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1
Steggles, Harrison. "Ultra-compact HII regions." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15813/.
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In this thesis I have studied hydrodynamical models of cometary HII regions and distributions of UCHII regions in simulated surveys, for comparison with CORNISH. I present the numerical method used to model the evolution of cometary HII regions produced by ZAMS stars of O and B spectral types, which are driving strong winds and are born off-centre from spherically symmetric cores with power-law (alpha = 2) density slopes. A model parameter grid was produced that spans stellar mass, age and core density. Exploring this parameter space I investigated limb-brightening, a feature commonly seen in cometary HII regions. It was found that all of the models produce this feature. The models have a cavity, bounded by a contact discontinuity separating hot shocked wind and ionised ambient gas, that is similar in size to the surrounding HII region. Due to early pressure confinement, shocks outside of the contact discontinuity were not seen, but the cavities were found to continue to grow. The cavity size in each model plateaus as the expansion of the HII region stagnates, which could be due to the Kelvin-Helmholtz instabilities at the interface mixing in cooler gas. SEDs of the models are similar to those from identical stars evolving in uniform density fields. The turn-over frequency is lower in the power-law models due to a higher proportion of low density gas covered by the HII regions. Following from this I have simulated CORNISH surveys for stars, varying the local density at the location of stellar birth. I have shown that the models used can reproduce the observed size and flux distributions in the CORNISH survey. Higher density environments generally lead to better fits to the observed size and flux distributions. A good match between the overall number of UCHII regions in the simulated surveys for a SFR = 1.5 solar masses per year can be achieved if it is considered that stars are born in a distribution of local densities rather than a single density.
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Giannakopoulou, Creighton Jean. "Molecular gas in HII regions of M101." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0014/NQ30597.pdf.
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Doherty, Ruth Mary. "Infrared spectroscopy of HII regions and starburst galaxies." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/27920.
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Observations of UCHII regions shown that HII region models with electron densities of ne = 104cm-3, electron temperatures in the range Te = 5,000-10,000K and a Galactic helium abundance can reproduce the observed HeI 2.058μm/Brγ ratios in these objects, subject to one condition. As the electron temperature is increased from Te=5,000K, microturbulence is incorporated into the model which counteracts the increase in the HeI 2.058μm/Brγ ratio with electron temperature. Microturbulent velocities of the order ~20kms-1 are required at Te=10,000K, in agreement with observed radio recombination line and high resolution HeI and HI measurements. Lower HeI 2.058μm/Brγ ratios are generally found in larger objects classed as compact HII regions, consistent with lower electron densities or lower stellar effective temperatures, or a combination of both effects in such objects. Alternative electron densities have been calculated from radio continuum measurements and provide evidence to suggest that electron densities are slightly lower in most of the compact HII regions than in the UCHII regions. Detailed density gradient modelling of the HeI 2.058μm/Brγ ratio has been performed, which reveals the need for realistic density distributions and explicit integration over the volume of the source when attempting to model specific HII regions. Accurate integrated electron densities or density gradients act as an alternative to microturbulence to bring theoretical HeI 2.058μm/Brγ ratios into agreement with observations for electron temperature models higher than Te = 5,000K. Finally, a large sample of starburst galaxies is analysed. The HeI 2.058μm/Brγ ratios are much lower than found in compact or UCHII regions consistent with the proposal that the integrated HeI 2.058μm/Brγ emission is generally dominated by low density giant HII regions present in these galaxies. Effective temperatures derived from the HeI 2.058μm/Brγ ratio are consistent with those estimated from FIR fine structure lines. From consideration of new models of the HeI 2.058μm/Brγ ratio, the combination of optical HeI/Hβ data with HeI 2.058μm/Brγ observations extends the sensitivity of these model ratios to a wider range of effective temperatures.
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Bosch, G. "Giant extragalactic HII regions : 30 Doradus and beyond." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596793.
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This thesis aims to study both the stellar and the gaseous components of a sample of GEHRs and analyse the possible mechanisms that govern these forming regions. As there are no giant HII regions in our Galaxy, GEHRs from our Local Group of galaxies provide us with the data needed to understand these regions. Much has been done in this direction, and I review the latest efforts and our current knowledge in Chapter 1. Chapter 2 is focused on the analysis of the stellar population of the object that can better help us to understand GEHRs: 30 Doradus, our closest and largest neighbouring starburst. I have performed spectral classification over 175 stars in the region which allowed me to study their spatial distribution and combine with new photometry to estimate the initial mass function (IMF) and the star formation history of the stellar cluster. The results indicate a normal IMF and the existence of three distinct bursts of star formation. I also discuss the evidence found towards and against mass segregation of stars in the cluster. I have used a subset of the mentioned spectroscopic data to study the kinematics of the stars in 30 Doradus in Chapter 3. From the data I found evidence of partial dynamical mass segregation supporting the findings of the previous chapter. Assuming the cluster is virialised, I have also estimated its dynamical mass, and found it to be several times larger than the one estimated photometrically. However, more and higher resolution spectra are needed to better constrain the final value. In Chapter 4 I investigate the effect that an underlying population of binary stars could introduce in the kinematical analysis mentioned above. I have used Monte Carlo techniques to construct an artificial population of binary stars, and simulated observations of such a population to measure its kinematical parameters.
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Obonyo, Willice Odhiambo. "Open clusters and HII regions of our Galaxy." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/19997.
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Open clusters are essential laboratories for understanding stellar evolution, as they allow constraints to be placed on stellar ages and luminosities. As distance indicators they are also important tracers of star formation in the Milky Way. One such cluster is Trumpler 27 that we identified for detailed study.The aim of the study is to estimate the distance, radial velocity, age, membership and reddening of the cluster using both spectroscopic and photometric techniques. We used new spectroscopic data collected from SAAO's 1.9m telescope together with existing photometric data from catalogues in the study of Trumpler 27. The spectra collected were classified using spectral atlases to determine the reddening in the field. Stars of the cluster were identified using selection techniques that made use of both infrared and optical Q parameters, spatial distribution and photometric techniques. The result from this work suggest that Trumpler 27 is made up of ~ 55 stars which are at different stages of evolution. The stars include main sequence stars, blue supergiants, two cool supergiants and maybe two WR stars.
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Kerton, Charles Robert. "Multiwavelength studies of dust associated with galactic HII regions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ49819.pdf.
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Tibaldo, Riccardo. "Caratteristiche principali di emissione di regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14089/.
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Si trattano le caratteristiche principali di regioni HII. Un particolare approfondimento viene condotto ai processi di generazione di fotoni, come emissione free-free, free-bound e bound-bound, e di interazione con la materia nei processi di estinzione. Dopodiché si impostano le equazioni di equilibrio: termico e di ionizzazione. Inoltre vengono forniti tre esempi di spettri in modo tale da verificare empiricamente i risultati teorici.
Un capitolo finale è riservato allo studio delle abbondanze chimiche e del caso particolare delle Ultra-Compact HII.
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Costa, Allison Hainline. "A study of magnetic fields in HII regions using Faraday rotation." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6085.
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Massive young stars dynamically modify their surroundings, altering their stellar nurseries and the gas that exists between stars. With my research, I assess the modification of the Galactic magnetic field within HII regions and stellar bubbles associated with OB stars. Because HII regions are plasmas, magnetic fields should be important to the dynamics of the region. Understanding how the magnetic field is modified in these structures is critical for inputs to simulations and for assessing stellar feedback. To obtain information on the properties of the magnetic field, I measure the Faraday rotation of linearly polarized radio waves that pass through the plasma of the HII region.
In this thesis, I present results of Faraday rotation studies of two Galactic \HII regions. The first is the Rosette Nebula (l = 206 deg, b = -1.2 deg), and the second is IC 1805 (l = 135 deg, b = 0.9 deg), which is associated with the W4 Superbubble. I measure positive rotation measure (RM) values in excess of +40 to +1200 rad m^-2 due to the shell of the Rosette nebula and a background RM of +147 rad m^-2 due to the general interstellar medium in this area of the Galactic plane. In the area of IC 1805, I measure negative RM values between +600 and --800 rad m^-2 due to the HII region. The sign of the RM across each HII region is consistent with the expected polarity of the large-scale Galactic magnetic field that follows the Perseus spiral arm in the clockwise direction, as suggested by Van Eck et al. (2011, ApJ, 728, 14).
I find that the Rosette Nebula and IC 1805 constitute a "Faraday rotation anomaly", or a region of increased RM relative to the general Galactic background value. Although the RM observed on lines of sight through the region vary substantially, the |RM| due to the nebula is commonly 100 -- 1000 rad m^-2. In spite of this, the observed RMs are not as large as simple, analytic models of magnetic field amplification in HII regions (such as by magnetic flux conservation in a swept-up shell) might indicate. This suggests that the Galactic field is not increased by a substantial factor within the ionized gas in an HII region. Finally, these results show intriguing indications that some of the largest values of |RM| occur for lines of sight that pass outside the fully ionized shell of the IC 1805 HII region, but pass through the Photodissociation Region (PDR) associated with IC 1805.
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Vigil, Miquela 1981. "Star formation in the HII regions RCW 38, RCW 36, and RCW 108." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28615.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004."June 2004."
Includes bibliographical references (leaves 41-42).
I present 1.2 mm observations of the HII regions RCW 38, RCW 36, and RCW 108 which reveal the distributions of dust associated with the three regions. The dust emission in RCW 38 exhibits a ring like structure centered around an O-star. A bright knot in the ring was determined to contain 15% of the total dust by mass in the region and roughly coincided with regions of high emission at various infrared wavelengths as well as 6 cm continuum emission. The dust emission in RCW 36 extended along a ridge with a bright clump in the north of the ridge containing 70% of the mass of the entire cluster. The dust emission in RCW 108 is concentrated in a single tight knot with a faint extension to the south. The dust emission is compared to the infrared and radio emissions to attempt to describe the characteristics of possible areas of active star formation.
Miquela Vigil.
S.M.
