Thursday, November 22, 2012

1211.4914 (Richard A. Frazin)

Utilization of the Wavefront Sensor and Short-Exposure Images for Simultaneous Estimation of Static Speckle and Exoplanet Intensity    [PDF]

Richard A. Frazin
This paper provides a framework for incorporation of the wavefront sensor sensor measurements in the context of observing modes in which the science camera takes very short exposures. In this formulation, the wavefront sensor measurements provide a means to jointly the static speckle and the planetary signal. For simplicity, the mathematical development assumes a simple optical system with an idealized Lyot coronagraph. Unlike currently used methods, in which increasing the observation time beyond a certain threshold is useless, this method produces estimates whose error covariances are inversely proportional to the observation time due to the fact that the (quasi-)static speckle and planetary emission are jointly estimated. The method can easily be extended to include angular (due to diurnal field rotation) and spectral diversity. Numerical experiments are performed with wavefront data from the AEOS Adaptive Optics System sensing at 850 nm. These experiments assume a science camera wavelength of $2.2 \mu$, that the measured wavefronts are exact, an ideal coronagraph, and a Gaussian approximation of shot-noise. A number of static aberrations are introduced, including one with a spatial frequency exactly corresponding the planet location. Using only 4 seconds of observation time, a planetary intensity of $\sim 0.2$ photons/millisecond, a stellar intensity of $\sim 9$ photons/millisecond/pixel at the planet's location, the short-exposure estimation method recovers the correct amplitudes of all static aberrations as well the correct planet brightness with a contrast ratio of $10^{-6}$ with 17% accuracy. The ideal coronagraph itself provides about 95% extinction in the frames with the highest Strehl ratios.
View original: http://arxiv.org/abs/1211.4914

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