Pulsation Modes Research Articles

A diffuse core in Saturn revealed by ring seismology

The best constraints on the internal structures of giant planets have historically originated from measurements of their gravity fields1,2,3. These data are inherently mostly sensitive to a planet’s outer regions, stymieing efforts to measure the mass and compactness of the cores of Jupiter2,4,5 and Saturn6,7. However, studies of Saturn’s rings have detected waves driven by pulsation modes within the planet8,9,10,11, offering independent seismic probes of Saturn’s interior12,13,14. The observations reveal gravity-mode pulsations, which indicate that part of Saturn’s deep interior is stable against convection13. Here, we compare structural models with gravity and seismic measurements from Cassini to show that the data can only be explained by a diffuse, stably stratified core–envelope transition region in Saturn extending to approximately 60% of the planet’s radius and containing approximately 17 Earth masses of ice and rock. This gradual distribution of heavy elements constrains mixing processes at work in Saturn, and it may reflect the planet’s primordial structure and accretion history.

A triplet of the only pulsation mode detected in the DAV star G132–12

Hydrogen atmosphere pulsating white dwarfs, also known as DAV stars, are the most abundant type of pulsating white dwarfs. High-temperature DAV stars in general exhibit a small number of pulsation modes and stable frequencies. G132–12 is one of the pulsating hydrogen atmosphere white dwarf stars which lies close to the blue edge of the instability strip. Previous researches reported that G132–12 might have only one pulsation mode with the period of 212.69 s. To study the pulsation properties of G132–12 in detail, we carried out a bi-site observation campaign in October 2019. Time series photometric data were collected during around 154 h in total. A Fourier analysis reveals three frequencies which are identified as the triplet of an l = 1 g-mode pulsation with the period of 212.499 s. The rotational period is derived as P rot = 35.0 ± 6.7 h and the inclination of the rotational axis to the line of sight is 70°. G132–12 could be an ideal target for measuring the cooling scale of this white dwarf star with only one excited pulsation mode detected.

Observational and Theoretical Studies of 27 δ Scuti Stars with Investigation of the Period–Luminosity Relation

The multi-color CCD photometric study of 27 δ Scuti stars is presented. By using approximately three years of photometric observations, we obtained the times of maxima and magnitude changes during the observation time interval for each star. The ephemerides of our δ Scuti stars were calculated based on the Markov Chain Monte Carlo (MCMC) method using the observed times of maxima and the period of the stars’ oscillations. We used the Gaia EDR3 parallaxes to calculate the luminosities and also the absolute magnitudes of these δ Scuti stars. The fundamental physical parameters of all the stars in our sample such as masses and radii were estimated. We determined the pulsation modes of the stars based on the pulsation constants. Moreover, the period–luminosity (P–L) relation of δ Scuti stars was investigated and discussed. Then, by using a machine learning classification, new P–L relations for fundamental and overtone modes are presented.

The Changing Lightcurve of the Double-mode RR Lyrae Variable Star V338 Boo

Abstract We present an analysis of the lightcurve extracted from Transiting Exoplanet Survey Satellite (TESS) Full Frame Images (FFIs) of the double-mode RR Lyrae V338 Boo. We find that the fundamental mode pulsation is changing in amplitude across the 54 days of observations. The first overtone mode pulsation also changes, but on a much smaller scale. Harmonics and combinations of the primary pulsation modes also exhibit unusual behavior. Possible connections with other changes in RR Lyrae pulsations are discussed, but a full understanding of the cause of the changes seen in V338 Boo should shed light on some of the most difficult and unanswered questions in stellar pulsation theory, and astrophysics more generally.

