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

We use models of stellar angular momentum evolution to determine ages for ∼500 stars in the APOGEE-Kepler Cool Dwarfs sample. We focus on lower-main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover

We present deep spectrophotometry of 18 H II regions in the nearby massive spiral galaxies M 101 and M 31. We have obtained direct determinations of electron temperature in all the nebulae. We detect the C II 4267 Å line in several H II regions, permitting to derive the radial gradient of C/H in both galaxies. We also determine the radial gradients

We analyzed the Kepler/K2 Campaign 11 data to validate the periods and amplitudes for the 32 apparently variable central stars of planetary nebulae (PNe) in the sample of 140 PNe in the field. The K2 data yield good values for the periods, but the amplitudes are always too low by up to 10X due to dilution of the photometry from both the nebula and

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