Detection of a repeated transit signature in the light curve of the enigma star KIC 8462852: a 928-day period?

Abstract: As revealed by its peculiar Kepler light curve, the enigmatic star KIC 8462852 undergoes short and deep flux dimmings at a priori unrelated epochs. It presents nonetheless all other characteristics of a quiet 1 Gyr old F3V star. These dimmings resemble the absorption features expected for the transit of dust cometary tails. The exocomet scenario is therefore most commonly advocated. We reanalyzed the Kepler data and extracted a new high-quality light curve to allow for the search of shallow signature of single or a few exocomets. We discovered that among the 22 flux dimming events that we identified, two events present a striking similarity. These events occurred 928.25 days apart, lasted for 4.4 days with a drop of the star brightness by 1000 ppm. We show that the light curve of these events is well explained by the occultation of the star by a giant ring system, or the transit of a string of half a dozen of exocomets with a typical dust production rate of 10$^5$-10$^6$ kg/s. Assuming that these two similar events are related to the transit of the same object, we derive a period of 928.25 days. The following transit was expected in March 2017 but bad weather prohibited us to detect it from ground-based spectroscopy. We predict that the next event will occur from the 3rd to the 8th of October 2019.

• The paper identifies a potential 928.25-day periodicity between two similar dimming events in the light curve of the enigmatic star KIC 8462852, suggesting a recurring transit signature.
• The study explores two primary models to explain these periodic dips: a string of transiting exocomets similar to those observed around eta Pictoris, or the transit of a massive ringed planet system.
• Confirming this periodicity through future observations during predicted transit times is crucial for distinguishing between the proposed exocometary and ringed planet scenarios and understanding the nature of the object causing the dimming.

Analysis of Repeated Transit Signature in KIC 8462852: Potential Exocometary Activity

Introduction to KIC 8462852 Observations

In analyzing the peculiar photometric data from the star KIC 8462852, the research offers compelling insights into possible exocometary activity or ringed planet transits. This F3V-type star, cataloged by the Kepler mission, has been a subject of curiosity due to its unexplained and erratic light curve dimming events that have evoked numerous hypotheses since their discovery. Despite KIC 8462852 being otherwise quiescent, the drastic reductions in stellar brightness have piqued interest regarding an exocomet hypothesis or planetary models.

Discovery of Periodic Transit Events

In a detailed reanalysis of the Kepler data, the researchers identified 22 distinct dimming occurrences, among which two events showed remarkable periodicity and similarity. These events, separated by a 928.25-day interval and each featuring a 1000 ppm brightness dip over 4.4 days, present a potential periodic transit signature not observed in other dips. The periodic behaviour strongly suggests a recurring phenomenon, possibly indicating a celestial orbiting body interacting with the star.

Evaluation of Data Integrity

To ensure the reliability of the observed phenomena, the study thoroughly excludes systemic errors—instrumental, pixel-level biases, or interference from nearby astronomical bodies—that could mimic such dimming events. The light curve's precision, bolstered by detailed cotrending basis vector (CBV) corrections, affirms the astrophysical authenticity of these dips.

Proposed Models for the Dimming Events

The paper explores two primary models to explain these findings:

1. Exocomet Transit Model: Postulating the presence of a string of half a dozen exocomets, the model suggests periodic passages causing these measurable dips. These sweeps, similar in their extended tails and composition to known Solar System comets such as Hale-Bopp, generate a pattern consistent with observations of $\beta$ Pictoris. This scenario aligns with the observed light curve's characteristics, offering a realistic explanation of the phenomenon through known celestial mechanics.
2. Ringed Planet Model: Alternatively, the study suggests the transit of a giant exoplanetary ring system. This configuration involves a planet orbiting KIC 8462852, encircled by rings expansive enough to cause prolonged transit dips. By modeling such a system where planetary rings extend across several stellar radii, the study fits the observed symmetric light curve elements efficiently, reminiscent of theoretical models like J1407b.

Implications and Future Research Directions

The identification of a potential 928-day periodicity in KIC 8462852’s dimming invites further verification and characterization of the object causing these transits. Confirming the nature of these transiting bodies during anticipated future events—such as the next predicted opportunity in October 2019—could substantiate or refute these theoretical models.

Future spectroscopic and photometric observations during predicted transit events, especially using instruments capable of high precision, will be critical. These observations could ascertain variables such as occupation depths and potential spectral line variations, thereby elucidating the nature of the transiting body, be it a series of comets or a ringed planet system.

In conclusion, this study enriches the discourse on KIC 8462852 by providing credible analysis and models that guide future investigations. As observational technology progresses, the potential to reach definitive conclusions on this fascinating star draws closer, holding promise for advancements in our understanding of exocometary systems and ringed exoplanets alike.