Mass transfer between stars in binary systems profoundly impacts their evolution, yet many aspects of this process---especially the stability, mass loss, and eventual fate of such systems---remain poorly understood. One promising avenue to constrain these processes is through the identification and characterisation of systems undergoing active mass transfer. Inspired by the slow brightening preceding stellar merger transients, we worked on a method to identify Galactic mass-transferring binaries in which the donor is a Hertzsprung gap (HG) star. We constructed an initial sample of HG stars using the Early Data Release 3 contribution catalogue, and we identified candidate mass-transferring systems by selecting sources that exhibit Balmer emission features (as seen in the low-resolution XP spectra), mid-infrared excess (from WISE photometry), and photometric variability (inferred from the error in the G-band magnitude). This multi-criteria selection yielded a sample of 67 candidates, which we further analysed using complementary photometric and spectroscopic data, as well as information from cross-matched archival catalogues. Among our candidates, we identified at least nine eclipsing binaries and some sources that are potential binaries as well. Three sources in our sample are strong candidates for mass-transferring binaries with a yellow component, and three more are binaries with a Be star. Notably, three sources in our sample are strong candidates for hosting a compact companion, based on their ultraviolet or X-ray signatures. The main sources of contamination in our search are hot but highly reddened stars---primarily Oe and Be stars---as well as regular pulsating stars such as δ Scuti and Cepheid variables. As an additional outcome of this work, we present a refined new catalogue of 308 HG stars, selected using improved extinction corrections and stricter emission-line criteria. This enhanced sample is expected to contain a significantly higher fraction of scientifically valuable mass-transferring binaries. Gaia Starhorse Gaia Gaia

Blue straggler stars (BSSs) are exotic objects, which, being the results of processes such as mass transfer, mergers, or collisions, are considered key objects in the study of their host clusters' dynamics. While many studies on astrometric, spectroscopic, and photometric properties of BSSs in clusters have been conducted, there are few works in the literature regarding their pulsations and internal structure, which can indeed retain traces of their origin. In this work we computed and analysed a grid of collisional BSSs at low metallicity (Z = 0.01; Z_⊙), finding that collision products present a peculiar chemical stratification that leads to periodicities in the period-spacing pattern of high-order gravity modes. These seismic fingerprints provide a unique opportunity to constrain the formation pathways of BSSs in globular clusters.

A major challenge in modeling classical Cepheids is the treatment of convection, particularly its complex interplay with pulsation. This inherently three-dimensional (3D) process is typically approximated in one-dimensional (1D) hydrocodes, using dimensionless turbulent convection (TC) free parameters. Calibrating these parameters is essential for reproducing key observational features, such as the light curve amplitudes, secondary bumps, and the red edge of the instability strip (IS). In this work, we calibrate the TC parameters adopted from the publicly available Modules for Experiments in Stellar Astrophysics-Radial Stellar Pulsations ( code. We carried out a comparison using both the observational data of classical Cepheids and stellar parameter constraints from the Stellingwerf code. This is one of the few codes currently available that are capable of replicating a wide range of observed features of the classical pulsators. We computed the multiband (V, I, and K_s) . We compared the resulting period-luminosity (PL), period-radius (PR), and period-mass-radius (PMR) relations with the prediction of Stellingwerf's model. light curves for 18 observed Large Magellanic Cloud (LMC) Cepheids, using stellar parameters determined on the basis of Stellingwerf's code. By fine-tuning the mixing-length and eddy viscosity parameters, we calibrated the TC treatment in MESA-RSP We successfully reproduced the multiband (V, I, and K_s) light curves for 18 observed LMC Cepheids using the stellar parameters determined with Stellingwerf's code. We also finetuned the mixing-length and eddy viscosity parameters in Our models yielded PL, PR, and PMR relations that were consistent with the previous results. Interestingly, although our results are broadly in agreement with previous works, we explicitly identified distinct mass-luminosity (ML) relations for fundamental-mode (FU) and first-overtone (FO) Cepheids for the first time. This suggests that the macroscopic phenomena affecting the ML relation depend on the stellar mass itself and/or on the effective temperature range. Our investigation is focused on the calibration of the TC parameters, but we did not find a single set of convective parameter values that was sufficient to reproduce all the light curves. In addition, no statistically significant correlation was found between the stellar properties (e.g., the effective temperature or the stellar mass) and the convection parameters, although subtle trends for the period and effective temperature have been noted. As for the inferred Cepheid distances, our application of the model-fitting technique yields reddened distance moduli, in good agreement with those reported in previous works. This result is not surprising, given that we adopted the same input stellar parameters, with only minor differences in the adopted model atmospheres.

