Teegarden's star is a late-type M-dwarf planet host, typically showing only rather low levels of activity. In this paper we present an extensive characterisation of this activity at photospheric, chromospheric, and coronal levels. We specifically investigated TESS observations of Teegarden's star, which showed two very large flares with an

Context. Binary systems play a crucial role in massive star evolution. Systems composed of B-type and O-type stars are of particular interest due to their potential to lead to very energetic phenomena or the merging of exotic compact objects. Aims. We aim to determine the orbital period variations of a sample of B+B and O+B massive overcontact

Context. The ionization of diffuse gas located far above the energetic midplane OB stars poses a challenge to the commonly accepted notion that radiation from OB stars is the primary ionization source for gas in galaxies. Aims. We investigated the sources of ionizing radiation, specifically leaking midplane H II regions and/or in situ hot low-mass

This study investigates the active regions of the M3.0V star G 80–21 using the observed data from the CARMENES project with synthetic spectra generated by the RH1.5D radiative transfer code. The CARMENES project aims to search for exoplanets around M dwarfs using high-resolution near-infrared and optical echelle spectrographs. By comparing the