Specphot: a comparison of spectroscopic and photometric exoplanet follow-up methods

Abstract

ABSTRACT We set out a simulation to explore the follow-up of exoplanet candidates. We look at comparing photometric (transit method) and spectroscopic (Doppler shift method) techniques using three instruments: Next-Generation Transit Survey, High-Accuracy Radial-velocity Planetary Search, and CORALIE. We take into account the precision of follow-up and required observing time in attempt to rank each method for a given set of planetary system parameters. The methods are assessed on two criteria: signal-to-noise ratio (S/N) of the detection and follow-up time before characterization. We find that different follow-up techniques are preferred for different regions of parameter space. For S/N, we find that the ratio of spectroscopic to photometric S/N for a given system goes like $R_{\rm p}/P^{{1}/{3}}$. For follow-up time, we find that photometry is favoured for the shortest period systems (<10 d) as well as systems with small planet radii. Spectroscopy is then preferred for systems with larger radius, and thus more massive planets (given our assumed mass–radius relationship). Finally, we attempt to account for the availability of telescopes and weight the two methods accordingly.