Advanced Exposure - Time Calculations : Undersampling , Dithering , Cosmic

Advanced Exposure-Time Calculations: Undersampling, Dithering, Cosmic Rays, Astrometry, and Ellipticities

Towards Optimal Analysis of HST Crowded Stellar Fields

Abstract. A Nordic group is using the Hubble Space Telescope in a study of stellar populations in the Bar of the Large Magellanic Cloud. Through Strömgren uvby photometry, we determine ages, metallicities, and the luminosity function. We have designed and applied an exposure dithering pattern in order to decrease the effects of undersampling. This also enables a detailed study of detector prope...

Associations of WFPC2 Exposures

Unlike NICMOS and STIS, where a dataset might be constituted of a set of exposures, the WFPC2 data set’s structure was thought to be a repository of all the files belonging to a single exposure. Lacking higher level of abstraction, there is no simple way of tracing back which observation strategy (e.g., cosmic ray rejection, dithering) a WFPC2 PI decided to employ. Building associations of WFPC...

Message Passing Algorithms for Compressed Sensing

Compressed sensing aims to undersample certain high-dimensional signals yet accurately reconstruct them by exploiting signal characteristics. Accurate reconstruction is possible when the object to be recovered is sufficiently sparse in a known basis. Currently, the best known sparsity-undersampling tradeoff is achieved when reconstructing by convex optimization, which is expensive in important ...

Time Delays in Cosmic Ray Propagation

Cosmic Rays (CR) travel at speeds essentially indistinguishable from the speed of light. However whilst travelling through magnetic fields, both regular and turbulent, they are delayed behind the light since they are usually charged particles and their paths are not linear. Those delays can be so long that they are an impediment to correctly identifying sources which may be variable in time. Fu...