OO Aql is a rare W UMa-type eclipsing binary in which the two solar-type stars may have only recently evolved into contact . The binary has an unusually high mass ratio ( 0.84 ) , and a relatively long orbital period ( 0 \fd 506 ) for it spectral type ( mid-G ) . Twelve ultraviolet spectra of OO Aql were obtained in 1988 with the IUE satellite , including a series of consecutive observations that cover nearly a complete orbital cycle . Chromospheric activity is studied by means of the Mg ii h + k emission at 2800 Å . The Mg ii emission is found to vary , even when the emission is normalized to the adjacent continuum flux . This variation may be correlated with orbital phase in the 1988 observations . It also appears that the normalized Mg ii emission varies with time , as seen in spectra obtained at two different epochs in 1988 and when compared with two spectra obtained several years earlier . The level of chromospheric activity in OO Aql is less than that of other W UMa-type binaries of similar colors , but this is attributed to its early stage of contact binary evolution . Ultraviolet light curves were composed from measurements of the ultraviolet continuum in the spectra . These were analyzed along with visible light curves of OO Aql to determine the system parameters . The large wavelength range in the light curves enabled a well-constrained fit to a cool spot in the system .