Classifying Stars in the Small Magellanic Cloud

Every physics major either has to do a senior thesis or a senior project entering their fourth year. You may be wondering, how does an undergrad physics major decide on what they want to do as a senior thesis? For me, it was simply following the love and passion that I have for astrophysics and astronomy.

My professor, Dr. Luke Keller, was just starting on his research on determining how planets form and what environments they need to create a habitable planet. Before we could delve deep into looking into planets we had to start at the beginning of how planets form, and that was by their stars.


My research began with taking spectrum from eight low and intermediate mass Young Stellar Objects (YSO’s) in the Small Magellanic Cloud (SMC) and determining their effective surface temperatures. To determine their effective surface temperatures, I took model stellar spectrum created by Dr. Robert L. Kurucz for various amounts of stars we find in the universe. I inputted his models and overlaid his spectrum with the spectrum of the YSO that I was determining to see if both spectrum matched. Once I found a fit, and its effective surface temperature was calculated, it led to determining the YSO stellar mass and age by plotting this data on an Hertzsprung-Russell (HR) diagram. In an HR Diagram, luminosity is on the y-axis and the effective surface temperature is on the x-axis. Luminosity of each YSO was determined by finding the difference of the YSO apparent magnitude and absolute magnitude and then taking into consideration the distance we are from SMC. With each YSO’s luminosity calculated, I was then able to figure out each YSO mass and age by plotting on the HR diagram and seeing which isochrone line and evolutionary track it fell on to determine its age and mass. With each YSO surface temperature, luminosity, age and mass calculated it was determined that these were in fact young pre-main sequence stars. My next investigation was to see why my spectrum has emission lines rather than absorption lines where the Balmer jump would be. What caused all this emission was due to an accretion disk surrounding each star. Each star was forming its own planets with a low metallicity environment, in comparison to the Milky Way, which has a high metallicity environment. A difference in metallicity leads to a difference in planet formation and will result in more gaseous planets to form rather than terrestrial planets. What I concluded was that these 8 YSOs were young pre-main sequence stars with a circumstellar disk around them that would eventually turn into planets. Just from my research Dr. Luke Keller and future students are now able to investigate just what causes planet formation in these types of environments and what type of planets will form in the future. As well as, seeing how planet formation occurred in our early universe because the universe in the beginning had such a low metallicity environment.

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