Molecular Line Emission from Planet-Forming Disks with ALMA

The physical and chemical conditions in the protoplanetary disk set the initial conditions for planet formation. Constraining the properties of disks is of key importance for understanding how planets assemble. Observations of molecular lines in disks provide valuable information on disk properties. This thesis presents ALMA observations, analysis and modelling of molecular line emission from four disks that all exhibit evidence for forming planets. Using the first-ever observations of 13C17O in protoplanetary disks, the CO gas mass of the HD 163296 and HL Tau disks are robustly constrained. The new masses are a factor of 2-10 times higher than existing estimates using C18O, and highlight the potential gravitational instability of the HL Tau disk. Analysis of the radial distribution of HCO+ and H13CO+ in the HD 97048 disk reveals a low ratio that can be explained via chemical fractionation. This indicates that the gas temperature in the outer disk is low (approx. 10 K) despite this disk being hosted by an A-type star. Both silicon and sulphur bearing volatiles are observed to be significantly depleted in disks, similar to dark clouds. Multiple lines of SO and SiO are targeted towards HD 100546 and HD 97048. The detection of the shock tracer SO in the HD 100546 disk is attributed to either a disk wind or a circumplanetary disk. Complementary chemical modelling reveals the molecular carriers of S and Si in the two sources, and predicts SiS as tracer of S and Si in disks. This thesis shows that 13C17O is a robust tracer of disk gas mass, HCO+ isotopologue emission may trace reservoirs of cold gas in typically warm disks, and Si and S bearing molecules are useful probes of shock induced structures such as circumplanetary disks

From Wicked Problems to Wicked Solutions: An Investigation of the Partnership Approach To Delivering Public Health and Adapting to the Pandemic

In the field of Public Health, Partnership Working aims to enhance policymaking in order to improve the health and wellbeing of a population and reduce health inequalities. This is reflected in Welsh Government’s establishment of Boards such as the Public Services Boards and Regional Partnership Boards as embedded in the Wellbeing of Future Generations (2015) and the Social Services and Wellbeing Act (2014). These Boards not only demonstrate the Welsh Government’s focus on the importance of the health and wellbeing of the population but also aim to engender a sense of national belonging. However, as policy literature demonstrates, there are barriers that can hinder the effectiveness of partnership working. This thesis is made up of two major components. The first is an investigation into the delivery of Health and Wellbeing Goals via Partnership Working, with a particular focus on Public Services Boards (PSBs) in South Wales. This first study uses one-to-one interviews to identify the various views of members of the Public Services Board surrounding the definition and understanding of the concept of Partnership Working. It distinguishes the existing Partnership Working relationships within the PSBs and thus identifies the main existing perceptions of the barriers and facilitators to effective Partnership Working practice within the PSBs. The second major component to this thesis intends to build upon the results of the first study by utilising the unprecedented event of COVID-19 as a case study of how a global crisis can put a strain on Partnership Working practices and service delivery. However, this section of the thesis also intends to examine whether an event such as COVID-19 can in fact bring unintentional opportunities for the Boards to re-evaluate their practices and priorities and to ultimately make improvements to the delivery of services in their communities. In its conclusion this thesis makes recommendations based on the learning brought forth from the pandemic and the ways in which this learning can be maintained

Performing Selves:Distance and Identification in the Experimental Performance Work of Imitating the Dog (ITD), Desperate Optimists and Insomniac Productions.

This thesis counters the common postmodern privileging of distance over identification within artistic practice. After Brecht, identification in the theatre has predominantly been imagined as a conservative operation that always aligns us with the status quo. These theories could be described in Eve Sedgwick's terms as 'paranoid' practices that necessarily detest the objects they investigate. At the same time, as Sedgwick maintains, they assume a position of absolute knowledge (2003, p. 138). In other words, paranoid practices implicitly claim to reveal or expose underlying formations of brutality. I argue instead that itd's practice is not intent on denying identification, but rather holds distance and identification together. Our work recognises that identification is a necessary subjective practice, whilst also asking what is at stake in our specific investments and identifications. I maintain that itd's work gets close to its objects: it caresses their forms with love. At the same time, it always negotiates the place of distance, yet without disgust and without definite knowledge. Distance, in this thesis, is a place of engagement and contemplation: even of provisional judgement. Concomitantly, I argue that these very investments sustain us, give us a place to be in the world, whilst being the most productive form of giving and understanding

