Now almost 70 years since its introduction, the effective or half-light radius has become a very popular choice for characterising galaxy size. However, the effective radius measures the concentration of light within galaxies and thus does not capture our intuitive definition of size which is related to the edge or boundary of objects. For this

Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample

Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies 1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a

A prominent jet-driven outflow of CO(2-1) molecular gas is found along the kinematic minor axis of the Seyfert 2 galaxy ESO 420-G13, at a distance of 340-600 pc from the nucleus. The wind morphology resembles the characteristic funnel shape, formed by a highly collimated filamentary emission at the base, and likely traces the jet propagation

Sunspots are intense collections of magnetic fields that pierce through the Sun's photosphere, with their signatures extending upwards into the outermost extremities of the solar corona 1. Cutting-edge observations and simulations are providing insights into the underlying wave generation 2, configuration 3,4 and damping 5 mechanisms found in

This thesis addresses several topics in the study of the more massive and O-rich asymptotic giant branch (AGB) stars in our Galaxy. In particular, the main goals are the exploration of the circumstellar effects on the abundance determination in solar metallicity massive AGB stars by using more realistic pseudo-dynamical model atmospheres and the