Ground-based direct detection of close-in extra-solar planets with nulling and high order adaptive optics

Abstract

Ground-based direct detection of extra-solar planets is very challenging due to high planet to star brightness contrasts. For giant close-in planets, such as have been discovered by the radial velocity method, closer than 0.1 AU, the reflected light is predicted to be fairly high yielding a contrast ratio ranging from 10 −4 to 10 −5 at near infra-red wavelengths. In this paper, we investigate direct detection of reflected light from such planets using nulling interferometry, and high-order adaptive optics in conjunction with large double aperture ground-based telescopes. In this configuration, at least 10 −3 suppression of the entire stellar Airy pattern with small loss of planet flux as close as 0.03 arcsec is achievable. Distinguishing residual starlight from the planet signal is achieved by using the center of gravity shift method or multicolor differential imaging. Using these assumptions, we derive exposure times from a few minutes to several hours for direct detection of many of the known extra-solar planets with several short-baseline double aperture telescopes such as the Large Binocular Telescope (LBT), the Very Large Telescope (VLT) and the Keck Telescope.

High-contrast coronagraph for ground-based imaging of Jupiter-like planets

“…Introducing a high precision AO system can greatly reduce the diffraction halo to a great amount (Langlois et al 2006). After AO correction lights will enter the coronagraph system that is composed of collimated and imaged mirrors, high-quality step-transmission filter and cross-shaped mask.…”

“…Detection of a planet that is roughly 15 mag fainter than its host requires a halo 10 4 times fainter than the central image peak. Introducing a high precision AO system can greatly reduce the diffraction halo (Langlois et al 2006). After AO correction, light signals will enter the coronagraph system, which is composed of collimated and imaged mirrors, and then pass through a high-quality step-transmission filter and a cross-shaped mask.…”

“…For NASA's Terrestrial Planet Finder Coronagraph, a contrast of 10 −10 at an angular distance better than 4λ/D is required (Brown &Burrows 1990). However, direct detection of a young Jupiter-like planet may be possible using large ground-based telescopes equipped with a state-of-the-art adaptive optics (AO) system (Masciadri et al 2005;Langlois et al 2006). Hot Jupiters are supposed to still be self-luminous due to on-going accretion (Marley et al 2007) and, therefore, are sufficiently bright for direct imaging.…”

“…contrast of 10 -10 at an angular distance better than 4λ/D is required (Brown &Burrows 1990).However, direct detection of the young Jupiter-like planet maybe possible using large ground-based telescopes equipped with state-of-the-art adaptive optics (AO) system (Masciadri et al 2005;Langlois et al 2006).Hot Jupiters are supposed to be still self-luminous due to on-going accretion (Marley et al 2007) and therefore sufficiently bright for direct imaging. In 2008 three Jupiter-size planets around their star HR8799 have been direct detected using 8-m Gemini and 10-m Keck telescopes (Marois et al 2008).…”