The strategic placement of astronomical observatories critically influences their ability to monitor celestial objects effectively. Traditional positioning methods rely on heuristic rules and fixed criteria, which may limit adaptability to changing conditions. In this study, we present a reinforcement learning framework that optimizes observatory placement by accounting for both time-dependent and geometric constraints. Using Unity machine learning-Agents in conjunction with the DE440 planetary and lunar ephemeris, the reinforcement learning (RL) agent learns to maximize celestial coverage while considering environmental factors such as cloud cover, light pollution, and geographic limitations. Environmental constraints are modeled as dynamic heatmaps, enabling the agent to adapt to real-time site suitability conditions. Comparative experiments with heuristic and static placement strategies show that the RL-based approach achieves higher coverage and improved operational efficiency. The methodology is applicable to ground-based observatories, including extensions to adaptive network design for large-scale sky surveillance.

A deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at ∼0.1” resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach H∼25.5 AB mag (5σ) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint Gaia-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.

Einstein Telescope (ET) is the European project for a gravitational-wave (GW) observatory of third-generation. In this paper we present a comprehensive discussion of its science objectives, providing state-of-the-art predictions for the capabilities of ET in both geometries currently under consideration, a single-site triangular configuration or two L-shaped detectors. We discuss the impact that ET will have on domains as broad and diverse as fundamental physics, cosmology, early Universe, astrophysics of compact objects, physics of matter in extreme conditions, and dynamics of stellar collapse. We discuss how the study of extreme astrophysical events will be enhanced by multi-messenger observations. We highlight the ET synergies with ground-based and space-borne GW observatories, including multi-band investigations of the same sources, improved parameter estimation, and complementary information on astrophysical or cosmological mechanisms obtained combining observations from different frequency bands. We present advancements in waveform modeling dedicated to third-generation observatories, along with open tools developed within the ET Collaboration for assessing the scientific potentials of different detector configurations. We finally discuss the data analysis challenges posed by third-generation observatories, which will enable access to large populations of sources and provide unprecedented precision.

Context. γ Persei is a long-period eclipsing binary system (P≈ 14.6 years) containing a red giant primary, and it is well known for its multi-faceted classification as a visual and spectroscopic binary. Its brightness and binary nature together make it a valuable target for both photometric and spectroscopic studies, particularly in the context of asteroseismology and stellar evolution, as the primary star likely formed through a stellar merger. Aims. We aim to determine the seismic parameters ν_ max, Δν, and the oscillation amplitudes of the primary component, an evolved giant, to estimate its seismic mass - which we can compare to its estimated dynamic mass. Methods. We use Transiting Exoplanet Survey Satellite (TESS) data obtained during Sectors 58, 85, and 86 and to complement the space-based observations, we incorporate high-resolution RV measurements acquired by the Stellar Observations Network Group (SONG) during two distinct epochs; 2017 and 2024. Results. We successfully detect solar-like oscillations in γ Per and infer a seismic mass of 3.25±0.13 M_⊙, which is slightly below the dynamical mass. We find the photometric oscillation amplitudes to be significantly lower than predicted from scaling relations, but in line with other high-mass red giants. We also find that radial velocity amplitudes along the Hertzsprung-Russell diagram cannot be fitted uniformly with current scaling relations.

Context. Turbulent convection models in nonlinear radial stellar pulsation models rely on an extra equation for turbulent kinetic energy and fail to adequately explain mode-selection problems. Since multidimensional calculations are computationally expensive, it is reasonable to search for generalizations of physically grounded 1D models that approximate multidimensional results with sufficient accuracy, at least in a given parameter range. A natural way of progressing from one-equation models is to use additional nonlocal equations. While these types of models also exist in the literature, they have not been adopted for this type of object. Aims. We aim to adapt the three-equation turbulent convection model from Kuhfuss to radial stellar pulsation modeling. Methods. We use a Reynolds-stress one-point closure approach to derive our extensions alongside the model, while using additional models from the literature to close the anisotropy and dissipation terms. Results. We provide five extensions to the original model. These include an enhanced dissipation correction to the mixing length, a local anisotropy model replacing eddy viscosity, a second-order correction for turbulent ion transport in the atmosphere (alongside opacity effects), and turbulent damping of entropy fluctuations and convective flux.

