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We show that present experiments imply that neutrinos are nonstandard at the 87\% C.L., independently of solar or nuclear physics. Moreover, if neutrinos are standard, the $^7$Be flux must be almost zero. Even if we arbitrarily disregard one of the experiments, the neutrino flux must still be less than half of the value predicted by standard solar models., 8 pages in RevTeX 3.0 plus 2 figures in uuencoded postscript files. Full postscript version available via anonymous ftp from risc0.ca.infn.it:/pub/private/lissia/infnfe-10-94.ps (192.84.132.4) Submitted to Physics Letters B

The GALLEX result, together with the constraints from the observed value o f the solar constant, yields strong limits on the flux of neutrinos from the pp-I termination of the pp-chain, 62⩽ φ pp+pep [10 9 cm −2 s −1 ] ⩽65 , provided that neutrinos are standard. This conclusion is essentially independent of solar models and it implies that the pp-chain is shifted towards the pp-I termination, in comparison with the SSM predictions. As a consequence, we derive an upper bound on Berillium neutrinos: φ Be ⩽3×10 9 cm −2 s −1 , the violation of this bound being a clear signal of non-standard neutrino properties. We also find that, for a large class of solar models built so as to enhance the pp-I termination, the pep-neutrino flux is stable around φ pep ≈ 1.5×10 8 cm −2 s −1 . Detection of pep neutrinos will clearly discriminate standard neutrinos against MSW oscillations, this latter model giving φ MSW pep ⩽3×10 7 cm −2 s −1 .

For standard neutrinos, recent solar neutrino results together with the assumption of a nuclearly powered Sun imply severe constraints on the individual components of the total neutrino flux: \Phi_{Be}, Comment: 20 pages in RevTeX 3.0 plus 14 figures in uuencoded postscript files

The high accuracy reached by solar limb observations, by helioseismic measurements and by Standard Solar Models (SSMs) calculations suggests that general relativity corrections are included when discussing the solar radius. The Allen value (R$_{\odot}$ = 695.99 $\pm$ 0.07 Mm) has to be reduced by 1.5 Km. This correction, which is small as compared with present accuracy, should be kept in mind for future more precise measurements and/or calculations.

We discuss implications of a new measurement of $^{14}N(p, \gamma)^{15}O$ concerning solar neutrinos, solar models and globular cluster dating. Predictions for the gallium and chlorine experiments are reduced by 2 and 0.1 SNU respectively. Predictions for helioseismic observables are unchanged within uncertainties. The age of globular clusters as deduced from the Turn-Off luminosity is increased by about 0.7 Gyr., Comment: 15 pages, 7 ps figures included, revtex style

Zero Age Main Sequence (ZAMS) models with updated physical inputs are presented for selected assumptions about the chemical composition, covering the ranges 0.6 < M/Mo < 1.2, 0.0001 < Z < 0.04, 0.23 < Y < 0.34.The HR diagram location of the ZAMS as a function of Y and Z is discussed both in the theoretical and in the observational HR diagrams, showing that the V magnitude presents an increased dependence on Z to be taken into account when discussing observational evidences. Analytical relations quantifying both these dependences are derived. Implications for the galactic helium to heavier elements enrichment are finally discussed., 4 pages, 4 postscript figures, accepted for publication on Astronomy & Astrophysics

The Gaia-ESO Survey provides the largest database of homogeneously-determined lithium abundances and stellar parameters for open star clusters of different age and metallicity. It is therefore well suited to investigate young stellar evolution and to provide independent age estimates in young clusters. We present the lithium results for a sample of young clusters of ages between 10 and 100 Myr, and compare the observed lithium depletion patterns with models of lithium depletion in pre-main sequence stars.

We present deep and accurate optical photometry of the Local Group starburst galaxy IC10. The photometry is based on two sets of images collected with the Advanced Camera for Surveys and with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We provide new estimates of the Red Giant Branch tip (TRGB) magnitude, m_{F814W}^{TRGB}=21.90+-0.03, and of the reddening, E(B-V)=0.78+-0.06, using field stars in the Small Magellanic Cloud (SMC) as a reference. Adopting the SMC and two globulars, Omega Centauri and 47 Tucanae, as references we estimate the distance modulus to IC10: independent calibrations give weighted average distances of mu=24.51+-0.08 (TRGB) and mu=24.56+-0.08 (RR Lyrae). We also provide a new theoretical calibration for the TRGB luminosity, and using these predictions we find a very similar distance to IC10 (mu~24.60+-0.15). These results suggest that IC10 is a likely member of the M31 subgroup., Comment: 4 pages, 4 figures, ApJ Letters accepted

