Point spread function (PSF) models are critical to Hubble Space Telescope (HST) data analysis. Astronomers unfamiliar
with optical simulation techniques need access to PSF models that properly match the conditions of their observations,
so any HST modeling software needs to be both easy-to-use and have detailed information on the telescope and
instruments. The Tiny Tim PSF simulation software package has been the standard HST modeling software since its
release in early 1992. We discuss the evolution of Tiny Tim over the years as new instruments and optical properties
have been incorporated. We also demonstrate how Tiny Tim PSF models have been used for HST data analysis. Tiny
Tim is freely available from tinytim.stsci.edu.
With the completion of the first generation instrumentation set on the Very Large Telescope, a total of eleven instruments are now provided at the VLT/VLTI for science operations. For each of them, ESO provides automatic data reduction facilities in the form of instrument pipelines developed in collaboration with the instrument consortia. The pipelines are deployed in different environments, at the observatory and at the ESO headquarters, for on-line assessment of observations, instruments and detector monitoring, as well as data quality control and products generation. A number of VLT pipelines are also distributed to the user community together with front-end applications for batch and interactive usage. The main application of the pipeline is to support the Quality Control process. However, ESO also aims to deliver pipelines that can generate science ready products for a major fraction of the scientific needs of the users. This paper provides an overview of the current developments for the VLT/VLTI next generation of instruments and of the prototyping studies of new tools for science users.
The current generation of 8-10m optical ground-based telescopes have a symbiotic relationship with space telescopes. For direct imaging in the optical the former can collect photons relatively cheaply but the latter can still achieve, even in the era of adaptive optics, significantly higher spatial resolution, point-spread function stability and astrometric fidelity over fields of a few arcminutes. The large archives of HST imaging already in place, when combined with the ease of access to ground-based data afforded by the virtual observatory currently under development, will make space-ground data fusion a powerful tool for the future. We describe a photometric image restoration method that we have developed which allows the efficient and accurate use of high-resolution space imaging of crowded fields to extract high quality photometry from very crowded ground-based images. We illustrate the method using HST and ESO VLT/FORS imaging of a globular cluster and demonstrate quantitatively the photometric measurements quality that can achieved using the data fusion approach instead of just using data from just one telescope. This method can handle most of the common difficulties encountered when attempting this problem such as determining the geometric mapping to the requisite precision, deriving the PSF and the background.
We have developed a method for the linear reconstruction of an image from undersampled, dithered data, which has been sued to create the distributed, combined Hubble Deep Field images - the deepest optical images yet taken of the universe. The algorithm known as variable-pixel linear reconstruction, preserves photometry and resolution, can weight input images according to the statistical significance of each pixel, and removes the effects of geometric distortion both on image shape and photometry. In this paper, the algorithm and its implementation are described, and measurements of the photometric accuracy and image fidelity are presented. In addition, we describe the use drizzling to combine dithered images in the presence of cosmic rays.
KEYWORDS: Point spread functions, Radio optics, Image restoration, Astronomy, Monochromatic aberrations, Cameras, Optical fiber cables, Data analysis, Radio astronomy, Space telescopes
Images and spectra obtained with the Hubble Space Telescope (HST) in its current configuration suffer from severe spherical aberration and are therefore routinely restored for visualization and scientific evaluation. Among the non-linear, iterative restoration methods investigated so far, the Richardson-Lucy (RL) algorithm stands out for the quality of the restorations it delivers at modest computational cost. In this contribution we summarize our experience so far with restoration methodology applied to HST imagery and make a first attempt at drawing some general conclusions about its usefulness.
Perry Greenfield, Francesco Paresce, David Baxter, Philip Hodge, Richard Hook, Peter Jakobsen, Robert Jedrzejewski, Anatonella Nota, William Sparks, Nigel Towers, Robin Laurance, Duccio Macchetto
An overview of the Faint Object Camera and its performance to date is presented. In particular, the detector's efficiency, the spatial uniformity of response, distortion characteristics, detector and sky background, detector linearity, spectrography, and operation are discussed. The effect of the severe spherical aberration of the telescope's primary mirror on the camera's point spread function is reviewed, as well as the impact it has on the camera's general performance. The scientific implications of the performance and the spherical aberration are outlined, with emphasis on possible remedies for spherical aberration, hardware remedies, and stellar population studies.
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