Astronomische Nachrichten最新文献

Neutron stars, particularly magnetars, exhibit extreme physical conditions with some of the strongest magnetic fields in the universe. Understanding the evolution of these magnetic fields is crucial for interpreting their observed properties, such as high braking indices and X-ray emissions. In this work, we investigate the decay of multipole magnetic fields in neutron stars by incorporating general relativistic (GR) effects into the induction equations. We derive GR-corrected evolution equations for dipole ($��l�=�1�$), quadrupole ($��l�=�2�$), and octupole ($��l�=�3�$) fields, considering both toroidal and poloidal components. Our calculations show that GR effects significantly extend the magnetic field decay timescales, with the redshift factor $��z�\approx �0.23�$ for a typical neutron star. We find that the GR-corrected decay timescales better align with observed characteristics of magnetars. Additionally, we discuss the implications of our model for X-ray emissions and magnetic energy release rates in magnetars. Our results highlight the importance of GR corrections for accurate predictions of magnetic field evolution and related observational phenomena.

NGC 4527 is a nearby edge-on spiral galaxy with both starburst and AGN features, hosting a LINER nucleus. We present a radio study of the large-scale structure and nuclear region of this galaxy, based on new uGMRT observations at 700 and 1230 MHz. Our continuum maps reveal extended emission tracing the stellar disk, with no evidence of a radio halo. The spectral index distribution and the presence of PAHs across the disk are consistent with ongoing star formation. In the nuclear region we resolve three compact sources: one at the galactic centre and two symmetrically aligned with the major axis at $��\sim �400�$ pc. The spectral index values and the destruction of PAHs in the central source, together with previously detected X-rays emission, suggest the presence of a low-luminosity AGN. The two off-centre sources are consistent with a star formation ring, coincident with a molecular gas ring previously reported. We explore a scenario where super-Eddington accretion onto the black hole drives a dense wind that falls back onto the disk, triggering star formation in a circumnuclear ring.

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.