Exploring the pulsational properties of two ZZ Ceti stars

Context. We continued our ground-based observing project with the season-long observations of ZZ Ceti stars at the Konkoly Observatory. Our present targets are the newly discovered PM J22299+3024 and the already known LP 119–10 variables. LP 119–10 was also observed by the TESS space telescope in 120-second cadence mode. Aims. Our main aims are to characterise the pulsation properties of the targets and extract pulsation modes from the data for asteroseismic investigations. Methods. We performed a standard Fourier analysis of the daily, weekly, and entire data sets, together with test data of different combinations of weekly observations. We then performed asteroseismic fits utilising the observed and the calculated pulsation periods. For the calculations of model grids necessary for the fits, we applied the 2018 version of the White Dwarf Evolution Code. Results. We derived six possible pulsation modes for PM J22299+3024 and five plus two TESS pulsation frequencies for LP 119–10. We note that further pulsation frequencies may be present in the data sets, but we found their detection ambiguous, so we omitted them from the final frequency list. Our asteroseismic fits of PM J22299+3024 give 11 400 K and 0.46 M⊙ for the effective temperature and the stellar mass, respectively. The temperature is ≈800 K higher, while the mass of the model star is exactly the same as was earlier derived by spectroscopy. Our model fits of LP 119–10 put the effective temperature in the range of 11 800−11 900 K, which is again higher than the spectroscopic 11 290 K value. Moreover, our best model solutions give M* = 0.70 M⊙ mass for this target, which is near to the spectroscopic value of 0.65 M⊙ and likewise in the case of PM J22299+3024. The seismic distances of our best-fit model stars agree with the Gaia astrometric distances of PM J22299+3024 and LP 119–10 within the errors, validating our model results.

Modes of unsteadiness in shock wave and separation region interaction in hypersonic flow over a double wedge geometry

This study investigates different modes of unsteadiness that could be seen in a hypersonic flow over a double wedge configuration with a large separation region size. In the previous studies with a double wedge or a double cone configuration, small turn angles of the surfaces are seen to produce a small separation region that does not interact with the outside shock structures and produce a steady flow. However, a large separation region can be observed with large wedge angles that could interact with the outside shock waves and produce different types of unsteady flows. Some recent numerical studies on the double wedge configuration with a large fore-wedge angle (θ1) of 30° and various aft-wedge angles (θ2) at the free-stream flow Mach number (M∞) of 7 have shown that the flow exhibits periodically oscillating states. The current study investigates this geometric configuration over the parameter space of wedge length ratios (L1/L2) of 0.5, 1.0, 1.5, and 2.0 and aft-wedge angles (θ2) of 45°, 50°, 55°, and 60°. Three modes of unsteadiness are observed, namely, vibration mode, oscillation mode, and pulsation mode. The effect of the variation in geometric parameters on switching between different modes of unsteadiness is assessed, and it is shown that the unsteady characteristics of the flow are determined by the size of the separation region and location of the shock waves with respect to it.

Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations

ABSTRACT We analyse photometry of ∼2000 Galactic Cepheids available in the OGLE Collection of Variable Stars. We analyse both Galactic disc and Galactic bulge fields; stars classified both as single- and multiperiodic. Our goal was to search for additional low-amplitude variability. We extend the sample of multimode radial pulsators by identifying 10 new candidates for double mode and 6 new candidates for triple-mode pulsation. In the first overtone OGLE sample, we found 12 Cepheids with additional periodicity having period ratio $P_{\rm x}/P_{\rm 1O}\in (0.60,\, 0.65)$. These periodicities do not correspond to any other radial mode. While such variables are abundant in the Magellanic Clouds, only one Cepheid of this class was known in the Galaxy before our analysis. Comparing our sample with the Magellanic Cloud Cepheids, we note a systematic shift towards longer pulsation periods for more metal rich Galactic stars. Moreover, in 11 stars we find one more type of additional variability, with characteristic frequencies close to half of that reported in the group with (0.60, 0.65) period ratios. Two out of the above inventory show simultaneous presence of both signals. Most likely, origin of these signals is connected to excitation of non-radial pulsation modes. We report three Cepheids with low-amplitude periodic modulation of pulsation: two stars are single-mode fundamental and first overtone Cepheids and one is a double-mode Cepheid pulsating simultaneously in fundamental and in first overtone modes. Only the former mode is modulated. It is a first detection of periodic modulation of pulsation in this type of double-mode Cepheids.

