Characteristics of solar coronal streamers - Element abundance, temperature and density from coordinated CDS and UVCSSOHO observations

This paper presents the results from coordinated observations of streamers acquired by the SOHO Coronal Diagnostic Spectrometer (CDS) and UltraViolet Coronograph Spectrometer (UVCS) experiments. Data from different altitudes within the solar corona were taken, with the purpose of determining their p hysical parameters - densities, electron temperatures and element abundance s - and their changes over the altitude range between 1.02 and 1.6 R.. Furt her UVCS streamer data, taken about two months later are used for compariso n with the behaviour seen in two different streamers. Whenever possible, al ternative methods have been adopted to determine the same physical paramete r, as a cross check. In particular, the DEM technique has been applied to U VCS data, in order to compare abundance values derived in this way, with th ose obtained using the method of Raymond et al. (1997). We conclude that ab undances in the low corona covered by CDS data do not show evidence for abu ndance variation, with respect to photospheric values, while, at UVCS altit udes, a depletion of all element abundances is clearly evident. No clear ev idence of a FD? effect in streamers was found; we get contrasting results f rom the only two high FIP elements present in our spectra.