Some astrophysical implications of the new atomic data obtained in the present
study are now discussed by means of a comparison with the observed spectrum
of the planetary nebula NGC 7027 in the 654-1046 nm region. Possible observations
of lines involving high-nl Rydberg states in C II, C III and C IV are also
predicted in the 
< 654 nm spectral region of this nebula.
The 4d-5f and 4f-5g lines, appearing at 922.89 and 990.39 nm respectively in
the 654-1046 nm NGC 7027 spectrum (Baluteau et al. 1995) are strong enough
to imply other 4d-nf and 4f-ng recombination lines should
be detectable in the region 400-654 nm. For these series, our predicted
wavelengths are 615.14, 512.22, 462.03, 432.98, 414.35 and 401.58 nm for the
4d-nf (n = 6-11) transitions and 646.20, 534.24, 480.27, 449.12, 429.23,
415.61 and 405.82 nm for the 4f-ng (n = 6-12) lines. If we except the transitions
5d-9f, 5g-9h, 5g-11h and 5g-12h, blended or masked by other lines, all
members of the series 5d-nf (n = 8-11), 5f-ng (n = 8-12) and
5g-nh (n = 8-13) are observed in the NGC 7027 spectrum published by
Baluteau et al. (1995). However, in view of the relatively small calculated
oscillator strengths corresponding to these transitions for larger n-values,
only the first next members of these series could probably appear in the
< 654 nm spectral region. The transitions with n = 6 lower terms,
characterized by small f-values, are not observed in the NGC 7027 spectrum.
The large values of oscillator strengths for the 5f 1F
g1G (f = 1.11)
and 5f 3Fg 3G (f = 1.26) transitions observed in the
Baluteau et al. (1995) NGC 7027 spectrum suggest higher members of these series might be detectable.
The only 5f-ng transitions which might appear in the 400-654 nm spectral region
are predicted at 583.32, 456.84, 530.51 and 423.80 nm for 5f1-7g1, 5f1-8g1,
5f3-7g3 and 5f3-8g3 respectively. The 5g-6h and 6g-8h lines appearing
at 819.67 and 826.11 nm in the NGC 7027 spectrum are also characterized by large
oscillator strengths (f = 1.65 and 0.267 respectively) which implies other lines
from higher nh levels could be observable. These lines should appear at the following
predicted wavelengths: 513.09, 412.86 nm for 5g-nh (n = 7, 8), 651.51, 565.96,
515.85, 483.30, 460.68, 444.19, 431.72, 422.02, 414.31, 408.06 and 402.92 for 6g-nh
(n = 9-19). Some of the 7g-nh, 7h-ni and 7i-nk transitions are also
observed for n = 10-14 in the Baluteau et al. (1995) NGC 7027 spectrum. Consequently,
wavelength predictions for higher members of these series up to n = 30 are given
in Table 7.
In the 654-1046 nm region of the NGC 7027 spectrum, the highest members of the 8-n, 9-n and 10-n Rydberg series, detected by means of unblended lines, are situated at 773.57 nm (8-11), 674.69 nm (9-16) and 702.19 nm (10-23). Other lines in these series might be observable in the 400-654 nm region and their predicted wavelengths are reported in Table 8 up to n = 26, 30 and 30 for the 8-n, 9-n and 10-n series respectively. However, as already mentioned by Baluteau et al. (1995), all C IV lines involving quasi-hydrogenic levels with large principal quantum numbers should be systematically blended with homologous O IV and N IV lines.