LAUSR

Solar twins are stars of key importance to the field of astronomy and offer a multitude of science applications. Only a small number (≲ 200) of solar twins are known today, all of which are relatively close to our Sun (≲ 800 pc). The goal of our Survey for Distant Solar Twins (SDST) is to identify many more solar twin and solar analogue stars out to much larger distances (∼4 kpc). In this paper, we present a new method to identify solar twins using relatively low S/N, medium resolving power (R ∼ 28 000) spectra that will be typical of such distant targets observed with HERMES on the 3.9 m Anglo-Australian Telescope (AAT). We developed a novel approach, namely EPIC, to measure stellar parameters which we use to identify stars similar to our Sun. EPIC determines the stellar atmospheric parameters (effective temperature Teff, surface gravity log g and metallicity [Fe/H]) using differential equivalent width (EW) measurements of selected spectroscopic absorption features and a simple model, trained on previously analysed spectra, that connects these EWs to the stellar parameters. The reference for the EW measurements is a high S/N solar spectrum which is used to minimize several systematic effects. EPIC is fast, optimised for Sun-like stars and yields stellar parameter measurements with small enough uncertainties to enable spectroscopic identification of solar twin and analogue stars up to ∼4 kpc away using AAT/HERMES, i.e. σ(Teff, log g, [Fe/H]) = (50 K, 0.08 dex, 0.03 dex) on average at S/N = 25.