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Rauber, Aline Beatriz. "Catálogo de dados espectroscópicos de regiões hii e estudos aplicados." Universidade Federal de Santa Maria, 2009. http://repositorio.ufsm.br/handle/1/9196.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoQuantitative measurements of line intensities have been made since the beginning of the last century. The quantity and quality of the data available have increased drastically with the advent of electronic detectors. However, the data are widely scattered in the literature. In face of this, we compiled a catalog of emission-lines intensities. It contains data on HII regions in 41 galaxies, all totaling approximately 36 000 line intensities. We have constructed a table with 1 750 emission-lines observed, showing their transition probabilities and configurations or terms. We have standardized the identification of all the emission-lines of the catalog based on this table. The database was used for different studies. We checked the values of the ratios [OIII] λ5007/λ4959 and [NII] λ6583/λ6548 with the emission-line ratios from the HII regions in the catalog. The values found are in agreement with the theoretical ones. With the diagram λ6717/Hβ versus λ6731/Hβ, we verified that most of the objets in the catalog are near the low-density limit. We also present a comparison of different temperature indicators based on observational data from HII regions, HII galaxies and planetary nebulae extracted from the literature. We have found that there is not a unique relation between the temperature indicators of different ionization zones which allows a reliable derivation of one of these from another. We have constructed diagnostic diagrams comparing the emission-lines ratios [OI]/Hα, [OII]/Hβ, [OIII]/Hβ, [NII]/Hα, [SII]/Hα e [OII]/[OIII]. For them, we have distinguished the emission-line ratios of HII regions of different galaxies and, for data from our galaxy, we have distinguished different objects. We described the diagnostic diagrams using theoretical grids varying the ionization parameter and the chemical abundance. These were computed using a photoionization code and different spectral energy distributions. With the diagram [NII]/[OII] versus [OIII]/[OII], we have obtained the best separation between ionization parameter and metallicities. We observed large discrepancies between the chemical abundances of the grids of models and those determined from collisionaly excited lines.
Medidas quantitativas de intensidades de linhas de emissão têm sido feitas desde o in´ıcio do século passado. A quantidade e a qualidade dos dados disponíveis têm crescido drasticamente com o advento dos detectores eletrônicos. Porém, os dados estão amplamente espalhados na literatura. Diante disso, compilamos um catálogo de intensidades de linhas de emissão. Este contém dados de regiões HII de 41 galáxias, totalizando aproximadamente 36 000 intensidades de linhas. Construímos uma tabela com 1 750 linhas de emissão observadas, apresentando suas probabilidades de transição e configurações ou termos. Padronizamos a identificação de todas as linhas de emissão do catálogo com base nessa tabela. O banco de dados foi utilizado para diferentes estudos. Checamos os valores das razões [OIII] λ5007/λ4959 e [NII] λ6583/λ6548 com razões de linhas de emissão de regiões HII do catálogo. Os valores encontrados concordam com os teóricos. Com o diagrama λ6717/Hβ versus λ6731/Hβ, verificamos que a maior parte dos objetos do catálogo estão próximos ao limite de baixa densidade. Apresentamos também uma comparação de diferentes indicadores de temperatura baseada em dados observacionais de regiões HII, de galáxias HII e de nebulosas planetárias extraídos da literatura. Encontramos que não há uma única relação entre indicadores de temperaturas de diferentes zonas de ionização que permita uma derivação confiável de uma destas a partir da outra. Construímos diagramas de diagnóstico comparando as razões de linhas [OI]/Hα, [OII]/Hβ, [OIII]/Hβ, [NII]/Hα, [SII]/Hα e [OII]/[OIII]. Para eles, distinguimos as razões de linhas de emissão de regiões HII de galáxias diferentes e, para os dados de nossa galáxia, distinguimos os diferentes objetos. Descrevemos os diagramas de diagnóstico utilizando grades teóricas variando o parâmetro de ionização e a metalicidade. Estas foram calculadas usando um código de fotoionização e diferentes distribuições espectrais de energia. Com o diagrama [NII]/[OII] versus [OIII]/[OII], obtivemos a melhor separação entre o parâmetro de ionização e a metalicidade. Verificamos grandes discrep ancias entre as abundâncias químicas das grades de modelos e aquelas determinadas de linhas excitadas colisionalmente.
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Thompson, Mark Anthony. "Hot cores and HII regions : molecular line and continuum observations of massive star formation." Thesis, University of Kent, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298097.
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Moisés, Alessandro Pereira. "Braços espirais da galáxia: posição das regiões HII gigantes e formação estelar." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-26072010-120642/.
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Nesta tese é apresentado um catálogo fotométrico no infravermelho próximo de 35 Regiões HII, todas pertencentes ao disco Galáctico. Esta faixa espectral é útil uma vez que os comprimentos de onda são grandes o suficiente para se ter uma baixa extinção interestelar comparada ao visível, e são pequenos o suficiente para diagnosticar as fotosferas estelares. Foram obtidas imagens nas bandas J, H e K e imagens do Spitzer nos canais de 3,5, 5,8 e 8,0 m. Após a fotometria nas imagens JHK, foi possível construir diagramas cor-cor e cor-magnitude. Foram utilizadas imagens coloridas, compostas de uma combinação RGB das imagens nas três bandas, tanto para as imagens JHK quanto para as imagens do Spitzer. Estas imagens, junto com os diagramas, foram utilizadas para levantar candidatos a fontes ionizantes das regiões HII, assim como objetos ainda em estágios primordiais de evolução (CTTs e MYSOs). Estes dados também foram utilizados para associar à cada região HII um estágio evolutivo (de A até D, da região mais jovem à mais evoluída). Baseado na posição da Sequência Principal em diagramas cor-magnitude, foi possível comparar as distâncias cinemáticas com nossos dados. Além disso, quando possível, foram utilizadas distâncias de regiões HII determinadas por paralaxe espectrofotométrica (disponíveis na literatura) e utilizando duas leis de extinção interestelar extremas mostrou-se que estas distâncias são menores que suas contrapartidas cinemáticas, e estão em acordo com distâncias determinadas por outros métodos, como por paralaxe trigonométrica. Sabendo que estas regiões de formação estelar seguem a dinâmica do gás, o mapeamento da distribuição destas regiões permite checar a estrutura espiral da Via Láctea.In this work, a near infrared photometric catalog of 35 HII regions that belongs to the Galactic plane is presented. This spectral range is useful since the wavelengths are long enough to have less influence of the interstellar extinction compared to the visible domain, and they are small enough to still show stellar photospheric features. Images of these HII regions in the J, H and K-band together with IRAC-Spitzer images (channels 4.5, 5.8 and 8.0 m) were used. After the photometry in the JHK images, color-color and color-magnitude diagrams were constructed. These two group of images (JHK and 4.5, 5.8 and 8.0 m) colored in a RGB combination were used, together with the diagrams, to identify the ionizing sources candidates, as well as objects still embedded in their natal cocoon (CTTs and MYSOs). An evolutionary stage to these regions (from A to D, from the younger region to the more evolved) was inferred based on the images and diagrams. These diagrams were also used to infer if the kinematic distance is correct, based on the Main Sequence location. Non-kinematic distances to several HII regions, when it was possible, were collected from the literature. Using two extreme interstellar extinction laws, it was possible to compare these distances with the kinematic results. These non-kinematic distances are lower than that from kinematic techniques. Also, these distance discrepancies are in agreement with distances derived by others methodologies, as trigonometric parallax. Since these star forming regions follow the gas dynamics, mapping their distribution along the Galaxy allows to check the spiral pattern of the Milky Way.
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MOY, EMMANUEL. "Evolution spectrale des galaxies. Photoionisation et chocs dans les regions hii et les environnements de noyaux actifs." Paris 11, 2000. http://www.theses.fr/2000PA112252.
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Dans ce travail, nous presentons la modelisation que nous avons realise de l'emission nebulaire des regions hii. Nous decrivons le couplage que nous avons realise entre le code de synthese spectrale pegase et le code de photoionisation cloudy. Ce modele couple permet de predire le spectre d'un sursaut de formation d'etoiles en tenant compte des contributions stellaires et nebulaires et de l'extinction par la poussiere. L'ajustement des rapports de raies d'emission d'un echantillon local nous a permis de definir des scenarios reliant la metallicite et le niveau d'ionisation du gaz. L'analyse des largeurs equivalentes et des couleurs des memes objets nous a egalement fourni des contraintes sur leur formation d'etoiles passee et sur la distribution geometrique du gaz. Dans un deuxieme temps, nous presentons les resultats de l'analyse de spectres en emission d'objets actifs. Nous montrons que la photoionisation par l'objet central, et les chocs lies a la propagation du jet radio, simules respectivement a l'aide des modeles cloudy et mappingsiii, jouent en moyenne un role equivalent dans l'emission nebulaire etendue. Les meilleurs ajustements des rapports de raies d'emission, de l'ultraviolet jusqu'au proche infrarouge, sont obtenus a l'aide de modeles couplant les deux processus. Enfin, nous appliquons l'ensemble de ces modeles a l'analyse detaillee des observations obtenues sur la radio galaxie 3c171 a l'aide du spectrographe integral de champ oasis/cfht. Nous montrons comment la comparaison des cartes de rapports de raies avec les images radio nous a permis de mieux contraindre les roles respectifs du rayonnement de la source centrale, des chocs et des etoiles massives dans cet objet.
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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.
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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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Misanovic, Zdenka. "Search for young galactic supernova remnants." Thesis, The University of Sydney, 2001. http://hdl.handle.net/2123/795.
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A sample of 9 small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) and observed with the Australia Telescope Compact Array (ATCA) in the radio recombination line (RRL) at 5 GHz, in a search for young Galactic SNRs. Since the RRL emission is an unambiguous indicator of a thermal source, this method has been used to eliminate HII regions from the selected sample. In addition, the IRAS and MSX infrared data and spectral index measurements have been combined with the RRL studies to distinguish thermal and non-thermal sources in the selected sample. One source (G282.8-1.2) is identified here as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum and possible x-ray emission. However, the ATCA data are inconclusive and further studies are needed to confirm this result. Radio recombination line emission (H107 alpha) has been detected in 3 of the selected sources, eliminating them from the sample of SNR candidates. In addition, the parameters of the RRL emission from the identified HII regions have been used to estimate their properties. The RRL data are inconclusive for the remaining low brightness, extended sources in the sample. However, some of these sources are likely to be thermal HII regions according to the infrared and spectral index data. The selected method for distinguishing thermal and non-thermal Galactic radio sources seems promising. The selected ATCA configuration was appropriate for imaging relatively bright, compact sources, but a slightly modified observing technique is needed to successfully image low surface brightness, extended sources.
