25yr observations of the sdB star AQ Col

Photometric monitoring of AQ Col reveals a pulsation timing variation with a period of 486 days, interpreted as time delay due to reflex motion in a wide binary formed with an unseen companion with expected mass larger than 1.05M_{sun}_. The optical spectra and color-magnitude diagram of the system suggested that the companion is not a main-sequence star but a white dwarf or neutron star.

The pulsation timing variation also shows that the system has an eccentricity of 0.424, which is much larger than any known sdB long period binary system. That might be due to the existence of another short period companion to the sdB star. Two optical spectra obtained on 1996-December-5 show a radial velocity change of 49.1km/s in 46.1min, which suggests the hot subdwarf in the wide binary is itself a close binary formed with another unseen white dwarf or neutron star companion; if further observations show this interpretation to be correct, AQ Col is an interesting triple system worthy of further study.