Light element discontinuities in NGC 6402

Therefore, we obtained radial velocities and/or chemical abundances of 11 elements for 41 red giant branch stars using high resolution spectra obtained with the Magellan-M2FS instrument. We find NGC 6402 to be only moderately metal-poor with <[Fe/H]>=-1.13dex ({sigma}=0.05 dex) and to have a mean heliocentric radial velocity of -61.1km/s ({sigma}=8.5km/s).

In general, NGC 6402 exhibits mean composition properties that are similar to other inner Galaxy clusters, such as [{alpha}/Fe]~+0.3dex, [Cr,Ni/Fe]~0.0dex, and <[La/Eu]>=-0.08dex. Similarly, we find large star-to-star abundance variations for O, Na, Mg, Al, and Si that are indicative of gas that experienced high temperature proton-capture burning. Interestingly, we not only detect three distinct populations but also find large gaps in the [O/Fe], [Na/Fe], and [Al/Fe] distributions that may provide the first direct evidence of delayed formation for intermediate composition stars.