NGC 4372, which is also referred to as Caldwell 108, is an old globular cluster located in the southern constellation of Musca. It was discovered by James Dunlop on April 30, 1826, and cataloged as Dunlop 67. Positioned to the southwest of Gamma Muscae and the west of the southern extremity of the Dark Doodad Nebula (Sandqvist 149), it is found within the Great Plane of the Milky Way’s southern section, where a 3° narrow black streak is visible, almost 19000 lightyears away from Earth. Its RA is 12:25:45.60 hrs and Dec is -72:39:32.4 deg.
In a recent study, Mike Inglis (2004) stated that NGC 4372 “is partially obscured by dust lanes, but still appears as a large object some 10 arcseconds in diameter.” The cluster’s chemistry is remarkably unusual, resembling that of NGC 5694, with a significant lack of iron while possessing magnesium and titanium abundances that are beyond the levels found in our sun (Kovalev et al, 2019).
Taken by Ken Abremski, Feb 8-14, 2021
Data Collection
To explore the interplay between color, brightness, age, and chemical makeup of NGC 4372, my research began by acquiring images of the cluster in multiple filters via the Skynet Robotic Telescope Network. Specifically, I captured 15 images (5 in each of the B, V, and R filters) using the Prompt5 telescope located at the Cerro Tololo Inter-American Observatory in Chile. This telescope has a 0.4m aperture, a 4576.0mm focal length, with a focal ratio of 11.3, a CCD size of 102 um pixels, and a 10×10 arcmins field of view. The exposure durations of the B, V, and R filters were approximately 90 s, 60 s, and 60 s, respectively. The resulting images were then stacked using Afterglow, an image processing website, and the data derived was then analyzed using Cluster Pro Plus, both of which are the peripheral tools of Skynet.
The gleaming dome of the VÃctor M. Blanco 4-meter Telescope is flanked by two telescopes of the SMARTS Consortium in this image from Cerro Tololo Inter-American Observatory, a Program of NSF’s NOIRLab. Above the telescopes, the Large and Small Magellanic Clouds — two satellite galaxies that are neighbors to the Milky Way — hang over the scene. The starry band of the Milky Way itself streaks across the left hand side of the image, complete with dark lanes of dust.  The vibrant colors of the night sky are due to the faint hues of airglow and the first hints of dawn. As well as tinting the night sky, the long exposure of this image and the rotation of the Earth have caused very small star trails to form. If you look closely at the upper corners of this image, you can spot the tell-tale streaks of long-exposure astrophotography.
Data Analysis
Reddened colored image of NGC 4372, taken using Skynet’s Afterglow tool
Using Afterglow, I stacked Skynet’s black-and-white images and created two color images of the cluster. One image showed the cluster as it would appear from Earth, with Interstellar Reddening, and the other image showed its true form in space, De-Reddened. To produce the De-Reddened image, I had to fit Skynet and Afterglow data to an Isochrone model using Cluster Pro Plus software. This model helped determine the cluster’s age, proper motion, distance, log age, metallicity, and Interstellar Reddening and extinction. After knowing the E(B-V) value, I used it to remove Interstellar Reddening in Afterglow Photometry imaging and create the De-Reddened image.
De-Reddened colored image of NGC 4372, extracted using Skynet’s Afterglow tool
Upon examining the de-reddened image of the cluster, I have identified many blue stars amongst the ancient stars in the cluster which may indicate the possibility of the existence of blue stragglers in it. Through the isochrone model, I have found an estimation of 500 – 600 stars in the clusters with the cluster’s age being approximately 9.55 million years. There weren’t any signs of Nebulae and giants, however, the images and the isochrone model have provided the existence of bright orange stars. There were also some challenges associated with the research, like the existence of a bright star, HD 107947, which dominated the cluster with its bright blue light.
Data Comparison
The isochrone model of the data collected was then compared to the globular cluster’s data and its isochrone model as collected by a different source, the MWSC (Milky Way Star Cluster) Catalog. I plotted the Gaia data with those parameters and found some interesting details to compare and contrast.
My Observation Values
MWSC Parameter Values
Proper Motion in RA (with error)
-6.445 ± 0.296
-6.445Â 0.296
Proper Motion in Dec (with error)
3.326 ± 0.306
3.326Â 0.306
Distance (with error%)
5.98 ± 55.34
5.807Â 55.34
Log(Age (yr))
8.98
10.1
Metallicity (solar)
-0.28
-1.94
E(B-V)
0.23
0.389
Upon comparison, I found that the metallicity level in this graph is lower, resulting in an increased number of white stars in the cluster as compared to my graph. Furthermore, the isochrone curve in this graph distinctly follows the blue stars, unlike my graph. Additionally, a slight increase in both the distance and log(age) is observed in this graph. The accuracy of this graph can be attributed to the isochrone that better accounts for the blue stars in the cluster compared to my analysis. Moreover, this graph portrays brighter stars than my graph. In conclusion, my analysis exhibits only marginal enhancement in contrast to the previously published values for this cluster.
HR Diagram and Estimated Properties from My Observation of NGC 4372HR Diagram and Estimated Properties from MWSC Observation of NGC 4372
Conclusion
In conclusion, this project has provided insightful knowledge about the properties of NGC 4372, an old globular star cluster located in the southern constellation of Musca. Through data collection and analysis, including the use of the Skynet Robotic Telescope Network and Cluster Pro Plus software, the age, proper motion, distance, metallicity, and Interstellar Reddening of the cluster were determined. The resulting de-reddened image showed the presence of blue stars, and the isochrone model provided evidence of bright orange stars. Data comparison with the MWSC Catalog revealed a more accurate isochrone model and brighter stars in the cluster. This project highlights the importance of studying globular star clusters in understanding the evolution of the universe and the formation of stars.
I thank you for taking the time to read my blog post on the observation, data collection, and analysis of NGC 4372.
