Close Non-Radial Modes And Modulation In First Overtone Cepheids

Close non-radial modes are detected in a significant fraction of first overtone Cepheids. Such modes manifest as additional peaks in the power spectrum, close to the radial mode frequency. We revisit a sample of Cepheids with close non-radial modes previously analysed using OGLE-II data, and check their properties with the more extensive OGLE-III/IV data. The emerging qualitative picture is the same - in all stars we confirm the presence of a single additional peak close to the radial mode frequency. In one of them, we discover an additional peak located symmetrically on the other side of the radial mode frequency. This indicates that the pulsation of this star may be periodically modulated. For other stars, the interpretation in terms of non-radial modes remains the most likely scenario.