THE transient X-ray source Ariel 1118—61 has been discovered by Ariel V (refs 1, 2) and the best estimate for the position is (1950.0) α = 11 h 18 min 59s δ = −61° 35.3′. We point out here the presence in the error box of the long period Mira-type variable RS Cen (1950.0) α = 11 h 18 min 16.5 s δ = −61° 36.0′. It has been suggested that in the Mira-type variables o Ceti (Mira) and SY For the blue variable companion is a white dwarf illuminated by infalling material accreted from the strong wind of the M-type star3–5. The similarity between these systems and the (recurrent) nova T CrB has also been stressed5. We propose that some transient X-ray sources are binary systems consisting of a compact object in orbit around a long period variable. The accretion rate of material on to the compact object in such a system4 is ≲ 10−8 M⊙yr−1 which is just the rate required to produce X rays from a compact object. We note too the proposed identification6 of another transient X-ray source (2U1543—47) with a variable late-type giant.