Exoplanets with ELT-METIS

I. Estimating the direct imaging exoplanet yield around stars within 6.5 parsecs

¹ Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
e-mail: rpbowens@umich.edu
² STAR Institute, Université de Liège, Allée du Six Août 19c, 4000 Liège, Belgium
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ ETH Zurich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁵ Indian Institute of Science Education and Research (IISER) Pune, Dr. Homi Bhabha Rd, Pashan, Pune 411008, India
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

Received: 16 April 2021
Accepted: 29 June 2021

Abstract

Direct imaging is a powerful exoplanet discovery technique that is complementary to other techniques and offers great promise in the era of 30 m class telescopes. Space-based transit surveys have revolutionized our understanding of the frequency of planets at small orbital radii around Sun-like stars. The next generation of extremely large ground-based telescopes will have the angular resolution and sensitivity to directly image planets with R < 4 R_⊕ around the very nearest stars. Here, we predict yields from a direct imaging survey of a volume-limited sample of Sun-like stars with the Mid-Infrared ELT Imager and Spectrograph (METIS) instrument, planned for the 39 m European Southern Observatory Extremely Large Telescope (ELT) that is expected to be operational towards the end of the decade. Using Kepler occurrence rates, a sample of stars with spectral types A-K within 6.5 pc, and simulated contrast curves based on an advanced model of what is achievable from coronagraphic imaging with adaptive optics, we estimated the expected yield from METIS using Monte Carlo simulations. We find the METIS expected yield of planets in the N2 band (10.10−12.40 μm) is 1.14 planets, which is greater than comparable observations in the L (3.70−3.95 μm) and M (4.70−4.90 μm) bands. We also determined a 24.6% chance of detecting at least one Jovian planet in the background limited regime assuming a 1 h integration. We calculated the yield per star and estimate optimal observing revisit times to increase the yield. We also analyzed a northern hemisphere version of this survey and found there are additional targets worth considering. In conclusion, we present an observing strategy aimed to maximize the possible yield for limited telescope time, resulting in 1.48 expected planets in the N2 band.