The GALEX View of "Boyajian's Star" (KIC 8462852)

TL;DR

This study uses GALEX ultraviolet data to analyze the variability of Boyajian's Star, finding a 3% decrease in brightness over a year that suggests circumstellar dust rather than interstellar absorption.

Contribution

It provides the first UV variability constraints on Boyajian's Star using GALEX data, linking optical fading to potential circumstellar dust effects.

Findings

No short-term UV variability detected.

A 3% decrease in UV brightness over a year.

Variability consistent with circumstellar dust reddening.

Abstract

The enigmatic star KIC 8462852, informally known as "Boyajian's Star", has exhibited unexplained variability from both short timescale (days) dimming events, and years-long fading in the Kepler mission. No single physical mechanism has successfully explained these observations to date. Here we investigate the ultraviolet variability of KIC 8462852 on a range of timescales using data from the GALEX mission that occurred contemporaneously with the Kepler mission. The wide wavelength baseline between the Kepler and GALEX data provides a unique constraint on the nature of the variability. Using 1600 seconds of photon-counting data from four GALEX visits spread over 70 days in 2011, we find no coherent NUV variability in the system on 10-100 second or months timescales. Comparing the integrated flux from these 2011 visits to the 2012 NUV flux published in the GALEX-CAUSE Kepler survey, we find a 3% decrease in brightness for KIC 8462852. We find this level of variability is significant, but not necessarily unusual for stars of similar spectral type in the GALEX data. This decrease coincides with the secular optical fading reported by Montet & Simon (2016). We find the multi-wavelength variability is somewhat inconsistent with typical interstellar dust absorption, but instead favors a R$_V$ = 5.0 $\pm$ 0.9 reddening law potentially from circumstellar dust.