I am currently working on my Ph.D. thesis under the supervision of Dr. Steven Majewski, and the tentative title of my thesis is Searching for Evidence of Planet Accretion in Rapidly Rotating K Giant Stars . The idea is to test the hypothesis that a star can be "spun-up" by accreting a companion planet by looking for chemical changes in the atmosphere of the star that would occur if the material from the accreted planet gets broken up and mixed into the star's atmosphere.
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| Image Courtesy NASA/JPL-Caltech |
K giant stars are evolved stars that are both larger (in radius, not necessarily in mass) and cooler than our sun. Stars spend about 90% of their lives on what is called the Main Sequence , when their cores are busy fusing hydrogen into helium. When the stellar cores run out of hydrogen, the properties of the stars begin to change rapidly, i.e. they begin to evolve. For low mass stars (stars with about 2 times the mass of the sun or less), they go through a "red giant" phase. Red giants, which includes the K giants I am studying, have an inert helium core and thin layer outside the core where hydrogen is actively fusing to make helium. This thin nuclear-active shell progresses outward towards the surface while the star itself generally gets larger, brighter, and cooler.
These giant stars should be spinning relatively slowly because of the conservation of angular momentum. Think of figure skaters who spin faster when they pull their arms in and slower when they hold their arms out. Similarly, since the giant star expanded from a smaller star, it should also slow down. However, there is a small fraction of K giants that are spinning much faster than the should be able to. They are called "rapid rotators," and how they ended up spinning so quickly is still unclear. One hypothesis is that the star pulls in a companion planet and accretes it, thereby adding the planet's orbital angular momentum to the star's atmosphere (again think of the skater pulling her arms in). The recent disoveries of extrasolar planets known as "hot Jupiters", which are massive planets orbiting very close to their host star, lends credence to this hypothesis.
My research interests do extend beyond the scope of my current projects, and the following list shows the astronomical topics that I am particularly intrigued by.