Astronomy Education Research has shown that students have many challenges when it comes to understanding key concepts in Astronomy. Amongst these is a poor understanding of astronomical scales. Recently for example, both sizes and distances have been shown to present similar difficulties to students in both South Africa and Norway. It is difficult to attribute the findings simply to inadequate teaching due to the significant differences between the two countries with regard to language, culture, and the type of science teaching. It has, therefore, been suggested that since astronomical sizes and distances are beyond immediate human experience the explanation might in fact lie at a deeper cognitive level. The present thesis is aimed at exploring the link between astronomical sizes and distances as well as cognition. Part I The thesis focuses on investigating students' understanding of sizes and distances in astronomy. This was done by probing student notions of astronomical scales, using the size and distance questions from the Introductory Astronomy Questionnaire (IAQ), the instrument which led to the original findings noted previously. These questions were administered before and after a specially structured teaching intervention on sizes and distances. The results of this study in 2018 were found to be (a) in agreement with similar studies previously reported in South Africa and Norway, namely, that both sizes and distances in astronomy were poorly understood in both contexts and (b) that the teaching intervention was least effective for distances. Based on the findings above, the focus of the thesis shifted to a more fine-grained investigation of how students conceived of distances, as they increased from "human scale" to "beyond human scale". The study was carried out using the Grounded Theory Method (GTM). Data were generated by prompting written explanations from introductory astronomy students on how they engaged with three distances two of which may be considered to be within human experience while the third lies beyond the realm of direct experience. The distances used were 7 metres, 100 kilometres and the distance to the moon. The second distance was partly informed by the idea that we often communicate large distances to each other in terms of time. In addition, the framing of the questions excluded the possibility of visual explanations. The questions were administered to a cohort of introductory astronomy students at the University of Cape Town in 2019. A grounded analysis of the student responses was carried out to identify key ideas. The categories that emerged from the analysis showed clear evidence of students using different, unconnected types of explanations rather than simple extrapolations of one idea. A conceptual transition was identified relative to the body position of the respondents: body calibration and self-propelled body motion (or journeying). What was striking was that time was rarely mentioned explicitly. The way in which students expressed themselves was assumed to be an expression of the way in which they were thinking about different distance domains and suggestive of the cognitive perspective offered by "Embodied Cognition". Of particular interest was that nonstatic explanations were centered around the notion of a journey, and one of the key "thinking templates" in Embodied Cognition; the SOURCE-PATH-GOAL "Image Schema". Part II of the thesis summarizes key elements of Embodied Cognition that are pertinent to the present work and describes a pilot activity for teaching astronomical distances based on this account. Part II Theories of cognition can roughly be divided into two camps: those that assume that thinking is a "mentalese activity" involving symbolic manipulation. Most importantly, these symbolic elements are "amodal" in that they are not derived from the sensory modalities. On the other hand, Embodied Cognition assumes that these symbols arise from the sensory modalities, hence all thinking arises from bodily experience and its interactions with the environment in infancy. While there are several strands that feed into Embodied Cognition, of direct interest to the present work is that of Cognitive Linguistics and the notion of Conceptual Metaphor. In this view metaphors are not regarded as (mere) linguistic devices but as conceptual expressions that reflect cognitive schematic structures that relate to the bodily infant experience. These cognitive schematic structures or "Image Schemas" arise from repeated bodily actions repeatedly activating particular neural networks and form the basic building blocks of all abstract thought. A fair amount of such Image Schemas (or "thinking templates") have been identified of which the SOURCE-PATH-GOAL resonates most clearly with the data described earlier. This Image Schema comes about in infancy when a child learns that a toy on the far side of a room cannot be reached by grasping only but that moving the body from one place to another (crawling) is required. This is the basis of "Life is Journey or the Ph.D. Journey", for example. Another aspect of Embodied Cognition holds that understanding involves a mental simulation using the cognitive resources that are activated at the time. In order to see if activating the SPG / Journey "thinking template" prior to engaging with the teaching material would help in comprehending astronomical distances a two-part teaching activity (A and B) was developed around the notion of a journey. Part A was presented to the students as 'Journey to the observable edge of the UNIVERSE along UNIVERSity avenue" and required students to walk the length of the campus in a structured manner that is described in detail in the thesis. Part B, engagement with the teaching material, was carried out immediately afterwards in the Main Hall of the University. Thus, the thinking behind the two-part activity, piloted in 2020 just prior to Covid related lockdown, was that "journey" cognitive resources would be activated by the experience and would therefore be used in engaging with the teaching material regarding astronomical distances. Student evaluations were gathered in order to probe how students had engaged with the activity, including if any of the resources associated with journeying were expressed. A post-test ranking task showed that while results were mixed relative to previous studies overall there was a marked improvement for the present cohort. In summary the work shows clearly that there were two different modes of thinking about distances (i) based on counting and (2) based on the notion of the journey/journey-ing. Results were interpreted as the activation of schema described by embodied cognition. The difficulty that students experienced with astronomical distances was attributed to the lack of activating the Source-Path-Goal schema. In order to see whether there was a way to activate the Source-Path-Goal schema, an activity involving students walking was designed. The outcomes from the activity, indicated promising results with regard to student engagement with astronomical distance.

