Photometry of K2 Campaign 9 bulge data

TL;DR

This paper introduces a new photometric extraction method for dense stellar regions in K2 Campaign 9, significantly improving precision in crowded fields like the Galactic bulge for microlensing studies.

Contribution

We developed an advanced photometry technique extending the Causal Pixel Model to dense fields, combining pixel response functions, astrometric data, and astrophysical modeling.

Findings

Photometry precision improved by an order of magnitude.

Method successfully applied to microlensing events and eclipsing binaries.

Enhanced capability for dense stellar field analysis in K2 data.

Abstract

In its Campaign 9, K2 observed dense regions toward the Galactic bulge in order to constrain the microlensing parallaxes and probe for free-floating planets. Photometric reduction of the \emph{K2} bulge data poses a significant challenge due to a combination of the very high stellar density, large pixels of the Kepler camera, and the pointing drift of the spacecraft. Here we present a new method to extract K2 photometry in dense stellar regions. We extended the Causal Pixel Model developed for less-crowded fields, first by using the pixel response function together with accurate astrometric grids, second by combining signals from a few pixels, and third by simultaneously fitting for an astrophysical model. We tested the method on two microlensing events and a long-period eclipsing binary. The extracted K2 photometry is an order of magnitude more precise than the photometry from other method.