A new MAST High Level Science Product from K2 has been delivered that includes extracted lightcurves. Courtesy of Vanderburg & Johnson (2014), long-cadence targets from Campaigns 0 and 1 now have detrended, extracted lightcurves available at MAST, including 20 different photometric apertures. There’s a MAST Classic Search Interface so you can get lightcurves based on target IDs, coordinates, EPIC catalog fluxes, etc. You can also use our interactive plotter to explore the lightcurves using any of the photometric apertures before downloading the FITS files. Check out all the details here: http://archive.stsci.edu/prepds/k2sff/
This is exciting! The International Astronomical Union (IAU) is working Zooniverse, astronomical clubs and the public at large to name some number of exoworlds and host stars. Some of the work has already been done, some work is yet to do. The exciting part is that Planet Hunters will be assisting in some of the next steps! Let’s break down their milestones:
- July 2014: IAU compiled a list of 305 exoworlds confirmed prior to December 31, 2008 as candidates for naming.
- October 2014: The IAU opened http://www.nameexoworlds.org to permit astronomy organizations to register to take part. Planet Hunters completed this and was confirmed!
- January 2015: Planet Hunters, along with other clubs, will vote for the ExoWorlds they wish to name out of the list provided by the IAU.
- February 2015: Planet Hunters, along with other clubs, will send in proposals for the names of members of these selected ExoWorlds (including the host star), based on the rules in the IAU Exoplanet Naming Theme, together with a detailed supporting argument for their choice. Each group is allowed to name only one ExoWorld. More details on this stage will be given later.
- June 2015: the general public votes to rank the proposed names.
- July 2015: the IAU, via its Executive Committee Working Group on the Public Naming of Planets and Planetary Satellites, oversees the final stages of the contest, and validates the winning names from the vote.
- 3–14 August 2015: the results are announced at a special public ceremony held during the IAU XXIX General Assembly in Honolulu, USA
We are in the January 2015 milestone. You may have noticed that there is a new “Vote” button on the Planet Hunters classification ribbon. This button takes you to a poll which has been set up to collect Planet Hunter community input. We want your participation! So let’s name an ExoWorld!!!
Today we have a post by Andrew Vanderburg. Andrew is a graduate student at Harvard University who works on producing and correcting K2 light curves and searching them for planets. He recently joined the Planet Hunters team to provide K2 light curves for classification.
As readers of this blog are probably well aware, the K2 mission is an exciting new opportunity for the Kepler spacecraft to continue searching for exoplanets, even after the failure of two reaction wheels ended the original Kepler mission. Making K2 work is in several ways more complicated than Kepler, and previous posts have already discussed how Kepler is stabilized by balancing against solar radiation and pointing itself opposite the sun in the ecliptic plane. Even with this very clever strategy for data collection, getting high quality data from K2 is not straightforward.
Once it became clear in early 2014 that Kepler would be able to continue gathering data, one of the biggest uncertainties about the K2 mission was: “How well can Kepler measure photometry in this new operating mode?” If Kepler’s worsened ability to point itself degrades the quality of its data, it may be harder for the K2 mission to accomplish its goals of finding exoplanets in new environments and around different types of stars. When the Kepler team released data from a 9 day engineering test of the new operation mode taken in February 2014, we attempted to answer that question.
After four years of being spoiled by ultra-high-quality photometry from Kepler, our first look at the K2 data came as a bit of a shock. Unlike the pristine Kepler data, K2 data (shown compared to Kepler in the first image) had wild jagged features contaminating the light curve, which made it hard to see all but the deepest planet transits. In order to continue searching for small planets in the K2 mission, something would have to be done to improve the quality of the photometry.
We started out by trying to figure out what was causing the jagged features in K2 data. Since nothing had changed with the spacecraft other than the reaction wheel failure, it was a pretty good bet that the jagged noise was due to the decreased stability of the spacecraft. We checked to see if this was the case by measuring the apparently position of stars in the images Kepler took (shown in the second image), and comparing them to the measured brightness.
