NGC 5281 is a young age cluster in the southwest constellation Centaurus. It was discovered by Nicolas Louis de Lacaille in 1751-1752. It can be seen with the naked eye under dark skies as a 6th magnitude star, making it an accessible object for amateur astronomers without the need for telescopes. The cluster’s brightest stars form a line that is strikingly visible from Earth, yet the cluster itself is not densely packed. The brightest star has a magnitude of 6.61. There are 371 probable members within its angular radius. One of these is a Be star, known for its X-ray emissions, and is also a blue straggler, a star that appears to be younger than the cluster itself.
In a recent study, Almeida et al(2023) discusses the use of the Gaia satellite data to determine fundamental parameters of open clusters, including their masses. In examining the sample of 773 open clusters, the study found no significant evidence that clusters, including NGC 5281, lose or segregate mass with age. Mass segregation would imply that more massive stars gravitate towards the center of the cluster while less massive ones are pushed to the outskirts. The study’s findings on mass segregation have implications for our understanding of the dynamical evolution of star clusters and the lifecycle of their constituent stars.
In order to study NGC 5281 and investigate the relationships between the colours, brightnesses, and the age and chemical composition of the cluster as a whole, I collected 20 images in B, V and R filters with Prompt5 telescope located in La Serena, Chile. Also, with total exposure durations of 30s, 20s and 12s in these filters, with other imaging parameters, using Skynet. And I used Afterglow to stack, align and calibrate the images that I have collected. Finally, got the version of the tri-colour image. (As shown Figure 1, 2, 3, 4)
Also, I used Afterglow to gather the photometry data for the further analysis which was used for Cluster Astromancer as the data source. And I generated the isochrone model with these basic results about distance, proper motion, etc. (As shown Figure 5 and table below)
| Distance(kpc) | Proper Motion in RA(mas/yr) | Proper Motion in Dec(mas/yr) | Age in Years(Myrs) | Metallicity(solar) | E(B-V)(mag) | Mass(solar) | Log Age(yrs) |
| 1.63 | -4.78 | -2.42 | 28.18 | 0.1 | 0.35 | 1199 | 8.52 |
The plot helped me to determine the E(B-V)value of 0.35, and I got Figure 6 after I adjusted the value of that for the Figure 4.
Finally, I found the Milky Way Star Clusters Catalog data of a global survey of clusters in our Galaxy, published in 2012-2015, with cluster parameters estimated through isochrone modelling. According to the result from Kharchenko et al(2013), I generated the plot of the Gaia data with below parameters.(As shown Figure 7)
| Distance (pc) | Log Age(yrs) | Metallicity (solar) | E(B-V) (mag) |
| 1211 | 7.76 | N/A | 0.26 |
These parameters in Figure 7 match better. Figure 5 has a good fit at the brighter end of the data but deviates slightly at the fainter end, but the isochrone line of the plot above appears to align more closely with the main sequence of the data points, especially towards the lower right end of the sequence. The distance or age might be poorly estimated, as these would shift the isochrone vertically and horizontally, respectively.
Having completed my analysis I have a deep understanding of the star cluster. This project was the highlight of my life up to this point. The dedication to exploring the intricacies of star clusters has not only broadened my understanding of astrophysics but has also imbued me with a profound sense of accomplishment.