SO and SiS Emission Tracing an Embedded Planet and Compact 12^{12}CO and 13^{13}CO Counterparts in the HD 169142 Disk

Planets form in dusty, gas-rich disks around young stars, while at the same time, the planet formation process alters the physical and chemical structure of the disk itself. Embedded planets will locally heat the disk and sublimate volatile-rich ices, or in extreme cases, result in shocks that sputter heavy atoms such as Si from dust grains. This should cause chemical asymmetries detectable in molecular gas observations. Using high-angular-resolution ALMA archival data of the HD 169142 disk, we identify compact SO J=8$_8$-7$_7$ and SiS J=19-18 emission coincident with the position of a ${\sim}$2 M$_{\rm{Jup}}$ planet seen as a localized, Keplerian NIR feature within a gas-depleted, annular dust gap at ${\approx}$38 au. The SiS emission is located along an azimuthal arc and has a similar morphology as a known $^{12}$CO kinematic excess. This is the first tentative detection of SiS emission in a protoplanetary disk and suggests that the planet is driving sufficiently strong shocks to produce gas-phase SiS. We also report the discovery of compact $^{12}$CO and $^{13}$CO J=3-2 emission coincident with the planet location. Taken together, a planet-driven outflow provides the best explanation for the properties of the observed chemical asymmetries. We also resolve a bright, azimuthally-asymmetric SO ring at ${\approx}$24 au. While most of this SO emission originates from ice sublimation, its asymmetric distribution implies azimuthal temperature variations driven by a misaligned inner disk or planet-disk interactions. Overall, the HD 169142 disk shows several distinct chemical signatures related to giant planet formation and presents a powerful template for future searches of planet-related chemical asymmetries in protoplanetary disks.Comment: 22 pages, 12 figures, accepted for publication in ApJ

Tracing snowlines and C/O ratio in a planet-hosting disk: ALMA molecular line observations towards the HD169142 disk

The composition of a forming planet is set by the material it accretes from its parent protoplanetary disk. Therefore, it is crucial to map the chemical make-up of the gas in disks to understand the chemical environment of planet formation. This paper presents molecular line observations taken with the Atacama Large Millimeter/submillimeter Array of the planet-hosting disk around the young star HD 169142. We detect N2H+, CH3OH, [CI], DCN, CS, C34S, 13CS, H2CS, H2CO, HC3N and c-C3H2 in this system for the first time. Combining these data with the recent detection of SO and previously published DCO+ data, we estimate the location of H2O and CO snowlines and investigate radial variations in the gas phase C/O ratio. We find that the HD 169142 disk has a relatively low N2H+ flux compared to the disks around Herbig stars HD 163296 and MWC 480 indicating less CO freeze-out and place the CO snowline beyond the millimetre disk at ~150 au. The detection of CH3OH from the inner disk is consistent with the H2O snowline being located at the edge of the central dust cavity at ~20 au. The radially varying CS/SO ratio across the proposed H2O snowline location is consistent with this interpretation. Additionally, the detection of CH3OH in such a warm disk adds to the growing evidence supporting the inheritance of complex ices in disks from the earlier, colder stages of star formation. Finally, we propose that the giant HD 169142 b located at 37 au is forming between the CO2 and H2O snowlines where the local elemental make of the gas is expected to have C/O=1.0.Comment: Accepted A&A 13th August 202

Chemical signatures of a warped protoplanetary disc

Circumstellar discs may become warped or broken into distinct planes if there is a stellar or planetary companion with an orbit that is misaligned with respect to the disc. There is mounting observational evidence for protoplanetary discs with misaligned inner discs and warps that may be caused by such interactions with a previously undetected companion, giving us a tantalising indication of possible planets forming there. Hydrodynamical and radiative transfer models indicate that the temperature varies azimuthally in warped discs due to the variable angle at which the disc surface faces the star and this impacts the disc chemistry. We perform chemical modelling based on a hydrodynamical model of a protoplanetary disc with an embedded planet orbiting at a 12$^{\circ}$ inclination to the disc. Even for this small misalignment, abundances of species including CO and HCO$^+$ vary azimuthally and this results in detectable azimuthal variations in submillimetre line emission. Azimuthal variations in line emission may therefore indicate the presence of an unseen embedded companion. Nonaxisymmetric chemical abundances should be considered when interpreting molecular line maps of warped or shadowed protoplanetary discs.Comment: Accepted to MNRAS. 18 pages, 14 figure