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Misanovic, Zdenka. "A search for young galactic supernova remnants." University of Sydney. Physics, 2001. http://hdl.handle.net/2123/795.
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A sample of 9 small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) and observed with the Australia Telescope Compact Array (ATCA) in the radio recombination line (RRL) at 5 GHz, in a search for young Galactic SNRs. Since the RRL emission is an unambiguous indicator of a thermal source, this method has been used to eliminate HII regions from the selected sample. In addition, the IRAS and MSX infrared data and spectral index measurements have been combined with the RRL studies to distinguish thermal and non-thermal sources in the selected sample. One source (G282.8-1.2) is identified here as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum and possible x-ray emission. However, the ATCA data are inconclusive and further studies are needed to confirm this result. Radio recombination line emission (H107 alpha) has been detected in 3 of the selected sources, eliminating them from the sample of SNR candidates. In addition, the parameters of the RRL emission from the identified HII regions have been used to estimate their properties. The RRL data are inconclusive for the remaining low brightness, extended sources in the sample. However, some of these sources are likely to be thermal HII regions according to the infrared and spectral index data. The selected method for distinguishing thermal and non-thermal Galactic radio sources seems promising. The selected ATCA configuration was appropriate for imaging relatively bright, compact sources, but a slightly modified observing technique is needed to successfully image low surface brightness, extended sources.
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Lykins, Matt. "PHYSICAL CONDITIONS INCLUDING MAGNETIC FIELDS IN SEVERAL STAR FORMING REGIONS OF THE GALAXY." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/95.
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This document describes studies of two independent regions of the interstellar medium (ISM). These studies have the common element that both pertain to regions in our Galaxy that are known to be associated with present-day star formation. These studies aim to help us understand the ISM, star formation, and ultimately where we came from, since, after all, our star, the Sun, is itself the product of star formation 4.5 billion years ago. The first project measured the Zeeman Effect on the 21 cm H I absorption line in order to create a map of the line of sight magnetic fields near a star forming region called W3. From the map of the field, it was possible to create a three dimensional model of the magnetic field morphology. Also, calculating the various energies associated with W3 revealed that it is most likely in virial equilibrium, not expanding or contracting.
The second project used an instrument on the Hubble Space Telescope (HST) to measure the abundance of iron in a neutral region near the Orion Nebula called Orion’s Veil. One of the goals of this project is to investigate whether solid dust grains can be destroyed by ionizing radiation by comparing the amount of solid iron in Orion’s Veil to the amount in the nearby ionized regions. By measuring the depletion of iron in the neutral Veil and comparing it to the depletion of iron the H+ regions of the Orion Nebula, it was possible to conclude that iron was not being released into the gas phase by ultraviolet photons. In addition, oscillator strengths for two Fe II transitions were measured.
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Pinheiro, Márcio do Carmo. "Estudo multibanda do conteúdo estelar de regiões Hii do hemisfério sul." Universidade Federal de Santa Maria, 2012. http://repositorio.ufsm.br/handle/1/3909.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoWe present a multi-wavelength study of the stellar content of 11 optical/infrared Southern Galactic Hii regions with 10 h < α(J2000) < −17 h and −65° < δ(J2000) < −35°. Nine optical objects with no published or uncertain distances were examined in order to identify their ionising sources and to determine their distances, whereas young stellar objects (YSOs) and main sequence ionising stars were photometrically classified in the two infrared clusters. We carried out optical spectroscopy and UBV photometry of the stellar content of these Hii regions and obtained the distance of individual stars by spectroscopic parallax. To avoid using a fixed value for the total-to-selective extinction ratio RV , the reddening AV was determined directly by the colour-difference method. We classified as types O or B 24 out of the 31 stars for which optical spectra were obtained. In particular, we identified two new O stars in RCW98 and RCW99. The values for reddening obtained correspond to a mean hRV i = 3.44, which is about 10% higher of the mean value found for field stars over all directions of the Galaxy. For the Hii regions NGC3503, NGC6334, RCW55, RCW87, RCW98 e RCW99, we obtained more precise distances calculated as the median of the spectroscopic parallaxes obtained for two to six different stars in each nebulae, with an internal dispersion of less than 5%. Among the objects more obscured in the Norma region, we analysed the stellar content of the East part of the large complex of Hii regions GAL331.5-00.1, which contains eight bright extended radio sources. This study comprises the infrared clusters [DBS2003] 156 and [DBS2003] 157, respectively associated to Hii regions GAL331.11-00.51 and GAL331.31-00.34. In order to isolate the brightest 2MASS sources of their unresolved companions, we carried out JHK photometry with resolution better than 2MASS data. 47 Near-infrared (NIR) sources with Ks-band excess were identified following usual methods. Other 70 YSOs were also identified by using Mid-IR on-line data of the GLIMPSE survey. The search for radial-velocity measurements in the literature and the similarity between the stellar population explored have indicated the two regions as physically associated. With the determination of the spectroscopic parallaxes of four O-type and two B-type stars spread over the both clusters, this hypothesis was verified. The parallaxes of these 6 stars returned very compatible distances (hdhelioci = 3.30 ± 0.29 kpc). The Near- and Mid-IR counterparts of the IRAS source 16085-5138 was found close to the field of [DBS2003] 157. This source has showed typical colours of a Ultra-compact ii region (UCHii) and spectral index α = 3.6 between 2 and 25 μm, which is typical of YSOs immersed in protostellar envelopes. A lower limit to the bolometric luminosity of the protostar embedded was computed as L = 7.7×103L⊙ (M = 10M⊙), which corresponds to a BO-B1 zero-age star. The cluster [DBS2003] 157 was found to be spread over all ∼4′ × 4′ region demarcated by a intense shell-like dust emission, where a secondary massive star formation is going on, likely as a result of the interaction between this dust and stellar winds.
Apresentamos aqui um estudo multibanda do conteúdo estelar de onze regiões Hii do Hemisfério sul com 10 h < α(J2000) < −17 h e −65◦ < δ(J2000) < −35◦. Em 9 objetos ópticos, com valores de distância discrepantes ou sem nenhuma determinação anterior publicada, visamos identificar as fontes ionizantes e determinar suas distâncias, enquanto que, no estudo de dois outros objetos no infravermelho, buscamos não apenas identificar as fontes ionizantes, mas também objetos estelares jovens (YSOs) em seus campos. Nos primeiros, realizamos espectroscopia no óptico e fotometria UBV de seus conteúdos estelares e determinamos as distâncias das estrelas massivas por meio da paralaxe espectroscópica. A fim de evitar o uso de um valor fixo para a razão entre a extinção total e a seletiva à banda V , RV , a extinção AV na direção de cada estrela foi determinada diretamente através no método das diferenças de cor. De um total de 31 estrelas espectroscopicamente estudas, 24 foram classificadas como tipos O ou B, sendo duas novas estrelas tipo O encontradas em RCW98 e RCW99. As estimativas de AV implicaram um valor médio de hRV i = 3.44. Este resultado supera em 10% o valor médio encontrado para estrelas de campo sobre todas as direções da Galáxia. Para as regiões Hii NGC3503, NGC6334, RCW55, RCW87, RCW98 e RCW99, distâncias mais precisas foram estimadas como o valor mediano da paralaxe espectroscópica de 2 a 6 diferentes estrelas ionizantes, resultando em uma dispersão interna menor que 5%. Dentre os objetos mais obscurecidos pela extinção interestelar da região de Norma, analisamos o conte´udo estelar da região leste do grande complexo de regiões Hii brilhantes em radiofrequências GAL331.5-00.1. A área estudada engloba os aglomerados infravermelhos [DBS2003] 156 e [DBS2003] 157, respectivamente associados às regiões Hii GAL331.11-00.51 e GAL331.31-00.34. Observações fotométricas nas bandas J, H e Ks, com mais alta resolução que a fotometria 2MASS, foram realizadas nas direções desses objetos, o que possibilitou isolar as fontes infravermelhas mais brilhantes de estrelas companheiras não resolvidas e selecionar potenciais estrelas ionizantes para subsequente espectroscopia. 47 fontes com excesso de emissão intrínseca na banda Ks, típico em YSOs, foram identificadas seguindo os métodos usuais de análise da fotometria no IR próximo (NIR). Outros 70 YSOs foram identificados no IR médio (Mid-IR) usando dados do survey GLIMPSE. A pesquisa por medidas de velocidade radial na direção desses dois objetos e a semelhança das populações estelares indicou que as duas sub-regiões estudas deveriam estar fisicamente associadas. Esta hipótese foi reafirmada com a determinação da paralaxe espectroscópica de 4 estrelas tipo O e outras 2 tipo B nos dois aglomerados, que retornaram valores de distâncias heliocêntricas bastante compatíveis (hdhelioci = 3.30 ± 0.29 kpc). A contrapartida nos NIR e Mid-IR da fonte IRAS 16085-5138 foi encontrada junto ao aglomerado [DBS2003] 157. Esta fonte apresentou cores típicas de uma região Hii Ultracompacta (UCHii) e índice espectral entre 2 e 25 μm de α = 3.6, típico de YSO imerso em um envelope protoestelar. Um limite inferior para a luminosidade bolométrica da protoestrela embebida foi estimado em L = 7.7×103L⊙ (M = 10M⊙), o que corresponde a uma estrela de idade zero na faixa de BO-B1. O aglomerado [DBS2003] 157 mostrou-se estar espalhado sobre toda uma região de ∼4′ ×4′, demarcada por intensa emissão de poeira quente e espacialmente distribuída como uma nuvem em forma de concha.
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Purcell, Cormac Physics Faculty of Science UNSW. "What's in the brew? A study of the molecular environment of methanol masers and UCHII regions." Awarded by:University of New South Wales. School of Physics, 2006. http://handle.unsw.edu.au/1959.4/26996.