The top panel shows the brightness of one particular star called EPIC 60021426 over the course of a week of the engineering test, and the bottom two panels show the horizontal and vertical position of the star, as seen by Kepler, over the same time period. It turns out that just like a cell phone video taken by a person with shaky hands, the images Kepler took were jittering back and forth. And more importantly, the jagged pattern in the location of the star in the image looked very much like the pattern seen in the brightness data.
We concluded that the additional noise in the data was caused by Kepler moving back and forth ever so slightly as it rolled due to a slight imbalance between the spacecraft and the Solar wind. Every six hours or so, Kepler’s thrusters fired to bring the telescope back to its original position. But the most important thing we concluded was that the additional noise in K2 data is very predictable. If the noise is predictable, then it’s correctable.
The third image shows the brightness of a particular star (once again, EPIC 60021426) measured by K2 on the vertical axis, and the position of the star on the horizontal axis. The blue dots indicate brightness measurements during normal K2 operations, and they form a tight relation with the image position. The jagged noise in K2 data depends only on where the image falls on the Kepler camera. With this realization, it’s simple to draw a line through the points (the orange line in the image), and divide it away. The red points are points taken while Kepler’s thrusters were firing, and don’t fit the pattern of the rest of the points. We simply throw them out.
After dividing the orange line from the data and removing points taken during thruster fires, we are left with a “corrected” light curve. The fourth image shows the result of the correction. The top light curve (blue) shows the raw, uncorrected K2 data, and the bottom, orange light curve shows the corrected K2 data. The correction substantially improves the quality of the K2 data.
This type of processing improves the precision of K2 to where it’s close to that of Kepler — within a factor of two for most stars. This makes it possible to detect small planets, even when the planetary signals are much smaller than the jagged variations removed by this process. We discovered the first K2 exoplanet, HIP 116454, using this exact technique, and the one transit we found was totally obscured in the raw K2 data (as shown in the fifth image).
Even now, however, this process is not perfect, and we’re still working to make it better. There are quite frequently glitches and other errors that affect the light curves and make it difficult for computer algorithms to pick out all of the transit signals. Trained human eyes like yours will be crucial for picking out all of the exciting exoplanets that K2 will observe.
Now that were in the midst of the showing the first batch of science grade data from the K2 mission, I thought I’d give some more details about the K2 light curves and how K2 mission works.
Planet transits are small changes in the star’s light, a Jupiter-sized object produces only a 1% drop in the brightness of a Sun-like star and Earth-sized planets generate even smaller dips at the 0.01 % level. Kepler needs the stars to be precisely positioned on its imaging plane in order to achieve the photometric accuracy required to detect these drops in light. To do this the stars have been positioned and kept at the same location with millipixel precision. Kepler was able to achieve this during it’s primary mission and the first half of its extended mission To do this Kepler used three reaction wheels (one for x, y, and z directions) with one backup spare to finely nudge the spacecraft to keep the target stars positioned during a Quarter. Kepler suffered two reaction wheel failures and can no longer operate in this mode. This effectively ended the monitoring of the Kepler field, that Kepler was staring at for 4 years. The drift of the spacecraft was too large that the photometric precision was sufficient enough for a transiting planet search.
