Monday, June 4, 2012
3:00pm (334 JFB)
Title: Towards Optical Intensity Interferometry for High Angular Resolution Stellar Astrophysics
Most stars are detected as point sources, and recent developments in high angular resolution astronomy have enabled to image stars as extended objects with complex atmospheres and circumstellar environments. However, most neighboring stars are still beyond the angular resolution reach of current observatories.
Atmospheric Cherenkov Telescopes (ACT) are used in gamma-ray astronomy to investigate violent phenomena in the universe. However, this technique can also be used for stellar astrophysics on some isolated sources. Such is the case with the Xray binary LSI+61 303 which was detected in the TeV range. A gamma-ray attenuation model is developed and applied it to this system. This models allows to place constraints on fundamental properties of the system. However, a much better understanding of this system, and more so of nearby bright stellar systems, could be obtained with high angular resolution techniques.
Light detectors such as ACT, can be used as intensity interferometry receivers in the visible band (400 nm). Optical stellar intensity interferometry with air Cherenkov telescope arrays, composed of nearly 100 telescopes, will provide means to measure fundamental stellar parameters and also open the possibility of model-independent imaging. The phase of the complex degree of coherence is not measured in this technique. However, several model-independent phase reconstruction techniques have been developed. Here we implement a Cauchy-Riemann based algorithm to recover images from simulated data. We find that stellar images can be accurately reconstructed, and results are further improved with post-processing routines.
Finally, experimental efforts to measure intensity correlations are expounded. The functionality of analog and digital correlators is demonstrated. Intensity correlations have been measured for a simulated star emitting pseudo-thermal light, resulting in angular diameter measurements. The StarBase observatory, consisting of a pair of 3 m telescopes separated by 23 m, is described