The work is aimed at a study of the circumstellar disk of the bright
classical binary Be star {\pi} Aqr. We analysed variations of a double-peaked
profile of the H{\alpha} emission line in the spectrum of {\pi} Aqr that was
observed in many phases during ~40 orbital cycles in 2004--2013. We applied the
Discrete Fourier Transform (DFT) method to search for periodicity in the peak
intensity (V/R) ratio. Doppler tomography was used to study the structure of
the disk around the primary. The dominant frequency in the power spectrum of
the H{\alpha} V/R ratio is 0.011873 day^-1 that correspond to a period of
84.2(2) days and is in agreement with the earlier determined orbital period of
the system, Porb=84.1 days. The V/R ratio shows a sinusoidal variation
phase-locked with the orbital period. Doppler maps of all our spectra show a
non-uniform structure of the disk around the primary: a ring with the inner and
outer radii at Vin~ 450 km/s and Vout~ 200km/s, respectively, along with an
extended stable region (spot) at V_x ~ 225 km/s and V_y~100 km/s. The disk
radius of ~ 65 Rsun = 0.33 AU was estimated assuming Keplerian motion of a
particle on a circular orbit at the disk outer edge.Comment: 11 pages, 7 figures, 2 tables, published in A&
