Observations of AB Doradus, a nearby, rapidly-rotating K0 dwarf are analysed, and the surface magnetic field is shown to be approximated by a potential field. Evolving the surface magnetic field according to diffusion and the observed differential rotation still yields good correlation between the calculated and observed radial field after 30 days, contradictory to the results of Barnes et al. (1998), leading to the conclusion that there is an additional cause for the evolution of the magnetic field. The chromospheric magnetic field is modelled as a potential field with a source surface. Using the stability criteria g.B = 0 and B.V(g.B) < 0, places where prominences can be stable are investigated. For agreement with the results of Donati et al. (2000)- that prominences form preferentially near the equatorial plane and at and beyond corotation- it is necessary to add a quasidipolar field of maximum strength ~20G.

According to the current cosmological paradigm, ``Lambda Cold Dark Matter'' (LambdaCDM), only ~20% of the gravitating matter in the universe is made up of ordinary (i.e. baryonic) matter, while the rest consists of invisible dark matter (DM) particles, which existence can be inferred from their gravitational influence on baryonic matter and light. Despite the large success of the LambdaCDM model in explaining the large scale structure of the Universe and the conditions of the early Universe, there has been debate on whether this model can fully explain the observations of low mass (dwarf) galaxies. The Local Group (LG), which hosts most of the known dwarf galaxies, is a unique laboratory to test the predictions of the LambdaCDM model on small scales. I analyze the kinematics of LG members, including the Milky~Way-Andromeda (MW-M31) pair and dwarf galaxies, in order to constrain the mass of the LG. I construct samples of LG analogs from large cosmological N-body simulations, according to the following kinematics constraints: (a) the separation and relative velocity of the MW-M31 pair; (b) the receding velocity of dwarf galaxies in the outskirts of the LG. I find that these constraints yield a median total mass of 2*10^{12} solar masses for the MW and M31, but with a large uncertainty. Based on the mass and the kinematics constraints, I select twelve LG candidates for the APOSTLE simulations project. The APOSTLE project consists of high-resolution cosmological hydrodynamical simulations of the LG candidates, using the EAGLE galaxy formation model. I show that dwarf satellites of MW and M31 analogs in APOSTLE are in good agreement with observations, in terms of number, luminosity and kinematics. There have been tensions between the observed masses of LG dwarf spheroidals and the predictions of N-body simulations within the LambdaCDM framework; simulations tend to over-predict the mass of dwarfs. This problem is known as the ``too-big-to-fail'' problem. I find that the enclosed mass within the half-light radii of Galactic classical dwarf spheroidals, is in excellent agreement with the simulated satellites in APOSTLE, and that there is no too-big-to-fail problem in APOSTLE simulations. A few factors contribute in solving the problem: (a) the mass of haloes in hydrodynamical simulations are lower compared to their N-body counterparts; (b) stellar mass-halo mass relation in APOSTLE is different than the ones used to argue for the too-big-to-fail problem; (c) number of massive satellites correlates with the virial mass of the host, i.e. MW analogs with virial masses above ~ 3*10^{12} solar masses would have faced too-big-to-fail problems; (d) uncertainties in observations were underestimated in previous works. Stellar mass-halo mass relation in APOSTLE predicts that all isolated dwarf galaxies should live in haloes with maximum circular velocity (V_max) above 20 km/s. Satellite galaxies, however, can inhabit lower mass haloes due to tidal stripping which removes mass from the inner regions of satellites as they orbit their hosts. I examine all satellites of the MW and M31, and find that many of them live in haloes less massive than V_max=20 km/s. I additionally show that the low mass population is following a different trend in stellar mass-size relation compared to the rest of the satellites or field dwarfs. I use stellar mass-halo mass relation of APOSTLE field galaxies, along with tidal stripping trajectories derived in Penarrubia et al., in order to predict the properties of the progenitors of the LG satellites. According to this prediction, some satellites have lost a significant amount of dark matter as well as stellar mass. Cra~II, And~XIX, XXI, and XXV have lost 99 per-cent of their stellar mass in the past. I show that the mass discrepancy-acceleration relation of dwarf galaxies in the LG is at odds with MOdified Newtonian Dynamics (MOND) predictions, whereas tidal stripping can explain the observations very well. I compare observed velocity dispersion of LG satellites with the predicted values by MOND. The observations and MOND predictions are inconsistent, in particular in the regime of ultra faint dwarf galaxies. / Graduate

