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The emergence of magnetic field on stellar surfaces leads to the formation of magnetic features, such as dark spots and bright faculae. These features cause stellar brightness variations. Such variations have been extensively studied for the Sun. The plethora of photometric data obtained by both past (e.g. CoRoT and Kepler) and current space missions (TESS and Gaia) have underlined the needs for a better understanding and modelling of stellar brightness variations. One of the possible approaches for such modelling is to rely on the solar paradigm, i.e. to take a model which reproduces the observed variability of the solar brightness and extend it to other stars. We follow the SATIRE approach of calculating brightness variations, which was shown to reproduce the solar variability in great detail. To obtain the surface distribution of magnetic features, we employ the FEAT modelThis allows extending the SATIRE calculations to stars with different rotation periods and inclinations. This allows us toalso calculate the rotational variability of stars rotating faster than the Sun. Wecompare our results to the observed distribution of Kepler stars variability and provide a possible explanation forthe observed dependence of the rotational variability on the rotation period for stars rotating slower than 10 days by introducing different degrees of nesting of active regions.

The helicity of a magnetic field is a fundamental property that is conserved in ideal MHD. It can be explored in the stellar context by mapping large-scale magnetic fields across stellar surfaces using Zeeman-Doppler imaging. A recent study of 51 stars in the mass range 0.1-1.34 M$_\odot$ showed that the photospheric magnetic helicity density follows a single power law when plotted against the toroidal field energy, but splits into two branches when plotted against the poloidal field energy. These two branches divide stars above and below $\sim$ 0.5 M$_\odot$. We present here a novel method of visualising the helicity density in terms of the linkage of the toroidal and poloidal fields that are mapped across the stellar surface. This approach allows us to classify the field linkages that provide the helicity density for stars of different masses and rotation rates. We find that stars on the lower-mass branch tend to have toroidal fields that are non-axisymmetric and so link through regions of positive and negative poloidal field. A lower-mass star may have the same helicity density as a higher-mass star, despite having a stronger poloidal field. Lower-mass stars are therefore less efficient at generating large-scale helicity., Comment: 8 pages, 7 figures, 1 table

Planetary systems are found around a wide variety of stellar hosts. However, our understanding of which stellar properties influence planet formation is still largely biased towards main-sequence, solar-type stars. While low-mass stars (M dwarfs) have been recognised as promising targets in the search for small, rocky planets, detailed chemical studies of large samples of M dwarfs with planets are still missing. This is because the accurate determination of the stellar parameters and abundances of M dwarfs is a difficult task. To overcome this difficulty we developed a methodology to determine stellar abundances of elements other than iron for M dwarf stars form high-resolution, optical spectra. Our methodology is based on the use of principal component analysis and sparse Bayesian's method. We made use of a set of M dwarfs orbiting around an FGK primary with known abundances to train our methods. In this contribution we applied our methods to derive stellar metallicities and abundances of a large sample of M dwarfs observed within the framework of current radial velocity surveys. We discuss whether the correlations between the metallicity, individual chemical abundances, and mass of the star and the presence of different type of planets found for FGK stars still holds for the less massive M dwarf stars and set the results into the context of current planet formation models.