FIGURE 2. Final image of HR8799 and concomitant stellar point spread function profiles and limiting contrast curves.

From the following article:

An image of an exoplanet separated by two diffraction beamwidths from a star

E. Serabyn, D. Mawet & R. Burruss

Nature 464, 1018-1020(15 April 2010)

doi:10.1038/nature09007

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a, Final calibrated image of the HR8799 system obtained with the Ks-band vector vortex coronagraph on the well-corrected subaperture. The residual point spread function subtraction was performed with the LOCI algorithm20 using two reference stars (SAO 91022 and 108402) with V and K magnitudes similar to HR8799. The exposure time for each star was 800s. The stellar position is marked with a large cross, and the central 300milliarcseconds (1λ/D) radius region inside the dashed circle is blanked out. The position of HR8799b during the 1998 Hubble observations2 is shown by the small cross. Off-axis astrometry errors are dominated by plate scale and orientation uncertainties resulting from the limited numbers of reference binary stars observed until now. b, Azimuthally averaged point spread function profiles and limiting contrast curves. The black solid curve is the azimuthally averaged non-coronagraphic point spread function profile, and the blue solid curve is the azimuthal average of the post-coronagraph residual point spread function profile. The black dashed curve gives the 4σ azimuthal variations in the non-coronagraphic point spread function. The red dashed curve shows the radial dependence of the post-vortex semi-static speckle 4σ noise level after the modified Gerchberg–Saxton phase retrieval algorithm17 (obtained from the blue solid curve by subtracting the median-filtered residual point spread function). The green dashed curve shows the azimuthally averaged 4σ detection limit after reference-star subtraction with LOCI, and the blue dashed curve shows the 4σ photon noise estimated from the residual stellar flux and background. Flux accuracies are limited mostly by speckle variations and the reference-star subtraction procedure; in comparison, photometric errors due to Strehl ratio and atmospheric transmission variations are minor.

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