BAYESIAN ANALYSIS OF TWO STELLAR POPULATIONS IN GALACTIC GLOBULAR CLUSTERS I: STATISTICAL AND COMPUTATIONAL METHODS

We develop a Bayesian model for globular clusters composed of multiple stellar populations, extending earlier statistical models for open clusters composed of simple (single) stellar populations (e.g., van Dyk et al. 2009; Stein et al. 2013). Specifically, we model globular clusters with two populations that differ in helium abundance. Our model assumes a hierarchical structuring of the parameters in which physical properties—age, metallicity, helium abundance, distance, absorption, and initial mass—are common to (i) the cluster as a whole or to (ii) individual populations within a cluster, or are unique to (iii) individual stars. An adaptive Markov chain Monte Carlo (MCMC) algorithm is devised for model fitting that greatly improves convergence relative to its precursor non-adaptive MCMC algorithm. Our model and computational tools are incorporated into an open-source software suite known as BASE-9. We use numerical studies to demonstrate that our method can recover parameters of two-population clusters, and also show model misspecification can potentially be identified. As a proof of concept, we analyze the two stellar populations of globular cluster NGC 5272 using our model and methods. (BASE-9 is available from GitHub: https://github.com/argiopetech/base/releases)

Investigation of the role of morphology on the magnetic properties of Ca2Mn3O8 materials

Ca2Mn3O8 exhibits a complex layered structure comprised of Mn3O84- layers separated by Ca2+ ions. In contrast with the more traditional triangular Delafossite layered materials the Mn3O84- layers additionally exhibit an ordered vacancy which forms a 'bow-tie' like arrangement of the Mn4+ ions. We report a comprehensive study of the magnetic properties of a series of Ca2Mn3O8 materials with different morphologies. EXAFS and XANES analysis confirm no differences in either manganese environment or oxidation state between materials. Apparent differences in magnetic order from SQUID magnetometry can be rationalised by uncompensated surface spins arising as a result of changes to the surface:volume ratio between morphologies. Furthermore, these data suggest these materials are potentially frustrated in nature, due to the triangular connectivity of Mn4+ spins with a simple ‘spin-up/spin-down’ (↑↓) antiferromagnetic model unable to explain the data collected

Bayesian Analysis of Two Stellar Populations in Galactic Globular Clusters II: NGC 5024, NGC 5272, and NGC 6352

We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of Galactic Globular Clusters to find and characterize two stellar populations in NGC 5024 (M53), NGC 5272 (M3), and NGC 6352. For these three clusters, both single and double-population analyses are used to determine a best fit isochrone(s). We employ a sophisticated Bayesian analysis technique to simultaneously fit the cluster parameters (age, distance, absorption, and metallicity) that characterize each cluster. For the two-population analysis, unique population level helium values are also fit to each distinct population of the cluster and the relative proportions of the populations are determined. We find differences in helium ranging from $\sim$0.05 to 0.11 for these three clusters. Model grids with solar $\alpha$-element abundances ([$\alpha$/Fe] =0.0) and enhanced $\alpha$-elements ([$\alpha$/Fe]=0.4) are adopted.Comment: ApJ, 21 pages, 14 figures, 7 table

Storytelling with objects to explore digital archives

Finding media in archives is difficult while storytelling with photos can be fun and supports memory retrieval. Could the search for media become a natural part of the storytelling experience? This study investigates spatial interactions with objects as a means to encode information for retrieval while being embedded in the story flow. An experiment is carried out in which participants watch a short video and re-tell the story using cards each of which shows a character or object occurring in the video. Participants arrange the cards when telling the story. It is analyzed what information interactions with cards carry and how this information relates to the language of storytelling. Most participants align interactions with objects with the sentences of the story while some arrange the cards corresponding to the video scene. Spatial interactions with objects can carry information on their own or complemented by language

PZT-like structural phase transitions in the BiFeO3-KNbO3 solid solution

Despite the high prominence of the perovskites BiFeO3 and KNbO3 the solid solution between the two has received little attention. We report a detailed neutron and synchrotron x-ray powder diffraction, and Raman spectroscopy study which demonstrate an R3c → P4mm → Amm2 series of structural phase transitions similar to that exhibited by the PbZrO3 – PbTiO3 solid solution

Diversity, urban space and the right to the provincial city

Using three vignettes of the same physical space this article contributes to understanding of how the right to the city is contested in provincial England in the early twenty-first century. Oral history and ethnographic material gathered in Peterborough between 2010 and 2012 are drawn on to shed new light on the politics of diversity and urban space. This highlights the multiple place attachments and trans-spatial practices of all residents, including the white ethnic majority, as well as contrasting forms of active intervention in space with their different temporalities and affective intensities. The article carries its own diversity politics, seeking to reduce the harm done by racism through challenging the normalisation of the idea of a local, indigenous population, left out by multiculturalism. It simultaneously raises critical questions about capitalist regeneration strategies in terms of their impact both on class inequality and on the environment

From Vertices to Vortices in magnetic nanoislands

Recent studies in magnetic nanolithography show that a variety of complex magnetic states emerge as a function of a single magnetic island's aspect ratio. We propose a model which, in addition to fitting experiments, predicts magnetic states with continuous symmetry at particular aspect ratios and reveals a duality between vortex and vertex states. Our model then opens new means of engineering novel types of artificial spin systems, and their application to complex magnetic textures in devices and computing.Comment: 3 pages + epsilon + 18 supplementary materia