Extreme-Contrast Ratio Imaging of Bright Star Fields using Charge-Injection Devices
Sawant, Sailee Mangesh
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The intrinsic nature of many astronomical sources, such as exoplanets, binary and multiple star systems, circumstellar disks, and active galactic nuclei and their host galaxies, introduces challenging requirements for observational instrumentation and techniques. In each case, we encounter situations where the light from bright sources hampers our abilities to detect surrounding fainter targets. To explore and study all features of such extreme-contrast ratio (ECR) scenes, we must perform observations at the maximum possible contrast ratios. However, direct imaging of fainter objects in the vicinity of bright sources imposes limitations on the type of contrast ratios achievable using ground- and spacebased telescopes. The light from bright sources completely saturates conventional imaging instrumentations (e.g., charge-coupled devices). Consequently, several point-spread suppression techniques (e.g., coronagraphy and nulling interferometry) are implemented to mitigate bright source signals and achieve higher contrast ratios. However, these techniques have complex operational requirements that make faint signal detection technically intricate, expensive, and time-consuming. An alternative is to use appropriate instrumentations that can carry out direct ECR imaging free from the limitations of currently employed techniques. A class of imaging detectors, charge-injection devices (CIDs), have the intrinsic ability to achieve ECRs owing to their unique readout architectures and inherent antiblooming capabilities. An on-sky testing of a commercially available CID, the SpectraCAM XDR (SXDR), demonstrated raw contrast ratios from sub-optimal ground-based astronomical observations that imposed practical limits on the maximum achievable contrast ratios using CIDs. The main goal of this research is to quantify the CID imaging performance for ground-based direct ECR observations from a high-altitude observatory. In this dissertation, we demonstrate the direct ECR imaging capabilities of the SXDR using observations of several bright star fields from La Palma, Spain. We report the maximum direct contrast ratio of ∆mr = 18.54, log10(CR) = 7.41±0.08, or 1 part in 26 million. This is an order of magnitude higher compared to the previous CID results. We also present the results of an 8 months CID technology demonstration mission on-board the International Space Station. The on-orbit demonstrations qualified CIDs to Technology Readiness Level 8. As a result, CIDs can now be considered as astronomical imaging detectors for future space-based telescopes.