Volume phase holographic gratings for the Subaru Prime Focus Spectrograph: performance measurements of the prototype grating set

The Prime Focus Spectrograph (PFS) is a major instrument under development for the 8.2 m Subaru telescope. Four identical spectrograph modules are located in a room above one Nasmyth focus. A 55~m fiber optic cable feeds light to the spectrographs from a robotic positioner at the prime focus, behind the wide-field corrector developed for Hyper Suprime-Cam. The positioner contains 2400 fibers and covers a 1.3~degree hexagonal field of view. The spectrograph optical design consists of a Schmidt collimator, two dichroic beamsplitters to split the light into three channels, and for each channel a volume phase holographic (VPH) grating and a dual-corrector, modified Schmidt reimaging camera. This design provides a 275~mm collimated beam diameter, wide simultaneous wavelength coverage from 380~nm to 1.26~\textmu m, and good imaging performance at the fast f/1.05 focal ratio required from the cameras to avoid oversampling the fibers. The three channels are designated as the blue, red, and near-infrared (NIR), and cover the bandpasses 380--650~nm (blue), 630--970~nm (red), and 0.94--1.26~\textmu m (NIR). A mosaic of two Hamamatsu 2k$\times$4k, 15~\textmu m pixel CCDs records the spectra in the blue and red channels, while the NIR channel employs a 4k$\times$4k, substrate-removed HAWAII-4RG array from Teledyne, with 15~\textmu m pixels and a 1.7~\textmu m wavelength cutoff. VPH gratings were an obvious choice for PFS and a set of three prototype VPH gratings (one each of the blue, red, and NIR designs) was ordered and has been recently delivered. In this paper we present the design and specifications for the PFS gratings, the plan and setups used for testing both the prototype and final gratings, and results from recent optical testing of the prototype grating set.Comment: 18 pages, 20 figures SPIE Astronomical Telescopes and Instrumentation 2014, Montrea

Optical Design of the SuMIRe PFS Spectrograph

The SuMIRe Prime Focus Spectrograph (PFS), developed for the 8-m class SUBARU telescope, will consist of four identical spectrographs, each receiving 600 fibers from a 2394 fiber robotic positioner at the telescope prime focus. Each spectrograph includes three spectral channels to cover the wavelength range 0.38-1.26 um with a resolving power ranging between 2000 and 4000. A medium resolution mode is also implemented to reach a resolving power of 5000 at 0.8 um. Each spectrograph is made of 4 optical units: the entrance unit which produces three corrected collimated beams and three camera units (one per spectral channel). The beam is split by using two large dichroics; and in each arm, the light is dispersed by large VPH gratings. The proposed optical design was optimized to achieve the requested image quality while simplifying the manufacturing of the whole optical system. The camera design consists in an innovative Schmidt camera observing a large field-of-view (10 degrees) with a very fast beam. To achieve such a performance, the classical spherical mirror is replaced by a catadioptric mirror (i.e meniscus lens with a reflective surface on the rear side of the glass, like a Mangin mirror). This article focuses on the optical architecture of the PFS spectrograph and the perfornance achieved. We will first described the global optical design of the spectrograph. Then, we will focus on the Mangin-Schmidt camera design. The analysis of the optical performance and the results obtained are presented in the last section.Comment: 8 pages - submitted at SPIE Astronomical Telescopes - Instrumentation 2014 - Montrea

Combining social and nutritional perspectives: from adolescence to adulthood (the ASH30 study)

Purpose The purpose of this paper is to focus specifically on the benefits of using mixed methods to investigate dietary change from adolescence to adulthood exemplified using the findings from the ASH30 longitudinal study. The ASH30 study is a longitudinal dietary survey which provided quantitative evidence of dietary change and investigated factors influencing dietary change from adolescence to adulthood. Design/methodology/approach Two three-day food diaries were collected both in 1980 (aged 11-12 years) and 2000 (aged 31-32 years) from the same 198 respondents in North East England. In 2,000 questionnaires were used to collect perceptions of, and attributions for, dietary change and open-ended responses were analysed using content analysis. Findings The use of mixed methods brings added breadth and depth to the research which cannot be achieved by a single discipline or method. Determining what has influenced change in dietary behaviour from adolescence to adulthood is a complex and multifaceted task. Eating habits are influenced by multiple factors throughout the life course. Change in food intake between adolescence and adulthood related to life-course events and trajectories. The qualitative findings highlighted relevant contextual information such as themes of moral panics, the concept of “convenience” and “fresh” foods. Practical implications Adopting mixed method approaches to exploring dietary change should offer a rich perspective from which to base realistic interventions. Originality/value Longitudinal dietary surveys present an opportunity to understand the complex process of dietary change throughout the life course in terms both of how diets have changed but also of why they have changed

A Modified Magnitude System that Produces Well-Behaved Magnitudes, Colors, and Errors Even for Low Signal-to-Noise Ratio Measurements

We describe a modification of the usual definition of astronomical magnitudes, replacing the usual logarithm with an inverse hyperbolic sine function; we call these modified magnitudes `asinh magnitudes'. For objects detected at signal-to-noise ratios of greater than about five, our modified definition is essentially identical to the traditional one; for fainter objects (including those with a formally negative flux) our definition is well behaved, tending to a definite value with finite errors as the flux goes to zero. This new definition is especially useful when considering the colors of faint objects, as the difference of two `asinh' magnitudes measures the usual flux ratio for bright objects, while avoiding the problems caused by dividing two very uncertain values for faint objects. The Sloan Digital Sky Survey (SDSS) data products will use this scheme to express all magnitudes in their catalogs.Comment: 11 pages, including 3 postscript figures. Submitted to A

Cougars (Puma concolor) in The Northwest Territories and Wood Buffalo National Park

Extralimital reports of cougars (Puma concolor) at the northern limits of their range are rare. We documented at least 21 individual occurrences of cougars from the Northwest Territories and the Wood Buffalo National Park area between the years 1983 and 2000. Our evidence suggests that, at a minimum, transient cougars are regular visitors to northern Alberta and the Northwest Territories.La présence de couguars (Puma concolor) est rarement rapportée en dehors des limites septentrionales de territoire. On a documenté au moins 21 cas individuels de la présence de couguars dans les Territoires du Nord-Ouest et le parc national Wood Buffalo entre les années 1983 et 2000. Les éléments de preuve que nous apportons suggèrent que, à tout le moins, les couguars de passage sont des visiteurs réguliers du nord de l'Alberta et des Territoires du Nord-Ouest