Interaction of hot stars and of the interstellar medium. II. Exciting stars and spectra of the bright knot inside the diffuse nebula Sharpless 157.

The bright knot inside the diffuse nebula Sharpless 157 is probably excited maiuly by its central star Sh 2-157-1, which has been found to be a late 0-type star. The knot has an inhomogeneous brightness distribution. Spectra with dispersion 300 and 400 A/mm, obtained at the Observatoire de Haute Provence through an image-tube, show the ionization structure, a rather low degree of excitation, and emphasize the existence of a bar of high brightness. Key words: H ii regions - physical conditions - exciting stars - evolution