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Updating standard solar models

-44100 Ferrara , Italy 1 Max-Planck Institut for Astrophysics, K. Schwarzschild Str. 1, D-85740 Garching bei Mu ̈nchen , Germany 2 Send o print requests to: S. Degl'Innocenti , Dipartimento di Fisica ... 6). Acknowledgements. We warmly thank V. Castellani and G. Fiorentini for their advice. F. Ciacio and B. Ricci are grateful to CNR for a fellowship. S. Degl'Innocenti and B. Ricci acknowledge the

ΔY/ΔZ from the analysis of local K dwarfs

Context. The stellar helium-to-metal enrichment ratio, ΔY/ΔZ, is a widely studied astrophysical quantity. However, its value has still not been precisely constrained.Aims. This paper is focused on studying the main sources of uncertainty that affect the ΔY/ΔZ ratio derived from the analysis of the low-main sequence (MS) stars in the solar neighborhood.Methods. The possibility of...

Semen apoptotic M540 body levels correlate with testis abnormalities: a study in a cohort of infertile subjects

STUDY QUESTION What are the associations between semen apoptotic M540 bodies and other parameters of semen quality and sonographic alterations of the male genital tract in a cohort of infertile subjects?

Pre-main-sequence stars in the star-forming complex Sh 2-284

Located at the Galactic anticentre, Sh 2-284 is an H ii region that harbours several young open clusters. Dolidze 25, a rare metal-poor (Z∼ 0.004) young cluster, is one of these. Given its association with Sh 2-284, it is reasonable to assume a low metallicity for the whole H ii region. Sh 2-284 is expected to host a significant population of pre-main-sequence (PMS) stars of both...

Hipparcos open clusters and stellar evolution

By relying on recently improved Hipparcos parallaxes for the Hyades, Pleiades and Ursa Major clusters we find that stellar models with updated physical inputs reproduce nicely the location in the colour–magnitude diagram of main-sequence stars of different metallicities. Stars in the helium-burning phase are also discussed, showing that the luminosity of giants in the Hyades...

Theoretical stellar models for old galactic clusters

We present new evolutionary stellar models suitable for old Population I clusters, discussing both the consequences of the most recent improvements in the input physics and the effect of element diffusion within the stellar structures. Theoretical cluster isochrones are presented, covering the range of ages from 1 to 9 Gyr for the four selected choices of the metallicity Z = 0...

Relativistic effects on the solar radius

The high accuracy reached by solar limb observations, by helioseismic measurements and by Standard Solar Model (SSM) calculations suggests that general relativistic corrections must be included when discussing the solar radius. The Allen value (R⊙=695.99 ± 0.07 Mm) has to be reduced by 1.5 km. This correction, which is small compared with the present accuracy, should be kept in...

Updating standard solar models

-44100 Ferrara , Italy 1 Max-Planck Institut for Astrophysics, K. Schwarzschild Str. 1, D-85740 Garching bei Mu ̈nchen , Germany 2 Send o print requests to: S. Degl'Innocenti , Dipartimento di Fisica ... 6). Acknowledgements. We warmly thank V. Castellani and G. Fiorentini for their advice. F. Ciacio and B. Ricci are grateful to CNR for a fellowship. S. Degl'Innocenti and B. Ricci acknowledge the

Stellar models and Hyades: the Hipparcos test

We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed...

A pulsational approach to near-infrared and visual magnitudes of RR Lyr stars

In this paper, we present an improved theoretical scenario concerning near-infrared and visual magnitudes of RR Lyr variables, as based on up-to-date pulsating models. New relations connecting V and K absolute magnitudes with periods, mass, luminosity and metal content are discussed separately for fundamental and first-overtone pulsators. We also show that the V−K colours are...

Galactic models and white dwarf populations

We make use of a previous well-tested Galactic model, but describing the observational behaviour of the various stellar components in terms of suitable assumptions on their evolutionary status. In this way we are able to predict the expected distribution of Galactic white dwarfs (WDs), with results which appear in rather good agreement with recent estimates of the local WD...

Proton-induced lithium destruction cross-section and its astrophysical implications

Knowledge of the primordial nucleosynthesis offers a powerful tool to retrieve information on the baryon density of the Universe. In this context lithium isotopes play a crucial role and in particular we stress how important the bare nucleus cross-section for the 7Li(p, He reaction is. Recent application of the Trojan Horse Method led to an indirect measurement of that cross...