Recent stellar occultations indicate that Quaoar's apparent shape is consistent across all observed events, suggesting that the body is close to a Maclaurin spheroid rather than a triaxial ellipsoid. Such a nearly axisymmetric figure naturally implies a single-peaked rotational light curve with a period of ∼8.8 h, instead of the previously proposed double-peaked 17.7 h period. In this work, we investigate which patterns of surface albedo variation can reproduce the observed visible and infrared thermal emission light curves under this faster rotation scenario. We further show that while standard tidal evolution can explain Weywot's present orbit, it cannot explain Quaoar's 17.7 h rotation period. If the true rotation period is instead close to half this value, the tension largely disappears, and Quaoar's figure, primordial rotation, and the long-term tidal influence of Weywot become mutually consistent. Moreover, the dynamical evolution of Quaoar's inner ring provides independent constraints that could be tested using sufficiently high-resolution occultation measurements.

Ring systems have been found around several small bodies in the outer Solar System through stellar occultations. While such observations provide constraints on ring geometry and dynamical interactions, little is known about their origins, lifetimes, or compositions. Here, we report near-infrared stellar-occultation observations obtained with the James Webb Space Telescope (JWST) probing the ring system of the Centaur Chariklo. Our measurements show that Chariklo’s dense inner ring has become significantly more opaque than in previous occultations, suggesting ongoing replenishment or dynamical restructuring. In contrast, the outer ring exhibits a much weaker near-infrared occultation signature than previously observed. This discrepancy may reflect material loss, suggesting that the outer ring could be transient or may arise from wavelength-dependent opacity. These observations demonstrate the power of JWST occultations to probe the evolving structure of rings around small bodies and provide compelling evidence for unexpected changes in Chariklo’s ring system.

We investigated the millennial-scale evolution of narrow innermost rings composed of pebble-sized to sub-millimeter particles around the four known ring-bearing small bodies Chiron, Chariklo, Quaoar, and Haumea. Using a GPU-accelerated fourth-order Hermite integrator, we modeled the combined effects of solar radiation pressure, shadowing of the rings by the host body, heliocentric motion, and the non-axisymmetric gravitational field of the rotating triaxial central body. The calculations compare spherical and triaxial-body models, as well as coplanar and inclined ring configurations. In spherical models, solar radiation pressure efficiently excites particle eccentricities, leading to accretion onto the central body above a critical radiation-pressure parameter. This effect is strongest for the lower-mass systems, Chiron and Chariklo, where particles with relatively modest radiation forcing are rapidly removed. In contrast, when the triaxial shape of the host body is included, rapid apsidal precession suppresses radiation-pressure-driven eccentricity growth and prevents material loss from the ring over the simulated interval. The triaxial models also suppress the previously identified Sun-facing reorientation of highly inclined rings and instead produce moderate vertical broadening. Strongly confined rings persist for radiation-pressure parameters corresponding to particle sizes larger than about 7-40 mu m, depending on composition. Their characteristic radial widths are about 10 km for Chiron and Chariklo and about 40-70 km for Quaoar and Haumea. The vertical thicknesses of the rings are estimated to be on the order of 1 km for Chiron and Chariklo, and only several hundred meters for Quaoar and Haumea. Our results therefore suggest that narrow rings around triaxial small bodies in the solar system can plausibly retain sub-millimeter particles over dynamically relevant timescales shorter than Poynting-Robertson drag.

Mass loss in low-mass stars during the red giant branch (RGB) and early asymptotic giant branch (EAGB) phases plays a key role in shaping stellar evolution, yet its dependence on stellar parameters such as metallicity remains poorly constrained, with observational studies yielding conflicting trends. We present the first asteroseismic analysis of RGB and EAGB stars in NGC 5897, the most distant and metal-poor globular cluster observed by the Kepler space telescope during the K2 mission. We detected solar-like oscillations and derived the frequency of maximum power excess, ν_ max, for 20 RGB and 6 EAGB stars. Using asteroseismic scaling relations, we derived mean masses of M_ RGB = 0.74±0.01 M_⊙ and M_ EAGB=0.65± 0.03 M_⊙. The inferred integrated mass loss between the two phases is ΔM_ RGB-EAGB=0.08± 0.03 M_⊙. We present an updated mass-loss–metallicity relation for Type I globular clusters, extending it to the very metal-poor regime and supporting decreasing integrated RGB mass loss with decreasing metallicity.