Dwarf galaxies may form in the tidal tails of galaxy interactions. If these tidal dwarf galaxies (TDGs) detach from their parent galaxies, then an independent dwarf galaxy emerges. However, the lifespan of such objects is uncertain. Using IR, UV, and optical images, we conducted a search for detached TDGs from a set of 40 interacting galaxy pairs in the local Universe, and a control sample of 37 spiral galaxies. Both samples include 3.6 micron, 4.5 micron, 8 micron, and NUV images. In an earlier study (Smith et al. 2016), we used the IRAF daofind software (Stetson 1987) to search for star-forming regions within the main bodies of these galaxies and in their extended tidal tails. In the current study, we used the same procedure to search for such regions outside of the galaxies. We used two spatial scales to search for the TDGs, 1 kiloparsec and 2.5 kiloparsecs radius, and then used Spitzer infrared colors to identify and eliminate possible foreground stars and background quasars. The remaining objects may be detached tidal dwarfs that formed in the tails and then escaped. After comparing our observational results of the number of TDGs surrounding our interacting galaxies to the numbers around normal spirals, we find no significant difference in the number of candidate TDGs near interacting galaxy pairs compared to normal spiral galaxies. The most promising TDG candidates will be targeted by follow-up spectroscopic observations to determine their redshifts, metallicities, and their velocity structures. Younger TDGs are expected to have higher metallicities relative to their masses compared to primordial dwarf galaxies, relative to the standard mass-luminosity relationship for galaxies. Furthermore, TDGs should lack dark matter in contrast to primordial dwarf galaxies.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (C.I.T.E.S.) has always recognized Osteolaemus tetraspis osborni (Schmidt, 1919) as a geographic subspecies of the African dwarf-crocodile, taxonomically distinguished from the subspecies Osteolaemus tetraspis tetraspis Cope, 1861. These two subspecies are primarily based on anatomical evidence that is not visible on a whole living animal. The subspecies distinction is the internal degree of boniness of the septum between the two external nostrils. This character must be examined by dissection of the animal’s head. Therefore it is desirable that some reliable and diagnostic kind of externally visible identification character (such as coloration, measuring head proportions, or counting scales) should be searched for. Otherwise, any individual Osteolaemus tetraspis animal must be partly dissected to see what subspecies it is. In this thesis, approximately a dozen different external characters (mostly counting scales or rows of scales) are independently tested and compared with each other in an effort to determine which of them is the most useful as an identification tool for separating the Osteolaemus t. osborni subspecies from the O. t. tetraspis taxon. If none of these scalation details are found to be 100% reliable as a predictor of the appropriate geographic taxon, then some additional factors become relevant, such as their comparative difficulties in physically performing the investigation. Some kinds of scale-counts are easier to define and record than others. The new sample is 68 African dwarf-crocodiles, of which 53 are geographically in the COAST (O. t. tetraspis) taxon, and 15 are from the INTERIOR (O. t. osborni). The data was collected by field-work in numerous African nations, and the expedition sampled and travelled across the C.I.T.E.S. subspecies boundary between these two taxa in several ways. In comparison with earlier published reports about scalation characters in the Osteolaemus tetraspis species, this new sample is relatively large, and has remarkably good precision about locality data. Further, this expedition (the Zoer Osteolaemus Project, 2006-2007) exercised extreme care to apply clear definitions for the various characters (scale-counts, row-counts, etc.). Based on good samples, and on the high