Beryllium enhancement as evidence for accretion in a lithium-rich F dwarf

The early F dwarf star 'J37' in the open cluster NGC 6633 shows an unusual pattern of photospheric abundances, including an order-of-magnitude enhancement of lithium and iron-peak elements, but an under-abundance of carbon. As a consequence of its thin convection zone these anomalies have been attributed to either radiative diffusion or the accretion of hydrogen-depleted material. By comparing high-resolution Very Large Telescope/ UV-Visual Echelle Spectrograph spectra of J37 (and other F stars in NGC 6633) with syntheses of the Be II doublet region at 3131 angstrom, we establish that J37 also has a Be abundance [A(Be) = 3.0 +/- 0.5] that is at least 10 times the cosmic value. This contradicts radiative diffusion models that produce a Li over-abundance, as they also predict photospheric Be depletion. Instead, since Be is a highly refractory element, it supports the notion that J37 is the first clear example of a star that has accreted volatile-depleted material with a composition similar to chondritic meteorites, although some diffusion may be necessary to explain the low C and O abundances.