A binary with a δ Scuti star and an oscillating red giant: orbit and asteroseismology of KIC 9773821

ABSTRACT We study the δ Scuti – red giant (RG) binary KIC 9773821, the first double-pulsator binary of its kind. It was observed by Kepler during its 4-yr mission. Our aims are to ascertain whether the system is bound, rather than a chance alignment, and to identify the evolutionary state of the RG via asteroseismology. An extension of these aims is to determine a dynamical mass and an age prior for a δ Sct star, which may permit mode identification via further asteroseismic modelling. We determine spectroscopic parameters and radial velocities (RVs) for the RG component using HERMES@Mercator spectroscopy. Light arrival-time delays from the δ Sct pulsations are used with the red-giant RVs to determine that the system is bound and to infer its orbital parameters, including the binary mass ratio. We use asteroseismology to model the individual frequencies of the red giant to give a mass of $2.10^{+0.20}_{-0.10}$ M⊙ and an age of $1.08^{+0.06}_{-0.24}$ Gyr. We find that it is a helium-burning secondary clump star, confirm that it follows the standard $\nu _{\rm max}$ scaling relation, and confirm its observed period spacings match their theoretical counterparts in the modelling code mesa. Our results also constrain the mass and age of the δ Sct star. We leverage these constraints to construct δ Sct models in a reduced parameter space and identify four of its five pulsation modes.

The SparSpec algorithm and the application to the detection of spatial periodicities in tokamaks: using memory with relaxation * *[Note: This work is partially based on a 4th year bachelor project by one of the authors (LMP), performed while being a student at the SPC-EPFL under the supervision of the corresponding author (DTA)

A common problem in many complex physical systems is the determination of pulsation modes from irregularly sampled time-series, and there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. The aim of this report is studying the problem of detecting in real-time spatial periodicities in the spectrum of magnetic fluctuations in tokamaks, for which optimization of the algorithm run-time is essential. The main tool used hereafter will be the SparSpec algorithm, initially devised for astrophysical purposes and already applied to the analysis of magnetic fluctuation data in various tokamaks, both currently or previously operating (JET, TCV, Alcator C-mod) and under construction (ITER, DTT). For JET, the baseline version of the SparSpec algorithm, dubbed SS-H2, already regularly runs in real-time on a 1 ms clock for detecting Toroidal Alfvén Eigenmodes using synchronously-detected magnetic perturbation. It was noted that the solution is only slowly changing in time as the background plasma typically also slowly evolves. Therefore, as a specifically real-time acceleration tool, we will focus on the use of a memory with relaxation scheme, whereby solutions obtained at previous time points are used to provide weighted input constraints for the solution at the current time point. Use of the measurement uncertainties to weight the data, the spectral window and the ensuing penalization criterion (dubbed the SS-V5ν0 algorithm) is reported in a companion work. The behaviour of the SparSpec algorithm under a variety of simulated circumstances, and one actual test case from the JET tokamak, is analysed and appropriate conditions for the convergence of the memory-penalised solutions are derived. The tuning of the input parameters is discussed based on the results of our simulations. It is found that the implementation of SparSpec using such a memory with relaxation scheme is quite a complex procedure, and only when correctly optimized the results are superior, both in terms of the speed and the accuracy of the calculations, to those obtained with the SS-H2 and SS-V5ν0 versions of the SparSpec algorithm.

