Weekly Science Update

Wednesday, March 12, 2008
The Geometry of Coronal Flares Around Another Star
The corona of a star is the hot, gaseous outer region of its atmosphere. The sun's corona is over a million kelvin, and in some stars can be even ten times hotter. In sun-like stars the corona is threaded by intense magnetic fields that are thought to extend upwards from the surface as they do in our sun. These magnetic fields form loops that are twisted and sheared by the convective stirrings of the underlying dense atmosphere. When they snap, they produce flares that generate energetic charged particles and emit x-rays. Scientists have been trying to understand solar flares in order to improve our general understanding of the sun, but also because flare particles can cause significant disruption when they reach they earth.

Three SAO astronomers, Jeremy Drake, Barbara Ercolano, and David Garcia-Alvarez, along with five of their colleagues, have used the Chandra X-ray Observatory to study the first detailed geometric analysis of coronal emission around a star other than our sun. The object is HR 9024, a star of roughly solar appearance that is about 400 light-years away. The astronomers realized that when a flare erupts in the sun, it can trigger characteristic X-ray emission from iron atoms in the sun's much cooler atmosphere that acts as a kind of X-ray mirror. When Chandra detected that same iron emission from HR 9024 during a flare, the scientists found they if they assumed a similar X-ray mirror effect was operating, they could infer the physical size of the flare. They were able to simulate the emission using their detailed computer codes combined with a geometrical model of the distant star. They concluded that the light is consistent with having arisen from a single, flaring loop of length about one-half the radius of the star. The result provides further confidence in both the modeling of the emission, and in the idea that magnetic flares high above a star's surface can excite atoms on the surface to emit in X-rays.

Four CfA Projects Awarded Next-Generation Astronomy Status

Four CfA proposals for next-generation astronomy missions were selected to receive funding for further studies in a competitive NASA review. The projects selected are:

  • The next generation of X-ray astronomy principal investigator Roger Brissenden

  • A census of black holes in universe using the Energetic X-ray Survey Imaging Telescope principal investigator Jonathan Grindlay

  • Testing the Inflationary Big Bang universe using the Cosmic Inflation Probe (CIP) principal investigator Gary Melnick

  • Lunar radio telescopes to study the infant universe -- DALI (Dark Ages Lunar Interferometer) co-principal investigator Justin Kasper

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