1999PASP..111..482S

The chemically peculiar stars that inhabit the upper main sequence exhibit very extreme enhancements and deficiencies of several elements. In all likelihood, the primary cause of these anomalies is radiatively driven diffusion, although other mechanisms may also be important–such as mass loss and various kinds of mixing. Only by examining as many elements as possible will a cohesive theory explaining these abundance oddities materialize. To this end, we present high-resolution (R~62,500), high signal-to-noise ratio (S/N pixel^–1~120) observations of the 6708 Å Li I resonance doublet in a pair of Hg-Mn stars. No record of a lithium detection has been found for this type of chemically peculiar star. The atmospheres of the two program stars (HR 6158=28 Her=HD 149212; HR 8915=69 Peg=HD 220933) contain an inordinate amount of beryllium (Be); in fact, the Be abundances in these stars are among the highest known. While the LTE concentration of Be is several thousand times larger than cosmic {lsqb}A(Be)_i~1.27{rsqb} in both stars, lithium (Li) is detected in neither HR 6158 nor HR 8915. The calculated 3 σ (99{percnt} confidence level) upper limits place the maximum Li enhancements at 50 times and 80 times cosmic {lsqb}A(Li)_i~3.23{rsqb} for HR 6158 and HR 8915, respectively, or ~100 times smaller than the Be overabundances. These Li upper limits, which argue against a ``nucleosynthesis'' origin for the Be surfeit, provide yet another means of constraining the physical process (or processes) responsible for the Hg-Mn phenomenon in some A stars.