Long-Term Optical Spectroscopy of B[e] Star CI Cam in a Quiet State

Abstract

High-resolution optical spectra of the B[e] star CI Cam were obtained on arbitrary dates 2002–2023 using the 6-meter BTA telescope with the echelle spectrograph NES. The variability over time of the powerful emissions of H_α and He I profiles is found. For two-peak emissions with “rectangular” profiles, the intensity ratio of blue-shifted and red-shifted peaks is \({\text{V/R}} \geqslant 1\), except one date. A decrease in the intensity of all double-peaked emissions with “rectangular” profiles was revealed as they moved away in time from the 1998 outburst. The average radial velocity for emissions of this type for all observation dates varies in the range \({{V}_{r}}({\text{emis}}{-} d) = \) \( - (50.8 {\div} 55.7) \pm 0.2\) km/s. The half-amplitude of the change (standard deviation) is equal to \(\Delta {{V}_{r}} = 2.5\) km/s. The velocity for single-peaked ion emissions (Si III, Al III, Fe III) differs little from the values of \({{V}_{r}}({\text{emis}}{-} d)\), but the measurement accuracy for these emissions is worse: the average error for different dates ranges from 0.4 to 1.3 km/s. The systemic velocity is assumed to be \({{V}_{{{\text{sys}}}}} = - 55.4 \pm 0.6\) km/s according to the stable position of the forbidden emission [N II] 5755 Å. The position of single-peak emissions [O III] 4959 and 5007 Å is also stable: \({{V}_{r}}([{\text{O}}\;{\text{III}}]) = \) \( - 54.2 \pm 0.4\) km/s. Emissions [O I] 5577, 6300, 6363 Å, [Ca II] 7291 and 7324 Å are absent from the spectra. Appearance of the emission near 4686 Å is an infrequent event, its intensity rarely exceeds the noise level. Only a wide asymmetric emission with an intensity of about 16% above the continuum was registered in the spectrum for September 3, 2015. Questions arise about the use of this emission to estimate the period of variability of the star and about localization of this feature in the CI Cam system. The photospheric absorptions of N II, S II, and Fe III with a variable position are identified.