We have analyzed the ultraviolet spectra of 40 hydrogen-rich (DA) white dwarfs. These spectra have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and are publicly available via the MAST FUSE database. We derived the effective temperature and surface gravity by fitting the hydrogen Lyman spectral lines with model spectra. By applying white dwarf evolutionary models, we were able to determine the white dwarf mass, cooling age and absolute magnitude. These then allowed us to determine the distance to each star and its predicted gravitational redshift. We have identified several chemical elements in the white dwarf spectra. We determined the abundances of C, Si, P and S by measuring the equivalent widths of selected lines of these elements. Finally, we studied the spectra of J0623-376 and LM Com in more detail.

We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a data set that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch data set, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from 0.30(-0.10)(+0.09) to 0.34(-0.11)(+0.11), depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (similar to 0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km s(-1) and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of three. for binary fractions on the higher end of what has been seen in other dwarf spheroidals.

Doctor of Philosophy / Department of Psychology / Jerome Frieman / The present experiment investigated whether dwarf hamsters (Phodopus campbelli) demonstrate temporal discounting. This was investigated by comparing the behavior of dwarf hamsters and Sprague-Dawley rats (Rattus norvegicus) in an adjusting delay procedure and applying the theory of behavioral economics to explain the resulting behavior. Dwarf hamsters demonstrated temporal discounting and tolerated longer delays than did the more impulsive rats. There was not a statistically significant difference between these species concerning indifference points. There was a statistically significant difference in the slopes of their discounting functions and the delay at which the end criterion was met. Neither species exhibited sex differences with respect to these measures nor with storage of food. There were a number of differences between the species. Rats started responding quickly, whereas dwarf hamsters waited significantly longer. When faced with increasing delays, rats increased the number of pellets earned while dwarf hamsters earned the same amount. Finally, rats lost weight throughout the experiment while dwarf hamsters gained weight. There were also a number of similarities. When faced with an increasing delay, both rats and dwarf hamsters increased the number of responses made, and increased the number of times they timed out on Larger Later trials. Some of these findings disagree with previous research and predictions of the behavioral economic theory of demand, creating a need for further research.

