Image Credit: W. M. Keck Observatory
To study and follow-up planet candidates we find with Planet Hunters we need telescope time. Nights on telescopes are precious and astronomers apply twice or more a year asking for the telescope time they need for their proposed research projects.Yale University has access to ~16-20 nights a year on the Keck telescopes in Hawaii. In September, I applied for telescope time to get a night on Keck II in order to zoom in around the host stars of our planet candidates and see if there are other stars that are contributing light to the measured Kepler light curve.
In an ideal case the depth of the transit is equal to the squared ratio of the radius of the planet to the star’s radius. But if there is any additional light from a neighboring star in the photometric aperture this will dilute the transit making it shallower. Without knowledge of the contaminating stars, one is unable to accurately assess the planet properties, and will wrongly estimate a smaller radius for the planet. Kepler has relatively large pixels (with a pixel scale of 4” per pixel) and a typical 6” radius photometric aperture used to generate the Kepler light curves. This means that there could be stars contributing starlight to the Kepler light curve making the transit shallower.
Using Natural Guide Star (NGS) Adaptive Optics (AO) imaging with NIRC2 on the Keck II telescope, we can achieve 10 miliacrsecond per pixel resolution revealing close companions within 5” of the planet candidate host star.We’ve used AO observations in the past to study PH1. Those observations were crucial revealing the second pair of stars orbiting outside the orbit of the planet. Also those observations helped us get the correct parameters for the size of PH1.The AO imaging basically lets us remove some of the blurriness in the star that we see in our images caused by turbulence in the Earth’s upper atmosphere (this is what causes stars to twinkle when you look at the night sky). The AO system helps morph the telecope mirrors in real time to correct for the changing upper atmosphere and get the resolution to see what other stars share the Kepler photometric aperture summed up to make the Kepler light curves you review on the Planet Hunters website.
There’s good news. The Yale Time Allocation Committee (TAC) awarded us one night some time in June or July next year with NIRC2 for my proposal. Around December 1st, we’ll find out about the Keck telescope schedule and know exactly what night we’ll get to observe on Keck II. Since no one on the team has used the NIRC2 instrument before, we cannot remote observe from Yale, so some of the team will be heading to the Big Island in Hawaii. We won’t be observing from the summit of Mauna Kea (at 14,000 feet) . We’ll remote observe from sea level at Keck Headquarters in Waimea, Hawaii.