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In recent years the 6.67 GHz masing transition of CH3OH has proven to be a superior tracer of massive star formation (see Minier 2001). Maser sites often occur in proximity to UCHII regions, however, up to 75 per cent of sites have no detectable radio counterpart (Walsh 1998) and are instead hypothesised to trace the less evolved 'hot molecular core' phase of stellar evolution. This has been confirmed for a only handful of well known sources (e.g., Cesaroni 1994). Presented here are the results of multi-species molecular line observations towards warm, dusty clumps, undertaken with the goal of investigating the relationship between hot cores, UCHII regions and CH3OH masers. Data from the 22-m Mopra telescope is used extensively in this thesis and substantial efforts were made to calibrate the brightness temperature scale. Measurements conducted on SiO masers and planets show that the beam pattern is divided into a Gaussian main beam plus an inner error lobe, which in 2004 contained 1/3 of the power in the main beam. Full-width half-maximum beam sizes were measured from the data and the beam efficiencies were derived for the years 2000-2004. A 3-mm wavelength molecular line survey was conducted, using Mopra, towards 83 massive star-forming clumps associated with CH3OH masers. Emission from the transitions 13CO (1-0), N2H+ (1-0), HCO+ (1-0), HCN (1-0) and HNC (1-0) was detected towards 82 sources (99 per cent), while CH3OH emission was detected towards 78 sources (94 per cent). The warm gas tracer CH3CN was observed specifically to search for hot core chemistry, and was detected towards 58 sources (70 per cent), confirming that CH3OH masers are excellent tracers of hot cores. CH3CN is found to be brighter and more commonly detected towards masers associated with UCHII regions compared to 'isolated' masers. That CH3CN is detected towards isolated maser sources strongly suggests that these objects are internally heated. The molecular line data have been used to derive rotational temperatures and chemical abundances in the clumps and these properties have been compared between sub-samples associated with different indicators of evolution. In particular, CH3OH is found to be brighter and more abundant in UCHII regions and in sources with detected CH3CN, and may constitute a crude molecular clock in single dish observations. Gas-kinematics were analysed via asymmetries in the HCO+ line profiles. Approximately equal numbers of red and blue-skewed profiles, indicative of inward or outward motions, respectively, are found among all classes of object. Bolometric luminosities were derived via greybody fits to the sub-millimetre and mid-infrared spectral energy distributions, and an empirical gas-mass to luminosity relation of L proportional to M^0.68 was fit to the sample. This is a considerably shallower power law than L proportional to M^3 for massive main-sequence stars. In the mid-infrared, 12 sources were identified as 'infrared dark clouds' (IRDCs). Such objects have been hypothesised as precursors to the hot core phase of evolution, however, we find these sources have greater linewidths and rotational temperatures than the bulk of the sample, and one contains an embedded HII region The filamentary star forming region NGC3576 was also investigated via a molecular line and 23 GHz continuum mapping survey, utilising the ATCA, Mopra and Tidbinbilla telescopes. The results of these observations provide detailed information on the morphology, masses, kinematics, and physical and chemical conditions along the cloud. Analysis of NH3 data has revealed that the temperature and linewidth gradients exist in the western arm of the filament. Values are highest near to the central HII region, indicating that the embedded cluster of young stars is influencing the conditions in the bulk of the gas. Six new H2O masers were detected in the arms of the filament, all associated with clumps of NH3 emission. Star formation is clearly underway, however, clump masses range from 1 to 128 solar masses, possibly too low to harbour very massive stars. The lack of detected 23 GHz continuum emission in the arms supports this assertion.
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Pinheiro, Márcio do Carmo. "Classificação espectral e determinação de distância de estrelas em dez regiões HII do hemisfério sul." Universidade Federal de Santa Maria, 2009. http://repositorio.ufsm.br/handle/1/9195.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoIn order to determine distances of Southern Galactic HII regions, we carried out spectroscopic and photometric observations of the stellar content of a set of these objects. We have chosen objects only visible in the South hemisphere, with no published or uncertain distances. In this work, we present spectral classification based on intermediate dispersion spectra with a very high signal to noise ratio and on stellar UBV photometry, so that the distances have been determined using the usual method, the spectroscopic parallax. We picked up the 2MASS infrared photometry and assessed the reddening individually for each star, using the color-difference method. This way, we have estimated the totalto-selective extinction ratio for the most of the classified stars, and so, we have found a mean value 21% higher than the mean value of RV calculated on the whole directions of the Galaxy. As a result, we have found distances in general smaller than those already published on the literature, although confirming several spectral classifications. Besides that, large fluctuations around the values normally adopted were also observed, which would result in larger discrepancies between the stellar distances. At last, we have also extracted nebulae spectra in order to estimate the kinematics distances, so that we could compare the distance measurement results by different methods. In general, we have found reasonably compatible distances. However, in some cases large differences was found, suggesting that some objects present deviations of the circular motion.
Com o objetivo de determinar distâncias de regiões HII Galácticas observáveis no Hemisfério Sul, realizamos observações espectroscópicas e fotométricas do conteúdo estelar de um conjunto desses objetos. Demos preferência para aqueles objetos cuja observação só é possível no Hemisfério Sul, sem publicações de distância encontrada ou com grande dispersão entre os valores publicados. Neste trabalho, apresentamos classificação espectral baseada em espectros de dispersão intermediária, com elevada razão sinal / ruído e, também, classificação espectral via fotometria UBV , ambas com o objetivo de determinar as distâncias das regiões HII via paralaxe espectroscópica de suas estrelas ionizantes. Nós também extraímos as magnitudes dessas estrelas no infravermelho próximo diretamente do catálogo 2MASS e calculamos o avermelhamento individualmente para cada estrela usando o método das diferenças de cores. Assim, a razão entre a extinção total e a seletiva a banda V (RV ) foi estimada para a maior parte das estrelas, de forma que encontramos um valor médio 21% maior que o valor médio de RV calculado sobre todas as direções da Galáxia e, por este motivo, nós encontramos distâncias heliocêntricas, em geral, menores do que aquelas encontradas na literatura, mesmo confirmando a maior parte das classificações espectrais dadas por esses autores. Além disso, grandes flutuações em torno do valor médio foram encontradas, o que acarretaria maiores discrepâncias entre as distâncias estelares. Por fim, extraímos espectros nebulares dos objetos, com o objetivo de estimar suas distâncias cinemáticas e comparar os resultados obtidos com diferentes métodos. Em geral, encontramos distâncias razoavelmente compatíveis. Contudo, em alguns casos, grandes diferenças foram encontradas, sugerindo que alguns objetos como RCW 88 e NGC 3503 apresentam desvios do movimento circular.
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Mayo, Elizabeth Ann. "MAGNETIC FIELDS IN THE GALAXY." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_diss/596.
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The object of this dissertation is to provide an observational study of the effects of interstellar magnetic fields on star-formation regions. This is part of a long-standing research project that uses the techniques of radio astronomy to measure magnetic field strengths in the interstellar medium of our galaxy. Interstellar magnetic fields are believed to play a crucial role in the star-formation process therefore a comprehensive study of magnetic fields is necessary in understanding the origins of stars. These projects use observational data obtained from the Very Large Array (VLA) in Socorro, NM. The data reveal interstellar magnetic field strengths via the Zeeman effect in radio frequency spectral lines. This information provides an estimate of the magnetic energy in star-forming interstellar clouds in the Galaxy, and comparisons can be made with these energies and the energies of self-gravitation and internal motions. From these comparisons, a better understanding of the role of magnetic fields in the origins of stars will emerge. The regions observed include the giant molecular clouds and star-forming regions of Cygnus X and NGC 6334. NGC 6334 A is a compact HII region at the center of what is believed to be a large, rotating molecular torus (based on studies by Kramer et al. (1997)). This is a continuing study based on initial measurements of the HI and OH Zeeman effect (Sarma et al. (2000)). The current study includes OH observations performed by the VLA at a higher spatial resolution than previously published data, and allows for a better analysis of the spatial variations of the magnetic field. A new model of the region is also developed based on OH opacity studies, dust continuum maps, radio spectral lines, and infrared (IR) maps. The VLA has been used to study the Zeeman effect in the 21cm HI line seen in absorption against radio sources in the Cygnus-X region. These sources are mostly galactic nebulae or HII regions, and are bright and compact in this region of the spectrum. HI absorption lines are strong against these regions and the VLA is capable of detecting the weak Zeeman effect within them.
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Alves, Marta Isabel Rocha. "Diffuse radio recombination line emission on the galactic plane." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/diffuse-radio-recombination-line-emission-on-the-galactic-plane(54655adf-a0da-4f27-86fb-0d8ae43e1e80).html.
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A full-sky free-free template is increasingly important for the high-sensitivity Cosmic Microwave Background (CMB) experiments, such as Planck. On the Galactic plane, where free-free estimations from Halpha measurements become unreliable, Radio Recombination Lines (RRLs) can be used to determine the thermal brightness temperature unambiguously with no dust contamination. RRLs are a powerful tool for the diagnostic of the interstellar medium, tracing the ionised component, its electron temperature, velocity and radial distributions.This thesis describes the investigation of the ionised emission from HII regions and diffuse gas along the Galactic plane using RRLs, with the aim of providing a map of the free-free emission to complement the high latitude Halpha observations. Measuring the free-free emission on the Galactic plane is of great importance to understand and characterise other Galactic emission components: synchrotron, anomalous dust and thermal dust emission. The fully-sampled HI Parkes All-Sky Survey and associated deep Zone of Avoidance Survey are re-analysed to recover extended RRL emission. They include three RRLs (H166alpha, H167alpha and H168alpha) at frequencies near 1.4 GHz. A data cube covering l=20 degree to 44 degree and |b| < 4 degree is constructed of RRL spectra with velocity and spatial resolution of 20 km/s and 14.8 arcmin, respectively. Well-known HII regions are identified as well as the diffuse RRL emission on the Galactic plane.In order to convert the integrated RRL emission into a free-free brightness temperature a value of the electron temperature (Te) of the ionised gas is needed. Using the continuum and line data from the present survey, the variation of Te with Galactocentric radius was derived for the longitude range l=20 degree to 44 degree, with a mean Te on the Galactic plane of 6000 K. The derived Te variation was used to obtain the first direct measure of the free-free brightness in this region of the Galactic plane. Subtraction of this thermal emission from the total continuum at 1.4 GHz leaves the first direct measurement of the synchrotron emission. A narrow component of width 2 degree is identified in the synchrotron latitude distribution.Determining the free-free and synchrotron emission in this region of the Galactic plane identifies the anomalous microwave component, when combined with WMAP and IRIS data. The results are in agreement with models of small spinning dust grains.
