The discovery of anomalously high levels of [Si/Fe] among metal-poor giants in the bulge, disk, and halo of the Milky Way

Here, we report the discovery of a unique collection of giants, that exhibit anomalously high levels of [Si/Fe] and [Al/Fe] without noticeable carbon and nitrogen enhancement, clearly above typical Galactic levels, distinguishable from dwarf galaxypopulations in most chemical elements; their distinction is less apparent among other light-elements such as N and Mg. The newly identified mildly metal-poor sample's [Si/Fe] appear definitively anomalous, having a spread in [Si/Fe] from around $+0.6$ to $+1.1$ dex, compared with Galactic [Si/Fe]$<+0.5$. We confirm that most of the chemically anomalous Si-rich stars are on tight halo-like orbits passing through the bulge, similar to those found in other studies. Their chemical composition is, in general, similar to typical globular clusterstars with extreme abundance, although several differences exist. Furthermore, we did not detect any variation of the radial velocities that would support the binary hypothesis in this unique sample. Thus, the high aluminum and silicon abundances, and enhancements in their \textit{ s}- processelements relative to Solar abundance ratios, could be due to formation from gas that was already strongly enriched by SNe II.