The KIC 8462852 Light Curve From 2015.75 to 2018.18 Shows a Variable Secular Decline

TL;DR

This study presents extensive photometric data of KIC 8462852, revealing a continued secular decline and short-term dips, with evidence suggesting dust clouds as the cause of dimming, linking short and long-term variability.

Contribution

It provides the first detailed multi-year photometric analysis showing the connection between secular fading and short dips, supporting dust clouds as the cause.

Findings

Secular decline of 0.023 mags in B-band over three years.

Dips lasting 120-180 days superimposed on secular fading.

Dust particle sizes down to ~0.1 micron inferred from chromatic extinction.

Abstract

The star KIC 8462852 (Boyajian's Star) displays both fast dips of up to 20% on time scales of days, plus long-term secular fading by up to 19% on time scales from a year to a century. We report on CCD photometry of KIC 8462852 from 2015.75 to 2018.18, with 19,176 images making for 1,866 nightly magnitudes in BVRI. Our light curves show a continuing secular decline (by 0.023 +- 0.003 mags in the B-band) with three superposed dips with duration 120-180 days. This demonstrates that there is a continuum of dip durations from a day to a century, so that the secular fading is seen to be by the same physical mechanism as the short-duration Kepler dips. The BVRI light curves all have the same shape, with the slopes and amplitudes for VRI being systematically smaller than in the B-band by factors of 0.77 +- 0.05, 0.50 +- 0.05, and 0.31 +- 0.05. We rule out any hypothesis involving occultation of the primary star by any star, planet, solid body, or optically thick cloud. But these ratios are the same as that expected for ordinary extinction by dust clouds. This chromatic extinction implies dust particle sizes going down to ~0.1 micron, suggesting that this dust will be rapidly blown away by stellar radiation pressure, so the dust clouds must have formed within months. The modern infrared observations were taken at a time when there was at least 12.4% +- 1.3% dust coverage (as part of the secular dimming), and this is consistent with dimming originating in circumstellar dust.