Mass estimates of K giants are generally very uncertain. Traditionally, stellar masses of single field stars are determined by comparing their location in the Hertzsprung-Russell diagram with stellar evolutionary models. Applying an additional method to determine the mass is therefore of significant interest for understanding stellar evolution. We present the time series analysis of 11 K giants...

Context. Several clusters of red supergiants have been discovered in a small region of the Milky Way close to the base of the ScutumCrux Arm and the tip of the Long Bar. Population synthesis models indicate that they must be very massive to harbour so many supergiants. Amongst these clusters, Stephenson 2, with a core grouping of 26 red supergiants, is a strong candidate to be the most massive ...

Color-Magnitude Diagrams (CMDs) are plots that compare the magnitudes (luminosities) of stars in different wavelengths of light (colors). High nonlinear correlations among the mass, color, and surface temperature of newly formed stars induce a long narrow curved point cloud in a CMD known as the main sequence. Aging stars form new CMD groups of red giants and white dwarfs. The physical processe...

We first recall the observational and theoretical facts that constitute the so-called He problem. We then review the chemical anomalies that could be related to the destruction of He in red giants stars. We show how a simple consistent mechanism can lead to the destruction of He in low mass stars and simultaneously account for the low C/C ratios and low lithium abundances observed in giant star...

The asymptotic giant branch (AGB) evolution of stars is interesting from many points of view. It is the nal evolutionary phase for the large majority of all stars in the Universe that have left the main sequence. During this stage they contribute to the chemical evolution of galaxies, contribute to the integrated starlight of many galaxies, may provide the only interstellar matter there is in s...

The recent availability of stellar parallaxes provided by the Hipparcos star catalogue (ESA 1997) enables an accurate determination of the positions of single field giants in a theoretical H-R diagram and a reliable estimate of their masses. The present study combines these new astrometric data with previously published X-ray fluxes and rotational velocities. The results confirm the existence o...

Aims. Exo-planets are preferentially found around high metallicity main sequence stars. We aim at investigating whether evolved stars share this property, and what this tells about planet formation. Methods. Statistical tools and the basic concepts of stellar evolution theory are applied to published results as well as our own radial velocity and chemical analyses of evolved stars. Results. We ...

We present the results of an observational study of the efficiency of deep mixing in globular cluster red giants as a function of stellar metallicity. We determine [C/Fe] abundances based on low-resolution spectra taken with the Kast spectrograph on the 3m Shane telescope at Lick Observatory. Spectra centered on the 4300Å CH absorption band were taken for 42 bright red giants in 11 Galactic glo...

Spectral indices are useful tools for quantifying the strengths of features in moderate-resolution spectra and relating them to intrinsic stellar parameters. This paper focuses on the 4300Å CH G-band, a classic example of a feature interpreted through use of spectral indices. G-band index definitions, as applied to globular clusters of different metallicity, abound in the literature, and transf...