Recent K-band imaging with Keck I of the transient low-mass X-ray binary Aquila X-1 (= V1333 Aql) has resolved V1333 Aql into two stars lying approximately along the east-west direction and separated by 0.46" (Callanan et al. 1999), the easterly star contributing 60% of the combined flux at K. Observations in the z-band (1.05µ) indicated also that the easterly star was "somewhat bluer" and they speculated that it might be the true optical counterpart of Aql X-1.
In 1999 we obtained V and I-band frames of Aql X-1 both in quiescence and during outburst maximum with EFOSC-2 at the ESO 3.6-m telescope. We present here the results of our photometry and of our EFOSC-1 spectroscopy, and we show that the westerly star is the true counterpart.
© European Southern Observatory (ESO) 1999
Online publication: June 6, 1999