Optimization and Performance of Adaptive Optics for Imaging Extrasolar Planets

Abstract

A recent study by Angel (1994) using simplified analytical models indicated the feasibility of imaging extrasolar planets from the ground, making use of adaptive optics correction of a large telescope. We have performed detailed simulations of the method using computer codes that model propagation through atmospheric turbulence, adaptive correction, and broadband imaging. We confirm that high-resolution correction at the limit of photon noise errors reduces the halo intensity to 10 Ϫ6 of the peak star flux. Our work shows how to avoid systematic errors. Thus, we find that time delays between sensing the wave front and its detection lead to persistent structure in the stellar halo, which uncorrected would prevent rapid averaging of the residual halo speckle structure. A local wave front reconstructor that extrapolates ahead in time has been devised to remove this problem. We find the chromatic differences in wave front structure are small enough that the signal-to-noise ratio can be improved by wave front sensing and imaging in separate adjacent bands. We verify that correction of amplitude scintillation is needed and the optimum level of clipping is derived. A simulated image of a twin of the solar system at 8 pc is presented for the new 6.5 m telescope and the measured turbulence at the Multiple Mirror Telescope site. The Jupiter twin shows up at the 5 level in a 5 hr integration.

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

“…This latter expression is similar to the speckle variance estimated in Racine et al (1999). After adaptive optics compensation the speckle lifetime usually ranges from 1 to 100 ms (Ryan et al 1998) and can in theory be reduced to 1 ms by incorporating temporal prediction in the wavefront reconstruction (Stahl & Sandler 1995). For several specific known objects from Marcy's almanac of extra-solar planets 1 shown in Table 2, we estimate the exposure time for a 10-σ detection.…”

“…However, due to planet's faintness and its location very close to the parent star, the technical requirements are at the theoretical limits of performance and, hence, very challenging. Ground-based imaging or spectroscopy requires very high contrast, achievable only by using high-order adaptive optics (AO) to reduce the light scattered by atmospheric turbulence, such as described in Angel (1994); Stahl & Sandler (1995); Langlois et al (2003) and by using in addition a coronograph (Malbet 1996;Beuzit et al 1997;Roddier & Roddier 1997, Baudoz et al 2000Rouan et al 2000) or a nulling instrument (Bracewell 1978;Woolf & Angel 1997;Hinz et al 1998Hinz et al , 1999 to reduce the diffracted stellar light.…”

Scintillation Effects on a High‐Contrast Imaging Instrument for Direct Extrasolar Planets' Detection

“…In order to reach the required high contrast at small angular separations, CHEOPS was conceived (1) to achieve very small residual phase errors 2 'res and (2) to measure and to correct the wave front perturbations over small spatial size (a few centimeters) and (3) at high temporal frequency ($2 kHz). When one approaches these conditions, the atmospheric scintillation can become a nonnegligible noise factor (Angel 1994;Stahl & Sandler 1995). The principal task of this paper is to study scintillation effects produced on the polarimeter imager working in the I band.…”

Notch‐Filter Masks: Practical Image Masks for Planet‐finding Coronagraphs

“…Optical techniques for controlling diffracted light in planet-imaging telescopes have centered on two main designs: specially shaped and/or apodized pupils (Spergel 2001;Nisenson & Papaliolios 2001;Kasdin, Spergel & Littman 2001;Debes et al 2002;Kasdin et al 2003) and classical coronagraphs (Lyot 1939;Nakajima 1994;Stahl & Sandler 1995;Malbet et al 1995;Kuchner & Traub 2002). Shaped and apodized pupils produce a point spread function whose diffraction wings are suppressed in some regions of the image plane.…”