The vibrant school of printmaking which emerged and flourished in New Zealand between 1900 and 1950 forms the subject of this thesis. It examines the attitudes of the printmakers, many of whom regarded the print as the most democratic of art forms and one that should reflect the realities of everyday life. Their subject matter, contemporary city scenes, people at work and leisure, local landscapes, Mダori and indigenous flora and fauna, is analysed and revealed as anticipating by over a decade that of regionalist painters. They are also identified as the first New Zealand artists to draw attention to social and environmental issues. Trained under the British South Kensington art education system, New Zealand printmakers placed great importance on craftsmanship. Although some worked in a realist style others experimented with abstraction and surrealism, placing them among the forefront of New Zealand artists receptive to modern art. Expatriate New Zealand printmakers played significant roles in three major printmaking movements abroad, the Artists’ International Alliance, Atelier 17 and the Claude Flight Linocut Movement. The thesis redresses the failure of existing histories of New Zealand art to recognise the existence of a major twentieth-century art movement. It identifies the main factors contributing to the low status of printmaking in New Zealand. Commercial artists rather than those with a fine arts background led the Quoin Club, which initiated a New Zealand school of printmaking in 1916; Gordon Tovey’s overthrow of the South Kensington system in 1945 devalued the craftsmanship so important to printmakers; and the rise of modernism, which gave priority to formal values and abstraction, further exacerbated institutional indifference to the print. The adoption of Mダori imagery by printmakers resulted in recent art historians retrospectively accusing them of cultural appropriation. Even the few printmakers who attained some recognition were criticised for their involvement in textile and bookplate design and book-illustration. Key artists discussed in the thesis include James Boswell, Stephen Champ, Frederick Coventry, Rona Dyer, Arnold Goodwin, Thomas Gulliver, Trevor Lloyd, Stewart Maclennan, Gilbert Meadows, John L. Moore, E. Mervyn Taylor, Arthur

New Zealand Prints 1900-1950: An Unseen Heritage

Massive and intermediate-mass stars reside in binary systems much more frequently than low-mass stars. Binaries containing massive main-sequence (MS) component(s) are often characterised by eccentric orbits, and can be observed as eccentric ellipsoidal variables (EEVs). The orbital phase-dependent tidal potential acting on the components of EEV can induce tidally excited oscillations (TEOs). We investigate how the history of resonances between the eigenmode spectra of the EEV components and the tidal forcing frequencies depends on the initial parameters of the system. We synthesised 20,000 evolutionary models of the EEVs across the MS. Later, we calculated the eigenfrequencies for each model. We focused only on the $l=2$, $m=0,+2$ modes. Knowing the temporal changes in the orbital parameters of simulated EEVs and the changes of the eigenfrequency spectra for both components, we were able to determine so-called `resonance curves', which describe the overall chance of a resonance occurring. We analysed the resonance curves by constructing basic statistics for them and analysing their morphology using machine learning methods, including the Uniform Manifold Approximation and Projection tool. The EEV resonance curves from our sample are characterised by striking diversity, including the occurrence of exceptionally long resonances or the absence of resonances for long evolutionary times. Both components may be subject to increased resonance rates as they approach the TAMS. On average, we should observe TEOs more frequently in EEVs containing massive components than intermediate-mass ones. TEOs will be particularly well-pronounced for EEVs with the component(s) close to the TAMS. Given the total number of resonances and their rates, TEOs may play an important role in the transport of angular momentum within massive and intermediate-mass stars (mainly near TAMS).

/pdf/theoretical-investigation-of-the-occurrence-of-tidally-2ntht32x.pdf

Theoretical investigation of the occurrence of tidally excited oscillations in massive eccentric binary systems

The origin of the observed population of Wolf-Rayet (WR) stars in low-metallicity (low-Z) galaxies, such as the Small Magellanic Cloud (SMC), is not yet understood. Standard, single-star evolutionary models predict that WR stars should stem from very massive O-type star progenitors, but these are very rare. On the other hand, binary evolutionary models predict that WR stars could originate from primary stars in close binaries. We conduct an analysis of the massive O star, AzV 14, to spectroscopically determine its fundamental and stellar wind parameters, which are then used to investigate evolutionary paths from the O-type to the WR stage with stellar evolutionary models. Multi-epoch UV and optical spectra of AzV 14 are analyzed using the non-LTE stellar atmosphere code PoWR. An optical TESS light curve was extracted and analyzed using the PHOEBE code. The obtained parameters are put into an evolutionary context, using the MESA code. AzV 14 is a close binary system consisting of two similar main sequence stars with masses of 32 Msol. Both stars have weak stellar winds with mass-loss rates of log $\dot{M}$ = -7.7. Binary evolutionary models can explain the empirically derived stellar and orbital parameters. The model predicts that the primary will evolve into a WR star with T = 100 kK, while the secondary, which will accrete significant amounts of mass during the first mass transfer phase, will become a cooler WR star with T = 50 kK and are predicted to have compared to other WR stars increased oxygen abundances. This model prediction is supported by a spectroscopic analysis of a WR star in the SMC. We hypothesize that the populations of WR stars in low-Z galaxies may have bimodal temperature distributions. Hotter WR stars might originate from primary stars, while cooler WR stars are the evolutionary descendants of the secondary stars if they accreted a significant amount of mass.

