Chandra/44i Boo
Credit: CXC/M.Weiss

Coronal CatScan

Like the earth, stars themselves are magnetized. These magnetic fields are generally produced by the motion of hot material in the interior. But stellar magnetic fields are much more complex than the earth's magnetic field, since the hot ionized gas in a stellar interior moves in complicated flows and streams, producing localized strong magnetic fields. Stellar magnetic activity produces the stellar corona, a region of extremely hot gas (temperatures exceeding one million degrees) in the outer stellar atmosphere, and generates other observable phenomena like sunspots and stellar flares. Such phenomena has been studied on our Sun for over 400 years, but studies of these phenomena on other stars has been possible only recently. One useful means of studying stellar activity is to study the X-ray emission produced by the hot stellar corona. We can actually image the solar corona using space observatories like the Yohko satellite, but even the next nearest star is too far away for us to directly image the corona. But astronomers now are using the excellent spatial and spectral resolution of the Chandra X-ray observatory to effectively generate an image the stellar corona in the binary system 44i Bootis. 44i Boo is composed of 2 stars in a tight orbit, making a revolution every 3 hours, as shown above in this artist's conception of a closeup of the binary. The red arrow shows the direction of the stellar orbit. The rapid motion of the stars intensifies the magnetic field and produces a particularly bright corona. In 44i Boo, spectral line features produced by neon atoms were detected by Chandra, as shown by the graphs on the right side of the above image. The relative motion of the stars in their orbits produces a doppler shift this neon spectral line. By measuring the velocity of the neon lines astronomers can tell whether the the feature belongs to the star which is approaching us or the receding one. One surprising result is that most of the emission is produced by a particularly bright region near the pole of the larger star.

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Page Author: Dr. Michael F. Corcoran
Last modified November 26, 2001