Atomic data from the Iron Project.XLIV. Transition probabilities and line ratios for Fe VI with fluorescent excitation in planetary nebulae

Relativistic atomic structure calculations for electric dipole E1, electric quadrupole E2 and magnetic dipole M1 transition probabilities among the first 80 fine-structure levels of Fe VI, dominated by configurations 3d^3, 3d^24s, and 3d^24p, are carried out using the Breit-Pauli version of the code Superstructure. Experimental energies are used to improve the accuracy of these transition probabilities. Employing the 80-level collision-radiative (CR) model with these dipole and forbidden transition probabilities, and Iron Project R-matrix collisional data, we present a number of [Fe VI] line ratios applicable to spectral diagnostics of photoionized H II regions. It is shown that continuum fluorescent excitation needs to be considered in CR models in order to interpret the observed line ratios of optical [Fe VI] lines in planetary nebulae NGC 6741, IC 351, and NGC 7662. The analysis leads to parametrization of line ratios as function of, and as constraints on, the electron density and temperature, as well as the effective radiation temperature of the central source and a geometrical dilution factor. The spectral diagnostics may also help ascertain observational uncertainties. The method may be generally applicable to other objects with intensive background radiation fields, such as novae and active galactic nuclei. The extensive new Iron Project radiative and collisional calculations enable a consistent analysis of many line ratios for the complex iron ions.Comment: 25 pages, 8 figures, submitted to Astron.Astrophys. Suppl.Se

Minijet-associated Dilepton Production in Ultrarelativistic Heavy Ion Collisions

Dilepton production associated with minijets is calculated in ultrarelativistic heavy ion collisions using the first order approximation of the dilepton fragmentation functions of quarks and gluons. The full QCD evolution of the fragmentation functions is also studied. We find that the dilepton pairs from the fragmentation of minijets are comparable to direct Drell-Yan at $\sqrt{s}=200$ AGeV for small dilepton invariant mass $M\sim$ 1-2 GeV/c$^2$ while dominant over a large range of mass at $\sqrt{s}=6400$ AGeV.Comment: 23 pages in RevTex, 5 figures in uuencoded files, LBL-3440

Bose-Einstein condensation in an optical lattice

In this paper we develop an analytic expression for the critical temperature for a gas of ideal bosons in a combined harmonic lattice potential, relevant to current experiments using optical lattices. We give corrections to the critical temperature arising from effective mass modifications of the low energy spectrum, finite size effects and excited band states. We compute the critical temperature using numerical methods and compare to our analytic result. We study condensation in an optical lattice over a wide parameter regime and demonstrate that the critical temperature can be increased or reduced relative to the purely harmonic case by adjusting the harmonic trap frequency. We show that a simple numerical procedure based on a piecewise analytic density of states provides an accurate prediction for the critical temperature.Comment: 10 pages, 5 figure