Awarded Telescope Time on the Keck Telescope
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.
9 responses to “Awarded Telescope Time on the Keck Telescope”
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- December 5, 2012 -
- June 27, 2013 -
Why can’t you pick up faint background stars contributing contaminating light to the photometric aperture just by stacking images?
it’s resolution – you can’t get within 1.5 arcseconds without AO or lucky imaging or speckle imagining. All three of these techniques can help over cover the blurring caused by turbulence in the upper atmosphere. We did use the SARA-N 0.9m staked images to look around the the host stars of the PH1 system for other contaminators that were beyond 2 arcseconds
Interesting. If that particular night is cloudy is the team just out of luck? Also, hours of darkness are limited in June and July. I’m wondering how many planet candidates you think you’ll have time to assess. Thanks!
That’s a great question. We just get that night. So if the weather is bad or if the instrument breaks we’re out of luck because other nights are assigned to other astronomers so there’s no room to reschedule. So hopefully (fingers crossed) the weather will be good, things will go smoothly, and we’ll get some good data.
I think 10-15 candidates if I remember correctly, but then again we’re all new to the instrument so we might be a bit slower than the average times to slew to new targets and acquire images. But that’s a good probably ballpark number.
I’ll use what influence I have with the weather gods. 🙂
I had the opportunity to accompany Alex Filippenko to the Keck a few years ago. He was with one of the teams that discovered “dark energy” and was observing for three nights. I think there were problems during two of those nights–not with the weather but with the instruments.
One more question. What criteria will you use to select the stars to observe? Do you just want some hits, that is stars most likely to have a planet, even if that planet is a hot Jupiter? Or will you be looking for those stars that might possibly have a rocky planet in the habitable zone? PH Planet candidates that aren’t duplicates with Kepler? Or just stars that seem to have something unusual going on?
Or will you decide when you get there?
Very cool about the observing.
To answer your question. It’s going to depend on what we find over the next 6-7 months. We submitted a target list from current planet candidates with the proposal to justify the time, but once you get the telescope time you can do what you want with it, if it is classical time (meaning you’re at the telescope doing the observing versus queue observing where someone else is executing your observations).
You can decide to change your target list because you don’t submit something formally to Keck until you’re at the telescope.. On the night of the observations you upload a starlist (a list with all the locations of all the targets you may want to go to during the night). Even then you can modify the list (add/remove targets depending on the weather conditions, etc). Though we’ll try and decide much sooner what stars to look at. Probably the week before the observing run, I’ll sit down with one of our collaborators and pick through what we’ll be observing.
More interesting targets that pop over the next several months will get priority, and then we’ll fill the night with other candidates that we plan to work on further. So basically we’ll decide when we get there, or a few days before, and we’ll adjust as the night continues if need be.