Kic 8462852 Faded at an Average Rate of 0.164 ± 0.013 Magnitudes Per Century From 1890 to 1989

Abstract

KIC 8462852 is a completely ordinary F3 main-sequence star, except that the light curve from Kepler shows episodes of unique and inexplicable day-long dips with up to 20% dimming. Here, I provide a light curve of 1338 Johnson B-band magnitudes from 1890 to 1989 taken from archival photographic plates at Harvard. KIC 8462852 displays a secular dimming at an average rate of 0.164 ± 0.013 mag per century. From the early-1890s to the late1980s, KIC 8462852 faded by 0.193 ± 0.030 mag. The decline is not an artifact because nearby check stars have closely flat light curves. This century-long dimming is unprecedented for any F-type main-sequence star. Thus, the Harvard light curve provides the first confirmation (past the several dips seen in the Kepler light curve alone) that KIC 8462852 has anything unusual. The century-long dimming and the day-long dips are both just extreme ends of a spectrum of timescales for unique dimming events. By Ockham's Razor, two such unique and similar effects are very likely produced by one physical mechanism. This one mechanism does not appear as any isolated catastrophic event in the last century, but rather must be some ongoing process with continuous effects. Within the context of dust-occultation models, the century-long dimming trend requires 10 4 -10 7 times as much dust as for the deepest Kepler dip. Within the context of the comet-family idea, the century-long dimming trend requires an estimated 648,000 giant comets (each with 200 km diameter) all orchestrated to pass in front of the star within the last century.

Where Is the Flux Going? The Long-term Photometric Variability of Boyajian’s Star

“…The results of Schaefer (2016) and Montet & Simon (2016) have generally been assumed to indicate that the brightness of Boyajian's Star is monotonically decreasing with time. While the ASAS-SN measurements are consistent with that picture, the longer time baseline afforded by the ASAS data demonstrates that in fact the star's variability may be more complicated, with multiple slow dimming and brightening episodes over the past decade.…”

“…Until the recent study by Meng et al (2017), all detections of both the long-term dimming of Boyajian's Star and the brief dips in brightness have relied on photometry in a single band (Schaefer 2016;Montet & Simon 2016). Although we find that the ASAS I-band observations indicate fading as well, the larger uncertainties of those measurements prevent us from confidently detecting any color changes in the star over the past decade.…”

“…While these models can potentially account for the dipping activ-ity without violating the infrared constraints, they were severely challenged by the finding by Schaefer (2016) that Boyajian's Star appears to have been monotonically fading since the late 19th century, with a total change in its brightness of 0.16 mag from 1890 to 1989. The interpretation of the archival photographic measurements for the star has been controversial (Hippke et al 2016(Hippke et al , 2017, but Montet & Simon (2016) demonstrated using Kepler full-frame images that the star's brightness did steadily decline by a total of ∼ 3% over the four years of Kepler 's main mission.…”

“…In particular, Metzger et al (2017) show that the ingestion of a planet and the accompanying destruction of its satellite system could produce both brief dips and a long-term dimming with a rate comparable to that measured by Schaefer (2016) and Montet & Simon (2016), providing the first simultaneous explanation for all aspects of the star's variability. Foukal (2017) argues instead that the convective structure of the star may be able to store enough energy to explain the dips and longer-term fading.…”

The First Post-Kepler Brightness Dips of KIC 8462852

“…While Hippke et al (2016) claim the dimming found by Schaefer (2016) is spurious, the unique longer-term variability was again identified with the Kepler full-frame images, which show that KIC 8462852 underwent secular dimming by a total of 3% during the four-year (2009)(2010)(2011)(2012)(2013) Kepler time baseline (Montet & Simon 2016). More recently, Meng et al (2017) presented over 15 months of space-and ground-based photometry from Swift, Spitzer, and AstroLAB IRIS, showing that this variability continues even today.…”