Candidates and Upgrades
Hello everyone, graduate student John here. The time has finally arrived and we have the first batch of candidates up for you. To top it off, we have also managed some interface updates which should make marking transits faster and easier (yeah, Stuart!).
First, the candidates. I have a blog post coming out shortly which will explain how we made our selections so for now I will just give you the results. If you roll on over to the Candidates page, you will find that there are 132 new stars. That breaks down into 90 new potential planet candidates and 42 potential eclipsing binaries. We are still hard at work modeling these systems, so don’t have much more information than that it made the cut. We thought you would rather see them now and we will add the periods and radii as we do the fits.
Along with the new candidates, you can now see stars which you viewed which are possible planet or eclipsing binary candidates.
Which brings us to the other interface updates: transit marking. Now when you want to mark a transit on a star, you can simply drag a box around all of the points in the transit. Once drawn, the boxes work exactly as they did before. This should help us get more precise transit center information to more easily track down interesting candidates. Another perk is that clicking on any of the transit boxes will zoom you to that location on the plot.
Bring on the new data!
John M. Brewer
New Kepler Data: Feb 1
By Zak Kaplan (Yale undergrad)
Planet Hunters has just completed its first analysis of the Kepler data! With your classifications, we were able to extract information about all of the 150,000 light curves. We would like to thank the more than 16,000 registered users who have helped make Planet Hunters such a success. Special thanks to the collectors and the top 14 users who each analyzed over 5000 light curves, accounting for over 10% of the 1.3 million classifications.
To give a better idea of what you’re measuring in a transit curve, a planet crossing a star causes about the same dimming of light as a small fruit fly passing in front of a car headlight. Now imagine that car is a few thousand light-years away, and you get a sense of just how amazing the Kepler data and your work have been.
The Kepler team will have a press conference on 2 February 2011, announcing their new candidates and releasing new data that will more than quadruple the amount of data that we can serve to you. You can join the live broadcast on NASA TV at 1pm EST and we will post the Kepler press release here next Wednesday.
For the past week, the Exoplanet Research Team at Yale has been analyzing over 3500 light curves that you marked with promising transits. We found that PH users marked transits that we would have missed. From this first set of data, we have culled approximately 300 strong planet candidates, as well as several new eclipsing binary star systems. We are formatting the new Candidates pages now so that they will appear before the Kepler press conference. Then, you can check to see which objects you detected independently, before the Kepler team announced them. It will be especially interesting to see if there are some good candidates that you all found that are not on their new list. If so, we will ask the Kepler team for feedback on your new candidates.
We hope you will help continue to prove the power of citizen science, as we look for more planets beyond our solar system. Until then, keep on hunting!
Talk Updates
Our two new community collaboration websites, Milky Way Talk and Planet Hunters Talk, had some updates this week. We thought it was worth going over them in this blog post. We’ve had a lot of feedback about Talk and are working to implement the most-requested features.
The biggest difference you’ll see when logging into Talk is that your discussions are now easier to manage and track. A new, large box on the main page shows all the new and updated discussions since your last login. You can refine these using the two drop-down boxes at the top of this section. You can chose to show discussions from the last 24 hours, the last week, or since any date using a pop-up calendar. You can also chose to only see discussions that you are a part of, which should help you keep track of your conversations.
In addition to these changes, you’ll also find a lot more metadata around the discussions, telling you who last posted, how many people are taking part, and who started the discussion, where relevant. Users within these discussions are now highlighted if they are part of the development team or the science team. This is something a lot of you asked for.
The other item that has been changed with this Talk update is pagination. There are now easy-to-use buttons on the discussions, collections and objects on the front page. These mean that you can browse back through time and see more than just the most recent items. As Talk has grown more popular, this feature has become more necessary.
Another change to the front page is that we now show the most-recent items by default, and not the trending items. You can still see the trending items by clicking the link at the top. Users told us they preferred to see recent activity initially so we made the change. Similarly, the ‘trending keywords’ list now appears on the front page at all times.
On Planet Hunters Talk, when you’re viewing a light curve, Kepler Planet Candidates are now identified as a “Kepler Favorite”.
Finally, page titles are now meaningful. This means that if you bookmark or share a link, you’ll remember why. Collections are named and objects will be title dusing their Zooniverse ID (e.g. APH….). Several of you have also noted our lack of a favicon (the little icon next to the URL in your browser bar). This is coming shortly as well.
