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Science Forum Index » Astro Forum » FLAMES leave astronomers in a spin (Forwarded)...
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| Andrew Yee... |
 Posted: Mon May 05, 2008 10:12 pm |
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ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE
Issued by RAS Press Officers:
Dr Robert Massey
Tel: +44 (0)20 7734 3307 / 4582
Anita Heward
Tel: +44 (0)1483 420904
NATIONAL ASTRONOMY MEETING PRESS ROOM (31 MARCH - 4 APRIL ONLY):
Tel: +44 (0)2890 975262 / 975263 / 975264
NAM 2008
http://nam2008.qub.ac.uk
Royal Astronomical Society
http://www.ras.org.uk
CONTACT
Professor Philip Dufton
Head of Astronomy Research Centre
Department of Physics and Astronomy
Queen's University
Belfast
Co. Antrim, BT7 1NN
Tel: 028 90973552
EMBARGOED UNTIL 0001 BST, 2 April 2008
Ref.: PN 08/23 (NAM 14)
FLAMES leave astronomers in a spin
A surprising analysis of material churned up from the depths of massive
stars shows that the mixing processes in these hot, bright stars are much
more complicated than thought. The results will be presented at the RAS
National Astronomy Meeting held at Queen's University Belfast on Wednesday
2nd April.
The study, led by astronomers from Queen's University, used the FLAMES
instrument on the Very Large Telescope (VLT) to decipher the spectra of
light emitted by over 800 stars and estimate the chemical composition of
the stars' surfaces. This is the most extensive survey of massive stars
ever undertaken.
Massive stars rotate at speeds of up to a million kilometres per hour and
this rotation drives huge circulatory currents. Models predict that gas
from the star's core, containing nitrogen and other elements produced in
fusion reactions, should be thrust up to the surface. In the study, the
team used the concentration of nitrogen measured at the surface to analyse
the efficiency of mixing in the star. They found that nearly half the
stars did not have the levels of nitrogen predicted, indicating rotation
is not the only factor driving mixing.
Ian Hunter, who led the study, said: "Current models of star rotation
could be compared to a food processor -- as you turn up the speed, the
mixing between the layers of a star becomes more thorough and more
nitrogen should be visible at the surface. However, 20% of the stars we
looked at were slow rotators that were rich in nitrogen and another 20%
were fast rotators without much nitrogen. The food processor model doesn't
seem to be working, or at least can't explain the whole picture."
The FLAMES instrument can observe 140 stars at the same time and take a
detailed spectrum of each simultaneously. Professor Philip Dufton, of
Queen's University, commented, "We've known for nearly a hundred years
that very massive stars spin fast but how this affects their behaviour is
still quite a controversial subject. It's only now, with this unique
European instrument, that we can study enough stars to draw some
conclusions."
The team believe that magnetic fields could explain the slow rotating,
well-mixed group. Previous studies imply a link between fossil magnetic
fields, intrinsic magnetic fields left over from the star formation stage,
and nitrogen-rich stellar surfaces. However, the physical processes
involved in this magnetically driven mixing are still unknown.
The rapidly rotating, nitrogen-poor stars would fit in with model
predictions if they were in binary systems. However, the surveys do not
appear to show any evidence of companions for stars in this group.
Professor Norbert Langer of the University of Utrecht commented, "There is
a mystery here that we need to understand. We now have to look at what is
missing in our models -- possibly magnetic fields -- or maybe there are
more stars in double systems than we thought and we don't fully understand
how they interact. After 100 years of studying spinning stars we still
can't explain all we see."
The stars analysed are located in two nearby galaxies, the Large and Small
Magellanic Clouds. The study was carried out over 100 hours of VLT time by
a consortium comprising 20 scientists from five European countries.
IMAGES
For images and further information, see:
http://star.pst.qub.ac.uk/hotstars/
NOTES FOR EDITORS
RAS NATIONAL ASTRONOMY MEETING
The RAS National Astronomy Meeting (NAM 2008) is hosted by Queen's
University Belfast. It is principally sponsored by the RAS and the STFC.
NAM 2008 is being held together with the UK Solar Physics (UKSP) and
Magnetosphere, Ionosphere and Solar-Terrestrial (MIST) spring meetings.
VLT-FLAMES
The Fibre Large Array Multi-Element Spectrograph (FLAMES) has been in
operation since 2001 on the Very Large Telescope at the European Southern
Observatory in Chile.
For details, see:
http://www.eso.org/instruments/flames/
MASSIVE STARS
Massive stars have surface temperatures typically five times that of the
Sun and hence appear as white hot objects. They are also extremely bright,
pouring out typically one hundred thousand times as much light as the Sun.
The closest such star to the earth is Rigel, at the foot of Orion which is
a hot star more than 15 times bigger than the Sun.
In 1925 Arthur Eddington proposed that if massive stars spin fast then
they would not be perfect spheres and this would lead to massive
circulating currents inside the star. |
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