This paper deals with theoretical predictions for He burning models in a range of masses covering the so-called Red Giant Branch phase transition. Taking as a guideline the observational constraints given by Hipparcos parallaxes to the predicted luminosity of models originated from Red Giant progenitors with He core undergoing electron degeneracy, we compare models by various authors as recently appeared in the literature, disclosing sensitive differences in the predicted luminosity. The solidity of these theoretical predictions is investigated by exploring the effects of varying the assumptions about the efficiency of core overshooting or the amount of mass loss, giving quantitative estimates of the related uncertainties. However, one finds that theoretical predictions concerning the luminosity of the red giant clump in the Hipparcos sample is scarcely affected by these mechanisms.A comparison among theoretical predictions as recently given by different authors convincingly demonstrates that the different luminosity predictions are the natural results of evolutionary codes with different - but all reasonable- input physics. In this context observations suggests that stellar models based on the most updated input physics are possibly overestimating the luminosity of these structures, raising doubts on several current predictions concerning the luminosity of HB stars in galactic globulars., Comment: 8 pages, 7 postscript figures, accepted for publication on Astronomy and Astrophysics

This paper develops a method for obtaining the star formation histories of a mixed, resolved population through the use of color-magnitude diagrams (CMDs). The method provides insight into the local star formation rate, analyzing the observations of the Hipparcos satellite through a comparison with synthetic CMDs computed for different histories with an updated stellar evolution library. Parallax and photometric uncertainties are included explicitly and corrected using the Bayesian Richardson-Lucy algorithm. We first describe our verification studies using artificial data sets. From this sensitivity study, the critical factors determining the success of a recovery for a known star formation rate are a partial knowledge of the IMF and the age-metallicity relation, and sample contamination by clusters and moving groups (special populations whose histories are different than that of the whole sample). Unresolved binaries are less important impediments. We highlight how these limit the method. For the real field sample, complete to Mv < 3.5, we find that the solar neighborhood star formation rate has a characteristic timescale for variation of about 6 Gyr, with a maximum activity close to 3 Gyr ago. The similarity of this finding with column integrated star formation rates may indicate a global origin, possibly a collision with a satellite galaxy. We also discuss applications of this technique to general photometric surveys of other complex systems (e.g. Local Group dwarf galaxies) where the distances are well known., Accepted for publication in Astronomy and Astrophysics

We present U, B, V, I (SUSI@NTT) and J,Ks (SOFI@NTT) photometry of the Large Magellanic Cloud (LMC) cluster Reticulum. The observing strategy and data reduction (DAOPHOTII/ALLFRAME) allowed us to reach an accuracy of the order of 0.01 – 0.03 mag in all the bands at limiting magnitudes typical of RR Lyrae stars. Reticulum hosts a sizable sample of RR Lyrae stars (32), and we supply an accurate distance estimate using the RR Lyrae K-band Period-Luminosity-Metallicity (PLZK) relation. This method presents several advantages when compared with the MV vs [Fe/H] relation, since it is only marginally affected by off-ZAHB evolutionary effects and reddening corrections.

This paper discusses low mass, metal poor stars, presenting new evolutionary computations which take into account the inward diffusion of both He and heavy elements during the H burning phase. The investigation has been extended to He burning models, discussing the luminosity of the Zero Age Horizontal Branch (ZAHB) models originated from progenitors with efficient element diffusion. We find that diffusion of heavy elements plays a non-negligible role in the evolutionary paths of the model. One finds that element diffusion has a sensitive influence on evolutionary models, a less significant effect on the isochrone turn off and, finally, a rather marginal impact on the difference in luminosity between the ZAHB and the isochrone Turn-Off (TO). The consequences of these results on current evaluations of globular cluster ages are discussed in connection with possible sources of errors., 15 pages, Tex, 3 latex tables, postscript figures, in publication on Astronomy and Astrophysics

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 on the metallicity Z= 0.007, 0.010, 0.015 and 0.020. Theoretical uncertainties on the efficiency of superadiabatic convection are discussed in some details. Isochrone fitting to the CM diagrams of the two well observed galactic clusters NGC2420 and M67 indicates that a mixing length parameter alpha = 1.9 appears adequate for reproducing the observed color of cool giant stars. The problems in matching theoretical preditions to the observed slope of MS stars are discussed., Comment: 7 pages, 14 postscript figures, accepted for publication on MNRAS