The Kepler field will be high in the sky starting in the next month or so and continuing over the Summer months. Thanks to all of your hard work and classifications, the science team has been writing observing proposals to ask for telescope time on the the Keck telescopes in Hawaii to follow up on our best planet candidates. We’ll learn in a few months whether we have been granted the nights. So stay tuned!
In the meantime, the team is continuing to search for new planet candidates with your classifications and Talk comments. You have been analyzing light curves from Quarter 7 released by NASA during Kepler’s primary mission. To begin searching the first data release of Kepler’s extended mission, Quarter 13, we need to finish Quarter 7. We need your help to make room for the new light curves.
As with any new data, there are now new chances to find even more planets. Let’s make the final push so that by April we could be looking at Q13 data. Please get clicking today at http://planethunters.org
The Keck Observatory observing schedule was released online over the weekend. It’s released twice a year around June 1st and December 1st listing the exact dates those astronomers who have been awarded with telescope time will have on the 10-m Keck telescopes located on Mauna Kea. I was awarded one night by the Yale Time Allocation Committee (TAC) with the NIRC2 instrument and Natural Guide Star Adaptive Optics to zoom in around Planet Hunters’ planet candidate host stars and look for contaminating stars that may be contributing light to the Kepler light curve. This will allow us to better assess the planet radius and the false positive likelihood for those candidates. To learn more about NIRC2 and Natural Guide Star Adaptive Optics, check out a previous guest blog by Justin Crepp.
Our observing night on Keck II has been scheduled for June 28, 2013. The Kepler field (in the constellations Cygnus and Lyra and part of the Summer Triangle), will be high in the sky for most of the night and easily observable from Hawaii. Below, I’ve plotted the airmass (Y axis scale on the left ) and altitude (Y axis scale on the right) of the Kepler field for our scheduled night. Except for about an hour at the beginning of the night, the Kepler field will be above 30 degrees altitude and easily observable from Keck for the duration of the night.
Part of the science team will be heading out to Keck Headquarters on the Big Island of Hawaii to observe. Let’s hope the night is clear. If it rains or is really cloudy, we’ll be out of luck. The rest of the nights on Keck II are scheduled for other observing projects and assigned to other astronomers. We would then have to try again next year and reapply to the Yale TAC for the telescope time. I’m hoping (fingers crossed) that the weather will cooperate and that we end up with lots of useful data.
We won’t be going up to the summit of Mauna Kea (at 14,000 feet!) where the telescope is located on June 28th. A telescope operator will be run the telescope from up at 14,000 feet. We’ll remote observe from sea level at Keck Headquarters (shown below) in Waimea, Hawaii where we won’t have to worry about the effects of being at high altitude.
The operator will drive and control the telescope and the adaptive optics equipment. We as the night’s observers will control the camera and run the show determining where we want to point on the sky and in what order. We’ll plan and think more about the run next year in June closer to when we fly out to Hawaii. We’ll make sure to blog, tweet, live chat and keep you all up to date on how the night and the observing goes.
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.
Today we have a guest post from Bill Keel. Bill is a member of the science team for Galaxy Zoo, and is more accustomed to dealing with stars by the billion than one at a time. He is a University of Alabama astronomer, weekend trombonist, and occasional photographer, being gradually trained by two cats with names out of Tolkien. Both his Twitter stream and his posts on the Galaxy Zoo forum can be found under the name NGC3314, and his other professional exploits may be found at http://astronomy.ua.edu/keel.
Kepler is sometimes most effective when properly backed up by other instruments, since its design was tightly optimized for precision in measuring bright stars at the expense of other things (such as angular resolution). Here’s a case showing how interpretation of Kepler results on planetary transits can be assisted by fairly routine ground-based measurements.In late June, I got an email request from Meg Schwamb:
“We’ve found a planet with ~130 days orbit going around a eclipsing binary. The eclipsing binary has a 20 day orbit so the planet is circumbinary and there’s a third star in the binary+planet system orbiting out at ~1000 AU with a period of 10E4-10E5 years. We’ve been following up the system with Keck observations.“ [We didn't yet know at the time that this third star would itself turn out to be a binary star].
