In order to check possible dependencies of Stark widths
on temperature we have plotted the ratios
versus
temperature T for each one of the lines. Figure 5
shows an example of these plots for the 407.216 nm OII line.
The available data in the literature are also included.
Although in some cases the widths seem to show very slight
tendency to decrease with increasing temperature,
the scarcity of available data and the inherent uncertainties
in the measurements make it difficult to establish any functional
relationship, at least in the temperature range considered in
this experiment. This behavior is common for every measured line.
In Table 2 the Stark FWHM value
is listed
for
obtained from the mean of the ratios
.
The electron temperature is assumed to be around 40000 K.
The 32 measured OII lines, with their lower and
upper transition levels assuming LS-coupling
(Striganov & Sventistskii 1968),
are arranged by transition arrays and multiplets according to upper level
increasing energy. The number of data and mean is shown for each
line, with the corresponding standard statistical error
.
For comparison, Table 2 shows other experimental available data
Platisa et al. (1975);
Djenize et al. (1991, 1998).
The accuracy of these data is specified for each case in the Table 2 caption
and takes values around 15% according to the authors.
The similar accuracy of the
present work takes advantage of a much more extensive
set of data and lines. In this way, more reliable uncertainties for each line
can be derived from the resulting statistical dispersions. All
data have been normalised to
,
assuming a linear
dependence with
and dividing by this value.
When available, the ratio of
the measured values to theoretical values
is shown,
i.e. semi-classical and semi-empirical approaches calculated in
Griem (1974);
Hey & Bryan (1977);
Hey & Breger (1980);
Dimitrijevic (1982) and also
results of Puric et al. (1988). These are always for
and taking, if possible, T=40000 K.
Our experimental results are usually
in good agreement within the same transition arrays and multiplets, as
can be seen in Table 2. Also there is good agreement with the
theoretical data of Griem and with the measurements of Platisa et al.
or Djenize et al. within 20% uncertainty ranges.
Very reliable Stark data and good experimental profiles of OII emission lines
are noticeably difficult to obtain. Also
the different plasma experimental conditions, mainly the different
temperature ranges, could explain some discrepancies like those corresponding
to the 408.929 nm line. Agreement with Griem, Dimitrijevic and
Hey & Breger is good. The work of Hey & Bryan perhaps
slightly underestimates the widths, while the formulae given in the work
of Puric et al. (1988) clearly tend to underestimate the widths when
applied to
and
transitions of OII specie.
Puric et al. (1988) calculated their formula within a
semiempirical approach and studied width dependencies on
upper level ionization potential working with results
of species with different ionization stages, from OII to OV, but mainly OIII.
Taking into account an electron density uncertainty of 10% we can estimate the average final uncertainty of the Stark widths given in this work around 20%, although with a strong dependence on the line. Perhaps the main error source for the narrowest transitions (often the most intense) is the unknown kinetic emitter temperature in deconvolution procedure. For some other transitions the error comes from weakeness of plasma emission. In spite of the few reliable data which can be obtained for most of the difficult lines, particular uncertainties can be inferred from statistical dispersions. Future high accuracy measurements should extend and complete the lack of OII Stark experimental data.
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Transit. | Multiplet | n | ![]() |
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(nm) | array | (pm) | [1] | [2] | [3] | [4] | [5] | [6] | [7] | [8] | |||
465.084 | ![]() |
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9 | 22.5 | 3.7 | 23.7 | 0.71 | 0.73 | 1.37 | ||||
463.885 | ![]() |
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8 | 22.0 | 3.3 | 22.9 | 0.70 | 0.72 | 1.35 | ||||
464.181 | ![]() |
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11 | 22.3 | 6.0 | 22.1 | 0.71 | 0.73 | 1.36 | ||||
464.914 | ![]() |
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12 | 20.9 | 2.0 | 22.9 | 0.67 | 1.16 | 0.73 | 0.68 | 1.27 | ||
434.556 | ![]() |
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6 | 25.8 | 4.4 | 1.19 | 0.96 | 1.77 | |||||
436.689 | ![]() |
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11 | 24.8 | 7.9 | 22.1 | 1.13 | 0.92 | 1.69 | ||||
433.686 | ![]() |
![]() |
7 | 20.2 | 5.6 | 0.93 | 0.75 | 1.39 | |||||
431.714 | ![]() |
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9 | 25.6 | 5.7 | 21.9 | 1.18 | 1.62 | 1.06 | 0.95 | 1.78 | ||
434.943 | ![]() |
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9 | 25.3 | 9.0 | 1.16 | 0.94 | 1.73 | |||||
431.963 | ![]() |
![]() |
10 | 26.1 | 6.3 | 1.20 | 0.97 | 1.81 | |||||
459.617 |
![]() |
![]() |
8 | 27.2 | 4.1 | 24.6 | 15-13.6* | 1.49 | 0.97 | ||||
459.097 |
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11 | 22.3 | 7.6 | 25.4 | |||||||
435.127 |
![]() |
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9 | 22.5 | 7.1 | ||||||||
434.742 |
![]() |
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5 | 31.1 | 8.3 | 21.9 | 1.87 | 1.21 | |||||
408.512 |
![]() |
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6 | 25.2 | 7.6 | 0.98 | 2.15 | ||||||
407.886 |
![]() |
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9 | 20.0 | 4.0 | 0.78 | 1.71 | ||||||
409.294 |
![]() |
![]() |
5 | 21.3 | 2.3 | 23.5 | 0.83 | 0.96 | 0.71 | 1.81 | |||
407.216 |
![]() |
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11 | 23.9 | 2.0 | 22.7 | 0.92 | 2.04 | |||||
407.587 |
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10 | 19.7 | 3.3 | 23.5 | 0.76 | 1.68 | |||||
415.330 |
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7 | 29.3 | 4.9 | 25.6 | 1.13 | 1.19 | 0.93 | 2.38 | |||
415.654 |
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6 | 32.9 | 9.8 | 1.26 | 2.67 | ||||||
413.281 |
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9 | 29.9 | 8.3 | 25.4 | 1.15 | 2.45 | |||||
412.148 |
![]() |
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6 | 24.2 | 8.6 | 0.94 | 2.00 | ||||||
411.079 |
![]() |
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7 | 21.9 | 5.4 | 0.81 | 1.81 | ||||||
411.922 |
![]() |
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8 | 24.8 | 6.8 | 0.90 | 2.05 | ||||||
411.203 |
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5 | 34.3 | 8.0 | 2.83 | |||||||
444.821 |
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10 | 34.3 | 9.0 | ||||||||
432.748 |
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6 | 38.2 | 5.1 | ||||||||
430.382 |
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6 | 118.6 | 23.5 | 95.6 | |||||||
408.929 |
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9 | 100.9 | 18.6 | 66.4 | |||||||
447.788 |
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6 | 127.0 | 20.1 | ||||||||
414.609 |
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7 | 43.2 | 10.0 |
Acknowledgements
We thank Drs. I. de la Rosa, C. Pérez and M.A. Gigosos for their help, S. González for his work in the experimental device, the Dirección General de Investigación Científica y Técnica (Ministerio de Educación y Ciencia) of Spain for its financial support under Contract No. PB-94-0216, and also the Consejería de Educación y Cultura de la Junta de Castilla y León (VA96-96).
Copyright The European Southern Observatory (ESO)