1913 20160701171655.0 10.1007/BF00640694 DOI ASTROimport-70 Denoyelle, J. 1990 Main-sequence broadening in the double cluster H and Chi Persei Precise photometric observations of stars in the double cluster h and Chi Persei reveal a large spread in the colors and magnitudes of the upper main sequence; half of the stars are variables that are Be stars or related stars. The reported age difference between both clusters is found to be spurious. Rotation apparently affects both the intrinsic and the observed colors of the early-type stars in h and Chi Persei. This result questions the validity of photometric calibrations that heavily rely on h and Chi Persei or similar clusters. Waelkens, C. Cuypers, J. Degryse, K. Heynderickx, D. Lampens, P. Poedts, S. Polfliet, R. Rufener, F. Smeyers, P. Astrophysics and Space Science 169 1990 109-111 http://esoads.eso.org/abs/1990Ap%26SS.169..109D published in REFERD