alpha :a constant that is not a constant?

We review the observational information on the constancy of the fine structure constant alpha. We find that small improvements on the measurement of ^{187}Re lifetime can provide significant progress in exploring the range of variability suggested by QSO data. We also discuss the effects of a time varying alpha on stellar structure and evolution. We find that radioactive dating of ancient stars can offer a new observational window.Comment: 9 pages with 3 ps figures included, to appear on the Proc. of ESO-CERN-ESA Symposium on Astronomy, Cosmology and Fundamental Physics, Garching bei Munchen, Germany March 4-7, 200

Helioseismic tests of diffusion theory

We present a quantitative estimate of the accuracy of the calculated diffusion coefficients, by comparing predictions of solar models with observational data provided by helioseismology. By taking into account the major uncertainties in building solar models we conclude that helioseismology confirms the diffusion efficiency adopted in SSM calculations, to the 10% level.Comment: 5 pages with 1 ps figure included, LaTeX file with l-aa.sty, submitted to Astronomy and Astrophysic

Bounds on hep neutrinos

The excess of highest energy solar-neutrino events recently observed by Superkamiokande can be in principle explained by anomalously high $hep$-neutrino flux $\Phi_{\nu}(hep)$. Without using SSM calculations, from the solar luminosity constraint we derive that $\Phi_\nu(hep)/S_{13}$ cannot exceed the SSM estimate by more than a factor three. If one makes the additional hypothesis that $hep$ neutrino production occurs where the $^3$He concentration is at equilibrium, helioseismology gives an upper bound which is (less then) two times the SSM prediction. We argue that the anomalous $hep$-neutrino flux of order of that observed by Superkamiokande cannot be explained by astrophysics, but rather by a large production cross-section.Comment: 7 pages, RevTeX fil

Helioseismology and the solar age

The problem of measuring the solar age by means of helioseismology hasbeen recently revisited by Guenther & Demarque (1997) and by Weiss & Schlattl (1998). Different best values for $t_{\rm seis}$ and different assessment of the uncertainty resulted from these two works. We show that depending on the way seismic data are used, one may obtain the value $t_{\rm seis}\approx 4.6$ Gy, close to the age of the oldest meteorites, $t_{\rm met}=4.57$ Gy, like in the first paper, or above 5 Gy like in the second paper. The discrepancy in the seismic estimates of the solar age may be eliminated by assuming higher than the standard metal abundance and/or an upward revision of the opacities in the solar radiative interior.We argue that the most accurate and robust seismic measure of the solar age are the small frequency separations, $D_{\ell,n}=\nu_{l,n}-\nu_{\ell+1,n-1}$, for spherical harmonic degrees $\ell=0,2$ and radial orders $n\gg\ell$.The seismic age inferred by minimization of the sum of squared differences between the model and the solar small separations is $t_{\rm seis}=4.66\pm0.11$, a number consistent with meteoritic data.Our analysis supports earlier suggestions of using small frequency separations as stellar age indicators.Comment: 8 pages + 4 ps figures included, LaTeX file with l-aa.sty, submitted to Astronomy and Astrophysic

Helioseismology and solar neutrinos: an update

We review recent advances concerning helioseismology, solar models and solar neutrinos. Particularly we address the following points: i) helioseismic tests of recent SSMs; ii) predictions of the Beryllium neutrino flux based on helioseismology; iii) helioseismic tests regarding the screening of nuclear reactions in the Sun.Comment: 7 pages with 6 eps figure included, LaTeX file with espcrc2.sty, to appear on the Proceedings of "EuroConference on Frontiers in Particle Astrophysics and Cosmology", San Feliu de Guixols, Spain, 30 September -5 October 200