VARIABILITY OF REEMISSION SPECTRAL LINES IN THE SPECTRUM HD 179218

Abstract

The Herbig Ae/Be type stars (HAeBe) are pre-main sequence (PMS) objects of intermediate mass 2 − 10M⊙ and are considered to be the progenitors of Vega type stars, which are surrounded with a residual protoplanetary disks. Spectral monitoring of individual objects has shown that in the spectra of these stars are observed variable emission and absorption lines.The same features are also characteristic of classical T Tauri stars (CTTS). HD 179218 (MWC 614, Sp B9-A2) is an isolated HAe/Be type star. Our previous observations were discovered 40 days’ timescale quasiperiodic variations of the hydrogen lines Hα and Hβ. In this report we have presented results of analysis of spectral variation of the disc reemission spectral lines He I, Si II, D NaI, [OI]. According to our spectra, the D1 and D2 NaI lines are shown an inverse –P Cyg profile. Line parameters also show a synchronous change with a change in the hydrogen lines. It also shows a wave-like variation of parameters with a characteristic time of 10-20 days.The ratio of the values of the equivalent widths of the EW(D2)/EW(D1) lines showed a monotonic de-crease from 1.7 to 0.5, which indicates a smooth variation of the physical condition in the star’s disk.The absorption spectral lines SiII λ 6347 and 6371 Å show the absence of synchronous changes with changes in the hydrogen and sodium doubletlines.The existence of stratification in the distribution of radial velocities for different spectral lines was found. Lines with a high ionization potential show
positive rates (for example, HeI, SiII), while lines with a low ionization potential have negative velocities (for example, D NaI).This suggests that lines with high ionization potential can form in the accretion zone of the disk. Possible mechanisms of the observed variability of the star are discussed.