The growing interest in solar twins is motivated by the possibility of comparing them directly to the Sun .
To carry on this kind of analysis , we need to know their physical characteristics with precision .
Our first objective is to use asteroseismology and interferometry on the brightest of them : 18 Sco .
We observed the star during 12 nights with HARPS for seismology and used the PAVO beam-combiner at CHARA for interferometry .
An average large frequency separation 134.4 \pm 0.3 \mu Hz and angular and linear radiuses of 0.6759 \pm 0.0062 mas and 1.010 \pm 0.009 R _ { \odot } were estimated .
We used these values to derive the mass of the star , 1.02 \pm 0.03 M _ { \odot } .