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Desmurs, Jean-François. "Recherche et cartographie VLBI des masers OH dans les régions de formation d'étoiles massives : observations interférométriques millimétriques de Lynds 1551." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10255.
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Les travaux presentes dans cette these portent essentiellement sur l'etude des regions de formation d'etoiles massives. Pour cela nous avons etudie l'emission maser des deux transitions principales du premier etat excite du radical hydroxyl (a 6031 et 6035 mhz). Nous avons conduit un releve sur toutes les regions hii ayant une forte luminosite dans l'infrarouge lointain, plus quelques autres sources connues pour leur emission maser dans l'etat fondamental de oh. Sur les 256 sources de notre catalogue, 15 nouvelles sources furent decouvertes en emission et 3 en absorption. Nous avons pu mesurer l'intensite du champ magnetique de ces regions par l'intermediaire de l'effet zeeman qui d'une maniere globale semble en accord avec le sens de rotation de la galaxie. Nous avons etudie 6 de ces sources grace par la technique vlbi. Nous avons obtenu des franges d'interference pour toutes les sources et cartographie w3(oh). Les cartes laissent apparaitre une structure complexe et certains points d'emission maser apparaissent resolus. Notre resolution de 5 milliarcsecondes nous a permis de deduire sans ambiguite possible des paires zeeman qui montrent un champ magnetique variant entre 1 et 10 milligauss. Nous avons egalement observe avec l'interferometre du plateau de bure une etoile de faible masse en formation, l1551, obtenant ainsi la premiere carte millimetrique ayant une resolution inferieure a l'arc seconde. Nous calculons une masse a partir de nos observations de c170 mais surtout cela nous a permis de quantifier la qualite du site de l'interferometre en nous permettant d'en estimer le seeing.
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Polles, Fiorella Lucia. "Properties of the interstellar medium of the star-forming galaxy, IC10, at various spatial scales." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS276/document.
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Les propriétés du milieu interstellaire (MIS) influencent fortement l’environnement et les processus menant à la formation d’étoiles qui, à son tour, dicte l’évolution d’une galaxie. Les galaxies naines du Groupe Local sont de parfaits laboratoires pour comprendre comment le contenu en métaux (ou métallicité) du MIS affecte l’interaction entre le gaz, la poussière et les étoiles. Mon travail de thèse porte sur les propriétés physiques des régions HII et du gaz diffus ionisé de la galaxie naine IC10, de métallicité 1/3 solaire. La proximité de cette galaxie (d=700kpc) permet l’analyse du MIS à différentes échelles spatiales: des nuages brillants compacts (25pc) au corps entier de la galaxie formant des étoiles (650pc). Afin de mesurer les propriétés physiques du MIS, j’ai modélisé les raies d’émission en infrarouge observées avec Spitzer et Herschel grâce à des modèles de photoionisation et de photodissociation. Je présente une exploration complète de plusieurs méthodes pour déterminer, de manière la plus fiable et selon les contraintes disponibles, les propriétés du MIS à diverses échelles. J’ai contraint les propriétés des nuages compacts les plus brillants dans IC10 et montré que l’émission à plus grande échelle (300pc) est dominée par celle de ces nuages. Enfin, je démontre le besoin d’un modèle à plusieurs composantes pour reproduire les observations dans leur ensembleThe properties of the Interstellar Medium (ISM) strongly influence the environment and processes that lead to star-formation, which in turn, drives the evolution of a galaxy. Dwarf galaxies in the Local Group are perfect laboratories to investigate how the metal-poor ISM affects the interplay between gas, dust and stars. In this thesis, I investigate the properties of the HII regions and the diffuse ionized gas of the nearby dwarf galaxy IC10, which has a metallicity of 1/3 solar. Its proximity (d=700 kpc) enables the analysis on different spatial scales: from the compact clumps (~25 pc) to the whole star-forming body of the galaxy (~650pc). In order to measure the physical properties of the ISM, I model the infrared emission lines observed with Spitzer and Herschel with photoionization and photodissociation models. I present an extensive exploration of different methods to determine the most reliable ISM properties, based on the available constraints. I determined the properties of the brightest star-forming clumps within the galaxy and show that the emission at large scales (~300 pc) is dominated by that of the compact, bright clumps that lie within the region. I further demonstrate the need for a multi-component model to fully reproduce the observations
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Silva, Patricia da. "Estudo de núcleos de galáxias gêmeas da Via Láctea." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-15052018-163511/.
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Este trabalho consiste no estudo de cubos de dados das regiões centrais de quatro galáxias com mesmo tipo morfológico da Via Láctea: NGC 1566, NGC 6744, NGC 613 e NGC 134. As observações foram feitas no período de 2013 a 2015 com o Integral Field Unit do Gemini Multi-Object Spectrograph do telescópio Gemini Sul. Foram utilizadas técnicas de análise de dados como Tomografia PCA, síntese espectral e Penalized Pixel Fitting. Além disso, para todos objetos, foram calculadas razões de linhas de emissão dos espectros das regiões centrais, imagens da emissão de [SII] 6716, 6731 das nuvens de alta e baixa densidades foram feitas e, em dois casos (NGC 1566 e NGC 613), analisaram-se imagens do Hubble Space Telescope para melhor entendimento do ambiente circumnuclear. Foram encontrados 6 espectros com emissão compatível com a de AGNs na amostra, sendo que, em duas galáxias, existe a possibilidade de AGNs duplos: NGC 6744 e NGC 613. No geral, todas as galáxias apresentaram populações estelares de idades variadas em suas regiões centrais, porém, predominantemente, com metalicidades altas (0.02 e 0.05). Todas as galáxias apresentaram cinemática estelar compatível com discos de rotação em torno do núcleo e, em duas galáxias (NGC 1566 e NGC 6744), foi observado um decréscimo da dispersão de velocidades estelar em direção ao núcleo, possivelmente devido à presença de estrelas jovens massivas. A emissão do featureless continuum do núcleo da galáxia de Seyfert NGC 1566 foi, pela primeira vez, isolada e estudada, sendo que foi encontrado um índice espectral igual 1.7. Uma amostra de quatro galáxias não é estatisticamente conclusiva e será necessário ampliar a amostra para um melhor entendimento global dos núcleos de galáxias de mesmo tipo morfológico da Via Láctea.This work involved the analysis of data cubes of four nuclear regions of galaxies that have the same morphological type of the Milky Way: NGC 1566, NGC 6744, NGC 613 and NGC 134. The observations were taken in the period of 2013 to 2015 with the Integral Field Unit of Gemini Multi-object Spectrograph on the Gemini South telescope. The data were analyzed using techniques like PCA Tomography, spectral synthesis and the Penalized Pixel Fitting process. Besides that, for all the objects, emission-line ratios of the central regions were calculated, images of the emission-lines [SII]6716, 6731 of clouds of high and low densities were made and, in two cases (NGC 1566 and NGC 6744), their Hubble Space Telescope images were analyzed for better understanding of their circumnuclear regions. 6 spectra of the sample had emission compatible with that of AGNs, in two galaxies, there is a possibility of double AGN: NGC 613 and NGC 6744. In general, all the galaxies presented stellar populations with varying ages in their central regions, however mainly with high metallicities (0.02 and 0.05). All the galaxies presented stellar kinematics compatible with rotation disks around the central source and, in two galaxies (NGC 1566 and NGC 6744), there was a stellar dispersion velocity decrease toward the nuclei, possibly due to the presence of massive young stars. The featureless continuum emission of the Seyfert galaxy NGC 1566 was, for the rst time, isolated and studied. It was found that its spectral index is equal to 1.7. A sample of four galaxies is not conclusive and it is necessary to enlarge this sample to a better global understanding of the nuclei of galaxies with the same morphological type of the Milky Way.
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Verliat, Antoine. "Origine du moment cinétique et influence des jets protostellaires sur la formation d'étoiles." Electronic Thesis or Diss., université Paris-Saclay, 2021. http://www.theses.fr/2021UPASP058.
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Le milieu interstellaire, berceau des étoiles, constitue un terrain de jeu fantastique pour un physicien par sa richesse et la complexité des phénomènes mis en jeu. Comprendre les détails de la formation stellaire est un des grands défis de l’astrophysique moderne. La complexité des problèmes étudiés dans cette thèse fait des simulations numériques un outil précieux qui m’a permis d’étudier deux aspects fondamentaux de la formation stellaire. La première partie de mon travail est consacrée à comprendre l’origine de la rotation des disques de gaz et de poussière entourant les jeunes étoiles, dans lesquels se forment les planètes. La seconde est l’étude de la formation des amas d’étoiles. S’il est reconnu que les étoiles se forment en groupe, les processus influant sur la formation de ces amas et sur leur structure sont mal connus. L’étude sera particulièrement focalisée sur l’influence des jets de matière émis par les jeunes étoiles sur ces amasThe interstellar medium is the cradle of stars. It is a fantastic playground for physicists due to its richness and the complexity of the phenomena involved. Understanding the details of star formation is one of the great challenges of modern astrophysics.The complexity of the problems studied in this thesis makes numerical simulations a valuable tool. It has allowed me to study two fundamental aspects of star formation. The first part of my work is devoted to understanding the origin of the rotation of the disks made of gas and dust that surround young stars and in which planets form. The second is the study of the formation of star clusters. While it is known that stars form in clusters, the processes that influence the formation of these clusters and their structure are poorly understood. The study will focus particularly on the influence of jets of matter emitted by young stars on these clusters
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Tremblin, Pascal. "Impact de l'ionisation sur les nuages moléculaires et la formation des étoiles Simulations numériques et observations." Phd thesis, Université Paris-Diderot - Paris VII, 2012. http://tel.archives-ouvertes.fr/tel-00786668.
