We report a multisite photometric campaign for the β Cephei star 12 Lacertae. 750 h of high‐quality differential photoelectric Strömgren, Johnson and Geneva time‐series photometry were obtained with nine telescopes during 190 nights. Our frequency analysis results in the detection of 23 sinusoidal signals in the light curves. Ten of those correspond to independent pulsation modes, and the remainder are combination frequencies. We find some slow aperiodic variability such as that seemingly present in several β Cephei stars. We perform mode identification from our colour photometry, derive the spherical degree ℓ for the five strongest modes unambiguously and provide constraints on ℓ for the weaker modes. We find a mixture of modes of 0 ≤ℓ≤ 4. In particular, we prove that the previously suspected rotationally split triplet within the modes of 12 Lac consists of modes of different ℓ; their equal frequency splitting must thus be accidental. One of the periodic signals we detected in the light curves is argued to be a linearly stable mode excited to visible amplitude by non‐linear mode coupling via a 2:1 resonance. We also find a low‐frequency signal in the light variations whose physical nature is unclear; it could be a parent or daughter mode resonantly coupled. The remaining combination frequencies are consistent with simple light‐curve distortions. The range of excited pulsation frequencies of 12 Lac may be sufficiently large that it cannot be reproduced by standard models. We suspect that the star has a larger metal abundance in the pulsational driving zone, a hypothesis also capable of explaining the presence of β Cephei stars in the Large Magellanic Cloud.

Abstract. The first multisite photometric campaign devoted to the rapidly oscillating mass-accreting (primary) component of the Algol-type eclipsing binary system AS Eri has confirmed the presence of rapid pulsations with frequency 59.03116 d −1 , and revealed the second and third oscillation modes with frequencies 62.5631 d −1 and 61.6743 d −1 , respectively. These modes are related to the 5−6 overtone oscillations and are among the shortest periods excited in non-magnetic MS A-F stars. The nearly equator-on visibility of eclipsing binaries help to narrow the range of possible mode identifications for the detectable modes as radial or (l, m) = (1, ±1), (l, m) = (2, ±2) and (l, m) = (2, ±0). We checked the high-order pulsation-to-orbital synchronization (POS) using the trial mode identification and the Doppler effect correction for frequencies of non-radial pulsation. We found that (l, m, n) = (1, 1, 5) or (2, 2, 5) and (l, m, n) = (2, −2, 6) identifications for f 1 and f 2 modes respectively satisfied the highorder POS. These mode identifications are in agreement with the range of modes visible in disk integrated light of an equator-on visible pulsating component. The wavelength distribution of pulsation amplitudes in AS Eri is largest in the Strömgren u filter and decreases toward longer wavelengths. We place AS Eri and other known mass-accreting pulsating components of Algols on HR-diagram. They are located inside the instability strip on the Main Sequence. We also discuss the peculiar evolutionary status of primary components in Algols and stress that they are not normal δ Scuti stars, but form a separate group of pulsators. Finally, we discuss proximity and eclipse effects, and have simulated the effect of primary minimum data gaps that may produce the 1/P orb alias sidelobes in DFT analysis of eclipsing binary data. Aliases from gaps in primary minimum observations seem to be the principal limitation on spectral window functions in asteroseismic studies of eclipsing binaries.

We present precise relative radial velocity (RV) measurements for the rapidly oscillating Ap (roAp) star 33 Librae measured from high‐resolution data spanning the wavelength interval 5000–6200 Å. We find that the pulsational radial velocity amplitude determined over a broad wavelength range (≈100 Å) depends on the spectral region that is examined and can be as high as 60 m s−1 at 5600 Å and as low as 7 m s−1 in the 5900 Å region. RV measurements of individual spectral lines can show higher amplitudes than results obtained using a ‘broad‐band’ measurement that includes many spectral lines. The acoustic cross‐sections of the atmosphere, i.e. the phase and amplitude of the pulsations, as a function of optical depth are found for spectral lines of Ca, Cr, Fe, La, Ce, Gd, Er and Nd. This analysis shows that pulsation phase is variable through the atmosphere and that Nd iii lines pulsate almost 180° out of phase with those of Nd ii features and are formed significantly higher in the stellar atmosphere. This conclusively establishes the presence of at least one radial node to the pulsations in the upper stellar atmosphere. We have estimated that this acoustic node is located above an optical depth log τ < −4.5 and below the level where the Nd iii lines are formed. We also suspect that there may be a second atmospheric node in the lower atmosphere below or at log τ≃−0.9 and close to continuum formation level. The histogram of pulsational phases for all individual spectral features shows a bimodal Gaussian distribution with 17 per cent of the lines having a pulsational phase ≈165° out of phase with most other spectral lines. This is also consistent with the presence of a radial node in the stellar atmosphere. The accumulation of phase due to a running wave component can explain the 165° phase difference as well as the broader width (by a factor of 2) of one of the Gaussian components of the phase distribution. We also found evidence for phase variations as a function of effective Landég‐factors. This may be the influence of magnetic field and magnetic intensification effect on depths of spectral line formation and shows that the magnetic field is controlling the pulsations. Our RV measurements for 33 Lib suggest that we are seeing evidence of vertical structure to the oscillations as well as the influence of the distribution of elements on the stellar surface. We suggest and briefly discuss a new semi‐empirical tomographic procedure for mono‐ and multimode roAp stars that will use acoustic cross‐sections obtained on different chemical elements and different pulsation modes for restoring the abundance and acoustic profiles throughout the stellar atmosphere and across the stellar surface.

