Speckle Noise and Dynamic Range in Coronagraphic Images

Abstract

This paper is concerned with the theoretical properties of high-contrast coronagraphic images in the context of exoplanet searches. We derive and analyze the statistical properties of the residual starlight in coronagraphic images and describe the effect of a coronagraph on the speckle and photon noise. Current observations with coronagraphic instruments have shown that the main limitations to high-contrast imaging are due to residual quasi-static speckles. We tackle this problem in this paper and propose a generalization of our statistical model to include the description of static, quasi-static, and fast residual atmospheric speckles. The results provide insight into the effects on the dynamic range of wave front control, coronagraphy, active speckle reduction, and differential speckle calibration. The study is focused on ground-based imaging with extreme adaptive optics, but the approach is general enough to be applicable to space, with different parameters.

Speckle temporal stability in XAO coronagraphic images

“…In Paper I, we examined and discussed our data using the statistical model of the noise variance in high-contrast imaging proposed by Soummer et al (2007). Following the same formalism as for Paper I, we briefly recall here the main equations.…”

“…Following the same formalism as for Paper I, we briefly recall here the main equations. Soummer et al (2007) proposes the following analytical expression for the variance of the intensity, including speckle and photon noise in the presence of static, quasi-static, and quickly varying aberrations, in the context of a propagation through a coronagraph:…”

“…We showed that quasi-static aberrations exhibit a linear power law with time and are interacting through the pinning effect with static speckles. We examined and discussed this effect using the statistical model of the noise variance in the high-contrast imaging proposed by Soummer et al (2007). In particular, we found that quasi-static speckles, fast-evolving on the level of a few angstroms to nanometers on a timescale of a few seconds, explained the evolution of our sensitivity through amplification of the systematics.…”

“…In Sect. 2, we briefly recall the formalism of the statistical model of the noise variance in the high-contrast imaging context proposed by Soummer et al (2007) and used in Paper I to discuss our former results. In Sect.…”

Scintillation correction for astronomical photometry on large and extremely large telescopes with tomographic atmospheric reconstruction

“…However, as no AO system is perfect, the residual phase aberration can result in a complicated spatially and temporally varying point spread function (PSF; for example Cagigal & Canales 2000;Currie et al 2000;Osborn, Myers & Love 2009;Baena Gallé & Gladysz 2011). Even in medium-to high-order correction regimes, quasi-static speckles due to non-common path errors and uncorrected aberrations can add complexity to the PSF (Fitzgerald & Graham 2006;Soummer et al 2007;Osborn 2012). These variations in the PSF make separating the light from different objects difficult.…”