This thesis presents a multi-wavelength exploration of the emissions from magnetic cataclysmic variable (mCV) stars with specific focus on the eclipsing AM Her system, UZ Fornacis (hereafter UZ For). The main objective of this thesis is to investigate the underlying emission mechanisms as well as the accretion dynamics in this system with the intention of increasing our understanding of this class of objects as a whole. The presence of a strong magnetic field in UZ For makes it an interesting object in terms of how the magnetic field dominates the accretion dynamics and its influence on the emission processes. The eclipsing characteristics of this system, with a clearly defined ingress and egress of the main accretion spot, can be exploited to gain further insights through precise eclipse timings. The first part of this thesis presents 33 new mid-eclipse times spanning eight years of observations on UZ For. The new observations are used to test the two-planet model previously proposed to explain the periodic variations in the eclipse times of UZ For measured over the past ∼35 years. The results show that the proposed model does indeed follow the general trend of the new eclipse times. However, there are significant departures. In order to accommodate the new eclipse times, the two-planet model requires that one or both of the planets have highly eccentric orbits, i.e. e ≥ 0.4. Such multiple planet orbits are considered to be unstable. Whilst our new observations are consistent with two cyclic variations as previously predicted, significant residuals remain. This study explores the possibility that either additional cyclic terms, possibly associated with more planets, or other mechanisms, such as the Applegate mechanism are contributing to the eclipse time variations. The second part of this thesis presents phase-resolved spectroscopy of UZ For which allowed us to do a detailed Doppler tomography study of this target. The averaged blue spectrum is dominated by single- and/or double-peaked emission from HeII 4686 Å and the Balmer lines, as well as weak emission from HeI lines and the CIII/NIII blend at 4650Å. The averaged red spectrum shows strong emission from CaII lines at 8498 Å and 8542 Å and possibly weak emission from the NaI doublet at 8183 Å and 8194 Å. The strength of HeII 4686 Å line is comparable to that of Hβ line and this is typical for AM Her systems in a high state of accretion. The ratio of Hγ/Hβ ' 1 implying that these emission lines were formed in an optically thick region, that is, a region of high optical depth in the lines. Doppler tomography of the strongest features in the blue, HeII 4686Å and the Balmer lines (e.g. Hβ line), using both the standard and inside-out maps, revealed the presence of three emission regions: 1) the irradiated face of the secondary star, 2) the ballistic stream and the threading region, and 3) the magnetically confined accretion stream. The Doppler maps of emission lines in the red spectrum show the presence of emission from the irradiated face of the secondary star as well as emission from various parts of the ballistic and magnetically confined accretion stream. Also presented are the respective modulation Doppler maps of each line. These show that both the ballistic and magnetically confined accretion stream are modulated as well as the irradiated face of the secondary star. In addition to the above, the first simultaneous optical and MeerKAT radio observations of the eclipsing AM Her system UZ For are also presented. The optical data include SALT circular spectropolarimetry taken around the eclipse and SHOC and MeerLICHT photometry. The total intensity spectrum shows broad emission features with the continuum that rises in the blue. The percentage circularly polarized spectra show that UZ For is negatively polarized (up to ∼ −8%) in the blue and decreasing gradually towards the red. The circularly polarized spectrum shows the presence of three cyclotron emission features at ∼4500 Å, 6000 Å and 7700 Å, corresponding to harmonic numbers 4, 3 and 2, respectively. These features are dominant before the eclipse and disappears after the eclipse. The harmonics are consistent with the magnetic field strength of ∼57 MG seen at a viewing angle of 70◦ . To aid with the interpretation of the circular spectropolarimetry, simultaneous circular and linear photopolarimetric observations of UZ For obtained with the HIPPO instrument several weeks leading to the SALT observations were also analysed. The results show that UZ For is ∼ −5% circularly and 5% linearly polarized before the eclipse. A burst of linear polarization is seen just after the eclipse reaching ∼10%. After the eclipse, negative circular polarization reaching ∼ −5% is observed. Both linear and circular polarization are consistent with zero after phase 1.1. The MeerKAT radio observations show a faint source which has a peak flux density of 30.7 ± 5.4 µJy/beam at 1.28 GHz (L-band) at the position of UZ For. This marks the first detection of UZ For at L-band. This study demonstrates that multi-wavelength observations are essential to understanding the various emission processes that are at work in mCVs. The results presented in this thesis shows that UZ For is one of the most interesting AM Her systems known to date. The circular spectropolarimetry results are consistent with those from literature and shows that the SALT telescope will be able to observe other systems like this for detailed analysis. Furthermore, the eclipse times of this system is consistent with the presence of two planets and makes UZ For the second AM Her system after HU Aqr shown to harbour planets and in which additional observations still support earlier conclusions. The radio detection of this system with MeerKAT opens a window to studying other low flux density AM Her systems at L-band radio frequencies in the southern sky.

