NGC2129 is an open cluster in the constellation Gemini. It is located approximately ~7,200 light years from the Sun inside the Local spiral arm. The discoverer of this open cluster is unclear as some sites say it was William Herschel who discovered it in February 6, 1782 while other’s have nothing listed.  NGC2129 is a very young cluster whose age has been estimated at 10 million years.

In a recent examination of NGC2129 it was found that the brightness of this small and young cluster was mainly due to two close B-Type stars,  HD 250289 (B2III) and HD 250290 (B3I). With the two stars sharing the same proper motion and radial velocity it is likely that the two constitute a binary system. This makes this cluster very special due to how young and small its size truly is compared to other clusters in the Milky Way galaxy. Future studying of this cluster could reveal more facts that might not be known now and could open many other possibilities for similar clusters. 

In order to study NGC2129 and investigate the relationships between colours, brightness, and the age and chemical composition of the cluster as a whole, I collected 15 images in B, V, R filters with the Prompt 5 Telescope located in Cerro Tololo Inter-American Observatory, with total exposure durations of 90.32s, 50s, and 33.87s in the B, V, R filters respectively and other imaging parameters such as #Exps set to 5 and setting Exposure Efficiency to Generic 16-inch.

Then using Afterglow, we combine the 5 sets of B, V, and R exposures into 1 each. Then we apply the filters of Blue to the B set, Red to the R set, and Green to the V set. The result of this is:

We then combine these 3 photos and download the photometric color calibrated image of NGC 2129, which displays realistic colors for the stars in this cluster as they appear from Earth:

Using photometry in Afterglow we are able to obtain the values that are required by Cluster Astromancer in a CSV file. We upload this CSV file to Cluster Astromancer to better understand our cluster and use field star removal, archive fetching, and isochrone matching on Cluster Astromancer to reveal data on the NGC 2129 cluster. Using the values we are able to plot different graphs and fine tuning these graphs to contain a best fit line. We create RP vs BP-RP, V vs B-V, R vs B-R, and H vs J-H plots, and use them to refine our isochrone matching parameters:

Using the sites above and with the fine tuned graph I was able to retrieve these basic results with a score value of 0.290315 in Astronomicon:

Name:	NGC2129
Classification:	OPEN
Number of stars:	237
Mass:	1999 (solar)
Physical Radius:	3.58 (ly)
RA:	90.26° 6h 1m 2.4s
Dec:	23.33° 23° 19′ 48.0″
Galactic Longitude:	6.587° 6° 35′ 13.1″
Galactic Latitude:	0.133° 0° 7′ 58.2″
Angular Radius:	0.085° 0° 5′ 6.3″
Proper Motion RA:	0.22 (mas/yr)
Proper Motion Dec:	-2.16 (mas/yr)
Velocity Dispersion:	0.25 (mas/yr)
Distance:	0.74 (kpc)
Log Age:	7.48 log(yrs)
Age:	30.20 (Myrs)
Metallicity:	-0.4 (solar)
Reddening E(B-V):	0.75 (mag)

Using the E(B-V) value that has been calculated from the fine tuned graph and star removal we are able to retrieve a new image of the star cluster NGC 2129 but now de-reddened, so the image represents the cluster as it would appear from Earth if all the intergalactic dust along our line of sight were removed:

The study of this star cluster was part of Lab 4.1 and 4.2 and combined many aspects of the formula’s and things we were taught in class. The process of using different programs and values allowed us to study the star cluster and determine its different properties. We were able to see that the apparent image of the star cluster would make us believe that it was older than its true age due to the apparent picture being more red than it really is. After following the procedures of star removal, and after graphing each star’s brightness against its color we should find that the stars in a young cluster range from bright blue (i.e. luminous and hot) to dim red (i.e. dim and cool). Using the graphs we were able to come to a de-reddened image that shows that NGC 2129 contains much more blue stars than initially seen, confirming the fact that NGC 2129 is a relatively young star cluster.

I think the most challenging aspect of studying this star cluster was to fine tune the graph to be a better fit in the whole range. Looking at the graphs we see that the RP vs BP-RP graph is a very good fit but the V vs B-V graph is not so good, so trying to get most of the graphs to be a good fit was quite hard. Also because my star cluster was so small it was difficult to see what stars were part of the cluster and which were not. Compared to other star clusters that contained many stars it was hard to do star removal perfectly.

NGC 2129 was also studied by Kharchenko et al (2013) who found these parameters:

Distance:	1.65 (kpc)
Log Age:	7.48 log(yrs)
Metallicity:	0 (solar)
Reddening E(B-V):	0.75 (mag)

Using this data we are able to plot the RP vs BP-RP and H vs J-H graphs:

Comparing Kharchenko’s values to mine there is not much difference except for the distance that seems to be quite large of a difference, also additionally the metallicity is off by a bit. The resulting graphs of Kharchenko are very similar to the ones that I determined using my own values. And I would say that my own graphs are a bit more precise from the bottom of the graph compared to Kharchenko’s.

Overall this assignment has been very entertaining and fun for me, and allowed me to understand the concepts taught in class much better due to seeing the application of the concepts. Being able to see the difference between apparent and absolute magnitudes and how that causes the photo of a star to be different was very intriguing. Also additionally seeing the relation between the color and mass of stars helps me understand the many different aspects of stars and star clusters.