ABSTRACT The Gaia Data Release 3 (DR3) is an important step in the realization of the future Gaia reference frame. Ideally, across G magnitudes from 3 to 21, the Gaia DR2 and DR3 objects with their positions (, ) and proper motions (, ) should be expressed in a nonrotating reference frame relative to distant extragalactic sources (mostly quasars—QSOs) and in accordance with the International Celestial Reference System (ICRS). There are comparison data for mag objects using Gaia's observations of QSOs, but it is not possible for brighter objects. The QSOs are faint objects in optical domain (just small amount of QSOs for mag) and the validation of the bright part of Gaia reference frame is difficult. We did it and investigated a spin of the indicated rotation of the Gaia bright star reference frame. It is mas year −1 from the other papers. We determined two spin components (, ) of the Gaia bright star reference frame (DR2 and DR3) using our original GD catalog of of 1653 stars. The original data help to avoid spin in the Gaia bright star reference frame.
ABSTRACT We present relative astrometric measurements of visual double stars, made in 2019 with the speckle camera PISCO at the 1‐m Epsilon telescope of the C2PU facility (Observatoire de la Côte d'Azur, Calern site). Our observing list contains orbital couples as well as double stars whose motion is still uncertain. From our observations of 698 multiple stars, we obtained 679 new measurements with angular separations in the range 0″.1–7″.5, and an average accuracy of 0″.007. The mean error on the position angles is 0°.5. Most of the position angles were determined without the usual 180° ambiguity with the application of the direct vector method, the restricted correlation technique, and/or by inspection of the long integration files. We present new and revised orbits for STT531 AB, STT77 AB, STF1338 AB, COU1746, STT260, A1109 AB, HU1291, and A632 AB, partly derived from our PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types.
In recent years, citizen science became an integral part of astronomy. Numerous projects contribute to important studies by involving large communities. While these are getting quite some attention, there are also individual efforts, which are nevertheless very valuable. Here, we report on results of a search for compact optical emission line nebulae, which are signposts of both young and evolved stars. The increased brightness in red photometric bands due to the contribution of shock-excited emission lines has been used as a tracer when examining optical broadband surveys. With the help of public databases, we identified and characterized associated sources if possible. Most of them are young stellar objects (YSOs).
ABSTRACT A series of extreme‐variability phenomena associated with supermassive black holes (SMBHs) in galactic nuclei are being revealed with increasing frequency in recent years thanks to enhanced survey capabilities across the electromagnetic spectrum. The observation of these extreme phenomena has opened the way to the study of the physics of SMBHs in real time—something that, until a decade ago, was exclusively associated with stellar‐mass black holes. A conference to discuss the physical processes powering these objects was held at ESAC, Madrid, Spain in June 2025.
Bouncing cosmologies offer an alternative to the standard CDM model by avoiding the problem of the initial cosmological singularity by construction. In these models, the universe undergoes a contraction phase that begins in a nearly flat and dilute state, followed by a bounce, after which the universe transitions into the expanding phase described by the CDM model. During contraction, most large-scale structures are expected to be erased. Black holes, however, as shown by several previous investigations, may persist through the bounce. The goal of this work is to analyze the evolution of a black hole population throughout the contraction, bounce, and expansion phases. Additionally, we investigate how the presence of black holes influences the properties of the background cosmological fluid. To this end, we develop a cosmological model involving two interacting fluids. Our findings indicate that the cosmological fluid alters its properties in a spacetime with fixed geometry.
This research examines the possibility whether the curvatures found in conventional General Relativity (GR) are the only existing ones, using both analytical and numerical techniques. To this end, we introduce a thorough investigation of Riemann curvatures in the spacetime surrounding a Kerr-Newmann black hole, which is distinguished by its specific electric charges and rotational dynamics. We apply a geometric quantization ansatz that centers on the quantization of the metric tensor, from which the complete set of field equations can be derived. The conformal transformation of the standard metric tensor upholds all the principles of GR while also extending its applicability to lower (quantum) scales. We recognize two types of Riemann curvatures. In addition to the positive curvatures present in classical GR formulations, we also find significant negative curvatures at lower (quantum) scales. This may indicate quantum sources of gravitation that classical GR does not seem equipped to explore.