Extreme ultraviolet and X-ray photons from the Sun generate a partially ionized region in the atmosphere of a planet called an ionosphere. Solar activity, including solar flares, coronal mass ejections, and changes in the ionizing irradiance affect planetary ionospheres on short and long timescales. These effects are significant because the ionosphere is a reservoir from which atmospheric species are lost to space, and changes to a planet’s ionosphere have implications for atmospheric loss and planetary habitability over the course of solar system history. This dissertation aims to fill a gap in our understanding of how the ionospheres of Venus and Mars react to solar activity; namely, how the electron density and ion composition respond to changing solar irradiance in the highly variable region above the ionospheric peak. Using remote sensing observations from Venus Express and Mars Global Surveyor, I find that the observed increases in electron density during periods of high solar irradiance exceed the predictions of photochemical equilibrium theory at high altitudes at both Venus and Mars. I use one-dimensional photochemical equilibrium models to show that the overall expansion of the neutral atmosphere due to increasing neutral temperature is the dominant factor in determining how electron densities in the dayside ionosphere above the ionospheric peak react to changing solar irradiance. Using in situ observations from Pioneer Venus and MAVEN, I show that the expansion of the neutral atmosphere can also alter the ion composition at both planets. Assessing the observations in a fixed neutral number density frame rather than a fixed altitude frame reveals differences between the planets. At Mars, changes in the ion composition are driven by increasing solar flux. At Venus, changes in the ion composition are driven by changes to the composition of the neutral atmosphere as well as increasing solar flux. Thus, higher solar irradiance increases the electron density and alters the makeup of the ions available to be lost to space. Because the neutral atmosphere is so important to ionospheric behavior, I find that for the best interpretation of ionospheric data, simultaneous in situ observations of the neutral atmosphere should be analyzed wherever possible.

Aiming at understanding the role of stellar feedback in galaxy evolution, I present a study of the hot interstellar medium in several representative galaxies, based primarily on X-ray observations as well as theoretical modelling. I find that, in the massive disk galaxies NGC2613 and M104, the observed amount of hot gas is much less than that predicted by current galaxy formation models. Such a discrepancy suggests a lack of appropriate treatments of stellar/AGN feedback in these models. I also find that stellar feedback, primarily in the form of mass loss from evolved stars and energy released from supernovae, and presumably consumed by the hot gas, is largely absent from the inner regions of M104, a galaxy of a substantial content of evolved stars but little current star formation. A natural understanding of this phenomenon is that the hot gas is in the form of a galactic-scale outflow, by which the bulk of the stellar feedback is transported to the outer regions and perhaps into the intergalactic space. A comparison between the observed sub-galactic gas structures and model predictions indicate that this outflow is probably subsonic rather than being a classical supersonic galactic wind. Such outflows are likely prevalent in most early-type galaxies of intermediate masses in the present-day universe and thus play a crucial role in the evolution of such galaxies. For the first time I identify the presence of diffuse hot gas in and around the bulge of the Andromeda Galaxy (M31), our well-known neighbor. Both the morphology and energetics of the hot gas suggest that it is also in the form of a large-scale outflow. Assisted with multiwavelength observations toward the circumnuclear regions of M31, I further reveal the relation between the hot gas and other cooler phases of the interstellar medium. I suggest that thermal evaporation, mostly likely energized by Type Ia supernovae, acts to continuously turn cold gas into hot, a process that naturally leads to the inactivity of the central supermassive blackhole as well as the launch of the hot gas outflow. Such a mechanism plays an important role in regulating the multi-phase interstellar medium in the circumnuclear environment and transporting stellar feedback to the outer galactic regions.

