3,383 research outputs found
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
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