There are more changes planned for Talk, but these significant updates to the front page were worth noting on the blog. For example, we plan to start integrating social media links into the Talk sites, along with more updates as time goes by. Talk continues to evolve and we welcome feedback. Post comments and suggestions on the Feature Requests Thread or Board Upgrades thread on Talk or send us an email at team@planethunters.org.
More star info…
Thanks again for your amazing work and feedback. We are working to keep up with you! There is now a data-download button (thanks to Chris, Arfon, Michael, and Stuart!) on the star pages. We are also integrating information about stars that are known eclipsing binaries (EB), Kepler planet candidates (PC) and false positives (FP). Here is an ascii list of light curves with this information. On this list, the APH number is given, followed by the Kepler ID and a flag (EB, PC, FP). For EB objects, D indicates detached binaries, SD is semi-detached, OC is an overcontact binary. Kepler PC stars include columns with the prospective period and planet radius (in Jupiter radii units).
One note about false positives: There are light curves that masquerade as transiting planets. For example, light from a bright foreground star is spread out over several pixels on the CCD detector. The halo of starlight is swept up into a single brightness measurement by the Kepler team’s software. However, in some cases a more distant eclipsing binary (EB) star system blends into the edges of the foreground star. Since the EB is more distant, it is fainter and contributes a smaller fraction of the light. In this case, the background eclipse produces a diluted signal that looks very much like a transiting planet. There are a couple of ways to eliminate these imposters:
- the Kepler team has software that looks for pixel contamination and identifies the star as a false positive (FP). When available, we are listing this information on the light curve and star pages.
- Follow up radial velocity measurements of the bright star will also include the background blended eclipsing binary. A large velocity signal can be a give away sign that the light curve does not arise from a transiting planet.
This follow-up is a critical effort, required to move an object from a transit candidate to a planet.
Uncertainty
Hello, I’m John, a graduate student at Yale University and a member of the Science Team. We have had some questions about the non-light curve information on the star pages, including: how accurate is the data, and why is it missing occasionally? This post will give you some background on where this data comes from and how to interpret it.
Before the Kepler spacecraft was launched, a lot of thought went into finding the optimal patch of sky to observe. Then, many years were spent collecting as much data as possible, from the ground, about the stars in that patch of sky. Photometry (a measure of star brightness, like you have been looking at on planethunters.org) was taken through multiple filters of most stars and spectra (with more detailed information) were taken of the brightest stars. These measurements all went into selecting the most promising stars for the Kepler mission to look at.
From these measurements, it is possible to calculate certain values which are useful in interpreting the data from Kepler. This includes spectral type, effective temperature, surface gravity, and radius. All of these values were compiled into the Kepler Input Catalog, which we use to show you the information on the star pages. However, because this data was taken en-masse and many of the stars are quite dim there is sometimes a large uncertainty in these parameters or there may be no derived values at all. When you look at the stellar radius on a star page, that number could be off by as much as 50%!
After interesting stars are found, much effort goes into closely examining the star with larger telescopes, more frequent observations with Kepler, or both. This results in much more accurate determinations of all parameters. One recent paper (Metcalfe et al. 2010) determined the radius and age of a Kepler star to within 1%.
Some of you have already been calculating the size of the transiting companion using the duration of the transit and the stellar radius. It has been great to see the phenomenal work people are doing in seeking to understand these stars. Keep in mind though that until more accurate follow up data can be taken, there will be a large amount of uncertainty in those numbers.
A word from the Kepler Team
Dear Planet Hunters: Dr. Natalie Batalha, Deputy Science Team Lead for the Kepler Mission, asked us to post the following message:
Welcome! We are so glad you’re here!
I’m sure I speak for the entire Kepler team when I say how happy we are that Zooniverse is being applied to the Kepler data. For some time now, I’ve watched the public actively work with archived data from other missions. The folks at Unmanned Spaceflight, for example, regularly share the latest images they’ve doctored up from Solar System missions like MER and Cassini. And the SOHO mission recently hit a milestone, discovering its 2000th comet on December 26th, 2010. The discoverer was not part of any formal SOHO science team but rather an astronomy student at Jagiellonian University in Krakow, Poland. I’ve added “Citizen Scientist” to my urban dictionary and appreciate its tremendous potential.
That’s all well and fine when it comes to Martian landscapes, comets, and sunlight glinting off the surface of methane lakes millions of miles away. But how in the world could we entice the public to look at boring old lightcurves? PlanetHunters.org has done exactly that. Not only are thousands of people looking at light curves, they are getting just as hooked on their variety as we are! Welcome to the ranks of those who love light curves.
