Context.
The full third
Gaia
data release will provide, for the first time, the calibrated spectra obtained with the blue and red
Gaia
slitless spectrophotometers (BP and RP, respectively).
Gaia
is a ...very complex mission and cannot be considered as a single instrument, but rather as many instruments. The two lines of sight with wide fields of view introduce strong variations of the observations across the large focal plane with more than one hundred different detectors. The main challenge when facing
Gaia
spectral calibration is that no lamp spectra or flat fields are available during the mission. Also, the significant size of the line spread function with respect to the dispersion of the prisms produces alien photons contaminating neighbouring positions of the spectra. This makes the calibration special and different from standard approaches.
Aims.
This work gives a detailed description of the internal calibration model for the spectrophotometric data used to obtain the content of the
Gaia
catalogue. The main purpose of the internal calibration is to bring all the epoch spectra onto a common flux and pixel (pseudo-wavelength) scale, taking into account variations over the focal plane and with time, producing a mean spectrum from all the observations of the same source.
Methods.
In order to describe all observations on a common mean flux and pseudo-wavelength scale, we constructed a suitable representation of the internally calibrated mean spectra via basis functions, and we described the transformation between non-calibrated epoch spectra and calibrated mean spectra via a discrete convolution, parametrising the convolution kernel to recover the relevant coefficients.
Results.
The model proposed here for the internal calibration of the
Gaia
spectrophotometric observations is able to combine all observations into a mean instrument to allow the comparison of different sources and observations obtained with different instrumental conditions along the mission and the generation of mean spectra from a number of observations of the same source. We derived a calibration model that can handle the self-calibrating nature of the problem. The output of this model provides the internal mean spectra, not as a sampled function (flux and wavelength), but as a linear combination of basis functions, although sampled spectra can easily be derived from them.
Context.
Low-resolution spectroscopy is a frequently used technique. Aperture prism spectroscopy in particular is an important tool for large-scale survey observations. The ongoing ESA space mission
...Gaia
is the currently most relevant example.
Aims.
In this work we analyse the fundamental limitations of the calibration of low-resolution spectrophotometric observations and introduce a calibration method that avoids simplifying assumptions on the smearing effects of the line spread functions.
Methods.
To this aim, we developed a functional analytic mathematical formulation of the problem of spectrophotometric calibration. In this formulation, the calibration process can be described as a linear mapping between two suitably constructed Hilbert spaces, independently of the resolution of the spectrophotometric instrument.
Results.
The presented calibration method can provide a formally unusual but precise calibration of low-resolution spectrophotometry with non-negligible widths of line spread functions. We used the
Gaia
spectrophotometric instruments to demonstrate that the calibration method of this work can potentially provide a significantly better calibration than methods neglecting the smearing effects of the line spread functions.
Gaia Data Release 1 Arenou, F; Luri, X; Babusiaux, C ...
Astronomy and astrophysics (Berlin),
03/2017, Letnik:
599
Journal Article
Recenzirano
Odprti dostop
Context. Before the publication of the Gaia Catalogue, the contents of the first data release have undergone multiple dedicated validation tests. Aims. These tests aim to provide in-depth analysis of ...the Catalogue content in order to detect anomalies and individual problems in specific objects or in overall statistical properties, and either to filter them before the public release or to describe the different caveats on the release for an optimal exploitation of the data. Methods. Dedicated methods using either Gaia internal data, external catalogues, or models have been developed for the validation processes. They test normal stars as well as various populations such as open or globular clusters, double stars, variable stars, and quasars. Properties of coverage, accuracy, and precision of the data are provided by the numerous tests presented here and are jointly analysed to assess the data release content. Results. This independent validation confirms the quality of the published data, Gaia DR1 being the most precise all-sky astrometric and photometric catalogue to date. However, several limitations in terms of completeness, and astrometric or photometric quality are identified and described. Figures describing the relevant properties of the release are shown, and the testing activities carried out validating the user interfaces are also described. A particular emphasis is made on the statistical use of the data in scientific exploitation.
Gaia Data Release 1 Carrasco, J M; Evans, D W; Montegriffo, P ...