We present new theoretical light curves in the Rubin-LSST filters for a fine grid of BL Her models computed using MESA-RSP. We also derive new theoretical period-luminosity (PL) and period-Wesenheit (PW) relations in the Rubin-LSST filters with the goal to study the effect of convection parameters and metallicity on these relations. The grid of BL Her models was computed with the input stellar parameters: metallicity (-2.0 dex≤[Fe/H]≤ 0.0 dex), stellar mass (0.5M_⊙-0.8M_⊙), stellar luminosity (50L_⊙-300L_⊙), and effective temperature (across the full extent of the instability strip; in steps of 50K) and using four sets of convection parameters. Bolometric correction tables from MIST were used to transform the theoretical bolometric light curves of the BL Her models into the Rubin-LSST ugrizy filters. The PL relations of the BL Her models exhibit steeper slopes but smaller dispersion with increasing wavelengths in the Rubin-LSST filters. The PL and PW slopes for the complete set of BL Her models computed with radiative cooling (sets B and D) are statistically similar across the grizy filters. The BL Her models exhibit weak or negligible effect of metallicity on the PL relations for wavelengths longer than the g filter for both the cases of the complete set of models as well as the low-mass models. However, we find significant effect of metallicity on the PL relation in the u filter. Strong metallicity effects are observed in the PWZ relations involving the u filter and are found to have significant contribution from the high-metallicity BL Her models. Due to negligible metallicity effect for relations involving the Wesenheit indices W(i,g-i), W(z,i-z) and W(y,g-y), we recommend these filter combinations for BL Her stars when observed with the Rubin-LSST to be used as reliable standard candles.

Context. Classical T Tauri stars are newly formed, low-mass stars, which may display both periodic and random variations in their brightness. These systems are surrounded by a circumstellar disk, from which material falls onto the stellar surface. The interaction between the star and the circumstellar disk is time dependent, leading to short- or long-term physical changes in the physical environment, and hence variability of the system. Aims. DR Tau is a highly variable young star. By compiling a large dataset with high-cadence photometric, and high-resolution spectroscopic observations, we aim to examine the short- and long-term variability of the system, and identify the underlying physical mechanisms. Methods. We combined multifilter ground-based optical, near-infrared, and space-based mid-infrared (Spitzer Space Telescope) monitoring observations from 2009, 2017, and 2021 with high-cadence optical Kepler K2 and TESS light curves. We complemented our photometric dataset with spectropolarimetric monitoring observations obtained with the CFHT/ESPaDOnS instrument in 2016, which provided high-resolution data at optical wavelengths. Results. Our results reveal that DR Tau exhibits stochastic photometric variability not only on daily, but also on hourly timescales, with a peak-to-peak amplitude of 1.4 mag probably originating from accretion related variations. Our ground-based multifilter photometry shows that the shape of the light curves are similar at all wavelengths, although the amplitude of the variability decreases with increasing wavelength. This trend toward the infrared wavelengths suggests that part of the disk may be optically thick and invariable. In addition to this, the high-cadence Kepler and TESS data allowed us to carry out a detailed period analysis. The spectroscopic analysis showed that the H alpha line presents the most complex line profile with several components, but the significance of the components changes over time. This suggests the presence and variation of both accretion flow and wind. Broad and narrow components can be clearly distinguished in the He I and the Ca II lines, which suggests a contribution from both the accretion flow and the post-shock region. The CFHT/ESPaDOnS data suggest that the strength of the longitudinal magnetic field varies between 400 and 1800 G. Conclusions. DR Tau exhibits a high level of photometric and spectroscopic variability on both short and long timescales, which is caused by the combination of accretion, wind, stellar activity, and obscuration by circumstellar matter. Furthermore, the significance of the physical mechanisms that cause the observed variability changes over time.

Aims. The primary aim of this research is to evaluate several convolutional neural network-based object detection algorithms for identifying oscillation-like patterns in light curves of eclipsing binaries. This involved creating a robust detection framework that can effectively process both synthetic light curves and real observational data. Methods. The study employs several state-of-the-art object detection algorithms, including Single Shot MultiBox Detector, Faster Region-based Convolutional Neural Network, You Only Look Once, and EfficientDet, as well as a custom non-pretrained model implemented from scratch. Synthetic light curve images and images derived from observational TESS light curves of known eclipsing binaries with a pulsating component were constructed with corresponding annotation files using custom scripts. The models were trained and validated on established datasets, which was followed by testing on unseen Kepler data to assess their generalisation performance. The statistical metrics were also calculated to review the quality of each model. Results. The results indicate that the pre-trained models exhibit high accuracy and reliability in detecting the targeted patterns. The Faster Region-based Convolutional Neural Network and You Only Look Once in particular showed superior performance in terms of object detection evaluation metrics on the validation dataset, including a mean average precision value exceeding 99%. The Single Shot MultiBox Detector, on the other hand, is the fastest, although it shows a slightly lower performance, with a mean average precision of 97%. These findings highlight the potential of these models to significantly contribute to the automated determination of pulsating components in eclipsing binary systems and thus facilitate more efficient and comprehensive astrophysical investigations.

