Gaia Early Data Release 3: Gaia photometric science alerts

Context. Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky. Aims. We present the Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia. Methods. We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours. Results. We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, CE = 0.46, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is CI = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec. Conclusions. The per-Transit photometry for Gaia transients is precise to 1% at G = 13, and 3% at G = 19. The per-Transit astrometry is accurate to 55 mas when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge. © S. T. Hodgkin et al. 2021

Dust in Supernovae and Supernova Remnants II: Processing and survival

Observations have recently shown that supernovae are efficient dust factories, as predicted for a long time by theoretical models. The rapid evolution of their stellar progenitors combined with their efficiency in precipitating refractory elements from the gas phase into dust grains make supernovae the major potential suppliers of dust in the early Universe, where more conventional sources like Asymptotic Giant Branch (AGB) stars did not have time to evolve. However, dust yields inferred from observations of young supernovae or derived from models do not reflect the net amount of supernova-condensed dust able to be expelled from the remnants and reach the interstellar medium. The cavity where the dust is formed and initially resides is crossed by the high velocity reverse shock which is generated by the pressure of the circumstellar material shocked by the expanding supernova blast wave. Depending on grain composition and initial size, processing by the reverse shock may lead to substantial dust erosion and even complete destruction. The goal of this review is to present the state of the art about processing and survival of dust inside supernova remnants, in terms of theoretical modelling and comparison to observations

Environmental Emissions and Production Economics: Implications of the Materials Balance

In modeling emissions, the literature has usually specified an explicit emission function, or treated emissions as a production input. We examine the validity of these approaches, taking into account the materials balance principle. We show that a technology can equivalently be described by (i) a production function with material and nonmaterial inputs and bounded marginal product of the material input, (ii) a well-behaved production function with emissions as an input, and (iii) a well-behaved emission function, if the materials balance is accounted for as an additional condition. We offer a forma derivation of common, but not rigorously established modeling approaches. Copyright 2007, Oxford University Press.

Weak Disposability in Nonparametric Production Analysis with Undesirable Outputs

Weak disposability of outputs means that firms can abate harmful emissions by decreasing the activity level. Modeling weak disposability in nonparametric production analysis has caused some confusion. This article identifies a dilemma in these approaches: conventional formulations implicitly and unintentionally assume all firms apply uniform abatement factors. However, it is usually cost-effective to abate emissions in those firms where the marginal abatement costs are lowest. This article presents a simple formulation of weak disposability that allows for non-uniform abatement factors and preserves the linear structure of the model. Copyright 2005, Oxford University Press.

Spatial environmental efficiency indicators in regional waste generation: a nonparametric approach

This paper computes and analyses, for the first time, environmental efficiencies in waste generation of 116 European regions in NUTS 2 level in five European countries over the period of 2008–2010. For this reason, different data envelopment analysis (DEA) model formulations are used for modeling the pollutant in the form of waste generation as a regular output and as a regular input. In the latter case, we also use the notion of eco-efficiency. The empirical findings reveal environmental inefficiencies among the regions, indicating the lack of a uniform regional environmental policy among the European countries. This finding is observed not only for regions between different countries but also among the regions within countries, implying the need for implementation of unified appropriate municipal environmental policies in waste management. © 2014 University of Newcastle upon Tyn

Piecemeal Multilateral Environmental Policy Reforms under Asymmetric Oligopoly

We develop a general two-country model with oligopolistic interdependence in which a fixed number of firms make their output and emission decisions simultaneously. We examine the effect of multilateral reforms of emission taxes on global emission levels. With sufficient asymmetry in pollution intensities between the two countries, a proportional multilateral increase in emission tax rates can increase global emission levels. However, a multilateral equal increase of emission tax rates unambiguously reduces global emission levels. We also consider the case of free entry and exit of firms, and find a rule of multilateral reforms which unambiguously lowers total emission levels. Copyright 2007 Blackwell Publishing, Inc..