Astronomische Nachrichten最新文献

We present evidence of surface spectral diversity on asteroids (7) Iris and (10) Hygiea based on Johnson–Cousins (B–V, V–R) and ATLAS (c–o) color indices. For Iris, B–V shows significant rotational modulation, revealing localized heterogeneities associated with features such as the Xanthos and Porphyra craters. Its B–R spectral slope, $��6.4�\%�$ per $��100��\mathrm{nm}�$, matches that of Q/S-type asteroids, while phase-resolved variations suggest combined effects of composition, topography, and illumination geometry. In contrast, Hygiea is spectrally uniform: neither B–V nor V–R varies with rotation, and its B–R slope, $��3.1�\%�$ per $��100��\mathrm{nm}�$, is typical of the B/C-complex. The c–o distributions for both objects do not show a clear dependence on Earth-based viewing geometry. We estimate the c–o index of near-Earth asteroid $��2024��{\mathrm{YR}}_4�$ as 0.5, consistent with a redder K/L-type surface. This result indicates that c–o can discriminate between S- and C-complex asteroids, similar to V–R. These findings demonstrate the diagnostic value of broadband colors for characterizing asteroid surfaces and provide new insights into the compositional and evolutionary diversity of main-belt asteroids.

Prominences (PRs) are among the most common solar phenomena, yet their full physical picture, particularly their chromospheric mm emission, remains incomplete. The new Atacama Large Millimeter/submillimeter Array (ALMA) presents an opportunity to study PRs at mm and sub-mm wavelengths through a combination of measurements and theoretical modeling. We utilize ALMA single-dish measurements alongside data from other radio instruments to model the PR brightness temperature through adaptation and modification of the 1D semi-empirical Avrett–Tian–Landi–Curdt–Wülser (ATLCW) quiet-Sun (QS) model. The calculated and measured PR brightness temperatures were found to be lower than the measured QS value and predictions from the unperturbed ATLCW QS model across the ALMA wavelength range, consistent with PRs appearing in absorption. The PR density was found to be 60–163 times higher and temperature 155–163 times lower than the QS level, aligning with previous measurements. A key finding emerged with the non-hydrostatic equilibrium assumption, yielding a more physically consistent PR brightness temperature. This suggests that PR stability is most likely maintained by its magnetic field obeying magnetostatic conditions rather than by pure hydrostatic equilibrium, supporting recent studies. Additionally, our results confirm that thermal bremsstrahlung is the dominant radiation mechanism for PRs at mm and sub-mm wavelengths.

We study the spin evolution of the young X-ray pulsar PSR J0537-6910 in the Large Magellanic Cloud, the fastest-spinning isolated pulsar known to date with a rotation period of 16 ms, which provides a unique laboratory for probing the early angular momentum evolution of a neutron star. Motivated by the observed discrepancy that most pulsars exhibit less than three braking indices in contrast to what is predicted by a magnetospheric dipolar slow-down law, we propose a hybrid Magnetic Dipole Radiation and Wind (MDRW) model that incorporates both magnetic dipole radiation (MDR) and particle wind contributions. By assuming $��n�=�2�$, we derive analytical solutions for the spin evolution equations under different ages (1–4 kyr). We show that the initial spin period range (10.5–14.3 ms) predicted by the MDRW model significantly exceeds the values derived from the classical MDR framework (7.0–14.4 ms), which is in agreement with physical expectations for neutron star birth scenarios. Furthermore, the MDRW model reveals an equal partitioning of rotational energy loss between magnetic dipole radiation and particle wind components ($��d�=�f�=�0.5�$) when $��n�=�2�$, highlighting the interplay of the various mechanisms in the spin-down of young pulsars. This also provides a new approach to estimating the period evolution of pulsars.