Galactic bulges of early-type spirals and elliptical galaxies comprise primarily old stars, which account for more than half of the total stellar mass in the local Universe. These stars collectively generate a long-lasting feedback via stellar mass loss and Type Ia supernovae. According to the empirical stellar mass loss and supernova rates, the stellar ejecta can be heated to more than 107 K, forming a very hot, diffuse, and iron-rich interstellar medium. Conventionally a strong galactic wind is expected, especially in low- and intermediate-mass early-type galaxies which have a relatively shallow potential well. X-ray observations, however, have revealed that both the temperature and iron abundance of the interstellar medium in such galaxies are unexpectedly low, leading to the so-called “missing feedback” and “missing metal” problems. As an effort to address the above outstanding issues, we have carried out a series of hydrodynamic simulations of galactic bulge feedback on various scales. On galactic halo scales, we demonstrate that the feedback from galactic bulges can play an essential role in the halo gas dynamics and the evolution of their host galaxies. We approximately divide the bulge stellar feedback into two phases: (1) a starbusrt-induced blastwave from the formation of the bulge built up through frequent major mergers at high redshifts; and (2) a gradual feedback from long-lived low mass stars. The combination of the two can heat the surrounding gas beyond the virial radius and stop further gas accretion, which naturally produces a baryon deficit around Milky Way-like galaxies and explains the lack of large-scale X-ray halos. On galactic bulge scales, we study the collective 3-dimensional effects of supernovae with their blastwaves resolved. We find that the sporadic explosions of supernovae can produce a wealth of substructures in the diffuse hot gas and significantly affect the spectroscopic properties of the X-ray-emitting gas. The differential emission measure in the temperature space has a broad lognormal-like distribution. Such distribution enhances the X-ray emission at both low and high energy bands. We further show that the SN Ia ejecta is not well-mixed with the ambient medium and the X-ray emission is primarily from the shocked stellar wind materials which in general have low metallicities. These 3-dimensional effects provide a promising explanation to the above “missing feedback” and “missing metal” problems. In addition, we demonstrate that the supernova iron ejecta forms a very hot bubbles, which have relatively larger radial velocities driven by buoyancy, resulting in a smaller iron mass fraction in the bulk outflow. These distinct properties give a natural explanation to the observed positive iron abundance gradient which has been a puzzle for decades.

Stellar bow shocks result from the supersonic collision of stellar winds ejected by runaway stars and the interstellar medium (ISM). Studying their properties provides constraints on mass-loss rates, stellar wind velocities and the properties of the ISM. In this work, we study the formation of bow shocks from stars at the tail end of the runaway velocity distribution which we refer to as high-velocity runaway (HVR) stars. We use PLUTO, a magneto-hydrodynamics grid code, to simulate these bow shocks, performing hydrodynamic simulations in 2- and 3-dimensions, while including thermal conduction and detailed radiative cooling/heating. Extensive 3D freely expanding stellar wind models testing the numerics in PLUTO, e.g., grid geometries, solvers, limiters and convergence with resolution are presented. Further 2D adiabatic, thermal conduction and radiative cooling models for runaways moving at v∗ ∼ 40 km/s were conducted, and verified through comparison with analytic models and the literature. We then present the main focus of this work, our results for HVRs with space velocities of 200 km/s and 400 km/s, for stars in both main-sequence (MS) and red-supergiant (RSG) phases, and moving through different ISM phases: the hot ionized medium (HIM), H II regions (HII), warm neutral medium (WNM) and cold neutral medium (CNM). We demonstrate that the star's evolutionary phase; ISM phase; relative space velocity; thermal conduction and radiative cooling/heating, all have significant impact on the morphology and evolution of the bow shocks. We studied all the HVR bow shock models focusing primarily on the properties of the reverse shock and the contact discontinuity. We also studied the development of instabilities and numerical artifacts. The latter we suggest is mainly due to the carbuncle phenomenon, while the former are due to the non-linear thin-shell, Kelvin-Helmholtz and Rayleigh–Taylor instabilities. Furthermore, we discuss results from comparing 2D and 3D models to determine the effect of dimensionality on the growth of these instabilities and the carbuncle phenomenon. This study serves as the foundation of future work in which we will i) investigate the potential of observing these HVR bow shocks by making multi-wavelength estimates using established radiative transfer codes (e.g., TORUS) and producing synthetic images at different wavelengths (e.g., ultraviolet, Hα, infrared and radio), ii) couple these hydrodynamic models to established stellar evolutionary codes (e.g., MESA), and iii) include the effect of magnetic field and stellar rotation.

