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We present a prescription to correct large-scale intensity variations affecting imaging data taken with the Wide Field Imager (WFI) at the MPG/ESO 2.2 m telescope at the European Southern Observatory at La Silla in Chile. Such smoothly varying, large-scale gradients are primarily caused by non-uniform illumination due to stray light, which cannot be removed using standard flatfield procedures. By comparing our observations to the well-calibrated, homogeneous multi-colour photometry from the Sloan Digital Sky Survey we characterise the intensity gradients across the camera by second-order polynomials. The application of these polynomials to our data removes the gradients and reduces the overall scatter. We also demonstrate that applying our correction to an independent WFI dataset significantly reduces its large-scale variations, indicating that our prescription provides a generally valid and simple tool for calibrating WFI photometry.
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Quantum techniques can be used to enhance the signal-to-noise ratio in optical imaging. Leveraging the latest advances in single photon avalanche diode array cameras and multi-photon detection techniques, here we introduce a super-sensitive phase imager, which uses space-polarization hyper-entanglement to operate over a large field-of-view without the need of scanning operation. We show quantum-enhanced imaging of birefringent and non-birefringent phase samples over large areas, with sensitivity improvements over equivalent classical measurements carried out with equal number of photons. The practical applicability is demonstrated by imaging a biomedical protein microarray sample. Our quantum-enhanced phase imaging technology is inherently scalable to high resolution images, and represents an essential step towards practical quantum imaging.
The University of Hawaii Wide-Field Imager (UHWFI) is a focal compressor system designed to project the full half-degree field of the UH 2.2 m telescope onto the refurbished UH 8Kx8K CCD camera. The optics use Ohara glasses and are mounted in an oil-filled cell to minimize light losses and ghost images from the large number of internal lens surfaces. The UHWFI is equipped with a six-position filter wheel and a rotating sector blade shutter,both driven by stepper motors. The instrument saw first light in 2004 in an engineering mode. After filling the lens cell with index matching oil, integration of all software components into the user interface, tuning of the CCD performance, and the purchase of the final filter set, UHWFI is now fully commissioned at the UH 2.2 m telescope.
Astronomical widefield imaging of interferometric radio data is computationally expensive, especially for the large data volumes created by modern non-coplanar many-element arrays. We present a new widefield interferometric imager that uses the w-stacking algorithm and can make use of the w-snapshot algorithm. The performance dependencies of CASAs w-projection and our new imager are analysed and analytical functions are derived that describe the required computing cost for both imagers. On data from the Murchison Widefield Array, we find our new method to be an order of magnitude faster than w-projection, as well as being capable of full-sky imaging at full resolution and with correct polarisation correction. We predict the computing costs for several other arrays and estimate that our imager is a factor of 2-12 faster, depending on the array configuration. We estimate the computing cost for imaging the low-frequency Square-Kilometre Array observations to be 60 PetaFLOPS with current techniques. We find that combining w-stacking with the w-snapshot algorithm does not significantly improve computing requirements over pure w-stacking. The source code of our new imager is publicly released.
The large-scale distribution of globular clusters in the central region of the Coma cluster of galaxies is derived through the analysis of Hubble Space Telescope/Advanced Camera for Surveys data. Data from three different HST observing programs are combined in order to obtain a full surface density map of globular clusters in the core of Coma. A total of 22,426 Globular cluster candidates were selected through a detailed morphological inspection and the analysis of their magnitude and colors in two wavebands, F475W (Sloan g) and F814W (I). The spatial distribution of globular clusters defines three main overdensities in Coma that can be associated with NGC 4889, NGC 4874, and IC 4051 but have spatial scales five to six times larger than individual galaxies. The highest surface density of globular clusters in Coma is spatially coincidental with NGC 4889. The most extended overdensity of globular clusters is associated with NGC 4874. Intracluster globular clusters also form clear bridges between Coma galaxies. Red globular clusters, which agglomerate around the center of the three main subgroups, reach higher surface densities than blue ones.
The Wide Field Imager (WFI) is one of the two scientific instruments proposed for the Athena+ X-ray observatory. It will provide imaging in the 0.1-15 keV band over a wide field, simultaneously with spectrally and time-resolved photon counting. The instrument is designed to make optimal use of the grasp (collecting area times solid angle product) provided by the optical design of the Athena+ mirror system (Willingale et al. 2013), by combining a sensitive approx. 40 diameter field of view (baseline; 50 goal) DEPFET detector with a pixel size properly sampling the angular resolution of 5 arc sec on-axis (half energy width).This synthesis makes the WFI a very powerful survey instrument, significantly surpassing currently existing capabilities (Nandra et al. 2013; Aird et al. 2013). In addition, the WFI will provide unprecedented simultaneous high-time resolution and high count rate capabilities for the observation of bright sources with low pile-up and high efficiency. In this paper, we summarize the instrument design, the status of the technology development, and the baseline performance.
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