Demonstration of The Principle
The sequence of images below shows how lucky imaging works. From a series of 50,000 images taken at a speed of almost 40 images per second, five different long exposure images have been created. Additionally, a single exposure with very low image quality and another single exposure with very high image quality are shown at the beginning of the demo sequence.
| Single exposure with very low image quality, not selected for Lucky Imaging. | ||
| Single exposure with very high image quality, selected for Lucky Imaging. | ||
| The image shows the sum of all 50,000 images, which is almost the same as the 21 minutes (50,000/40 seconds) long exposure seeing limited image. It looks like a typical star image, slightly elongated. The full width at half maximum (FWHM) of the seeing disk is around 0.9 arcsec. | ||
| The image shows the sum of all 50,000 single images but here with the center of gravity (centroid) of each image shifted to the same reference position. This is the tip-tilt corrected, or image stabilized, long exposure image. It already shows more details - two objects - than the seeing limited image. | ||
| The image shows the 25,000 (50% selection) best images added together with the brightest pixel in each image moved to the same reference position. In this image, we can almost see three objects. | ||
| The image shows the 5,000 (10% selection) best images added together with the brightest pixel in each image moved to the same reference position. The surrounding seeing halo is further reduced, an airy ring around the brightest object becomes clearly visible. | ||
| The image shows the 500 (1% selection) best images added together with the brightest pixel in each image moved to the same reference position. The seeing halo is further reduced. The signal-to-noise ratio of the brightest object is the highest in this image. |
The difference between the seeing limited image and the best 1% images selected result is quite remarkable: a triple system can be detected. The brightest component in the West is a V=14.9 magnitude M4V star. This component is the lucky imaging reference source. The weakest - tertiary - component a M7-M8 spectral type star. The distance of the system is about 45 pc. Airy rings can be seen, which indicate that the diffraction limit of the Calar Alto Observatory's 2.2m telescope was reached. The signal to noise ratio of the point sources increases with stronger selection. The seeing halo on the other side is more suppressed. The separation between the two brightest objects is around 0.55 arcsec and between the two faintest objects less than 0.15 arcsec. At a distance of 45 pc this corresponds to 6.75 times the distance between Earth and Sun, around 1 billion kilometers (109 km).
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