Uma previsão fundamental do cenário L cold dark matter (LCDM) na formação de estruturas é que os halos galácticos de DM do tamanho da Via Láctea (MW) crescem pela acreção de subsistemas menores. Neste contexto, simulações deNcorpos prevêem um número de sub-halos de matéria escura, cujo tamanho e massa são comparáveis às galáxias anãs, que é muito maior do que as galáxias satélites conhecidas. Este é o que se convencionu chamar de problema das satélites faltantes (MSP). A interpretação mais popular do MSP é que os sub-halos de matéria escura menores são extremamente ineficientes na formação de estrelas, o que torna mais difícil detectá-los. Com a chegada dos grandes levantamentos fotométricos, nos últimos anos, a descoberta de uma nova população de galáxias satélites que orbitam a MW fornece evidências empíricas para acreditar que realmente existem várias galáxias pouco luminosas não detectadas ou que simplesmente habitam regiões no céu que ainda não foram observadas. Neste trabalho implementamos um algoritmo estatístico eficiente para detectar subestruturas ultra fracas da MW. O código, chamado SPARSEX, foi testado e otimizado usando um conjunto de objetos estelares previamente identificados nos dados do Sloan Digital Sky Survey (SDSS), conseguindo recuperar todos os objetos com sucesso. Além disso, a aplicação do algoritmo aos dados dos dois primeiro anos do Dark Energy Survey (DES) deu como resultado centenas de candidatos a sistemas estelares. Dezessete sistemas estelares detectados em comum com outras técnicas de busca por subestruturas, implementadas dentro do grupo de colaboração do DES, foram publicados em três artigos em 2015. Um dos candidatos publicados é o aglomerado estelar DES 1. DES1 foi detectado pelo código SPARSEX com uma alta significância estatística e aparece nas imagens do DES como uma concentração compacta de fontes pontuais azuis. O sistema estelar é consistente com uma população velha e pobre em metal. Assumindo dois diferentes perfis de densidade, os quais permitem estimar a probabilidade de que cada estrela realmente pertença ao sistema, determinamos uma distância heliocêntrica e uma magnitude absoluta total num intervalo de 77.6—87.1 kpc e 3.00 . MV . 2.21, respectivamente. O raio à meia-luz desse objeto, rh 9.88 pc, e a luminosidade são consistentes com um aglomerado estelar de baixa luminosidade do halo externo. DES1 também é x alongado (e 0.6), o que faz supor que este objeto está em estágio avançado de dissolução. Mais tarde, através de uma cuidadosa reanálise de nossos resultados, dois novos candidatos foram detectados, DES J01111341 e DES J0225+0304. Os candidatos estão localizados a uma distância heliocêntrica de 25 kpc e parecem também estar dominados por populações estelares velhas e pobres em metais. Suas distâncias ao plano orbital da galáxia anã de Sagitário, 1.73 kpc (DES J01111341) e 0.50 kpc (DES J0225+0304), indicam que eles estão possivelmente associados com a corrente da anã de Sagitário. O raio à meia-luz (rh ' 4.55 pc) e a luminosidade (MV ' +0.3) de DES J01111341 são consistentes com um aglomerado estelar ultra fraco, enquanto o raio à meia-luz (rh ' 18.55 pc) e a luminosidade (MV ' 1.1) de DES J0225+0304 colocam este objeto em uma região ambígua do plano tamanho-luminosidade entre aglomerados estelares e galáxias anãs. Determinações dos parâmetros característicos da corrente de Sagitário, tais como o espalhamento de metalicidade (2.18 . [Fe/H] . 0.95) e o gradiente de distância (23 kpc . D . 29 kpc), dentro da área amostrada do DES no hemisfério sul, também indicam uma possível associação com estes sistemas. Se esses objetos forem confirmados através de follow-up espectroscópico como sistemas ligados gravitacionalmente e compartilharem uma trajetoria Galáctica com a corrente de Sagitário, DES J01111341 e DES J0225+0304 seriam os primeiros sistemas estelares ultra fracos associados com tal corrente. Recentemente, nós reportamos a descoberta de um novo aglomerado estelar, DES 3. O novo sistema foi detectado como uma sobredensidade estelar nos dados do primeiro ano do DES e confirmado com follow-up fotométrico obtido com o Southerm Astrophysical Research (SOAR) Telecope. Nós determinamos que DES 3 está localizado a uma distância heliocêntrica de 76 kpc e é dominado por uma população velha (' 9.8Ganos) e pobre em metal ([Fe/H] ' 1.88). Embora os valores de idade e metalicidade de DES 3 são semelhantes aos aglomerados globulares, o seu raio à meia-luz (rh 6.5 pc) e a luminosidade (MV 1.9) são mais indicativos de um aglomerados estelar fraco. Com base no tamanho angular aparente, o DES 3, com um valor de rh 0.03, está entre os menores aglomerados estelares fracos conhecidos até à data. Estas novas detecções indicam que o censo de satélites da MW é ainda incompleto. A identificação e estudo de novos satélites em futuros surveys, como por exemplo o Large Synoptic Survey Telescope (LSST) será crucial para a nossa compreensão das subestruturas existentes no halo Galáctico e a evolução da Galáxia como um todo. / A fundamental prediction of the L cold dark matter (LCDM) scenario of structure formation is that galactic DM haloes of the size of the Milky Way (MW) grow by the accretion of smaller sub-systems. In this context, Nbody simulations predict a number of dark matter subhalos, with size and mass comparable to dwarf galaxies, but which is much larger than currently known satellite galaxies. This is what is conventionally called the missing satellites problem (MSP). The most popular interpretation of the MSP is that the smaller dark matter subhalos are extremely inefficient in star formation, making it more difficult to detect them. With the arrival of large photometric surveys, in recent years, the discovery of a new population of satellite galaxies orbiting the MW provides empirical evidence to believe that there are actually several low luminosity galaxies that were not yet detected or that simply inhabit regions in the sky that have not yet been observed. In this work we present an efficient statistical algorithm to detect ultra-faint MW substructures. The code, called SPARSEX, was tested and optimized using a set of stellar objects previously identified in the Sloan Digital Sky Survey (SDSS) data. It has detected successfully all known objects. In addition, the algorithm was applied on the first two years of Dark Energy Survey (DES) data, resulting in hundreds of stellar system candidates. Seventeen stellar systems detected in common with other substructure search techniques implemented within the DES collaboration were published in three papers in 2015. In particular, one published candidate is a star cluster, DES 1. DES 1 was detected by the SPARSEX code with high statistical significance and appears in DES images as a compact concentration of blue point sources. The stellar system is consistent with being dominated by an old and metal-poor population. Assuming two different density profiles, based on which we may evaluate a membership probability for each star, we determined a heliocentric distance and total absolute magnitude in the ranges of 77.6—87.1 kpc and 3.00 . MV . 2.21, respectively. The half-light radius of this object, rh 9.88 pc, and luminosity are consistent with a low-mass halo star cluster. DES1 is also elongated (e 0.6), which suggests that this object is in advanced stage of dissolution. Later, through a careful reanalysis of our results, two new candidates were detected, DES J01111341 e DES J0225+0304. The candidates are located at a heliocentric xii distance of 25 kpc and appear to have old and metal-poor populations as well. Their distances to the Sagittarius dwarf orbital plane, 1.73 kpc (DES J01111341) and 0.50 kpc (DES J0225+0304), indicate that they are possibly associated with the Sagittarius dwarf stream. The half-light radius (rh ' 4.55 pc) and luminosity (MV ' +0.3) of DES J01111341 are consistent with it being an ultra-faint star cluster, while the half-light radius (rh ' 18.55 pc) and luminosity (MV ' 1.1) of DES J0225+0304 place it in an ambiguous region of size-luminosity space between star clusters and dwarf galaxies. Determinations of the characteristic parameters of the Sagittarius stream, such as its metallicity spread (2.18 . [Fe/H] . 0.95) and distance gradient (23 kpc . D . 29 kpc), within the DES footprint in the Southern hemisphere, also indicate a possible association with these systems. If theses objects are confirmed through spectroscopic follow-up to be gravitationally bound systems and to share a Galactic trajectory with the Sagittarius stream, DES J01111341 and DES J0225+0304 would be the first ultra-faint stellar systems associated with the Sagittarius stream. Recently, we reported the discovery of a new star cluster, DES 3. The new system was detected as a stellar overdensity in first-year DES data, and confirmed with deeper photometry from the Southern Astrophysical Research (SOAR) telescope. We determine that DES 3 is located at a heliocentric distance of 76 kpc and it is dominated by an old (' 9.8 Gyr) and metal-poor ([Fe/H] ' 1.88) population. While the age and metallicity values of DES 3 are similar to globular clusters, its half-light radius (rh 6.5 pc) and luminosity (MV 1.9) are more indicative of faint star clusters. Based on the apparent angular size, DES 3, with a value of rh 0.03, is among the smallest faint star clusters known to date. These new detections indicate that the MW satellites census is still incomplete. The identification and study of new satellites in future surveys, such as the Large Synoptic Survey Telescope (LSST), will be crucial to our understanding of substructures in the Galactic halo and the evolution of the Galaxy as a whole.