Hilda asteroids, which orbit in a 3:2 resonance with Jupiter, serve as key indicators of dynamical processes in the early solar system. Their spin rates, an important probe of these mechanisms, can constrain their density and collisional evolution, offering valuable insights into their origin. In this paper, we report on the identification of three fast-rotating Hilda asteroids with spin periods in the 3.2--3.7 h range using data from the Transiting Exoplanet Survey Satellite. These rotation periods are significantly shorter than the previous $\sim$5.0 h shortest rotation periods obtained from ground-based observations in the $\sim$10 km size range, and are comparable with the $\sim$3.0 h breakup limit of Hildas a few km in size, derived from the FOSSIL survey. These fast-rotating asteroids require either considerable cohesion (in the order of a few kPa), or densities $\rho$ $\gtrsim$1.5 $gm^{-3}$, in contrast to the typically assumed $\rho$ $\lesssim$1 $gm^{-3}$, to prevent rotational break-up. C-type asteroids, which are common in the outer main belt, have densities of $\rho$ $\approx$1.5 $gm^{-3}$ and are known to comprise a small but notable fraction of Hildas. The observed occurrence rate of the $\leq$4 h rotation periods may be explained by the 10-15% fraction of C-type asteroids, likely mixed into these populations from the outer main belt during giant planet dynamical interactions in the early solar system.

Context. 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. Aims. 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. Methods. 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. Results. The structure of the convective zone depends significantly on the model size below an angular size of 9 degrees. 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. Conclusions. 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.

Understanding where elements were formed has been a key goal in astrophysics for nearly a century, with answers involving cosmology, stellar burning, and cosmic explosions. Since 1957, the origin of the heaviest elements (formed via the rapid neutron capture process; r-process) has remained a mystery, identified as a key question to answer this century by the US National Research Council. With the advent of gravitational wave astronomy and recent measurements by the James Webb Space Telescope we now know that neutron star mergers are a key site of heavy element nucleosynthesis. We must now understand the heavy element yield of these events as well as mapping when these mergers occurred back through cosmic time, currently thought to peak when the universe was half its current age. This requires an extremely sensitive ultraviolet, optical, and infrared telescope which can respond rapidly to external discoveries of neutron star mergers. We here describe how the Habitable Worlds Observatory can provide the first complete answer to one of the questions of the century.

In this project we use data obtained by Zwicky Transient Facility to develop and test a neural-network-based, multiband classification algorithm to classify periodic variable stars (i.e. pulsating variable stars and eclipsing binaries). The aim is to utilize the algorithm on LSST data once they become available. Phase-folded light curve images and period information were used from five different variable star types: Classical and Type II Cepheids, δ Scuti stars, eclipsing binaries, and RR Lyrae stars. The data is taken from the 17th data release of ZTF, from which we used two passbands, g and r in this project. The periods were calculated from the raw data and this information was used as an additional numerical input in the neural network. For the training and testing process a supervised machine learning method was created, the neural network contains Convolutional Neural Networks concatenated with Fully Connected Layers. During the training-validation process the training accuracy reached 99

Context. During the primary Kepler mission, between 2009 and 2013, about 150 000 pre-selected targets were observed with a 29.42 minute-long cadence. However, a survey of background stars that fall within the field of view of the downloaded apertures of the primary targets has revealed a number of interesting objects. In previous papers we have presented surveys of short-period eclipsing binaries and RR Lyrae stars. Aims. The current survey of the Kepler background is concentrated on identifying longer-period eclipsing binaries and pulsating stars. These will be the subject of later papers. In the course of this survey, in addition to eclipsing binaries and pulsating stars, seven exoplanet candidates have been uncovered and in this paper we report on these candidates. Methods. We used Lomb-Scargle, light curve transit search, and phase dispersion minimisation methods to reveal pixels that show significant periodicities, resulting in the identification of the seven exoplanet candidates. We prepared the light curves for analysis using Pytransit software and cross-matched the pixel coordinates with Gaia and other catalogues to identify the sources. Results. We identify seven hot Jupiter exoplanet candidates with planet radii ranging from 0.8878 to 1.5174 RJup and periods ranging from 2.5089 to 4.7918 days.

