The linear polarization produced by scattering processes in the spectral lines of the IR triplet of Ca II can be observed near the edge of the solar disk. The cause of this polarization was considered a true enigma until the year 2003, in which IAC researchers could carry out sophisticated calculations based on the quantum theory of the spectral line polarization. In this way, they could demonstrate that the physical origin of the enigmatic polarization is the presence of "atomic polarization" in the lower levels of such spectral lines, which produces dichroism (i.e., selective absorption of the polarization components of the radiation beam that propagates towards the observer) without the need of a magnetic field. This result is important because it provides a way to detect extremely weak magnetic fields in Astrophysics, both in the solar atmosphere and in other astrophysical plasmas (e.g., in the atmospheres of supernovae).
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The recently discovered phosphorus-rich stars pose a challenge to stellar evolution and nucleosynthesis (that is, the formation of chemical elements in stellar interiors) theory, as none of the existing models can explain their extremely peculiar chemical abundances pattern. Apart from the large phosphorus (P) enhancement, such stars also show enhancement in other light (O, Mg, Si, Al) and heavy (e.g., Ce) elements. Thanks to the Spanish Service Time at the Nordic Optical Telescope, we have recently obtained high-resolution optical spectra of two optically bright phosphorus-rich starsAdvertised on
Umbral flashes are sudden brightenings commonly visible in the core of some chromospheric lines. Theoretical and numerical modeling suggests that they are produced by the propagation of shock waves. According to these models and early observations, umbral flashes are associated with upflows. However, recent studies have reported umbral flashes in downflowing atmospheres. We aim to understand the origin of downflowing umbral flashes. We explore how the existence of standing waves in the umbral chromosphere impacts the generation of flashed profiles. We performed numerical simulations of waveAdvertised on
Can neural networks distinguish computer simulated galaxy images from observed galaxies? This is the question that has been addressed in this work. For years, reproducing the morphological diversity of galaxies has been a problem for cosmological simulations. The new generation of simulations, such as Illustris TNG, are becoming more and more realistic. But enough to fool a neural network? In this work it is shown that it does not. Using unsupervised deep generative models, it is shown that, despite the fact that realism increases greatly in the last generation of simulations and withAdvertised on