16th April 2009
EMBARGOED UNTIL 0001 BST, 20th April 2009
Ref.: RAS PN 09/16 (NAM 3)
Dr. Robert Massey
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EWASS press page: http://www.star.herts.ac.uk/ewass/press
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RAS PN 09/16 (NAM 3, EMBARGOED): SOLAR SIGMOIDS EXPLAINED
'Sigmoids' are S-shaped structures found in the outer atmosphere of the Sun (the corona), seen with X-ray telescopes and thought to be a crucial part of explosive events like solar flares. Now a group of astronomers have developed the first model to reproduce and explain the nature of the different stages of a sigmoid’s life. Professor Alan Hood and Dr. Vasilis Archontis, both from the Mathematical Institute at St. Andrews University, Scotland, will present the team’s results at the European Week of Astronomy and Space Science conference at the University of Hertfordshire. Prof. Hood will present some of the work in a talk on Monday 20th April, supplemented by a poster by Dr. Vasilis Archontis on Thursday 23rd April, which will cover the model in more detail.
Recently, the X-Ray Telescope (XRT) on board the Hinode space mission was used to obtain the first images of the formation and eruption phase of a sigmoid at high resolution. These observations revealed that the structure of the sigmoid is complex: it consists of many, differently oriented, loops that all together form two opposite J-like bundles or an overall S-shape. They also showed that at the end of its life the sigmoid produces a 'flare' eruption.
Over the years a series of theoretical and numerical models have been proposed to explain the nature of sigmoids but until now there was no explanation on how such complex structures form, erupt and fade away. The new model describes how sigmoids consist of many thin and twisted layers (or ribbons) of strong electric current. When these layers interact it leads to the formation of the observed powerful flares and the eruption of strong magnetic fields which carry highly energetic particles into interplanetary space.
Dr. Archontis sees the connection between the two astronomers’ model and work on predicting solar flares. He remarks, “Sigmoids work as 'mangers' or 'cocoons' for solar eruptions. There is a high probability that they will result in powerful eruptions and other explosive events. Our model helps scientists understand how this happens.”
Prof. Hood adds that these events have real significance for life on Earth, “Sigmoids are among the most interesting features for scientists trying to forecast the solar eruptions – events that can disrupt telecommunications, damage satellites and affect the way navigation systems are operated'.
CONTACTSDr. Vasilis Archontis
St. Andrews University
Tel: +44 (0)1334 461648
Mob: +44 (0)7940 334572
Prof. Alan W. Hood
St. Andrews University
Media & PR Officer
University of Hertfordshire
Tel: +44 (0)1707 28 4095
IMAGESThe Hinode and model images of the sigmoids are available from
CaptionsSigmoid 1. The left panel shows one snapshot from the St Andrews model and the right panel the 'corresponding' snapshot from the Hinode satellite observations. The two images both show the 'internal complex structure' of the solar sigmoid, which has been observed at very high resolution and is reproduced in the model. The 'sigmoids' consist of a network of thin 'ribbons' where the electric current is strong and the material is heated to between 1 and 2 million degrees Celsius. Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)
Sigmoid2. Running from top to bottom, these figures show the evolution of the sigmoid over three hours leading up to its final eruption. Columns 1 and 2 show results from the St Andrews model. The left column shows the strength of electric current predicted by the model and the central panel shows predictions of temperature. Column 3 shows the development of the sigmoid observed by Hinode.
The model successfully predicts the shape of the sigmoid, internal structure and distribution of heat along its length. Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)
NOTES FOR EDITORS
THE EUROPEAN WEEK OF ASTRONOMY AND SPACE SCIENCEMore than 1000 astronomers and space scientists will gather at the University of Hertfordshire for the European Week of Astronomy and Space Science (EWASS), incorporating the 2009 Royal Astronomical Society National Astronomy Meeting (RAS NAM 2009) and the European Astronomical Society Joint Meeting (JENAM 2009). The meeting runs from 20th to 23rd April 2009.
EWASS is held in conjunction with the UK Solar Physics (UKSP) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meetings. The conference includes scientific sessions organised by the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA).
EWASS is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Hertfordshire, Hatfield.