Is U Aquarii a Thorne-Zytkow object?

The R Coronae Borealis (RCB) star U Aqr was known to show an unusual abunda nce pattern with respect to the post-iron peak elements. The abundances of elements in the light s-process peak-Rb, Sr, Y, and Zr-are greatly enhanced , whereas elements representative of the heavy s-process peak, such as Ba, do not exhibit large abundance enhancements. Recent calculations of the abu ndances of elements formed by rapid proton capture in Thorne-Zytkow objects indicate that qualitatively the abundance pattern of post-iron peak elemen ts in Thorne-Zytkow objects appeared to match that observed in U Aqr. New h igh-resolution spectra of U Aqr and two other stars are used to explore the possibility that U Aqr is a Thorne-Zytkow object. Our spectra show that on the basis of the light s-process elements, in particular the absence of an enhancement of Mo, Cu, and Zn, it does not appear that U Aqr is a good can didate for a Thorne-Zytkow object. However, the light s-process abundance p attern resembles that of Sakurai's star that has recently begun to show RCB characteristics. We suggest that these stars represent a possible source f or the "weak" component of the solar system a-process distribution of heavy elements.