Bars are common in disc galaxies along with many associated structures such as disc-like bulges, boxy/peanut bulges, rings, etc. They are a sign of maturity of disc galaxies and can play an important role in their evolution. In this thesis, I investigate the specific role bars play in quenching the star formation in, and shaping of their host galaxies. In order to test how bars affect their host galaxies, I study the discs, bars and bulges of what is currently the largest sample of barred galaxies (~3,500), selected with visual morphologies from the Galaxy Zoo project. I perform multi-wavelength and multi-component photometric decomposition, with the novel GALFITM software. With the detailed structural analysis I obtain physical quantities such as the bar- and bulge-to-total luminosity ratios, effective radii, Sérsic indices and colours of the individual components. I find a clear difference in the colours of the components, the discs being bluer than the bars and bulges. An overwhelming fraction of bulge components have Sérsic indices consistent with being disc-like bulges. I compare the barred galaxies with a mass- and environment-matched volume-limited sample of unbarred galaxies, finding that the discs of unbarred galaxies are bluer compared to the discs of barred galaxies, while there is only a small difference in the colours of the bulges. I suggest that this is evidence for secular evolution via bars that leads to the build-up of disc-like bulges and to the quenching of star formation in the galaxy discs. I identify a subsample of unbarred galaxies that are better fitted with an additional component, identified as an inner lens/oval. I find that their structural properties are similar to barred galaxies, and speculate that lenses might be former bars. Using the decompositions, I identify a sample of 271 late-type galaxies with curious bars that are off-centre from the disc. I measure offsets up to 2.5 kpc between the photometric centres of the stellar disc and stellar bar, which are in good agreement with predictions from simulations of dwarf-dwarf tidal interactions. The median mass of these galaxies is 10^9.6 M_⊙, and they are similar to the Large Magellanic Cloud, which also has an offset bar. Very few high mass galaxies with significant bulges show offsets, thus I suggest that the self-gravity of a significant bulge prevents the disc and bar from getting displaced with respect to each other. I conduct a search for companions to test the hypothesis of tidal interactions, but find that a similar fraction of galaxies with offset bars have companions within 100 kpc as galaxies with centred bars. Since many of these galaxies appear isolated, interactions might not be the only way to produce an offset bar. One suggested alternative is that the dark matter haloes surrounding the galaxies are lopsided, which distorts the potential, and imprints the lopsidedness and offsets onto the galaxy discs. I investigate the asymmetries in the kinematics of a subsample of such galaxies using data from the MaNGA survey, and find that the perturbations in the haloes are ~ 6% for both galaxies with off-centre and centred bars. I also measure the amplitude of non-circular motions in the outer discs due to an oval potential and find only minor departures from circularity, suggesting that the dark matter haloes are consistent with being spherical (axis ratio q ≳ 0.96). Therefore, the lopsidedness of the dark matter haloes cannot be the origin of the offsets. Either small companions are missed due to the incompleteness of the Sloan Digital Sky Survey spectroscopic survey, or interactions with dark matter satellites might explain the offsets. Modeling the kinematics of these galaxies, I find that the Hα gas rotation is centred closer to the centre of the bar than the centre of stellar rotation, suggesting that, in general, the bars are located closer to the dynamical centres of these galaxies than the discs. This implies that the discs are offset in these galaxies, not the bars. If offsets are characteristic of low mass galaxies only, high mass galaxies show vertically extended bars, known as boxy/peanut bulges. I investigate, for the first time, the formation and evolution of these structures associated to bars, from z≈0 to z=1. I compare two samples of moderately inclined galaxies with masses M_* > 10¹⁰ M_⊙, imaged by the Sloan Digital Sky Survey and the Hubble Space Telescope. Using a novel technique to classify bar isophotes, and based on the visual inspection of three expert astronomers, I find an evolving fraction of galaxies having boxy/peanut bulges from 30% at z≈0 to ~ 0% at z=1, and a strong correlation with stellar mass. I find 26 galaxies (15 at higher redshifts) in the phase of bar buckling, the mechanism proposed to form boxy/peanut bulges. The peak redshift of buckling is z≈0.75, where the bar buckling fraction is 4 times higher than in the local Universe. My observations suggest that many, if not all, of the boxy/peanut bulges are formed via buckling, ~ 2 Gyr after bar formation, with the buckling phase lasting for approximately 0.8 Gyr. I discuss my findings in the context of the evolution of barred galaxies and propose ideas for future work - applying similar decomposition techniques to higher redshift, and better resolution datasets, using integral field spectroscopic data to study the stellar populations of barred galaxies in greater detail, as well as a novel project to identify large nuclear discs in galaxies.

