A 2 epoch proper motion catalogue from the UKIDSS Large Area Survey

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedThe UKIDSS Large Area Survey (LAS) began in 2005, with the start of the UKIDSS program as a 7 year effort to survey roughly 4000 square degrees at high galactic latitudes in Y, J, H and K bands. The survey also included a significant quantity of 2-epoch J band observations, with epoch baselines ranging from 2 to 7 years. We present a proper motion catalogue for the 1500 square degrees of the 2 epoch LAS data, which includes some 800,000 sources with motions detected above the 5 sigma level. We developed a bespoke proper motion pipeline which applies a source-unique second order polynomial transformation to UKIDSS array coordinates of each source to counter potential local non-uniformity in the focal plane. Our catalogue agrees well with the proper motion data supplied in the current WFCAM Science Archive (WSA) DR9 catalogue where there is overlap, and in various optical catalogues, but it benefits from some improvements. One improvement is that we provide absolute proper motions, using LAS galaxies for the relative to absolute correction. Also, by using unique, local, 2nd order polynomial tranformations, as opposed to the linear transformations in the WSA, we correct better for any local distortions in the focal plane, not including the radial distortion that is removed by their pipeline

Spitzer Mid-Infrared Photometry of 500 - 750 K Brown Dwarfs

Mid-infrared data, including Spitzer warm-IRAC [3.6] and [4.5] photometry, is critical for understanding the cold population of brown dwarfs now being found, objects which have more in common with planets than stars. As effective temperature (T_eff) drops from 800 K to 400 K, the fraction of flux emitted beyond 3 microns increases rapidly, from about 40% to >75%. This rapid increase makes a color like H-[4.5] a very sensitive temperature indicator, and it can be combined with a gravity- and metallicity-sensitive color like H-K to constrain all three of these fundamental properties, which in turn gives us mass and age for these slowly cooling objects. Determination of mid-infrared color trends also allows better exploitation of the WISE mission by the community. We use new Spitzer Cycle 6 IRAC photometry, together with published data, to present trends of color with type for L0 to T10 dwarfs. We also use the atmospheric and evolutionary models of Saumon & Marley to investigate the masses and ages of 13 very late-type T dwarfs, which have H-[4.5] > 3.2 and T_eff ~ 500 K to 750 K.Comment: To be published in the on-line version of the Proceedings of Cool Stars 16 (ASP Conference Series). This is an updated version of Leggett et al. 2010 ApJ 710 1627; a photometry compilation is available at http://www.gemini.edu/staff/slegget

On the topological classification of binary trees using the Horton-Strahler index

The Horton-Strahler (HS) index $r=\max{(i,j)}+\delta_{i,j}$ has been shown to be relevant to a number of physical (such at diffusion limited aggregation) geological (river networks), biological (pulmonary arteries, blood vessels, various species of trees) and computational (use of registers) applications. Here we revisit the enumeration problem of the HS index on the rooted, unlabeled, plane binary set of trees, and enumerate the same index on the ambilateral set of rooted, plane binary set of trees of $n$ leaves. The ambilateral set is a set of trees whose elements cannot be obtained from each other via an arbitrary number of reflections with respect to vertical axes passing through any of the nodes on the tree. For the unlabeled set we give an alternate derivation to the existing exact solution. Extending this technique for the ambilateral set, which is described by an infinite series of non-linear functional equations, we are able to give a double-exponentially converging approximant to the generating functions in a neighborhood of their convergence circle, and derive an explicit asymptotic form for the number of such trees.Comment: 14 pages, 7 embedded postscript figures, some minor changes and typos correcte

The discovery of a T6.5 subdwarf

We report the discovery of ULAS J131610.28+075553.0, an sdT6.5 dwarf in the UKIDSS Large Area Survey 2 epoch proper motion catalogue. This object displays significant spectral peculiarity, with the largest yet seen deviations from T6 and T7 templates in the Y and K bands for this subtype. Its large, similar to 1 arcsec yr(-1), proper motion suggests a large tangential velocity of V-tan approximate to 240-340 km s(-1), if we assume its M-J lies within the typical range for T6.5 dwarfs. This makes it a candidate for membership of the Galactic halo population. However, other metal-poor T dwarfs exhibit significant under luminosity both in specific bands and bolometrically. As a result, it is likely that its velocity is somewhat smaller, and we conclude it is a likely thick disc or halo member. This object represents the only T dwarf earlier than T8 to be classified as a subdwarf, and is a significant addition to the currently small number of known unambiguously substellar subdwarfs.Peer reviewe

