The K2 Bright Star Survey I: Methodology and Data Release

TL;DR

This paper introduces a novel halo-based method for extracting precise light curves of bright stars from K2 data, enabling detailed variability analysis and releasing a comprehensive catalog of bright star observations.

Contribution

It presents a new halo light curve extraction technique that works effectively for both saturated and unsaturated stars, improving data quality for bright star analysis.

Findings

Effective extraction of light curves from bright stars using halo method

Detection of widespread stellar variability including pulsation and rotation

Public release of a catalog of 161 bright stars with variability classifications

Abstract

While the Kepler Mission was designed to look at tens of thousands of faint stars (V > 12), brighter stars that saturated the detector are important because they can be and have been observed very accurately by other instruments. By analyzing the unsaturated scattered-light `halo' around these stars, we have retrieved precise light curves of most of the brightest stars in K2 fields from Campaign~4 onwards. The halo method does not depend on the detailed cause and form of systematics, and we show that it is effective at extracting light curves from both normal and saturated stars. The key methodology is to optimize the weights of a linear combination of pixel time series with respect to an objective function. We test a range of such objective functions, finding that lagged Total Variation, a generalization of Total Variation, performs well on both saturated and unsaturated K2 targets. Applying this to the bright stars across the K2 Campaigns reveals stellar variability ubiquitously, including effects of stellar pulsation, rotation, and binarity. We describe our pipeline and present a catalogue of the 161 bright stars, with classifications of their variability, asteroseismic parameters for red giants with well-measured solar-like oscillations, and remarks on interesting objects. These light curves are publicly available as a High Level Science Product from the Mikulski Archive for Space Telescopes (MAST).