Incidence of high-amplitude δ Scuti type variable stars

An order-of-magnitude estimate for the incidence of high-amplitude δ Scuti-type variable stars (HADS) in the δ Scuti area of the H-R diagram is calculated. Using a model for the stellar distribution in the Milky Way, we calculate the number of stars that are expected to fall in the δ Scuti area of the H-R diagram within the magnitude range and sky coverage of the ROTSE Survey for Variables I (RSV1). The incidence of the HADS phenomenon is then obtained by comparing the number of stars calculated by the model and the actual, observed number of HADS in the RSV1. We find that ∼ 0.3 % of the stars that lie in the δ Scuti area of the H-R diagram within the RSV1 observational limits exhibit the HADS phenomenon. This number is much lower than the incidence of the low-amplitude δ Scuti stars (LADS), ∼ 1/3, implying that the HADS phenomenon takes place in a very small fraction of stars and/or its duration is very short, compared to the LADS.