Aims. We present detailed analysis of the vertical pulsation mode cross-section in ten rapidly oscillating Ap (roAp) stars based on spectroscopic time-series observations. The aim of this analysis is to derive from observations a complete picture of how the amplitude and phase of magnetoacoustic waves depend on depth. Methods. We use the unique properties of roAp stars, in particular chemical stratification, to resolve the vertical structure of p-modes. Our approach consists of characterising pulsational behaviour of a carefully chosen, but extensive sample of spectral lines. We analyse the resulting amplitude-phase diagrams and interpret observations in terms of pulsation wave propagation. Results. We find common features in the pulsational behaviour of roAp stars. Within a sample of representative elements the lowest amplitudes are detected for Eu ii (and Fe in 33 Lib and in HD 19918), then pulsations go through the layers where Hα core, Nd, and Pr lines are formed. There RV amplitude reaches its maximum, and after that decreases in most stars. The maximum RV of the second REE ions is always delayed relative to the first ions. The largest phase shifts are detected in Tb iii and Th iii lines. Pulsational variability of the Th iii lines is detected here for the first time. The Y ii lines deviate from this picture, showing even lower amplitudes than Eu ii lines but half a period phase shift relative to other weakly pulsating lines. We measured an extra broadening, equivalent to a macroturbulent velocity from 4 to 11−12 km s −1 (where maximum values are observed for Tb iii and Th iii lines), for pulsating REE lines. The surface magnetic field strength is derived for the first time for three roAp stars: HD 9289 (2 kG), HD 12932 (1.7 kG), and HD 19918 (1.6 kG). Conclusions. The roAp stars exhibit similarity in the depth-dependence of pulsation phase and amplitude, indicating similar chemical stratification and comparable vertical mode cross-sections. In general, pulsations waves are represented by a superposition of the running and standing wave components. In the atmospheres of roAp stars with the pulsation frequency below the acoustic cut-off frequency, pulsations have a standing-wave character in the deeper layers and behave like a running wave in the outer layers. Cooler roAp stars develop a running wave higher in the atmosphere. In stars with pulsation frequency close to the acoustic cut-off one, pulsation waves have a running character starting from deep layers. The transition from standing to running wave is accompanied by an increase in the turbulent broadening of spectral lines.

Aims. We have investigated the structure of the pulsating atmosphere of one of the best studied rapidly oscillating Ap stars, HD 24712. Methods. For this purpose we analyzed spectra collected during [2001][2002][2003][2004]. An extensive data set was obtained in 2004 simultaneously with the photometry of the Canadian MOST mini-satellite. This allows us to connect directly atmospheric dynamics observed as radial velocity variations with light variations seen in photometry. Results. We directly derived for the first time and for different chemical elements, respectively ions, phase shifts between photometric and radial velocity pulsation maxima indicating, as we suggest, different line formation depths in the atmosphere. This allowed us to estimate for the first time the propagation velocity of a pulsation wave in the outer stellar atmosphere of a roAp star to be slightly lower than the sound speed. We confirm large pulsation amplitudes (150-400 m s −1 ) for REE lines and the Hα core, while spectral lines of the other elements (Mg, Si, Ca, and Fe-peak elements) have nearly constant velocities. We did not find different pulsation amplitudes and phases for the lines of rare-earth elements before and after the Balmer jump, which supports the hypothesis of REE concentration in the upper atmosphere above the hydrogen line-forming layers. We also discuss radial velocity amplitudes and phases measured for individual spectral lines as tools for a 3D tomography of the atmosphere of HD 24712.

We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR 1217) based on non-adiabatic analyses taking into account the effect of dipole magnetic fields. We have found that all the pulsation modes appropriate for HD 24712 are damped, i.e. the κ-mechanism excitation in the hydrogen ionization layers is not strong enough to excite high-order p modes with periods consistent with observed ones, all of which are found to be above the acoustic cut-off frequencies of our models.The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with modified l = 2 and 3 modes, respectively. The large frequency separation (≈68 μHz) is reproduced by models which lay within the error box of HD 24712 on the Hertzsprung-Russell diagram. The nearly equally spaced frequencies of HD 24712 indicate the small frequency separation to be as small as ≈0.5 μHz. However, the small separation derived from theoretical l = 1 and 2 modes is found to be larger than ∼3 μHz. The problem of equal spacing could be resolved by assuming that the spacings correspond to pairs of l = 2 and 0 modes; this is possible because magnetic fields significantly modify the frequencies of l = 0 modes. The amplitude distribution on the stellar surface is strongly affected by the magnetic field resulting in the predominant concentration at the polar regions. The modified amplitude distribution of a quasi-quadrapole mode predicts a rotational amplitude modulation consistent with the observed one.Amplitudes and phases of radial velocity variations for various spectral lines are converted to relations of amplitude/phase versus optical depth in the atmosphere. Oscillation phase delays gradually outward in the outermost layers indicating the presence of waves propagating outward. The phase changes steeply around log τ ∼ −3.5, which supports a T -τ relation having a small temperature inversion there.

