The Ne VIII (770) resonance line: solar wavelengths determined by SUMER on SOHO
I.E. Dammasch 1,
K. Wilhelm 1,
W. Curdt 1 and
D.M. Hassler 2
Received 18 December 1998 / Accepted 1 February 1999
The investigation of the source and acceleration of the solar wind was among the prime scientific goals of SOHO - ESA's and NASA's Solar and Heliospheric Observatory. For the coronal regions closest to the Sun, the bright extreme ultraviolet (EUV) resonance lines of the Ne VIII spectrum at 770 Å and 780 Å with a formation temperature of 630 000 K are promising targets for detecting the initial solar wind outflow. The investigations published up to now using data obtained by SUMER - the Solar Ultraviolet Measurements of Emitted Radiation spectrometer - on SOHO gave conflicting results. They accepted a rest wavelength of 770.409 Å for the brighter Ne VIII line as reported in the literature. We deduce the solar wavelength of this line for several conditions on the Sun and derive a rest wavelength of (770.428 0.003) Å and outflow speeds in coronal hole regions of 9 km s-1. This is in agreement with other recent studies using SUMER data. The rest wavelength determination is based on the assumptions of no average Doppler shift above the solar limb and a comparison with laboratory wavelengths of cool chromospheric lines. Quiet Sun areas exhibit an average blue shift of (1 1) km s-1 in this line.
Key words: atomic data line: identification Sun: corona Sun: solar wind Sun: UV radiation
Send offprint requests to: I.E. Dammasch (Dammasch@linmpi.mpg.de)
This article contains no SIMBAD objects.
© European Southern Observatory (ESO) 1999
Online publication: May 6, 1999