Direct imaging of extra-solar planets in star forming regions: Lessons learned from a false positive around IM Lup

Abstract

Most exoplanet imagers consist of ground-based adaptive optics coronagraphic cameras which are currently limited in contrast, sensitivity and astrometric precision, but advantageously observe in the near-IR (1- 5μm). Because of these practical limitations, our current observational aim at detecting and characterizing planets puts heavy constraints on target selection, observing strategies, data reduction, and follow-up. Most surveys so far have thus targeted young systems (1-100Myr) to catch the putative remnant thermal radiation of giant planets, which peaks in the near-IR. They also favor systems in the solar neighborhood (d<80pc), which eases angular resolution requirements but also ensures a good knowledge of the distance and proper motion, which are critical to secure the planet status, and enable subsequent characterization. Because of their youth, it is very tempting to target the nearby star forming regions, which are typically twice as far as the bulk of objects usually combed for planets by direct imaging. Probing these interesting reservoirs sets additional constraints that we review in this paper by presenting the planet search that we initiated in 2008 around the disk-bearing T Tauri star IM Lup (Lupus star forming region, 140-190pc). We show and discuss why age determination, the choice of evolutionary model for the central star and the planet, precise knowledge of the host star proper motion, relative or absolute astrometric accuracy, and patience are the key ingredients for exoplanet searches around more distant young stars. Unfortunately, most of the time, precision and perseverance are not paying off: we discovered a candidate companion around IM Lup in 2008, which we report here to be an unbound background object. We nevertheless review in details the lessons learned from our endeavor, and additionally present the best detection limits ever calculated for IM Lup.

8 pages, 3 figures, 3 tables, accepted to A&A

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Cited by in corpus (8)

• The Coupled Physical Structure of Gas and Dust in the IM Lup Protoplanetary Disk
• Constraining Gas-Phase Carbon, Oxygen, and Nitrogen in the IM Lup Protoplanetary Disk
• First evidence of external disc photoevaporation in a low mass star forming region: the case of IM Lup
• The SEEDS High Contrast Imaging Survey of Exoplanets around Young Stellar Objects
• Astrophysical false positives in direct imaging for exoplanets: a white dwarf close to a rejuvenated star
• Evidence for a Cosmic Ray Gradient in the IM Lup Protoplanetary Disk
• Molecules with ALMA at Planet-forming Scales (MAPS). X. Studying deuteration at high angular resolution toward protoplanetary disks
• Stable and unstable accretion in the classical T Tauri stars IM Lup and RU Lup as observed by MOST