NGC 3677 – The Pearl Cluster

NGC 3677 is a relatively young open cluster in the Southern constellation Centaurus. First observed by Nicolas Louis de Lacaille between 1752-1752. NGC 3677 is often called ‘the pearl cluster’ coined by Ray Palmer in 2006 (Bakich, 2016).

Image 1. NGC 3677 without interstellar reddening.

To determine the relationships of color, brightness, age, and metallicity with regard to NGC3677, 15 images were taken in total with varying filters. Five were taken in the V-filter for 35-second exposures, five were taken in the R-filter for 20-second exposures, and five were taken in the B-filter for 40-second exposures. All of these images were taken by the Prompt5 telescope located at the Cerro Tololo Inter-American Observatory in Chile. I used Afterglow for photometric analysis and photo coloring. I also used Cluster Pro Plus to plot NGC 3677 on a Hertzsprung-Russell Diagram. Using Figure 2, I determined the distance to be about 2 kpcs away with an age of a little over 31 million years. The proper motion in RA was determined to be -6.702 mas/year and in Dec to be 1.015 mas/year.

Image 2. NGC 3677 with interstellar reddening.

NGC 3677 contains many bright young blue stars with two bright red giants. This cluster was relatively easy to analyze as it was not too large and was only about 2kpc away. The cluster fits the isochrone model very closely with only a few stars beneath the model.

The Milky Way Star Clusters (MWSC) catalog states that the age of NGC 3677 is 89 million years, the distance is 1.685 kpc, the reddening is 0.208, and the metallicity was not yet estimated. Plotting the data with these parameters (Figure 1.) produced a graph that did not plot all stars and lined up with the center of the star sequence rather than the bottom. The absence of metallicity may have skewed the graph as well as the underestimation of the age.

Figure 1. An isochrone model with the MWSC parameters.

Figure 2. An isochrone with my parameters.

Interestingly, another article published in 2013 found 36 variable stars in NGC 3677 with periods ranging between 0.1 and 0.7 days. These variables in this cluster also seem to be situated in an area of the Hertzsprung-Russell (HR) where little pulsation is predicted. These researchers also discovered several eclipsing binaries, delta scutis, slowly pulsating B-type stars, and others.

This cluster project overall has expanded my understanding of distant astronomical objects. It gave me the opportunity to study and color a cluster with a unique age and distance. It has overall increased my interest in astronomical research and methods.