Calcium Abundance in the Solar Wind

Abstract

We report on the calcium abundance in the solar wind for an extended time period around the 1996 solar minimum. Data were recorded with the Mass Time-of-Flight (MTOF) sensor of the Charge, Element, and Isotope Analysis System (CELIAS) instrument on the SOHO spacecraft. The Ca/O abundance is 0.017+/-0.003 for slow solar wind (V_SW<400 km s^-1) and 0.0053+/-0.0014 for fast solar wind (V_SW>500 km s^-1). Compared to the photospheric Ca/O abundance ratio of (Ca/O)_PS=0.00421+/-0.00079, the solar wind clearly shows strong first ionization potential (FIP) fractionation as is expected for a low-FIP element. The Ca/H abundance is A_Ca=6.63+/-0.05 and A_Ca=6.21+/-0.10 for slow and fast solar winds, respectively. For comparison, the photospheric Ca abundance is A_Ca=6.36+/-0.02.