ESA Science & Technology - Publication Archive
Methods. We correlated extended X-ray sources from the second XMM-Newton source catalogue (2XMM) with the SDSS in order to identify new clusters of galaxies. Distant cluster candidates in empty SDSS fields were imaged in the r- and z-bands with the Large Binocular Telescope. We extracted the X-ray spectra of the cluster candidates and fitted thermal plasma models to the data.
Results. We determined the redshift 0.99 ± 0.03 for 2XMM J083026.2+524133 from its X-ray spectrum. With a bolometric luminosity of 1.8 × 1045 erg s-1 this is the most X-ray luminous cluster at redshifts z>1. We measured a gas temperature of 8.2 ± 0.9 keV and estimate a cluster mass M500 = 5.6 × 1014 MSun. The optical imaging revealed a rich cluster of galaxies.
Beyond their intrinsic interest, ground-based observations have proven their usefulness in supporting spacecraft observations of Solar System bodies. Probably the most spectacular illustration ever was provided during the descent of the Huygens Probe on Titan, when the radio astronomy segment detected the "channel A" carrier signal from Huygens and allowed the recovery of the Doppler Wind Experiment that had been compromised by the failure of the corresponding Cassini channel (Lebreton et al., 2005). Furthermore, ground-based science observations performed during or around the Huygens mission provided new, complementary information on Titan's atmosphere and surface, helping to put the Huygens observations into context (Witasse et al., 2006). Another example of a successful ground-based campaign is the Deep Impact event, when numerous Earth-based and Earth-orbiting observatories monitored comet 9P/Tempel 1 when it was hit by the impactor (Meech et al., 2005).
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The NIRSpec OA (optical assembly) design largely relies on SiC components. The properties of the SiC material and very tight stability budgets required a dedicated development process. Starting from validation of design principles by breadboard testing, this paper describes the development process up to the SM test of the NIRSpec optical assembly. From breadboard testing the design of the mounting interface was established. The test programme also included gluing processes, torque free mounting of mirrors and verification of stability of friction joints. The basic design rules for the mirrors to cope with distortion of mirror surfaces due to bi-metallic bending effects and flatness deficiencies were derived. A modular design using 3 TMAs (Three Mirror Anastigmats) was followed for the OA. From the overall design, budget allocations and design loads for the TMAs were determined. The detailed design process was then driven by distortion budget allocations derived from optical analysis. Due to stringent stability requirements and high mechanical loads, most elements needed several design iterations to meet the budget allocations. Finally, distortions and displacements of the optical elements under the predictable in-orbit conditions were calculated and used in the optical model. The effects can be partially compensated by adjustment. The budget allocation was then revised to account for non-predictable effects only.
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