The region around this star from our perspective is very busy (like the whole Kepler field), and the Kepler measurement includes light from additional faint stars. One, in particular, appears about 3 arcseconds away from the star of interest, well within the 6-acsecond radius of a Kepler measurement. Knowing its brightness would help narrow down the planet’s properties, making sure we have the right starting points in brightness for the Kepler target star my itself.
My institution is a partner in the SARA consortium, which operates telescopes in Arizona and Chile remotely. As a result, I have fairly regular nights scheduled, and indeed there were a couple of nights I could use at our northern telescope, a 0.9m instrument on Kitt Peak, Arizona, in July (just before shutdown for the monsoon season). After a couple of tries when the weather didn’t quite cooperate, including one night that was clear but the air to turbulent for this project, I got an hour’s worth of images on the evening of July 17. The image quality (seeing, in astronomical jargon) was 1.5-1.8 arcseconds, meaning that these values give the diameter across which a stars image drops to half its peak intensity due to atmospheric turbulence. That makes separating stars 3 arcseconds apart tractable. The timing worked out well during the night – the field was within 15 degrees of the zenith, minimizing atmospheric and tracking problems.
Trying to get precision measurements of bright and faint stars simultaneously takes some care – good data on the faint star isn’t much help if the bright star is hopelessly saturated in the data. So instead of one long exposure, I took 60 1-minute observations, using a red filter to roughly match the midpoint of the very broad spectral band used by Kepler. For further analysis, that gave both the grand average of all 60, and I also used averages of subsets of 10 to help estimate certain sources of error in the processing.
Even though the fainter interfering star was clearly separated from the bright one in these images, there was enough spillover to need correction.I tried several procedures or this – the most successful took as a reference point a similarly bright star with no companion in that direction, subtracting variously scaled versions of its image to eliminate as much of the bright star’s light as possible (the subtracted images looked a little odd in the middle – much later I realized that might come from the very close companion star seen in other data).
To make sure we understood how our brightness measurements relate to the Kepler data, I checked published magnitudes for Kepler stars in this neighborhood. This gave me some bad moments until I realized that the published values were often based on short exposures with a telescope no bigger than I was using – bright stars are OK, faint stars become quickly much less accurate. Phew. Now I know this, so that if it comes up again, I’m ready.
The result? That fainter star has magnitude R=18.73, making it only 1.02% as bright as the Kepler target with planet. Other contaminating stars are still fainter, down to 0.03% of the target star’s red-light intensity.
The Kepler field is located in the constellations Cygnus and Lyra. You can find the Kepler field by looking for the Summer Triangle, the corners which are composed of the brightest stars in the constellations Aquila, Cygnus, and Lyra: Altair, Deneb, and Vega. Along the Deneb and Vega side, you’ll find the stars that make up the Kepler targets. As its name implies, the Summer Triangle and the Kepler field are high in the Northern skies during the Summer months.
As August ends and we enter September, the Kepler field is slowly getting lower in the sky each night. By the end of the month it will be difficult to observe from telescopes in the Northern Hemisphere like the Keck telescopes on Mauna Kea in Hawaii and the WIYN telescope on Kitt Peak in Arizona. Astronomers studying the stars and confirming the planet candidates in the Kepler field will have to wait until next year to observe starting about May when the Kepler field will rise again above the horizon for a large fraction of the night.
Even though we won’t be able to observe the Kepler field for several months, if we want to use the Keck telescopes to study Planet Hunters candidates next year we have to decide now what we’re going to do, what telescopes we need, and how many nights because of how observing time on these telescopes is decided.
Observing time on telescope is limited and highly coveted. Astronomers compete to get time of these telescopes to observe, and there are more good observing projects than are nights to give on telescopes like Keck, Gemini, and the VLT (Very Large Telescope). For Keck and those telescopes on Kitt Peak, the time on these precious resources is divided between the institutions that built and maintain these telescopes. In addition a small portion of nights goes to NASA and the National Optical Astronomy Observatory, and the observing time from these two institutions is up for grabs and open to all astronomers at US institutions.