Investigating the asymmetric chemistry in the disk around the young star HD 142527

The atmospheric composition of planets is determined by the chemistry of the disks in which they form. Studying the gas-phase molecular composition of disks thus allows us to infer what the atmospheric composition of forming planets might be. Recent observations of the IRS 48 disk have shown that (asymmetric) dust traps can directly impact the observable chemistry, through radial and vertical transport, and the sublimation of ices. The asymmetric HD 142527 disk provides another good opportunity to investigate the role of dust traps in setting the disk's chemical composition. In this work, we use archival ALMA observations of the HD 142527 disk to obtain an as large as possible molecular inventory, which allows us to investigate the possible influence of the asymmetric dust trap on the disk's chemistry. We present the first ALMA detections of [C I], 13C18O, DCO+, H2CO and additional transition of HCO+ and CS in this disk. In addition, we have acquired upper limits for non-detected species such as SO and CH3OH. For the majority of the observed molecules, a decrement in the emission at the location of the dust trap is found. For the main CO isotopologues continuum over-subtraction likely causes the observed asymmetry, while for CS and HCN we propose that the observed asymmetries are likely due to shadows cast by the misaligned inner disk. As the emission of the observed molecules is not co-spatial with the dust trap and no SO or CH3OH are found, thermal sublimation of icy mantles does not appear to play a major role in changing the gas-phase composition of the outer disk in HD 142527 disk. Using our observations of 13C18O and DCO+ and a RADMC-3D model, we determine the CO snowline to be located beyond the dust traps, favouring cold gas-phase formation of H2CO, rather than the hydrogenation of CO-ice and subsequent sublimation.Comment: Accepted for publication in A&A on 12/04/202

Synthesis of novel 6-enaminopurines

Two different approaches have been used for the synthesis of 6-enaminopurines 6 from 5-amino-4-cyanoformimidoyl imidazoles 1. In the first approach imidazoles 1 were reacted with ethoxymethylenemalononitrile or ethoxymethylenecyanoacetate under mild experimental conditions and this led to 9-substituted-6-(1-amino-2,2-dicyanovinyl) purines 6a-f or 9-substituted-6-(1-amino-2-cyano-2-methoxycarbonylvinyl) purines 6g-k. These reactions are postulated to occur through an imidazo-pyrrolidine intermediate 7, which rapidly rearranges to the 6-enaminopurine 6. In the second approach 6-methoxyformimidoyl purines 3, prepared in two efficient steps from 5-amino-4-cyanoformimidoyl imidazoles 1, were reacted with malononitrile and methylcyanoacetate with a mild acid catalysis (ammonium acetate or piperidinium acetate) to give 6-enaminopurines 6a, 6d, 6f, 6g and 6k in very good yields. Only low yields were obtained for the 6-enaminopurine 6j, as competing nucleophilic attack on C-8 of either 3d or 6j causes ring opening with formation of pyrimido-pyrimidines 11 and 10a respectively.Universidade do Minho. Fundação para a Ciência e Tecnologia - PRAXIS/C/QUI/10101/1998

Resolved Debris Discs Around A Stars in the Herschel DEBRIS Survey

The majority of debris discs discovered so far have only been detected through infrared excess emission above stellar photospheres. While disc properties can be inferred from unresolved photometry alone under various assumptions for the physical properties of dust grains, there is a degeneracy between disc radius and dust temperature that depends on the grain size distribution and optical properties. By resolving the disc we can measure the actual location of the dust. The launch of Herschel, with an angular resolution superior to previous far-infrared telescopes, allows us to spatially resolve more discs and locate the dust directly. Here we present the nine resolved discs around A stars between 20 and 40 pc observed by the DEBRIS survey. We use these data to investigate the disc radii by fitting narrow ring models to images at 70, 100 and 160 {\mu}m and by fitting blackbodies to full spectral energy distributions. We do this with the aim of finding an improved way of estimating disc radii for unresolved systems. The ratio between the resolved and blackbody radii varies between 1 and 2.5. This ratio is inversely correlated with luminosity and any remaining discrepancies are most likely explained by differences to the minimum size of grain in the size distribution or differences in composition. We find that three of the systems are well fit by a narrow ring, two systems are borderline cases and the other four likely require wider or multiple rings to fully explain the observations, reflecting the diversity of planetary systems.Comment: 19 pages, 13 figures, 6 tables. Accepted for publication in MNRA