Utilizing Astrometric Orbits to Obtain Coronagraphic Images

TL;DR

This paper proposes a method to use astrometric orbit data to optimize the scheduling of direct imaging observations, significantly improving detection efficiency of exoplanets in planned missions.

Contribution

It introduces a novel strategy to utilize known astrometric orbits for planning imaging sequences, reducing the number of observations needed to detect planets.

Findings

Number of observations needed ranges from 2 to 7.

Probable number of observations ranges from 1.5 to 3.1.

Approach is highly effective for internal coronagraph and nuller missions.

Abstract

We present an approach for utilizing astrometric orbit information to improve the yield of planetary images and spectra from a follow-on direct detection mission. This approach is based on the notion-strictly hypothetical-that if a particular star could be observed continuously, the instrument would in time observe all portions of the habitable zone so that no planet residing therein could be missed. This strategy could not be implemented in any realistic mission scenario. But if an exoplanet's orbit is known from astrometric observation, then it may be possible to plan and schedule a sequence of imaging observations that is the equivalent of continuous observation. A series of images-optimally spaced in time-could be recorded to examine contiguous segments of the orbit. In time, all segments would be examined, leading to the inevitable detection of the planet. In this paper, we show how astrometric orbit information can be used to construct such a sequence. Using stars from astrometric and imaging target lists, we find that the number of observations in this sequence typically ranges from 2 to 7, representing the maximum number of observations required to find the planet. The probable number of observations ranges from 1.5 to 3.1. This is a dramatic improvement in efficiency over previous methods proposed for utilizing astrometric orbits. We examine how the implementation of this approach is complicated and limited by operational constraints. We find that it can be fully implemented for internal coronagraph and visual nuller missions, with a success rate approaching 100%. External occulter missions will also benefit, but to a lesser degree.