So how does proposing and getting observing time exactly work? Usually twice a year, there is a call for proposals, asking astronomers to propose for time that they want and justify what they need it for. Then the TAC (Time Allocation Committee) meets, ranking each proposal. The top ranked proposals will get the time they ask for on the telescopes. Many times there will be good proposals that won’t get any time because the telescopes are oversubscribed, more people apply than time is available. At most you’ll be able to get a few nights on these telescopes if you are lucky.
The nights on the telescopes from February 2013 through July 2013 are allocated this Fall. A place like Yale, we have access to the WIYN 3.5-m telescope at Kitt Peak, the SMARTS telescopes in Chile. We also have ~10 nights a semester on the Keck telescopes in Hawaii allotted to Yale observers. So this week and next week, I’ll be writing a telescope proposal where I need to justify what I want to do and why it is important. I’ll need to determine what instrument I need and how it needs to be set up. I’ll have decide how many nights are required to get the observations and come up with a list of targets to observe. If all goes well and with a bit of luck I get the time, when the Summer Triangle is high in the sky again next year, I’ll fly to the Big Island of Hawaii and take those observations I’m planning now.
I wanted to give a brief update on the short period planets paper that just recently got accepted to Astrophysical Journal. Once you’ve gone through the referee process and the paper gets accepted. You go through the editorial stage of the paper where the journal formats your paper into the nice two column format of the journal and puts your figures into the text so that everything looks seamless and coherent. On top of that, a copy editor reads your paper searching and correcting for typos, grammatical errors, and formatting errors. Once this has been done, you receive the proofs of your paper, what it will look like in the final print version in the general. One version, the ‘redline’ copy, highlights the corrections and changes from the copy editor and the other shows how the paper will look in journal format including where all the figures will be positioned. So I just got the proofs for my paper a few days, and I’ve gone through and checked the copy editor’s modifications. For the ones I disagree with, I can submit a response explaining my reasoning and those edits may be modified. Now that the proofs are in and reviewed, the next step is publication (expected to be formally in August). The paper is online in pre-print format so everyone can read the results early, but the publishing in the journal is considered the official stamp of approval that the publication is scientifically valid and that the results have been peer-reviewed.
So what’s next? We’ll right now I’m working on some observing follow-up of our highest priority planet candidates. We’ve been getting follow-up observations to help study and confirm if these are real planet transits. I was helping to observe on the Keck telescopes Monday and Tuesday nights (Hawaiian time). I didn’t get to be go out Hawaii or Mauna Kea. I was observing remotely from the comforts of home (well, the Yale Keck remote observing run across from my office in New Haven). So Tuesday and Wednesday morning on the East coast I was helping to drive the Keck I around and take high resolution spectra including observations of a Planet Hunters candidate or two. Additionally, we’re looking for new planet candidates and we could use your help. I’ve run an adapted version of my transit selection pipeline from Q1 data and I’ve applied it to all the classifications from Q2-Q5 that we have complete. We have a large list of potential unknown planet candidates. We need help sorting through identifying those light curves from our top list have actual planet transits similar to what we did for the short period planet analysis. If you’d like to help with the sorting, we could use all the help we can get. Go to http://www.review.planethunters.org now.
Today’s blog post come’s from guest blogger Justin Crepp, co-author on our first Planet Hunters paper. Justin is an expert in adaptive optics and fellow planet hunter. He’s going to tell you more about the observations he carried out to help follow up our planet candidates.
Dear Planet Hunters,
Thank you for your diligent work identifying new Kepler planet candidates!
I am a postdoc at Caltech and my job (normally) entails searching for exoplanets using high-contrast imaging, a technique that involves trying to “take a picture” of faint companions in orbit around bright stars. As you can imagine, this is a challenging task: it requires adaptive optics to correct for the blurring effects of Earth’s turbulent atmosphere (as well as other hardware and some advanced data processing). Ironically, the same technology that I use to detect planets directly can also help to find transiting planets. By eliminating false-positives with imaging observations, we can dramatically reduce the likelihood that a nearby object, such as an eclipsing binary star, is mimicking the periodic signal of a transiting planet. In other words, I am often very anxious to see faint points of light next to bright stars, but, in the case of Kepler targets, it is best not to find any sources in the immediate vicinity of the star.