Capture-recapture has been identified as a possible use case for estimating the underlying size of astrophysical transient populations. In this work, we present a series of exploratory analyses using capture-recapture methods from biostatistics. In the first of three separate analyses, we reproduce results of Laycock (2017). Strategically sampled X-ray lightcurves of simulated populations of high mass X-ray binaries (HMXBs) are used to probe estimator behaviour and efficiency. Overall, these statistically closed population estimators converge to the input population with increasing number of observations, yet estimator efficiency is shown to be significantly be affected by sampling strategy. I then employ nonstandard estimator models to account for variations in capture probability of individuals within the population, categorised into ‘behavioural', ‘temporal', and ‘heterogeneous' effects. In the second analysis, we present a methodology for closed population capture-recapture analysis using real data from the OGLE-IV XROM survey. The data samples consisted of observations that were grouped into epochs. The large variation in quiescent magnitude of the population creates heterogeneity in the capture probability of sources which requires non-standard modelling. Estimation of population size is therefore limited by the choice of observational magnitude threshold. Bias corrected estimation proves to be potentially useful in this context. In the third and final investigation, we present a ‘robust design' approach with a population of Dwarf Nova located towards and in the Galactic Bulge identified from the OGLE-II, -III, and -IV phases. This approach combines closed and open population practices that allows new individuals identified between the survey phases to be added to the study sample for dynamical estimation. These investigations provide a future course for population size estimation of transients and variable stellar population alongside population synthesis simulations. The generation of capture histories remain non-trivial through the choice of observation grouping, brightness scale, and imposed flux threshold. Further, there remain several unexplored avenues of inquiry and refinement for this methodology pertaining to astronomy using explanatory variables in the modelling. Recommendations are made for further exploration of the topic.

In this thesis I present the results of optical spectroscopic analyses of four Polars and the spectra of five new systems. The results of four candidate magnetic cataclysmic variables, which were selected from the ROSAT Bright Survey, are also presented. Time resolved spectra are used for the dual purpose of conducting Doppler tomographical studies and searching for any evidence of cyclotron beaming. The first five chapters are introductory and background sections, including a review of all individual objects with magnetic field strengths determined by cyclotron spectroscopy. In Chapter 6 I discuss the observations, data reduction and analysis techniques while the results of individual objects are presented in Chapter 7. Results are presented for the two Polars HU Aqr and QS Tel, which were selected as test objects to confirm the techniques of Doppler tomography and cyclotron spectroscopy, respectively. Doppler maps, similar to those previously obtained, are produced for HU Aqr. Two cyclotron humps are also detected in the HU Aqr spectra corresponding to a magnetic field of 39 MG, again similar to values quoted in the literature. A complex cyclotron spectrum for QS Tel indicates that the second magnetic pole is more dominant than in previous studies. Spectra are presented for the new Polars RX J1313-32, RX J1141-64, RX J1610+03, RX J0153-59, RX J0501-03, RX J0512-72 and.RX J0515+01. More extensive observations were made for RX Jl313-32 and RX Jll41-64, with Doppler maps derived for RX J1313-32 while the RX J1141-64 spectra show a rise in the spectral slope, indicative of cyclotron radiation. Four ROSAT Bright Survey sources, RBS 0324, RBS 0372, RBS 0490 & RBS 1969, were selected to search for any evidence of them being magnetic cataclysmic variables. More detailed spectroscopy and photometry was obtained for RBS 0324, the only RBS source which shows evidence of being a magnetic system. The other RBS systems are all probably dwarf novae in quiescence.

Upcoming surveys with new radio observatories such as the Square Kilometer Array will generate a wealth of imaging data containing large numbers of radio sources. Different classes of radio sources can be used as tracers of the cosmic environment, including the dark matter density field, to address key cosmological questions. Classifying these sources based on morphology is thus an important step toward achieving the science goals of next generation radio surveys. Extended Radio Sources have been traditionally classified as Fanaroff-Riley (FR) I and II, although some exhibit more complex 'bent' morphologies arising from environmental factors or intrinsic properties. In this work we present the FIRST Classifier, an on-line system for automated classification of Compact and Extended radio sources. We developed the FIRST Classifier based on a trained Deep Convolutional Neural Network Model to automate the morphological classification of compact and extended radio sources observed in the FIRST radio survey. Our model was trained independently for 20 times and achieved an average accuracy, precision, recall and F1 of 0.98. The current version of the FIRST classifier is able to identify the morphological class for a single source or for a list of sources as Compact or Extended (FRI, FRII and BENT).

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