12 days of data from Kepler 17

Here is a preliminary result from my Ph.D. research that I showed in my AAS 225 talk earlier in January. This is from the final of four journal publications that will make up my thesis. My adviser Prof. Leslie Hebb and I are working (hard!) to model the evolution of starspots on the Sun-like star, Kepler 17. I am working hard to get PhD paper #3 out to publication, and to finalize these results for publication before I graduate (shameless plug for my CV). I'm sharing this video here because I think it's an elegant visualization of the method we are using, while also demonstrating the challenges and possibilities!

This video shows a single 12-day portion of data from Kepler 17. The data (in black) come from NASA's Kepler mission. The model (in red) is our best estimate of the star+planet conditions during one full rotation of the star, or about 12 days. We then repeat this analysis every 12 days over a span of 4 years (Earth years, that is!) to learn about the evolution of the starspot features we see.



When the planet crosses in front of it's host star, we sometimes observe a "bump" in the transit. This is caused by the planet crossing or occulting a dark starspot region on the stellar surface (akin to a Sunspot). The animation shows the rotating star with spots (top), the full 12-days of data (middle), and zoom-ins during the planetary transit (bottom).

The planet (Kepler 17b) has a very short "year" indeed, going around it's host star every 1.5 days. This means during the 12 days it takes Kepler 17 to rotate, the planet eclipses 8 times! With this remarkable geometry, we are able to deduce and map the locations and sizes of at least 8 starspots. Previous techniques using imaging data without a transiting exoplanet could at most infer the approximate properties for 2 or 3 starspots. With this method we believe we can robustly detect up to 10x more starspots, and even trace their evolution. While this model has 8 spots included, there is strong evidence in the 4 year dataset that times fewer and sometimes even more spots are observed! This information will unlock details about magnetic fields and the inner workings of stars beyond our Sun. For reference, only a small handful of stars currently have detailed information about their magnetic fields or starspots. Our characterization of Kepler 17 will likely be the most detailed ever analysis of spots on any star besides the Sun.

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