KIC 9845907: A δ Scuti Star with the First Overtone as the Dominant Frequency and with Many Equidistant Structures in Its Spectrum

In this paper, we present an analysis of the pulsating behavior of Kepler target KIC 9845907. Using the data from Kepler, we detected 85 significant frequencies, including the first overtone f1 = 17.597 day−1 as the dominant frequency, the non-radial independent frequency f3 = 31.428 day−1 (ℓ = 1), as well as two modulation terms fm1 = 0.065 day−1 and fm2 = 1.693 day−1. We found fourteen pairs of triplet structures with fm1 or fm2, four pairs of which can further form quintuplet structures. We note these are the most intriguing features discovered in this study and they were recognized for the first time in δ Scuti stars. We discussed several possible explanations, i.e., beating, the Blazhko effect, combination mode hypothesis, nonlinear mode coupling, large separation, and stellar rotational splitting for these equidistant structures. Our asteroseismic models indicate this modulation with fm1 might be related to the rotational splitting. The study of more δ Scuti stars with triplet and/or quintuplet structures using high-precision space photometry would be helpful to further explore its origin.China (grant Nos. U1938104 and 12003020)FEDER/Junta de Andalucía-Consejería de Economía y ConocimientoE-FQM-041- UGR18 by Universidad de GranadaSpanish State Research Agency (AEI) project PID2019-107061GB-06