Josh Kim ’15 recently discovered that an existing star had eclipsing variable properties, which were previously unknown, while researching for his Winter Term Astronomy Research class, led by Caroline Odden, Instructor in Physics. In January, the class took a series of pictures of the night sky. Kim then searched the images in mid-February for variable stars and was able to identify one. Stars are usually constant in their brightness. Variable stars are stars whose degree of brightness changes. There are two main reasons why the degree of brightness might vary, said Kim. The first is that star itself is oscillating in size and this is called a pulsating variable. The second reason is that the star is actually a system of two stars, a binary star system. When the two stars rotate around each other, one eclipses the other and decreases the amount of light seen from earth. The star that Kim found is a binary star system. He was able to deduce this from the data and images collected during the astronomy course. Kim said that the stars were so close to each other that they appeared to be only one star at first. “I was looking for a variable star, but I never expected that there was actually going to be a variable star. I was searching the image, but only just in case I would find something,” said Kim. Kim said that when the observatory takes images, they take three to five minute exposures. According to Kim, starlight can be extremely faint and exposing the camera for minutes at a time is necessary. The star that Kim found is 630 times dimmer than the faintest star the naked eye can see. The American Association Variable Star Observers (AAVSO) is the official organization that handles discoveries concerning variable stars. The AAVSO produces a catalogue of all the variable stars that have been discovered, listed by coordinates. Upon detecting the variable star, Kim looked up the star on the AAVSO catalogue and was not able to find it. According to Kim, there is also a catalog that covers all stars known to man called the 2Mass Star Catalog. When Kim searched this catalogue, he found that the star was, in fact, there. “A lot of people say that I discovered a star, but I didn’t discover a star. I discovered that the star has special properties,” said Kim. It was previously unknown that the star was variable and part of a binary star system. “I think my discovery is unique and special because, not only is it a binary star system, it is a binary star system that has a very short rotation period,” said Kim. The rotation period is the amount of time it takes for a star to return to its original position. Kim said that most eclipsing variable stars have rotation period ranging from days to many years. In contrast, the rotation period of Kim’s star is only 8.3 hours. “That means that the two stars are really close to each other. It’s called a contact binary. In that way, my discovery is special,” said Kim. Kim was aided by Odden and John Briggs ’77, who works as a professional astronomer in Colorado. Briggs also worked at Andover as a visiting physicist and often helps students with research projects. Upon hearing about the star, Briggs took many images of the star from Colorado. Kim, Odden and Briggs confirmed the discovery by reviewing the combined data in a cumulative graph. Before Winter Term, Kim did not have any knowledge of astronomy. He credits Odden for his newly found interest and passion, but acknowledges that he still has much to learn. “I think astronomy is a field that you can do a lot of research with. I basically did experiment-based learning. I learned astronomy bit by bit through the process of doing research and experimenting,” said Kim. Kim plans to publish a paper about his discovery. He will write about the discovery and analysis of the star in the Journal of the American Association of Variable Star Observers. When reflecting upon his experience, Kim said that what impressed him the most was the importance of collaboration in science. “I did learn a lot about how scientists work together in terms of gathering data and asking each other about discoveries and interpretations,” said Kim. Kim used equipment in the Andover observatory, primarily a 16-inch reflector telescope. John Briggs, an astronomer in Colorado, used the same telescope. Kim said he looks forward to studying all the aspects of physics, including astronomy, in college. In the future, Kim hopes to be an amateur astronomer while pursuing careers in other fields.