Astron. Astrophys. 329, 721-724 (1998)

2. Data for calculations

For quantitative evaluation of the line sensitivity, we shall use the indicator, which gives a relative change of the line depression for a 1 change of the atmospheric parameter. The indicator shows how the line absorption (in percentage) has changed, if the atmospheric parameter has increased by 1 in the region of line formation. The sign of the indicator + (-) testifies that the line absorption was increased (reduced). For the description of the spectral line sensitivity, it is enough to use the indicators for the central line depth () and for the equivalent width (). The most interesting in the spectral analysis problems is the study of the line sensitivity to the temperature (T), the gas pressure () and the microturbulent velocity (). Therefore, the sensitivity indicators were calculated only for these atmospheric parameters.

Calculations of indicators were performed for 604 absorption lines of Fe I and 58 Fe II lines. The line parameters are listed in the table. The condition of choice of the spectral lines is the absence of blends in the line profiles. In the solar spectrum, there are not enough such lines. To start, the line profiles were simply examined in the Atlas of the solar spectrum (Delbouille et al. 1973). Further, the bisectors of these lines were calculated and compared with an average bisector of the given group of lines. The line groups were chosen for different excitation potentials of the lower level, the central line depths, and the line wavelengths. The list of lines was purposely extended at the expense of lines with weaker blends to receive the maximum of lines suitable (or conditionally suitable) for the analysis of the fine structure of the line profiles and primarily of all for study of the line asymmetries. Partially, this list of lines in the range 505.0-665.0 nm was already used by Brandt & Gadun (1993, 1995) for study of changes in the spectral line parameters above the active areas.

The calculations of the sensitivity indicators were performed using the SPANSAT codes (Gadun & Sheminova 1988) in an LTE approximation. For some lines used in this study, NLTE effects may be essential. For example, as is shown in Sheminova & Matveev 1984, the equivalent widths and central depths of Fe I weak lines with low excitation potentials decrease by 10%, on the average, when deviations from LTE are taken account. In calculations of the sensitivity indicators, we used the HOLMU model atmosphere (Holweger & Müller 1974) with excitation temperature based on observations of the Fe I line profiles. Thus, the probable NLTE effects for Fe I lines are taken into account in an indirect way. The values of micro () and macroturbulent () velocities, which vary with height in the photosphere, were taken from Gurtovenko & Kostyk (1989):

The Van der Vaals damping constant was taken with the correction factor 1.3. The line oscillator strengths and the solar iron abundance were found by comparison between calculated and observed central line depths.

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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