In order to characterize optical turbulence,we have developed a single star SCIDAR(SSS)for measurement of the distribution of C2n with height.The SSS consists of a 40 cm telescope and a CCD camera for fast sampling of stellar scintillation pattern.Spatiotemporal auto and cross-correlation functions of the single star images are computed,providing vertical profiles of optical turbulence intensity C2n(h)and wind speed V(h).Using this new SSS experiment,profiles of turbulence can be obtained from the ground to the top of atmosphere,allowing the determination of seeing,isoplanatic angle and coherence time.Detailed characteristics of atmospheric optical turbulence are important for active and passive imaging,astronomical site testing,adaptive optics,laser communications,target tracking and designation,and laser beam control.We plan to improve the robotization of the SSS to be able to use it routinely even under harsh weather and altitude conditions that we expect to encounter on the high Tibetan plateau or at Dome A in Antarctica.SSS will also be applied for the site testing campaign of the future Chinese extremely large telescope.
LIU LiYongYAO YongQiangVERNIN JeanWANG HongShuaiCHADID MeriemeWANG YiPingGIORDANO ChristopheYIN JiaQIAN Xuan
High resolution deep imaging from space and adaptive optics techniques with large ground-based facilities have enabled studies examining faint host galaxies of high redshift quasi-stellar objects (QSOs). However, the related image processing techniques, especially for a precise point-spread function (PSF) reconstruction and characterization of the host galaxy light profiles, have yet to be optimized. We present here the scientific performance of a principal component analysis (PCA) based PSF subtraction of the central bright point source of high redshift QSO images, as well as further characterization of the host galaxy profile by directly fitting a Sèrsic model to the residual image using the Markov Chain Monte Carlo (MCMC) algorithm. With a set of reference PSF star images which represent interleaving exposures between the QSO imaging, we can create an orthogonal basis of eigen-images and restore the PSF of QSO images by projecting the QSO images onto the basis. In this way, we can quantify the modes in which the PSF varies with time by a basis function that characterizes the temporal variations of the reference star as well as the QSO images. To verify the algorithm, we performed a simulation and applied this method to one of the high-z QSO targets from Mechtley et al. We demonstrate that the PCA-based PSF subtraction and further modeling of the galaxy’s light profile using MCMC fitting would sufficiently remove the effects from central dominating point sources, and improve characterization ability for the host galaxies of high-z QSOs to the background noise level which is much better than previous two-component fitting procedures.