The SparSpec algorithm and the application to the detection of spatial periodicities in tokamaks: error weighting the penalization criterion to improve the performance of the algorithm * *[Note: this work is partially based on a 4th year bachelor project by one of the authors (LMP), performed while being a student at the SPC-EPFL under the supervision of the corresponding author

A common problem in many complex physical systems is the determination of pulsation modes from irregularly sampled time-series, and there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. The aim of this report is studying the problem of detecting discrete spatial periodicities in the spectrum of magnetic fluctuations in tokamaks, for which the optimization of the algorithm performance is essential, particularly when multiple sensors are used with different measurement uncertainties, and some of the processed output signals are then used in real-time for discharge control. The main tool used hereafter will be the SparSpec algorithm, initially devised for astrophysical purposes and already applied to the analysis of magnetic fluctuations in various tokamaks. In its baseline version, dubbed SS-H2, the SparSpec algorithm runs in currently or previously operating tokamaks (JET, TCV and Alcator C-mod), and is foreseen to be deployed for data analysis in tokamak under construction (ITER, DTT). For JET, SS-H2 regularly runs also in real-time on a 1ms clock for detecting Alfvén Eigenmodes using synchronously-measured magnetic perturbations. On JET and TCV, it was noted that often a reduced set of sensors had to be used as the measurement uncertainties were not the same for all available sensors, somewhat deteriorating the overall performance of the algorithm. Hence, as part of a major update of the SparSpec algorithm, specifically intended for accelerating the real-time performance, use of the measurement uncertainties to weight the data, the spectral window and the ensuing penalization criterion was introduced. The behaviour of this new version of the SparSpec algorithm under a variety of simulated circumstances is analysed. It is found that the implementation of SparSpec using such error weighting produces superior results to those obtained with SS-H2, both in terms of the speed and the accuracy of the calculations. A test on actual data from the JET tokamak also shows a clear improvement in the performance of the algorithm.

Eclipsing Systems with Pulsating Components (Types β Cep, δ Sct, γ Dor or Red Giant) in the Era of High-Accuracy Space Data

Eclipsing systems are essential objects for understanding the properties of stars and stellar systems. Eclipsing systems with pulsating components are furthermore advantageous because they provide accurate constraints on the component properties, as well as a complementary method for pulsation mode determination, crucial for precise asteroseismology. The outcome of space missions aiming at delivering high-accuracy light curves for many thousands of stars in search of planetary systems has also generated new insights in the field of variable stars and revived the interest of binary systems in general. The detection of eclipsing systems with pulsating components has particularly benefitted from this, and progress in this field is growing fast. In this review, we showcase some of the recent results obtained from studies of eclipsing systems with pulsating components based on data acquired by the space missions Kepler or TESS. We consider different system configurations including semi-detached eclipsing binaries in (near-)circular orbits, a (near-)circular and non-synchronized eclipsing binary with a chemically peculiar component, eclipsing binaries showing the heartbeat phenomenon, as well as detached, eccentric double-lined systems. All display one or more pulsating component(s). Among the great variety of known classes of pulsating stars, we discuss unevolved or slightly evolved pulsators of spectral type B, A or F and red giants with solar-like oscillations. Some systems exhibit additional phenomena such as tidal effects, angular momentum transfer, (occasional) mass transfer between the components and/or magnetic activity. How these phenomena and the orbital changes affect the different types of pulsations excited in one or more components, offers a new window of opportunity to better understand the physics of pulsations.

KIC 5950759: a high-amplitude δ Sct star with amplitude and frequency modulation near the terminal age main sequence

ABSTRACT Among the intermediate mass pulsating stars known as δ Sct stars is a subset of high-amplitude and predominantly radial-mode pulsators known as high-amplitude δ Sct (HADS) stars. From more than 2000 δ Sct stars observed by the Kepler space mission, only two HADS stars were detected. We investigate the more perplexing of these two HADS stars, KIC 5950759. We study its variability using ground- and space-based photometry, determine its atmospheric parameters from spectroscopy and perform asteroseismic modelling to constrain its mass and evolutionary stage. From spectroscopy, we find that KIC 5950759 is a metal-poor star, which is in agreement with the inferred metallicity needed to reproduce its pulsation mode frequencies from non-adiabatic pulsation models. Furthermore, we combine ground-based WASP and Kepler space photometry, and measure a linear change in period of order $\dot{P}/P \simeq 10^{-6}$ yr−1 for both the fundamental and first overtone radial modes across a time base of several years, which is at least two orders of magnitude larger than predicted by evolution models, and is the largest measured period change in a δ Sct star to date. Our analysis indicates that KIC 5950759 is a metal-poor HADS star near the short-lived contraction phase and the terminal-age main sequence, with its sub-solar metallicity making it a candidate SX Phe star. KIC 5950759 is a unique object among the thousands of known δ Sct stars and warrants further study to ascertain why its pulsation modes are evolving remarkably faster than predicted by stellar evolution.