This is where K2 comes in. The K2 mission repurposes the Kepler spacecraft. Kepler has thrusters but they are used for coarser pointing corrections, they can’t be used to be the fine adjustments that used to be achieved with the third reaction wheel, but you can use the Sun in a way to be that reaction wheel. This is how K2 works. If Kepler is pointed observing fields that are along the plane of the Solar System, than the two working reaction wheels are used to maintain the x-y locations of the stars on the focal plane with the Sun and thrusters taking care of the rest. Kepler is positioned such that the irradiation of the Sun is balanced which basically keeps the spacecraft from rotating. This is a quasi-stable and every 6 hours or so the spacecraft will start to roll. The thrusters can then be used to roll the spacecraft back to it’s original orientation. (You can see this in the raw light curves just plotted. You can see a Nike check-like feature that dips slowly and rapidly goes up.The light curve processing Andrew does tries to remove as many of those artifacts and others as possible. It does a pretty good job, though occasionally there may be an artifact that remains. ) This scheme works pretty well at keeping the stars on Kepler’s focal view located on the same pixels and achieves photometric precision about 3x time worse than what the original Kepler mission was achieving. With this, we can still find planets around other stars, especially smaller cooler stars.
The K2 light curves we’re currently showing on Planet Hunters come from Campaign 0. Campaign 0 is the first full science grade test field data for the K2 mission. Kepler was staring at a field centered around see a region of the sky plotted in the star chart below. The observations commenced on March 12 and the campaign was completed on March 27th of this year. Campaign 0 serves as a full shake down of the performance of the spacecraft in this new mode of operating. The specific targets Kepler monitored in the Campaign 0 were community driven with astronomer putting proposals for what they wanted to be observed, and were decided by a Time Allocation Committee (TAC) organized by the Kepler team. You can learn more about the observing proposals and selected targets for Campaign 0 here.
On the site we’re only showing roughly 30 days worth of data, that’s because the light curves derived from the second half of Campaign 0 are more indicative of what the rest of the K2 mission will be like, so we’re only looking at that data. The observations at the start of the Campaign 0 were taken with Kepler not in fine pointing mode with a guide star and thus the positional consistency of the target stars over time on the imager is lower, causing a decrease in the photometric accuracy. Therefore we’re focusing on the better quality second half data. Future K2 Campaigns will have the full ~75 days worth of data in fine point mode, and we plan on showing all of the observations on the Planet Hunters website in the future.
We are showing light curves from the Kepler 2-wheel mission for Campaign 0 (a.k.a. “K2 C-0″) now and wanted to explain some issues that you may notice with these data. The K2 C-0 data are poorer quality than what you are used to seeing. The Kepler team is still working optimize the light curves, and this has been made more difficult by instabilities in the pointing control of the spacecraft. You can expect to see more trends and glitches. Furthermore, the first few weeks of K2 C-0 data were not useable so the length of the light curve (in days) is shorter than what you might have expected. All of this should improve for the next campaign, C-1.
A second issue with the K2 C-0 data is that we don’t have access to information about the stars. We know the EPIC numbers, coordinates, brightness of the stars, and the program numbers (telling us who requested observation of the stars). Postdoctoral Fellow Ji Wang has been an enormous help – he wrote a program to filter the published 2MASS and Sloan catalogs and to search for stars within a small radius about the EPIC coordinates. Ji then used the stellar brightness to obtain an unambiguous identification. This helps, but we still don’t know the stellar gravities (radii), masses or spectral types. Therefore, the information we can display for each of the K2 C-0 stars is much more limited than what you are used to seeing.
Since we don’t know the stellar radii, we are not able to make up accurate simulations for the K2 C0 data. To compensate we will show these light curves to more people than usual to build up consensus about the presence of transits.
The K2 data have many more selection effects than the original Kepler data because the targets are drawn from several guest observer programs. However, this is part of the fun – scavenger hunting for planets among the K2 stars is sure to be an adventure!
We are also trying to improve our turn-around time for PH results. Instead of waiting until we obtain telescope time to carry out follow-up data and publish a paper (sometimes a year later!) we will put the high probability transit candidates that you identify on the “Planet Hunters Object of Interest” (or PHOI – which I think is pronounced something like “fooey”). This is supposed to be a fun home-grown analog of the “Kepler Objects of Interest.”
Thanks to Andrew Vanderburg at Harvard University who has extracted these K2 C-0 light curves for Planet Hunters.
