Kic 8462852: Transit of a Large Comet Family

Abstract

We investigate the plausibility of a cometary source of the unusual transits observed in the KIC 8462852 light curve. A single comet of similar size to those in our solar system produces a transit depth of the order of 10 −3 lasting less than a day which is much smaller and shorter than the largest dip observed (∼ 20% for ∼ 3 days), but a large, closely traveling cluster of comets can fit the observed depths and durations. We find that a series of large comet swarms, with all but one on the same orbit, provides a good fit for the KIC 8462852 data during Quarters 16 and 17, but does not explain the large dip observed during Quarter 8. However, the transit dips only loosely constrain the orbits and can be fit by swarms with periastrons differing by a factor of 10. To reach a transit depth of ∼ 0.2, the comets need to be in a close group of ∼ 30, if they are ∼ 100 km in radius or in a group of ∼ 300 if they are ∼ 10 km in radius. The total number of comets required to fit all of the dips is ∼ 70 ∼100 km or ∼ 700 ∼ 10 km comets.A single comet family from a tidally disrupted Ceres-sized progenitor or the start of a Late Heavy Bombardment period explains the last ∼ 60 days of the unusual KIC 8462852 light curve.

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

“…Published ideas to account for the unusual changes in the brightness of Boyajian's Star generally suffer from one of two flaws: they are either statistically unlikely (e.g., Metzger et al 2017) or they explain only one aspect of the observed flux variations (e.g., Bodman & Quillen 2016;Makarov & Goldin 2016;Sheikh et al 2016;Neslušan & Budaj 2017;Ballesteros et al 2017;Katz 2017). The hypotheses that can potentially account for both the brief dips and the long-term variability include the consumption of a planet (Metzger et al 2017), an internal obstruction of heat flux in the star (Foukal 2017), or an intervening disk-bearing object (Wright & Sigurðsson 2016).…”

“…Initial attempts to explain the dips focused on circumstellar material, perhaps in the form of debris from a collision of planetesimals (Boyajian et al 2016) or a large family of comets (Bodman & Quillen 2016). 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 First Post-Kepler Brightness Dips of KIC 8462852

“…These included broad categories of solutions such as those invoking occulting material in the solar system, material in the interstellar medium (ISM) or orbiting an intervening compact object, circumstellar material, and variations intrinsic to the star. Specific models for the brightness variations have been explored by Katz (2017), who modeled a circumstellar ring; Makarov & Goldin (2016), who suggested interstellar "comets"; giant circumstellar exocomets, suggested by Boyajian et al (2016) and modeled by Bodman & Quillen (2016); Neslušan & Budaj (2017), who modeled dust clouds associated with a smaller number of more massive bodies; Ballesteros et al (2018), who suggested a ringed planet and associated Trojan asteroid swarms; Sheikh et al (2016), who find the statistics of the dips to be consistent with intrinsic processes; Metzger et al (2017), who model the consumption of a secondary body; and Foukal (2017a), who invoke intrinsic variations perhaps related to magnetocovection.…”

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

“…Most of the proposed scenarios are ruled out due to the lack of any infrared excess. Bodman & Quillen (2016) investigate the idea of a comet family, but find that they need implausibly large comets in large numbers, plus a contrived disruption history. Further, the comet hypothesis cannot explain many of the dip light curves.…”