Flares occur on only a small section of the face of the sun, while flares on stars like HR 1099 involve the entire star and produce massive outflows. Because HR 1099 is far away from us, at 90 light years, we cannot image it directly, and must rely upon spectroscopy to determine the conditions existing in its atmosphere. The latest results will lead to improved knowledge of flare physics by increasing our knowledge of the types of activities that occur on other stars, and challenging current models that attempt to explain flares. Osten, who is affiliated with CU-Boulder's Center for Astrophysics and Space Astronomy, presented the findings at the national meeting of the American Astronomical Society June 5 in Rochester, New York. Thomas Ayres, Alexander Brown and Jeffrey Linsky, all of CU-Boulder, worked on the project.
Stellar flares are violent releases of energy and gas from the outer atmospheres of stars.
The sun and many sun-like stars produce flares, and binary stars like HR 1099 can experience flares that are a million times more energetic than the largest flare seen on the sun, she said. Gaining a better understanding of how flares happen on other stars will help scientists figure out what causes them on the sun, where they cause geomagnetic storms that can trigger power outages and communication blackouts on Earth. The flares on HR 1099 were only seen at 100,000 degrees, recorded by spectral lines in the ultraviolet range accessible to the Hubble, while spectra taken by Chandra in the X-ray region, which probe temperatures near one million degrees, showed no brightening of lines. The ultraviolet lines broadened dramatically, according to Osten, and reached supersonic velocities during the several hours that the flares occurred. During that time, the Chandra X-ray Observatory focused its spectrometer for a day and a half cataloguing light changes, while the National Science Foundation's Very Large Array observed radio emission changes and the Hubble Space Telescope chronicled the ultraviolet spectrum changes for seven hours.