Abstract δ Scuti stars in binary or multiple systems serve as crucial probes for studying stellar pulsation and evolution. However, many such systems are not ideal for asteroseismology due to uncertainties in mass transfer with close companions and the challenges of dynamically measuring all components’ physical properties. The triple system DG Leo, comprising an inner binary and a distant δ Scuti star, is an ideal target due to its well-separated pulsator. By combining new TESS photometry with archival spectroscopy, our dynamical analysis shows that the system’s three components share similar masses, radii, and luminosities within errors, occupying coincident Hertzsprung–Russell diagram positions, indicative of coeval evolution. By fitting seven observed δ Scuti frequencies through asteroseismic modeling with dynamically constrained theoretical grids, we simultaneously trace the pulsating star’s evolution and constrain the triple system’s evolutionary stage, with the derived fundamental parameters showing consistency with the dynamical solutions. Our analysis reveals that all three components of DG Leo are in the post-main-sequence phase, with a system age of 0.766 4 − 0.1258 + 0.1402 Gyr. Additionally, the δ Scuti component shows multiple nonradial modes with significant mixed-character frequencies, providing precise constraints on its convective core extent ( R cz / R = 0.056 2 − 0.0021 + 0.0137 ).

At this time, the list of known magnetic δ Scuti stars is extremely limited, with only a select number of well-studied examples. We seek to expand this list, by retrieving targets from a variety of sources and demonstrating that they present simultaneously a surface magnetic field signature and δ Scuti pulsations. We obtained archival and new spectropolarimetric datasets for a variety of known δ Scuti stars and analysed them using the least squares deconvolution method to generate mean Stokes I and V profiles for each target, from which we can determine longitudinal magnetic field measurements. Additionally, we assessed photometric data from the TESS satellite to discern frequency peaks consistent with δ Scuti pulsations in known magnetic stars, and to identify magnetic candidates via rotational modulation. We present a compiled list of all the confirmed magnetic δ Scuti stars discovered to date, containing 13 stars. The majority of this sample lies outside the usual δ Scuti instability strip in the Hertzsprung-Russell diagram, though we do not observe any specific correlations between magnetic field strength and various stellar parameters. This indicates that strong global magnetic fields play a fundamental role in shaping interior structure and processes. Magnetic fields thus must be included in realistic stellar models in order to more accurately predict structure and evolution. This work constitutes the largest database to date of strongly magnetic δ Scuti stars, one that will continue to grow over time with subsequent studies.

Abstract We present a systematic investigation of β Cephei (BCEP) stars by integrating photometric data from the Transiting Exoplanet Survey Satellite (TESS) with astrometric parameters from Gaia Data Release 3. Utilizing TESS’s short-cadence (SC) and full-frame image (FFI) photometry, along with Gaia parallaxes and temperatures derived from the Extended Stellar Parametrizer for Hot Stars pipeline, we identify 88 new BCEP stars and candidates—85 from SC data and three from SPOC-processed FFI observations. These targets exhibit visual magnitudes ranging from 8.0 to 12.0 mag, parallaxes between 0.11 and 1.74 mas, effective temperatures of 18,000–30,000 K, and luminosities from 1500–38,000 L ⊙ , consistent with previously cataloged BCEP populations, thereby demonstrating the robustness of our classification criteria. Key findings include: (1) a significant detection disparity between SC and FFI datasets, with 30% of SC targets exceeding 18,000 K compared to only 0.7% in FFI, reflecting observational biases toward high-luminosity, hotter stars in SC data; (2) four samples near the red edge of the theoretical instability strip, exhibiting sparse pulsation modes that are important samples for testing pulsation models under low-mass, low-temperature conditions; and (3) spatial clustering within the Galactic disk (∣ b ∣ < 20°), with two high-latitude outliers likely representing runaway stars ejected from disk environments. Our analysis underscores the critical role of space-based photometry in detecting low-amplitude pulsators and the transformative potential of multisurvey integration in the era of time-domain astronomy. These results provide new samples to constrain stellar pulsation theories of massive stars and to study Galactic dynamics.