Abstract. Starspots are usually associated with the action of magnetic fields at stellar surfaces. However, an inhomogeneous chemical distribution of mercury was found recently for the mercury-manganese (HgMn) star α And -a well-established member of a non-magnetic subclass of the chemically peculiar stars of the upper main sequence. In this study we present first results of the high-resolution survey of the Hg  3984 Å resonance line in the spectra of rapidly rotating HgMn stars with atmospheric parameters similar to those of α And. We use spectrum synthesis modelling and take advantage of the Doppler resolution of stellar surfaces to probe the horizontal structure of mercury distribution. Clear signatures of spots are found in the Hg  3984 Å line profiles of HR 1185 and HR 8723. Two observations of the latter star separated by two days give evidence for line profile variability. We conclude that inhomogeneous distribution of Hg is a common phenomenon for the rapidly rotating HgMn stars in the 13 000-13 800 K effective temperature range independent of the stellar evolutionary stage. These results establish the existence of a new class of spectrum variable spotted B-type stars. It is suggested that the observed Hg inhomogeneities arise from dynamical instabilities in the chemical diffusion processes and are unrelated to magnetic phenomena.

The World Space Observatory UltraViolet (WSO-UV) is an international space mission devoted to UV spectroscopy and imaging. The observatory includes a 170 cm aperture telescope capable of high-resolution and long slit low-resolution spectroscopy, and deep UV and optical imaging. The observatory is designed for observations in the ultraviolet domain where most of astrophysical processes can be efficiently studied with unprecedented capability.

The rapidly oscillating Ap (roAp) star 10 Aquilae (10 Aql) shows one of the lowest photometric pulsation amplitudes and is characterized by an unusual spectroscopic pulsational behaviour compared to other roAp stars. In summer 2006 this star became target of an intense observing campaign, that combined ground‐based spectroscopy with space photometry obtained with the MOST (Microvariability & Oscillations Stars) satellite. More than 1000 spectra were taken during seven nights over a time‐span of 21 d with high‐resolution spectrographs at the 8‐m European Southern Observatory (ESO) Very Large Telescope (VLT) and 3.6‐m Telescopio Nazionale Galileo (TNG) giving access to radial velocity variations of about 150 lines from different chemical species. A comparison of pulsation signatures in lines formed at different atmospheric heights allowed us to resolve the vertical structure of individual pulsation modes in 10 Aql which is the first time for a multiperiodic roAp star. Taking advantage of the clear oscillation patterns seen in a number of rare earth ions and using the contemporaneous MOST photometry to resolve aliasing in the radial velocity measurements, we improve also the determination of pulsation frequencies. The inferred propagation of pulsation waves in 10 Aql is qualitatively similar to other roAp stars: pulsation amplitudes become measurable in the layers where Y and Eu are concentrated, increase in layers where the Hα core is formed, reach a maximum of 200–300 m s−1 in the layers probed by Ce, Sm, Dy lines and then decrease to 20–50 m s−1 in the layers where Nd iii and Pr iii lines are formed. A unique pulsation feature of 10 Aql is a second pulsation maximum indicated by Tb iii lines which form in the uppermost atmospheric layers and oscillate with amplitudes of up to 350 m s−1. The dramatic decline of pulsations in the atmospheric layers probed by the strong Pr iii and Nd iii lines accounts for the apparent peculiarity of 10 Aql when compared to other roAp stars. The phase–amplitude diagrams and bisector measurements of the Nd iii 5102 Å line reveal a rapid change of phase and amplitude with height for all three main pulsation modes, indicating the presence of a pulsation node in the stellar atmosphere. Finally, we report the discovery of a puzzling asymmetry of the strong Nd iii lines with their blue wing extending up to −50 km s−1, which is about 25 times the estimated value of ve sin i.

We present the results of the photometric and spectroscopic monitoring of the luminous Ap star HD 103498. The time‐series photometric observations were carried out on 17 nights using a three‐channel fast photometer attached to the 1.04‐m optical telescope at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. The photometric data from five nights in 2007 show a clear signature of 15‐min periodicity. However, the follow‐up observations during 2007–2009 did not reproduce any such periodicity. To confirm the photometric light variations, time‐series spectroscopic observations were carried out with the 2.56‐m Nordic Optical Telescope (NOT) at La Palma on 2009 February 2. No radial velocity variations were present in this data set, which is in full agreement with the photometric observations taken around the same date. Model atmosphere and abundance analysis of HD 103498 show that the star is evolved from the main sequence and its atmospheric abundances are similar to those of two other evolved Ap stars, HD 133792 and HD 204411: large overabundances of Si, Cr and Fe and moderate overabundances of the rare‐earth elements. These chemical properties and a higher effective temperature distinguish HD 103498 from any known roAp star.

We report a discovery of the Zeeman resolved spectral lines, corresponding to the extremely large magnetic field modulus B s = 17.5 kG, in the cool Ap star HD 178892. The mean longitudinal field of this star reaches 7.5 kG, and its rotational modulation implies the strength of the dipolar magnetic component B p ≥ 23 kG. We have revised rotation period of the star using the All Sky Automated Survey photometry and determined P = 8.2478 d. Rotation phases of the magnetic and photometric maxima of the star coincide with each other. We obtained Geneva photometric observation of HD 178892 and estimated T eff = 7700 ± 250 K using photometry and the hydrogen Balmer lines. Preliminary abundance analysis reveals abundance pattern typical of rapidly oscillating Ap stars.