The effect of the centrifugal acceleration on period spacings of gravito-inertial modes in intermediate-mass stars

Context. The Kepler and Transiting Exoplanet Survey Satellite (TESS) space telescopes delivered high-precision, long-duration photometric time series for hundreds of main-sequence stars, revealing their numerous gravito-inertial (g) pulsation modes. This high precision allows us to evaluate increasingly detailed theoretical stellar models. Recent theoretical work extended the traditional approximation of rotation, a framework to evaluate the effect of the Coriolis acceleration on g modes, to include the effects of the centrifugal acceleration in the approximation of slightly deformed stars, which so far have mostly been neglected in asteroseismology. This extension of the traditional approximation was conceived by re-deriving the traditional approximation in a centrifugally-deformed, spheroidal coordinate system. Aims. We explore the effect of the centrifugal acceleration on g modes and assess its detectability in space-based photometric observations. Methods. We implemented the new theoretical framework to calculate the centrifugal deformation of pre-computed 1D spherical stellar structure models and computed the corresponding g-mode frequencies, assuming uniform rotation. The framework was evaluated for a grid of stellar structure models covering a relevant parameter space for observed g-mode pulsators. Results. The centrifugal acceleration modifies the effect of the Coriolis acceleration on g modes, narrowing the equatorial band in which they are trapped. Furthermore, the centrifugal acceleration causes the pulsation periods and period spacings of the most common g modes (prograde dipole modes and r modes) to increase with values similar to the observational uncertainties of the measured period spacing values in Kepler and TESS data. Conclusions. The effect of the centrifugal acceleration on g modes is formally detectable in modern space photometry. The implementation of the used theoretical framework in stellar structure and pulsation codes will allow for more precise asteroseismic modelling of centrifugally deformed stars in order to assess its effect on mode excitation, trapping, and damping.

Probing hybrid stars with gravitational waves via interfacial modes

One of the uncertainties in nuclear physics is whether a phase transition between hadronic nuclear matter to quark matter exists in supranuclear matter equations of state. Such a feature can be probed via gravitational-wave signals from binary neutron star inspirals that contain information of the induced tides. The dynamical part of the tides is caused by the resonance of pulsation modes of stars, which causes a shift in the gravitational-wave phase. In this paper, we investigate the dynamical tides of the interfacial mode ($i$-mode) of spherical degree $l=2$, a non-radial mode caused by an interface associated with a quark-hadron phase transition inside a hybrid star. In particular, we focus on hybrid stars with a crystalline quark matter core and a fluid hadronic envelope. We find that the resonant frequency of such $i$-modes typically ranges from 300Hz to 1500Hz, and the frequency increases as the shear modulus of the quark core increases. We next estimate the detectability of such a mode with existing and future gravitational-wave events from the inspiral waveform with a Fisher analysis. We find that GW170817 and GW190425 have the potential to detect the $i$-mode if the quark-hadron phase transition occurs at sufficiently low pressure and the shear modulus of the quark matter phase is large enough. We also find that the third-generation gravitational-wave detectors can further probe the $i$-mode with intermediate transition pressure. This finding opens a new, interesting direction for probing the existence of quark core inside a neutron star.

