1999/01/07 by M. R. Garcia, P. J. Callanan, John McCarthy +4 · 4 citations
Physics and Astronomy · #Advanced X-ray Imaging Techniques #Astrophysical Phenomena and Observations #X-ray Spectroscopy and Fluorescence Analysis #astro-ph
paper · pdf · doi:10.1086/307283
Accepted for publication in ApJ, 12 pages, 5 figures
arxiv created 1999/01/07 · openalex publication_date 1999/06/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
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 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° (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 6707 Å line is less than 0.3 Å, which is similar to the measured strength of this line in several other X-ray transients.