The Determination of the Solar Wind Argon Abundance with SOHO/CELIAS/MTOF

Authors: J. M. Weygand, P. Wurz, P. Bochsler, F. M. Ipavich, and J. A. Paquette
Reference: EGS 2000 Conference


This study is about the first direct measurements of the solar wind argon elemental abundance with the Mass Time Of Flight (MTOF) sensor of the CELIAS instrument on the SOHO spacecraft. Argon is highly volatile and a minor element in the solar wind. Because of its volatility inferences about the solar argon abundance from planetary samples are impossible. However, it is possible to determine the solar argon abundance observations from solar wind. Spectrograms of the solar wind are obtained with the the high-resolution mass spectrometer SOHO/CELIAS/MTOF. Obtaining the argon abundance from the solar wind is straight forward since both the 36Ar and 38Ar are not contaminated by doubly charged ions of higher mass, nor are either one sitting on the shoulder of an abundant element. The main difficulty is the low signal to noise ratio in both argon peaks.

Relating argon (FIP ~ 15.7 eV) to calcium (FIP ~ 6.1 eV) will make it possible to investigate the FIP effect for another two elements with different FIP properties, but neighboring masses (like for Na/Ne). Using neighboring masses (i.e., masses with similar M/Q values) will help minimize the solar wind mass fractionation affects. The preliminary Ar/Ca abundance ratio for the fast solar wind appears to be 0.7±0.2. This value is within of a factor of two of the photospheric Ar/Ca abundance ratio (1.10±0.01) [Grevesse and Sauval, 1998] which is consistent with a weak FIP effect in the coronal hole associated solar wind.

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Last Update: April 2, 1999, James Weygand