This NGC2419 image was taken in April 2012 with 2 hours of 1X1 luminance data and 4.5 hours total of RGB data 2X2 (all 10min. subs) @ -10C from CAV with the 14.5-inch RCOS and Apogee U16M. Few deep-sky objects challenge the astrophotographer like planetary nebulae and globular clusters, but for different reasons. Many planetary nebulae are bright but are also small so high resolution (good sampling/long focal length, fine focus and good seeing) is critical to creating a good image. Likewise, globular cluster images are judged by the quality and quantity of stars in the image. The Hubble Space Telescope produces tiny pinpoint stars in globulars that yield spectacular images! Most Milky Way globs hover around the central hub of our galaxy and are, therefore, only about 25,000 light-years away (M13 is 22K ly distance). Obviously, to get a good globular cluster image, it would make sense to pick a glob that is large or as close as possible to get the best resolution such as Omega Centauri or M13. But I chose a rogue globular cluster NGC2419 in Lynx because I had heard it was 300,000 ly away (farther than the Magellanic Clouds) and thought it would be a challenge to resolve. This distant glob is the Milky Way’s version of the Andromeda Galaxy’s G1 globular cluster, both thought to have been born elsewhere and “captured”. So I was very pleasantly surprised when I processed the attached distant globular cluster image not only resolved but showing many distinct blue and yellow stars of varying size. A little further research disclosed that this cluster is extraordinarily massive and bright and has a peculiar chemistry and structure. I sure didn’t expect to get this much resolution on a glob 10 times more distant than the average glob! Turns out that the glob’s half-light radius is 5 times larger than other globs of similar luminosity (see link below). This observation suggests that NGC2419 is actually a remnant nucleus of a dwarf elliptical satellite galaxy that has been long-ago accreted (swallowed) by our Milky Way Galaxy! A peculiarity of globular clusters I have noticed on images is the presence of dual yellow and blue star populations. I have seen this in other globs I have imaged like M13 and M15 but never expected to see this in such a remote glob! I put this question out there for anyone to answer. Is this apparent dual star population an artifact of processing or is it real? The M13 Hubble image (link below) also shows yellow and blue stars if you look closely at that image. Are these blue stars in NGC2419 the same type “blue stragglers” well seen in NGC6397 (link below)? I assume the yellow members are old population II stars. The bright stars in the NGC2419 image are foreground 7-8th magn.; the brightest is SAO60232.
http://en.wikipedia.org/wiki/File:Heart_of_M13_Hercules_Globular_Cluster.jpg – Hubble Image – Heart of close glob M13 – see yellow and blue stars
http://en.wikipedia.org/wiki/Globular_cluster — good wiki write-up on globs
http://en.wikipedia.org/wiki/Blue_straggler – Blue straggler wiki – magnify image of NGC 6397!
http://authors.library.caltech.edu/28309/1/Cohen2011p16390Astrophys_J.pdf – Good reading about NGC2419
http://authors.library.caltech.edu/21512/1/Cohen2010p12231Astrophys_J.pdf – NGC2419 – Remnant of Accreted Dwarf Galaxy
http://en.wikipedia.org/wiki/Mayall_II – Andromeda’s G1 Glob