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Old 26-01-2012, 07:10 PM
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Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 7,191
Why do Star Images grow? - Part2

Well, I never give up....
Without boring everyone (again!) I've put the detail in the attached doc files.
Here's the executive summary:
1. All stars recorded on the one frame have exactly the same FWHM.
2. Depending on the exposure and the gain/ white point settings the apparent size of the star image can be altered. Faint stars can appear smaller than the FWHM.
3. When the brighter star image satuarates the chip, the size of the star image can grow well beyond the FWHM.
This is summarised in the attached graph.

These factors are important in the field of Photometry, where eventually I found the answer.
Attached Thumbnails
Click for full-size image (fig18_2_edit.jpg)
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Attached Files
File Type: doc Why do star Images grow_Sec1.doc (96.0 KB, 36 views)
File Type: doc Why do star Images grow Part2_sect2.doc (103.0 KB, 23 views)
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