Short-period line profile and light variations in the Beta Cephei star 19 Monocerotis

We present an analysis of 555 high-dispersion echelle spectra of 19 Mon obtained from two sites as well as 115 Stromgren uvby observations. We show that three periodicities are present at 5.22994, 0.17019 and 4.88956 cycle d - 1 . The first periodicity has by far the largest amplitude. Photometric amplitude ratios and phase differences indicate an l = 2 mode, while the line profile variations unequivocally point to l = 2,m = -2. Because of the low amplitudes of the other two modes, very little can be said concerning them. Although 19 Mon was originally selected on the basis of its classification as a marginal Be star, the Be nature of the star is not supported by our observations.