Structural-Kinematic Features of Gas Environment of Unusual Herbig Ae Star HD 179218. I. Rapid Spectral Variability

Abstract

The spectroscopic material obtained from 2015 to 2021 for the young Herbig Ae star HD 179218 is described and analyzed. The profiles of the H\(\beta\) and He I \(\lambda 5876\) lines and their variability on different time scales are studied. Analysis of the observation results showed that the profiles of the H\(\beta\) line in the spectrum of HD 179218 have the shape of a single emission component with local absorption features superimposed on it, the radial velocities of which vary from the blue to the red edge of the emission. On certain dates, one can simultaneously observe several components persisting for at least three days. Over 17 observation dates, the H\(\beta\) and He I \(\lambda 5876\) line profiles looked like the inverse profile of P Cyg, the red boundary of which \(v_{\textrm{red}}\) varied from date to date from \(+235\) to \(+390\) km s\({}^{-1}\). Analysis of variations in the parameter \(v_{\textrm{red}}\) for these lines by the Lafleur–Kinman method showed the presence of a regular component with the period \(P=1.341\pm 0.002\) days corresponding to the expected rotation period of the star. The detected variability of HD 179218 may be a sign of magnetospheric accretion. The object’s rotation axis inclination is determined, \(i=23^{\circ}\pm 3^{\circ}\). The pattern of the observed variability of HD 179218 can be explained by the peculiarities of its magnetism.