Variability of newly identified B-type stars observed by Kepler

ABSTRACT Recent re-determination of stellar atmospheric parameters for a sample of stars observed during the Kepler mission allowed to enlarge the number of Kepler B-type stars. We present the detailed frequency analysis for all these objects. All stars exhibit pulsational variability with maximum amplitudes at frequencies corresponding to high-order g modes. Peaks that could be identified with low-order p/g modes are also extracted for a few stars. We identified some patters in the oscillation spectra that can be associated with the period spacings that can results from the asymptotic nature of the detected pulsational modes. We also tentatively confront the observed oscillation characteristics with predictions from linear non-adiabatic computations of stellar pulsations. For high-order g modes the traditional approximation was employed to include the effects of rotation on the frequency values and mode instability.

Stability and pulsation of the first dark stars

ABSTRACT The first bright objects to form in the Universe might not have been ‘ordinary’ fusion-powered stars, but ‘dark stars’ (DSs) powered by the annihilation of dark matter (DM) in the form of weakly interacting massive particles (WIMPs). If discovered, DSs can provide a unique laboratory to test DM models. DSs are born with a mass of the order of M⊙ and may grow to a few million solar masses; in this work we investigate the properties of early DSs with masses up to $\sim \! 1000 \, \mathrm{ M}_\odot$, fueled by WIMPS weighing 100 GeV. We improve the previous implementation of the DM energy source into the stellar evolution code mesa. We show that the growth of DSs is not limited by astrophysical effects: DSs up to $\sim \!1000 \, \mathrm{ M}_{\odot }$ exhibit no dynamical instabilities; DSs are not subject to mass-loss driven by super-Eddington winds. We test the assumption of previous work that the injected energy per WIMP annihilation is constant throughout the star; relaxing this assumption does not change the properties of the DSs. Furthermore, we study DS pulsations, for the first time investigating non-adiabatic pulsation modes, using the linear pulsation code gyre. We find that acoustic modes in DSs of masses smaller than $\sim \! 200 \, \mathrm{ M}_\odot$ are excited by the κ − γ and γ mechanism in layers where hydrogen or helium is (partially) ionized. Moreover, we show that the mass-loss rates potentially induced by pulsations are negligible compared to the accretion rates.

Finite element method for optimal transformer connection based on induction motor characteristics analysis

The Voltage Sags (VSs) may cause irrecoverable impacts on the sensitive loads, such as moving into plugging mode and high pulsations of the torque. So, the various effects of VSs on these loads should be studied, considering all conditions. The non–linear performance of the transformer causes the calculation of VS problem to be complicated. Therefore, a robustness approach should be chosen to solve the problem. In this paper, a novel classification of VS is carried out by using the non–linear solver of the transient Finite Element Method (FEM). In the proposed method, the non–linear behavior of the iron core of the transformer applied using the Jiles–Atherton (JA) vector hysteresis model to increase the precision of the results. To obtain a comprehensive classification, different connections of transformer windings as well as various types of short circuits are considered, and the influence of these classes on the Induction Motor (IM) performance is rendered. To show the accuracy of the proposed method, the VS results of other methods and FEM are compared with IEC standard data by introducing an evaluation metric. The comparison outcomes verified the effectiveness of the proposed method, as the average of errors obtained 4.9%, which is lower than other approaches. Furthermore, an IM is considered to characterize its speed and torque variations. Based on the IM speed deterioration, the best–to–worst connections of the transformer windings are appointed. Finally, the simulation results demonstrate that under single phase SC, when the primary connection of the transformer is Star or grounded Star, the deterioration of speed is lower than others, which are related to the first to third classes. In essence, the key obtained result is that the results of VS calculations with FEM could be a proper database, because of its ability in solving the non-linear problems with minimum errors.