We analyzed long-term periodic variations of the supercycle (the interval between two superoutbursts) of four ER UMa-type dwarf novae (ER UMa, V1159 Ori, DI UMa, and IX Dra). Using multi-year V-band and visual (vis) photometry obtained from AAVSO, we constructed light curves, identified the epochs of individual superoutbursts, derived their ephemerides, and constructed O-C diagrams. The O-C residuals follow a structured, repeating pattern (quasi-periodic) across all four of the above-mentioned dwarf novae, indicating systematic modulation of the timing of the O-C residuals. Multi-year cycles were detected using a generalized Lomb-Scargle periodogram. This long-term periodic variation in ER UMa systems is consistent with a cycle similar to the solar activity cycle, likely generated by the dynamo effect in the secondary star. This Magnetic activity-driven phases changes in Roche-lobe filling can explain the enhanced mass-transfer rates and shortened supercycles in ER UMa systems. The results of magnetic activity in the donor also support the persistence of residual donor magnetic braking below the period gap in cataclysmic variables, challenging evolutionary models in which angular momentum loss (AML) declines abruptly across the fully convective boundary at the upper edge (similar to 3 h) of the period gap rather than undergoing a smooth transition.
The decipherment of Inka mathematics stands at a crossroads. Rojas-Gamarra and Stepanova (2015) proposed a positional, base-10 interpretation of the Yupana and Khipu. In contrast, Overmann and Florio (2025) argue for a non-positional, additive system based on the visual ambiguity of khipu knots. This paper resolves this contradiction by demonstrating that both interpretations capture different operational layers of a unified system grounded in Andean quaternary logic. We introduce the Quaternary Algebraic Framework, showing that the values {1,2,3,5} on the Yupana form a complete basis for representing any natural number. We prove a Unification Theorem demonstrating that the Inka system was hybrid by design: operating positionally during calculation on the Yupana and additively during recording on the Khipu. The visual ambiguity of the knots emerges as a designed feature enabling this dual functionality. The "error" in Guam & aacute;n Poma's drawing is reinterpreted not as a mistake but as evidence of transition between operational modes. A computational implementation validates the framework and reveals inherent error detection. This work establishes Inka mathematics as a unique, sophisticated system that challenges Western categorical distinctions between additive and positional numeration.
We investigate the solar wind mass-loss rate and its relationship with open solar magnetic flux (OSF) over Solar Cycles 23-25 using OMNI, SIDC, and SOHO/LASCO data. The solar wind mass-loss rate correlates more strongly with OSF than with sunspot number, establishing OSF as a superior predictor of heliospheric mass-loss.
The goal of this study is to confirm the feasibility of the use of digitized low dispersive MtWilson Michigan Southern Sky H survey astronomical photographic plates for modern astrophysical research. The detection of highly redshifted objects, such as early galaxies and quasars, is fundamental to understanding the universe's evolution and its large-scale structure. Archival low-dispersion spectroscopy (LDS) plates, though lacking modern metadata, represent a rich but underutilized resource for identifying such objects. This report presents a computational method for analyzing LDS plates to detect peculiar compact, non-dispersed features, hypothesized to correspond to objects with peculiar spectra, for example, high-redshift sources. By focusing on localized objects with peculiar spectra limited to very narrow spectral coverage rather than typical elongated spectra, the methodology circumvents the challenges posed by incomplete plate information. The proposed approach employs image processing algorithms to identify candidates, marking them directly on the original plates for further study. Preliminary results suggest the potential of this method in uncovering scientifically valuable insights from historical observational data. This work highlights the role of computational techniques in repurposing archival materials for modern astrophysical research.
