Jean-Marc Defise

Publications (2)2.78 Total impact

• Source

  Available from: Russell A. Howard

  Article: First Imaging of Coronal Mass Ejections in the Heliosphere Viewed from Outside the Sun – Earth Line

  Richard A. Harrison, Christopher J. Davis, Christopher J. Eyles, Danielle Bewsher, Steve R. Crothers, Jackie A. Davies, Russell A. Howard, Daniel J. Moses, Dennis G. Socker, Jeffrey S. Newmark, Jean-Philippe Halain, Jean-Marc Defise, Emmanuel Mazy, Pierre Rochus, David F. Webb, George M. Simnett
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  ABSTRACT: We show for the first time images of solar coronal mass ejections (CMEs) viewed using the Heliospheric Imager (HI) instrument aboard the NASA STEREO spacecraft. The HI instruments are wide-angle imaging systems designed to detect CMEs in the heliosphere, in particular, for the first time, observing the propagation of such events along the Sun – Earth line, that is, those directed towards Earth. At the time of writing the STEREO spacecraft are still close to the Earth and the full advantage of the HI dual-imaging has yet to be realised. However, even these early results show that despite severe technical challenges in their design and implementation, the HI instruments can successfully detect CMEs in the heliosphere, and this is an extremely important milestone for CME research. For the principal event being analysed here we demonstrate an ability to track a CME from the corona to over 40 degrees. The time – altitude history shows a constant speed of ascent over at least the first 50 solar radii and some evidence for deceleration at distances of over 20 degrees. Comparisons of associated coronagraph data and the HI images show that the basic structure of the CME remains clearly intact as it propagates from the corona into the heliosphere. Extracting the CME signal requires a consideration of the F-coronal intensity distribution, which can be identified from the HI data. Thus we present the preliminary results on this measured F-coronal intensity and compare these to the modelled F-corona of Koutchmy and Lamy (IAU Colloq. 85, 63, 1985). This analysis demonstrates that CME material some two orders of magnitude weaker than the F-corona can be detected; a specific example at 40 solar radii revealed CME intensities as low as 1.7×10−14 of the solar brightness. These observations herald a new era in CME research as we extend our capability for tracking, in particular, Earth-directed CMEs into the heliosphere.
  Solar Physics 12/2007; 247(1):171-193. · 2.78 Impact Factor
• Source

  Available from: ulg.ac.be

  Article: STEREO: Heliospheric Imager design, pre-flight, and in-flight response comparison

  Jean-Philippe Halain, Emmanuel Mazy, Jean-Marc Defise, Pierre Rochus, J Daniel Moses, Jeffrey S Newmark, Clarence Korendyke, Russ Howard, Chris Eyles, Richard Harrison, Chris Davis
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  ABSTRACT: The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO observatories launched in October 2006. The two HI instruments provide stereographic image pairs of solar coronal plasma and coronal mass ejections (CME) over a field of view ranging from 13 to 330 R 0 . The HI instrument is a combination of two refractive optical systems with a two stage multi-vane baffle system. The key challenge of the instrument design is the rejection of the solar disk light by the front baffle, with total straylight attenuation at the detector level of the order of 10 -13 to 10 -15 . Optical systems and baffles were designed and tested to reach the required rejection. This paper presents the pre-flight optical tests performed under vacuum on the two HI flight models in flight temperature conditions. These tests included an end-to-end straylight verification of the front baffle efficiency, a co-alignment and an optical calibration of the optical systems. A comparison of the theoretical predictions of the instrument response and performances with the calibration results is presented. The instrument in-flight photometric and stray light performances are also presented and compared with the expected results.