We report the discovery of a nearby FU Ori-type outburst (FUor), PR Ori B, in the L1641 cluster of the Orion star-forming region. The high-amplitude variability was first identified in the NEOWISE (3-5 μm) photometry of the unresolved PR Ori binary system. Long-term, resolved optical photometric monitoring demonstrates that PR Ori B is the driver of a ΔG=5mag outburst, while PR Ori A has remained constant over the last 20 years. The near-IR spectrum of PR Ori B changes from a late K-type spectral type during quiescence to a viscously heated disk during outburst, including deep absorption in ^12CO and H_2O bands. The optical spectrum also exhibits features that are commonly associated with FUors, including P Cygni profiles in Na I D lines and absorption in the Ca II infrared triplet. The luminosity of the outburst (L_acc∼30–40 L_⊙) is similar to that commonly observed in FUors. The comparison of Spitzer/IRS and VLT/VISIR spectroscopy shows some evidence of silicate crystallisation during the outburst. PR Ori B is one of the closest and brightest FUors discovered over the last few years, only one magnitude fainter than the archetype of the class FU Ori. The proximity and brightness will allow for future high angular resolution observations to probe the physics of the inner disk and to evaluate changes in the disk due to the increased luminosity.

2022 EB5, 2023 CX1 and 2024 BX1: these are the three recent imminent impactor discoveries from the Piszkéstető Mountain Station of the Konkoly Observatory. They make up about one percent of all NEO discoveries from our observatory and here we provide a detailed description of our approach and methodology that led to this noticeable observational sensitivity to these meter-sized impactors. After outlining the historical background of astronomical discoveries from Hungary, we introduce our recently upgraded survey instrumentation and outline the observational strategy and its implementation. We highlight the importance of strong feedback between analysis and ongoing data collection, maximizing the value of immediate follow-up. Finally, we discuss plans for moving forward to increase the sensitivity and the temporal coverage of our survey.

The diversity of Type IIn supernovae is largely driven by the properties of the circumstellar material (CSM) they explode into. We examine the temporal evolution of SN 2019vxm, an interacting supernova that belongs to the class of long-lasting Type IIn events, using multicolor photometry spanning the ultraviolet, optical and near-infrared wavelengths, including over 650 days of optical and 1500 days of IR coverage. The evolution of the spectral energy distribution and bolometric luminosity, as well as the effective temperature and radius of the photosphere, indicates that the supernova was initially surrounded by an optically thick CSM, which was heated and pushed outward by the forward shock of the impacting ejecta. About 80-100 days after the explosion the forward shock and the photosphere decouples, and we observe the receding photosphere of the H-recombination front within the now thinned CSM. Near-IR measurements reveal long-lasting, slowly cooling emission from circumstellar dust around SN 2019vxm and an IR rebrightening about one year after explosion, which we tentatively identify as a signature of an outer CSM region. We find that due to the moving photosphere and the transition from optically thick to partially thin inner CSM, modeling the explosion and subsequent interaction of the ejecta with the CSM to infer progenitor and CSM masses faces difficulties. Nevertheless, the inferred high masses and extremely high mass-loss rates point to a massive progenitor undergoing intense pre-supernova mass loss.

We present a photometric and spectroscopic study of the superluminous Type Ia supernova SN 2022erq. Its early spectra, dominated by iron-group elements with weak intermediate-mass features, might indicate highly efficient nuclear burning, broadly similar to that inferred for some overluminous SNe Ia. The rapid emergence and persistence of narrow Balmer emission lines superposed on this iron-rich spectrum provide clear evidence of long-lived interaction with a hydrogen-rich circumstellar medium (CSM), establishing SN 2022erq as a member of the rare Ia-CSM class. SN 2022erq reached a peak bolometric luminosity of about 8 x 10^43 erg/s and exhibited an exceptionally slow post-peak decline, indicating that its light curve is dominated by long-duration ejecta-CSM interaction. By combining H-alpha diagnostics with bolometric light-curve modeling, we reconstruct the pre-explosion mass-loss history of the progenitor. The mass-loss rate escalated by one order of magnitude over the final decades, rising from about 0.04 to about 0.6 solar masses per year. This surge produced a massive, extended CSM shell of about 3 solar masses out to about 3.5 x 10^16 cm. The young stellar environment (about 100 Myr) together with this substantial, extensive CSM points to a progenitor system consisting of a white dwarf and an intermediate-mass companion that underwent increasing mass loss prior to explosion.

