traçam o campo magnético no plano do céu diretamente, e pode-se obter sua intensidade utilizando o método de Chandrasekhar & Fermi. A partir do catálogo polarimétrico gerado neste trabalho, conseguimos observar que o campo magnético na PNM possui direção bastante irregular, porém é provável a existência de dois padrões em larga escala o primeiro alinhado com a Ponte pan-Magelânica e o segundo alinhado com a Barra da PNM. Obtivemos para o campo magnético regular Bcéu = (1,84 ± 0,11) uG e para o campo turbulento dB = (2,920 ± 0,098) uG. Esse resultado evidencia que na PNM o campo aleatório domina com relação ao de larga escala, justificando a observação de uma configuração tão irregular para os vetores de polarização. Correlacionando os mapas de polarização com estruturas presentes no MI da PNM, pudemos verificar a presença de diversos shells que podem possuir campos magnéticos da ordem de algumas dezenas de uG. Também foi possível observar ambientes onde o campo regular parece ter sido destruído pela turbulência e outros onde ele pode ainda não ter tido tempo de se formar. Derivamos a relação entre polarização e avermelhamento, e obtivemos como resultado que ela é da ordem de P/Av ~ 2, o que indica que na PNM a eficiência para polarização pode ser menor do que na Galáxia, talvez devido a alta turbulência e/ou ao fato de que nela o campo regular é muito baixo. Por fim, a partir da estimativa para as densidades de energia do campo magnético e para o movimento de rotação e de turbulência do gás, pudemos mostrar que o campo magnético possui importância dinâmica para PNM, sendo a componente turbulenta a maior responsável pela pressão magnética.The Small Magellanic Cloud (SMC) is a gas rich irregular galaxy which, together with the Large Magellanic Cloud (LMC), orbit the Milky Way (MW). They form a triple system in constant interaction. The SMC is a metal poor galaxy and, due to this, its interstellar medium (ISM) presents different properties from the Galaxy\'s ISM. In addition to that, the importance of magnetic fields on galactic scales is being recognized nowadays. Therefore, the aim of this project was to study the magnetic field structure of the SMC and its relationship with other components of SMC\'s ISM. For this purpose we have used starlight optical polarimetric data, obtained at Cerro Tololo Inter-American Observatory. We have constructed a polarization catalog containing a total of 7,207 stars in 28 fields in the Northeast/Wing sections of the SMC. The polarimetric vector maps trace the ISM magnetic field component in the plane of the sky and one can estimate its intensity towards a given region using the Chandrasekhar & Fermi method. Making use of the polarimetric catalog from this work, we have found that the magnetic field in the SMC, although varying from region to region, nevertheless shows two large scale patterns - the first one aligned with the Magellanic Bridge and a second one aligned with the SMC\'s Bar. We derived for the regular sky-projected magnetic field a value of Bsky = (1.84 ± 0.11) uG, and for the turbulent magnetic field dB = (2.920 ± 0.098) uG. These results evidence that in the SMC the random field prevails over the large scale field, which explains the irregular configuration of the polarization vectors often seen. Correlating the polarization maps with structures present on the SMC\'s ISM, we could identify the presence of several shells which may have magnetic fields up to a few tens uG. It was also possible to observe environments where the regular field seems to have been destroyed due to turbulence, and others where it seems that the large scale magnetic field has not enough time to be formed. Studying the relationship with polarization and reddening, we have obtained a value for P/Av ~ 2, which may indicate that the polarization efficiency in the SMC is smaller than in the Galaxy, perhaps due to a higher turbulence and/or because of a smaller regular magnetic field. Lastly, we have estimated the energy density for the magnetic field and for the rotation and turbulent gas motions. We showed that the magnetic field is dynamically important in the SMC\'s ISM, and that the turbulent component is the largest contributor to the magnetic pressure.
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Gutiérrez, Soto Juan. "Non-radial pulsations in be stars. Preparation of the corot space mission." Doctoral thesis, Universitat de València, 2006. http://hdl.handle.net/10803/9886.
