Abstract
Computer simulations show that in a one-dimensional lattice with quartic anharmonic localized modes can move with a constant velocity that is smaller than the sound velocity (subsonic solitons). In this paper we present an analytical investigation of the wing of the subsonic soliton, which allows for the calculation of the dispersion relation of these modes. The total envelope of the displacement is calculated numerically by means of a Gaussian error integral method, and the obtained solutions are tested via direct numerical simulations. Among many results. it is found that subsonic solitons with velocity very close to the sound velocity are possible.