Error correction and evaluation in astronomical speckle interferometry with low-light CCD camera
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Error correction and evaluation in astronomical speckle interferometry with low‑light CCD camera Susumu Kuwamura1 · Shotaro Ono1 · Noriaki Miura1 · Fumiaki Tsumuraya2 · Makoto Sakamoto3 · Naoshi Baba4 Received: 20 February 2020 / Accepted: 8 September 2020 © The Optical Society of Japan 2020
Abstract In the astronomical speckle interferometry, low-light CCD cameras such as the electron bombarded/multiplying CCDs (EB/ EMCCDs) are being widely used for taking the faint speckle images. The detector noise affects the power spectral estimate of the astronomical object as well as the speckle noise does. The estimation errors of the object power spectrum are results of the propagation of the random fluctuations due to those noises. We have formulated a method for correcting and evaluating the estimation errors based on our detection model developed for EB/EMCCDs and the conventional model of the speckle noise. In our method, the error correction and evaluation are accomplished with the aid of the auxiliary data known as the dark and flat frames. The unbiased estimator of the object power spectrum and its SNR evaluator as derived above are verified using simulated data, where we have adopted the values of the detector parameters as obtained by measuring the actually used EMCCD camera in our observations. The results of the simulated experiments show that, within the diffraction cutoff frequency, our power spectral estimator is unbiased, and our SNR evaluator for that is useful except below the seeing cutoff. Keywords Astronomical speckle interferometry · Detector and speckle noises · EMCCD · Error propagation · Noise bias · Flat and dark frames
1 Introduction When we observe stars using a telescope on the ground, the images are deteriorated due to the atmospheric turbulence. There has been used a technique called astronomical speckle interferometry [1–3] as a representative method that postprocesses the deteriorated observed images with a software to recover the diffraction-limited resolution of the telescope. Briefly, this technique estimates the squared modulus of the Fourier transform of the original object image (object power spectrum) from a series of the atmospherically deteriorated short-exposure images called speckle images.
* Susumu Kuwamura [email protected]‑it.ac.jp 1
Kitami Institute of Technology, 165 Koen‑cho, Kitami, Hokkaido 090‑8507, Japan
2
Nishi-Harima Astronomical Observatory, Sayo‑cho, Hyogo 679‑53, Japan
3
Nenohoshi Educational Company, Tatsuno, Hyogo, Japan
4
Hokkaido University, Sapporo 060‑8628, Japan
The noises included in the speckle data are propagated, and appear as systematic and random errors in the estimate of the object power spectrum. Correcting and evaluating these errors are important to ensure the reliability of various astronomical parameter values derived from the object power spectrum. There are two noise sources, speckle and detector noises, that cause errors of the object power spectrum, and the characteristics of these noises should be taken in
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