Full textAbstract:
The general objective of the present work is to contribute to the knowledge of the physics of Be Stars. In particular, we are interested in studying and characterizing their pulsational properties. A very suitable tool to reach this goal is the study and analysis of photometric time series with the maximum time baseline, density and photometric accuracy.The space mission COROT scheduled to be launched in December 2006, will provide ultra high precision, relative stellar photometry for very long continuous observing runs. Up to ten stars will be observed in the seismology fields with a photometric accuracy of a few 10-4 and color information during 150 days.The observations of Be stars with COROT will provide photometric time series with unprecedented quality. Their analysis will allow us to qualitatively improve our knowledge and understanding of the pulsational characteristics of Be stars. In consequence, we have started a research project aimed at observing Be stars both in the seismology and exoplanet fields of COROT.In this thesis we present the first step of this project, which is the preparation and study of the sample of Be stars that will be observed by COROT. We have performed photometric analysis of all Be stars located in the seismology fields (Chap. 2). Special emphasis has been given to two stars (NW Ser and V1446 Aql) in which we have detected multiperiodic variability and these variations have been modeled in terms of stellar pulsations (Chap. 3). We have also performed an in-depth spectroscopic study of NW Ser and identified the non-radial pulsating modes taking into account the rotational effects (Chap. 4). A technique to search for faint Be stars based on CCD photometry has been developed and is presented in Chap. 5. We also present a list of faint Be stars located in the exoplanet fields of COROT detected with this technique and which we propose as targets for COROT. In addition, we have proven that our period-analysis techniques are suitable to detect multiperiodicity in large temporal baseline data. In particular, we have detected non-radial pulsations in some Be stars in the low-metallicity galaxy Small Magellanic Clouds (Chap. 6). The current theoretical models do not predict the presence of pulsational instabilities in such low-metallicity environment, and therefore, our results point towards the necessity of new and improved models.
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Martin, Nicolas F., Valentin Jungbluth, David L. Nidever, Eric F. Bell, Gurtina Besla, Robert D. Blum, Maria-Rosa L. Cioni, et al. "SMASH 1: A VERY FAINT GLOBULAR CLUSTER DISRUPTING IN THE OUTER REACHES OF THE LMC?" IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621946.
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We present the discovery of a very faint stellar system, SMASH 1, that is potentially a satellite of the Large Magellanic Cloud. Found within the Survey of the MAgellanic Stellar History (SMASH), SMASH 1 is a compact (r(h) 9.1(-3.4)(+5.9)pc) and very low luminosity (M-V = -1.0 +/- 0.9, L-V = 10(2.3 +/- 0.4) L-circle dot) stellar system that is revealed by its sparsely populated main sequence and a handful of red giant branch candidate member stars. The photometric properties of these stars are compatible with a metal-poor ([Fe/H] = -2.2) and old (13 Gyr) isochrone located at a distance modulus of similar to 18.8, i.e., a distance of similar to 57 kpc. Situated at 11 degrees.3 from the LMC in projection, its three-dimensional distance from the Cloud is similar to 13 kpc, consistent with a connection to the LMC, whose tidal radius is at least 16 kpc. Although the nature of SMASH 1 remains uncertain, its compactness favors it being a stellar cluster and hence dark-matter free. If this is the case, its dynamical tidal radius is only less than or similar to 19 pc at this distance from the LMC, and smaller than the system's extent on the sky. Its low luminosity and apparent high ellipticity (epsilon = 0.62(-0.21)(+0.17)) with its major axis pointing toward the LMC may well be the tell-tale sign of its imminent tidal demise.
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Bitsakis, T., P. Bonfini, R. A. González-Lópezlira, V. H. Ramírez-Siordia, G. Bruzual, S. Charlot, G. Maravelias, and D. Zaritsky. "A Novel Method to Automatically Detect and Measure the Ages of Star Clusters in Nearby Galaxies: Application to the Large Magellanic Cloud." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625508.
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We present our new, fully automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of observations and Monte-Carlo simulations to define stellar overdensities in the data. It decontaminates the cluster color-magnitude diagrams and, using a revised version of the Bayesian isochrone fitting code of Ramirez-Siordia et al., estimates the ages of the clusters. Comparisons of our estimates with those from other surveys show the superiority of our method to extract and measure the ages of star clusters, even in the most crowded fields. An application of our method is shown for the high-resolution, multiband imaging of the Large Magellanic Cloud. We detect 4850 clusters in the 7 deg(2) we surveyed, 3451 of which have not been reported before. Our findings suggest multiple epochs of star cluster formation, with the most probable occurring similar to 310 Myr ago. Several of these events are consistent with the epochs of the interactions among the Large and Small Magellanic Clouds, and the Galaxy, as predicted by N-body numerical simulations. Finally, the spatially resolved star cluster formation history may suggest an inside-out cluster formation scenario throughout the LMC, for the past 1 Gyr.
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Rest, Armin. "Galactic structure, near and far /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/5425.
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