Photometry of Very Bright Stars with Kepler and K2 Smear Data

TL;DR

This paper demonstrates a novel method to extract high-precision photometry for very bright stars from Kepler and K2 data using collateral smear measurements, enabling studies of bright stellar objects previously unobservable due to saturation.

Contribution

The authors introduce a new technique utilizing collateral smear data to recover light curves of bright stars in Kepler and K2 datasets, expanding observational capabilities.

Findings

Successfully reconstructed light curves for bright stars like delta Scuti variables and red giants.

Compared aperture and smear photometry, showing smear data can be a reliable alternative.

Method applicable to most Kepler and K2 fields, broadening the scope of stellar observations.

Abstract

High-precision time series photometry with the Kepler satellite has been crucial to our understanding both of exoplanets, and via asteroseismology, of stellar physics. After the failure of two reaction wheels, the Kepler satellite has been repurposed as Kepler-2 (K2), observing fields close to the ecliptic plane. As these fields contain many more bright stars than the original Kepler field, K2 provides an unprecedented opportunity to study nearby objects amenable to detailed follow-up with ground-based instruments. Due to bandwidth constraints, only a small fraction of pixels can be downloaded, with the result that most bright stars which saturate the detector are not observed. We show that engineering data acquired for photometric calibration, consisting of collateral `smear' measurements, can be used to reconstruct light curves for bright targets not otherwise observable with Kepler/K2. Here we present some examples from Kepler Quarter 6 and K2 Campaign 3, including the delta Scuti variables HD 178875 and 70 Aqr, and the red giant HR 8500 displaying solar-like oscillations. We compare aperture and smear photometry where possible, and also study targets not previously observed. These encouraging results suggest this new method can be applied to most Kepler and K2 fields.