Detection Limits of Exoplanetary Atmospheres with 2-m Class Telescopes

Transmission spectroscopy is an important technique to probe the atmospheres of exoplanets. With the advent of the Transiting Exoplanet Survey Satellite (TESS) and, in the future, of the PLAnetary Transits and Oscillations of stars (PLATO), more and more transiting planets around bright stars will be found and the observing time of current large telescopes used to apply these techniques will not suffice. We demonstrate here that 2-m class telescopes equipped with spectrographs with high resolving power may be used for a certain number of potential targets. We obtained a timeseries of high-resolution Fiber-fed Extended Range Optical Spectrograph (FEROS) spectra at the 2.2-m telescope at La Silla of the very hot-Jupiter hosting planet, WASP-18b, and show that our upper limit is consistent with the expectations. This is the first analysis of its kind using 2-m class telescopes, and it serves to highlight their potential. In this context, we then proceed to discuss the suitability of this class of telescopes for the upcoming flood of scientifically interesting targets from the TESS space mission, and propose a methodology to select the most promising targets. This is of particular significance given that observing time on 2-m class telescopes is more readily available than on large 8-m class facilities.

Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 098.A-9039(C).