# M47 (NGC 2478 or NGC 2422) Carson Williams

M47 is an open cluster in the constellation Puppis. An open cluster is a group of a few thousand stars that were formed from the same cloud and have roughly the same age. This objects discovery, also known as NGC 2422 or NGC 2478, first went unnoticed when Messier had an error in the calculation of the position which resulted in him being given credit for a nonexistent object. Caroline Herschel would later find the object again, and should have received credit for the discovery. However, when her brother William rediscovered the object and added it to his catalog, that record resulted in his receiving the credit for the discovery. NGC 2422 consists of about 50 fairly bright stars spread across a region about half a degree in diameter. At its estimated distance of 1600 light years, this corresponds to a physical diameter of about 15 light years. The hottest main sequence star in the cluster is a spectral type B2, this suggests an age for the cluster of about 80 million years.

Below are some HR diagrams. HR diagrams plot the star's brightness against its temperature. This can tell us the age of the cluster; and what stars are in the cluster, due to its main sequence stars. What we did was create our own HR diagrams. We first used Visual Pinpoint to create files that gave exact information on the positions and brightnesses of the stars in the images that we took. Next, Larry Molnar, a professor from Calvin College, created a program using Python to make the data for the HR diagrams. We then used Logger Pro to create a graph of the data which gets us our HR diagram. Note that for our purposes, it is the range of magnitude that matters rather than the actual amount of magnitude.

The first diagram is an outline of what some of the clusters should look like. It has no actual data. The second diagram is a plot of V against V-R. V standing for visual, and R standing for red. The third diagram is a plot of V against B-V. B standing for blue. We can see our main sequence stars are in line with what the first diagram shows. The further down we go, the more "noise" or misinformation we get. This is most likely due to the background stars that are not inside the cluster. But if we look to the right of the top main sequence stars we can see that we have a few red giants. This can also be seen in the picture above, where we have both blue and red stars. This is what we should expect given this particular cluster. We can compare this to the Pleiades which has a visual magnitude range of 10 and a B-V magnitude range of 1.2. This coincides very well with our B-V diagram, leading to the conclusion that they are very similar open clusters; both having hot B type stars; and both being relatively the same age.

Source: Australia Telescope Outreach and Education ;  Credit: Mike Guidry, University of Tennessee

References:

cseligman "NGC 2422"

http://cseligman.com/text/atlas/ngc24.htm#2422

Wikipidea "open cluster"

https://en.wikipedia.org/wiki/Open_cluster

 Right Ascension (J2000) 07:36:35 Declination (J2000) -14:28:47 Filters used B (Blue), R (Red), V (Green) Exposure x number of images for each filter B, V, and R (1s X3);(90s X3) Image dimension 1092x736 pixels; 23.8x16.1 arcminutes Date/time observed March 16, 2016, 3:20 UT Distance 490 +- 27 pc (http://cseligman.com/text/atlas/ngc24.htm#2422) Scale 0.14 pc/arcminute

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