Photometry
M15 Globular Cluster
Project Overview
M15 (AKA NGC 7078) is a globular cluster that can be spotted within the constellation Pegasus. The cluster is unique because it not only contains over 100,000 stars, but it also contains many variable stars, pulsars, a double neutron star system, and possibly a black hole at its center. Additionally, M15 contains Pease 1, the first planetary nebula found in a globular cluster. Even more interesting, images taken by the Hubble Space Telescope provide us with the ability to perform photometry on the cluster to determine its age and distance.
Three images were obtained from the MAST website. Each image was a different filter and had slightly different parameters. The filters were f450w, f606w, and f814w. Absolute Zero points were calculated for each filter to account for the magnitude shift due to the different exposure times.
Analysis & Results
Once the images were downloaded, they were displayed in DS9 and analyzed with Image Reduction and Analysis Facility (IRAF). After compiling a single magnitude file containing all three filters, excel was used to create color magnitude diagrams. Isochrones were plotted to determine age and distance. The reddening and extinction in each filter were determined using the E(B-V) from a previously published article.
Comparing figures 1-3 the age of M15 was determined to be 12.0 ± 1.5 billion years old. Furthermore, the distance of the cluster was found to be 15.85 ± 4.10 thousand parsecs. These results were consistent with ages and distances reported in additional sources.
M15 Globular Cluster from Hubble Space Telescope Image Archive
Project Achievements
The goal of the project was to learn about photometric methods as an astrophysical technique. Photometry is to astrophysical techniques as sculpting is to art. However, there aren’t infinite mediums to study the stars like there are to express yourself through art. Light and Gravity is all we know of. This makes photometry an essential tool in studying the universe. I presented this project and its findings at Geneseo’s Annual GREAT (Geneseo Recognizing Excellence, Achievement, and Talent) Day. Personally, I made some achievements through this study as well. The late-night efforts required to process all the images and understand the data was a step up in work load that got me ready for the next big project. In a sense, it widened my horizons of work ethic. I was and still am very proud of this achievement.