Aql X-1 in Outburst and Quiescence

We present photometry and spectroscopy of the soft x-ray transient Aql X-1. Optical photometry during an active state shows a strong (0.6 mag peak-to-peak) modulation at a period of 19 hours. Infrared (K-band) photometry during a quiescent state limits any ellipsoidal variations to < 0.07 mag (peak-to-peak), which implies an inclination i < 31 (90% limit). Spectroscopy in a quiescent state shows at most very small radial velocity variations, which implies a very low inclination of i < 12 (90% limit). The low inclination is rather unexpected given the large photometric modulation seen in the active state. The upper limit to the equivalent width of the anomalous Li 6707Å line is < 0.3Å, which is similar to the measured strength of this line in several other x-ray transients. Subject headings: binaries: close — stars: individual (Aql X-1) — stars: neutron — X-rays: stars