DETAILED EVIDENCE FOR FLARE-TO-FLARE VARIATIONS OF THE CORONAL CALCIUM ABUNDANCE

The analysis of X-ray solar hare spectra obtained by the Bent Crystal Spectrometer on board the Solar Maximum Mission satellite is presented . The ratio of the Ca XIX resonance line intensity to the nearby conti nuum is used to measure the calcium abundance relative to hydrogen (A( Ca)). A description of the spectroscopic method of determining the abs olute calcium abundance is given. Possible instrumental and solar effe cts that might influence the abundance estimates are evaluated. Over 5 000 spectra from more than 100 flares are analyzed. We find a flare-to -flare variation for A(Ca) that is not correlated with flare size, H a lpha importance, or with several other flare characteristics. For flar es observed from two active regions, the observed value of A(Ca) incre ases as a function of time. The average for all hares is [A(Ca)] = (5. 77 +/- 1.41) x 10(-6). A discussion of investigated correlations of de rived A(Ca) values with several flare characteristics is presented.