quality scalation data collected in 2006-2007 in Africa, it is concluded that none (zero) of these dorsal and ventral skin characters (with the possible exception of the two kinds of ventral scale-counts, for which the INTERIOR sample was only 3 animals) yield satisfactory results for discriminating subspecies of dwarfcrocodiles in the general part of the continent that was examined. All of these many kinds of scalation features fail to 100% reliably predict the correct subspecies (COAST or INTERIOR) outcome. Some characters never (0,00%) work, while other characters work part of the time, but not one gives the level of predictability that is required by C.I.T.E.S. for quick and accurate taxonomic identification in Osteolaemus tetraspis with these two subspecies as regulated taxa. All of the literature scalation characters required detailed special examination procedures, usually involving physically handling the animal. This thesis invents and recommends a new kind of character which has the advantage that just looking at the dorsal surface of the crocodile is often sufficient, and sometimes it can be done through a telescope. For this “permit-free” scalation character, properly taken photographs can include the normal (tourist at the zoo) view from the side and slightly above. It is not necessary to look straight down at the animal, as long as the number of transverse rows on the base of the neck, and along the length of the body, and on the proximal half of the tail can be counted. Neither the old nor the new characters work 100% of the time, and although the permitfree count of transverse rows on the dorsum is slightly more predictive than any of the others, even this new method yields remarkably poor results. However, given a large enough sample (for example bushmeat or stuffed animals or flat hornback hides passing through a local market over a long period of time), it is predicted that an interesting indication of subspecies identification could, in a statistical way, possibly be obtained. In the final analysis, though, African dwarf-crocodile scale-counts do not appear to support the model of two taxa in Osteolaemus tetraspis as a species, and therefore they do not support the inclusion of Osteolaemus tetraspis osborni as a regulated taxon on the C.I.T.E.S. list of crocodilians. AFRIKAANS : Het CITES verdrag (“Convention on International Trade in Endangered Species of Wild Fauna and Flora”) heeft Osteolaemus tetraspis osborni (Schmidt, 1919) altijd erkent als een geografische ondersoort van de Afrikaanse dwergkrokodil, die onderscheiden kan worden van Osteolaemus tetraspis tetraspis Cope, 1861. Deze twee ondersoorten zijn primair gebaseerd op anatomisch bewijs dat niet zichtbaar is op een puntgaaf en levend dier. Het onderscheid tussen de ondersoorten is de interne graad van het aanwezig bot van de afscheiding tussen de twee uitwendige neusgaten. Dit karakter zal moeten worden onderzocht middels een autopsie op het hoofd van het dier. Daarom is het wenselijk dat er gezocht wordt naar een aantal betrouwbare en diagnostieke vormen van uitwendig zichtbare identificatie karakters (zoals kleuring, het meten van hoofdproporties, of het tellen van schubben). Zo niet, dan zal ieder individueel Osteolaemus tetraspis dier gedeeltelijk moeten worden ontleed om te zien welke ondersoort het betreft. In deze scriptie zijn ongeveer een twaalftal verschillende uitwendige karakters (met name het tellen van schubben of rijen van schubben) onafhankelijk van elkaar getest en onderling vergeleken in een poging om vast te stellen welke van hen het meest bruikbaar is als een middel ter identificatie voor het onderscheiden van de Osteolaemus t. osborni ondersoort en de O. t. tetraspis taxon. Wanneer geen van deze schubbenkleed details als 100% betrouwbaar wordt beschouwd als voorspeller van de van toepassing zijnde taxon, dan worden een aantal aanvullende factoren relevant, zoals de moeilijkheidsgraad van de fysieke uitvoering van het onderzoek. Sommige schubbentellingen zijn eenvoudiger te definiëren en te registreren dan andere. De nieuwe sample bestaat uit 68 Afrikaanse dwergkrokodillen, waarvan er 53 geografisch gezien in de KUST (O. t. tetraspis) taxon zitten en er 15 zijn van het BINNENLAND (O. t. osborni). De gegevens zijn verzameld middels veldwerk in een groot aantal Afrikaanse landen en de expeditie verzamelde op verscheidene manieren gegevens van deze taxa aan beide zijden van de C.I.T.E.S. ondersoorten grens. In vergelijking met eerder gepubliceerde rapporten over schubbenkleed karakters in de soort Osteolaemus tetraspis, is deze nieuwe sample