Table 3: Summary of model atoms used in the disk model calculations. For each ion we list the number of NLTE levels and the number of line transitions. In brackets we give the number of lines in the wavelength range covered by our optical spectra after fine-structure splitting for detailed line-profile calculations.

Element	Ion	NLTE levels	Lines
H	I	10	45 (8)
	II	1	-
He	I	29	61 (16)
	II	14	91 (14)
	III	1	-
C	I	7	4 (0)
	II	38	160 (42)
	III	58	329 (143)
	IV	9	17 (2)
	V	1	-
O	I	1	-
	II	29	82 (56)
	III	36	42 (47)
	IV	11	5 (0)
	V	6	4 (0)
	VI	1	-
Ne	I	3	0
	II	68	232 (49)
	III	4	0 (0)
	IV	1	-