Astronomische Nachrichten最新文献

Strongly magnetized white dwarfs, characterized by surface magnetic fields of $��{10}^9�-�{10}^{12}�$ G, harbor extreme interior conditions that necessitate a reevaluation of the equation of state. Building upon Dong et al. (2023), this work advances the understanding of relativistic electron pressure in superhigh magnetic fields. We investigate the interplay between magnetic field strength and stellar properties, including density, mass-radius relations, and total pressure. Our results reveal that strong magnetization can significantly enhance white dwarf masses beyond the Chandrasekhar limit, with maximal magnetic fields reaching $��{10}^{15}�$ G. This study not only refines the theoretical framework for white dwarf magnetization but also provides a foundation for exploring magnetized neutron stars.

We discuss some aspects of stellar evolution in binary systems. While single stars can swell following the chemical evolution of their interior, stars belonging to binary systems cannot overflow the size of the Roche lobe, if so hydrostatic equilibrium is strictly impossible. The system is forced to exchange mass between its members through the inner Lagrangian point. In the first part of the paper, we discuss the standard evolution of binaries that have a non-degenerate donor star and a compact companion. We show that the model fails when to account for the occurrence of binary pulsars when they predict a long-standing mass transfer episode. Models including irradiation feedback and evaporation in close binaries are examined next. Following these sections, we discuss the case of systems with a black hole (BH). We show that if BHs are born non-rotating, binary interaction seems insufficient to speed them up, an indication that BH's rotation is a feature present at birth. Finally, we discuss Blue Straggler Stars detected in open and globular clusters. Since they cannot be understood as single-born stars, we evaluate one of the proposed channels is mass transfer in close binaries, and discuss its viability and the limitations of the present models.

High-velocity stars are interesting targets to unveil the formation of the Milky Way. In fact they can be recently accreted from an infalling dwarf galaxies or they can be the result of a turbulent merging of galaxies. Gaia is providing the community a way to select stars for their kinematics and the radial velocity, one of the speed components, is derived from the Gaia RVS spectrum. High absolute radial velocity values are sensitive to be false positive. They are rare and as such they are more easily impacted than lower velocity stars, by contamination by very low SNR spurious measures. We here investigate a sample of 26 stars with Gaia absolute radial velocity in excess of 500 km/s with spectroscopic follow-up observations with UVES. For all but one star the extreme radial velocity is confirmed and these stars are all metal-poor and, as expected, enhanced in the $��\alpha �$ elements. The complete chemical inventory confirm the large star-to-star scatter for the heavy elements and their on average larger ratio over iron with respect to the Sun, in agreement with the literature.

We examine in this brief review some of the emerging controversies and problems of the standard $��\Lambda �$CDM Cosmology. We make a few autobiographical notes and point out two psychological/sociological attitudes that may difficult the solution of the problems and therefore to the advance on the discipline. Criticisms to Inflation and Large-Scale Structure are exposed, and the general construction of a consensual Cosmology, even a non-standard one, highlighted.

Black hole accretion and jet formation are very fundamental and important physical processes in astrophysics. Despite the great progress made in the last decades, our knowledge of the physics of BHs remains highly incomplete. The compact radio cores and/or weak jets are usually observed in nearby LLAGNs, which can help us to better understand and explore the jet and accretion physics due to their proximity and fruitful multi-waveband observations. In this short review, we studied the recent multi-waveband observations of the SMBH activities in LLAGNs and found that the high-resolution millimeter/submillimeter observations are very important for the nearby LLAGNs. The centers of LLAGNs are believed to be powered by hot accretion flow and jets. The aim of this review is to model the multi-wavelength spectral energy distribution (SED) of LLAGNs, and all the data we used here in the literature correspond to the core emission. We found these important features in LLAGNs are hard to fit by pure ADAF or jet models, which implies that they may come from different regions around the SMBH. We usually use the coupled ADAF and jet model to fit the multi-wavelength SED of LLAGNs and found that the submillimeter bump can be naturally modeled by the synchrotron emission of the thermal electrons in ADAF, which is very useful for us to constrain the physical parameters in the accretion disk and jet.

G166.0 + 4.3 (VRO 42.05.01) is a mixed-morphology supernova remnant (SNR) having a different spatial distribution of emission viewed in radio and X-rays. A sharp edge-brightened circular shape of the shell and wing component is visible in radio wavelength, whereas X-ray emission is dominated by a bright spot in the wing, without any edge-brightened structures. The observed shape of this SNR, looking like a shock propagation through the medium of different densities, can be a result of the shock encountering the density discontinuity in the interstellar medium, which makes favorable conditions for the particles' acceleration up to very high energy. Thus, the G166 + 4.3 SNR became a candidate for the investigation of particle acceleration in SNR shocks at high- and very-high energies. At TeV energies, the SHALON telescopes discovered extended emission, with the main contribution to the very-high-energy gamma-ray fluxes given by the regions correlated with the shells visible in the radio energies. But the main contribution to the TeV gamma-ray flux comes from the west part of the SNR, where the maximum of X-ray emission is located. The origin of the very-high-energy gamma-ray emission from G166 + 4.3 SNR is explored.

Low-frequency spectral studies of radio pulsars represent a key method for uncovering their emission mechanisms, magnetospheric structure, and signal interactions with the surrounding interstellar medium (ISM). In recent years, more next-generation low-frequency radio telescopes (e.g., LOFAR, LWA and MWA) have enriched the observational window below 350 MHz, enabling more detailed explorations of the ISM effects, such as absorption and scattering, resulting in diverse spectral behaviors observed across different pulsars. This paper reviews the morphology of pulsar radio spectra, advances in spectral modeling, and the key physical processes governing the low-frequency emission. Looking ahead, next-generation instruments such as SKA-Low—with their unprecedented sensitivity—are expected to resolve outstanding questions in pulsar emission processes, offering insights into the extreme physical regimes governing these exotic objects.

Neutron stars are natural laboratories of cold, dense strong interacting matter. In this article, we briefly review the gravitational waves related to neutron stars. Tidal deformability is a significant value that relates the observation of gravitational waves to the equation of state of cold, dense matter. The implicants of GW170817 and GW190814 are discussed. We also give an outlook for future work.

Active galactic nuclei (AGN) especially of blazar type are among the most luminous objects that have been detected through the whole range of the electromagnetic spectrum. It is generally believed that the powered by the central black hole AGN jets are responsible for the observed features like highly variable non-thermal emission characterized by spectral energy distribution extending from radio frequencies up to very high energy gamma-rays. The investigations of the physical properties of jets as well as the mechanisms of jet launching and localization of emissions in AGN are carried out with multi-wavelength observations of active galaxies at the different activity states to trace the temporal changes of fluxes and spectral behavior. NGC 1275 is one of the nearest and extensively studied active galaxies at the energy range from radio band to very high energy gamma-rays. Its multi-wavelength long-term observations resulted in the broadband spectral energy distribution of NGC 1275 obtained simultaneously or quasi-simultaneously and revealed the short-term and long-term timescale variability of emission fluxes from this AGN. Modeling of the NGC 1275 spectral energy distribution at the different activity states was made to estimate the jet physical parameters which may help to understand the changes in the temporal and spectral behavior of NGC 1275 active galactic nucleus.