The Kepler spacecraft is a new piece of technology. Never before have humans stared at stars with such unwavering precision and patience. And whenever humanity does something new, there are sure to be surprises. One of the biggest surprises to me so far is the impact that Kepler is having on stellar astrophysics. Who knew, for example, that a star like RR Lyrae — one of the brightest and well-studied objects in the sky — would blow the dust off textbooks written on this class of star? Who knew we’d see such a symphony of variability occurring just below the noise levels typical of ground-based telescopes?
But the name of the game here is planet hunting. I’ve heard people wonder why they should bother to hunt for planets when the Kepler team has spent years designing savvy computer algorithms to do exactly that — algorithms that can tease signals out of the noise that the human eyes cannot even see. The answer is simple.
Kepler relies, in large part, on automation. We are a relatively small team. There are currently less than 15 scientists working in the Kepler Science Office here at Ames. In the early days, there were only 5 of us! Let’s say we divided up the 150,000 stars we are monitoring amongst the 15 scientists at Ames. We’d each be responsible for 10,000 stars. If we spent only 60 seconds looking at each star, it’d take us over 160 hours to finish out allotment. That’s a solid month of doing nothing else but looking at light curves. Just in time since more data comes down from the spacecraft each month and the process would have to start all over again. Such a plan would never have earned taxpayer dollars. We need our scientists doing other things — like monitoring the instrument and optimizing the software and vetting out the false positives and interpreting the results. And so we write computer software that combs through the data searching for transit-like features.
It’s a challenge to design a one-size-fits-all approach to transit detection. The transit are buried in the light curves of stars with widely different properties and behaviors. You’d build one kind of tool for finding a needle in a haystack but a different kind of tool for finding a needle in a swamp. We don’t even yet know what all the possibilities are because we’ve never looked at stars with this kind of precision.
Another consideration is that the software pipeline requires 3 transits for complete modeling and pipeline generation of they key statistics that are used to vet out the false positives — astrophysical signals masquerading as planet transits. It’s certainly true that we’ve gone back and cherry-picked some of the more compelling light curves displaying less than 3 transits — especially those of the brightest stars. However, many such signals are still lurking in the archive.
So what else did our algorithms miss? Ah, let’s find out, shall we? We’re here with you, ready to help. Come stand here in the crow’s nest and experience the thrill of discovery with us. We welcome your keen eyes!
A huge thank you to the folks at planethunters.org for putting this together.
Natalie Batalha
Deputy Science Team Lead
Kepler Mission
Przykłady tranzytów
Niedawno zespół Keplera ogłosił odkrycie pięciu gwiazd, z których każda posiada układ planetarny złożony z kilku planet (Steffen i in., 2010). Zdjęcie po lewej przedstawia wykres krzywej blasku gwiazdy SPH10102031 (Kepler ID 10723750) w pierwszym kwartale (Q1). Widać na nim dwa spadki jasności spowodowane przez tranzyty dwóch różnych planet. Tranzyty nie powtarzają się, ponieważ okresy orbitalne tych planet są dłuższe od badanego przedziału czasu. Pierwszy spadek jasności spowodowany jest przez planetę mniej więcej wielkości Jowisza. Aby pokazać typowy, prostokątny kształt wykresu w miejscu tranzytu planety, na zdjęciu po prawej prezentujemy powiększenie drugiego przypadku tranzytu. Tranzyt ten ma głębokość ok. 0,25%, co przy zakładanym promieniu gwiazdy pozwala stwierdzić, że promień tej planety jest ok. 7,6 razy większy od promienia Ziemi (czyli planeta ta jest większa od Neptuna, ale mniejsza od Jowisza).
Poniżej przedstawiamy wykresy krzywych blasku dwóch innych gwiazd z pracy Steffena i in. z 2010 roku. Zdjęcie po lewej przedstawia krzywą blasku gwiazdy SPH10120491 (Kepler ID 8394721) w pierwszym kwartale. Widać na nim spadki jasności spowodowane przez tranzyty trzech różnych planet! Jeden z nich jest bardzo wyraźny i spowodowany przez planetę o promieniu 6,5 razy większym od promienia Ziemi. Planeta ta dokonuje tranzytu tylko raz w ciągu 35 dni. Na wykresie widać również tranzyty dwóch innych planet, które są nieco mniej wyraźne. Ich promień jest zaledwie kilka razy większy od promienia Ziemi. Jedna z tych planet dokonuje tranzytu co 13,5 dnia, a druga – co 27,4 dnia.
