Infrared spectroscopy of symbiotic stars. II. Orbits for five S-type systems with two-year periods

Infrared radial velocities have been used to determine orbital elements for the cool giants of five well-known symbiotic systems, Z And, AG Dra, V443 Her, AX Per, and FG Ser, all of which have orbital periods near the two-yea r mean period for S-type symbiotics. The new orbits are in general agreemen t with previous orbits derived from optical velocities. From the combined o ptical and infrared velocities, improved orbital elements for the five syst ems have been determined. Each of the orbital periods has been determined s olely from the radial-velocity data. The orbits are circular and have quite small mass functions of 0.001-0.03 M-.. The infrared velocities of AG Dra do not show the large orbital velocity residuals found for its optical radi al velocities.