Context. Blazars, comprising BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars, are the most luminous extragalactic sources that dominate the γ-ray sky. They account for approximately 56% of the sources listed in the recent Fermi-LAT (Large Area Telescope) catalogue (4FGL-DR4). The optical and UV spectra of BL Lacs are nearly

We review the existing distance estimates to the black hole X-ray binary Swift J1727.8─1613, present new radio and near-UV spectra to update the distance constraints, and discuss the accuracies and caveats of the associated methodologies. We use line-of-sight H I absorption spectra captured using the MeerKAT radio telescope to estimate a maximum

Context. We analyze the optical variability of the flat-spectrum radio quasar (FSRQ) Ton 599 using BVRI photometry from the Whole Earth Blazar Telescope (WEBT) collaboration (2011─2023), complemented by photometric and spectroscopic data from the Steward Observatory monitoring program. Aims. We aim to characterize short- and long-term optical

Non-uniformity plays an important role for MHD waves. For a uniform plasma of infinite extent the MHD waves can be subdivided in two classes with distinct properties. The first class contains the Alfvén waves. The Alfvén waves are incompressible and propagate parallel vorticity. They do not have a parallel component of displacement, they do not

TOI-282 is a bright (V = 9.38) F8 main-sequence star known to host three transiting long-period (P b = 22.9 d, P c = 56.0 d, and P d = 84.3 d) small (R p ≍ 2─4 R ⊕) planets. The orbital period ratio of the two outermost planets, namely TOI-282 c and d, is close to the 3:2 commensurability, suggesting that the planets might be trapped in a mean

We present a radiation-magnetohydrodynamics (RMHD) simulation of a magnetic cancellation event. The model is calculated with the Bifrost code and spans from the uppermost convection zone to the corona. The cancellation occurs between the positive polarity of an emerged magnetic bipole and a preexisting negative polarity. We try both to understand