Frequency analysis of the Delta Scuti star 21 Monocerotis.

A total of 1247 V observations of 21 Mon obtained in 1970-71 and 1972-73 were subjected to Fourier analysis for their component frequencies. In the two groups of data separated by a 2-yr gap, no frequencies were found common to both data groups. Within the more extensive data group (1972-73) the component frequencies were found to be present throughout the 58-day time base of the observations but with amplitude or phase variations or both on time scales as short as one week.