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À toutes les échelles de l'Astrophysique, l'impact de l'ionisation venant des étoiles massives est une question cruciale. A l'échelle galactique, l'ionisation peut réguler la formation des étoiles en soutenant les nuages moléculaires contre l'effondrement gravitationnel et à l'échelle stellaire, diverses indications pointent vers une naissance possible du système solaire à proximité des étoiles massives. À l'échelle du nuage moléculaire, il est clair que le gaz chaud et ionisé comprime le gaz froid qui l'entoure, conduisant à la formation des piliers, des globules, et des coquilles de gas dense dans lesquelles des coeurs pré-stellaires sont observés. Quels sont les mécanismes de formation de ces structures? La formation de ces coeurs pré-stellaires est-elle déclenchée par l'ionisation ou préexistante ? Les étoiles massives ont-elles un impact sur la distribution en densité du gaz environnant ? Ont-elles un impact sur la distribution des étoiles en fonction de leur masse (la fonction de masse initiale, IMF) ? Cette thèse vise à apporter des éléments de réponse à ces questions, en se concentrant en particulier sur la compréhension de la formation des structures entre le gaz froid et ionisé. Nous présentons l'état de l'art des travaux théoriques et des observations des régions ionisées (régions Hii) et nous introduisons les outils numériques qui ont été développés pour modéliser l'ionisation dans les simulations d'hydrodynamique turbulente effectuées avec le code HERACLES. Grâce aux simulations, nous présentons un nouveau modèle pour la formation des piliers basés sur la courbure et l'effondrement de la coquille dense sur elle-même et un nouveau modèle pour la formation de globules basé sur la turbulence du gaz froid. Plusieurs diagnostics ont été développés pour tester ces nouveaux modèles sur les observations. Si les piliers sont formés par l'effondrement de la coquille dense sur elle-même, le spectre en vitesse d'un pilier en formation présente un spectre avec une composante décalée vers le rouge et une composante décalée vers le bleu correspondant aux parties de la coquille en avant-plan et en arrière-plan qui rentrent en collision sur la ligne de visée. Si les globules émergent en raison de la turbulence du nuage moléculaire, le spectre en vitesse de ces globules est décalé à des vitesses différentes de celles de la coquille, des piliers et des coeurs denses qui suivent l'expansion globale de la région H ii. Un autre diagnostic est l'impact de la compression sur la fonction de densité de probabilité (PDF) du gaz froid. La distribution a un double pic lorsque la pression dynamique turbulente est faible par rapport à la pression du gaz ionisé. Il s'agit de la signature de la compression causée par l'expansion de la bulle ionisée. Quand la turbulence est élevée, les deux pics fusionnent et la compression peut encore être identifiée, mais la signature est moins claire. Nous avons utilisé des cartes de densité de colonne Herschel et des données de raies moléculaires pour caractériser la structure en densité et vitesse de l'interface entre le gaz ionisé et le gaz froid dans plusieurs régions : RCW 120, RCW 36, Cygnus X, la Nébuleuse de la Rosette et de l'Aigle. En plus des diagnostics issus des simulations, des prédictions analytiques des paramètres de la coquille et des piliers ont été testées et confrontées aux observations. Dans toutes ces régions, les modèles analytiques et les diagnostics issus des simulations donnent des résultats concluants. La structure en vitesse d'un pilier en formation dans la nébuleuse de la Rosette suggère qu'il a été formé par l'effondrement de la coquille sur elle-même et la dispersion des vitesses moyennes des globules dans Cygnus X et dans la Nébuleuse de la Rosette tend à confirmer leur origine turbulente. La compression due au gaz ionisé est visible sur la PDF du gaz froid dans la plupart des régions étudiées. Ce résultat est important pour le lien entre l'IMF et les propriétés globales du nuage. Si l'IMF peut être déduite de la PDF d'un nuage, l'impact des étoiles massives sur la PDF doit être pris en compte. En outre, nous présentons des simulations dédiées de RCW 36 qui suggèrent que les coeurs denses au bord du gaz ionisé ne sont pas pré-existants, leur formation a été déclenchée par la compression due à l'ionisation. En conséquence, l'ionisation des étoiles massives est un processus clé qui doit être pris en compte pour la compréhension de l'IMF. En annexe, nous présentons également des travaux réalisés en parallèle de cette thèse : l'échange de charge dans la collision entre vents planétaires et stellaires, en collaboration avec le professeur E. Chiang, à l'école d'été ISIMA 2011 à Pékin; et le test de site en sub-millimétrique sur la station Concordia en Antarctique avec l'équipe CAMISTIC (PI : G. Durand).
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Lefloch, Bertrand. "Formation et évolution des globules cométaires." Phd thesis, Université Joseph Fourier (Grenoble), 1994. http://tel.archives-ouvertes.fr/tel-00686752.
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Les Globules Cométaires sont des petits nuages denses que l'on observe fréquemment dans l'environnement d'étoiles 0 - B dans les régions HI!. Ces nuages sont remarquables par leur bord brillant et leur structure cométaire. Le sujet de cette thèse est une étude de la formation et de l'évolution de ces objets d'un point de vue numérique, analytique et observationnel. Nous montrons que le mécanisme de photo-ionisation par les étoiles proches (Implosion Radiative) peut rendre compte à lui-seul de la formation des globules cométaires. Numériquement, il ressort que la séquence d'évolution comprend deux principales étapes: une phase d'implosion brève suivie de la phase cométaire communément observée, beaucoup plus longue. Bien que difficile à observer, seule la première phase possède une signature spectroscopique indiscutable de la photo-ionisation. Sous certaines conditions d'ionisation des instabilités de type Rayleigh-Taylor à petite et grande échelle se développent dans le front d'ionisation et conduisent éventuellement à la destruction des nuages. Tous les globules en phase cométaire apparaissent être soutenus contre la pression du milieu extérieur par un champ magnétique statique qui semble suivre la loi de Heiles. Une étude analytique montre que tous ces nuages sont gravitationnellement stables. Les cartes de brillance synthétisées à partir des modèles numériques reproduisent avec vraisemblance les morphologies observées de nuages cométaires. Des observations radio-millimétriques du globule CG7S dans la région HII S190 ont permis de tester de manière non-ambigüe le modèle d'Implosion Radiative. Les caractéristiques observationelles de CG7S sont en bon accord avec les prédictions du modèle et ont pu être reproduites numériquement de manière satisfaisante. CG7S apparaît comme un des tous premiers nuages pré-cométaires observés à ce jour.
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Corrias, Maria Elena. "Caratteristiche di emissione delle regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10954/.
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Le regioni HII sono nubi di idrogeno ionizzato da stelle di recente formazione, massicce e calde. Tali stelle, spesso raggruppate in ammassi, emettono copiosamente fotoni di lunghezza d’onda λ ≤ 912 Å, capaci di ionizzare quasi totalmente il gas che le circonda, composto prevalentemente da idrogeno, ma in cui sono presenti anche elementi ionizzati più pesanti, come He, O, N, C e Ne. Le dimensioni tipiche di queste regioni vanno da 10 a 100 pc, con densità dell’ordine di 10 cm−3. Queste caratteristiche le collocano all’interno del WIM (Warm Ionized Medium), che, insieme con HIM (Hot Ionized Medium), WNM (Warm Neutral Medium) ed CNM (Cold Neutral Medium), costituisce la varietà di fasi in cui si presenta il mezzo interstellare (ISM, InterStellar Medium).
Il tema che ci prestiamo ad affrontare è molto vasto e per comprendere a fondo i processi che determinano le caratteristiche delle regioni HII sarebbero necessarie molte altre pagine; lo scopo che questo testo si propone di raggiungere, senza alcuna pretesa di completezza, è dunque quello di presentare l’argomento, approfondendone ed evidenziandone alcuni particolari tratti.
Prima di tutto descriveremo le regioni HII in generale, con brevi indicazioni in merito alla loro formazione e struttura. A seguire ci concentreremo sulla descrizione dei processi che determinano gli spettri osservati: inizialmente mostreremo quali siano i processi fisici che generano l’emissione nel continuo, concentrandoci poi su quello più importante, la Bremmstrahlung. Affronteremo poi una breve digressione riguardo al processo di ricombinazione ione-elettrone nei plasmi astrofisici ed alle regole di selezione nelle transizioni elettroniche, concetti necessari per comprendere ciò che segue, cioè la presenza di righe in emissione negli spettri delle regioni foto-ionizzate. Infine ci soffermeremo sulle regioni HII Ultra-Compatte (UC HII Region), oggetto di numerosi recenti studi.
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Ceccia, Domenico. "Caratteristiche di emissione delle regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15843/.
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Prendiamo in considerazione la nostra Galassia, e osserviamo una precisa regione che emette della radiazione tramite alcuni processi. La regione considerata è rilevata nei bracci della nostra Galassia, e soprattutto dove vi è presente dell’ idrogeno ionizzato, che è l’ elemento dominante in queste regioni che stiamo osservando. Stiamo parlando delle regioni HII. In questo elaborato andremo ad analizzare e capire cos’ è una regione HII e le sue principali caratteristiche, la sua formazione e collocazione, ma soprattutto capire quali sono i principali meccanismi che portano all’emissione di radiazione. Questi processi di emissione sono strettamente legati all’ osservazione della radiazione degli spettri elettromagnetici, che possono essere di due tipi. Abbiamo i “Processi nel Continuo” dove i fotoni vengono emessi in un ampio intervallo di lunghezza d’onda, frequenza ed energia, nel nostro caso parleremo di Bremsstrahlung, e i “Processi in riga” dove lo spettro elettromagnetico non appare più come un continuo ma presenta righe di assorbimento o emissione, e nel nostro caso parleremo di processi di ricombinazione. Nell’ultimo capitolo introdurremo dei recenti studi sulle regioni HII Ultra-Compatte e le andremo ad analizzare in termini di parametri fisici e di emissione.
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Borghi, Nicola. "Caratteristiche principali dell'emissione di regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16213/.
