We have analysed data from five XMM-Newton observations of XB 1254 - 690 , one of them simultaneous with INTEGRAL , to investigate the mechanism responsible for the highly variable dips durations and depths seen from this low-mass X-ray binary .
Deep dips were present during two observations , shallow dips during one and no dips were detected during the remaining two observations .
At high ( 1–4 s ) time resolution “ shallow dips ” are seen to include a few , very rapid , deep dips whilst the “ deep ” dips consist of many similar very rapid , deep , fluctuations .
The folded V-band Optical Monitor light curves obtained when the source was undergoing deep , shallow and no detectable dipping exhibit sinusoid-like variations with different amplitudes and phases .
We fit EPIC spectra obtained from ” persistent ” or dip-free intervals with a model consisting of disc-blackbody and thermal comptonisation components together with Gaussian emission features at 1 and 6.6 keV modified by absorption due to cold and photo-ionised material .
None of the spectral parameters appears to be strongly correlated with the dip depth except for the temperature of the disc blackbody which is coolest ( kT \sim 1.8 keV ) when deep dips are present and warmest ( kT \sim 2.1 keV ) when no dips are detectable .
We propose that the changes in both disc temperature and optical modulation could be explained by the presence of a tilted accretion disc in the system .
We provide a revised estimate of the orbital period of 0.16388875 \pm 0.00000017 day .