Photometric and astrometric vagaries of the enigma star KIC 8462852

TL;DR

This study applies PCA-based pre-whitening to Kepler data of KIC 8462852, revealing intrinsic flux and astrometric variations, confirming small dips and a 0.88-day periodicity, and suggesting a complex origin involving interstellar objects.

Contribution

The paper introduces a PCA-based method to effectively remove instrumental noise, enabling detailed analysis of intrinsic stellar and astrometric variability in KIC 8462852.

Findings

Detected multiple small flux dips ranging from 0.1% to 7%.

Confirmed a stable 0.88-day flux periodicity with ~90 ppm amplitude.

Identified a weak variability-induced motion effect in astrometry.

Abstract

We apply a PCA-based pre-whitening method to the entire collection of main Kepler mission long-cadence data for KIC 8462852 spanning four years. This technique removes the correlated variations of instrumental origin in both the detected light curves and astrometry, resolving intrinsic changes in flux and image position of less than 100 ppm and 1 mas, respectively. Beside the major dips in the light curve during mission quarters 8 and 16, when the flux dropped by up to 20%, we confirm multiple smaller dips across the time span of observation with amplitudes ranging from 0.1% to 7%. A variation of flux with a period of 0.88 d and a half-amplitude of approximately 90 ppm is confirmed in the PCA-cleaned data. We find that the phase of the wave is steady over the entire 15-month interval. We confidently detect a weak variability-induced motion (VIM) effect in the cleaned astrometric trajectories, when the moment-based centroids shift synchronously with the flux dips by up to 0.0008 pixels on the detector. The inconsistent magnitude and direction of VIM effects within the same quarter point at more than one source of photometric variability in the blended image. The 0.88 d periodicity comes from a different source, not from the target star KIC 8462852. We discuss a possible interpretation of the bizarre properties of the source as a swarm of interstellar junk (comets and planetoids) crossing the line of sight to the star and its optical companions at approximately 7 mas per year.