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SkyMapper Protected Science Project

Super-metal rich stars in the solar neighbourhood

Martin Asplund (RSAA), Luca Casagrande (RSAA), David Nataf (RSAA), Jane Lin (RSAA)

How metal-rich can stars become? In the solar neighbourhood there are frequent claims that some stars have as high [Fe/H] as +0.5 or even higher. Such extremely high metallicities in even quite old stars is very difficult to explain given that the present-day interstellar medium only has solar metallicity. One possibility is that these stars have migrated radially from the inner Galactic disk or even the bulge due to transient interactions with spiral arms or the bar. These stars thus trace a critical, until recently overlooked, process for understanding the evolution of galaxies like the Milky Way. Super-metal rich stars are readily identifiable through their SkyMapper colours and we intend to compile a complete census of such stars in the solar neighbourhood. These will be observed spectroscopically both with GALAH and dedicated programs with HERMES/AAT and other telescopes, including high-resolution infrared spectroscopy (the optical spectra of these metal-rich stars are severely blended, making an accurate analysis difficult while the infrared regions contain numerous clean lines for parameter and abundance purposes). We will also investigate the possibility of using SkyMapper colours to identify alpha-enhanced metal-rich stars that may have a particular origin distinct from other metal-rich stars. Identifying metal-rich stars is helpful to guide exoplanet searches as the frequency of close-in giant planets increase rapidly with stellar metallicity.