Is Transit or Radial Velocity Method Better for Detecting Worlds in the Habitable Zone?

TRANSIT AND RADIAL VELOCITY SURVEY EFFICIENCY COMPARISON FOR A HABITABLE ZONE EARTH

Authors:

Burke et al

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 habitable zone (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 σrv ~ 0.6 m s–1 precision has comparable efficiency in terms of observing time to a transit survey with the requisite photometric precision σphot ~ 300 ppm to find a transiting Earth-sized exoplanet in the HZ of late M dwarfs. For super-Earths, a σrv ~ 2.0 m s–1 precision radial velocity survey has comparable efficiency to a transit survey with σphot ~ 2300 ppm.