The 71-second variation of DQ Herculis.

Photoelectric observations of the old nova DQ Her obtained at the Princeton University Observatory and Kitt Peak National Observatory have been used to determine an accurate period for the 71 variation. By using the autocorrelation technique and a least squares method we find the period in 1969 to be 718.06547 + 08.00002. This represents a significant change in the period since Walker's 1961 observations, as expected from the rate of period change we detected using data spanning the period 1967-1971. Allowing for the rate of period change, it has been possible to combine all the observations from 1954 to 1971 ( 10 cycles) to obtain accurate values of P and P and an estimate of P . We find that the period has been decreasing steadily on a time scale (P/P) of 2.64 >c 108 years; error or phase jitter as measured by the rms value of the (0 - C) timing is only 483 The extreme stability of the period compared with expected damping or evolutionary time scales makes plausible a rotational interpretation of the origin of the periodic light variations. Subject headings: novae - pulsation - stars, individual