We report on the identification of the three fastest rotating Jovian trojans with reliable population assignments known to date, discovered using light curve data from the Transiting Exoplanet Satellite Survey mission and confirmed by Zwicky Transient Facility data. For two of our targets the rotation periods are moderately below the previously accepted similar to 5 h Jovian trojan breakup limit (4.26 and 4.75 h); however, the rotation period of (13383) was found to be P = 2.926 h, leading to a density estimate of rho approximate to 1.6 g cm-3, higher than the generally accepted less than or similar to 1 g cm-3 density limit of Jovian trojans. If associated with lower densities, this rotation rate requires considerable cohesion, of the order of a few kilopascals. The relatively high albedo (pV approximate to 0.11) and fast rotation suggest that (13383) may have undergone an energetic collision that spun up the body and exposed bright material to the surface.

In the era of photometry with space-based telescopes, such as CHaracterizing ExOPlanets Satellite, James Webb Space Telescope, PLAnetary Transits and Oscillations of stars, and Atmospheric Remote-sensing Infrared Exoplanet Large-survey, the road has opened for detecting subtle distortions in exoplanet transit light curves-resulting from their non-spherical shape. We investigate the prospects of retrieval of rotational flatness (oblateness) of exoplanets at various noise levels. We present a novel method for calculating the transit light curves based on the Gauss-Legendre quadrature. We compare it in the non-rotating limit to the available analytical models. We conduct injection-and-retrieval tests to assess the precision and accuracy of the retrievable oblateness values. We find that the light curve calculation technique is about 25% faster than a well-known analytical counterpart, while still being precise enough. We show that a 3 sigma oblateness detection is possible for a planet orbiting bright enough stars, by exploiting a precise estimate on the stellar density obtained e.g., from asteroseismology. We also show that for noise levels >= 256 ppm (expressed as point-to-point scatter with a 60 s exposure time) detection of planetary oblateness is not reliable.

We identified 125 individual light curves of Hilda asteroids observed by the K2 mission. We found that despite of the mixed taxonomies, the Hilda group highly resembles the Trojans in the distribution of rotation periods and amplitudes, and even the LR group (mostly C- and X-type) Hildas follow this rule. Contrary to the Main Belt, the Hilda group lacks the very fast rotators. The ratio of extremely slow rotators (P > 100 hr) is a surprising 18%, which is unique in the solar system. The occurrence rate of asteroids with multiple periods (4%) and asteroids with three maxima in the light curves (5%) can be signs of a high rate of binarity, which we can estimate as 25% within the Hilda group. Based on our extraction of 10 thousand full asteroid light curves from the first year observations by TESS (P\'al et al. 2020) we can compare the distribution of rotation period and shape asphericity in the most populated asteroid families overall in the Main Belt. We reveal internal structure of some asteroid families in respect to rotation statistics and signs of rotation properties evolving with age.

Context. Over recent years, additional low-amplitude non-radial modes have been detected in many first-overtone RR Lyrae stars. These non-radial modes form a characteristic period ratio with the dominant first overtone of around 0.61. The incidence rate of this phenomenon varies from population to population. It is also strongly dependent on the quality of the analyzed data. Current models aimed at explaining these additional signals involve non-radial modes of degrees of 8 and 9. Aims. Using synthetic horizontal branch populations, we investigate the incidence rate of first-overtone RR Lyrae stars with non-radial modes, depending on the population properties, namely, ages and metallicities. We compare our results with the observed results for globular clusters and the vast collection of field first-overtone RR Lyrae stars to test the model predictions. Methods. We used synthetic horizontal branches combined with pulsation models to predict how the incidence rate would depend on the age and metallicity of the population. To test whether the results based on synthetic horizontal branches are realistic, we compared them to incidence rates observed by TESS in first-overtone field RR Lyrae stars, using photometric metallicity values from a newly established calibration for TESS. Results. The analysis of synthetic horizontal branches indicates that the incidence rate decreases with decreasing metallicity. We inferred the photometric metallicity for RR Lyrae stars observed by TESS and showed that the theoretical predictions are in agreement with the observations. Using the same method, we also concluded that the metallicity distribution of RR Lyrae stars showing an additional mode with a period-ratio around 0.68 appears to be different from that of 1) all first-overtone stars and 2) those showing additional non-radial modes.