Abstract Pulsation plays a vital role in the evolution of massive stars found in eclipsing binaries. Although massive stars are uncommon compared to their less-massive counterparts, the frequency and intrinsic characteristics of these stars in eclipsing binaries, as well as their reliance on primary mass and environment, act as significant tools for studying pulsation. Thanks to the all-sky Transiting Exoplanet Survey Satellite (TESS) mission, a multitude of systems have been discovered and examined in detail. We have examined the TESS light curves of numerous eclipsing binaries containing high-mass stars and compiled a list of 15 objects exhibiting intrinsic variability, utilising archival multi-epoch spectra to identify spectroscopic features. The light curves were analysed in order to ascertain the physical properties of the systems and to eliminate the effects of binarity in the residual light curves that are suitable for asteroseismic analysis. Precise measurements of mass and radius have been obtained for all systems. We examined the residual light curves for signs of pulsation and, among our sample of 15 objects, identified 12 confirmed cases of slowly pulsating B (SPB) stars and three potential cases of hybrid (SPB+β Cephei) star pulsation. The observation and subsequent modelling of stellar pulsations in massive stars have revealed essential missing parameters in the stellar structure and evolution models of these stars; as a result, asteroseismology has been offering new insights for calibrating stellar physics within a highly degenerate area of the Hertzsprung-Russell diagram.

The variability of B-type stars offers valuable insights into the interiors of stars and the processes that drive pulsation and rotation in massive stars. In this study, we present the classification of the variability of 197 B-type stars observed in various Kepler/K2 campaigns, including 73 newly classified stars from Campaigns 13–18. For these stars, we derived atmospheric and evolutionary parameters using space-based photometry and ground-based spectroscopy. We obtained spectroscopic data for 34 targets with high-resolution instruments at OPD/LNA, which were supplemented by archival LAMOST spectra. After correcting for instrumental systematics, we analyzed the light curves using Fourier transforms and wavelet decomposition to identify both periodic and stochastic signals. The identified variability types included SPB stars, β Cephei/SPB hybrids, fast-rotating pulsators, stochastic low-frequency variables, eclipsing binaries, and rotational variables. We also revised classifications of misidentified stars using Gaia astrometry, confirming the main-sequence nature of objects once considered subdwarfs. Our results indicate that hot-star variability exists along a continuum shaped by mass, rotation, and internal mixing rather than distinct instability domains. This study enhances our understanding of B-type star variability and supports future asteroseismic modeling with missions like PLATO.

Photometric data from the Transiting Exoplanet Survey Satellite (TESS) mission and radial velocities from the Gaia mission and ground-based observations were used to model the light curves and calculate the physical parameters of the eccentric eclipsing systems CH Ind, V577 Oph, CX Phe, and TIC 35481236. The components of these systems have temperatures between 6450 and 7500 K, masses between 1.4 and 1.85 M⊙, and radii between 1.49 and 3.05 R⊙. The residuals of these models were analyzed further, using the Fourier method to reveal the pulsational frequencies of their oscillating components. Due to the similarity of the components of each system, the eclipses were used as spatial filters to determine which member is, in fact, the pulsating star. CH Ind was found to pulsate in 46 frequencies; its primary component is a γ Dor star and the secondary is a δ Sct star. The primary component of V577 Oph oscillates in both the regimes of γ Dor and δ Sct stars. Moreover, using past timings of minima, an eclipse timing variation analysis was also performed for V577 Oph, resulting in the calculation of the apsidal motion parameters and the existence of a third body around the system. Both components of CX Phe were found to be δ Sct stars; its primary has three independent frequencies in the range of 14.5–17.4 d−1 and its secondary has two main modes of 5.19 and 7.22 d−1. The analysis of TIC 35481236 indicates the hybrid δ Sct-γ Dor nature of its secondary component. Finally, the physical and pulsational properties of the δ Sct stars of these systems were compared with those of other δ Sct star members of binaries in evolutionary diagrams.

