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Context. Solar active regions (ARs) are often surrounded by dark large areas of reduced emission compared to the quiet Sun, observed at various wavelengths corresponding to the chromosphere, transition region (TR), and corona, known as dark halos (DHs). The mechanisms behind the darker emission of DHs remain unclear and merit a wider scope of study. Aims. This study aims to investigate for the first time the fine structure of a DH observed by the EUV High Resolution Imager (HRIEUV) on board the ESA's Solar Orbiter (SO) mission and its appearance in the TR. Aims. We utilized the extensive 1 hour dataset from SO on 19 March 2022, which includes high-resolution observations of NOAA 12967 and part of the surrounding DH. We analyzed the dynamics of the HRIEUV DH fine structure and its appearance in the HRILyα image. We also analyzed the Spectral Imaging of the Coronal Environment (SPICE) Lyβ, C III, N VI, O VI, and Ne VIII lines, which sample the TR in the log T(K) ∼ 4.0–5.8 range. This analysis was complemented with a simultaneous BLOS magnetogram taken by the High Resolution Telescope (HRT). Methods. We report the presence of a peculiar fine structure that has not been observed for the quiet Sun. It is characterized by combined bright EUV bundles and dark regions, arranged and interconnected in such a way that they cannot be clearly separated. They form a spatial continuum extending approximately radially from the AR core, suggesting a deep connection between the DH and the AR. Additionally, we find that the bright EUV bundles are observed in all the SPICE TR lines and the HRILyα band and present photospheric BLOS footprints in the HRT magnetogram. This spatial correlation indicates that the origin of the 174 Å DH may lie in the low atmosphere: the photosphere and chromosphere. [ABSTRACT FROM AUTHOR]

Intermediate polars are a class of cataclysmic variables in which a white dwarf accretes material from a companion star. The intermediate polar nature confirmation usually derives from the detection of two periods in both X -ray and optical photometry. In this respect, the high-energy signal is often characterized by modulations on the white dwarf spin and the orbital period. However, noting that the periodograms may be characterized by strong features also at the synodic period and/or other sidebands, the timing analysis of the X -ray signal may offer the unique possibility to firmly discover an intermediate polar candidate. Here, we concentrate on a sample of five cataclysmic variable binary candidates: i.e. SAXJ1748.2-2808, 1RXS J211336.1 + 542226, CXOGC J174622.7-285218, CXOGC J174517.4-290650, and V381 Vel, listed in the IPHome catalogue. Our main aim is to confirm if they belong to the intermediate polar class or not. The results of our analysis show that we can safely assess the intermediate polar nature of all the considered sources, apart for the case of V381 Vel which instead behaves like a cataclysmic variable of the polar subclass. Moreover, the source SAXJ1748.2-2808, previously classified as an HMXB, appears to be, most likely, an intermediate polar variable. [ABSTRACT FROM AUTHOR]