The ultra-compact Low Mass X-ray Binary ( LMXB ) X1916-053 , composed of a neutron star and a semi-degenerated white dwarf , exhibits periodic X-ray dips with variable width and depth .
We have developed new methods to parameterize the dip to systematically study its variations .
This helps to further understand binary and accretion disk behaviors .
The RXTE 1998 observations clearly show a 4.87d periodic variation of the dip width .
This is probably due to the nodal precession of the accretion disk , although there are no significant sidebands in the spectrum from the epoch folding search .
From the negative superhump model ( 15 ) , the mass ratio can be estimated as q = 0.045 .
Combined with more than 24 years of historical data , we found an orbital period derivative of \dot { P } _ { orb } / P _ { orb } = ( 1.62 \pm 0.48 ) \times 10 ^ { -7 } yr ^ { -1 } and established a quadratic ephemeris for the X-ray dips .
The period derivative seems inconsistent with the prediction of the standard model of binary orbital evolution proposed by Rappaport et .
al .
( 16 ) .
On the other hand , the radiation-driven model ( 21 ) may properly interpret the period derivative even though the large mass outflow predicted by this model has never been observed in this system .
With the best ephemeris , we obtained that the standard deviation of primary dips are smaller than that of secondary dips .
This means that the primary dips are more stable than the secondary dips .
Thus , we conclude that the primary dips of X1916-053 occur from the bulge at the rim instead of the ring of the disk proposed by Frank et .
al .
( 7 ) .