Introduction

NGC 2345 is a young open cluster in the Southern hemisphere constellation of Canis Major. It was discovered in 1836 by British astronomer John Herschel, with an angular size of 10.9 x 10.9 arcmin. Located at an RA of 07h 08m 18s and DEC of -13° 11′ 56″, it is situated close to the celestial equator and is therefore partly visible from both hemispheres during certain times of the year. Given its visual magnitude of 7.7, NGC 2345 is actually visible with the use of a 40-50 mm binocular or a small telescope! If you are interested in observing right now, the cluster is below the horizon from Greenwich, United Kingdom with a rise time of 14:35 and set time of 0:14 (times are relative to London’s time zone). 

Young open clusters are amazing tracers of spiral structure and very helpful in studying recent stars for our galaxy. This is because they act as indicators of variation in the abundance of heavy chemical elements throughout the galactic disc (Lada & Lada 2003). This particular cluster is also known for its high fraction of Be stars (~10%), which are a heterogenous set of stars of B spectral types and emission lines, making it a fascinating target for studying stellar evolution.

 

Previous Mentions

NGC 2345 is a decently researched cluster, being mentioned in its first traceable study in 1974 going all the way up to just last year. As such, it understandably has some unique features discovered throughout the 20th and 21st centuries. It is known that the cluster has seven blue and red supergiants, and a 2019 Alonso-Santiago et al. study reveals a new red supergiant. A study by Holanda et al. (2018) discusses that there are five bright K-type giants, with one of them being a spectroscopic binary system.

An aspect commonly discussed in many papers is the cluster’s unusually low metallicity (around -0.33). In fact, Holanda et. al further state that the cluster has a turn-off mass of 5.4 M⊙, making NGC 2345 a useful target for a high-resolution spectroscopy analysis in order to understand the effects of mixing and dredge-up. Furthermore, it can help search for a relationship between abundance ratios and age when compared with older stars. This provides yet another compelling reason to further expense the time and resources for studying the cluster more!

 

Data

I used Skynet to collect 15 total images, 5 in the B, V, and R filters with one exposure in each. The duration was set to 50s in the B filter, 30s in V, and 15s in R. I inputted a Max Sun Elevation of -15 degrees, Min Target Elevation of 30 degrees, Max Moon Phase of 50%, and Min Moon Separation of 60 degrees. The exposure efficiency was Generic 16-inch, and my images were captured using the PROMPT-MO-1, Prompt2, and Prompt5 telescopes. This observation was repeated five times with at least one hour in between each.

I then used Afterglow to colourize my cluster using a Midtone stretch mode, background level percentile of 1%, midtone level percentile of 99%, and saturation level percentile of 99.999%. I also entered the extinction value of 0.69 mag determined from my observations below to produce these images.

 

Observations

When studying NGC 2345 and investigating the relationships between the brightnesses, age and chemical composition of the cluster, I used Cluster Pro Plus. In order to most accurately fit an isochrone model to my data, I was able to obtain an RA of -1.33 with an uncertainty of 0.131 mas/yr, a DEC of 1.391 with an uncertainty of 0.129 mas/yr, a distance of 2.77 kpc with an uncertainty of 25%, and an E(B-V) extinction value of 0.69 mag. I found a log(Age) of 7.65 log(yrs) which equates to roughly 44.6 million years, and my graph stated that there were 297 cluster stars. I also found a metallicity of -0.35 solar, which coincides with the small metallicity mentioned in the papers above. 

As my cluster is on the younger side, it is dominated by main sequence stars that are fusing hydrogen into helium in their cores. This is why you can only see a handful of yellow-red supergiants in my data, as it coincides with the very few found in the 2018 and 2019 papers. Since NGC 2345 is a young cluster, it makes sense as to why we can’t see any clear blue stragglers. This is further reinforced by this 2007 Ahumada and Lapasset paper presenting 0 candidates for blue stragglers in the cluster.

 

MWSC Data

My cluster was studied by Kharchenko et al (2013), who found parameters that I plotted alongside Gaia data. I found an RA of -1.33 with an uncertainty of 0.131 mas/yr, a DEC of 1.391 with an uncertainty of 0.129 mas/yr, a distance of 2.605 kpc with an uncertainty of 25%, and an E(B-V) extinction value of 0.687 mag. I found a log(Age) of 7.9 log(yrs) equating to about 79.4 million years. This is a significantly different age than my own data, however, young clusters are known for their variable ages.

I believe that my analysis improves on the previously published parameters of NGC 2345 as the stars more accurately fit the isochrone model and trend in my graph with fewer stars fitting outside the model. Both of our models had similar RA and DEC, distance, and E(B-V) values. The E(B-V) value, however, could have been poorly estimated in the MWSC graph as it seems that it should be smaller to fit the trend in a nicer manner. It is worth noting that a metallicity of 0 was inputted as the MSWC spreadsheet did not have a value listed, which explains the large disparity. The number of cluster stars is also quite similar to my data as it lists 293. 

 

Conclusion

My data:  log(age) = 7.65 log(yrs) | Metallicity = -0.35 solar | E(B-V) = 0.69 mag

MWSC data: log(age) = 7.9 log(yrs) | Metallicity = 0 solar | E(B-V) = 0.687 mag

Although this cluster project was not the highlight of my life (sorry Professor), I still feel very fulfilled as I got practice in imaging, analyzing, and colouring a real-life cluster that will help provide more accurate data toward its composition and parameters as a whole. I was definitely very engaged throughout this project as this is a quite fascinating topic and I am very satisfied with my results. It was a lot of fun to learn more about the different types of star clusters and what makes them the way they are!