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Le regioni HII sono, in prima approssimazione, nubi di idrogeno ionizzato dai fotoni di stelle OB. Tali stelle massicce hanno temperature superficiali T∗>10^4 K e una vita media relativamente breve. Se all'interno della regione di formazione si osservano stelle a diversi stage evolutivi, è possibile seguire e studiare in dettaglio l'evoluzione delle regioni HII ad esse associate. Il mezzo interstellare ionizzato (WIM) si trova immerso in un mezzo neutro (WNM e CNM) dal quale la formazione stellare ha avuto origine. Pertanto per avere una panoramica completa delle caratteristiche di emissione non ci si può fermare al solo processo di ionizzazione. In questo testo verranno illustrate le principali caratteristiche di emissione con un approccio pancromatico e verranno accennati alcuni processi di emissione secondari. Inizialmente si assumerà un equilibrio tra la fotoionizzazione e la ricombinazione, definendo teoricamente la Sfera di Strömgren. La si assumerà costituita solamente di idrogeno, in seguito verranno brevemente discussi gli effetti dell'elio, dei `metalli' e di ulteriori processi dinamici. A questo punto si potranno giustificare le prime features osservative: le righe di ricombinazione, o RLs. In seguito si discuterà della formazione delle righe "proibite", o meglio CELs (Collisionally Excited Lines), che sono il principale processo di raffreddamento di tali regioni. Con l'accenno alle righe di ricombinazione radio si chiuderà la panoramica sui processi di emissione in riga. Nel capitolo finale sono trattati i principali processi di emissione nel continuo, ossia quelli dovuti a transizioni libero-libero (Bremsstrahlung) e alle polveri. Spesso ci si soffermerà sull'importanza di uno studio dettagliato delle regioni HII con riferimenti allo stato dell'arte della ricerca astrofisica.
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Pignataro, Giada Venusta. "Caratteristiche principali dell'emissione di regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16358/.
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In questo elaborato ci si ripropone di studiare l'emissione delle regioni HII. Si può definire una regione HII come una zona molto calda di idrogeno ionizzato, che si trova in un background di idrogeno neutro più freddo. Vengono analizzati i processi di emissione nel continuo e in riga, e analizzate in particolare le nebulose planetarie.
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Tedino, Simone. "Caratteristiche principali dell’emissione di regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17875/.
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La formazione stellare ha inizio quando massicce nubi di gas freddo collassano a causa della gravità. Le stelle così formatesi, giovani, calde ed estremamente massive, vengono classificate come stelle di classe spettrale O-B, caratterizzate da una temperatura superficiale media dell’ordine di 10^4/5 K. A queste temperature esse sono in grado di generare intensi flussi di radiazione ultravioletta (UV) che si compongono di fotoni di lunghezza d’onda <= 912 A°, e conseguente energia maggiore a hv=13.6eV, corrispondente al valore specifico del potenziale di ionizzazione dell’idrogeno (H). Questa radiazione particolarmente intensa è dunque in grado di ionizzare quasi totalmente il gas che le circonda, dando origine a spettacolari nebulose ad emissione, le regioni HII. Il tema affrontato necessiterebbe di uno studio approfondito che va ben oltre la trattazione presente, ma, senza pretese di completezza, l' elaborato si impegna ad analizzare con sufficiente dettaglio le principali caratteristiche che contraddistinguono le regioni HII. Si analizza inizialmente l'impostazione dell'equilibrio di fotoionizzazione per poter poi mostrare le caratteristiche fisico-strutturali e le principali caratteristiche di emissioni radiative tipiche di tali nebulose.
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Bianchera, Sergio. "Caratteristiche principali dell'emissione delle regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/19907/.
Full textAbstract:
Le regioni HII sono nubi di gas composte principalmente da idrogeno ionizzato. Si sviluppano attorno popolazioni di stelle giovani e molto massive di tipo O-B che riscaldano il materiale circostante. Queste regioni si possono trovare solo nelle galassie a spirale andando a comporre il Warm Ionized Medium, collocandosi principalmente nei bracci a spirale e circondate dal Cold Neutral Medium. In questo testo andremo a introdurre le principali caratteristiche astrofisiche di queste regioni, soffermandoci sui meccanismi di emissione nel continuo e in riga, approfondendo anche alcuni casi particolari tipici di queste regioni. Purtroppo la vastità dell’argomento in esame obbliga a sintetizzare e semplificare la maggior parte delle informazioni.
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Pasquale, Lorenzo. "Caratteristiche principali dell'emissione di regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21224/.
Full textAbstract:
Le Regioni HII sono plasmi astrofisici composti da idrogeno ionizzato che si formano a seguito della foto-ionizzazione, da parte di stelle giovani e massive, del mezzo neutro e freddo tipico delle regioni di formazione stellare.
Lo studio del loro spettro e dei loro processi di emissione illustrati esaustivamente in questo elaborato è di cruciale importanza in quanto fornisce informazioni riguardo non solo la formazione e l’evoluzione stellare ma anche riguardo le abbondanze chimiche dell’ISM, la distanza delle galassie e la loro dinamica interna. In particolare il tipico spettro di una regione HII è caratterizzato da righe in emissione (di ricombinazione e collisionali) sommate ad un continuo piuttosto debole, dovuto ai fenomeni di bremsstrahlung, free-bound ed alla radiazione infrarossa emessa dalle polveri.
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Zanetti, Francesca. "Caratteristiche principali dell'emissione di regioni HII." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24847/.
Full textAbstract:
Le regioni HII sono regioni del mezzo interstellare costituite da idrogeno ionizzato. Il processo di ionizzazione si deve alle stelle giovani e di grande massa che sono in grado di produrre un flusso continuo di fotoni ultravioletti. Nella trattazione che segue, si accennerà alla struttura e all'evoluzione di tali regioni. Si analizzeranno nel dettaglio i processi fisici che determinano l'emissione di radiazione, sia nel continuo che in riga. A partire dalle caratteristiche spettrali si deriveranno le caratteristiche osservabili di tali regioni. Inoltre, si evidenzierà il ruolo della riga H alpha come tracciante della formazione stellare.
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Clayton, C. A. "Echelle observations of HII complexes." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382745.
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Watkins, Aaron Emery. "A New Perspective on Galaxy Evolution From the Low Density Outskirts of Galaxies." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1499354382030385.
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Radcliffe, David Byrom. "The effect of a stellar wind on an expanding HII region." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328005.
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Su, Hongquan. "Mapping the Galaxy in 3D Using Observations of HII Region Absorption with the MWA." Thesis, Curtin University, 2022. http://hdl.handle.net/20.500.11937/89104.
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This thesis measures the distribution of the diffuse synchrotron emission in the Galactic Plane using data from the GaLactic and Extragalactic All-sky MWA survey (GLEAM) in the frequency range 72-231 MHz. It improves the method of calculating the synchrotron emissivity along sight lines intersecting HII regions, and increases the number of such measurements from tens to hundreds. A further 588 HII regions are identified using both their emission and absorption features in the GLEAM maps.
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Піддубна, Анна Іванівна, Анна Ивановна Поддубная, Anna Ivanivna Piddubna, J. K. Okafor, and V. I. Okam. "HIV in region of Nigeria." Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/15969.
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Mbuche, Joseph Kasu. "The perceptions of community members regarding reasons why HIV prevalence rate is high in Zambezi Region than in the other thirteen regions of Namibia." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97922.
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Thesis (MPhil)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Republic of Namibia situated at the South West of Africa near Atlantic Ocean is a country in Sub-Saharan Africa region. It was divided into fourteen political administrative regions during the delimitation committee of 2013. Namibia has a population of 3 million according to the census report of 2011 (Census report 2011). The prevalence rate of HIV in Zambezi Region is higher than in other thirteen regions of Namibia. Zambezi Region is geographically located between the four SADC countries such as Zambia, Angola, Botswana and Zimbabwe. Trans–Caprivi high way is believed to contribute to the high prevalence rate of 37.7 % according to the sentinel survey report of pregnant women of 2012.The traditional beliefs and customs are affecting HIV/AIDS programmes that are implemented in the region by stakeholders and the Ministry of Health and Social Services. Namibia as a country since 1992 to 2014 has conducted sentinel surveys among pregnant women and National testing days from 2008 to find out how to address HIV and AIDS epidemic in the country. Zambezi Region according to the sentinel survey reports has the highest HIV prevalence rate among pregnant women than the other thirteen regions. The reasons that are causing the high prevalence rate of HIV in this part of the country are not yet know to the citizens. The researcher in this research has used the qualitative approach method, to investigate the perceptions of community members regarding reasons of higher HIV prevalence rate in Zambezi Region. Sampling was conducted using purposive sampling in all six constituencies of the region in which 30 participants of 15 females and 15 males were interviewed. The semi - structured interview qualitative method was used to collect data from respondents. This study is the eye opener as the reasons that are contributing to the high HIV prevalence rate in Zambezi Region have been discovered.
AFRIKAANSE OPSOMMING: Nie beskikbaar
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Pepe, Francesco Alfonso. "Far-infrared imaging of the HII region-molecular cloud complex W51A with a balloon-borne telescope /." [S.l.] : [s.n.], 1995. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10992.
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Foster, Tyler J. "A multi-wavelength study of an HII region/supernova remnant pair in a rich galactic environment." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ59804.pdf.
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Vigil, Miquela 1981. "H107[alpha] recombination-line emission, 4800-MHz and 1666-MHz continuum emission in the HII region RCW38." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/114111.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2003.Cataloged from PDF version of thesis. In title on title page, "[alpha] appears as lower case Greek letter. "May 21, 2003."
Includes bibliographical references (page 31).
We present results from observations of H107[alpha] recombination-line emission and the related 4800 MHz continuum emission of the HII region RCW 38 using the Australia Telescope Compact Array. We find the continuum emission to be concentrated in a ring-like structure with the 05 star, IRS2, approximately centered in the cavity within the ring. The temperature of the ionized gas ranges from 5200 to 7500 K and the emission is optically thin. The H107[alpha] line emission appears to be confined within the continuum ring. We also find the continuum ring to encircle the peak in the diffuse X-ray gas. The radio continuum emission matches closely to NIR observations with a bright western ridge containing the peak in the 10[mu]m emission known as IRS1 (Frogel et al. 1974) apparent in both observations. From calculations of continuum and line parameters, we estimate the spectral type of the ionizing source for the region to be an 05/06 star which is consistent with the spectral type of IRS2.
by Miquela Vigil.
