Reduced Activity And Large Particles From the Disintegrating Planet Candidate KIC 12557548b

TL;DR

This study analyzes the dust particle sizes in the debris tail of the disintegrating exoplanet candidate KIC 12557548b by measuring its transmission spectrum across optical and infrared wavelengths, revealing larger particles than previously predicted.

Contribution

It provides the first infrared transmission spectrum of KIC 12557548b's debris, constraining particle sizes to be larger than ~0.2-0.5 um, refining models of the planet's disintegration process.

Findings

Infrared spectrum is flat, indicating larger dust particles.

Optical transit depths are lower than Kepler average, suggesting variability or suppression of optical signals.

Particles are likely > 0.2-0.5 um, larger than initial predictions.

Abstract

The intriguing exoplanet candidate KIC 12557548b is believed to have a comet-like tail of dusty debris trailing a small rocky planet. The tail of debris scatters up to 1.3% of the stellar light in the Kepler observatory's bandpass (0.42 um to 0.9 um). Observing the tail's transit depth at multiple wavelengths can reveal the composition and particle size of the debris, constraining the makeup and lifetime of the sub-Mercury planet. Early dust particle size predictions from the scattering of the comet-like tail pointed towards a dust size of ~0.1 um for silicate compositions. These small particles would produce a much deeper optical transit depth than near-infrared transit depth. We measure a transmission spectrum for KIC 12557548b using the SpeX spectrograph (covering 0.8 um to 2.4 um) simultaneously with the MORIS imager taking r' (0.63 um) photometry on the Infrared Telescope Facility for eight nights and one night in H band (1.63 um) using the Wide-Field IR Camera at the Palomar 200-inch telescope. The infrared spectra are plagued by systematic errors, but we argue that sufficient precision is obtained when using differential spectroscopic calibration when combining multiple nights. The average differential transmission spectrum is flat, supporting findings that KIC 12557548b's debris is likely composed of larger particles > ~0.5 um for pyroxene and olivine and > ~0.2 um for iron and corundum. The r' photometric transit depths are all below the average Kepler value, suggesting that the observations occurred during a weak period or that the mechanisms producing optical broadband transit depths are suppressed.