Abstract We study the Cowling approximation by analytical means as applied to a system of linear differential equations arising from models of non-radial stellar pulsation. We consider various asymptotic cases, including those of high harmonic degree and high oscillation frequency. Our methods involve a reformulation of the system in terms of an integro-differential equation for which certain Hilbert-space methods apply. By way of a more complete asymptotic study, we extend our results to certain fundamental solution sets, characterized according to certain multi-point boundary-value problems: Such asymptotics further enable us to produce sharp estimates as confirmation of our general results.

Abstract Betelgeuse—the closest M-supergiant to the Sun—has recently been predicted to host a lower-mass stellar companion that orbits the primary with a period of ∼6 yr. The putative stellar companion is thought to cause the long photometric modulation observed in Betelgeuse, which cannot be explained by stellar pulsations. Additionally, radial velocity and astrometric data also point to a stellar companion. Here we present diffraction-limited optical speckle imaging observations obtained on the 8.1 m Gemini North telescope in 2020 and 2024. The 2020 observations were taken during the Great Dimming event and at a time when the stellar companion was predicted to be unobservable because it was directly in line with Betelgeuse itself. The 2024 observations were taken 3 days after the predicted time of greatest elongation for the companion. A comparison of the 2020 and 2024 data reveals no companion in 2020 (as expected) and the probable detection of a companion in 2024. The presumed stellar companion has an angular separation and position angle of 52 mas and 115° east of north, respectively, which is in excellent agreement with predictions from dynamical considerations. The detected companion is roughly 6 magnitudes fainter than Betelgeuse at 466 nm. While this is only a 1.5σ detection, five results are in reasonable agreement with the predictions: the appearance of the companion at quadrature; the angular separation from Betelgeuse; the position angle with respect to Betelgeuse; the magnitude difference; and the estimated mass of the companion.

Abstract KOI-1755 (KIC 5302006) was initially identified by the Kepler mission as a candidate exoplanet host but subsequently classified as a false positive due to suspected background contamination. The target star itself exhibits intrinsic stellar pulsations, accompanied by transit-like dimming events, complicating a straightforward identification of the signal source. In this study, we carried out a detailed pixel-level reanalysis of KOI-1755 using the Kepler Target Pixel Files (TPFs) to clarify the origin of these transit-like signals. Through careful pixel-level flux modeling, centroid shift measurements, and cross-matching with the Gaia DR3 catalog, we conclusively determined that the dimming signals originate from a faint background eclipsing binary (EB), rather than KOI-1755 itself. We then developed a specialized photometric method to effectively remove contamination from nearby stars, allowing us to reliably extract the EB's uncontaminated light curve directly from the TPFs data. Analysis of this extracted light curve confirmed the contaminating source to be an EB system composed of two dwarf stars with a clear eclipse period of approximately 6.14 days. Our study provides a concrete example of how background EBs can mimic planetary transit signals, highlighting the importance of detailed pixel-level analyses for correctly identifying astrophysical false positives. Furthermore, our method demonstrates significant potential for uncovering previously hidden variable-star information within archival Kepler data, thus emphasizing the continuing scientific value of mining and reanalyzing existing data sets.

