Status Report

Planet Hunters X. KIC 8462852 Where’s the Flux?

By SpaceRef Editor
October 22, 2015
Filed under , ,

Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux down to below the 20% level. The dipping activity can last for between 5 and 80 days.

We characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, and Fourier analyses of the Kepler light curve. We determine that KIC 8462852 is a main-sequence F3 V/IV star, with a rotation period ~0.88 d, that exhibits no significant IR excess. In this paper, we describe various scenarios to explain the mysterious events in the Kepler light curve, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps orbiting a normal main-sequence star, we conclude that the scenario most consistent with the data is the passage of a family of exocomet fragments, all of which are associated with a single previous breakup event. We discuss the necessity of future observations to help interpret the system.

T. S. Boyajian, D. M. LaCourse, S. A. Rappaport, D. Fabrycky, D. A. Fischer, D. Gandolfi, G. M. Kennedy, M. C. Liu, A. Moor, K. Olah, K. Vida, M. C. Wyatt, W. M. J. Best, F. Ciesla, B. Csak, T. J. Dupuy, G. Handler, K. Heng, H. Korhonen, J. Kovacs, T. Kozakis, L. Kriskovics, J. R. Schmitt, Gy. Szabo, R. Szabo, J. Wang, S. Goodman, A. Hoekstra, K. J. Jek
(Submitted on 11 Sep 2015)

Comments: Submitted to MNRAS. 15 pages, 12 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1509.03622 [astro-ph.SR] (or arXiv:1509.03622v1 [astro-ph.SR] for this version)
Submission history
From: Tabetha Boyajian
[v1] Fri, 11 Sep 2015 19:39:53 GMT (3011kb,D)

For over four years, NASA’s Kepler mission measured the brightness of objects within a 100 square-degree patch of sky in the direction of the constellations Cygnus and Lyrae. The program’s targets were primarily selected to address the Kepler mission goals of discovering Earth-like planets orbiting other stars. Kepler targeted over > 150, 000 stars, primarily with a 30-minute observing cadence, leading to over 2.5-billion data points per year (> 10 billion data points over the nominal mission lifetime).

The Kepler mission’s data processing and identification of transiting planet candidates was done in an automated manner through sophisticated computer algorithms (e.g., Jenkins et al. 2010). Complementary to this analysis, the Zooniverse citizen science network provided the means to crowd source the review of light curves with the Planet Hunters project1 (e.g., Fischer et al. 2012). In this framework, Planet Hunter volunteers view 30 day segments of light curves in the ‘Classify’ web interface. A volunteer’s main task is to identify signals of transiting planets by harnessing the human eye’s unique ability for pattern recognition. This process has shown to have a detection efficiency to identify planetary transits > 85% using the first Quarter of Kepler data (Schwamb et al. 2012). The Planet Hunters project has now discovered almost a hundred exoplanet candidates, including several confirmed systems (Fischer et al. 2012; Lintott et al. 2013; Schwamb et al. 2013; Wang et al. 2013; Schmitt et al. 2014).

Because Planet Hunter volunteers look at every light curve by eye, serendipitous discoveries are inevitable, especially in rich data sets such as that which Kepler has provided. As such, a key aspect of the Planet Hunters project is the ‘Talk’ interface. ‘Talk’ is a backend site where volunteers can discuss light curves and present further analysis on objects viewed in the main ‘Classify’ interface. In a handful of cases, such as the discovery of the unusual cataclysmic variable, KIC 9406652 (Gies et al. 2013), the default aperture mask used to generate the Kepler light curve was not perfectly centered on the object of interest. Because of this, interesting events in the Kepler light curve would appear to come and go as a result of the shifting orientation of the aperture mask when the spacecraft underwent a quarterly rotation. Events such as these are tagged and discussed on ‘Talk’, making it possible to return to the raw data target pixel files (TPF) to extract improved light curves with modified aperture masks, for example.

This paper presents the discovery of a mysterious dipping source, KIC 8462852, from the Planet Hunters project. In just the first quarter of Kepler data, Planet Hunter volunteers identified KIC 8462852’s light curve as a “bizarre”, “interesting”, “giant transit” (Q1 event depth was 0.5% with a duration of 4 days). As new Kepler data were released in subsequent quarters, discussions continued on ‘Talk’ about KIC 8462852’s light curve peculiarities, particularly ramping up pace in the final observations quarters of the Kepler mission.

In this work we examine the full 4 years of Kepler observations of KIC8462852 as well as supplemental information provided by additional groundand space-based observations. In Section 2, we characterize KIC8462852 using Kepler photometry, spectroscopic analysis, AO imaging, and spectral energy distribution analysis. We discover a wide M-dwarf companion to the sys-tem and argue that with the data sets we have in-hand, we can exclude the presence of an additional gravitationally bound companion nearby. In Section 4, we visit possible explanations for the peculiar observations of KIC 8462852, including instrumental artifacts, intrinsic/extrinsic variability, and a variety of scenarios invoking light-blocking events. In Section 5, we conclude by discussing future observations needed to constrain the nature of the object.

SpaceRef staff editor.