Spectroscopic and evolutionary analyses of the binary system AzV 14 outline paths toward the WR stage at low metallicity

Most massive stars are believed to be born in close binary systems where they can exchange mass, which impacts the evolution of both binary components. Their evolution is of great interest in the search for the progenitors of gravitational waves. However, there are unknowns in the physics of mass transfer as observational examples are rare, especially at low metallicity. Nearby low-metallicity environments are particularly interesting hunting grounds for interacting systems as they act as the closest proxy for the early universe where we can resolve individual stars. Using multi-epoch spectroscopic data, we complete a consistent spectral and orbital analysis of the early-type massive binary SSN 7 hosting a ON If$^\ast$+O5.5 V((f)) star. Using these detailed results, we constrain an evolutionary scenario that can help us to understand binary evolution in low metallicity. We were able to derive reliable radial velocities of the two components from the multi-epoch data, which were used to constrain the orbital parameters. The spectroscopic data covers the UV, optical, and near-IR, allowing a consistent analysis with the stellar atmosphere code, PoWR. Given the stellar and orbital parameters, we interpreted the results using binary evolutionary models. The two stars in the system have comparable luminosities of ${\log (L_1/L_{\odot}) = 5.75}$ and ${\log (L_2/L_{\odot}) = 5.78}$ for the primary and secondary, respectively, but have different temperatures (${T_1=43.6\,\mathrm{kK}}$ and ${T_2=38.7\,\mathrm{kK}}$). The primary ($32\,M_{\odot}$) is less massive than the secondary ($55\,M_{\odot}$), suggesting mass exchange. The mass estimates are confirmed by the orbital analysis. The revisited orbital period is $3\,\mathrm{d}$. Our evolutionary models also predict mass exchange. Currently, the system is a contact binary undergoing a slow Case A phase, making it the most massive [Abridged]

A low-metallicity massive contact binary undergoing slow Case A mass transfer: A detailed spectroscopic and orbital analysis of SSN 7 in NGC 346 in the SMC

Context. Massive stars at low metallicity are among the main feedback agents in the early Universe and in present-day star forming galaxies. When in binaries, these stars are potential progenitors of gravitational-wave events. Knowledge of stellar masses is a prereq-uisite to understanding evolution and feedback of low-metallicity massive stars. Aims. Using abundant spectroscopic and photometric measurements of an outstandingly bright eclipsing binary, we compare its dynamic, spectroscopic, and evolutionary mass estimates and develop a binary evolution scenario. Methods. We comprehensively studied the eclipsing binary system, AzV476, in the Small Magellanic Cloud (SMC). The light curve and radial velocities were analyzed to obtain the orbital parameters. The photometric and spectroscopic data in the UV and optical were analyzed using the Potsdam Wolf–Rayet (PoWR) model atmospheres. The obtained results are interpreted using detailed binary-evolution tracks including mass transfer. Results. AzV476 consists of an O4IV-III((f))p primary and an O9.5:Vn secondary. Both components have similar current masses (20 M (cid:12) and 18 M (cid:12) ) obtained consistently from both the orbital and spectroscopic analysis. The effective temperatures are 42kK and 32kK, respectively. The wind mass-loss rate of log( ˙ M / ( M (cid:12) yr − 1 )) = − 6 . 2 of the primary is a factor of ten higher than a recent empir- ical prescription for single O stars in the SMC. Only close-binary evolution with mass transfer can reproduce the current stellar and orbital parameters, including orbital separation, eccentricity, and the rapid rotation of the secondary. The binary evolutionary model reveals that the primary has lost about half of its initial mass and is already core helium burning. Conclusions. Our comprehensive analysis of AzV476 yields a consistent set of parameters and suggests previous case B mass trans- fer. The derived stellar masses agree within their uncertainties. The moderate masses of AzV476 underline the scarcity of bright massive stars in the SMC. The core helium burning nature of the primary indicates that stripped stars might be hidden among OB-type populations.

/pdf/the-earliest-o-type-eclipsing-binary-in-the-small-magellanic-hsdmk2o9.pdf

Dorothee E. Pauli

Papers

The earliest O-type eclipsing binary in the Small Magellanic Cloud, AzV 476: A comprehensive analysis reveals surprisingly low stellar masses

Mina Arndt (1885-1926) : the making of a New Zealand artist