Summary: Electron densities above a polar coronal hole based on
improved Si ix density diagnostics
J.G. Doyle
Armagh Observatory, Armagh BT61 9DG, N. Ireland.
jgd@star.arm.ac.uk
F.P. Keenan, R.S.I. Ryans and K.M. Aggarwal
Dept. of Pure & Applied Physics, Queens University Belfast, Belfast BT7 1NN, N.
Ireland.
F.Keenan@qub.ac.uk; R.Ryans@qub.ac.uk; K.Aggarwal@qub.ac.uk
A. Fludra
Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
fludra@cds8.nascom.nasa.gov
(Received ..... ; Accepted in final form .....)
Abstract. Using new close­coupling excitation rates for the C­like ion Si ix, density­
diagnostic ratios based on Si ix lines have been re­evaluated and applied to a
sequence of CDS observations taken above a polar coronal hole. The derived electron
densities are in excellent agreement with previous values of Ne estimated from the
N--like ion Si viii for another coronal hole. The confirmed trend is for a fall­off of
one order of magnitude within the first 0:3R fi above the limb. These densities are
well fitted with an analytic formulae for the density profile out to at least 8R fi , by

Source: Armagh Observatory

Collections: Physics