Abstract
The results of a search for amplitude modulation of pulsation modes in 983 δ Sct stars, which have effective temperatures between 6400 ⩽ Teff ⩽ 10 000 K in the Kepler Input Catalogue and were continuously observed by the Kepler Space Telescope for 4 yr, are presented. A total of 603 δ Sct stars (61.3 per cent) are found to exhibit at least one pulsation mode that varies significantly in amplitude over 4 yr. Furthermore, it is found that amplitude modulation is not restricted to a specific region within the classical instability strip in the HR diagram, therefore its cause is not necessarily dependent on stellar parameters such as Teff or log g . On the other hand, many δ Sct stars show constant pulsation amplitudes demonstrating that the cause of pulsational non-linearity in these stars is not well understood.
Highlights
The multiperiodic pulsators known as δ Sct stars are the most common group of variable A and F stars, and are found at the intersection of the classical instability strip and the main sequence in the HR diagram
KIC 2304168 has an effective temperature of Teff = 7220 ± 270 K and a surface gravity of log g = 3.67 ± 0.19 [7], which are consistent with the results from stellar modelling [1]
The identification of radial pulsation modes in this star is indicated by the period ratio of ν1 = 8.107739 d−1 and ν2 = 10.495495 d−1 being 0.7725, which is predicted by stellar models [9]
Summary
The multiperiodic pulsators known as δ Sct stars are the most common group of variable A and F stars, and are found at the intersection of the classical instability strip and the main sequence in the HR diagram. Δ Sct stars typically range from A2 to F2 in spectral type [8] and within the effective temperature range of 6300 ≤ Teff ≤ 8600 K [10]. Pulsations in δ Sct stars are excited by the κ-mechanism operating in the He ii ionisation zone, which produces low radial order pressure (p) modes. Typical pulsation periods observed in δ Sct stars are of order a few hours, but can be as short as 15 min [10]. The results from a search for amplitude modulation and non-linearity using 983 δ Sct stars that were continuously observed by Kepler for 4 yr are presented [4]
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