We present the analysis of 3 h of a rapid time series of precise stellar radial velocity (RV) measurements (σ = 4.5 m s −1 ) of the cool Ap star β CrB. The integrated RV measurements spanning the wavelength interval 5000-6000 Å show significant variations (false alarm probability = 10 −5 ) with a period of 16.21 min (ν = 1028.17 µHz) and an amplitude of 3.54 ± 0.56 m s −1 . The RV measured over a much narrower wavelength interval reveals one spectral feature at λ6272.0 Å pulsating with the same 16.21-min period and an amplitude of 138 ± 23 m s −1 . These observations establish β CrB to be a low-amplitude rapidly oscillating Ap star.

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high‐resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B‐stars (SPB)‐like g‐mode with frequency 0.3428 d−1 reported before is detected in our spectroscopy. We identify the four main modes as (ℓ1, m1) = (1, 1), (ℓ2, m2) = (0, 0), (ℓ3, m3) = (1, 0) and (ℓ4, m4) = (2, 1) for f1= 5.178 964 d−1, f2= 5.334 224 d−1, f3= 5.066 316 d−1 and f4= 5.490 133 d−1, respectively. Our seismic modelling shows that f2 is likely the radial first overtone and that the core overshooting parameter αov is lower than 0.4 local pressure scale heights.

Abstract We report the results of optical follow-up observations of 29 gravitational-wave triggers during the first half of the LIGO-Virgo Collaboration (LVC) O3 run with the Gravitational-wave Optical Transient Observer (GOTO) in its prototype 4-telescope configuration (GOTO-4). While no viable electromagnetic counterpart candidate was identified, we estimate our 3D (volumetric) coverage using test light curves of on- and off-axis gamma-ray bursts and kilonovae. In cases where the source region was observable immediately, GOTO-4 was able to respond to a GW alert in less than a minute. The average time of first observation was 8.79 hours after receiving an alert (9.90 hours after trigger). A mean of 732.3 square degrees were tiled per event, representing on average 45.3 per cent of the LVC probability map, or 70.3 per cent of the observable probability. This coverage will further improve as the facility scales up alongside the localisation performance of the evolving gravitational-wave detector network. Even in its 4-telescope prototype configuration, GOTO is capable of detecting AT2017gfo-like kilonovae beyond 200 Mpc in favourable observing conditions. We cannot currently place meaningful electromagnetic limits on the population of distant ($\hat{D}_L = 1.3$ Gpc) binary black hole mergers because our test models are too faint to recover at this distance. However, as GOTO is upgraded towards its full 32-telescope, 2 node (La Palma & Australia) configuration, it is expected to be sufficiently sensitive to cover the predicted O4 binary neutron star merger volume, and will be able to respond to both northern and southern triggers.

We give a brief review on the present status of our research of A-F pulsating components of semi-detached Algol-type systems. We suggest a new asteroseismic approach for estimating the evolutionary stage of the mass-accreting components of Algols during rapid and slow masstransfer phases, asynchronization and differential rotation.

The interior physics of stars is currently not well constrained for early-type stars. This is particularly pertinent for multiple systems as binary interaction becomes more prevalent for more massive stars, which strongly affects their evolution. High-precision photometry from the Transiting Exoplanet Survey Satellite (TESS) mission offers the opportunity to remedy the dearth of observations of pulsating stars that show evidence of binary interaction, specifically pulsating mass-accreting components of semidetached Algol-type eclipsing binary (oEA) systems. We present the TESS light curve of the circular eclipsing binary system U Gru (TIC 147201138), which shows evidence for free heat-driven pressure modes and a series of tidally-perturbed pressure modes. We highlight the asteroseismic potential of studying pulsating stars in binary systems, and demonstrate how tidal asteroseismology can be applied to infer the influence of binary interaction on stellar structure.