A Technique to Derive Improved Proper Motions for Kepler Objects of Interest

TL;DR

This paper presents a method to derive more precise proper motions for Kepler Objects of Interest by combining Kepler pixel data with existing catalogs, improving stellar classification and aiding in exoplanet studies.

Contribution

The authors develop a technique that enhances proper motion accuracy for Kepler stars by integrating Kepler pixel data with existing astrometric catalogs, surpassing previous catalog precision.

Findings

Proper motions with an average error of 1.0 mas/yr achieved for a test field.

Improved reduced proper motion diagrams enable better stellar luminosity classification.

Method applicable to future small-field astrometry and the entire Kepler field.

Abstract

We outline an approach yielding proper motions with higher precision than exists in present catalogs for a sample of stars in the Kepler field. To increase proper motion precision we combine first moment centroids of Kepler pixel data from a single Season with existing catalog positions and proper motions. We use this astrometry to produce improved reduced proper motion diagrams, analogous to a Hertzsprung-Russell diagram, for stars identified as Kepler Objects of Interest. The more precise the relative proper motions, the better the discrimination between stellar luminosity classes. With UCAC4 and PPMXL epoch 2000 positions (and proper motions from those catalogs as quasi-bayesian priors) astrometry for a single test Channel (21) and Season (0) spanning two years yields proper motions with an average per-coordinate proper motion error of 1.0 millisecond of arc per year, over a factor of three better than existing catalogs. We apply a mapping between a reduced proper motion diagram and an HR diagram, both constructed using HST parallaxes and proper motions, to estimate Kepler Object of Interest K-band absolute magnitudes. The techniques discussed apply to any future small-field astrometry as well as the rest of the Kepler field.