Astronomy and astrophysics (Berlin),
11/2016, Letnik:
595
Journal Article
Recenzirano
Odprti dostop
Context. Gaia is an ESA cornerstone mission launched on 19 December 2013 aiming to obtain the most complete and precise 3D map of our Galaxy by observing more than one billion sources. This paper is ...part of a series of documents explaining the data processing and its results for Gaia Data Release 1, focussing on the G band photometry. Aims. This paper describes the calibration model of the Gaia photometric passband for Gaia Data Release 1. Methods. The overall principle of splitting the process into internal and external calibrations is outlined. In the internal calibration, a self-consistent photometric system is generated. Then, the external calibration provides the link to the absolute photometric flux scales. Results. The Gaia photometric calibration pipeline explained here was applied to the first data release with good results. Details are given of the various calibration elements including the mathematical formulation of the models used and of the extraction and preparation of the required input parameters (e.g. colour terms). The external calibration in this first release provides the absolute zero point and photometric transformations from the GaiaG passband to other common photometric systems. Conclusions. This paper describes the photometric calibration implemented for the first Gaia data release and the instrumental effects taken into account. For this first release no aperture losses, radiation damage, and other second-order effects have not yet been implemented in the calibration.
Context. Based on an initial expectation from laboratory measurements or instrument simulations, photometric passbands are usually subject to refinements. These refinements use photometric ...observations of astronomical sources with known spectral energy distribution. Aims. This work investigates the methods for and limitations in determining passbands from photometric observations. A simple general formalism for passband determinations from photometric measurements is derived. The results are applied to the passbands of HIPPARCOS, Tycho, and Gaia DR1. Methods. The problem of passband determination is formulated in a basic functional analytic framework. For the solution of the resulting equations, functional principal component analysis is applied. Results. We find that, given a set of calibration sources, the passband can be described with respect to the set of calibration sources as the sum of two functions, one which is uniquely determined by the set of calibration sources, and one which is entirely unconstrained. The constrained components for the HIPPARCOS, Tycho, and Gaia DR1 passbands are determined, and the unconstrained components are estimated.
Digest Fenker, Jessica; McCulloch, Graham A.; Vasconcellos, Mariana Mira ...
Evolution,
08/2021, Letnik:
75, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Dispersal-associated traits —such as flight ability— influence how species move across the landscape, and can dramatically impact their distributions and patterns of genetic structure. Ortego et al. ...examine genomic data from two recently diverged alpine grasshopper lineages with distinct wing sizes to assess the demographic impacts of flight loss. The authors showed that flight loss may lead to asymmetric introgression during speciation, and can significantly increase rates of intraspecific diversification.
Aim for heterogeneous biodiversity restoration Toma, Tiago S P; Oliveira, Hernani F M; Overbeck, Gerhard E ...
Science (American Association for the Advancement of Science),
01/2024, Letnik:
383, Številka:
6681
Journal Article
The success of adaptive management in conservation has been questioned and the objective-based management paradigm on which it is based has been heavily criticized. Soft systems thinking and ...sociallearning theory expose errors in the assumption that complex systems can be dispassionately managed by objective observers and highlight the fact that conservation is a social process in which objectives are contested and learning is context dependent. We used these insights to rethink adaptive management in a way that focuses on the social processes involved in management and decision making. Our approach to adaptive management is based on the following assumptions: action toward a common goal is an emergent property of complex social relationships; the introduction of new knowledge, alternative values, and new ways of understanding the world can become a stimulating force for learning, creativity, and change; learning is contextual and is fundamentally about practice; and defining the goal to be addressed is continuous and in principle never ends. We believe five key activities are crucial to defining the goal that is to be addressed in an adaptive-management context and to determining the objectives that are desirable and feasible to the participants: situate the problem in its social and ecological context; raise awareness about alternative views of a problem and encourage enquiry and deconstruction of frames of reference; undertake collaborative actions; and reflect on learning. El éxito del manejo adaptativo en conservación ha sido cuestionado y el paradigma de manejo basado en objetivos en que se fundamenta ha sido criticado severamente. Los sistemas de pensamiento blandos y la teoría del aprendizaje social exponen errores en la suposición de que los sistemas complejos pueden ser manejados desapasionadamente por observadores objetivos y resaltan el hecho de que la conservación es un proceso social en el que los objetivos son contestados y el aprendizaje depende del contexto. Utilizamos estas ideas para repensar el manejo adaptativo de manera que se enfoque en los procesos sociales involucrados en el manejo y en la toma de decisiones. Nuestra aproximación al manejo adaptativo se basa en los supuestos siguientes: la acción hacia una meta común es una propiedad emergente de relaciones sociales complejas; la introducción de conocimiento nuevo, valores alternativos y nuevas formas de entender el mundo puede convertirse en una fuerza estimulante para el aprendizaje, la creatividad y el cambio; el aprendizaje es contextual y trata fundamentalmente sobre la práctica; y la definición de la meta a alcanzar es continua y, en principio, nunca termina. Consideramos que cinco actividades son cruciales para la definición de la meta a alcanzar en un contexto de manejo adaptativo y para la determinación de los objetivos que son deseables y factibles para los participantes: ubicar el problema en su contexto social y económico; promover conciencia sobre visiones alternativas de un problema y fomentar el cuestionamiento y la deconstrucción de marcos de referencia; emprender acciones de colaboración; y reflejar en aprendizaje.
