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Aims. The work is aimed at studying the circumstellar disk of the bright classical binary Be star π Aqr. Methods. We analysed variations of a double-peaked profile of the Hα emission line in the spectrum of π 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 ratio (V/R). Doppler tomography was used to study the structure of the disk around the primary. Results. The dominant frequency in the power spectrum of the Hα V/R ratio is 0.011873 day-1, which corresponds to a period of 84.2(2) days and agrees with the earlier determined orbital period of the system, Porb = 84.1 days. The V/R shows a sinusoidal variation that is 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-1 and Vout ≈ 200 km s-1, respectively, along with an extended stable region (spot) at Vx ≈ 225 km s-1 and Vy ≈ 100 km s-1. The disk radius of ≈65 R☉ = 0.33 AU was estimated by assuming Keplerian motion of a particle on a circular orbit at the disk's outer edge. [ABSTRACT FROM AUTHOR]

We describe the results of the world-wide observing campaign of the highly eccentric Be binary system δ Scorpii 2011 periastron passage which involved professional and amateur astronomers. Our spectroscopic observations provided a precise measurement of the system orbital period at 10.8092±0.0005 yr. Fitting of the He ii 4686Å line radial velocity curve determined the periastron passage time on 2011 July 3, UT 9:20 with a 0.9-day uncertainty. Both these results are in a very good agreement with recent findings from interferometry. We also derived new evolutionary masses of the binary components (13 and 8.2M☉) and a new distance of 136 pc from the Sun, consistent with the HIPPARCOS parallax. The radial velocity and profile variations observed in the Hα line near the 2011 periastron reflected the interaction of the secondary component and the circumstellar disk around the primary component. Using these data, we estimated a disk radius of 150R☉. Our analysis of the radial velocity variations measured during the periastron passage time in 2000 and 2011 along with those measured during the 20th century, the high eccentricity of the system, and the presence of a bow shock-like structure around it suggest that δ Sco might be a runaway triple system. The third component should be external to the known binary and move on an elliptical orbit that is tilted by at least 40° with respect to the binary orbital plane for such a system to be stable and responsible for the observed long-term radial velocity variations. [ABSTRACT FROM AUTHOR]