ASCA observation of the dipping X-ray source XB 1916-053

We present the results of timing and spectral studies of the dipping X-ray source XB 1916-053, observed by ASCA during its performance verification ph ase. The detected dipping activity is consistent with previous observations , with a period of 3008 s and an intermittent secondary dip observed roughl y 0.4 out of phase with the primary dip. The energy spectra of different in tensity states are fitted with a power law with partial covering fraction a bsorption and interstellar absorption. The increase in the hardness ratio d uring the primary and secondary dips, and the increase in the covering frac tion and column density with decreasing X-ray intensity, all imply that the dipping is caused by the photoabsorbing materials that have been suggested to be where the accreted flow hits the outer edge of the disk materials. T he spectra at all intensity levels show no apparent evidence for Fe or Ne e mission lines. This may be due to the low metal abundance in the accretion flow. Alternatively, the X-ray luminosity of the central source may be too weak to excite emission lines, which are assumed to be produced by X-ray ph otoionization of the disk materials.