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While star formation and destruction may lie at the opposite ends of a star's life cycle, they display remarkable similarities. Both star forming regions and pre-planetary nebulae can be detected by observing molecular transitions in the millimetre/submillimetre regime. During specific phases they also present us with similar morphologies, with a central disk or waist and bipolar outflow, embedded within a larger cloud of gas and dust. This thesis focuses on the development and use of a pipeline to model such sources, as observed with high resolution interferometers, in order to understand the physics common to both. In the past decade ALMA has revolutionized millimetre/submillimetre astronomy, initiated by the discovery of rings in the protoplanetary disk of HL Tau. More recently, it has been used to probe the chemistry of protoplanetary disks down to a scale of just $10~{\rm au}$ in an effort to better understand the conditions necessary for planet formation. It can also be used to answer other open questions, such as how bipolar jets are launched in protostellar cores by observing their fine inner structure. ALMA can also be employed to address questions regarding pre-planetary nebulae (PPNe) and planetary nebulae (PNe), such as why PNe are observed with a lower mass than the expected mass ejected from stars during the formation of said PNe, or even why an unexpectedly large fraction of non-spherical PNe are observed. However, to continue capitalizing on these complex data, software must be developed to simplify the modelling process and match newly observed species. The pipeline presented here combines the 3-D morpho-kinematic capabilities of {\sc shape} to create physical models, the 3-D non-LTE radiative transfer code {\sc mollie} to simulate the emission of light and the ability of {\sc casa} to reproduce the complex effects introduced by the use of interferometers. The potential of {\sc mollie} itself has been expanded in this thesis by the addition of the HCN isotopologues H$^{13}$CN and DCN, as well as the molecule SO to the catalog of species whose emission it can simulate. The 3-D modelling environment of {\sc shape} is perfectly suited to drawing the shape and defining the physical properties of the many substructures observed by ALMA. The addition of these new species in {\sc mollie} will allow a larger fraction of ALMA data to be modelled to better define the physics for the areas of interest that could answer the open questions. The pipeline is used to model both a star formation and destruction source, L1527 and the Boomerang Nebula, respectively. Previously, the full line profile of C$^{18}$O (2--1) ALMA data of L1527 had only been modelled with an outer radius of $1,000~{\rm au}$. Here, all of the matter that is responsible for the P-Cygni profile is included by extending the radius to $6,200~{\rm au}$ to better match single dish observations. This results in a disk with a density profile that is over an order of magnitude lower, which could slow the formation of planets within it. The bipolar outflow is modelled for the first time with ALMA C$^{18}$O (2--1) data. While it matches previous models of CS (5--4), the sensitivity of the data is too low for strong conclusions. Data of all three observed SO lines, SO (6$_5$--5$_4$), SO (7$_6$--6$_5$) and SO (7$_8$--6$_7$), are modelled together for the first time. Previously, only the SO (7$_6$--6$_5$) and SO (7$_8$--6$_7$) had been modelled together. The results, a thin SO ring with a thickness of $15~{\rm au}$ and temperature of $32~{\rm K}$, favour the previous lone modelling of SO (6$_5$--5$_4$). As the SO (7$_6$--6$_5$) and SO (7$_8$--6$_7$) lines both involve the $J = 7$ to $J = 6$ transition, they are not independent of each other and therefore do not provide as strong a constraint if they are just modelled together. It is advised that lines with different $J$ levels are selected for future modelling and observations of multiple lines of SO. Since the surprising discovery, in 1997, that the Boomerang Nebula is colder than the cosmic microwave background (CMB), it remains a unique object. CO (1--0), CO (2--1), CO (3--2) and $^{13}$CO (3--2) ALMA data of the Boomerang Nebula are modelled to create a complete model. Previously, the ultra cool shell of the nebula, composed of H$_2$, was modelled as a two stage adiabatic explosion. However, an analytic solution for a diatomic equation of state, required for H$_2$, does not exist, so a monatomic equation of state was assumed. Here a new, numerical, approach is employed to obtain the more accurate diatomic solution. The result is that a monatomic solution will cool the shell to a temperature that is three orders of magnitude lower than the `best fitting' proper diatomic model. A much shorter expansion time-scale of $\sim100~{\rm days}$ and higher mass of $5~{\rm M_{\astrosun}}$, compared to the previous values of $5.8$ to $17.6~{\rm yrs}$ and $\ge 3.3~{\rm M_{\astrosun}}$, respectively. The shorter time-scale matches previous modelling of common envelope merger, the source of the shell. The high mass may explain why a similar absorption signal is not detected in other sources, such a mass is not common. Alternatively, the bias of interferometers that will filter out the shell without support, the shell of the Boomerang having a less complex chemical composition than other shells, allowing it to cool more efficiently, or because the shell heats back up quickly. Regardless of the reason why the shell of the Boomerang Nebula is observed, it is concluded that all other PNe and PPNe have a similar, as of yet unobserved, shell that would account for the lower than expected observed mass of PNe.

