The exact mechanisms leading to chromospheric heating are still ill-defined. While the presence of magnetic elements is undoubtedly necessary, the details of the heating, and its spatio-temporal distribution remain poorly understood. We contribute to this topic by analyzing the behavior of hot chromospheric fibrils surrounding network and plage elements, identified via the broader Hα profiles observed along their length; the H-α spectral line width has been shown to correlate with the local chromospheric temperatures through comparison with the ALMA millimeter-continuum brightness temperature. We make use of loop tracing and analysis software to investigate characteristics of the chromospheric hot fibrils including their length, number density, and transverse spatial extension in an enhanced network region.

Solar simulations and observations showed that the detection of Earth twins around Sun-like stars is difficult in radial velocities with current methods techniques. The Sun has proved to be very useful to test processes, models, and analysis methods. The convective blueshift effect, dominating for the Sun, decreases towards lower mass stars, providing more suitable conditions to detect low mass planets. We describe the basic processes at work and how we extended a realistic solar model of radial velocity, photometry, astrometry and LogR′HK variability, using a coherent grid of stellar parameters covering a large range in mass and average activity levels. We present selected results concerning the impact of magnetic activity on Earth-mass planet detectability as a function of stellar type. We show how such realistic simulations can help characterizing the effect of stellar activity on RV and astrometric exoplanet detection.

We address the importance of historical full-disc Ca II K spectroheliograms for solar activity and irradiance reconstruction studies. We review our work on processing such data to enable them to be used in irradiance reconstructions. We also present our preliminary estimates of the plage areas from five of the longest available historical Ca II K archives.