Apsidal motion and the third-body problem in the binary HS Her

Our analysis of a 22-year uniform series of photoelectric UBV measurements of HS Her, started in 1969 - 1983 by D. Ya. Martynov and completed by us in 1984 - 1991, enabled us to determine new times of minima and revise some times of minima published earlier. Combined with other published data, this information can be used to improve the system's apsidal elements: U-obs = (89.7 +/- 5.1) years and log (k) over bar (obs)(2) = - 2.33( 4), testifying to a somewhat stronger concentration of matter towards the center than is predicted by current models for main-sequence stars ( log (k) over bar (th)(2)= -2.21). This provides additional evidence that the system's secondary is at the pre-main-sequence stage of evolution, as we suggested earlier based on our analysis of the system's photometric elements. We confirm the presence of a third body in the system in a long-period eccentric orbit, as was first suggested in 2002 by Wolf et al. However, in contrast to the results of that paper, we demonstrate that the currently available observational data are insufficient to reliably determine this orbit's parameters. We estimate the mass of the third body to be M-3 = (1.0-2.0) M-. for M-1 = 5M(.) and M-2 = 1.6 M-..