Context. IMaX/Sunrise has recently reported the temporal evolution of highly dynamic and strongly Doppler shifted Stokes V signals in the quiet Sun. Aims: We...
Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors
Aims: We try to identify ultra-cool dwarfs from the seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7) with SDSS i-z and r-z colors. We also obtain...
Ultra-deep imaging of NGC 1052-DF2 and NGC 1052-DF4 to unravel their origins
A number of scenarios have been proposed to explain the low velocity dispersion (and hence possible absence of dark matter) of the low surface brightness...
UltraCompCAT: A comprehensive catalogue of ultra-compact and short orbital period X-ray binaries
Ultracompact X-ray binaries (UCXBs) are a distinctive but elusive family of low-mass X-ray binaries (LMXBs) characterised by their tight orbits and degenerate...
Uncertainties in the solar photospheric oxygen abundance
Aims: The purpose of this work is to better understand the confidence limits of the photospheric solar oxygen abundance derived from three-dimensional models...
Uncertainty-aware blob detection with an application to integrated-light stellar population recoveries
Context. Blob detection is a common problem in astronomy. One example is in stellar population modelling, where the distribution of stellar ages and...
Uncovering the true periods of the young sub-Neptunes orbiting TOI-2076
Context. TOI-2076 is a transiting three-planet system of sub-Neptunes orbiting a bright (G = 8.9 mag), young (340 ± 80 Myr) K-type star. Although a validated...
Understanding internetwork magnetic fields as determined from visible and infrared spectral lines
We present numerical experiments aimed at understanding why near-infrared observations systematically deliver weak magnetic fields in the internetwork, whereas...
Understanding the evolution and dust formation of carbon stars in the Large Magellanic Cloud via the JWST
Context. Carbon stars have been, and still are, extensively studied. Given their complex internal structure and their peculiar chemical composition, they are...