relatief groot en heeft het opvallend nauwkeurige plaatsgegevens. Verder heeft deze expeditie (het Zoer Osteolaemus Project, 2006-2007) voor zeer duidelijke definities gezorgd voor de verschillende karakters (schubbentellingen, rij-tellingen, enz.). Op basis van goede samples en de hoge kwaliteit van de in 2006-2007 in Afrika verzamelde schubbenkleed gegevens, kan worden geconcludeerd dat geen (nul) van deze rug en buik huidkarakters (met mogelijk uitzondering van de twee schubbentelllingen op de buik, waarvan de BINNENLAND sample slechts 3 dieren was) bevredigende resultaten geeft om ondersoorten in dit breedvoerig onderzochte deel van het continent te kunnen onderscheiden. Al deze schubbenkleed kenmerken schieten te kort om 100% betrouwbaar de juiste ondersoort te voorspellen (KUST of BINNENLAND). Sommige karakters werken nooit (0,00%), andere gedeeltelijk, maar geen enkele geeft het door C.I.T.E.S. vereiste niveau van voorspelbaarheid voor een snelle en accurate identificatie van Osteolaemus tetraspis met deze twee ondersoorten als gereguleerde taxa. Alle schubbenkleed karakters uit de literatuur vereisten gedetailleerde en speciale onderzoeksprocedures, waaronder vaak het fysiek hanteren van het dier. Deze scriptie vindt uit en beveelt aan een nieuw karakter, welke het voordeel heeft dat enkel het kijken naar de bovenkant van de krokodil voldoende is en soms met behulp van een verrekijker kan gebeuren. Voor deze “vergunning-vrije” schubbenkleed karakter kunnen fatsoenlijk genomen foto’s het normale (toerist in een dierentuin) aanzicht weergeven van de zijkant en lichtelijk van boven. Het is niet nodig om recht boven het dier naar beneden te kijken, zolang het aantal rijen van de basis van de nek in de lengterichting van het lijf tot ongeveer de helft van de staart kunnen worden geteld. Noch de oude, noch de nieuwe karakters werken in 100% van de gevallen en ondanks dat de “vergunning-vrije” telling van dwars op de bovenkant van het dier lopende rijen een iets betere voorspelling geeft dan alle andere, heeft zelfs deze nieuwe methode opvallend slechte resultaten. Echter, met een sample die groot genoeg is (bijvoorbeeld “bushmeat” of opgezette dieren of huiden, die over een lange periode op lokale markten worden verhandeld) ligt het in de lijn der verwachting dat er een interessante indicatie voor de identificatie van ondersoorten (op een statistische manier) kan worden verkregen. Al met al kan worden gezegd dat schubbentellingen in Afrikaanse dwergkrokodillen niet het model van twee taxa in Osteolaemus tetraspis ondersteunen en daarmee Osteolaemus tetraspis osborni niet erkennen als een gereguleerd taxon in de C.I.T.E.S. lijst van krokodillen. / Dissertation (MSc)--University of Pretoria, 2010. / Animal and Wildlife Sciences / unrestricted

1D stellar evolution and nucleosynthesis simulations have traditionally modeled the mixing within convection zones as a diffusive process. The fluids within a convection zone are advecting and do not diffuse. However the diffusive approximation is valid when the burning timescale of an exothermic reaction is longer than the convective turn over timescale to which the mixing of those species is approximated over. Since it is 1D, it also assumes that the material is isotropically distributed within the convection zone. In the He-flash convection zones of rapidly accreting white dwarfs (RAWD) H is ingested and burned well within the convective turn over time of 38 minutes. The H is burned through the exothermic 12C(p,γ)13N reac- tion, Q = 1.944 MeV, and then the unstable 13N, with a half-life of 9.6 minutes, will decay to 13C which will undergo the 13C(α,n)16O reaction releasing neutrons. The neutron densities, depending on the H-ingestion rates and mixing details, reach Nn ≈ 1013 − 1015 cm−3 which starts the i-process within the convection zone. The H burning provides energy to the flow leading to the dynamic details of the flow being important for the mixing of the H and thus the i-process nucleosynthesis. This is a convective-reactive environment. The isotropic, well mixed over many convective turn over timescales, and long burning timescale assumptions for H in the diffusive approximation are broken in the convective-reactive environment of a He-shell flash convection zone in a RAWD. To more accurately model convective-reactive mixing environments, a 1D two stream advective mixing model is formulated. A downstream advects H-rich material from the top of the convection zone down to the H-burning region while the upstream advects H-poor material back up to the upper convective boundary. The mixing