X Persei

J. D. Dorren, Biruni Observatory; and E. F. Guinan and G. P. McCook, Villanova Observatory, write: "Photoelectric observations of X Per obtained at Biruni and Villanova Observatories, when combined with other photoelectric data back to 1964, show that the star has undergone three light increases of ~ 0.6 magnitude at 6-yr intervals. Earlier visual observations made by Kempf and Muller (1916, Astron. Nachr. 202, 330) also suggest the same pattern with a somewhat longer ~ 7-yr period. The last maximum (V = 6.33) occurred during early 1978. Between 1974 Apr. and 1977 Mar. the star remained nearly constant at V = 6.70. Our most recent observation (1979 Apr. 7.03 UT, V = 6.77) suggests that the brightness is still declining. This is the faintest the star has been since 1904, when it fell to magnitude 6.90. If the light changes behave as in the past, we expect the decline in light to continue until the end of 1979 and then level off near V = 6.9, remaining at this level for 3 yr before undergoing another light increase. There appears to be a similarity between the photometric behavior of X Per and symbiotic stars as well as slow recurrent novae. The major photometric, spectroscopic and x-ray data appear to be consistent with a binary system with an O9V primary and a neutron-star companion in an orbit of period ~ 581 days."