S.B.
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Lazzarini, Chiara. "L'atomo di idrogeno: righe, serie e sua importanza in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19489/.
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L'idrogeno è l'atomo più semplice che la natura abbia creato, ma è tutt'altro che trascurabile la sua presenza nell'Universo. Infatti, si tratta dell'atomo più abbandonante, ovvero rappresenta il 74 % di tutta la materia barionica. La sua semplicità lo rende il miglior candidato per lo studio e la comprensione delle righe spettrali. Dalla spettroscopia e dalle prime formule sulle righe spettrali nacque la teoria dei livelli energetici quantizzati nell'atomo ed essa è una delle prime radici della meccanica quantistica. Nell'elaborato viene illustrata la scoperta delle serie spettrali dell'idrogeno e la sua evoluzione fino alla teoria atomica di Bohr. Successivamente, si utilizza qualche nozione di meccanica quantistica per spiegare in dettaglio il fenomeno delle righe spettrali. Infine, vengono illustrati alcuni fenomeni astrofisici legati all'idrogeno, il cui studio è stato possibile grazie all'analisi delle righe spettrali.
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Cherid, Hafsa. "Regions of the CD127 Cytoplasmic Tail Necessary for HIV-1 Tat Binding." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31556.
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Impaired cell mediated immunity is the clinical hallmark of HIV infection yet the manner in which CD8 T-cells are disabled is not yet fully understood. IL-7 signalling is essential for normal CD8 T-cell development and function. Our lab has previously shown decreased expression of the IL-7 receptor a-chain (CD127) on circulating CD8 T-cells in HIV+ patients is mediated by the HIV Tat protein which results in poor CD8 T-cell function. Soluble Tat protein is secreted by infected CD4 T-cells and taken up by neighbouring uninfected CD8 T-cells through endocytosis. Once in the cytoplasm, Tat translocates to the inner leaflet of the cell membrane where it binds directly to the cytoplasmic tail of CD127 inducing receptor aggregation, internalization, and degradation by the proteasome. By removing CD127 from the cell surface, the HIV Tat protein is able to reduce IL-7 signaling and impair CD8 T-cell proliferation and function.
To determine which domain(s) in the cytoplamic tail of CD127 are required for interaction with Tat, a series of plasmids encoding for CD127 deletion mutants were successfully created. These series of mutant CD127 coding sequences were transfected into a eukaryotic expression system, the Jurakt cell line, where CD127 mutants were successfully expressed. Before determine which region on CD127 is required for Tat binding, an optimized Ni-NTA column system was used to successfully isolate histidine-tagged HIV-1 Tat at a high yield and purity from E. coli. This HIV Tat protein was used to treat the lysates of the Jurakt cells transfected with the panel of CD127 mutants. CD127 was then immunoprecipitated, followed by Western analysis of the immune complexes to detect Tat protein. Tat was immunoprecipitated with all CD127 mutants suggests neither tyrosine 449, box 1, the acidic region, serine region nor C-tail are specifically required for Tat binding to CD127.
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Paopongsawan, Pasakorn. "Behaviour of gold in stream sediments, Huai Hin, Loei region, northeastern Thailand." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/30268.
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Stream sediment sampling for gold exploration has encountered various problems: these include location and type of sample to be taken, determination of the appropriate sample size in view of gold particle sparsity, and the apparently erratic distribution of gold in stream sediments. Study of the behavior of gold in stream sediments could help to solve these problems and is needed to guide systematic exploration for gold in Thailand.
The Huai Hin Laep, an intermittent third order stream in Loei region, northeastern Thailand, drains a hilly area underlain by highly weathered sandstones, shales, andesites, and tuffs, blanketed by residual lateritic and podzolic soils. The stream reach is approximately 8 km long with an average gradient of 0.008. The original mixed evergreen forest has been logged and cleared for agricultural purposes.
Active stream sediment samples collected from point bars and pavements along the stream reach were processed to obtain 8 size fractions. Of these, five size fractions between 0.425 and 0.053 mm were separated into heavy and light mineral fractions, and analyzed for gold by fire assay-atomic absorption spectrophotometry. The -0.053 mm sediment fraction was split, pulverized and further split prior to analysis. The corresponding dry-sieved -0.150 mm sediment fraction was also processed and analyzed for gold. Results show that in both point-bar and pavement samples gold is concentrated in the heavy mineral fractions, whereas in all but six samples, the corresponding light fractions and the -0.053 mm fraction contain < 5 ppb gold. Similarly, thirteen out of the sixteen -0.150 mm sediment samples contain less than 5 ppb gold. Gold content is typically higher at pavement than at point-bar sites where gold concentrations are closely correlated with narrow stream channel, shallow channel depth, high flow velocity, coarse-grained sediment texture and high bed roughness, indicating that higher energy conditions favour accumulations of gold.
Estimates of numbers of free gold particles suggest that analysis of heavy mineral concentrates (between 0.425 and 0.053 mm fraction) from a 40 kg -12 mm field sample from either point-bar or pavement site has a high chance of detecting anomalous gold. In contrast, the probability of reliably detecting gold in a 30 g analytical subsample is very low.
With respect to mineral exploration, conventional stream sediment samples will usually fail to detect the gold anomaly in the Huai Hin Laep. This probably results from the dilution of the Au-rich heavy mineral fractions by the barren light minerals and large amounts of silt-clay. The presence of anomalous concentrations of gold would, however, be recognized through the use of field pan concentrates or heavy mineral separates. During regional surveys, samples for this purpose should be collected from either pavement sites or high energy point-bar sites characterized by a narrow channel, shallow depth, high flow velocity and large amount of coarse grained sediment along the lower reaches of the third order streams. Subsequently, detailed follow-up surveys should consist of more detailed sampling of either 40 kg -12 mm sediments or field pan concentrates from at least 20 kg of sediments along the stream. Anomalous concentrations of gold at the lower reaches of the stream may result from accumulation of gold by hydraulic processes rather than the location of gold mineralization. High gold concentrations at low energy sites characterized by slow flow velocity, low bed roughness and fine grained sediment texture may indicate proximity to the source of gold.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Okeke, Michael Ifeanyi. "Behaviors Related to HIV Infections in Rural Versus Urban Regions of Nigeria." ScholarWorks, 2016. https://scholarworks.waldenu.edu/dissertations/2165.
Full textAbstract:
Efforts by the Federal Republic of Nigeria and international nongovernmental agencies to reduce the impact of HIV in Nigeria have not yielded the anticipated results. This study focused on the association between attitude, religious beliefs, knowledge of HIV, sexual risk behavior, and HIV epidemiology in rural and urban Nigeria. This quantitative study used social-cognitive theory and problem theory. The study was based on the Nigerian Demographic and Health Survey (NDHS) 2013 data including a sample of 33,006 participants. Specific covariates including gender, sexual partners over the past years, age at first sexual encounter, socioeconomic status, and literacy level were obtained from the sample. Two hypotheses from each research question were tested to guide the study methodology. Linear regression results suggested that knowledge, attitude, location, and religion predicted sexual risk behavior. Muslims showed the least sexual risk behaviors compared to other religions while more positive attitudes and more knowledge increased sexual risk behaviours. Location had no significant impact on sexual risk behavior. Spearman correlation results depicted a relationship between knowledge and sexual risk behaviors of urban and rural Nigerians separately. More knowledge depicted an increase in sexual risk behaviors. The study results may be useful to Ministry of Health and program planners in constructing culturally based HIV interventions. The significant relationship between knowledge, attitude towards sex, and religious practices may be incorporated with theoretical knowledge on social-cognitive variables to enhance further understanding of the way in which individuals may engage in preventive behaviors to reduce HIV and its effects in Nigeria. Reductions in the spread of HIV/AIDS would lead to a healthy and more productive society.
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Frumence, Gasto. "The role of social capital in HIV prevention: experiences from the Kagera region of Tanzania." Doctoral thesis, Umeå universitet, Epidemiologi och global hälsa, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-49319.
Full textAbstract:
Background The role of social capital for promoting health has been extensively studied in recent years but there are few attempts to investigate the possible influence of social capital on HIV prevention,particularly in developing countries. The overall aims of this thesis are to investigate the links between social capital and HIV infection and to contribute to the theoretical framework of the role of social capital for HIV prevention. Methods Key informant interviews with leaders of organizations, networks, social groups and communities and focus group discussions with members and non-members of the social groups and networks were conducted to map out and characterize various forms of social capital that may influenceHIV prevention. A quantitative community survey was carried out in three case communities toestimate the influence of social capital on HIV risk behaviors. A cross-sectional survey was conducted to estimate the HIV prevalence in the urban district representing a high HIV prevalence zone to determine the association between social capital and HIV infection. Main findings In early 1990’s many of the social groups in Kagera region were formed because of poverty and many AIDS related deaths. This formation of groups enhanced people’s social and economic support to group members during bereavement and celebrations as well as provided loans that empowered members economically. The social groups also put in place strict rules of conduct, which helped to create new norms, values and trust, which influenced sexual health andthereby enhanced HIV prevention. Formal organizations worked together with social groups and facilitated networking and provided avenues for exchange of information including healtheducation on HIV/AIDS. Individuals who had access to high levels of structural and cognitive social capital were more likely to use condoms with their casual sex partners compared to individuals with access to low levels. Women with access to high levels of structural social capital were more likely to use condoms with casual sex partners compared to those with low levels. Individuals with access to low levels of structural social capital were less likely to be tested for HIV compared to those with access to high levels. However, there was no association between access to cognitive social capital and being tested for HIV. Individuals who had access to low levels of both structural and cognitive social capital were more likely to be HIV positive compared to individuals who had access to high levels with a similar pattern among men and women. Conclusion This thesis indicates that social capital in its structural and cognitive forms is protective to HIV infection and has played an important role in the observed decline in HIV trends in the Kagera region. Structural and cognitive social capital has enabled community members to decrease number of sexual partners, delay sexual debut for the young generation, reduce opportunities for casual sex and empower community members to demand or use condoms. It is recommended that policy makers and programme managers consider involving grassroots’ social groups and networks in the design and delivery of interventions strategies to reduce HIV transmission.