After imaging the M13 starfield for a little over three and a half hours at F/2.2 I was curious to see how deep (magnitude limit) the starfield actually was. Using the annotation script in PixInsight and downloading the Gaia EDR3 star catalogs to its max, I animated a series of frames listing the magnitudes of the stars. The animation starts with the initial image I posted earlier in Astrobin (see full res image here
https://www.astrobin.com/qkgyfe/) and then steps through 1 magnitude fainter every three seconds. Magnitudes (violet labels) start at 10th and brighter since there aren't many bright stars in the field and no naked eye (6th mag) stars. The animation appears to peak (most numerous) at the dimmest star frame - the limit of the Gaia EDR3 catalog - or between 20th and 21st magnitude. Looking at this faintest of fields shows many of fainter stars that are as yet uncatalogued and are fainter than 21st magnitude!
Knowing that with a difference of one magnitude between stars means that a star will be 2.512 x brighter/dimmer to each one another, this animation is showing a total brightness of 2.512 x E13 (brightest star~8 & dimmest ~21; 21 - 8 = 13) for about 160, 000 x difference of the brightest stars compared to the dimmest of stars in this starfield!
Many variables have gone into this animation process i.e. length of exposures, processing technique and label crowding, so I'm not sure that there is any scientific value performed in this exercise. Repeating the procedure using the Gaia parallax and proper motion data would interesting and fairly easy to do and might be of interest.
Hope you enjoy this effort.
Dan
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