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.

中文翻译：

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B[e] 星 CI 鹿豹在光学范围内

摘要

我们报告了 CI Cam 自 1998 年爆发以来 24 年内的光度和光谱监测结果。在此期间，我们发现一个系统组件在 He II 4686 Å 发射线发射，在周期为 \ ( 19\overset{\textrm{d}}{.}407\)天和 0.44–0.49 的离心率。观察到光亮度的变化具有相同的周期，平均幅度为\(0\overset{\textrm{m}}{.}04\)。He II径向速度变化的总振幅约为380 km s \({}^{-1}\). 线的等效宽度在几十分钟的时间尺度以及轨道周期上是可变的。当组件通过轨道的降节点时，观察到 He II 线的最大等效宽度。He II 4686 Å 的发射强度随时间逐渐增加。铁发射线的高分辨率光谱和星周星云中形成的禁止氮线检测到数十年尺度的缓慢视向速度变化。B型星原来是一个脉动变星。在 2005 年至 2009 年期间，脉动呈多周期性，主导周期为\(0\overset{\textrm{d}}{.}5223\) , \(0\overset{\textrm{d}}{.}41539 \)和\(0\overset{\textrm{d}}{.}26630\)天。然而，自 2012 年以来，它在 \(0\overset{\textrm{d}}{.}403{-}0\overset{\textrm{d}}{.}408 中以可变周期的单一模式脉动\)日期范围取决于恒星的光度。我们将 2005-2009 年的脉动识别为径向模式的共振，并将残余稳定模式识别为第一泛音。脉动在几个月的尺度上是连贯的，它们的平均振幅是\(0\overset{\textrm{m}}{.}02{-}0\overset{\textrm{m}}{.}04\ )。脉动数据将主成分的光谱类型限制在 B0–B2 III，与系统的距离限制在 2.5–4.5 kpc，绝对视觉震级 \ (M_{V}\)限制在\(-3\覆盖{\textrm{m}}{.}7\)到\(-4\overset{\textrm{m}}{.}9\). 由于观察到的脉动周期，完全排除了将 CI Cam 主成分分类为 B[e] 超巨星的可能性。CI Cam 可能是第一次质量交换后阶段的系统，可能归因于具有 B[e] 现象的 FS CMa 型天体群。