European Space Operations Centre

About: European Space Operations Centre is a government organization based out in Darmstadt, Germany. It is known for research contribution in the topics: Orbit determination & Satellite. The organization has 309 authors who have published 331 publications receiving 10399 citations. The organization is also known as: ESOC.

X-ray observations of the Ophiuchus, PKS 0745–191 and Cygnus-A clusters of galaxies

Abstract: Observations are reported of the X-ray emission from three bright clusters of galaxies at low Galactic latitudes: the Ophiuchus, PKS 0745-191, and Cygnus-A clusters. Temperatures and iron abundances are determined from Exosat spectral data. Images of the Ophiuchus cluster show it to have a high central density and a cooling flow. Measurements of a high gas density around PKS 0745-191 and are confirmed, and it is shown that the X-ray emission is centered on the radio galaxy. The PKS 0745-191 cluster is the most distant object for which an abundance has been measured from X-ray spectra. The spectrum of Cygnus-A contains a highly absorbed power-law component that is identified with the nucleus of the radio source.

The pointing system of the Herschel space observatory

Abstract: We present the activities carried out to calibrate and characterise the performance of the elements of attitude control and measurement on board the Herschel spacecraft The main calibration parameters and the evolution of the indicators of the pointing performance are described, from the initial values derived from the observations carried out in the performance verification phase to those attained in the last year and half of mission, an absolute pointing error around or even below 1 arcsec, a spatial relative pointing error of some 1 arcsec and a pointing stability below 02 arsec The actions carried out at the ground segment to improve the spacecraft pointing measurements are outlined On-going and future developments towards a final refinement of the Herschel astrometry are also summarised A brief description of the different components of the attitude control and measurement system (both in the space and in the ground segments) is also given for reference We stress the importance of the cooperation between the different actors (scientists, flight dynamics and systems engineers, attitude control and measurement hardware designers, star-tracker manufacturers, etc) to attain the final level of performance

Low-Level Cloud Motion Winds from Meteosat High-Resolution Visible Imagery

Abstract: Low-level wind fields over the Atlantic have been derived from clouds in Meteosat high-resolution visible images experimentally with one production cycle per day over a period of more than 1 yr. The cloud motion winds from VIS imagery (VIS-CMW) use a template size of 32 × 32 VIS pixels, corresponding to about 80 km × 80 km at the subsatellite point, which is four times better than for the corresponding IR (infrared window) winds (160 km × 160 km). The yield is increased through the better spatial resolution of the VIS images and a better contrast between cloud and ocean surface, which effectively leads to an increase in wind vectors by a factor of 6. This implies a much better description of the low-level atmospheric flow by the VIS-CMW as compared to IR winds. The impact of the new VIS-CMW has been tested with a data assimilation experiment at the European Centre for Medium-Range Weather Forecasts, and small positive improvements have been found. The mean vector rms difference versus the verifyi...

XMM-Newton and Optical Follow-up Observations of SDSS J093249.57+472523.0 and SDSS J102347.67+003841.2

Abstract: We report follow-up XMM-Newton and ground-based optical observations of the unusual X-ray binary SDSS J102347.67+003841.2 (=FIRST J102347.6+003841) and a new candidate intermediate polar (IP) found in the Sloan Digital Sky Survey: SDSS J093249.57+472523.0. SDSS J1023 was observed in its low state, with similar magnitude/color (V = 17.4 and B = 17.9) and smooth orbital modulation as seen in most previous observations. We further refine the ephemeris (for photometric minimum) to HJD(TT)min = 2,453,081.8546(3) + E0.198094(1) days. It is easily detected in X-rays at an unabsorbed flux (0.01–10.0 keV) of 5 × 10-13 ergs cm-2 s-1. Fitting a variety of models we find that (1) either a hot (kT 15 keV) optically thin plasma emission model (bremsstrahlung or MEKAL) or a simple power law can provide adequate fits to the data; (2) these models prefer a low column density ~1019 cm-2; (3) a neutron star atmosphere plus power-law model (as found for quiescent low-mass X-ray binaries) can also produce a good fit (for plausible distances), although only for a much higher column ≈4 × 1020 cm-2 and a very cool atmosphere (kT 50 eV). These results support the case that SDSS J1023 is a transient LMXB and indeed place it in the subclass of such systems whose quiescent X-ray emission is dominated by a hard power-law component. Our optical photometry of SDSS J0932 reveals that it is a high-inclination eclipsing system. From our two epochs of data and seven eclipse times, we are able to derive a best-fit ephemeris for minimum light: HJD(TT)min = 2,453,122.2324(1) + E0.0661618(4) days, although aliases, with one cycle count different between epochs, are acceptable. The X-ray spectrum is well fit by either a hard bremsstrahlung or power law, with a partial covering absorption model, with a high covering fraction ~0.9 and column ≈1023 cm-2. Combined with its optical characteristics—high excitation emission lines and its brightness, yielding a large FX/Fopt ratio—this highly absorbed X-ray spectrum argues that SDSS J0932 is a strong IP candidate. However, only more extensive optical photometry and a detection of its spin or spin-orbit beat frequency can confirm this classification.