High Angular Resolution in 2010-2020: A comparison between possible post-VLT/VLTI instruments L. Arnold a , A.M. Lagrange b , D. Mourard c , P. Riaud d,e , M. Ferrari f , S. Gillet d , P. Kern b , L. Koechlin g , A. Labeyrie d , O. Lardi` ere d , F. Malbet b , G. Perrin e , G. Rousset h , M. Tallon i a OHP CNRS, Observatoire de Haute-Provence, 04870 St-Michel-l’Observatoire, France b LAOG, Observatoire de Grenoble, 38041, Grenoble, France c Dpt Fresnel, Observatoire de la Cˆ ote d’Azur, 06460 Caussols, France d LISE, Observatoire de Haute-Provence, 04870 St-Michel-l’Observatoire, France e Observatoire de Paris-Meudon, 92195 Meudon, France f LAM, Observatoire Astronomique de Marseille-Provence, 13248 Marseille, France g Laboratoire d’Astrophysique de Toulouse, 31400 Toulouse, France h ONERA, 92322 Chatillon, France i CRAL, Observatoire de Lyon, 69561 Saint Genis-Laval cedex, France ABSTRACT The 8-m class telescopes are now in full operation, while 100-m baseline interferometers (VLTI, KeckI) are starting routine operation too. A working group from the French high angular resolution community tried to identify what could be our post-VLT/VLTI instruments after 2010. Possible future instruments, ground or space-based, can be split into three main categories: Extremely large filled aperture telescopes, diluted interferometric arrays for direct imaging, and diluted interferometric arrays for aperture synthesis imaging. These concepts are compared in terms of observing capabilities and performances (spatial resolution, field of view, imaging capability, sensitivity, photometric dynamical range, etc.), technological issues (adaptive optics, phasing, instrument mount, etc.) and R&D priorities. Keywords: Extremely large telescope, ELT, interferometric array, hypertelescope, science performance, high angular resolution, high dynamics imaging, coronagraphy, prospective. 1. INTRODUCTION The aim of this article, based on a more complete work by the French high-angular resolution prospective working group, 1 is to identify the different categories of possible post-VLT/VLTI instruments that will be available in 2010 and after, and to compare them in terms of observing capabilities and performances (spatial resolution, field of view, imaging capabilities, sensitivity, photometric dynamic range, etc.) and in terms of technological issues (adaptive optics, phasing, instrument mount, etc.). This work was motivated by the different studies started for extremely large telescopes (ELT) 2, 3 or interferometers. 4, 5 We give the list of scientific criteria (Sect.2) that have been used to compare the main categories of future instruments (Sect.3). In Sect.4, we discuss the R&D priorities that we have identified. 2. SCIENTIFIC PERFORMANCE CRITERIA We consider that all instruments will be equipped with adaptive optics (AO). The ten following criteria have been considered (see also Table 1): i) spatial resolution (i.e. wavelength/diameter ratio), Send correspondence to L. Arnold, E-mail: arnold@obs-hp.fr, Telephone: +33 4 92 70 64 07