Gaia's FPA: sampling the sky in silicon

Kohley, R.; Garé, P.; Vetel, Cyril; Marchais, Denis; Chassat, François

doi:10.1117/12.926144

Cited by 18 publications

(16 citation statements)

References 12 publications

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“…The RVS spectrometer CCDs are displaced vertically (in the across-scan direction) to correct for a lateral optical displacement of the light beam caused by the RVS optics such that the RVS CCD rows are aligned with the astrometric and photometric CCD rows on the sky; the resulting semi-simultaneity of the astrometric, photometric, and spectroscopic transit data is advantageous for stellar variability, science alerts, spectroscopic binaries, etc. Image from de Bruijne et al (2010a), Kohley et al (2012), courtesy Airbus DS and Boostec Industries.…”

Section: Focal Plane Assemblymentioning

confidence: 99%

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TheGaiamission

Prusti¹,

Bruijne²,

Brown³

et al. 2016

A&A

5,553

1,139

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Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.

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Section: Focal Plane Assemblymentioning

confidence: 99%

“…The focal plane assembly of Gaia (for a detailed description, see Kohley et al 2012;Crowley et al 2016b) is common to both telescopes and has five main functions: (i) metrology (wave-front sensing [WFS] and basic angle monitoring [BAM]; Sects. 3.3.3 and 3.3.4); (ii) object detection in the sky mapper (SM; Sect.…”

Section: Focal Plane Assemblymentioning

confidence: 99%

TheGaiamission

Prusti¹,

Bruijne²,

Brown³

et al. 2016

A&A

5,553

1,139

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“…For further general information on the FPA, see Kohley et al (2012). For a report on the on-orbit performance during payload commissioning of the BAM and WFS instruments, see Mora et al (2014).…”

Section: Gaia Focal Planementioning

confidence: 99%

GaiaData Release 1

Crowley

Kohley

Hambly

et al. 2016

A&A

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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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“…The Gaia focal-plane assembly (e.g., Kohley et al 2012), with 106 CCD detectors, has five dedicated functions: 4 CCDs for metrology, i.e., basic-angle monitoring and wave-front sensing (Gielesen et al 2012;Mora & Vosteen 2012), 14 Sky Mapper (SM) CCDs for object detection and rejection of prompt-particle events, 62 Astrometric Field (AF) CCDs, 14 Blue-Photometer/Red-Photometer (BP/RP) CCDs for low-resolution spectro-photometry, and 12 Radial-VelocitySpectrograph (RVS) CCDs for radial velocities and mediumresolution spectra. The AF, BP/RP, and RVS CCDs see the superimposed light coming from the two telescopes, which look at the sky separated by a basic angle of 106.5 deg along the scan direction.…”

Section: Introductionmentioning

confidence: 99%

Detecting stars, galaxies, and asteroids withGaia

Bruijne

Allen

Azaz

et al. 2015

A&A

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Context. Gaia is Europe's space astrometry mission, aiming to make a three-dimensional map of 1000 million stars in our Milky Way to unravel its kinematical, dynamical, and chemical structure and evolution.Aims. We present a study of Gaia's detection capability of objects, in particular non-saturated stars, double stars, unresolved external galaxies, and asteroids. Gaia's on-board detection software autonomously discriminates stars from spurious objects like cosmic rays and solar protons. For this, parametrised criteria of the shape of the point spread function are used, which need to be calibrated and tuned. This study aims to provide an optimum set of parameters for these filters. Methods. We developed a validated emulation of the on-board detection software, which has 20 free, so-called rejection parameters which govern the boundaries between stars on the one hand and sharp (high-frequency) or extended (low-frequency) events on the other hand. We evaluate the detection and rejection performance of the algorithm using catalogues of simulated single stars, resolved and unresolved double stars, cosmic rays, solar protons, unresolved external galaxies, and asteroids. Results. We optimised the rejection parameters, improving -with respect to the functional baseline -the detection performance of single stars and of unresolved and resolved double stars, while, at the same time, improving the rejection performance of cosmic rays and of solar protons. The optimised rejection parameters also remove the artefact of the functional-baseline parameters that the reduction of the detection probability of stars as a function of magnitude already sets in before the nominal faint-end threshold at G = 20 mag. We find, as a result of the rectangular pixel size, that the minimum separation to resolve a close, equal-brightness double star is 0.23 arcsec in the along-scan and 0.70 arcsec in the across-scan direction, independent of the brightness of the primary. To resolve double stars with ∆G > 0 mag, larger separations are required. We find that, whereas the optimised rejection parameters have no significant impact on the detectability of pure de Vaucouleurs profiles, they do significantly improve the detection of pure exponential-disk profiles, and hence also the detection of unresolved external galaxies with intermediate profiles. We also find that the optimised rejection parameters provide detection gains for asteroids fainter than 20 mag and for fast-moving near-Earth objects fainter than 18 mag, although this gain comes at the expense of a modest detection-probability loss for bright, fast-moving near-Earth objects. The major side effect of the optimised parameters is that spurious ghosts in the wings of bright stars essentially pass unfiltered.

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Gaia's FPA: sampling the sky in silicon

Cited by 18 publications

References 12 publications

TheGaiamission

TheGaiamission

GaiaData Release 1

Detecting stars, galaxies, and asteroids withGaia

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