Aquila X-1 in outburst and quiescence

We present photometry and spectroscopy of the soft X-ray transient Aq1 X-1. Optical photometry during an active state shows a strong (0.6 mag peak-to- peak) modulation at a period of 19 hr. Infrared (K' band) photometry during a quiescent state limits any ellipsoidal variations to less than 0.07 mag (peak-to-peak), which implies an inclination i < 31 degrees (90% limit). Sp ectroscopy in a quiescent state shows at most very small radial velocity va riations, which implies a very low inclination of i < 12 degrees (90% limit ). The low inclination is rather unexpected given the large photometric mod ulation seen in the active state. The upper limit to the equivalent width o f the anomalous Li 6707 Angstrom line is less than 0.3 Angstrom, which is s imilar to the measured strength of this line in several other X-ray transie nts.