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Astron. Astrophys. 346, 285-294 (1999)


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The Ne VIII ([FORMULA]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

1 Max-Planck-Institut für Aeronomie, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau, Germany
2 Southwest Research Institute, 1050 Walnut St., Suite 426, Boulder, CO 80302, USA

Received 18 December 1998 / Accepted 1 February 1999

Abstract

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 [FORMULA] 0.003) Å and outflow speeds in coronal hole regions of [FORMULA] 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 [FORMULA] 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)

© European Southern Observatory (ESO) 1999

Online publication: May 6, 1999

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