An HST COS Far UV spectrum ( 1170 Å to 1800 Å ) was obtained for the short orbital period recurrent novae ( T Pyxidis subclass ) , CI Aquilae .
CI Aql is the only classical CV known to have two eclipses of sensible depth per orbit cycle and also have pre- and post-outburst light curves that are steady enough to allow estimates of mass and orbital period changes .
Our FUV spectral analysis with model accretion disks and NLTE high gravity photospheres , together with the Gaia parallax , reveal CI Aql ’ s FUV light is dominated by an optically thick accretion disk with an accretion rate of the order of 4 \times 10 ^ { -8 } M _ { \sun } / yr .
Its database of light curves , radial velocity curves , and eclipse timings is among the best for any CV .
Its orbit period ( P ) , dP / dt , and reference time are re-derived via simultaneous analysis of the three data types , giving a dimensionless post-outburst dP / dt of -2.49 \pm 0.95 \times 10 ^ { -10 } .
Lack of information on loss of orbital to rotational angular momentum leads to some uncertainty in the translation of dP / dt to white dwarf mass change rate , dM _ { 1 } / dt , but within the modest range of +4.8 \times 10 ^ { -8 } to +7.8 \times 10 ^ { -8 } M _ { \sun } / yr .
The estimated white dwarf mass change through outburst for CI Aql , based on simple differencing of its pre- and post outburst orbit period , is unchanged from the previously published +5.3 \times 10 ^ { -6 } M _ { \sun } .
At the WD ’ s estimated mass increase rate , it will terminate as a Type Ia supernova within 10 million years .