Astromodal wave dynamics in multifluidic structure-forming cloud complexes

The evolutionary dynamics of bimodal pulsational mode, arising because of the long-range conjugational gravito-electrostatic interplay in viscoelastic polytropic complex multicomponent astroclouds with partial ionisation, is classically examined using a non-relativistic generalised hydrodynamic model approach. The equilibrium distribution of the diversified constitutive species forms a globally quasi-neutral hydrostatic homogeneous configuration. The primitive set of the astrocloud structuring equations specifically includes polytropic (hydrodynamic action) and nonlinear logatropic barotropic (turbulence action) effects simultaneously. A normal mode analysis over the perturbed cloud results in a unique form of sextic polynomial dispersion relation with variable poly-parametric coefficients. A numerical analysis technique is provided to show the exact nature of the modified viscoelastic (turbo-viscoelastic) pulsational mode in the two extreme hydrodynamic and kinetic regimes. It is seen that, in the former regime, the dust–charge ratio (negatively-to-positively charged grains) plays a destabilising role to the instability. In contrast, the dust–mass ratio (negatively-to-positively charged grains) develops a stabilising influence in the wave-dynamical processes. In the latter regime, the viscoelastic relaxation velocity associated with the positively charged grains acts as an amplitude stabiliser. Conversely, the viscoelastic relaxation velocity of the negatively charged grain fluid introduces destabilising influences. The unique features of the propagatory and non-propagatory mode characteristics are elaborately illustrated. The reliability of the investigated results is judiciously validated by comparing the results with the specific reports available in the literature. Lastly, the first-hand astronomical implications and applications of our study are summarily outlined.

A precise asteroseismic age and metallicity for HD 139614: a pre-main-sequence star with a protoplanetary disc in Upper Centaurus–Lupus

ABSTRACT HD 139614 is known to be a ∼14-Myr-old, possibly pre-main-sequence star in the Sco-Cen OB association in the Upper Centaurus-Lupus subgroup, with a slightly warped circumstellar disc containing ring structures hinting at one or more planets. The star’s chemical abundance pattern is metal-deficient except for volatile elements, which places it in the λ Boo class and suggests it has recently accreted gas-rich but dust-poor material. We identify seven dipole and four radial pulsation modes among its δ Sct pulsations using the TESS light curve and an échelle diagram. Precision modelling with the mesa stellar evolution and gyre stellar oscillation programs confirms it is on the pre-main sequence. Asteroseismic, grid-based modelling suggests an age of 10.75 ± 0.77 Myr, a mass of 1.52 ± 0.02 M ⊙, and a global metal abundance of Z = 0.0100 ± 0.0010. This represents the first asteroseismic determination of the bulk metallicity of a λ Boo star. The precise age and metallicity offer a benchmark for age estimates in Upper Centaurus–Lupus, and for understanding disc retention and planet formation around intermediate-mass stars.

Tidally perturbed pulsations in the pre-main sequence δ Scuti binary RS Cha

Context. Stellar components in binaries are subject to tidal forces which influence asteroseismic properties. Tidally pertubed pulsations have been reported for different objects but none of these are in their pre-main sequence phase of evolution. This makes RS Cha, consisting of two δ Scuti stars and with pulsational characteristics influenced by tidal effects, the first such object observed. Aims. We aim to investigate the pulsational properties of the eclipsing binary RS Cha in terms of the theory of tidally perturbed pulsations. Methods. Based on photometric time series obtained from the TESS satellite, we performed binary modelling using PHOEBE to interpret the binary light curve and to allow the investigation of the pulsations of both components in RS Cha. We modelled the detrended light curve with the superposition of linear modes. The frequencies were then interpreted as self excited modes perturbed by tidal forces. Results. We find evidence for tidally perturbed modes, which enables the identification of pulsation modes. RS Cha mainly exhibits dipole modes, while one prominent l = 2 or l = 3 mode is also inferred. The latter verifies previous results from spectroscopic time series. Conclusion. This work shows that RS Cha is an ideal candidate to test the theory of tidally perturbed pulsations within the framework of asteroseismic modelling. The identification of multiple pulsation modes using this theory is unprecedented and will be a keystone in the future of pre-main sequence asteroseismology. However, amplitude modulation caused by the changing light ratio during the orbital phase in an eclipsing binary also plays a significant role, which can complicate mode identification.