  In numerous low-mass X-ray binaries kHz quasi-periodic oscillations (kHz
QPOs) are detected. We observed the atoll sources GX 9+1 and GX 9+9 with the
RXTE satellite. Both sources were on the (upper) banana branch during our
observations. No kHz QPOs were detected, with upper limits of 1.3-1.8 %. It is
known from other atoll sources (e.g. 4U 1636-53 and 4U 1820-30) that when they
are in the upper banana branch the kHz QPOs are not detected. Thus, it remains
possible that when GX 9+1 and GX 9+9 are observed longer on the lower banana,
or even in the island state, kHz QPOs are detected in these sources.

Astrophysics