The one-dimensional treatment of turbulent convection had large successes until the early 2000s. However, the recent abundance and precision of observational data shows that this problem is far from solved. Even so, ongoing theoretical debates about proper one-equation-based treatment of convection and new results show that it has various other theoretical difficulties as well. A more modern approach should be developed by using multidimensional models. We established a new theoretical framework for comparison between one-dimensional and multidimensional convection models by mapping the two-dimensional structure of the convective zone and optimizing the modeling parameters of the SPHERLS code. We constructed a series of static envelope models for the same RR Lyrae stars, but with different horizontal sizes and resolutions. We then used a series of statistical methods to quantify the sizes of convective eddies, map the energy cascade, and describe the different structural parts of the convective zone. These include integral length scales, Fourier series, and the determination of the convective flux through horizontal averaging. The structure of the convective zone depends significantly on the model size below an angular size of $9^̧irc$. Models of at least this size are more consistent, and the horizontal resolution of earlier studies is adequate to describe the granulation pattern in the large eddy simulation approach. In quasi-static RR Lyrae stars, the convective zone consists of two distinct dynamically unstable regions that are loosely connected. Approximately half of the convective flux is supplied by the transport of ionization energy in the partial hydrogen ionization zone. The 2D models presented in this work with the described size and resolution parameters can be used for comparison against 1D models. The structure of the convective zone urges reconsideration of some recent approaches to describe the convective flux currently used in radial stellar pulsation codes, which will be addressed in a separate paper.

Context. Stars on the asymptotic giant branch (AGB) can exhibit acoustic pulsation modes of different radial orders, along with non-radial modes, throughout their evolution. These pulsations are essential to the mass-loss process and influence the evolutionary pathways of AGB stars. Period-luminosity (P−L) relations serve as a valuable diagnostic for understanding stellar evolution along the AGB. Three-dimensional (3D) radiation-hydrodynamic (RHD) simulations provide a powerful tool for investigating pulsation phenomena driven by convective processes and their non-linear coupling with stellar oscillations. Aims. We investigate multi-mode pulsations in AGB stars using advanced 3D ‘star-in-a-box’ simulations with the CO5BOLD RHD code. Signatures of these multi-mode pulsations were weak in our previous 3D models. Our focus is on identifying and characterising the various pulsation modes, examining their persistence and transitions, and comparing the results with one-dimensional (1D) model predictions and observational data where applicable. Methods. We produced a new model grid comprising AGB stars with current masses of 0.7, 0.8, and 1 M⊙. Fourier analysis was applied to dynamic, time-dependent quantities to extract dominant pulsation modes and their corresponding periods. Additionally, wavelet transforms were employed to identify mode-switching behaviour over time. Results. The simulations reveal radial, non-radial, fundamental, and overtone modes, with their transitions and dominance depending on stellar parameters. The models successfully reproduce the P–L sequences found in AGB stars. Mode-switching phenomena are found in both the models and wavelet analyses of observational data, allowing us to infer similarities in the underlying pulsation dynamics. The results confirm the dependence of pulsation periods on mean stellar density and underscore the significant role of convection for the amplitude of multi-mode pulsations. Conclusions. These 3D simulations highlight the natural emergence of multi-mode pulsations, including both radial and non-radial modes, driven by the self-consistent interplay of convection and oscillations. Our findings underscore the value of 3D RHD models in capturing the non-linear behaviour of AGB pulsations, providing insights into mode switching, envelope structures, and potential links to episodic mass-loss events.

Abstract Blue large-amplitude pulsators (BLAPs) are a recently discovered class of short-period pulsating variable stars. In this work, we present new information on these stars based on photometric and spectroscopic data obtained for known and new objects detected by the Optical Gravitational Lensing Experiment (OGLE) survey. BLAPs are evolved objects with pulsation periods in the range of 3–75 minutes, stretching between subdwarf B-type stars and upper main-sequence stars in the Hertzsprung–Russell diagram. In general, BLAPs are single-mode stars pulsating in the fundamental radial mode. Their phase-folded light curves are typically sawtooth-shaped, but many longer-period objects exhibit an additional bump. The long-term OGLE observations show that the period change rates of BLAPs are usually of the order of 10−7 yr−1 and in a quarter of the sample are negative. The spectroscopic data indicate that BLAPs form a homogeneous group in the period, surface gravity, and effective temperature spaces. However, we observe a split into two groups in terms of helium-to-hydrogen content. The atmospheres of He-enriched BLAPs are more abundant in metals (about 5 times) than the atmosphere of the Sun. We discover that BLAPs obey a period–gravity relationship and we use the distance to OGLE-BLAP-009 to derive a period–luminosity relation. Most of the stars observed in the OGLE Galactic bulge fields seem to reside in the bulge, while the remaining objects likely are in the foreground Galactic disk.

