8.1.4. Atomic database for the absorbers¶

The continuum opacities are taken from Verner & Yakovlev (1995). Line opacities and wavelengths for most ions are from Verner et al. (1996), with the following additions and exceptions:

8.1.4.1. K-shell transitions¶

For some hydrogenic ions (C, N, O, Ne, Mg, Si, S and Ar) we added the transitions from principal quantum numbers 11–20 to the ground using our own SPEX database.

8.1.4.1.1. C-K transitions¶

Three inner-shell K-shell transitions for C I were calculated by Raassen using the Cowan code, but here only the oscillator strengths were calculated, and therefore calculated equivalent widths for large optical depths will be too weak. We added two C IV lines from the work of Nahar et al. (2001).

8.1.4.1.2. N-K transitions¶

For N I the K-shell transitions were calculated by Raassen using the Cowan code. We adjusted the wavelength of the strongest 1s–2p line acording to measurements. However, for the 1s–2p lines towards $1s 2s^2 2p^4$ $^4 P$ , we used oscilator strengths and Auger widths from Garcia et al. (2009).

Inner-shell K-shell transitions for N II were also calculated by Raassen using the Cowan code, but here only the oscillator strengths were calculated, and therefore calculated equivalent widths for large optical depths will be too weak. The exception to this are the 1s–2p absorption lines to the $1s 2s^2 2p^3$ $^3 S_1$ , $^3 P_1$ and $^3 D_1$ levels, for which we use Garcia et al. (2009).

For N III we added the 1s–2p absorption lines towards the $1s 2s^2 2p^2$ $^2 S$ , $^2 P$ and $^2 D_{3/2}$ levels from the paper by Garcia et al. (2009). Wavelengths are theoretical, so may be somewhat off.

For N IV we added the 1s–2p absorption lines towards the $1s 2s^2 2p$ $^1P_1$ and $1s 2p^3$ $^1 P_1$ levels from the paper by Garcia et al. (2009). Wavelengths are theoretical, so may be somewhat off.

For N V we added the 1s–2p absorption lines towards the $1s(2S)2s2p(3P)$ $^2 P$ doublet and $1s(2S)2s2p(1P)$ $^2 P$ doublet from the paper by Garcia et al. (2009). Wavelengths were corrected according to the measurements of Beiersdorfer et al. (1999).

For N VI we added the 1s–np lines for $n=5-7$ from our SPEX database.

8.1.4.1.3. O-K transitions¶

We included the inner shell K-shell transitions of oxygen ions (O I – O VI) from earlier work of Behar (HULLAC calculations, private commumication).

We adjusted the wavelength of the strongest line to $22.370\pm0.010$ Å, taken from Gu et al. (2005).

The two 1s–2p $^2 P_{1/2,3/2}$ lines of O IV were adjusted to 22.741 and 22.739 Å, respectively following Gu et al. (2005). The lines to the $^2 D_{3/2}$ and $^2 S_{1/2}$ terms were not adjusted as no values are given by Gu et al. (2005).

For O III, Gu et al. (2005) give only a single line instead of the three dominant lines to $^3 D_1$ , $^3 S_1$ , $^3 P_1$ . The oscillator-strength weighted average wavelength for these three lines using Behar’s HULLAC calculations is 23.058 Å, compared to 23.065 Å as given by Gu et al. (2005). Other sets of calculation differ much from this, up to 0.05–0.10 Å Olalla et al., 2002; Pradhan et al., 2003; Juett et al., 2004; so we keep the Behar values lacking more reliable calculations.

For O II, Juett et al. (2004) identified a feature in observed Chandra HETGS spectra towards several sources with the 1s–2p line from this ion; their measured wavelength is 23.351 $\pm$ 0.003 Å. This identification seems to be justified given the Auger electron measurements of Krause (1994) and Caldwell et al. (1994) as cited by Garcia et al. (2005). The relevant transitions are from the ground $^4 S_{3/2}$ to the $^4 P_{5/2}$ , $^4 P_{3/2}$ , and $^4 P_{1/2}$ levels; the oscillator strength weighted wavelength from Behar is 23.3012 Å. Therefore we shift the wavelengths of these transitions by $+0.0498$ Å in order to match the Juett et al. (2004) value.

Finally, in a similar way we shift the strong 1s–2p doublet from to match the weighted average of the value found by Juett et al. (2004) with the Chandra HETGS (23.508 $\pm$ 0.003 Å) and in Mrk 421 with RGS (23.5130 $\pm$ 0.0022 Å) to (23.5113 $\pm$ 0.0018 Å). For all O I lines, we have updated the oscillator strengths and transition rates to values obtained by Ton Raassen using Cowan’s code, and benchmarked to an adjusted wavelength scale.

Lines from O VII up to $n=100$ were calculated by extrapolation of the data for $n \le 10$ .

8.1.4.1.4. Ne-K to Ca-K transitions¶

The strongest K-shell transitions from Li-like to F-like ions of Ne, Mg, Al, Si, S, Ar, and Ca were taken from Behar & Netzer (2002).

8.1.4.1.5. Fe-K transitions¶

K-shell transitions in Fe II – Fe XXIV were included from the series of papers by Palmeri et al. (2003), Mendoza et al. (2004), and Bautista et al. (2004).

In addition, the strongest 1s–3p transitions in Fe XXIII were added from Behar & Netzer (2002).

8.1.4.2. L-shell transitions¶

8.1.4.2.1. Fe-L transitions¶

For the L-shell ions of iron (Fe XVII - Fe XXIV) we used HULLAC calculations. The wavelengths of these L-shell transitions were adjusted according to Phillips et al. (1999). Also the L-shell ions of Si VIII – Si XII, S X – S XIV and Ar XV were calculated using the HULLAC code. In addition, we added the 2p–3d inner shell resonance lines of Fe I - Fe XVI from Behar et al. (2001). These inner shell resonance lines occur mainly in the 16 - 17 Å band and appear to be extremely important diagnostic tools, since the normal resonance lines of these lowly ionized iron ions have their wavelengths mainly in the inaccessible EUV band.

8.1.4.2.2. Ni-L transitions¶

L-shell transitions of Ni I – Ni XVIII were calculated by Raassen using Cowan’s code, with the neglect of line broadening due to auto-ionizations.

8.1.4.3. M-shell transitions¶

For M-shell transitions of Fe ions, we have used data calculated by Ehud Behar using HULLAC (Fe I – Fe XVI). The calculations for (Fe VI – Fe XVI) were replaced on November 21, 2008 by updated calculations by Ming Feng Gu using FAC and compared with the NGC 3783 spectrum in Gu et al. (2006). They represent slight ( ~ 0.03 Angstrom) shifts from Behar’s initial calculations. Also, they exhibit typically 2–3 times higher total transition rates (Auger rates).