Transit and Radial Velocity Survey Efficiency Comparison for a Habitable Zone Earth

TL;DR

This paper compares the efficiency of transit and radial velocity surveys in detecting Earth-like exoplanets in the habitable zone of late-type stars, providing a framework to evaluate observational strategies.

Contribution

It introduces a framework using hypergeometric probability to compare survey efficiencies and estimates the observing time and precision needed for both methods.

Findings

Radial velocity with ~0.6 m/s is as efficient as transit surveys with ~300 ppm for late M-dwarfs.

Radial velocity with ~2.0 m/s is comparable to transit surveys with ~2300 ppm for Super-Earths.

The framework aids in optimizing observational strategies for exoplanet detection.

Abstract

Transit and radial velocity searches are two techniques for identifying nearby extrasolar planets to Earth that transit bright stars. Identifying a robust sample of these exoplanets around bright stars for detailed atmospheric characterization is a major observational undertaking. In this study we describe a framework that answers the question of whether a transit or radial velocity survey is more efficient at finding transiting exoplanets given the same amount of observing time. Within the framework we show that a transit survey's window function can be approximated using the hypergeometric probability distribution. We estimate the observing time required for a transit survey to find a transiting Earth-sized exoplanet in the HZ with an emphasis on late type stars. We also estimate the radial velocity precision necessary to detect the equivalent HZ Earth-mass exoplanet that also transits when using an equal amount of observing time as the transit survey. We find that a radial velocity survey with sig_rv~0.6 m/s precision has comparable efficiency in terms of observing time to a transit survey with the requisite photometric precision sig_phot~300 ppm to find a transiting Earth-sized exoplanet in the HZ of late M~dwarfs. For Super-Earths, a sig_rv~2.0 m/s precision radial velocity survey has comparable efficiency to a transit survey with sig_phot~2300 ppm.