ABSTRACT We present a detailed analysis of the light curves and pulsation properties of first overtone (FO) Cepheids in the Magellanic Clouds (MCs) obtained using observations and predictions from stellar pulsation models. Multiwavelength observational light curves were compiled from the literature (OGLE-IV, Gaia, and VMC). We investigate the period–amplitude (PA), period–colour (PC), period–luminosity (PL), and amplitude–colour (AC) relations for FO Cepheids at multiwavelengths. We find that the PA distribution of FO Cepheids in the MCs modelled using a Gaussian Mixture Model shows that the Small Magellanic Cloud (SMC) consists of higher amplitude stars than the Large Magellanic Cloud (LMC). We find multiple break-points in the PC/PL/AC relations for FO/fundamental Cepheids in the optical and near-infrared bands including the one near to $P=2.5$ d in the MCs, using piecewise regression analysis and F-test statistics. Similarly, for the LMC FO Cepheids, we find a break-point in the PC/PL/AC relations near $P=0.58$ d. The slopes of the PC relations for LMC FO Cepheids are found to be shallow for $0.58<P(\rm d)< 2.5$ but steeper for $P< 0.58$ d and $P>2.5$ d. We complemented the observed relations using theoretical models for FO Cepheids with chemical compositions $Z= 0.008$ and $Z = 0.004$, appropriate for the LMC and SMC, respectively, computed with mesa-rsp. Our results show that the pulsation properties of FO Cepheids in PC/PL/AC relations and colour–magnitude diagram are strongly correlated and their connections can provide stringent constraints for the theoretical pulsation models.

A fraction of planetary nebulae (PNe) presents ring-like features in their halos and outermost envelopes. These are thought to be the relic of the last mass loss gaps at the end of the asymptotic giant branch (AGB) phase, providing information on cyclic mass-loss modulations associated either with stellar pulsations or binary interactions. We aim at characterizing the spatial and physical properties of the ring-like features around IC,418, the iconic Spirograph Nebula. Deep Very Large Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) integral field spectroscopic observations and sharp Hubble Space Telescope (HST) images have been investigated to search for the faintest arc-like features and to characterize their physical properties. Up to 10 concentric arc-like features are detected, with a notable change in the inter-ring gap, which is smaller for the innermost rings. This is interpreted as evidence of the interaction of the expanding nebula with the arc-like features, which otherwise would expand slower. The nebula proper motion also affects the shape and gap between arc-like features. The extinction radial profile decreases outward, indicating the presence of dust. Otherwise the electronic temperature (T_ e ) and density (n_ e ) derived both from emission line radial profiles and integrated spectra extracted show values around 10000 K and 8000 cm^-3, respectively. Collectively these results indicate distinct differences between the inner nebula, which is denser and more extincted, and the ring-like structures.

Abstract We report seismic analyses of five pulsating subdwarf B (sdBV) stars observed during Kepler’s K2 mission, each with a white dwarf companion. We find three of the five to be g-mode-dominated hybrid pulsators. For the other two, we only detect g modes. We determine rotation periods from frequency multiplets for four stars and each rotates subsynchronously to its binary period, including PG 0101+039 and PG 0902+124 both with binary periods near 0.57 days and spin periods near 9 days. We detect frequency multiplets in both p and g modes for PG 0101+039 and LT Cnc and determine that PG 0101+039 rotates like a solid body while LT Cnc rotates differentially radially with the envelope spinning faster than deeper layers. Mostly we find these five stars to be quite similar to one another, spectroscopically and seismically. We find the p modes of the three hybrid pulsators to have gaps between regions of power, which we interpret as overtones and apply a technique to assign modes. We examine their g mode period spacings and deviations thereof and again, find the stars to be similar with period spacings near the average of 250 s and deviations mostly under 25 s. We compare Kepler-observed sdBV stars of different binary types and likely-single pulsators.

