Chase observations from spacelab 2 - the chase team

Abstract

The Coronal Helium Abundance Spacelab Experiment (CHASE) was designed and built in the UK by groups at the Rutherford Appleton Laboratory and at the Mullard Space Science Laboratory. The main objective of the experiment was to improve the measurement of the abundance of helium in the Sun, which currently is uncertain by a factor of approximately three. Since most of this helium must be of primordial origin, being formed within a few minutes of the big bang, such a measurement would also have significant cosmological implications. The instrument consisted of a grazing incidence telescope feeding a 1200 lines mm-1 diffraction grating. Parts of the dispersed spectrum were then observed around the Rowland circle with channel electron multipliers and a channel multiplier array plate. During the flight, good observations were made of the Lyman-α lines of hydrogen at 1216 A and of ionised helium at 304 A, both in the corona, where the lines are formed by resonance scattering, and on the solar disc where excitation of the lines is much more complex. The spectrometer was also able to observe many other transition region and coronal lines in ions of O, S and Fe. Images in these lines clearly show how the magnetic fields in active regions constrain the material in arch-shaped loops with the hot material towards the top. © 1987.