The J=2-l, v=0 emissions of 2 8 SiO, 2 , SiO, and 3 0 SiO from three late-type stars were simultaneously observed with the Nobeyama 45-m telescope in Jaunuary 1987. The relative intensities of ( 2 *SiO ] / ( 30 SiO ) were measured to be 2.4 for X Cyg, 1.5 for NML Tau, and 2.9 for Villi Oph. These values are lower limits for the relative isotope abundance of ( 2 , S i ] / ( 3 0 S i ) , and are larger than the terrestrial value of 1.51. Recent theoretical studies suggest that hydrostatic

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... nthesis and supernova explosions result in smaller values of ( 2 , S n / ( 3 0 S i ) than solar. These models cannot explain the observed excess of 2 , S i .