Flare found on ultra-fast rotating star puzzles astronomers (Forwarded)

ESO Education and Public Relations Dept.

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Uwe Wolter
Hamburg Observatory, Germany
Phone: +49 40 42891 4130

For Immediate Release: 19 December 2007

ESO Science Release 53/07

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Speedy Mic's Photograph

Flare found on ultra-fast rotating star puzzles astronomers

Using observations from ESO's VLT, astronomers were able for the first
time to reconstruct the site of a flare on a solar-like star located 150
light years away. The study of this young star, nicknamed 'Speedy Mic'
because of its fast rotation, will help scientists better understand the
youth of our Sun.

The astronomers [1] observed the star BO Microscopii [2] during two
consecutive nights in October 2006, simultaneously with the UVES
spectrograph on ESO's Very Large Telescope and ESA's XMM-Newton X-ray
satellite.

Using a technique called 'Doppler imaging' [3], the astronomers
reconstructed images of the surface of the star, detecting the presence of
several spots. A few are near the visible pole, while most spots are
asymmetrically distributed at mid-latitudes.

"The image we could secure of Speedy Mic is, given its distance, a real
achievement, that allows us to localise for the first time ever the source
of a flare and its surrounding," says Uwe Wolter, lead author of the paper
relating the discovery.

The X-ray observations indeed identified several flares, which are sudden
and vast releases of energy. For one of them, the astronomers could
pinpoint its origin on the surface of the star. The flare, lasting about 4
hours, was a hundred times more energetic than a large solar flare and
considerably larger than solar coronal loops.

The surprising finding, the team says, was the location of the flare.
Contrary to our Sun, the site of the observed flare does not correspond to
the detected spots [4].

"Interestingly, the flare occurs on a rather inconspicuous portion of the
star's surface, away from the main concentration of activity in terms of
dark spots," explains Wolter.

Speedy Mic is a very young star: with an age of only about 30 million
years, it is roughly 150 times younger than the Sun. "It is very likely
that our young Sun was a fast rotator as well," says Wolter. "Studying
Speedy Mic is thus like observing our own host star while still in its
infancy. These studies may also contribute to the understanding of current
solar eruptions which can cause havoc in our telecommunications and power
distributions."

The team reports their results in the journal Astronomy and Astrophysics
("Doppler imaging an X-ray flare on the ultrafast rotator BO Mic - A
contemporaneous multiwavelength study using XMM-Newton and VLT", by. U.
Wolter et al.).

Notes

[1] The team is composed of U. Wolter, J. Robrade, and J. Schmitt (Hamburg
Observatory, Germany), and J. Ness (Arizona State University, USA).

[2] BO Microscopii (or BO Mic and nicknamed 'Speedy Mic') is a young star
with a mass about 90 % the mass of our Sun. It is located 150 light years
away towards the Microscope constellation. Speedy Mic owns its name
because of its very fast rotation: it completes a full turn in about 9
hours. The object rotates thus 66 times as fast as our Sun, which results
in much stronger magnetic fields than on the Sun.

[3] Speedy Mic is a star slightly smaller than the Sun and is about ten
million times further away from us than the Sun. Trying to see spots on
its surface is thus as challenging as trying to directly obtain a
photograph of the footsteps of Neil Armstrong on the Moon, and be able to
see details in it. This is impossible to achieve even with the best
telescopes: to obtain an image with such amount of details, you would need
a telescope with a 400 km wide mirror! Astronomers make therefore use of
indirect imaging techniques, such as Doppler imaging, to achieve this
incredible prowess. Doppler imaging makes use of the information contained
in the slightly changing spectra observed as a star rotates. In this case,
the astronomers obtained 142 spectra of the star with the UVES
spectrograph on ESO's VLT.

[4] Sunspots, which are cooler, but still very hot regions of the Sun's
surface, are known to be regions of intense magnetic activity.

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