On the reactions p + p -> p + Lambda + K^+ and p + p -> p + Sigma^0 + K^+ near thresholds

The cross sections for the reactions of the strange production p + p -> p + Lambda + K^+ and p + p -> p + Sigma^0 + K^+ near thresholds of the final states p Lambda K^+ and p Sigma^0 K^+ are calculated in the effective Lagrangian approach. Our approach is based on the dominant contribution of the one-pion exchange and strong interaction of the colliding protons in the initial state. The theoretical values of the cross sections agree reasonably well with the experimental data. The polarization properties of the Lambda and Sigma^0 hyperons are discussed.Comment: 15 pages, 1 Postscript figure, Latex, to appear in Eur. Phys. J

The Pulsation Mode and Distance of the Cepheid FF Aquilae

The determination of pulsation mode and distance for field Cepheids is a complicated problem best resolved by a luminosity estimate. For illustration a technique based on spectroscopic luminosity discrimination is applied to the 4.47d s-Cepheid FF Aql. Line ratios in high dispersion spectra of the variable yield values of =-3.40+-0.02 s.e.(+-0.04 s.d.), average effective temperature Teff=6195+-24 K, and intrinsic color (-)o = +0.506+-0.007, corresponding to a reddening of E(B-V)=0.25+-0.01, or E(B-V)(B0)=0.26+-0.01. The skewed light curve, intrinsic color, and luminosity of FF Aql are consistent with fundamental mode pulsation for a small amplitude classical Cepheid on the blue side of the instability strip, not a sinusoidal pulsator. A distance of 413+-14 pc is estimated from the Cepheid's angular diameter in conjunction with a mean radius of =39.0+-0.7 Rsun inferred from its luminosity and effective temperature. The dust extinction towards FF Aql is described by a ratio of total-to-selective extinction of Rv=Av/E(B-V)=3.16+-0.34 according to the star's apparent distance modulus.Comment: To appear in ApJ