John N. Bahcall

Solar Models: Current Epoch and Time Dependences, Neutrinos, and Helioseismological Properties

We calculate accurate solar models and report the detailed time dependences of important solar quantities. We use helioseismology to constrain the luminosity evolution of the Sun and report the discovery of semiconvection in evolved solar models that include diffusion. In addition, we compare the computed sound speeds with the results of p-mode observations by BiSON, GOLF, GONG, LOWL, and MDI instruments. We contrast the neutrino predictions from a set of eight standard-like solar models and four deviant (or deficient) solar models with the results of solar neutrino experiments. For solar neutrino and helioseismological applications, we present present-epoch numerical tabulations of characteristics of the standard solar model as a function of solar radius, including the principal physical and composition variables, sound speeds, neutrino fluxes, and functions needed for calculating solar neutrino oscillations.

The universe at faint magnitudes. I - Models for the galaxy and the predicted star counts

A detailed model is constructed for the disk and spheroid components of the Galaxy from which the distribution of visible stars and mass in the Galaxy is calculated. The application of star counts to the determination of galactic structure parameters is demonstrated. The possibility of detecting a halo component with the aid of star counts is also investigated quantitatively.

High-energy neutrinos from cosmological gamma-ray burst fireballs

Observations suggest that {gamma}-ray bursts (GRBs) are produced by the dissipation of the kinetic energy of a relativistic fireball. We show that a large fraction, {ge}10{percent}, of the fireball energy is expected to be converted by photomeson production to a burst of {approximately}10{sup 14}eV neutrinos. A km{sup 2} neutrino detector would observe at least several tens of events per year correlated with GRBs, and test for neutrino properties (e.g., flavor oscillations, for which upward moving {tau}{close_quote}s would be a unique signature, and coupling to gravity) with an accuracy many orders of magnitude better than is currently possible. {copyright} {ital 1997} {ital The American Physical Society}

Solar models with helium and heavy element diffusion

Helium and heavy-element diffusion are both included in precise calculations of solar models. In addition, improvements in the input data for solar interior models are described for nuclear reaction rates, the solar luminosity, the solar age, heavy-element abundances, radiative opacities, helium and metal diffusion rates, and neutrino interaction cross sections. The effects on the neutrino fluxes of each change in the input physics are evaluated separately by constructing a series of solar models with one additional improvement added at each stage. The effective 1 σ uncertainties in the individual input quantities are estimated and used to evaluate the uncertainties in the calculated neutrino fluxes and the calculated event rates for solar neutrino experiments. The calculated neutrino event rates, including all of the improvements, are 9.3-1.4+1.2 SNU for the 37Cl experiment and 137-7+8 SNU for the 71Ga experiments. The calculated flux of 7Be neutrinos is 5.1 (1.00-0.07+0.06)×10^9 cm^-2 s^-1 and the flux of 8B neutrinos is 6.6(1.00-0.17+0.14)×10^6 cm^-2 s^-1. The primordial helium abundance found for this model is Y=0.278. The present-day surface abundance of the model is Ys=0.247, in agreement with the helioseismological measurement of Ys=0.242±0.003 determined by Hernandez and Christensen-Dalsgaard (1994). The computed depth of the convective zone is R=0.712R⊙, in agreement with the observed value determined from p-mode oscillation data of R=0.713±0.003R⊙ found by Christensen-Dalsgaard et al. (1991). Although the present results increase the predicted event rate in the four operating solar neutrino experiments by almost 1 σ (theoretical uncertainty), they only slightly increase the difficulty of explaining the existing experiments with standard physics (i.e., by assuming that nothing happens to the neutrinos after they are created in the center of the sun). For an extreme model in which all diffusion (helium and heavy-element diffusion) is neglected, the event rates are 7.0-1.0+0.9 SNU for the 37Cl experiment and 126-6+6 SNU for the 71Ga experiments, while the 7Be and 8B neutrino fluxes are, respectively, 4.5(1.00-0.07+0.06)×10^9 cm^-2 s^-1 and 4.9(1.00-0.17+0.14)×10^6 cm^-2 s^-1. For the no-diffusion model, the computed value of the depth of the convective zone is R=0.726R⊙, which disagrees with the observed helioseismological value. The calculated surface abundance of helium, Ys=0.268, is also in disagreement with the p-mode measurement. The authors conclude that helioseismology provides strong evidence for element diffusion and therefore for the somewhat larger solar neutrino event rates calculated in this paper.

High-energy neutrinos from astrophysical sources: An Upper bound

We show that cosmic-ray observations set a model-independent upper bound of

Hubble Space Telescope Images of a Sample of 20 Nearby Luminous Quasars

{E}_{\ensuremath{\nu}}^{2}{\ensuremath{\Phi}}_{\ensuremath{\nu}}l2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}{\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{c}\mathrm{m}}^{2}\mathrm{}\mathrm{s}\mathrm{}\mathrm{sr}

Solar fusion cross-sections

to the intensity of high-energy neutrinos produced by photo-meson (or

Hubble Space Telescope Images of a Sample of Twenty Nearby Luminous Quasars

p\ensuremath{-}p)

Element Diffusion in the Solar Interior

interactions in sources of size not much larger than the proton photo-meson (or

New Solar Opacities, Abundances, Helioseismology, and Neutrino Fluxes

p\ensuremath{-}p)