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

Abstract

We present ∼ 800 days of photometric monitoring of Boyajian's Star (KIC 8462852) from the AllSky Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian's Star has steadily decreased at a rate of 6.3 ± 1.4 mmag yr −1 , such that the star is now 1.5% fainter than it was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian's Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in the same ASAS-SN field and demonstrate that the recent fading is significant at 99.4% confidence. The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models for the star's behavior proposed to date.

The First Post-Kepler Brightness Dips of KIC 8462852

“…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. Further results from ground-based data over 27 months with ASAS-SN data, and from 2006 to 2017 with ASAS data also confirm such dimmings, with possible signs of periodic behavior (Simon et al 2017). Thus, KIC 8462852 is known to display complex dip-like variations with a continuum of duration timescales ranging from a day to a week to a month to a year to a decade to a century.…”

“…These data also provide the means of informing planned triggered observations such as high-resolution spectroscopy to study the events in more detail. Furthermore, extended photometric monitoring will enable us to characterize the star's long-term variability (Montet & Simon 2016;Schaefer 2016;Meng et al 2017;Simon et al 2017), which is thought to be linked to the dips in some way. All-in-all, the apparent low duty cycle of the dips, unclear predictions on when they will recur, and fairly unconstrained multiyear timescales of the long-term variability will require a committed, intensive monitoring program spanning the next decade and beyond.…”

The KIC 8462852 light curve from 2015.75 to 2018.18 shows a variable secular decline

“…The existence of secular fading was soon confirmed with the quarterly Kepler fullframe images from 2009.3 to 2013.3, showing a decline at a rate of near 0.341±0.041% per year for the first thousand days (for a drop of 0.9%), then a fast drop by 2% over ∼200 days, followed by a slow decline for the last 200 days (Montet & Simon 2016). The existence of variable secular declines has been further confirmed over 15 months with Swift data, Spitzer data, and AstroLAB IRIS data (Meng et al 2018), plus confirmations from ground-based data over 27 months with ASAS-SN data, and from 2006 to 2017 with ASAS data (Simon et al 2018). The near-ultraviolet (centered at 2317Å) 1 Claims by Hippke et al (2016) are refuted as being due to multiple technical errors, see for example https://www.centauridreams.org/?p=35666.…”

“…But this solution does not work. The problem is that the modern data has a tremendous scatter in the B magnitude, from 12.26 to 12.80 (see Table 4 of Simon et al 2018). This huge scatter cannot be due to variability of Boyajian's Star (see Figure 3).…”

Reddened Dimming of Boyajian’s Star Supports Internal Storage of Its “Missing” Flux

“…Simon, Shappee & Pojmanski et al 2017). Obscuration by circumstellar grains larger than the wavelength of the observed light (e.g.…”