The first science data from the new Kepler K2 mission is up on Planet Hunters just waiting to be looked at for new planets, eclipsing binaries, and whatever else lies in the data. This is a set of completely new stars! (Check out the K2 page for more information about the K2 mission.)
This data may go fast, so get classifying now! But don’t worry, there will be more K2 data when the next quarter is released. And when each K2 quarter is finished, keep classifying stars from the four-year Kepler mission to help solve one of the biggest mysteries in astronomy: how common are planets?
The light curves you see on Planet Hunters are not always the light of a single star. Kepler has very very precise but blurry vision. The CCD pixels on Kepler’s focal plane are very big, four arcseconds to be exact. The light measured at each observation from several of these pixels are added together to create the light curve you see on Planet Hunters. So what does this exactly mean? In some cases the Kepler stars are pretty isolated, but in others there are fainter background stars that appear nearby in the sky can get blended with the light from the Kepler target star. It turns out you can hide a lot within 4 arcseconds.
This stellar contamination can impact what we see in the final light curve. If the main Kepler star has a transiting planet, the contaminating star can dilute the transits. The transits will look shallower than they really are, and you’ll estimate a small planet radius. Sometimes the fainter contaminating star is an eclipsing binary. Combined with the light from the brighter Kepler target star, the stellar eclipses from the eclipsing binary are diluted. The secondary eclipse (when the fainter cooler star goes behind the larger brighter star and the smaller cooler star’s light is blocked out) can be diluted such that it’s not seen and the primary stellar eclipse (when the smaller cooler star transits in front of the larger brighter star and blocks out a portion of the brighter star’s light) get shallower, looking like a planet transit. Other times depending on the brightness of the eclipsing binary, it will look like the main Kepler target is the eclipsing binary when it’s not.
This is something the Kepler mission always had to deal with and there are some observational checks and data tests that can help determine whether the transit-like signal is likely coming from the actual Kepler target star. You can take follow-up observations like we did for PH1 b and PH2 b using telescopes with adaptive optics that minimize the blurring effects of the Earth’s atmosphere to zoom in around the Kepler target star to look for contaminating stars. Also you can look for shifts in the position of the brightest pixel during and before and after a transit which signals the transit signal isn’t coming from the primary Kepler target star. Also you can look at the individual pixel by pixel light curves from Kepler (Kepler reads out a subimage around each target star and a small number of those pixels get added together to make the Kepler light curve)and see if the transit signal or eclipsing binary signal is present in every pixel or if you see say an eclipsing binary signal in one pixel making the light curve and in pixels near by around a different star. Here’s an example from some of the Planet Hunters volunteers who examined to see if an eclipsing binary was contaminating a light curve.
Despite Kepler’s slightly blurry eyes, we can use a host of techniques to try and rule out false positives, identify where there is stellar contamination, and still find planets. So bear this in mind when you see the light curves, that although it’s likely most of the star’s light is from the Kepler target star, a tiny portion (in most cases) is contributed by neighboring stars.
As part of the new Planet Hunters classification interface, the Summary page (see below) suggests some hashtags you could use to label the light curves you’re seeing in Talk and in the Talk comment area on the Summary page. A few people on Talk have asked for a full list, so here’s a handy list of the first set of hashtags suggested by the science team at launch of the new Planet Hunters.
RR Lyrae Star - Pulsating star with periods ~1/2 day
Pulsating star with periods >1 day.
Pulsators – Rapid up and down changes in brightness on the order of a few hours
Eclipsing binary - A star transits another star, often exhibiting V-shape and uneven transit depth
Cataclysmic variable - Cataclysmic variables (cv’s) are a class of stars where the sudden ignition of material on the surface of a white dwarf results in gigantic increase in brightness for several days before returning to natural quiescent state.
Variable star – Change in brightness on timescales greater than 1 day. May be periodic or non-periodic.
