Additional periodicities in TESS 1O Cepheids

We applied standard Fourier analysis and classified the additional signals according to the ratio of their period to the overtone pulsation period. We find 127 stars in total that exhibit additional periodicities. In 17 of these stars, the periodicities can be identified as a second radial overtone.

A further 83 of the stars were observed to display periodic signals with a Px/P1O ratio in the range 0.60-0.65. In 15 stars, the P1O/Px is found to be ~0.68; six of these stars are also found to be in the previous group. Furthermore, we observed the presence of low-amplitude signals in 22 stars outside the aforementioned period ratio ranges.

It is possible that some are direct detections of non-radial modes, with no harmonic frequency peak in the 0.60-0.65 period range. Most of the properties of the additional signals detected in this study are consistent with previous findings regarding Cepheids in the Magellanic Clouds. However, TESS measurements reveal that the amplitudes and frequencies of these signals often vary within a TESS sector, a phenomenon that challenges theoretical models.

We also find that reliable analysis of these signals with TESS is possible for a moderate fraction of overtone Cepheids. The primary constraints are the limited extent of the data and the relatively poor photometric quality in some Galactic fields. Further careful corrections to the light curves may improve detectability.