Multifractal charactarization as a function of timescale in the light curves with planetary signal observed by the kepler mission

TL;DR

This study uses multifractal analysis to characterize the variability in Kepler light curves caused by stellar rotation, starspots, and planetary transits, providing a new framework for modeling stellar activity across different timescales.

Contribution

It introduces a multifractal analysis framework to explain dynamical properties of stellar light curves as a function of timescale, specifically applied to the Kepler-30 system.

Findings

Stellar flux variations due to rotation can be modeled with four multifractal indexes.

The indexes effectively replicate the flux modulation caused by starspots.

The method simplifies spot modeling for current and future space missions.

Abstract

Astrophysical data, in the domains of time, involve a wide range of stellar variability phenomena, among them the magnetic activity of the order of a few hours until the signature of an extra-solar planet which can cover a scale of time of a few days until tens of years. Numerous instruments are being developed to detect Earth-sized exoplanets. Exoplanets with this dimension challenge scientific instrumentation and the field of research in the data processing. In this context, our study offers a powerful framework to explain dynamical properties as a function of timescale in light curves with the planetary signal. For that, we selected the stellar target Kepler-30 to test our methods and procedures. In this sense, we investigate the multifractal behavior of the Kepler-30 system composed of a sun-like star with a rotation period of ~16 days and three planets with masses between 2 Earth and 2.5 Jupiter masses. Furthermore, this system has an orbital period varying from 29 to 143 days and orbits almost coplanar. This system is highly interesting because starspots dynamics are strongly affected by the passing of a planet in front of the star. We used about 1600 days of high-precision photometry collected by the Kepler mission to investigate the quasi-periodic variation caused by the rotation of the star and the effect of spot evolution as a function of timescale. We applied indexes extract from multifractal analysis to model the flux rotational modulation induced by active regions. Our results that stellar flux variations in Kepler-30 star caused by rotational modulation can be replicated in detail with just four recent-known multifractal indexes. These indexes will greatly simplify spot modelling of current TESS and future PLATO data.