High-resolution elemental abundance analysis of the open cluster IC 4756
  We present detailed elemental abundances of 12 subgiants in the open cluster
IC 4756 including Na, Al, Mg, Si, Ca, Ti, Cr, Ni, Fe, Zn and Ba. We measure the
cluster to have [Fe/H] = -0.01 +/- 0.10. Most of the measured star-to-star
[X/H] abundance variation is below sigma < 0.03, as expected from a coeval
stellar population preserving natal abundance patterns, supporting the use of
elemental abundances as a probe to reconstruct dispersed clusters. We find
discrepancies between Cr I and Cr II abundances as well as between Ti I and Ti
II abundances, where the ionized abundances are larger by about 0.2 dex. This
follows other such studies which demonstrate the effects of overionization in
cool stars. IC 4756 are supersolar in Mg, Si, Na and Al, but are solar in the
other elements. The fact that IC 4756 is supersolar in some alpha-elements (Mg,
Si) but solar in the others (Ca, Ti) suggests that the production of
alpha-elements is not simply one dimensional and could be exploited for
chemical tagging.