The products of stellar mergers between two massive main-sequence stars appear as seemingly normal main-sequence stars after a phase of thermal relaxation, if not for certain peculiarities. These peculiarities, such as strong magnetic fields, chemically enriched surfaces, rejuvenated cores, and masses above the main-sequence turnoff mass, have been proposed to indicate merger or mass accretion origins. Since these peculiarities are not limited to the merger product's surface, we use asteroseismology to predict how the differences in the internal structure of a merger product and a genuine single star manifest via properties of non-radial stellar pulsations. We use the result of a 3D (magneto)hydrodynamic simulation of a stellar merger between a 9 and an 8 M⊙ main-sequence star, which was mapped to 1D and evolved through the main sequence. We compare the predicted pressure and gravity modes for the merger product model with those predicted for a corresponding genuine single-star model. The pressure-mode frequencies are consistently lower for the merger product than for the genuine single star, and the differences between them are more than a thousand times larger than the current best observational uncertainties for measured mode frequencies of this kind. Even though the absolute differences in gravity-mode period spacings vary in value and sign throughout the main-sequence life of both stars, they, too, are larger than the current best observational uncertainties for such long-period modes. This, combined with additional variability in the merger product's period spacing patterns, shows the potential of identifying merger products in future-forward modelling. We also attempt to replicate the merger product's structure using three widely applied 1D merger prescriptions and repeat the asteroseismic analysis. Although none of the 1D prescriptions reproduces the entire merger product's structure, we conclude that the prescription with shock heating shows the highest potential, provided that it can be calibrated on binary-evolution-driven 3D merger simulations. Our work focuses on a particular kind of massive main-sequence merger and should be expanded to encompass the various possible merger product structures predicted to exist in the Universe.

While δ Scuti stars --- intermediate-mass stars pulsating with periods of $<0.3$ d --- are the most numerous class of κ-mechanism pulsators in the instability strip, the short periods and small peak-to-peak amplitudes have left them understudied and under-utilized. Recently, large-scale time-domain surveys have significantly increased the number of identified δ Scuti stars, enabling more comprehensive investigations into their properties. Notably, the Tsinghua University–Ma Huateng Telescopes for Survey (TMTS), with its high-cadence observations at 1-minute intervals, has identified thousands of δ Scuti stars, greatly expanding the sample of these short-period pulsating variables. This study makes use of multiband photometric time-series data to refine the period-luminosity (P-L) relations of δ Scuti stars and show how observed P-L relations can be used to simultaneously infer dust obscuration and distance. Using spectroscopy, we also study the dependence of the P-L relations on metallicity. Using the δ Scuti stars from the TMTS catalogs of Periodic Variable Stars, we cross-matched the dataset with Pan-STARRS1, 2MASS, and WISE to obtain photometric measurements across optical (g, r, i, z, and y), near-infrared (J, H, and K_s), and mid-infrared (W1, W2, and W3) bands, respectively. Parallax data, used as Bayesian priors, were retrieved from Gaia DR3, and line-of-sight dust extinction priors were estimated from a 3D dust map. Using PyMC we performed a simultaneous determination of the 11-band P-L relations of δ Scuti stars. The simultaneous determination of multiband P-L relations of δ Scuti stars not only yields precise measurements of these relations, but also greatly improves constraints on the distance moduli and color excesses, as evidenced by the reduced uncertainties in the posterior distributions. Furthermore, our methodology enables an independent estimation of the color excess through the P-L relations, offering a potential complement to existing 3D dust maps. Moreover, by cross-matching with LAMOST DR7, we investigated the influence of metallicity on the P-L relations. Our analysis reveals that incorporating metallicity might reduce the intrinsic scatter at longer wavelengths. However, this result does not achieve 3σ significance, leaving open the possibility that the observed reduction is attributable to statistical fluctuations. We introduce an innovative approach to studying the P-L relations of δ Scuti stars, facilitating more comprehensive investigations into their utility as distance indicators and their significance in understanding stellar evolution. Our extensible methodology also enables the inference of dust extinction using pulsating stars beyond δ Scuti stars. Although the inclusion of metallicity in the P-L relations appears to reduce intrinsic scatter at longer wavelengths, further analysis is required to fully understand the impact of metal abundances on the properties of δ Scuti stars.