We present a new processing technique aimed at significantly improving the angular differential imaging method (ADI) in the context of high-contrast imaging of faint objects nearby bright stars in observations obtained with extreme adaptive optics (EXAO) systems. This technique, named "SFADI" for "Speckle-Free ADI", allows to improve the achievable contrast by means of speckles identification and suppression. This is possible in very high cadence data, which freeze the atmospheric evolution. Here we present simulations in which synthetic planets are injected into a real millisecond frame rate sequence, acquired at the LBT telescope at visible wavelength, and show that this technique can deliver low and uniform background, allowing unambiguous detection of 10 −5 contrast planets, from 100 to 300 mas separations, under poor and highly variable seeing conditions (0.8 to 1.5 arcsec FWHM) and in only 20 min of acquisition. A comparison with a standard ADI approach shows that the contrast limit is improved by a factor of 5. We extensively discuss the SFADI dependence on the various parameters like speckle identification threshold, frame integration time, and number of frames, as well as its ability to provide high-contrast imaging for extended sources, and also to work with fast acquisitions.
In this work we explore the possibility of using recurrence quantification analysis (RQA) in astronomical high-contrast imaging to statistically discriminate the signal of faint objects from speckle noise. To this end, we tested RQA on a sequence of high frame rate (1 kHz) images acquired with the SHARK-VIS forerunner at the Large Binocular Telescope. Our tests show promising results in terms of detection contrasts at angular separations as small as 50 mas, especially when RQA is applied to a very short sequence of data (2 s). These results are discussed in light of possible science applications and with respect to other techniques such as, for example, angular differential imaging and speckle-free imaging.
The ciliate communities, living in different habitats of Lake Massaciuccoli and its marshland, were studied from June 1992 to July 1993. Ninety-three species were identified and their relative abundance and biomasses evaluated, both at the surface and at the bottom levels of four different stations (placed in the lake close to the shore of Piaggetta, Burlamacca canal, Collettore canal, and in one small shallow pond called Chiaro). The most interesting results are: (a) the great biodiversity of the ciliate communities found in Lake Massaciuccoli likely depends upon the wide range of different microhabitats available for these communities and present in the four stations chosen; (b) the communities of the Piaggetta and Burlamacca stations are similar to each other, mainly characterized in their seasonal dynamics at the surface level (open water); (c) the communities of the Collettore and the Chiaro stations are typical of shallow waters, characterized by very large amounts of organic debris on the bottom, as shown by the rich populations of filter-feeders and thigmotactic species which, in turn, constitute a good pabulum for the carnivorous species; (d) the major peaks of specimens density and biomass values were found during autumn 1992 and in early spring 1993.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.