Heartbeat star – Two stars get very close together but avoid collision. Their structure changes, and the light curve exhibits a shape like a cadiogram.
glitch – Occasional malfunction of data reduction pipeline.
Planet transit - A planet goes in front of a star and blocks a portion of the star light
Stellar flare – Sudden brightening of a star, often associated with massive material ejection. duration of a few hours. Typically non-periodic.
These listed above are suggested hashtags the science team has come up with. A light curve can definitely be described by more than one hashtag. Also do feel free to use your own hashtags too. There are many more ways to describe and sort the light curves and stars. You can see the most frequent hashtags being used by the Planet Hunters community on the left side of Talk under ‘popular hashtags’
Today we have a post from Joey Schmitt, a graduate student in the Astronomy department at Yale University, where he is working with the exoplanet group led by Debra Fischer, and in particular he has been working on the follow-up of Planet Hunters planet candidates.
We’re happy to announce the discovery of a new planet discovered by Planet Hunters volunteers, which is now published in The Astrophysical Journal. You can read the article for free on the arXiv here.
The star (PH3/Kepler-289/KOI-1353/KIC 7303287) is young and Sun-like. Two planets in the system, with periods of 35 and 126 days, had been previously validated statistically, the outer planet being a gas giant. However, Planet Hunters volunteers discovered a third transit signal between these two planets at a period of 66 days (PH3 c).
A quirk in the system allowed us to actually measure the mass of all the planets using only the exact times that each planet transited. The outer two planets, PH3 c and d, do not have a constant period like most planets do. Instead, it oscillates around an average value in a regular manner, which meant that it had been missed by computer algorithms but was easy to find for human eyes. In particular, the period of PH3 c changes by 10.5 hours in just 10 orbits due to the gravitational influence of the outer gas giant tugging on the middle planet. If Earth experienced such large changes, then if 2014 were 365 days long, 2024 would be 367.4 days long, almost two and a half days longer than 2014.
The new planet is about 2.7 times the radius of Earth and 4 times as massive. Its low density means that, despite its low mass, a large chunk of the planet must be composed of hydrogen and helium: 2% by mass and 50% by radius. The outer planet, on the other hand, is like a warm version of our Saturn, while the inner planet’s mass is poorly known. It could be mostly rocky, watery, or gassy.
We would like to thank all of the people involved in the project and all of the Planet Hunters volunteers for making this possible. We hope to find more gems like this in the future.
There were some big changes to the Planet Hunters website and our Talk discussion tool yesterday. Along with the main Planet Hunters website and classification interface being completely rebuilt, we are now pairing the main Planet Hunters website with the latest version of the Zooniverse’s Talk discussion tool. Now when you go to http://talk.planethunters.org it will take you to Planet Hunters Talk 2.0. In this blog, I’ll give you a brief overview and introduction to the new features added into Planet Hunters Talk.
What happened to the original Planet Hunters Talk?
Before I introduce the new features of Planet Hunters Talk 2.0, I wanted to give an update of what happened to the original Planet Hunters Talk. The original Planet Hunters talk is still online at http://oldtalk.planethunters.org, and you’ll find a link to it on the navigation bar of the New Talk. The original Talk is a repository of discussions and discoveries, and we’re not taking it offline or shutting it down. You can still log in and post there. The differences in how stars are treated between the two versions and the sheer volume of interconnected discussions and comments makes it very difficult and time consuming to attempt to migrate that content to Talk 2.0. There’s a very real chance we could do this incorrectly, so we thought the safest option was to leave the original Planet Hunters Talk online as resource and with all light curves shown from Planet Hunters 2.0 going to the new Talk.
Starcentric versus light curve chunk-centric
There are a few key differences between new Planet Hunters Talk and the original version. Firstly how we treat the stars is different. On the original Planet Hunters Talk, we treated each 30-day light curve section shown in the classification interface as a different entry in Talk with its own page, where people could leave 140 character comments and start side conversations. So a single star would have many discussions spread across different light curve Talk pages with no easy way to tell that someone had posted a comment about a different quarter. In the new version of Talk, we give each star a Talk page (with the APH ID representing the Planet Hunters ID for the star) so comments and conversations are grouped together from people who see the different light curves chunks from the star.
