Editing Lucky imaging (section)

==Demonstration of the principle==
The sequence of images below shows how lucky imaging works.<ref>{{cite journal |last=Hippler |first=Stefan |display-authors=etal |year=2009 |title=The AstraLux Sur Lucky Imaging Instrument at the NTT |url=http://www.eso.org/sci/publications/messenger/archive/no.137-sep09/messenger-no137.pdf |journal=The Messenger |volume=137 |pages=14–17 |bibcode=2009Msngr.137...14H}}</ref> 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. The astronomical target shown has the [[2MASS]] ID J03323578+2843554. North is up and East on the left.
{| class=wikitable
| valign="top" | [[File:LuckySingleExposureStrehl_3.5Percent.png|LuckySingleExposureStrehl 3.5Percent|150px]]
| valign="top" | Single exposure with low image quality, not selected for lucky imaging.
| valign="top" | [[File:Lucky Single Exposure Strehl 16Percent.png|Lucky Single Exposure Strehl 16Percent|150px]]
| valign="top" | Single exposure with very high image quality, selected for lucky imaging.
|-
| valign="top" | [[File:LuckyImagingDemonstration1.png|150px]] 
| valign="top" | This image shows the average of all 50,000 images, which is almost the same as the 21 minutes (50,000/40 seconds) long exposure [[Astronomical seeing|seeing]] limited image. It looks like a typical star image, slightly elongated. The full width at half maximum (FWHM) of the [[Astronomical seeing|seeing]] disk is around 0.9 arcsec.
| valign="top" | [[File:LuckyImagingDemonstration2.png|150px]] 
| valign="top" | This image shows the average 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 [[adaptive optics|tip-tilt]]-corrected, or image-stabilized, long-exposure image. It already shows more details — two objects — than the [[Astronomical seeing|seeing]]-limited image.
|-
| valign="top" | [[File:LuckyImagingDemonstration3.png|150px]] 
| valign="top" | This image shows the 25,000 (50% selection) best images averaged, after the brightest pixel in each image was moved to the same reference position. In this image, we can almost see three objects.
| valign="top" | [[File:LuckyImagingDemonstration4.png|150px]] 
| valign="top" | This image shows the 5,000 (10% selection) best images averaged, after the brightest pixel in each image was moved to the same reference position. The surrounding [[Astronomical seeing|seeing]] halo is further reduced, an [[Airy_disk|Airy ring]] around the brightest object becomes clearly visible.
|-
| valign="top" | [[File:LuckyImagingDemonstration5.png|150px]] 
| valign="top" | This image shows the 500 (1% selection) best images averaged, after the brightest pixel in each image was moved to the same reference position. The [[Astronomical seeing|seeing]] halo is further reduced. The [[signal-to-noise ratio]] of the brightest object is the highest in this image.
|}

The difference between the [[Astronomical seeing|seeing]] limited image (third image from top) and the best 1% images selected result is quite remarkable: a triple system has been detected. The brightest component in the West is a V=14.9 magnitude M4V star. This component is the lucky imaging reference source. The weaker component consists of two stars of spectral classes M4.5 and M5.5.<ref>{{Cite journal|doi = 10.1088/0004-637X/754/1/44|title = The Astralux Large M-Dwarf Multiplicity Survey|year = 2012|last1 = Janson|first1 = Markus|last2 = Hormuth|first2 = Felix|last3 = Bergfors|first3 = Carolina|last4 = Brandner|first4 = Wolfgang|last5 = Hippler|first5 = Stefan|last6 = Daemgen|first6 = Sebastian|last7 = Kudryavtseva|first7 = Natalia|last8 = Schmalzl|first8 = Eva|last9 = Schnupp|first9 = Carolin|last10 = Henning|first10 = Thomas|journal = The Astrophysical Journal|volume = 754|issue = 1|page = 44|arxiv = 1205.4718|bibcode = 2012ApJ...754...44J|s2cid = 118475425}}</ref> The distance of the system is about 45 [[parsec]]s (pc). Airy rings can be seen, which indicates that the diffraction limit of the [[Calar Alto Observatory]]'s 2.2 m telescope was reached. The signal to noise ratio of the point sources increases with stronger selection. The [[Astronomical seeing|seeing]] halo on the other side is more suppressed. The separation between the two brightest objects is around 0.53 arcsec and between the two faintest objects less than 0.16 arcsec. At a distance of 45 pc this corresponds to 7.2 times the distance between Earth and Sun, around 1 billion kilometers (10<sup>9</sup> km).