Comparing APEC to Other Plasma Codes

• Iron, APEC vs Raymond-Smith (in wavelength units) 
• Iron, APEC vs Raymond-Smith (in energy units)




Differences between ATOMDB Version 1.2.0 and MEKAL/SPEX

• Oxygen, APEC vs SPEX (in wavelength units) 
• Neon, APEC vs SPEX (in wavelength units)
• Silicon, APEC vs SPEX (in wavelength units)
• Iron, APEC vs SPEX (in wavelength units)
• Nickel, APEC vs SPEX (in wavelength units)
• Iron, APEC vs SPEX (in energy units)

 

a. ATOMDB does not yet include fluorescence lines, whereas SPEX does. The most significant implication is that APEC models do not include the Fe K 6.4 keV (1.9 Angstrom) line (see other CAVEATS).

b. For Oxygen the most significant differences occur in the O VIII Ly alpha/ O VIII Ly beta ratio, as shown by Smith et al. (2001) ( ADS).

Comparison of Oxygen Line Spectra at 40 Million K

c. Other H-like ions show a similar difference in Ly alpha/Ly beta ratio. Silicon also shows large differences in He-like emissivities at low temperatures, presumably caused by differences in the ionization balance. SPEX assumes Arnaud and Rothenflug (1985, A&AS, 60, 425), while APEC assumes Mazzotta et al. (1998, A&AS, 133, 403).

Comparison of Silicon Line Spectra at 2.5 Million K

d. Fe L-shell data show significant differences. Some effects can be attributed to the differences in ionization balance (SPEX assumes Arnaud and Raymond (1992, ApJ, 398, 394), while APEC assumes Mazzotta et al.). Other effects can be attributed to scaling laws used in SPEX, which are not used in APEC (see, e.g. Gu et al. 1999, ApJ, 518, 1002). For example, the large differences at low temperatures are from Fe XVII only, and must be related to the scaling laws. Differences at higher temperature appear to be a combination of scaling laws and ionization balance effects for Fe XXI to XXII. (The APEC calculations use the collision strengths produced by HULLAC and have been tested relative to the original calculations.)

Comparisons of Iron Line Spectra

Examples of noticeable differences between ATOMDB and MEKAL/SPEX at high resolution

a. The DR satellite lines appearing near the resonance lines show significant spectral structure not captured by assumptions introduced in SPEX (e.g. near O VII 21.7 Angstroms at 3 million K and Fe XVII 15.0 Angstroms at 2 million K). Proper treatment of the DR lines is important for distinguishing between line and continuum emission (see Brickhouse et al. 1995, ApJS, 97, 551).

Comparison of DR Satellite Line Spectra

b. Fine structure lines are split up in the ATOMDB, but not always in the SPEX list. For example, the O VIII H-alpha lines near 102.5 Angstroms should be treated carefully when trying to measure the density diagnostic Fe XXI 102.22 Angstrom line.

O VIII H alpha Fine Structure

c. Wavelength differences are also apparent. The ATOMDB has included the measurements of Brown et al. (1998, ApJ, 502, 1015) and Brown et al. (1999, Internal Report LLNL.JC-136647B). H- and He-like wavelengths in the ATOMDB are from relativistic quantum mechanics calculations and include fine structure.

d. SPEX includes inner shell excitation lines which are not currently included in the ATOMDB (see other CAVEATS), for example, the Fe line at 17.2 Angstroms; however, this line strength in SPEX is much stronger than in Raymond-Smith models and needs investigation. Note also wavelength differences noted in (c) above.

Fe XVII Comparison: Wavelengths and Inner Shell Excitation

e. The ATOMDB includes more lines at high principal quantum number than SPEX (see Brickhouse et al. 2000, ApJ, 530, 387). This is apparent near 10 Angstroms at 6 x 10^6 K). However, APEC models are still not necessarily complete enough in detail to achieve good spectral fits at high resolution, depending on the spectrum to fit. We do not believe APEC is complete enough yet at soft X-ray wavelengths to perform global fits to LETG spectra.

Iron Comparison: High n Lines

Ni Wavelength Comparisons at 4 Temperatures

b. The ATOMDB now replaces the CHIANTI calculations for Li-like ions with calculations by D. Liedahl using the HULLAC. The new calculations include levels up to principal quantum number n=7. The mutual lines are in good agreement. The new lines are apparent at the short wavelength end of the sample spectra.

Comparison of Lines from Li-like Ions