B[e] Star CI Camelopardalis in the Optical Range

Abstract

We report the results of photometric and spectroscopic monitoring of CI Cam within 24 years since its outburst in 1998. Over this time, we found a system component emitting in the He II 4686 Å emission line, on an elliptical orbit with a period of \(19\overset{\textrm{d}}{.}407\) days and an eccentricity of 0.44–0.49. The variations of the optical brightness are observed with the same period and with an average amplitude of \(0\overset{\textrm{m}}{.}04\). The total amplitude of the He II radial velocity variations is about 380 km s\({}^{-1}\). The equivalent width of the line is variable on a time scale of tens of minutes as well as with the orbital period. Maximum equivalent widths of the He II line are observed when the component passes the descending node of the orbit. The intensity of the He II 4686 Å emission gradually increases with time. Slow radial velocity variations on a scale of decades were detected by means of high resolution spectroscopy in the iron emission lines and a forbidden nitrogen line formed in the circumstellar nebula. The B-type star turned out to be a pulsating variable. During the period between 2005 and 2009, pulsations were multiperiodic with the dominant periods \(0\overset{\textrm{d}}{.}5223\), \(0\overset{\textrm{d}}{.}41539\), and \(0\overset{\textrm{d}}{.}26630\) days. However, since 2012 it has pulsated in a single mode with a variable period in the \(0\overset{\textrm{d}}{.}403{-}0\overset{\textrm{d}}{.}408\) day range depending on the star’s luminosity. We identify the 2005–2009 pulsations as a resonance of the radial modes, and the residual stable mode as the first overtone. The pulsations are coherent on a scale of several months, and their average amplitudes are \(0\overset{\textrm{m}}{.}02{-}0\overset{\textrm{m}}{.}04\). The pulsation data constrain the spectral type of the main component to B0–B2 III, the distance to the system to 2.5–4.5 kpc, and the absolute visual magnitude \(M_{V}\) to the range of \(-3\overset{\textrm{m}}{.}7\) to \(-4\overset{\textrm{m}}{.}9\). The classification of the CI Cam main component as a B[e] supergiant is completely ruled out due to the observed pulsation periods. CI Cam may be a system at the stage after the first mass exchange and may be attributed to the FS CMa-type group of objects with the B[e] phenomenon.