The aim of the thesis was to develop a code and pipeline for generating 3D photoionisation models of axisymmetric nebulae to better understand their ob- served structure and composition. This was achieved through a new code that amalgamated the features of popular (but separate) codes in astronomy; a 3D morpho-kinematic modelling application called Shape, a well known, large-scale spectral synthesis code called Cloudy and PyCloudy, a Python library that handles Cloudy. The resulting code presented in this thesis was called Py- Cross, an acronym for “PyCloudy Rendering of Shape Software”. The steep learning curves traditionally experienced when developing and using new codes overshadows the necessity for a formal software development lifecycle. As software development and coding is becoming an essential skill for new astronomers, who are often required to create their own codes for specific purposes, employing and adhering to a software development lifecycle during developing will help meet milestones while managing complex projects, thus ensuring reliability and quality. Here, a formal software development lifecycle and test driven development approach is described and employed in the development of the PyCross code. A detailed account of the code development, installation, functionality, user interface and operational overview is given using both theoretical and actual stellar objects. Creating photoionisation models for known planetary nebulae and novae can only be accomplished when there is sufficient information to determine the most significant physical parameters of the nebula and the central star. Presented here are novel approaches for various scientific methods/pipelines that can be employed with PyCross to generate photoionisation models. Over the course of this thesis PyCross has been used to develop, for the first time, 3D photoionisation models of novae V5668 Sagittarii (2015), V4362 Sagittarii (PTB 42) as well as planetary nebulae LoTr 1 and MyCn 18.

This thesis presents an investigation into the galactic population of planetary nebulae (PNe) whose progenitors have evolved through the engulfment of massive planets during the asymptotic giant branch (AGB) phase of their evolution. The objective of this research was to investigate the hypothesis that planet engulfment can aid in explaining the observed non-spherical planetary nebula (PN) population, as a complementary shaping mechanism to the binary hypothesis. This was performed by the design and development of a new research tool, simsplash (SIMulationS for the PLAnet Shaping Hypothesis), which was developed for the specific purpose of conducting, for the first time, a population synthesis of planet engulfment in planetary nebula progenitors. The first step in this investigation involved modelling the tidal evolution of planets orbiting PN progenitor stars to determine the importance of the adopted initial conditions and input physics in the stellar models and their effects on the orbital evolution of star-planet systems. The next step was to determine the probabilities of stars having and engulfing massive planets as a function of stellar mass and metallicity. This was achieved by combining the tidal evolution treatment with both the known exoplanet populations, as well as theoretical planet populations, and the occurrence rates of massive planets. Finally, taking into consideration the results from the analyses described above, a PN population synthesis was performed using the star formation history and metallicity evolution of the galaxy as well as varying forms of the initial mass function and planetary nebula formation constraints. The population of visible PNe in the present-day galaxy was calculated to consist of a total of 16,500+/-2,200 PNe, of which 240+/-20 PNe (1.5%) have evolved from the engulfment of a massive planet on the AGB and 3,300+/-200 PNe are the result of binary interactions (20%), translating to an expected non-spherical population of 21.5% of all PNe currently visible in the galaxy. The overall conclusion from this work is that while planet engulfment can explain a small fraction of the observed population of non-spherical PNe (7%), the hypothesis is not capable of resolving the mystery of the unexplained population of non-spherical planetary nebula morphologies. This conclusion adds support to the emerging view that not all low-to-intermediate mass stars can form visible PNe.

In this thesis, studies of the kinematic properties for a sample of Galactic bipolar planetary nebulae, based on optical and infrared observations, were performed us- ing a morpho–kinematic code, optical and NIR diagnostic diagrams, and techniques using data analyses. The mechanisms that form complex bipolar planetary nebulae remain unclear, and their shapes can be generated either as a planetary or symbiotic nebula. The origin of the material ionised by the white dwarf is very different in these two scenarios, and it complicates the understanding of the morphologies of planetary nebulae. The physical properties, structure, and dynamics of the bipolar nebulae, MyCn 18, M 2–9, Mz 3, Hen 2–104, and Abell 14, are each investigated in detail with the aim of understanding their nature, shaping mechanisms, and evolutionry history. For MyCn 18, VLT infrared images, VLT ISAAC infrared spectra, and long– slit optical echelle spectra are used to investigate the inner and outer regions of the nebula. The morpho–kinematic modelling tool shape was used to firmly constrain the structure and kinematics of the source. For M 2–9, Mz 3, and Hen 2–104, long– slit optical echelle spectra were used to investigate their morpho–kinematics using shape. Near–infrared data, as well as optical spectra, were used to separate Galac- tic symbiotic–type nebulae from genuine planetary nebulae, which included M 2–9, Mz 3, Hen 2–104, and MyCn 18, by means of a 2MASS J–H/H–Ks diagram and a λ4363/Hγ vs. λ5007/Hβ diagnostic diagram, respectively. For Abell 14, a detailed study of its 3-D morphology and kinematics were performed using shape. The overall conclusion is that, for each object, the kinematics, morphology, nebular evolution, and their nature, are better understood by means of morpho–kinematic and spectroscopic analyses.