Resolving the pulsation contents of 13 δ Scuti stars with TESS and K2

Abstract

Using the TESS and Kepler K2 light curve archives, I have reanalyzed 13 known $\delta$ Scuti stars. AD Ari is now reclassified as a rotating ellipsoidal binary variable. EX Cnc and HD 73712 are reclassified as hybrid $\delta$ Sct-$\gamma$ Dor pulsators. EX Cnc turns out to be an enticing asteroseismic target because of its three distinct groups of pulsation frequencies. The strong beating caused by two close frequencies is present in the star CD-54 7154. More than 71 pulsation frequencies were resolved for $\iota$ Boo and IT Dra with high significant levels, while V1821 Cyg, V2238 Cyg, BR Cnc, BU Cnc, and BV Cnc pulsate with a few dozen frequencies. In particular, K2 data revealed a significantly richer pulsational spectrum for the two $\delta$ Scuti stars BU Cnc and BV Cnc from six to 26. Unlike the other 12 stars, BN Cnc shows the simplest pulsation pattern. With high-precision and long-term space-based photometry, we are able to discern the pulsational contents of these stars more clearly and enhance our knowledge of them. This reanalysis using TESS and Kepler K2 data highlights the diversity of pulsational behavior among $\delta$ Scuti stars and the value of long-duration, high-precision photometry. Further asteroseismic modeling of these stars, particularly EX Cnc with its distinct frequency groups, promises to refine our understanding of their internal structures and pulsational mechanisms.