Emission-line intensity ratios in Fe XVII observed with a microcalorimeteron an electron beam ion trap

We report new observations of emission line intensity ratios of Fe XVII und er controlled experimental conditions, using the National Institute of Stan dards and Technology electron beam ion trap (EBIT) with a microcalorimeter detector. We compare our observations with collisional-radiative models usi ng atomic data computed in distorted wave and R-matrix approximations, whic h follow the transfer of the polarization of level populations through radi ative cascades. Our results for the intensity ratio of the 2p(6) S-1(0)-2p( 5)3d P-1(1) 15.014 Angstrom line to the 2p(6) S-1(0)- 2p(5) 3d D-3(1) 15.26 5 Angstrom line are 2.94 +/- 0.18 and 2.50 +/- 0.13 at beam energies of 900 and 1250 eV, respectively. These results are not consistent with collision al-radiative models and support conclusions from earlier EBIT work at the L awrence Livermore National Laboratory that the degree of resonance scatteri ng in the solar 15.014 Angstrom line has been overestimated in previous ana lyses. Further observations assess the intensity ratio of the three lines b etween the 2p(6)-2p(5)3s configurations to the three lines between the 2p(6 )-2p(5)3d configurations. Both R-matrix and distorted wave approximations a gree with each other and our experimental results much better than most sol ar and stellar observations, suggesting that other processes not present in our experiment must play a role in forming the Fe XVII spectrum in solar a nd astrophysical plasmas.