Abstract In this work, we investigate the applicability of asteroseismic scaling relation correction factors inferred from the comparison of APOKASC-3 seismic and Gaia radii of stars. Our findings suggest that applying these corrections beyond the scaling relation for the radius, e.g., in order to calculate stellar masses, requires a careful treatment of the underlying physical assumptions as well as further calibrations.

Interstellar extinction is a major obstacle in determining accurate stellar parameters from photometry near the Galactic disk. It is especially true for globular clusters at low galactic latitudes, which suffer from significant amounts of spatially variable reddening. Although differential reddening maps are available for tens of clusters, establishing and validating the absolute zero-point of relative maps is a challenge. In this study, we present a new approach to determine and evaluate absolute reddening zero-points for Galactic globular clusters by combining 3D reddening maps with Gaia DR3 RR Lyrae data. As a first case study, we investigate the low-latitude globular cluster M9. We compare the Gaia photometry and color data of the cluster member RR Lyrae stars to field RR Lyrae stars with accurate parallaxes and whose photometric metallicities match that of M9, as well as to theoretical models. We calculate the dereddened Gaia colors for the M9 stars based on three zero points. We confirm that the original SFD map by D. J. Schlegel et al. (1998) appears to be overcorrecting the reddening for at least some RR Lyrae stars, albeit not excessively. In contrast, the 3D Bayestar map and the recalibrated version of the SFD map provide physically plausible reddenings, which we accept as lower and upper limits for M9, respectively. Our results provide a physically motivated reddening range for M9 and outline a methodology that can be directly extended to other globular clusters that are accessible to the Gaia mission, and to other multicolor sky surveys, such as the Rubin Observatory.

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.

We present a new method and a corresponding code to compress the color magnitude diagram of a globular cluster into a representative curve, called a ridgeline, that can be more readily compared to isochrone models, among other applications. This compression method preserves the physical properties of the cluster, including the morphology of the CMD.

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.

We present new photometric observations of the core-collapse supernova SN 2023ixf occurred in M101, taken with the RC80 and BRC80 robotic telescopes in Hungary. The initial nickel mass from the late-phase bolometric light curve extending up to 400 days after explosion, is inferred as M_ Ni = 0.046 ± 0.007 M_⊙. The comparison of the bolometric light curve with models from hydrodynamical simulations as well as semi-analytic radiative diffusion codes reveals a relatively low-mass ejecta of M_ ej≲ 9 M_⊙, contrary to SN 2017eaw, another H-rich core-collapse event, which had M_ ej≳ 15 M_⊙.

Episodic accretion is a fundamental process in the build-up of the stellar mass. EX Lupi-type eruptive young stars (EXors) represent one of the main types of episodic accretion. We study the recently discovered EXor Gaia23bab during its 2023 outburst. We obtained optical and near-infrared photometry and spectroscopy to probe the variation of the physical properties of Gaia23bab during its recent outburst. We also collected archival photometry to study a previous outburst of the star. We used several accretion tracers, including the Ca ii triplet, He i , and various hydrogen lines from the Paschen and Brackett series, to measure the accretion rate during the outburst. The accretion rate is consistent with ∼2.0 × 10 −7 M ⊙ yr −1 . Comparing the line fluxes of the hydrogen Brackett series to predictions of Case B theory suggests excitation temperatures of 5000–10,000 K and electron densities of 10 9 –10 10 cm −3 . Comparison to the predictions of a model for T Tauri stars revealed that the fluxes of the Balmer series are consistent with temperatures of 5000–12,500 K and a hydrogen density of 10 8 cm −3 , while the fluxes of the Paschen series are consistent with temperatures in the range between 10,000 and 12,500 K and a hydrogen density of 10 11 cm −3 . The derived temperatures and densities confirm that Gaia23bab is a prototypical EXor, not only due to its accretion rate, but also based on the best-fit temperatures and densities revealed by the detected hydrogen lines.

Context. We analyse multi-colour photometric and spectroscopic observations of the young stellar object (YSO) Gaia20bdk. Aims. We aim to investigate the exact nature of the eruptive phenomenon that the star has been undergoing since 2018. Methods. We used public-domain archival photometry to characterise the quiescent phase and to establish the major physical parameters of the progenitor. We used our own optical and infrared (IR) photometry and spectroscopy, along with data from the public domain, to study the outburst. Results. Gaia20bdk is a member of the Sharpless 2-301 star-forming region, at a distance of 3.3 kpc. The progenitor is a rather massive 2.7 ± 0.5 M ⊙ , G7-type Class I young star, with an effective temperature of 5300 −300 +500 K and bolometric luminosity of 11 ± 2 L ⊙ . The optical and IR photometric and spectroscopic data obtained during the outburst reveal a variety of signatures commonly found in classical FU Ori-type stars (FUors). Our disc modelling gives a bolometric luminosity of 100 − 200 L ⊙ and mass accretion rate of 1 − 2 × 10 −5 M ⊙ yr −1 , also confirming the object’s FUor classification. Further monitoring is necessary to track the light changes, accretion rate, and spectral variations, as well as to understand the mechanisms behind the disc flickering.

