Amplitude Modulation in a δ Sct star HD 118660

In this paper, we report the detection of amplitude modulation in a δ Scuti star HD 118660. We found that the p-mode frequency at 24.3837 d‑1 varies periodically in amplitude with frequency 0.0558±0.00147 d‑1. However, all other modes are stable in both amplitude and phase which is clear evidence of non-conservation of visible pulsation mode energy. We constructed a two-frequency model by superimposing two sinusoids with frequencies ν1 = 24.3837 d‑1 and ν2 = 24.4420 d‑1 and corresponding phases ϕ1 = 0.5211 rad and ϕ2 = 0.9481 rad to mimic the observed variations of amplitude and phase with time. The plausible explanation of the amplitude modulation in HD 118660 is due to beating of two unresolved closed frequencies ν1 and ν2.