2016A&A...589A..27B

Context. Solar-analogue stars provide an excellent resource to study the Sun's evolution, i.e. the changes with time in stellar structure, activity, or rotation for solar-like stars. The unparalleled photometric data from the NASA space telescope Kepler allows us to study and characterise solar-like stars through asteroseismology.
Aims. We aim to spectroscopically investigate the fundamental parameter and chromospheric activity of solar analogues and twins, based on observations obtained with the HERMES spectrograph and combine them with asteroseismology. Therefore, we need to build a solar atlas for the spectrograph, to provide accurate calibrations of the spectroscopically determined abundances of solar- and late-type stars observed with this instrument and thus perform differential spectroscopic comparisons.
Methods. We acquire high-resolution and high signal-to-noise (S/N) spectroscopy to construct three solar reference spectra by observing the reflected light of the asteroids Vesta and Victoria and the jovian moon Europa (100<= S/N<= 450) with the HERMES spectrograph. We then observe the Kepler solar analogue KIC 3241581 (S/N∼170). For this star, the fundamental spectral parameters are extracted using a differential analysis. Sufficient S/N in the near ultraviolet allows us to investigate the chromospheric magnetic activity in both objects.
Results. We constructed three solar spectrum atlases from 385 to 900 nm, obtained with the HERMES spectrograph from observations of two bright asteroids and a jovian moon. A comparison between our solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent agreement. KIC 3241581 was found to be a long-periodic binary system. The fundamental parameter for the stellar primary component are T_eff=5689±11K, logg=4.385±0.005, [Fe/H]=+0.22±0.01, being in agreement with the published global seismic values, which confirms its status as solar analogue. The chromospheric activity level is compatible with the solar magnetic activity observed during 2014 and 2015.
Conclusions. Our solar atlas is an essential tool for the analysis of solar-like stars and to characterise solar analogues and twins with HERMES. The differential analysis, using the presented solar atlas from HERMES observations allows us to obtain the fundamental parameters with very high accuracy. KIC 3241581 is a metal-rich solar analogue with a solar-like activity level in a binary system of unknown period.