Recently, Delgado-Inglada and collaborators have shown that low-mass (between one and three times the mass of the Sun) planetary nebulae are rich in oxygen, but the standard theoretical models do not predict this. In this work we explain this phenomenon for the first time using theoretical models of nucleosynthesis (production of chemical elements in the interiors of stars) in their precursor AGB stars, which include convective processes, (which transport chemical elements created in the interior to the surface of the star) more efficient than in the standard models. This discovery calls

Previous numerical studies had apparently ruled out the possibility that flares in galaxy discs could give rise to the apparent breaks in their luminosity profiles when observed edge-on. However the studies have not, until now, analysed this hypothesis systematically using realistic models for the disc, the flare, and the bulge. We revisit this theme by analysing a series of models which sample a wide range of observationally based structural parameters for these three components. Using observational data, we have considered realistic distributions of bulge-to-disc ratios, morphological

Historically, globular clusters (GCs) have been used as laboratories for studying stellar evolution, because it was thought that all the stars in a globular cluster formed at the same time and thus have the same age. However since a couple of decades ago it has been known that almost all the globular clusters contain several stellar populations. In the first generation the chemical abundances, for example those of elements such as Al and Mg, show the composition of the original interstellar (or intra-cluster) medium. In the short time (astronomically) of only 500 million years the medium is

Ultra diffuse galaxies (UDGs) have the sizes of giants but the luminosities of dwarfs. A key to understanding their origins comes from their total masses, but their low surface brightnesses (mu > 25.0) generally prohibit dynamical studies. Here we report the first such measurements for a UDG (VCC 1287 in the Virgo cluster), based on its globular cluster system dynamics and size. From 7 GCs we measure a mean systemic velocity Vsys = 1071(-15+14) km/s, thereby confirming a Virgo-cluster association. We measure a velocity dispersion of 33(-10+16) km/s within 8.1 kpc, corresponding to an

For more than 70 years we have known that the weak recombination lines of the ions of elements, such as oxygen and carbon, give us values for their abundances that are much larger than those obtained using collisional lines, even though the collisional lines are 1,000 to 100,000 times brighter than the recombination lines. This discrepancy has cast constant doubt about one of the methods that has been mostly used to measure chemical abundances in the Universe. During the past few years the planetary nebulae group at the IAC have discovered that the planetary nebulae with the largest

The polarization of the Mg II k line at 279.5 nm encodes valuable information on the magnetic field of the upper solar chromosphere, where this strong resonance line originates. We have developed a novel radiative transfer code which allows us to account for scattering polarization and the Hanle and Zeeman effects, as well as partial frequency redistribution (PRD) phenomena (i.e., correlation effects between the incoming and outgoing photons in the scattering events). This non-LTE code, which treats the atomic system and the polarized radiation field quantum-mechanically, has been applied to