Three-Color Photometry of DY Herculis.

Over one thousand U, B, V observations were secured in the spring of 1959 for the short-period variable DY Herculis The variation in light for this star appears to be quite regular and repetitive, and no confirmation is obtained for suggested irregularities The colors and their variation are in fair agreement with those of Fitch and suggest a spectral range of AS-Fl after a reasonable estimate of reddening This range is close to that based on actual spectral types estimated by Bonsack At maximum light the star reaches V = 10 15, B - V = 0 29, U - B = 0 14, while at minimum the values are V = 10 65, B - V = 0.45, U - B = 0 14. The greatest range of variation is found in the blue and ultraviolet. A discussion of all available data suggests that the period has been essentially constant since 1950, and all observations since then are adequately described by the relation Max (helio.) = JD2433439 4871 + 0 14863127E. Serious departures of Soloviev's and Tsesevitch's earlier observations from this relation were investigated, and the data seem insufficient to clarify whether the period was different between 1936 and 1950, whether their times are in error, or whether the period is subject to continual change Neither Wesselink's or Baade's method of determining the radius is satisfactory for DY Her, although a somewhat uncertain value of 106 km is suggested by the latter. This value, together with an estimate of 2 X 106 km derived from Woltjer's work, leads to a tentative value of 1 5 X 106 km A median absolute visual magnitude, M , of about 2 1 is derived If the empirical mass luminosity holds, the pulsation constant, Q, is about 0067 day