Automated data analysis to rapidly derive and communicate ecological insights from satellite-tag data: A case study of reintroduced red kites

Analysis of satellite-telemetry data mostly occurs long after it has been collected, due to the time and effort needed to collate and interpret such material. Such delayed reporting does reduce the usefulness of such data for nature conservation when timely information about animal movements is required. To counter this problem we present a novel approach which combines automated analysis of satellite-telemetry data with rapid communication of insights derived from such data. A relatively simple algorithm (comprising speed of movement and turning angle calculated from fixes), allowed instantaneous detection of excursions away from settlement areas and automated calculation of home ranges on the remaining data Automating the detection of both excursions and home range calculations enabled us to disseminate ecological insights from satellite-tag data instantaneously through a dedicated web portal to inform conservationists and wider audiences. We recommend automated analysis, interpretation and communication of satellite tag and other ecological data to advance nature conservation research and practice

A Department-Wide Transition to a New Mode of Computer-Aided Assessment Using STACK

We focus on the integration of STACK—a Computer-Aided Assessment (CAA) technology—in the mathematics department of a high-ranking University in the United Kingdom. We study a department-wide project where instructors were expected to implement STACK into continuous assessment tasks for (nearly) all core modules across the first two years of undergraduate study. We present this work as a departmental case study, drawing on semi-structured interviews with six novice STACK assessment designers (and module leaders), supplemented by students’ responses to an open-response feedback questionnaire, and the reflections of a co-project lead (also first author). Our thematic analysis identified four themes related to the design of STACK-based assessments by novice to STACK tutors: the process of ‘STACKification’, technical challenges, users’ perspectives on the role of CAA, and finally, variations in assessment designers’ approaches to the role of feedback. In presenting our results, we are guided by Sangwin’s (2013) design principles for mathematics assessment. We consider various technical aspects of implementing STACK-based assessments as a first-time user, and the knowledge required to do so effectively and coherently. We conclude with a series of reflections on the role of CAA in undergraduate mathematics, and the ways in which such technology can be productively integrated with established practice

STACKification: automating assessments in tertiary mathematics

In this paper, we report on four university lecturers’ first-time experiences with computer-aided assessments. They were required to automate a significant proportion of the pre-existing weekly coursework for modules in first- or second-year undergraduate mathematics using STACK. We consider lecturers’ perspectives on the role of computer-aided assessments in course design for undergraduate mathematics; the knowledge of technical aspects required to implement STACKbased assessments; and the perceived merits of automated assessment for different aspects of mathematical study. We conclude with a series of reflections upon our departmental practice and the process of enculturating mathematicians into the realm of automated assessment

Search for the Standard Model Higgs boson produced in association with a vector boson and decaying to a b-quark pair with the ATLAS detector

An important question at present in particle physics is whether the recently discovered boson with a mass of about 125 GeV is the Standard Model Higgs boson. A Standard Model Higgs boson with a mass of 125 GeV will predominantly decay to b-quark pairs. This work presents the author's contribution to the search with the ATLAS detector for a Standard Model Higgs boson produced in association with a W or Z boson and decaying to b-quark pairs. In order to search for the decay modes ZH → vvb¯b, WH → lvb¯b and ZH → l¯lb¯b, where l is either an electron or muon, events with zero, one or two electrons or muons are considered in 20:3 fb¯1 of 8 TeV LHC data. A Standard Model Higgs boson is not observed decaying to b-quark pairs, although neither is this decay mode ruled out. A Standard Model Higgs boson with a mass of between 110 GeV and 115 GeV is excluded. For mH = 125 GeV the observed (expected) upper limit on the cross- section times the branching ratio is found to be 2.16 (1.07) times the Standard Model prediction. For a Standard Model Higgs boson with a mass of 125 GeV, the best fit signal strength is μ = 1:09 +0:43-0:42 (stat) +0:44-0:37 (syst) = 1:09 +0:61-0:56. The combined results are consistent with a Standard Model Higgs boson with a mass of 125 GeV. The author's own work is presented, including estimation of systematic uncertainties on WH → lvb¯b modelling, and future ATLAS data selection methods for WH → lvb¯b searches. Overviews of underlying theoretical matters and the experimental facilities used are given