KIC 9845907: A $\delta$ Scuti star with the first overtone as the dominant frequency and with many equidistant structures in its spectrum

TL;DR

This study analyzes Kepler data of the $\delta$ Scuti star KIC 9845907, revealing complex frequency structures including dominant overtone and equidistant triplet and quintuplet patterns, suggesting possible rotational splitting and nonlinear mode interactions.

Contribution

First detection of equidistant triplet and quintuplet structures in a $\delta$ Scuti star, providing new insights into its pulsation behavior and potential rotational effects.

Findings

Identified 85 significant pulsation frequencies.

Discovered triplet and quintuplet frequency structures.

Suggests rotational splitting as a possible cause.

Abstract

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 $f_{1}$ = 17.597 day$^{-1}$ as the dominant frequency, the non-radial independent frequency $f_{3}$ = 31.428 day$^{-1}$ ($\ell$=1), as well as two modulation terms $f_{m1}$ = 0.065 day$^{-1}$ and $f_{m2}$ = 1.693 day$^{-1}$. We found fourteen pairs of triplet structures with $f_{m1}$ or $f_{m2}$, 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 $\delta$ 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 $f_{m1}$ might be related to the rotational splitting. The study of more $\delta$ Scuti stars with triplet and/or quintuplet structures using high-precision space photometry would be helpful to further explore its origin.