The O9IV star HD 57682, discovered to be magnetic within the context of the Magnetism in Massive Stars (MiMeS) survey in 2009, is one of only eight convincingly detected magnetic O‐type stars. Among this select group, it stands out due to its sharp‐lined photospheric spectrum. Since its discovery, the MiMeS Collaboration has continued to obtain spectroscopic and magnetic observations in order to refine our knowledge of its magnetic field strength and geometry, rotational period and spectral properties and variability. In this paper we report new Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) spectropolarimetric observations of HD 57682, which are combined with previously published ESPaDOnS data and archival Hα spectroscopy. This data set is used to determine the rotational period (63.5708 ± 0.0057 d), refine the longitudinal magnetic field variation and magnetic geometry (dipole surface field strength of 880 ± 50 G and magnetic obliquity of 79° ± 4° as measured from the magnetic longitudinal field variations, assuming an inclination of 60°) and examine the phase variation of various lines. In particular, we demonstrate that the Hα equivalent width undergoes a double‐wave variation during a single rotation of the star, consistent with the derived magnetic geometry. We group the variable lines into two classes: those that, like Hα, exhibit non‐sinusoidal variability, often with multiple maxima during the rotation cycle, and those that vary essentially sinusoidally. Based on our modelling of the Hα emission, we show that the variability is consistent with emission being generated from an optically thick, flattened distribution of magnetically confined plasma that is roughly distributed about the magnetic equator. Finally, we discuss our findings in the magnetospheric framework proposed in our earlier study.

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 H α 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 H α 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, P orb = 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 V in ≈ 450 km s −1 and V out ≈ 200 km s −1 , respectively, along with an extended stable region (spot) at V x ≈ 225 km s −1 and V y ≈ 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.

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 4686 Å 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 8.2 M ) 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 150 R . 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.

Context. RRab stars are large amplitude pulsating stars in which the pulsation wave is a progressive wave. Consequently, strong shocks, stratification effects, and phase lag may exist between the variations associated with line profiles formed in different parts of the atmosphere, including the shock wake. The pulsation is associated with a large extension of the expanding atmosphere, and strong infalling motions are expected. Aims. The objective of this study is to provide a general overview of the dynamical structure of the atmosphere occurring over a typical pulsation cycle. Methods. We report new high-resolution observations with suitable time resolution of Hα and sodium lines in the brightest RR Lyrae star of the sky: RR Lyr (HD 182989). A detailed analysis of line profile variations over the whole pulsation cycle is performed to understand the dynamical structure of the atmosphere. Results. The main shock wave appears when it exits from the photosphere at ϕ 0.89, i.e., when the main Hα emission is observed. Whereas the acceleration phase of the shock is not observed, a significant deceleration of the shock front velocity is clearly present. The radiative stage of the shock wave is short: 4% of the pulsation period (0.892 < ϕ < 0.929). A Mach number M > 10 is required to get such a radiative shock. The sodium layer reaches its maximum expansion well before that of Hα (∆ϕ = 0.135). Thus, a rarefaction wave is induced between the Hα and sodium layers. A strong atmospheric compression occurring around ϕ = 0.36, which produces the third Hα emission, takes place in the highest part of the atmosphere. The region located lower in the atmosphere where the sodium line is formed is not involved. The amplification of gas turbulence seems mainly due to strong shock waves propagating in the atmosphere rather than to the global compression of the atmosphere caused by the pulsation. It has not yet been clearly established whether the microturbulence velocity increases or decreases with height in the atmosphere. Furthermore, it seems very probable that an interstellar component is visible within the sodium profile.

Context. The so-called Hα third emission occurs around pulsation phase ϕ = 0.30. It has been observed for the first time in 2011 in some RR Lyrae stars. The emission intensity is very weak, and its profile is a tiny persistent hump in the red side-line profile. Aims. We report the first observation of the Hα third emission in RR Lyr itself (HD 182989), the brightest RR Lyrae star in the sky. Methods. New spectra were collected in 2013−2014 with the AURELIE spectrograph (resolving power R = 22 700, T152, Observatoire de Haute-Provence, France) and in 2016−2017 with the eShel spectrograph (R = 11 000, T035, Observatoire de Chelles, France). In addition, observations obtained in 1997 with the ELODIE spectrograph (R = 42 000, T193, Observatoire de Haute-Provence, France) were reanalyzed. Results. The Hα third emission is clearly detected in the pulsation phase interval ϕ = 0.188−0.407, that is, during about 20% of the period. Its maximum flux with respect to the continuum is about 13%. The presence of this third emission and its strength both seem to depend only marginally on the Blazhko phase. The physical origin of the emission is probably due to the infalling motion of the highest atmospheric layers, which compresses and heats the gas that is located immediately above the rising shock wave. The infalling velocity of the hot compressed region is supersonic, almost 50 km s −1 , while the shock velocity may be much lower in these pulsation phases. Conclusions. When the Hα third emission appears, the shock is certainly no longer radiative because its intensity is not sufficient to produce a blueshifted emission component within the Hα profile. At phase ϕ = 0.40, the shock wave is certainly close to its complete dissipation in the atmosphere.