Emission-Line Intensity Ratios in Fe XVII Observed with a Microcalorimeter on an Electron Beam Ion Trap

We report new observations of emission line intensity ratios of Fe XVII under controlled experimental conditions, using the National Institute of Standards and Technology electron beam ion trap (EBIT) with a microcalorimeter detector. We compare our observations with collisional-radiative models using atomic data computed in distorted wave and R-matrix approximations, which follow the transfer of the polarization of level populations through radiative cascades. Our results for the intensity ratio of the 2p6 1S0-2p53d 1P1 15.014 A line to the 2p6 1S0-2p53d 3D1 15.265 A 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 collisional-radiative models and support conclusions from earlier EBIT work at the Lawrence Livermore National Laboratory that the degree of resonance scattering in the solar 15.014 A line has been overestimated in previous analyses. Further observations assess the intensity ratio of the three lines between the 2p6-2p53s configurations to the three lines between the 2p6-2p53d configurations. Both R-matrix and distorted wave approximations agree with each other and our experimental results much better than most solar and stellar observations, suggesting that other processes not present in our experiment must play a role in forming the Fe XVII spectrum in solar and astrophysical plasmas.

[1]  J. Schmelz,et al.  Fe XVII Soft X-Ray Lines: Theory and Data Comparisons , 1999 .

[2]  John M. Davis,et al.  Metalized polyimide filters for x-ray astronomy and other applications , 1997, Optics & Photonics.

[3]  Ryuichi Fujimoto,et al.  The microcalorimeter spectrometer on the ASTRO-E X-ray observatory , 2000 .

[4]  L. K. Harra-Murnion,et al.  Benchmarking the MEKAL spectral code with solar X-ray spectra , 1999 .

[5]  K. Widmann,et al.  Erratum: "Laboratory Measurements and Modeling of the Fe XVII X-Ray Spectrum" (ApJ, 502, 1015 [1998]) , 2000 .

[6]  K. Widmann,et al.  Laboratory Measurements and Modeling of the Fe XVII X-Ray Spectrum , 1998 .

[7]  P. Landecker,et al.  Solar flare x-ray spectra between 7. 8 and 23. 0 angstroms. Technical report , 1980 .

[8]  F. Keenan,et al.  Active Region Electron Density and Dimensions from Fe XVII X-Ray Lines , 1996 .

[9]  Clark,et al.  Relativistic cross sections for excitation of highly charged ions to specific magnetic sublevels by an electron beam. , 1990, Physical review. A, Atomic, molecular, and optical physics.

[10]  Manuel A. Bautista,et al.  CORRIGENDUM: Electron-impact inner-shell excitation of Fe XVIElectron-impact inner-shell excitation of Fe XVI , 2000 .

[11]  C. J. Wolfson,et al.  Solar flare X-ray spectra from the Solar Maximum Mission Flat Crystal Spectrometer , 1982 .

[12]  G. Doschek,et al.  Atomic data and spectral line intensities for Ne-like Fe XVII , 1992 .

[13]  B. Smith,et al.  Temperature diagnostic line ratios of Fe XVII , 1986 .

[14]  Effects of electron spiralling on the anisotropy and polarization of photon emission from an electron beam ion trap , 1999 .

[15]  M. Mohan,et al.  Collision Strengths from Ground Levels of Fe XVII by Including Relativistic Term Coupling Effects , 1997 .

[16]  Simon R. Bandler,et al.  Laboratory Astrophysics Survey of Key X-Ray Diagnostic Lines Using A Microcalorimeter on an Electron Beam Ion Trap , 2000 .

[17]  W. Goldstein,et al.  X-ray spectral signatures of photoionized plasmas , 1990 .

[18]  H. Friedman,et al.  SPECTRAL AND PHOTOMETRIC MEASUREMENTS OF SOLAR X-RAY EMISSION BELOW 60 A , 1965 .

[19]  J. H. Parkinson.  The analysis of a high resolution X-ray spectrum of a solar active region , 1975 .

[20]  J. Schmelz,et al.  Resonance Scattering of Fe xvii: A Density Diagnostic , 1992 .

[21]  D. Dewey,et al.  High-Resolution X-Ray Spectra of Capella: Initial Results from the Chandra High-Energy Transmission Grating Spectrometer , 2000, astro-ph/0006457.

[22]  Goldstein,et al.  Gain predictions for nickel-like gadolinium from a 181-level multiconfigurational distorted-wave collisional-radiative model. , 1988, Physical review. A, General physics.

[23]  S. O. Kastner,et al.  The Optically Thick Fe XVII Spectrum: X-Ray, Extreme-Ultraviolet, and Forbidden Line Ratios , 1999 .

[24]  Drake,et al.  First Light Measurements of Capella with the Low-Energy Transmission Grating Spectrometer aboard the Chandra X-Ray Observatory , 2000, The Astrophysical journal.

[25]  K. Evans,et al.  The Spectrum of Fe XVII in the Solar Corona , 1976 .

[26]  R. J. Speer,et al.  Rocket spectrogram of a solar flare in the 10-100 A region , 1985 .