Traditionally focused on Amazonian and Atlantic rainforests, studies on the origins of high Neotropical biodiversity have recently shifted to also investigate biodiversity processes in the South ...American dry diagonal, encompassing Chaco, Cerrado savannas, and Caatinga seasonally dry tropical forests. The plateau/depression hypothesis states that riparian forests in the Brazilian Shield in central Brazil are inhabited by Pleistocene lineages, with shallow divergences and signatures of population expansion. Moreover, riparian forests may have acted as a vegetation network in the Pleistocene, allowing gene/species flow across the South American dry diagonal. We tested these hypotheses using Colobosaura modesta, a small gymnophthalmid lizard from forested habitats in the Cerrado savannas and montane/submontane forests in the Caatinga. We conducted phylogeographic analyses using a multi-locus dataset, tested alternative demographic scenarios with Approximate Bayesian Computation, and also employed species delimitation tests. We recovered a history of recent colonization and expansion along riparian forests, associated with Pleistocene climate shifts, and the existence of a new species of Colobosaura restricted to the Serra do Cachimbo region. We also present evidence that riparian forests have provided an interconnected network for forest organisms within the South American dry diagonal and that Pleistocene events played an important role in their evolutionary history.
Gaia Data Release 1 Crowley, C; Kohley, R; Hambly, N C ...
Astronomy and astrophysics (Berlin),
11/2016, Letnik:
595
Journal Article
Recenzirano
Odprti dostop
The European Space Agency's Gaia satellite was launched into orbit around L2 in December 2013 with a payload containing 106 large-format scientific CCDs. The primary goal of the mission is to ...repeatedly obtain high-precision astrometric and photometric measurements of one thousand million stars over the course of five years. The scientific value of the down-linked data, and the operation of the onboard autonomous detection chain, relies on the high performance of the detectors. As Gaia slowly rotates and scans the sky, the CCDs are continuously operated in a mode where the line clock rate and the satellite rotation spin-rate are in synchronisation. Nominal mission operations began in July 2014 and the first data release is being prepared for release at the end of Summer 2016. In this paper we present an overview of the focal plane, the detector system, and strategies for on-orbit performance monitoring of the system. This is followed by a presentation of the performance results based on analysis of data acquired during a two-year window beginning at payload switch-on. Results for parameters such as readout noise and electronic offset behaviour are presented and we pay particular attention to the effects of the L2 radiation environment on the devices. The radiation-induced degradation in the charge transfer efficiency (CTE) in the (parallel) scan direction is clearly diagnosed; however, an extrapolation shows that charge transfer inefficiency (CTI) effects at end of mission will be approximately an order of magnitude less than predicted pre-flight. It is shown that the CTI in the serial register (horizontal direction) is still dominated by the traps inherent to the manufacturing process and that the radiation-induced degradation so far is only a few per cent. We also present results on the tracking of ionising radiation damage and hot pixel evolution. Finally, we summarise some of the detector effects discovered on-orbit which are still being investigated.
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