Isotopic abundances of silicon in four red giants

High-resolution spectra of Beta Peg, Omicron1 Ori, 10 Dra, and HR 1105 are analyzed in order to estimate Si-28/Si-29 and Si-28/Si-30 abundance ratios. The elimination of the Fourier Transform Spectrometer ripple, telluric N2O absorption, and the detector noise from the observations is discussed. The various methods used to derive the Si-28 and Si-29 abundance ratios are described. The equivalent and half widths of a number of strong and weak Si-28O lines, and the microturbulent and macroturbulent velocities of the Si-28O line are measured. The nucleosynthesis of Si-29 and Si-30 is examined. It is observed that the Si-28/Si-29 ratio is within 20 to 25 percent of the terrestrial ratio of 20 in Beta Peg and HR 1105, but that Si-29 is underabundant in 10 Dra and Omicron1 Ori; and Si-30 is underabundant in all four stars with respect to the terrestrial ratio of 30. (I.F.)