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Definition of the primary companion spectral type and luminosity class for CI Cam.



The spectrum of the primary companion in the CI Cam system is distorted and hided by the surrounding dusty and gaseous shell. For the first time, the absorption detailes of this companion were discovered in the lines of H-delta and H-epsilon by Hynes R.I., Clark J.S., Barsukova E.A., et al. (Astron. & Astrophys. V.392, 991, 2002). These are wide wings due to Stark effect in the star photosphere. In our spectrum taken with BTA in the blue region, it is well seen that the emission component of the shell decreases rapidly in the line profile as the number of Balmer line increases, and the wide absorption profiles loom. The width of hydrogen lines is known to depend on the pressure in the photosphere, and then on the luminosity and effective temperature of the star. We have studied this dependence using the spectra of normal B stars from the databases by Jacoby et al., ApJ Suppl V.56, p.257, 1984, and Toulouse-Tarbe Laboratory. The resolution of Jacoby spectra (4.5А) coincides with the resolution of our BTA/UAGS spectra (4.4A). But Toulouse-Tarbe spectra had higher resolution (2.9А), so the parameters estimated by this database were recalculated to our resolution. We choose H-delta (4101.74 A) and H-eta (3835.39 A) lines for the analysis, as their profiles in CI Cam were distorted by emissions least of all.

Dependence of full width FWZI of hydrogen lines on star spectral type and luminosity class. Green signs show I-II luminosity class, red signs of different tints - III-V class. Filled squars are the data from Jacoby database, circles are the modified data from Toulouse-Tarbe database. The location of check star, HD 52918 (B1V) is marked by open square, its spectrum was taken with BTA at the same night as CI Cam one. It is seen that CI Cam is located far out of the supergiants' region (class I-II).

FWZI is equal to 25A for CI Cam for the both lines. This means that the star undoubtly belongs to B4 III-V type.

Full width of lines depends on adopted continuum level and is estimated with the uncertainty of about 2-3A, so, check of these estimates is needed. Therefore, we measured correctly the half-width of these lines (FWHM) using the CENTER/GAUSS method of the MIDAS packet. Unfortunately, this method is unavailable to CI Cam because the central parts of the profile are distorted by the emission. The dependences between FWZI and FWHM for the normal B stars of the two databases are shown in the following Figure. Note that Toulouse-Tarbe data were again recalculated to lower resolution assuming that the profiles have the shape close to Gaussians. Clear connection between FWZI and FWHM is a reason to consider our estimates of spectral type and luminosity as reliable.

Dependence between measured half-width and estimated full width of selected hydrogen lines H-eta and H-delta. Designation is the same as in the previous Figure.