model includes a horizontal mass flux, γ, which describes the efficiency to which mass is mixed between the two streams. This predominately causes the homogenization of the material between the two streams. The radial mass flux, α, and the horizontal mass flux, γ, are calibrated from 3D hydrodynamic simulations of the RAWD in order to model the mixing within the He-flash shell convection zone. The downsampled 3D cartesian data output, the briquette data, from the 3D hy- drodynamic simulations is used to compute γ. This required using numerical tools to interpolate quantities onto spherical shells from 3D cartesian data and to decompose the radial velocity field into its spherical harmonic modes. Trilinear interpolation is the simplest 3D interpolation method that was tested and it was the interpolation method of choice due to the constraints it has on the interpolating function. The validity of using higher order methods on the briquette data was studied in detail but was determined to not be usable due to the computational effort and constraints of the methods. The two stream model post-processing of the H burning within the 3D hydro- dynamic simulations of the RAWD showed excellent agreement in the metrics of the total mass of H burned, the burning rate and burning location of H. This includes two models which undergo dramatic H-ingestion and burning events caused by a GOSH, Global Oscillations of Shell H-ingestion. By adding a network containing 1000’s of species to the 1D advective mixing model, the i-process from the RAWD is simulated and compared with a traditional 1D diffusive mixing model. The resulting neutron densities between the two models are comparable however the efficiency to which each produce the heaviest stable elements are different. To reproduce the elemental abun- dance distribution of the CEMP-r/s star CS31062-050, the diffusive model is run for 15 days of stellar time while the advective model is run for 20 days. The H-ingestion into the He-shell as predicted by the stellar evolution calculations lasts 30 days. The i-process material within the RAWD can be removed from it and participate in the galactic chemical evolution of the galaxy that it resides in. This is due to the RAWD possibly reaching the Chandrasekhar mass and from the loss of material through stellar winds and common envelope interactions with its nearby companion star. / Graduate

Dwarf mistletoes are Parasitic flowering plants that infect conifer tree species. The effects of Arceuthobium americanum on the seed crop of Pinus contorta were examined over a two year period to evaluate the effects of altered host reproductive success on host population dynamics. Heavily infected trees produced significantly fewer cones than uninfected trees during the first season in which cones were collected. Cone length, number of seeds per cone, individual seed mass, and total calories per seed were significantly reduced in moderately and heavily infected trees. Trees with different levels of infection showed trends consistent with the above but no significant differences were observed during the second season. The number of seeds that were produced, disseminated, and that germinated per square meter of forest floor was significantly less in heavily infected plots than in lightly infected plots. Survival of one year old seedlings, however, was significantly higher in heavily infected plots. Significant increases in the abundance of woody litter due to increases in mortality of mature trees and witches brooms were positively correlated with increases in seedling survival in heavily infected plots. Survival of trees less than 45 years of age also increased as the level of infection in plots increased. This increases the fraction of total density that saplings represent in heavily infected stands. The total basal area of plots with different levels of infection were uniform, implying that all available environmental resources are being utilized. The differences in age distribution between lightly and heavily infected plots, however, indicate that resources are partitioned differently between saplings and mature trees in plots with different levels of infection. Dominant host trees experienced higher mortality in heavily infected plots than in lightly infected plots. This reduces the total biomass of all mature trees. Increased mortality of dominant host trees frees resources which reduces intraspecific competition thereby contributing to increased sapling survival in heavily infected plots. Consequently, stand density increases as the level of infection increases.

