Related papers: 3He: Does the problem persists?
The origin of 3He abundance enhancements in coronal mass ejection (CME)-driven shock gradual solar energetic particle (SEP) events remains largely unexplained. Two mechanisms have been suggested - the re-acceleration of remnant flare…
A large number of stellar evolution models with [Fe/H] = -2.3 and -3.3 have been calculated in order to determine the primordial $^7$Li abundance and to test current stellar evolution models by a comparison to the extensive database of Li…
Population III stars supplied the first light and metals in the Universe, setting the pace of re-ionisation and early chemical enrichment. In dense haloes their evolution can be strongly influenced by the energy released when WIMPs…
Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the 3He(3He,2p)4He…
Standard models for the chemical evolution of the Galaxy are reviewed with particular emphasis on the history of the abundance gradients in the disk. The effects on the disk structure and metallicity of gas accretion are discussed, showing…
Both recent observations and stellar evolution models suggest that pair-instability supernovae (PISNe) could occur in the local Universe, at metallicities below Z_Sun/3. Previous PISN models were mostly produced at very low metallicities in…
In this review, I will discuss a few problems which point to the need for improved stellar evolution models of halo stars. Current stellar evolution models do not match the observed $^7$Li abundance patterns, suggesting that the input…
The star formation (SFH) and chemical enrichment (CEH) histories of Local Group galaxies are traditionally studied by analyzing their resolved stellar populations in a form of color-magnitude diagrams obtained with the Hubble Space…
Current numerical studies suggest that the first galaxies formed a few stars at a time and were enriched only gradually by the first heavy elements. However, the large box sizes in these models cannot resolve primordial supernova explosions…
This paper is the third in a series reporting on a study of carbon abundances in a carefully chosen sample of planetary nebulae representing a large range in progenitor mass and metallicity. We make use of the IUE Final Archive database…
We have observed the HC3N (J=10-9) and N2H+ (J=1-0) lines toward the Vela C molecular clouds with the Mopra 22 m telescope to study chemical characteristics of dense cores. The intensity distributions of these molecules are similar to each…
Motivated by the recent detection of metals in different components of the high redshift universe and by the abundance ratios measured in the extremely metal-poor stars of our Galaxy, we study the nucleosynthesis constraints that this…
Planetary nebulae (PNe) and their central stars (CSs) are ideal tools to test evolutionary theory: photospheric properties of their exciting stars give stringent constraints for theoretical predictions of stellar evolution. The nebular…
We demonstrate that among the potential sources of the primordial abundance variations of the proton-capture elements in globular-cluster stars proposed so far, such as the hot-bottom burning in massive AGB stars and H burning in the…
Aims. A sample of early B-type stars in OB associations and the field within the solar neighbourhood is studied comprehensively. Present-day abundances for the astrophysically most interesting chemical elements are derived. Methods.…
The time-scales of chemical enrichment are fundamental to understand the evolution of abundances and abundance ratios in galaxies. In particular, the time-scales for the enrichment by SNe II and SNe Ia are crucial in interpreting the…
In view of their nature, planetary nebulae have very short lifetimes, and the chemical abundances derived so far have a natural bias favoring younger objects. In this work, we report physical parameters and abundances for a sample of old…
We aim to derive the chemical behavior of a significant sample of PNe and HII regions in the irregular galaxy NGC 6822 The selected objects are distributed in different zones of the galaxy. Due to the faintness of PNe and HII regions in NGC…
We report new chemical abundances of 23 bright red giants of the globular cluster M3, based on high-resolution spectra obtained with the Keck I telescope. Combining these data with a previously-reported small sample of M3 giants obtained…
Emission from the molecular ion H$_3^+$ is a powerful diagnostic of the upper atmosphere of Jupiter, Saturn, and Uranus, but it remains undetected at Neptune. In search of this emission, we present near-infrared spectral observations of…