Magnetic fields are prevalent in a wide variety of low mass stellar systems and play an important role in their evolution. Yet the process through which these fields are generated is not well understood. To understand how such systems can generate strong field structures characterization of these fields is required. Radio emission traces the fields directly and the properties of this emission can be modeled leading to constraints on the field geometry and magnetic parameters. The new Karl Jansky Very Large Array (VLA) provides highly sensitive radio observations. My thesis involves combining VLA observations with the development of magnetospheric emission models in order to characterize the magnetic fields in two fully convective cool star systems: (1) Young Stellar Objects (YSOs); (2) Ultracool dwarf stars. I conducted multi epoch observations of DG Tau, a YSO with a highly active, collimated outflow. The radio emission observed from this source was found to be optically thick thermal emission with no indication of the magnetic activity observed in X-rays. I determined that the outflow is highly collimated very close to the central source, in agreement with jet launching models. Additionally, I constrained the mass loss of the ionized component of the jet and found that close to the central source the majority of mass is lost through this component. Using lower angular resolution observations, I detected shock formations in the extended jet of DG Tau and modeled their evolution with time. Taking full advantage of the upgraded bandwidth on the VLA, I made wideband observations of two UCDs, TVLM513-46 and 2M 0746+20. Combining these observations with previously published and archival VLA observations I was able to fully characterize the spectral and temporal properties of the radio emission. I found that the emission is dominated by a mildly polarized, non-thermal quiescent component with periodic strongly polarized flare emission. The spectral energy distribution and polarization of the quiescent emission is well modeled using gyrosynchrotron emission with a mean field B~100 G, mildly relativistic power-law electrons with a density ne~105-6 cm-3, and source size of R~2R*. We were able to model the pulsed emission by coherent electron cyclotron radiation from a small number of isolated loops of high magnetic field (2-3 kG) with scale heights~1.2-2.7 stellar radii. The loops are well-separated in magnetic longitude, and are not part of a single dipolar magnetosphere. The overall magnetic configuration of both stars appears to confirm recent suggestions that radio over-luminous UCD's have `weak field' non-axisymmetric topologies, but with isolated regions of high magnetic field.

Arceuthobium americanum is a vascular plant which is parasitic upon Pinus contorta var murrayana. Its documented effects include reductions in host growth, vigor and wood quality. The specific physiological changes that occur in the host are, for the most part, unknown.

No description available.

Errata attached to inside front cover. Bibliography: leaves [156-188]

Includes bibliographical references (l5 leaves) / vi, 126, [49] leaves, [17] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The aim of the work presented in this thesis was to develop molecular genetic markers for YD2 (the gene in barley which provides protection against barley yellow dwarf luteovirus) which could be used for the marker assisted selection of the gene in breeding programs and enable the gene to be cloned via a map-based approach. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1998