Improving the surface brightness-color relation for early-type stars using optical interferometry

Results. We determined the uniform disk angular diameter for the eight following stars: γ Ori, ζ Per, 8 Cyg, i{dotless} Her, λ Aql, ζ Peg, γ Lyr, and δ Cyg with V - K color ranging from -0.70 to 0.02 and typical precision of about 1.5%. Using our total sample of 132 stars with V - K colors index ranging from about - 1 to 4, we provide a revised SBC relation. For late-type stars (0 ≤ V - K ≤ 4), the results are consistent with previous studies. For early-type stars (- 1 ≤ V - K ≤ 0), our new VEGA/CHARA measurements combined with a careful selection of the stars (rejecting stars with environment or stars with a strong variability), allows us to reach an unprecedented precision of about 0.16 magnitude or ≃7% in terms of angular diameter.