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NGC 2437
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NGC 2437 (also Messier 46, M46 and OCL 601) is a magnitude 6.1 open star cluster located 5400 light-years away in the constellation Puppis.
The cluster contains about 500 stars, of which about 150 have magnitudes ranging from +10 to +13. The brightest of them belong to the A0 spectral type, and are about 100 times brighter than the Sun (the brightest is magnitude +8.7). Its spatial diameter is about 30 light-years.
The age is estimated as between 100 to 300 million years.
Within the cluster are seemingly the planetary nebulae NGC 2438 and PK 231+04.1 (HD 62099), however radial velocity studies (as well as the age of the nebula and clusters) indicate that they did not originate in Messier 46, and are foreground objects.

The cluster can be found about 5 degrees south of alpha Monoceros, and 1 degree to the east from the star cluster M47, as a hazy round glow in binoculars. In moderate telescope apertures (127-180 mm) most of the stars can be resolved. The planetary nebula NGC 2438 is just to the north-east of the center of M46. 

The cluster was first discovered by French astronomer Charles Messier using a 100 mm (four inch) refracting telescope from Hôtel de Cluny (now the Musée national du Moyen Age), in Paris, France on the 19th February 1771; and listed as number 46 in his catalogue of comet-like objects.

Right Ascension 07h 41m 46.8s, Declination -14° 48 36"

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Posts: 131433
Date:
Messier 46
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Title: The Open Cluster NGC 2437 (Messier 46) 
Authors: T. J. Davidge 

The stellar content of the open cluster NGC 2437 (Messier 46) is investigated using moderately deep u*,g', and r' MegaCam images. When compared with solar metallicity isochrones, the (g', u'-g') and (r', g'-r') CMDs are consistent with an age log(t_yr) = 8.35 ±0.15, a distance modulus 11.05 ±0.05, and a colour excess E(B-V) = 0.115 ±0.035. The r' luminosity function (LF) of main sequence stars in the magnitude range r' < 17 (i.e. masses > 0.8 solar) has a shape that follows solar neighbourhood star counts. However, at fainter magnitudes the cluster LF is flat, in contrast with what would be expected from solar neighbourhood counts. The clustering properties of stars in NGC 2437 are investigated by examining the two-point angular correlation functions of main sequence stars in different brightness ranges. Main sequence stars fainter than r' = 17 are less centrally concentrated than brighter stars and are found over a larger area of the sky, suggesting that there is a corona of faint main sequence stars around NGC 2437. Based on the flat LF and extended spatial distribution of faint stars, it is concluded that NGC 2437 is actively shedding stars with masses < 0.8 solar.

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