Context. The Pan-STARRS 3 pi survey has detected hundreds of thousands of variable stars thanks to its coverage and 4-year time span, even though the sampling of the light curves is relatively sparse. These light curves contain only 10-15 detections in each of the five filters (g, r, i, z, y). During the K2 mission, the Kepler space telescope observed along the ecliptic plane with a high sampling frequency, although only for about 80 days in each of its campaigns. Aims. Crossmatching and investigating the RR Lyrae stars observed by both K2 and Pan-STARRS can serve as a valuable tool to validate the classification and period determination of the ground-based survey. Methods. We used the Sesar catalogue of RR Lyrae stars detected by Pan-STARRS. After determining the overlap between the stars observed by both Pan-STARRS and K2, we also considered the Gaia DR3 SOS RR Lyrae catalogue data for the list of these stars wherever it was available. The frequencies of the light variations were calculated by applying the Lomb-Scargle periodogram method on the K2 light curves that were prepared with autoEAP photometry. The calculated frequencies of the stars then were compared with those given in the Sesar catalogue and the Gaia DR3 RR Lyrae catalogue. Results. We found that for the majority of the stars, the classification (95.6%) and the frequency determination (90.1%) of the Pan-STARRS RR Lyrae stars were consistent within 0.03 d(-1) with those that we derived from the K2 autoEAP light curves. For a significant subset of the sample, 7.4%, however, an offset of 1 or 2 d(-1) was found in the frequencies. These are the result of the sampling of the detections, because Pan-STARRS observations are affected by diurnal cycles, whereas Kepler carried out measurements quasi-continuously. We found that RRc subtypes are significantly more affected (25.3%) than RRab subtypes (3.7%), which is most likely caused by RRc stars having less sharp light curve features. Validation via space-based data will be important for future ground-based surveys, as well.

Context. Ultra-hot Jupiters (UHJs) orbiting pulsating A/F stars represent an important subset of the exoplanetary demographic. They are excellent candidates for the study of exoplanetary atmospheres, and are astrophysical laboratories for the investigation of planet-to-star interactions. Aims. We analysed the TESS light curve of the WASP-167 system, consisting of an F1V star and a substellar companion on a similar to 2.02 day orbit. Methods. We modelled the combination of the ellipsoidal variability and the Doppler beaming to measure the mass of WASP-167b, and the reflection effect to obtain constraints on the geometric albedo, while placing a special emphasis on noise separation. We implemented a basic model to determine the dayside (T-Day), nightside (T-Night), and intrinsic (T-Internal) temperatures of WASP-167b, and put a constraint on its Bond albedo. Results. We confirm the transit parameters of the planet seen in the literature. We find that a resonant similar to 2P(-1) stellar signal (which may originate from planet-to-star interactions) interferes with the phase curve analysis. After careful and thought-out treatment of this signal, we find M-p = 0.34 +/- 0.22 M-J. We measure a dayside temperature of 2790 +/- 100 K, classifying WASP-167b as an UHJ. We find a 2 sigma upper limit of 0.51 on its Bond albedo, and determine the geometric albedo at 0.34 +/- 0.11 (1 sigma uncertainty). Conclusions. With an occultation depth of 106.8 +/- 27.3 ppm in the TESS passband, the UHJ WASP-167b is an excellent target for atmospheric studies, especially those at thermal wavelength ranges, where the stellar pulsations are expected to be less influential.

Jovian Trojan and Hilda asteroids are of particular importance because they provide important constraints for Solar System formation and evolution models. Despite their large number, rotational characteristics are known for a relatively limited sample from ground-based observations. Rotation period and amplitude distributions derived from this sample are strongly affected by ground-based biases, as it was shown by recent studies using data from the K2 mission of the Kepler Space Telescope. An important result of these investigations is that there are a significantly larger number of slow rotators than previously thought. Here we present several week-long, uninterrupted light curves, in many cases spanning over multiple sectors for a large number of Jovian Trojans and Hildas, provided by the TESS mission. Our results are compared with the previous investigations of ground-based observations and K2 measurements, confirming the significance and the presence of slow rotators as it was hinted by earlier studies. We also investigate the difference between the rotational characteristics of the 'red' and 'less red' groups and that of the different collisional families. Figure 1.:Cleaned light curve, frequency spectrum and folded light curve of the Hilda asteroids (153) Hilda and (197558) 2004 FL122, observed by TESS.