The structure of the Akn 120 emitting region: The line shapes and long-term H_\beta line profile variation

Astronomical Observatory, Volgina 7, Belgrade, Yugoslavia

Corresponding author: L. Č. Popović, lpopovic@aob.bg.ac.yu

Received: 9 October 2000
Accepted: 6 December 2000

Abstract

To investigate the structure of the Akn 120 emitting region we have analysed the spectral line profiles of H_α, H_β, Ly_α, C III[1909], C IV[1549] and Mg II[2798] lines using a Gaussian-decomposition approach. The decomposed shape of the Akn 120 lines indicates three separated broad line-emitting regions, in two of them, the systematic motions of emitting gas are present. It seems that one of the two regions has a high random velocity of emitters (≈2500 km s^-1) and approaching line-of-sight velocities, and the other has a smaller random velocity of emitters (≈1000 km s^-1) and receding line-of-sight velocities. Also, we discuss the long-term H_β line shape variation in the spectra of Akn 120. The H_β line (from 96 spectra) was fitted with three broad and one narrow Gaussians through the entire period considered (1977-1990). The central broad as well as blue component of H_β and shelf (Fe II template) cause the H_β line shape variation. Besides the Gaussian decomposition of the shapes of the three hydrogen lines we propose here a disk model with two more regions located symmetrically to the disk plane. Using the fitting method with the disk model we obtained the parameters of the disk: ; , .