>Magister Scientiae - MSc / This work aims to study the dark matter content of the nearby (7.38 Mpc) dwarf galaxy IC 4710 using the HI line observations from the Australia Telescope Compact Array (ATCA). We produce the rst interferometric maps of the galaxy HI distribution and dynamics and use these maps to measure important quantities such as total HI mass, velocity width, and size. We create a dynamical model of the galaxy using a three-dimensional modeling technique. The rotation curve was obtained by tting a 3D tilted ring model to the HI data cube of galaxy IC 4710. The dynamical modeling of IC 4710 is being done for the rst time. We compare the model to the data cube to check for accuracy and found that they are in good agreement; this shows that the results are reliable. The obtained rotation curve is rising steeply until it reaches the maximum rotation velocity of 24.6 km s􀀀1 at a radius of 100 arcsec.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, February 6, 2015. / We explore indirect detections of Dark Matter, focusing on deep radio observations of six dwarf spheroidal galaxies (dSph), Carina, Fornax, BootesII, Hercules, Segue2, Sculptor. We discuss the WIMP Dark Matter particle annihilation process and describe brie y the particles produced in this process. We consider the emissions, which can result from electrons and positrons produced. We describe why dSph are the best observational targets for indirect Dark Matter detection at radio frequencies. We describe the theoretical framework for predicting Dark Matter synchrotron emissions and make some predictions for the six dSph of interest to us. We discuss ATCA observations of these dSph and explore the background source subtraction process in detail. We obtain an upper limit on the WIMP mass and compare our results to various other experiments. We discuss prospects for this work towards attaining an indirect Dark Matter detection.

Thesis (Ph.D.)--Boston University / This dissertation studies the interstellar medium (ISM) in dwarf galaxies. Dwarf galaxies are important because: 1) they constitute the largest fraction of extragalactic systems, and 2) they provide templates for primordial galaxies. Indeed, local active dwarf galaxies resemble primitive systems, since they are poor in dust and heavy elements and they are profusely forming massive stars. Because dwarf galaxies are nearby, however, they can be observed in much greater detail than distant primordial systems. Therefore studies of the ISM in nearby dwarf galaxies can be used to understand the processes at work in primitive galaxies. This work focuses on the effects of low heavy element abundances (i.e., low metallicities) on the star-forming ISM. Low metallicities are known to drastically affect the ISM. With decreasing metallicity, an increasingly large fraction of the molecular ISM is photodissociated into atoms and ions. We modeled and observed the emission of a sample of low metallicity dwarf galaxies in the millimeter, submillimeter, and far-infrared wavebands. The submillimeter waveband allows us to observe the mid-J rotational transitions of carbon monoxide (CO), the usual tracer of the molecular ISM, and the fine structure transit ions of neutral carbon ([C I]), a tracer of translucent and photodissociated material. We studied regions in the Large and Small Magellanic Clouds and the Northern Hemisphere dwarf galaxy IC 10. We find that the preponderant mechanism producing neutral carbon inside molecular clouds is photodissociation. We observe a moderate increase in the ratio of [C I] to CO emission for decreasing metallicity. Our models of clumpy, unresolved photo dissociation regions explain these observations as the natural result of an augmented fraction of photo dissociated material. Finally, our observations of the submillimeter thermal dust continuum in IC 10 find an abnormally low emissivity exponent for its graybody emission. We conclude that the unusual dust continuum is caused by the selective destruction of small grains, brought about by the combined effects of low metallicities and high radiation fields.

No description available.