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GPI Contrast and sensitivity
Achieved sensitivity is a function of many parameters, including contrast, inner working distance, brightness of the central star (if any), observing mode (dithered, sky-offset, sky-rotation), and, weather conditions.
Contrast as function of I-magnitude of the star
- The figure above shows typical GPIES contrasts for a 1-hour sequence (42 x 1 minute exposures) on targets as a function of magnitude
- The contrasts are most strongly correlated with target star magnitude and with atmospheric correlation timescale tau0.
- Contrast at 0.4 arcseconds is determined primarily by residual atmospheric speckles and correlates most strongly with seeing
- Contrast at 0.25 arcseconds is determined primarily by FPM centering and quasi-static errors
- Contrast at 0.8 arcsecods approaches photon-noise limits and hence is a strong function of star magnitude
- There is a significant benefit to having >20 degrees of field rotation to enhance ADI PyKLIP processing
Contrast relation betweeb 1 minute raw image contrast and 1h processed sequence
Image above shows the Correlation between raw 60-second contrasts and final 40-image combined contrasts after PyKLIP processing (contrast expressed in astronomical magnitudes).
Contrast as a function of accumulated field rotation
The image above shows the final pyKlip contrast vs field rotation.