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.

Globular clusters offer a powerful way to test the properties of stellar populations and the late stages of low-mass stellar evolution. For this paper we studied oscillating giant stars and overtone RR Lyrae-type pulsators in the nearest globular cluster, M4, with the help of high-precision, continuous light curves collected by the Kepler space telescope in the K2 mission. We determined the frequency composition of five RRc stars and modeled their physical parameters from linear pulsation models. We were able, for the first time, to compare seismic masses of RR Lyrae stars directly to the masses of the very similar red horizontal branch stars in the same stellar population, independently determined from asteroseismic scaling relations. We find average seismic masses of 0.648 +/- 0.028 M-circle dot for RR Lyrae stars and 0.657 +/- 0.034 M-circle dot for red horizontal branch stars. While the accuracy of our RR Lyrae masses still relies on the accuracy of evolutionary mass differences of neighboring horizontal branch subgroups, this result strongly indicates that RRc stars may indeed exhibit high-degree & ell; = 8 and 9 nonradial modes, and modeling these modes can provide realistic mass estimates. We compare the seismic masses of our red horizontal branch and RR Lyrae stars to evolutionary models and to theoretical mass relations, and highlight the limitations of these relations.

Among the growing number of small body rings in the solar system, the ring of Haumea has a special status as it is likely suitable for direct imaging in the visible and submillimeter wavelengths. In this paper, we highlight its sole detectability among Centaur/TNO rings using both the ALMA and the James Webb Space Telescope to provide direct constraints on the ring composition for the first time. To overcome the limitations of the currently used simple ring models, we introduce radiative transfer modeling for small body ring systems. Here we perform a thorough analysis of the Haumea ring considering different materials and grain sizes, assuming that the ring consists of small particles with sizes below 1 mm. We present spectral energy distributions of each model for future comparison with multiwavelength measurements, providing a diagnostic tool to determine the dominant grain size and characteristic material of the ring, which are essential inputs for ring formation and evolution theories. Our results also show that for some sub-micron carbon-like or silicate grains, their mid-infrared excess can be detected even if the ring is not resolved, providing a tracer for small grains around the object.

The Kepler space telescope collected continuous photometry of several Jovian Trojan asteroids in the Solar System during its K2 mission. We extracted light curves 43 new targets from K2 Campaigns 11-19 using our own photometric package developed for moving objects in the Kepler images which, together with the 56 asteroids from Campaign 6, brings the total sample size up to 99 asteroids. We calculated rotational frequencies and amplitudes for each object and their distributions, and we derived statistics on the binary fraction and possible compositions of these asteroids. We find and excess of very slow rotators (>100 hours) and a possible dichotomy in the period distribution. When compared to other space-based photometric results, we find that the distribution of Hilda rotation periods detected with K2 shows the same possible dichotomy, but the large sample of main-belt asteroids measured with the TESS space telescope does not. The excess of slow rotators corroborates with an outward origin, with synchronized binaries migrating inwareds from the Kuiper belt, and some of them dissociating along the way, creating very slowly rotating single objects. Both a low critical density limit and comparison with strengthless ellipsoid models indicate that none of the objects exceed the density of icy objects, further strengthening an inward migration scenario. We estimate a binary fraction of at least 21% based on the number of high-amplitude, long-period objects, in agreement with earlier results. Large photometric amplitudes are prevalent over the entire period range, and we cannot fit all objects with a strengtless model in rotational equilibrium.We highlight a few individual objects as well. (99306) 2001 SC101 is the only asteroid observed in to Campaigns, from different sides of the Sun, and we find clear differences in the light curve shape. (13062) Podarkes is the principal body of a proposed small family: we detect a rotation period of 245 hr which puts it into the very slow rotator group. Finally, we present the first continuous light curve of (11351) Leucus, one of the targets of the Lucy spacecraft, and confirm that it also rotates exceedingly slowly, with a period of 445 hr.