I recently had the pleasure of working with Debra Fischer, Meg Schwamb, and the rest of the Planet Hunters team, to observe the stars that you found to have intriguing light-curves. Armed with the Keck adaptive optics system and the NIRC2 camera, Tim Morton (Caltech grad student) and I were able to record deep images of each target on your list. After some careful analysis, we found that two of the stars you identified were free of contaminants, and therefore almost certainly (>95% confidence) transiting planet hosts.
I am proud to have contributed to such an exciting project, and would like to thank you once again for your dedication examining Kepler’s exquisite data. These are the lowest mass planets for which I have been a co-discoverer; in fact, one of them may be only several times the mass of Earth. I hope we get a chance to work together again sometime soon.
The images of the two final planet candidate stars (KIC 10905746 and KIC 6185331) and one of our candidates (KIC 8242434) that appears to be a background eclipsing binary system are shown below (regular 2MASS image left, Keck AO Justin took right):
Today’s blog post is brought to you by zookeeper extraordinaire Chris Lintott.
Last week Meg visited me in Chicago for two days of number crunching and data discussion and analysis. We got a lot done (and crushed Zooniverse developer Michael Parrish at shuffleboard) and I’ll write more about that soon, but a lot of our talk centered on a very unusual system unearthed by a few persistent Planet Hunters.
Once the team had – prompted by posts at Talk – taken a closer look at the system in question (we’re keeping the name under wraps for now) we were pretty excited, but also slightly worried. The system in question seems to have multiple transits, but they imply that there would be two large planets relatively close to each other. So close, in fact, that a back of the envelope calculation suggests that they would be expected to disrupt each other’s orbits. So unless our rough working is wrong (certainly possible) or we’ve caught the system in an unusual time during its evolution (surely unlikely) then there’s something mysterious here.
That, of course, is the perfect excuse for an observing run. We’re lucky enough to have access to the Keck telescopes on Mauna Kea in Hawai’i (probably my favourite place in the whole world). Observing at Keck is a little different from the telescopes that I’m used to – rather than trekking to the summit where a lack of oxygen can make observing difficult, Keck astronomers observe remotely, either from sea level in Hawai’i or from their home institutions.
The initial goal of our observations wasn’t to confirm the existence of the planets – the star in question is too faint to make that easy – but to rule out obvious problems. In particular, the team were worried that we weren’t looking at a single star, but receiving light from a combination of a nearby star and a background eclipsing binary which would then be responsible for some or all of the transits. If that’s the case then we should be able to see relatively large wobbles revealed by the stellar spectrum as the binary stars move back and forth. These will be larger than the faint wobble induced by the planets (if they exist) and checking whether they exist or not will take no more than a couple of observations, each lasting less than an hour.
I’ll report back on the Keck observations. Fingers crossed!
Hello PlanetHunters! The Kepler field is finally visible and tonight, grad student John Brewer and I began observing a few of the candidates that you identified. We are operating the Keck telescope in Hawaii remotely from New Haven, CT. The weather in New Haven may not be great tonight, but it’s perfect in Hawaii – we have clear skies!
There were several steps involved in selecting the best candidates to observe tonight.
- You all did the hard first step, classifying data from Q1 to identify prospective transits.
- Stuart extracted 3500 prospective transits from the database.
- We examined all of your selections by eye – about 100 planet candidates survived (many transits per candidates).
- Yale grad student, Matt Giguere, wrote computer programs to model the light curves and to search for evidence of blended background binary stars. Visiting grad student, Thibault Sartori, has been using this code for the past several weeks to model all of the planet candidates – about half of the 100 planet candidates survived that analysis.
- John and I will analyze the spectra we collect tonight to derive stellar parameters (temperature, surface gravity and chemical composition) – this will help to better constrain the planet radius.
- Jason Rowe and Natalie Batalha from the Kepler team kindly agreed to analyze our top candidates with the Kepler data verification pipeline to help eliminate additional false positives.
It will be tough to go to the next level and confirm any of these as planets because the stars are faint. It is sure easy to understand why the Kepler team has more than 1200 planet candidates, but currently only 11 confirmed planet-hosting stars. It is a long road from planet candidate to a bonafide planet!