ISPY-NACO Imaging Survey for Planets around Young stars

Survey description and results from the first 2.5 years of observations^★

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: rl@mpia.de
² Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
³ Observatoire Astronomique de l’Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
⁴ ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
⁵ Space Telescope Science Institute, Baltimore 21218, MD, USA
⁶ Department of Physics & Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK
⁷ The University of Western Ontario, Department of Physics and Astronomy, 1151 Richmond Avenue, London, ON N6A 3K7, Canada
⁸ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
⁹ Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE, UK
¹⁰ STAR Institute, University of Liège, Allée du Six Août 19c, 4000 Liège, Belgium
¹¹ Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
¹² Department of Astronomy, Stockholm University, Stockholm, Sweden

Received: 28 October 2019
Accepted: 4 February 2020

Abstract

Context. The occurrence rate of long-period (a ≳ 50 au) giant planets around young stars is highly uncertain since it is not only governed by the protoplanetary disc structure and planet formation process, but also reflects both dynamical re-structuring processes after planet formation as well as possible capture of planets not formed in situ. Direct imaging is currently the only feasible method to detect such wide-orbit planets and constrain their occurrence rate.

Aims. We aim to detect and characterise wide-orbit giant planets during and shortly after their formation phase within protoplanetary and debris discs around nearby young stars.

Methods. We carry out a large L′-band high-contrast direct imaging survey for giant planets around 200 young stars with protoplanetary or debris discs using the NACO instrument at the ESO Very Large Telescope on Cerro Paranal in Chile. We use very deep angular differential imaging observations with typically >60° field rotation, and employ a vector vortex coronagraph where feasible to achieve the best possible point source sensitivity down to an inner working angle of about 100 mas. This paper introduces the NACO Imaging Survey for Planets around Young stars (NACO-ISPY), its goals and strategy, the target list, and data reduction scheme, and presents preliminary results from the first 2.5 survey years.

Results. We achieve a mean 5 σ contrast of ΔL′ = 6.4 ± 0.1 mag at 150 mas and a background limit of L′_bg = 16.5±0.2 mag at >1.′′5. Our detection probability is >50% for companions with ≳8 M_Jup at semi-major axes of 80–200 au and >13 M_Jup at 30–250 au. It thus compares well to the detection space of other state-of-the-art high-contrast imaging surveys. We have already contributed to the characterisation of two new planets originally discovered by VLT/SPHERE, but we have not yet independently discovered new planets around any of our target stars. We have discovered two new close-in low-mass stellar companions around R CrA and HD 193571 and report in this paper the discovery of close co-moving low-mass stellar companions around HD 72660 and HD 92536. Furthermore, we report L′-band scattered light images of the discs around eleven stars, six of which have never been imaged at L′-band before.

Conclusions. The first 2.5 yr of the NACO-ISPY survey have already demonstrated that VLT/NACO combined with our survey strategy can achieve the anticipated sensitivity to detect giant planets and reveal new close stellar companions around our target stars.