Bayesian fitting of Taurus brown dwarf spectral energy distributions

We present derived stellar and disc parameters for a sample of Taurus brown dwarfs both with and without evidence of an associated disc. These parameters have been derived using an online fitting tool (http://bd-server.astro.ex.ac.uk/), which includes a statistically robust derivation of uncertainties, an indication of pa- rameter degeneracies, and a complete treatment of the input photometric and spectroscopic observations. The observations of the Taurus members with indications of disc presence have been fitted using a grid of theoretical models including detailed treatments of physical processes accepted for higher mass stars, such as dust sublimation, and a simple treatment of the accretion flux. This grid of models has been designed to test the validity of the adopted physical mechanisms, but we have also constructed models using parameterisation, for example semi-empirical dust sublimation radii, for users solely interested in parameter derivation and the quality of the fit. The parameters derived for the naked and disc brown dwarf systems are largely consistent with literature observations. However, our inner disc edge locations are consistently closer to the star than previous results and we also derive elevated accretion rates over non-SED based accretion rate derivations. For inner edge locations we attribute these differences to the detailed modelling we have performed of the disc structure, particularly at the crucial inner edge where departures in geometry from the often adopted vertical wall due to dust sublimation (and therefore accretion flux) can compensate for temperature (and therefore distance) changes to the inner edge of the dust disc. In the case of the elevated derived accretion rates, in some cases, this may be caused by the intrinsic stellar luminosities of the targets exceeding that predicted by the isochrones we have adopted.Comment: The paper contains 35 pages with 15 figures and 17 tables. Accepted for publication in MNRA

On the properties of discs around accreting brown dwarfs

We present a grid of models of accreting brown dwarf systems with circumstellar discs. The calculations involve a self-consistent solution of both vertical hydrostatic and radiative equilibrium along with a sophisticated treatment of dust sublimation. We have simulated observations of the spectral energy distributions and several broadband photometric systems. Analysis of the disc structures and simulated observations reveal a natural dichotomy in accretion rates, with \logmdot $>-$9 and $\leq -$9 classed as extreme and typical accretors respectively. Derivation of ages and masses from our simulated photometry using isochrones is demonstrated to be unreliable even for typical accretors. Although current brown dwarf disc candidate selection criteria have been shown to be largely reliable when applied to our model grid we suggest improved selection criteria in several colour indices. We show that as accretion rates increase brown dwarf disc systems are less likely to be correctly identified. This suggests that, within our grid, systems with higher accretion rates would be preferentially lost during brown dwarf target selection. We suggest that observations used to assert a $\dot{M}\propto M_*^2$ relationship may contain an intrinsic selection bias.Comment: 13 figures, 2 tables, 2 appendices and 25 pages. Accepted for publication in MNRA

Academic Speech Therapy: a provocation, using performative autoethnography

Two of my brothers had speech therapy. My eldest brother had a pronounced stammer throughout his childhood and now, even as an adult, when emotions get the better of him. My younger brother gets away with an occasional stutter. One of the problems with contemporary Universities is that educationalists, and by this, I mean the whole class of teaching and support staff, academics and managers, have forgotten how to speak. This also means we have forgotten how to speak about education. I thought I had escaped this particular affliction because I used to speak very quickly, and fluently, using all the vocabulary at my ‘Institutional’ disposal, vocabulary that my undergraduate degree had grafted onto my speech, that allowed my family to comment on the change in who I had become. My academic accent grew broad and thick, the more I specialized, the more I reproduced my knowledge in writing. This became the fast-paced disciplinary classification task of research, pedagogy, of a particular managerial kind that allows insider references of increasing subtlety, that constitutes acculturated habitus and distinction. Hence cultural capital is embodied (Bourdieu, 1986, p.17) and constitutes invisible pedagogies (Bernstein, 2003, p.201) whose currency is a learnt language of long sentences, multi-syllabic words and complex grammar; supported by references and evidence. Plus, a certain attitude

Mixed Forms in Visual Culture, Mary Anne Francis (2021)

