In this paper we investigate the impact that realistic scale-dependence systematic effects may have on cosmic shear tomography. We model spatially varying residual ellipticity and size variations in weak lensing measurements and propagate these through to predicted changes in the uncertainty and bias of cosmological parameters. We show that the survey strategy -whether it is regular or randomised -is an important factor in determining the impact of a systematic effect: a purely randomised survey strategy produces the smallest biases, at the expense of larger parameter uncertainties, and a very regularised survey strategy produces large biases, but unaffected uncertainties. However, by removing, or modelling, the affected scales (ℓ-modes) in the regular cases the biases are reduced to negligible levels. We find that the integral of the systematic power spectrum is not a good metric for dark energy performance, and we advocate that systematic effects should be modelled accurately in real space, where they enter the measurement process, and their effect subsequently propagated into power spectrum contributions.
Abstract. It is generally assumed that horizontal wind velocities are independent of height above the F1 region (> 300 km) due to the large molecular viscosity of the upper thermosphere. This assumption is used to compare two completely different methods of thermospheric neutral wind observation, using two distinct locations in the high-latitude Northern Hemisphere. The measurements are from ground-based Fabry–Perot interferometers (FPI) and from in situ accelerometer measurements onboard the challenging mini-satellite payload (CHAMP) satellite, which was in a near-polar orbit. The University College London (UCL) Kiruna Esrange Optical Platform Site (KEOPS) FPI is located in the vicinity of the auroral oval at the ESRANGE site near Kiruna, Sweden (67.8∘ N, 20.4∘ E). The UCL Longyearbyen FPI is a polar cap site, located at the Kjell Henriksen Observatory on Svalbard (78.1∘ N, 16.0∘ E). The comparison is carried out in a statistical sense, comparing a longer time series obtained during night-time hours in the winter months (DOY 300–65) with overflights of the CHAMP satellite between 2001 and 2007 over the observational sites, within ±2∘ latitude (±230 km horizontal range). The FPI is assumed to measure the line-of-sight winds at a height of ∼240 km, i.e. the peak emission height of the atomic oxygen 630.0 nm emission. The cross-track winds are derived from state-of-the-art precision accelerometer measurements at altitudes between ∼450 km (in 2001) and ∼350 km (in 2007), i.e. 100–200 km above the FPI wind observations. We show that CHAMP wind values at high latitudes are typically 1.5 to 2 times larger than FPI winds. In addition to testing the consistency of the different measurement approaches, the study aims to clarify the effects of viscosity on the height dependence of thermospheric winds.
Abstract. It is generally assumed that horizontal wind velocities are independent of height above the F1-region (> 300 km) due to the large viscosity of the upper thermosphere. This assumption is used to compare two completely different methods of thermospheric neutral wind observation, using two distinct locations in the high-latitude Northern Hemisphere. The measurements are from ground-based Fabry-Perot Interferometers (FPI), and from in-situ accelerometer measurements onboard the CHAMP satellite, which was in a near polar orbit. The UCL KEOPS FPI is located in the vicinity of the auroral oval at the ESRANGE site near Kiruna, Sweden (67.8° N, 20.4° E). The UCL Longyearbyen FPI is a polar cap site, located at the Kjell Henriksen Observatory on Svalbard (78.1° N, 16.0° E). The comparison is done in a statistical sense, comparing a longer time series obtained during nighttime hours in the winter months (November to January); with overflights of the CHAMP satellite between 2001 and 2007 over the observational sites, within ±2° (±220 km horizontal range). The FPI is assumed to measure the Doppler shift along the line-of-sight of winds at ~ 240 km height, i.e. the peak emission height of the atomic oxygen 630.0 nm emission. The components of winds at right angles to the CHAMP orbit are derived from state-of-the-art precision accelerometer measurements at altitudes. CHAMP was at altitudes between 450 km (in 2001) to 330 km (in 2007); i.e. 100–200 km above the FPI wind observations. We show that CHAMP winds at high latitudes are systematically 1.5–2 times larger than FPI winds. In addition to testing the consistency of the different measurement approaches, the study aims to clarify the effects of viscosity on the height dependence of thermospheric winds.
Details of the London pilot of the 'Discovery Project' are presented, where university-based astronomers were given the chance to pass on some real and applied knowledge of astronomy to a group of selected secondary school pupils. It was aimed at students in Key Stage 3 of their education, allowing them to be involved in real astronomical research at an early stage of their education, the chance to become the official discoverer of a new variable star, and to be listed in the International Variable Star Index database[1], all while learning and practising research-level skills. Future plans are discussed.
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