A new symmetry is presented for the case of imperfect fluids with vorticity in gravitational fields making use of the new tetrads previously introduced. We prove that this symmetry is a local symmetry of the metric tensor for a general imperfect fluid with vorticity. Therefore we conclude that the left hand side of the Einstein-Fluid equations is invariant under this local symmetry. This new symmetry is completely analogous to the local electromagnetic gauge symmetry in the sense that arises when the fluid four-velocity vectors are transformed into four-velocity vectors plus a local gradient of a local scalar function. The stress-energy tensor cannot be invariant only under this transformation. In order to make the stress-energy invariant under this local Abelian group, additional transformations are proposed for the energy density, pressure, the heat flow and viscous stresses. It is found the form of all of these proposed transformations by imposing invariance on the whole stress-energy tensor. As a byproduct we can use this symmetry to introduce a stress-energy tensor for vorticity invariant under the four-velocity gauge-like group of transformations. Applications in astrophysical evolution are developed for the neutron star superfluid that possesses large scale vorticity.
We present a theoretical analysis of the WDW approach to quantum cosmology extended to gravity theories with torsion. The dynamics of the FLRW universe is formulated as a classical Hamiltonian problem of point particle mechanics. Unlike in the WDW formalism, the Hamiltonian is not zero, though, and the third quantization does not enforce the cosmic time to vanish. The wave function of the Universe appears as a superposition of eigenfunctions of the quantum Hamiltonian with the cosmic time being the conjugate to its eigenvalues, spatial curvatures. The notion of weak measurement is then introduced to avoid the collapse of the total universal wave function upon measurements of the parameter set describing matter and spacetime. The collapse postulate of the standard Copenhagen quantum theory is discussed and the de Broglie-Bohm interpretation of the effective wave function introduced. The question of the boundary conditions for both, the wave function and the Bohmian guidance equation, is addressed. The corresponding numerical calculations will be published in a separate paper.
We present the results from a 3-year-long ultraviolet (UV) monitoring campaign of the broadline Seyfert 1 galaxy ESO 141-G55 using the International Ultraviolet Explorer (IUE). By modelling all individual, extinction-corrected UV spectra in the 1150-1978 and 1850-3348 & Aring; wavelength range, we have observed a significant variability in both UV continuum and line fluxes. Variabilities due to ionised UV lines like Siiv, Civ and Heii are delayed with respect to the UV continuum by 2.92(+0.54) (-0.61), 4.41(+0.44) (-0.54) and 4.11(+0.35) (-0.81) days, respectively. At a distance of similar to 0.004c, an outer accretion disk can be a possible site for the origin of UV lines.
The Southern Galactic Disk Survey (GDS) monitored a mosaic of 268 fields along a -wide stripe in the southern Galactic disk with simultaneous observations in and () from September 2010 to September 2019. The survey design and data characteristics, as well as first results in , were presented by Haas et al. (2012; Paper I). Hackstein et al. (2015; Paper II) extended the photometry and analysis process, and introduced the first catalogue including photometry of all 268 fields in and light curves comprising up to 272 observations per field made between September 2010 and May 2015. Here we describe our custom-made observational scheduler and conclude the GDS with light curves of up to 407 observations per field until September 2019 and light curves for a fraction of the fields. 113,449 distinct sources are identified as variables. Together with Paper II, we identified 77,592 variables that are not listed in either the International Variable Star Index (VSX) or the cross-match catalogue by Gavras et al. (2023). All emerging catalogues, comprising light curves, photometry and reduced images, are made publicly available via the German Astrophysical Virtual Observatory (GAVO).
The tidal field of a black hole can turn a star into a gas stream whose orbit can precess, especially if the a black hole is rapidly spinning. In this work, we investigate the impact of precession on the light curves of tidal disruption events (TDE). To do so, we perform two-dimensional radiation-hydrodynamic simulations of the interaction of the TDE wind and luminosity with the precessed stream wrapped around the black hole. Our results show that in events with black holes of similar to 10(6) M-circle dot and no orbit-spin inclination, the line of sight has little effect on the light curves, since the stream covers a small fraction of the solid angle as the precession is confined to the orbital plane. In the case of black holes of greater than or similar to 10(7)M(circle dot) and high inclination (i similar to 90 degrees), the light curve peaks can be delayed by similar to 100 days due to presence of the precessed stream blocking the radiation in the early phase of the event. We also discuss our efforts to model self-consistently the hydrodynamic evolution of a tidal stellar stream on curved spacetimes by the presence of a massive black hole.
