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4. FeH Solar identification

The probability of chance coincidence between laboratory and umbral wavenumbers can be tested by means of the Russell-Bowen formula (Engvold et al. 1980). In the method of wavelength coincidence, the procedure of identification is completed as the list of accurate wavelengths for a particular transition of the selected molecule and the stellar spectrum are compared for coincidences (Hansen 1985; Lambert 1988). The method of coincidence assumes an identification of the solar line with a laboratory line if the line is located within 0.05 tex2html_wrap_inline1565 of the listed laboratory value. In order to exclude the possibility of identifying a molecular band by chance, the number of coincidences found, should exceed the number of chance coincidences. In addition, the variation of relative line strength with rotational quantum number J is checked (see Sotirovski 1971). A quantitative measure of the significance of the coincidences is performed by using the following formula (Hansen 1985):


equation269

where tex2html_wrap_inline1615 is in tex2html_wrap_inline1565 and N represents successively all integer numbers between 0 and 40. An example of the resulting plots of mean residual intensities tex2html_wrap_inline1621 for a given band, versus shift in wavenumber relative to the predicted line positions, is shown in Fig. 1 (click here). The presence of a molecular band in the umbral spectrum shows up as a peak above the noise produced by random coincidences. All known FeH bands (Phillips et al. 1987) within the spectral range of the present umbral spectrum were checked with this procedure (Fawzy 1995). A slightly different version of this method was developed and used by Lambert (1988). Figure 1 shows a good example of the coincidence curve for the transition (1/2-1/2) of the lower (a) energy level of the tex2html_wrap_inline1543-doublet pair for the R-branch of the FeH (0-0) band. We have searched for all laboratory line positions of the bands (2-0), (1-0), (2-1), (0-0), (1-1), and (2-2) within the available range of the umbral spectrum tex2html_wrap_inline1641 Å; tex2html_wrap_inline1643). Figure 2 shows a part of the umbral spectrum of the studied sunspot with the locations of FeH lines of the (0-0) band. The laboratory, umbral wavenumbers and their differences tex2html_wrap_inline1647 are given in Tables 2-5 with the corresponding transitions for the identified bands (0-0), (1-0), (2-0), and (2-1) respectively. The numbers (1), (2), (3), and (4) are used for transitions (7/2-7/2), (5/2-5/2), (3/2-3/2), and (1/2-1/2), respectively, for either the upper (b), or the lower (a) energy level of tex2html_wrap_inline1543-doublet pair for both R and P-branches. The differences between laboratory and umbral wavenumbers of the identified lines are less than tex2html_wrap_inline1671.

  figure307
Figure 1: Example of the coincidence curve for the transition (1/2-1/2) of the R-branch of the (0-0) band

 figure313
Figure 2: Part of the umbral spectrum with locations of the FeH lines of the (0-0) band


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