The Red Giants EK Eri and OU And as Probable Descendents of Ap-stars: A Search for Abundance Anomalies

The red giants EK Eri and OU And, with magnetic fields B max =99 and 41 G, respectively, which presumably are descendents of magnetic Ap-stars, are studied. Their fundamental parameters are found and their chemical composition is analyzed. The abundances of 17 elements from lithium (Z=3) to hafnium (Z=72) are found for these giants, as well as for the comparison star βGem (Pollux). The abundance of nitrogen and the carbon isotope ratio 12 C/ 13 C are found using CN molecular lines. The low ratios 12 C/ 13 C=17.3 for EK Eri and 17.2 for βGem prove that these giants have passed through deep convective mixing in the First Dredge-Up (FDU) phase. For OU And, it was not possible to determine 12 C/ 13 C because of the relatively fast rotation and higher effective temperature of this star. but a high ratio N/C (higher than the sun by 1.1 dex) may serve to confirm that even this giant has also passed through an FDU phase. An analysis of the chemical composition led to an important conclusion: none of the three giants have any kinds of anomalies in the abundances of the heavy elements; in particular there are no excesses of any kind in the abundances of the rare-earth elements, which reach 4 dex in magnetic Ap-stars. The absence of such excesses may be a consequence of deep mixing during the FDU phase. In all three cases the abundances of carbon and nitrogen revealed the expected anomalies for stars of this type: a deficit of C from -0.3 to -0.6 dex and an excess of N from +0.3 to +0.6 dex. The theoretical prediction of a constant sum of C+N+O in the evolution process is confirmed: the combined abundance logε(C+N+O)=8.96-8.98 essentially coincides with the initial value of this quantity, specifically with the value of logε(C+N+O)=8.94 obtained for the sun and for early B-type MS stars. The Li 6707.76 Å line was detected in the spectra of all three stars, revealing a lithium abundance of logε(Li)=0.7-1.5; however, the presence of lithium in the atmospheres of giants that have passed through an FDU phase conflicts with the standard theory. Two of the observed phenomena that were unexpected for post-FDU giants, i.e., the existence of a magnetic field and the presence of lithium in the atmosphere, can be explained in terms of a single hypothesis: engulfment by a red giant of a planet with a mass several times that of Jupiter.