This is a complex textbook addressing key examples of mixed form over the last 500 years in Western European and Anglo-American cultures. With 80 colour illustrations, it is extremely well referenced in historical and contemporary sources, yet of distinctly different parts, including two wholly visual chapters. This is a standard Bloomsbury hardback, with the paperback version published in June 2023 at considerably reduced cost. The economies of aesthetic forms, early publishing circulation, is one facet of the book’s narrative, and the contrast between mixed forms exclusively for the wealthy and popular mixed forms, is central to the book’s dramatic, and hence performative, structure. We are taken to some of the earliest European curatorial and authorial contexts in which mixed forms, whether opulent object collections or folded paper publications, constituted both a material type and a conceptual category for aristocrat and manual worker respectively. The narrative style features a broad vocabulary, inter-related arguments with cross-chapter questioning that is difficult to precis or gloss. Is there some operational logic to this type of a book? If my interpretation is valid that this project’s distinctiveness aligns visual practices with forms of material production and with modes of reading and writing employing multidisciplinary operational concepts, then this might best be understood if represented in a table. The ‘table’ therefore also stands in as a publishing convention, for a detachable, general overview of what any narrative cannot achieve in sufficient detail: a comprehensive summary. The table below (see Table 1) is a formal feature and type of paratext, which here represents a visual and conceptual overview of the book from which the review is drawn

Reading writing breathing

This article addresses how breath is intra-active with reading and writing. The two meditation methods I used for concentrating on and writing the breath-experience were ‘attention on the breath’as taught within a Korean Seon (Zen) tradition, and writing this experience as ‘meditative enquiry’ [Stephens, T. 2021. ‘A Meditative Enquiry into Presence: Unmaking the Autoethnographic Self.’ Journal of Writing in Creative Practice 14 (2): 161–178]. Two ‘texts’ gradually converge into an intertwined experience of reading both academic and literary writing, blurring distinctions between them. Various theories are drawn from that un-do dualistic frameworks of epistemology assumed in reading academic texts. This raises questions for the embodied cognitive humanities, post-qualitative methodologies, and in autoethnographic and phenomenological writing as well as for creative writers. The article draws from cultural, philosophical, and literary studies, recent breath studies, and from the field of embodiment, to contextualise the ‘creative academic writing’ excerpts; leading to an unavoidable conclusion: this type of ‘new writing’ is not new but, rather, contiguous with practices of embodiment. Yet, how can a written fabrication of breathing be read, and does stylistic innovation present insurmountable problems for the academic validation of creative academic writing

What is rhythm in relation to photography?

This article elaborates a theory of rhythm in relation to photography and, in particular, argues for the importance of rhythm in the theorization of photographic temporality. The approach taken breaks with a number of significant strands in contemporary photography theory, namely, Aristotelian-influenced modes of formalist criticism, dualistic formulations of representation and definitions of photographic temporality based on its difference to cinema. Through an interrogation of definitions of rhythm, the article examines, first, a formalist heritage from Aristotle to Lessing and evident in Greenberg that assumes a naturalistic definition of rhythm based on linearity, regularity and anthropomorphic essentialism. The second strand is described through Frye's anticipation of a different rhythm, lyricism, that problematically compounds the subject as an entity defined in a dualistic paradigm. Against this background the article elaborates the possibilities inherent in Deleuze's notion of crystal time a rhythm of energetic intensity not dependent on linear temporality or subjectivism as a further, more credible, theorization of rhythmic temporality-as-texture

Photographic Non-Self

Non-self has unsurprisingly featured very little in explanatory material-object-based contemporary art history. Buddhist nonself has contributed to subjectivity research (Albahari, 2006, Siderits, 2011, 2015) but non-self in photography is, perhaps appropriately, absent. This chapter will explore how the experience of non-self might differ from but overlap with emptiness in the ‘history of art’ specifically ‘photography theory and practice’. My research in experiential non-self (Stephens, 2018, 2019, 2021a, 2021b) wrestles with the complexities of non-representation when articulating embodied affect, of childhood racial discrimination, for instance. Yet, embodied autobiographical non-self is an impossible category. This is a subjugated knowledge that disrupts self-hood, undermines historical artefacts -leaving us with no birth of photography- and ruptures socio-cultural identity. Can a contemporary secular Buddhist non-self function as liberatory? Photographic non-self might render ‘writing on/and photography’ disastrous, when indelibly marked by the failures of representation