Nir J . Shaviv

Learn More
We construct a Galactic cosmic ray (CR) diffusion model. The CR flux reaching the Solar System should periodically increase each crossing of a Galactic spiral arm. We confirm this prediction in the CR exposure age record of iron meteorites. We find that although the geological evidence for the occurrence of iceage epochs in the past eon is not unequivocal,(More)
The short term variability of the Galactic cosmic ray flux (CRF) reaching Earth has been previously associated with variations in the global low altitude cloud cover. This CRF variability arises from changes in the solar wind strength. However, cosmic ray variability also arises intrinsically from variable activity of and motion through the Milky Way. Thus,(More)
We examine radiatively driven mass loss from stars near and above the Eddington limit. Building upon the standard CAK theory of driving by scattering in an ensemble of lines with a power-law distribution of opacity, we first show that the formal divergence of such line-driven mass loss as a star approaches the Eddington limit is actually limited by the(More)
X iv :a st ro -p h/ 98 05 12 1v 2 1 2 M ay 1 99 8 Solar Fusion Cross Sections Eric G. Adelberger Nuclear Physics Laboratory, University of Washington, Seattle, WA 98195 Sam M. Austin Department of Physics and Astronomy and NSCL, Michigan State University, East Lansing, MI 48824 John N. Bahcall School of Natural Sciences, Institute for Advanced Study,(More)
The Milky Way spiral arm dynamics is studied using the birth place of open clusters. We separately study the nearby spiral arms, and find evidence for multiple spiral sets. In particular, the Sagittarius-Carina arm appears to be a superposition of two sets. The first has a pattern speed of ΩP,Carina,1 = 16.5 +1.2 −1.4sys ± 1.1stat km sec −1 kpc, while the(More)
A new δ(18)O Phanerozoic database, based on 24,000 low-Mg calcitic fossil shells, yields a prominent 32 Ma oscillation with a secondary 175 Ma frequency modulation. The periodicities and phases of these oscillations are consistent with parameters postulated for the vertical motion of the solar system across the galactic plane, modulated by the radial(More)
We consider the eeective Eddington luminosity in a locally inhomogeneous medium by averaging out the coarse, small scale behavior. We show that the ratio between the emitted ux and the average radiation force changes. The mean luminosity can therefore theoretically exceed the classical Eddington limit. It is further shown that acoustic modes are unstable(More)
Atmospheres having a significant radiative support are shown to be intrinsically unstable at luminosities above a critical fraction Γcrit ≈ 0.5− 0.85 of the Eddington limit, with the exact value depending on the boundary conditions. Two different types of absolute radiation-hydrodynamic instabilities of acoustic waves are found to take place even in the(More)