Evolution of the Ionizing Background at High Redshifts

We use a Maximum-Likelihood analysis to constrain the value and evolution of the ionizing background for 2<z<4.5, taking account of possible systematic errors. (The paper has a more detailed abstract)Comment: 12 figures (9 of those double plots), 17 pages. Accepted by MNRA

The Type Ic Supernova 1994I in M51: Detection of Helium and Spectral Evolution

We present a series of spectra of SN 1994I in M51, starting 1 week prior to maximum brightness. The nebular phase began about 2 months after the explosion; together with the rapid decline of the optical light, this suggests that the ejected mass was small. Although lines of He I in the optical region are weak or absent, consistent with the Type Ic classification, we detect strong He I λ10830 absorption during the first month past maximum. Thus, if SN 1994I is a typical Type Ic supernova, the atmospheres of these objects cannot be completely devoid of helium. The emission-line widths are smaller than predicted by the model of Nomoto and coworkers, in which the iron core of a low-mass carbon-oxygen star collapses. They are, however, larger than in Type Ib supernovae

Multiple Angle Observations Would Benefit Visible Band Remote Sensing Using Night Lights

The spatial and angular emission patterns of artificial and natural light emitted, scattered, and reflected from the Earth at night are far more complex than those for scattered and reflected solar radiation during daytime. In this commentary, we use examples to show that there is additional information contained in the angular distribution of emitted light. We argue that this information could be used to improve existing remote sensing retrievals based on night lights, and in some cases could make entirely new remote sensing analyses possible. This work will be challenging, so we hope this article will encourage researchers and funding agencies to pursue further study of how multi‐angle views can be analyzed or acquired

Contemporaneous Observations of Direct and Raman Scattered O VI in Symbiotic Stars

Symbiotic stars are binary systems consisting of a hot star, typically a white dwarf, and a cool giant companion. The wind from the cool star is ionized by the radiation from the hot star, resulting in the characteristic combination of sharp nebular emission lines and stellar molecular absorption lines in the optical spectrum. Most of the emission lines are readily identifiable with common ions. However, two strong, broad emission lines at $\lambda\lambda$ 6825, 7082 defied identification with known atoms and ions. In 1989 Schmid made the case that these long unidentified emission lines resulted from the Raman scattering of the O VI resonance photons at $\lambda\lambda$ 1032, 1038 by neutral hydrogen. We present contemporaneous far-UV and optical observations of direct and Raman scattered O VI lines for nine symbiotic stars obtained with the Hopkins Ultraviolet Telescope (Astro-2) and various ground-based telescopes. The O VI emission lines are present in every instance in which the $\lambda\lambda$ 6825, 7082 lines are present in support of the Schmid Raman scattering model. We calculate scattering efficiencies and interpret the results in terms of the Raman models. Additionally, we measure the flux of the Fe II fluorescence line at $\lambda$1776, which is excited by the O VI line at $\lambda$1032, and calculate the first estimates of the conversion efficiencies of this process.Comment: 48 pages, 5 figure

Commentary: Multiple Angle Observations Would Benefit Visible Band Remote Sensing using Night Lights

The spatial and angular emission patterns of artificial and natural light emitted, scattered, and reflected from the Earth at night are far more complex than those for scattered and reflected solar radiation during daytime. In this commentary, we use examples to show that there is additional information contained in the angular distribution of emitted light. We argue that this information could be used to improve existing remote sensing retrievals based on night lights, and in some cases could make entirely new remote sensing analyses possible. This work will be challenging, so we hope this article will encourage researchers and funding agencies to pursue further study of how multi-angle views can be analyzed or acquired

Public Lighting Recommendations

?Public lighting accounts for ?56 million in public expenditure annually and is a major item in council budgets. A large proportion of the 480,000 units in the lighting stock are in need of replacement with more efficient luminaires in order to meet energy and carbon reduction targets. The following document is predicated on the assumption that LED lighting will be increasingly used for public lighting and aims to mitigate the negative effects within the constraints of the drive for energy efficiency and lower carbon production. It is important to point out, however, that in line with the recommendations of bodies such as the Institution of Lighting Professionals the greatest savings will be made by dimming lights or removing unnecessary lighting. This document outlines aspects of public lighting in relation to the installation of LED lighting and the desirability to reduce both light levels and the blue spectral component. LED technology is known to have positive outcomes in terms of economic and environmental aspects (including carbon dioxide reduction) and the replacement of older lanterns with modern full cut-off designs which reduce or eliminate light emission above or near the horizontal provide further gains. We suggest that besides the introduction of this technology and also ?trimming and dimming? of lighting levels, the colour of the spectrum produced by LED installations and its relationship to the behaviour of human vision at low light levels should be considered when specifying and installing exterior lighting. Consideration of lighting colour and its impact can lead to a reduction in the level of lighting, its impact on the environment, and also potentially reduce human health effects such as sleep disruption. As we have closely followed UK practice in the past, we reference some recent developments, including reduced light levels as specified in BS5489 and also the forthcoming introduction of warmer colour LED lighting in residential areas. A large-scale statistical study of the effect of new lighting practices in England and Wales has detected no change in overall crime or traffic collisions due to restricted light levels and the introduction of white light. We recommend that luminaires with a correlated colour temperature (CCT) of 4000K operate at reduced lumen levels to take account of the increased blue light sensitivity of the human visual response. Such a reduction will lead to further energy savings as well as improved outcome environmentally. In keeping with developing UK practise we suggest that, as a general rule, LED luminaires with warmer colours (i.e., CCT values at or below 3000K) be specified for future installations. Finally, we recommend that pilot lighting schemes be tested in situ to verify the overall lighting design before rolling out more generally