Glowing Rings Found Common To All Magnetic Stars

  Astronomers typically segregate stars by their physical
  characteristics: temperature, size, age, composition. One
  particular group, young, hot, magnetic stars, that contain low
  amounts of heavy elements, have interested scientists for
  some time because they appeared different than their iron-rich
  magnetic counterparts. 

  Seeing commonality, finally

  The current thinking on how young stars become magnetic is
  this: There is a magnetic field already in the Universe. When
  stars collapse during formation, the particles drag a bit of that
  magnetic field with it. All stars have some magnetic field but it
  varies widely: Our Sun has a field the strength of 1 Gauss,
  while the stars that Smith studied have a magnetic field of a
  couple thousand Gauss. Why different stars have such different
  magnetic fields is still an unknown. 

  The magnetic fields of iron-poor stars create invisible cages in
  which their spewed material stays. Hydrogen, helium and other
  ionized atoms follow the magnetic fields from the poles and
  then turn back to the star's equator. These halos glow, but are
  barely visible, and were thought to be a characteristic special
  only to magnetic stars low in heavy elements. 

  That was the case until two scientists, Myron Smith of the
  Space Telescope Science Institute in Maryland, and Detlef
  Groote from the University of Hamburg in Germany, discovered
  all young, magnetic hot stars, regardless of composition,
  display the dimly glowing rings of ejected materials. 

  "What's exciting for science is that this may be seen in other
  types of stars, or maybe even galaxies," said Smith. "We can
  use this as a model to see if this is going on somewhere else;
  like gravity that makes an apple fall also makes the Moon
  travel around Earth. That type of universality is what is nice in
  science; a few physical laws can explain … bewilderingly
  different phenomenon."

            How donuts are made

  The signature of stellar magnetic fields is the donut effect on
  ejected star material. Ionized atoms are shot out at the poles,
  then pulled along by the magnetic field back toward the center
  of the star. Because material is ejected from both ends, the
  material eventually crashes into other particles at the magnetic
  equator. These intense particle collisions cause the ring of
  material to glow and radiate at very high temperatures. 

  This magnetic star commonality might seem obvious in
  hindsight but it took careful and powerful observations to bring
  the glowing ring theme to light.

  "People just didn't put these things together," said Smith.
  "When the spectra of the stars look different, this superficial
  appearance is kind of an obstacle to [seeing] commonality." 

  "The magnetic fields on stars are very difficult to measure. For
  stars, the (magnetic band's) light is so faint, you need really
  big telescopes," said Smith. And also, "These stars rotate
  rapidly, which blurs out the spectral lines."

                  Using old data for something new

  By studying UV images taken from 1978 to 1996 by the now
  non-existent International Ultraviolet Explorer (IUE), Groote and
  Smith were able to discover the commonality by studying UV
  emission spectra of two magnetic stars with low levels of heavy
  element emissions, and two with normal heavy element
  emissions.

  Smith's workplace, the Space Telescope Science Institute in
  Maryland, is home to NASA's visible and UV imaging archives.
  The astronomer lamented that archived data can be a "real
  treasure trove of information," but that scientists often have a
  bias for new data.

  By Heather Sparks
  Staff Writer
  posted: 09:00 am ET
  13 July 2001

http://www.space.com/scienceastronomy/astronomy/star_magnetic_010713.html
                   
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