Overview of Planet Hunters Talk 2.0
Talk Subject Page
Below is an example of a Talk page for star APH0000622 (http://talk.planethunters.org/#/subjects/APH0000622). Here you’ll be presented with a light curve viewer for the star with all available quarters of Kepler data for this star to peruse through (if you enter this page from the main classification interface the light curve chunk you reviewed in the classification interface will be automatically loaded in the light curve window). Later in the future, we plan to add scrolling and zooming capability to the light curve viewer. In addition we list the Kepler id for the star, and any other information we have for the star (like radius and temperature) and some useful links which we’ll describe in more detail in another blog post.Like original Talk, you can make collections, write 140 character comments, add hashtags, and have longer side discussions about the star and the light curve you reviewed.
Just like old Talk, if you have more to say than 140 characters there’s the ability in New Talk to start and have longer side discussions about the star. The difference is that now you have to select which topic, Help, Science or Chat your discussion will be about it and then click on the Post button to start the discussion. this is because the discussion is also linked and archived for easy access on the Discussion Boards (more about this in the next section).
New Talk has discussion boards (which you can navigate to with the top bar by clicking on Discussion Boards) like original Talk in three categories: Help, Science, and Chat. The main difference is there are now subboards under each of these three headings where you can post and start discussion threads.
You’ll notice that each of the three board categories has an ‘The Objects’ subboard. This is where you can also access the side discussions you make on the star Talk pages. They get linked and archived here for so they’re easy to find by the Planet Hunters community and the science team. In the old version of Talk a side discussions were often buried and hard to get to. Now you can quickly check out each ‘The Objects” board and see what longer discussions people were having about a given star.
Front Page/Recent Page
The font page of Talk accessible when you go directly to http://talk.planethunters.org ( or by clicking on the Recent tab in Talk) lists the most recent 140 character comments made on Talk as well as displays the latest comments in the discussion board threads for easy access. By clicking on the comment, you’ll get taken to the Talk page for the given star. By clicking on the discussion board post, will take you to directly to that thread.
You can either go directly to the Talk website by url – http://talk.planethunters.org or you can access Talk through the main Planet Hunters classification interface. Once your classification for a light curve is submitted in the main interface, a summary page appears (see below). Here you can directly write a 140 character comment about the light curve you saw (that will appear on the star’s Talk page) without leaving the classification interface. If you click ‘Discuss on Talk’ you’ll be brought to the Talk page for the star with the light curve chunk you reviewed queued up in the light curve viewer.
Direct/private messages on New Talk are a little different that has been done in the past for Planet Hunters. You won’t get an email when someone sends you a private message, instead the envelope icon on the top right of the navigation bar (by the return to classifying button) will tell if you have any unread messages. If you have an new unread message, the envelope will brighten and the number of unread messages will be listed. Clicking on the envelope or the Profile tab will take you to your list of messages.
More Features and Upgrades to Come
We wanted to get to the new interface out to you as fast as we could so that we’ll be ready for the K2 data which we’re currently processing and placing in a format the new interface can read in. There are some small finishing touches the Zooniverse developers will be adding in the coming days to new Planet Hunters Talk. Thanks for your patience as we go through these small growing pains with the project. If you have suggestions of features you would like to see in Talk, please post your ideas in this thread, and we’ll try our best to accommodate those requests.
Need Help? Ask the Planet Hunters Talk Moderators
The Planet Hunters Talk moderators (TonyJHoffman, constovich, and echo-lily-mai) are standing by ready and willing to help. So if you’ve got a question about the new Planet Hunters or Talk don’t hesitate to ask them.