There are many Rosette Nebula images to be found online and in print, captured with several types of telescopes and cameras, then post-processed using techniques often not discussed. For comparison purposes, I prefer photographs in the printed literature because they have to pass an editorial review at some level in order to be accepted for publication. Here are some references from my home library.
Many of the young stars near the centre of the Rosette Nebula were created by the surrounding gas and are now the sources that illuminate it. Although we know the open cluster NGC 2244 exists in that location, there are background and foreground stars that are not cluster members. Usually membership to such a cluster can be determined by distance, proper motion and spectral type. Membership to NGC 2244 was an important subject of research in the late 1970s and early 1980s because of its insight into stellar evolution.
The brightest star in the cluster is 12 Monocerotis (HD 46241), shown in this cropped Origin image. It has a visual magnitude of 5.830 and is a spectral type K0III according to Simbad data. It is interesting to note what Robert Burnham, Jr. wrote about this star.
"The brightest member, 12 Monocerotis, is a yellow giant of magnitude 5.85, of spectral type K0III. This star, however, must have an abnormally high luminosity (about 2500 suns) if it is at the same distance as the cluster; either it is a foreground object or the attribution to luminosity class III is very seriously in error. The normal luminosity of a type K0III star is about 30 times that of the Sun." From Burnham's Celestial Handbook: Volume Two, Dover Publications, Inc., New York, 1978, pp. 1196-1198.
In the book Stars and Clusters, Cecilia Payne-Gaposchkin, Harvard University Press, Cambridge, Massachusetts, 1979, a more pointed comment about the membership of 12 Monocerotis appeared in the caption for Figure 7.4 on page 100.
"NGC 2244. The brightest stars near the main sequence of this very young cluster are blue supergiants; probably the redder star, of luminosity class III, is not a member."
Since the late 1970s, 12 Monocerotis has been singled out as being a foreground star and not a member of the open cluster NGC 2244. Examples of this from Sky & Telescope magazine are found in the following issues:
To determine which stars belong to the open cluster NGC 2244 we have to turn to the scholarly literature. Two research papers are sufficient to allow me to label several high probability cluster members on my unprocessed Origin image shown here (note that the nebula regions are not as bright as the previous images).
Reference 1 uses UBV photoelectric and photographic photometry to analyze 400 stars, mostly in the central region of the nebula. Only stars brighter than visual magnitude 14 were considered. Since Celestron Origin can resolve stars fainter than magnitude 20, all of the stars in this study are visible in this image provided they fall within the boundaries of the 1.27° x 0.85° field of view. The authors identified 164 likely cluster members. Rather than label all of these stars, I decided to reduce the selection by correlating these stars with the most probable members determined by the proper motion study in Reference 2.
Marschall et al. used the same 400 stars from Reference 1 and added two more. Their NGC 2244 data were taken from analysis of the Yerkes 40-inch and Allegheny 30-inch refractor plates spanning a 60-year time period from 1914 to 1974. The limiting magnitudes of these plates (18 exposures) ranged from 12.0 to 14.5. In total, relative proper motions were estimated for 287 of the 402 stars in this study. In order to reduce the number of cluster members from 164 for labelling purposes, I arbitrarily chose the stars from the 164 in Reference 1 that also had kinematic-based probabilities greater than 80% from Reference 2. Consequently, I have labelled 49 highly probable members using yellow labels/arrows. I also identified these stars using the Aladin Sky Atlas.
It is noteworthy that three prominent stars labelled in red have been determined to be foreground stars including 12 Monocerotis.
The cluster members are labelled in yellow. I have included the visual magnitudes from the two references (R) and SkySafari 7 Pro (S).
1. HD 259012, 9.19R, 9.36S
2. HD 46056, 8.12R, 8.23S
3. HD 46149, 7.56R, 7.59S
4. HD 46106, 7.90R, 7.92S
5. HD 46150, 6.73R, 6.78S
6. HD 259105, 9.32R, 9.36S
7. HD 259172, 10.73R, 10.57S
8. HD 46202, 8.10R, 8.18S
9. HD 46223, 7.14R, 7.26S
10. HD 259135, 8.55R, 8.60S
11. TYC 0154-2504-1, 10.57R, 10.80S
12. TYC 0154-2480-1, 10.24R, 10.73S
13. TYC 0154-2337-1, 9.68R, 9.71S
14. GAIA 3131327137869407488, 13.00R, 12.96S
15. GAIA 3131335654785454848, 12.96R, 13.00S
16. GAIA 3131335689145193344, 11.97R, 11.96S
17. GAIA 3131335448627027456, 11.64R, 11.60S
18. GAIA 3131328546618525184, 13.45R, 13.41S
19. GAIA 3131328306100387584, 13.91R, 13.95S
20. GAIA 3131766633284595712, 13.09R, 13.01S
21. GAIA 3131386992533297792, 13.21R, 13.12S
22. GAIA 3131386580216467968, 12.46R, 12.42S
23. GAIA 3131383414821781504, 13.39R, 13.40S
24. GAIA 3131336002681686656, 11.24R, 11.22S
25. GAIA 3131335311195645056, 12.40R, 12.63S
26. GAIA 3131335036310165632, 11.94R, 11.95S
27. GAIA 3131335040608985216, 13.16R, 13.23S
28. GAIA 3131334800090848640, 12.57R, 12.60S
29. GAIA 3131334967590689536, 12.66R, 12.65S
30. GAIA 3131761376245008384, 12.56R, 12.49S
31. GAIA 3131338712802161408, 13.70R, 13.66S
32. GAIA 3131334147255713792, 12.94R, 12.96S
33. GAIA 3131332085671474816, 12.77R, 12.76S
34. GAIA 3131330775702613504, 12.84R, 12.97S
35. GAIA 3131331192318335104, 12.75R, 12.99S
36. GAIA 3131318204337676800, 11.31R, 11.37S
37. GAIA 3131317100528398592, 11.08R, 11.20S
38. GAIA 3131713478769318400, 12.57R, 12.59S
39. GAIA 3131708530967403520, 13.67R, 13.60S
40. GAIA 3131333906737530112, 13.54R, 13.54S
41. GAIA 3131318444855819008, 12.68R, 12.69S
42. GAIA 3131317688941573760, 13.56R, 13.49S
43. GAIA 3131317723301308032, 12.88R, 12.89S
44. GAIA 3131317139185784192, 12.61R, 12.73S
45. GAIA 3131313943730108672, 13.84R, 13.74S
46. GAIA 3131714818799058048, 12.85R, 12.87S
47. GAIA 3131709939716261504, 13.75R, 13.75S
48. GAIA 3131696470699235584, 13.33R, 13.37S
49. GAIA 3131764468620996224, 13.16R, 13.10S
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