We have shown that the true optical counterpart of the Aquila X-1 recurrent transient is the interloper reported by Callanan et al. (1999), located 0.48" West of the star previously assumed to be the candidate, now an ordinary mid to late-G type star. Photometry and low-resolution spectroscopy obtained in quiescence give for the new counterpart V = 21.6 and = +2.2 and suggest a star of K7 V spectral type, reddened by = 0.5 0.1 and located at 2.5 kpc. This makes Aql X-1 similar to most other soft X-ray transients which have late K (or M0) companions. We defer examination of the consequences of this new identification on existing optical photometry to a forthcoming article (Chevalier and Ilovaisky 1999c).
© European Southern Observatory (ESO) 1999
Online publication: June 6, 1999