Planetary nebulae represent a late evolutionary phase of low- to intermediate-mass stars. In this article, we present the serendipitous discovery of a previously unknown, faint potential Galactic planetary nebula (PN) in the constellation Camelopardalis, identified during a survey-inspection, aiming at the detection of dwarf companions of the spiral galaxy NGC 2403. Narrow-band imaging and spectroscopic observations of the nebula and its potential central star were obtained using a combination of amateur and professional telescopes. Our observations revealed a compact, dense, triangular structure-hereafter referred to as the Triangle Nebula-embedded within a broader elliptical region, which we call the Cam Nebula. Both are enclosed by an even fainter, nearly circular outer shell detectable only in deep, long-exposure images. This Shell Nebula and the Cam Nebula may be superpositions by chance, but we will assume they are connected. We designate the entire complex as TBG-N1. This is the first TBG nebula to avoid confusion with previously discovered TBG-DWs (dwarf galaxies). A candidate for the central star was identified near the geometric centre of the outer shell. Spectroscopic analysis provided estimates of the nebular electron temperature and density. The combined evidence from imaging, spectroscopy, and the photometric properties of the central star candidate supports the classification of TBG-N1 as a planetary nebula located at a distance of approximately 1 kpc. This discovery highlights the important role that collaborations between amateur and professional astronomers can play in uncovering and characterizing previously unrecognized celestial objects.
We analyze the Gamma-Ray Burst (GRB) redshift distribution using various density estimation methods. Several density estimators for one-dimensional point processes were tested for different sample sizes up to 1200 events. Our goal was to identify the "best" non-parametric radial density estimator for GRBs, and we found that Poisson noise significantly influences results. We identified Boundary Corrected Kernel Density Estimation as the most suitable method and applied it to a dataset of 542 GRBs with spectroscopic redshifts and reconstructed the GRB density function for different distances/redshifts. The relationship between the observed GRB redshift distribution and the cosmic star formation history is briefly discussed.
Gamma-ray bursts (GRBs) are the highest-energy explosions in the universe, emitting short bursts of intense gamma-ray and X-ray radiation. The Swift satellite's rapid response capability allows it to locate bursts instantly with the BAT detector and then start observing the X-ray afterglow within minutes with the XRT instrument. By analyzing the XRT spectra, we can measure not only the afterglow emission itself, but also the absorption effects in the intrinsic environment (progenitor environment, interstellar material). The extra absorption in the X-ray spectra can be used to estimate the intrinsic hydrogen column density (N-H,N-int), which provides information on the amount and ionization state of the matter surrounding the GRB.N(H,int )typically appears as an additional absorption component above the Galactic absorption in the spectral fit. Measurements based on Swift/XRT data provide important support for understanding the formation environment of GRBs and the physics of the early afterglow. The analysis ofthese parameters will also contribute to the identification of progenitors of GRBs (e.g., high-mass stars) and to the study of the interstellar material of high-redshift galaxies.
The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is an ESA M7 mission concept currently in Phase A, designed to exploit gamma-ray bursts to probe the early Universe while advancing multi-messenger and time-domain astrophysics. To achieve its ambitious goals, THESEUS will combine wide-band x-ray and gamma-ray monitors with an onboard InfraRed Telescope (IRT), providing autonomous arcsecond-scale localisation and high-precision redshift determination of near-infrared counterparts to high-energy transients. Achieving this precision requires a well-characterised detector response enabled by an internal Calibration Unit. The unit will ensure accurate calibration of the detector throughout the mission's 4-year nominal lifetime-and potentially beyond-using near-infrared LEDs as internal illumination sources. We highlight THESEUS science cases relevant for the Calibration Unit performance, discuss key challenges in the LED selection process and present the current status of the optical and mechanical design concept enabling a spatially uniform and temporally stable detector illumination within a structure that ensures long-term durability.
