  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 (0.506 d) 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 A. 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.
