To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Based on hydrostatic models we discuss the effects of molecular opacities and abundance changes concerning C, N or O on the atmospheric structures, spectra and photometric properties of C/M AGB giants.
We study the mixing in low-intermediate massive stars using eclipsing binaries. We compute stellar evolutionary models with a varying convective core overshooting parameter and different rotation rates. Using a Bayesian estimation method, we found that the coexistence of the two phenomena may be a reasonable explanation of the observed extra-mixing.
In the recent years it has been generally accepted that seismic parameters add an important observational constraint for the study of stellar populations and galaxy evolution. Padova-Trieste (PARSEC) evolutionary tracks are widely used to characterise stellar objects and stellar populations. Stellar models at the base of these studies suffer from uncertainties and, more important, degeneracy among different input parameters: stellar mass, chemical composition, central chemical mixing, age, etc. Adding seismic properties to the classic parameters for stars at different evolutionary states, from the H main-sequence to the asymptotic giant branch, is a powerful tool to calibrate physical processes in stellar models, and hence to improve our interpretation of Galactic and extra-Galactic observations.
Poly(lactide) (PLA) composites filled with electrospun nylon 6 fibers were prepared. This allowed us to simultaneously improve the mechanical properties and tune the degradation of the PLA matrix. The interfacial adhesion between the PLA matrix and the nylon fibers was good. The major effect of electrospun fibers on the matrix was that of modifying the semicrystalline framework, thickening the polymer lamellae. This allowed an increase in the mechanical properties of the material, and on the other hand to modify its degradation behavior. The modulus of the composites was increased up to 3-fold with respect to neat PLA. The peculiar morphology of matrix–filler interaction moreover slowed down the degradation rate of the material and improved the dimensional stability of the specimens during the degradation process. This shows the potential of electrospun fibers as a way to tune the durability of PLA-based products, widening the range of application of this promising material.
As part of our near-infrared photometric survey of nearby dwarf galaxies, we present recent results for Leo I and Leo II dwarf spheroidal galaxies. We selected O- and C-rich AGB stellar populations using two-color diagrams and compared their luminosity functions and star counts with the predictions of the most recent AGB theoretical models.
We study the evolution of the first stars in the universe (Population III) from the early pre–Main Sequence (MS) until the end of helium burning in the presence of WIMP dark matter annihilation inside the stellar structure. The two different mechanisms that can provide this energy source are the contemporary contraction of baryons and dark matter, and the capture of WIMPs by scattering off the gas with subsequent accumulation inside the star. We find that the first mechanism can generate an equilibrium phase, previously known as a dark star, which is transient and present in the very early stages of pre–MS evolution. The mechanism of scattering and capture acts later, and can support the star virtually forever, depending on environmental characteristics of the dark matter halo and on the specific WIMP model.
Accurate chemical abundances for the following planetary nebulae (PNe); NGC 6537, He 2-111, NGC 6302, NGC 6445, NGC 6741, NGC 7027, NGC 7662, NGC 2440 and NGC 5315 have been derived using data from the Infrared Space Observatory (ISO) and the International Ultraviolet Explorer (IUE). Optical data from the literature has also been used. These work has been published by Pottasch et al. (2001), Bernard Salas et al. (2001 and 2002). In particular, the use of the ISO data has reduced the need for ionization correction factors. Furthermore, infrared data avoid or reduce many problems when deriving these abundances, namely: temperature fluctuations in the nebula, and extinction corrections. The electron temperature (Te) and density of the PNe has been derived. For those PNe in which the Te has been derived for several ions a trend with the ionization potential is present. Ions with high stages of ionization give higher Te, probably because they are formed close to the central star. The chemical abundances measured in these PNe give some hint of the nucleosynthesis and mixing processes experienced by their progenitor stars. In this view, a preliminary comparison with synthetic TP-AGB models is made (Bernard Salas et al. (in prep.)). NGC 7027, NGC 6741, NGC 2440, and NGC 6445 are consistent with the occurrence of the 3rd dredge-up due to both C12 and He4 enrichment. NGC 6537, NGC 6302, and He 2-111 are likely to have stellar progenitors experiencing hot bottom burning due to the low C12 and high N14 abundances.
We present recent improvements and results of an extensive analysis of the TP-AGB phase performed by means of a synthetic model (Marigo 1998a, b; Marigo et al. 1998a, b). The improvements concern: i) the use of a homogeneous and accurate set of analytical relations (Wagenhuber & Groenewegen 1998); ii) a new treatment of envelope burning in the most massive TP-AGB stars (M > 3.5M⊙) to account for the possible break-down of the core mass-luminosity relation; iii) a better treatment of the third dredge-up to infer if and when the process takes place.
Extensive calculations of synthetic TP-AGB models have been carried out over the mass range (0.8M⊙ ÷ 5M⊙) and for three sets of initial metallicity (Z = 0.019, Z = 0.008, Z = 0.004). The formation of carbon stars is investigated addressing the following issues: a) the reproduction of the observed luminosity functions of carbons stars in both Magellanic Clouds, and b) the formation of very bright and optically obscured carbon stars.
Email your librarian or administrator to recommend adding this to your organisation's collection.