Zdjecia po prawej przedstawia wykres krzywej blasku gwiazdy SPH10017624 (Kepler 5972334). Widać na nim trzy spadki jasności spowodowane przez planetę wielkości Jowisza, której okres orbitalny trwa 15,4 dnia. Na tym wykresie druga planeta, o promieniu dwukrotnie większym od promienia Ziemi i okresie orbitalnym trwającym 2,4 dnia, jest praktycznie niezauważalna.
Aby lepiej przyjrzeć się wykresom oraz trochę poćwiczyć swoje umiejętności, przejdź do fantastycznych przykładów poniżej i używając zoomu, postaraj się zlokalizować tranzyty (niestety, nie będziesz mógł zapisać swoich wyników).
Transits (examples)
The Kepler team recently announced the detection of five stars, each with multiple transiting planets (Steffen et al, 2010). The left Figure below shows the Quarter 1 (Q1) light curve for the star SPH10102031 (Kepler ID 10723750) with two transit dips from two different planets. The transits do not repeat because the orbital periods are longer than the time baseline. The first transit dip is from a planet that is about the size of Jupiter. To highlight the typical boxy shape of a planet transit curve, we have zoomed in on the second transit event in the Figure below and on the right. The depth of the transit is about 0.25% and given the assumed radius of the star, the planet radius is about 7.6 times the radius of the Earth (larger than Neptune, but smaller than Jupiter).
Light curves for two other stars in the Steffen et al 2010 paper are shown below. The Figure on the left is the Q1 light curve for SPH10120491 (Kepler ID 8394721). This light curve contains transit dips from three different planets! One of these is very obvious and is caused by a planet that is 6.5 times the radius of Earth that only transits once during the 35-day light curve. However, there are two other transiting planets that are harder to see with radii of just a few times that of the Earth. One of these planets transits every 13.5 days and the other transits every 27.4 days.
The Figure above and to the right shows the light curve for SPH10017624 (Kepler 5972334). There are three transit dips from a Jupiter-sized planet that orbits every 15.4 days. In this Figure, it is virtually impossible to see the second planet, which has a radius just twice that of the Earth and transits every 2.4 days.
To get a better look and some practice (you won’t be able to save these), pull up these amazing light curves and use the zoom tool to identify the transits.
Variable stars (examples)
The reasons for changes in the brightness of a star can be divided into two categories: (1) orbiting companions or (2) stellar astrophysics.
(1) In principle, the variability from orbiting companions (this includes eclipsing binaries or transiting planets) should be as regular as clockwork. In practice, the variability can deviate from clockwork regularity if stellar binaries get too close together, if there are multiple transiting planets, if there is additional background electronic noise or astrophysical noise.
(2) Brightness variations caused by physical processes internal to the star (stellar astrophysics) can arise from pulsations of the star, starspots or flares. Flares are random spikes in the light curve brightness. Pulsations from stars (like RR Lyraes) are quasi-periodic: they can appear to be regular for a while and the cycles are relatively short (generally hours to a day or so). The Figure below shows two variable stars with short periods that might be best classified as “variable” and “pulsating.” These could be short period binary systems – this could quickly be verified with follow-up observations.
Starspots produce complex variations. As the star spins, the spots rotate in and out of view with a periodicity of a day or two (for the most rapidly spinning stars) to several days for slowly rotating stars (the Sun has a rotation period of 25 days). Starspots can form at different latitudes on the star. Since some latitudes rotate faster, spots can show multi-cyclical variations. The light curves below might be best classified as variable and irregular. However, a case could be made for classifying the light curve in the figure below (and left) as variable and regular. Even though the amplitude of the curves changes, the time from one peak to the next is about the same.
Quiet Stars (examples)
Thanks very much for your help with this project. At last count, roughly 50,000 light curves had been sorted at planethunters.org. Many of you have requested more examples about how to classify stellar variability, so we’ll start with the easiest case. All of the light curves below are examples of quiet stars. Random variations in brightness occur because of photon noise (similar to shot noise in electronics). The number of photons that are collected are small enough that there random fluctuations that have nothing to do with the actual brightness of the star. Photon noise (or Poisson noise) produces scatter, but the data remain in a nearly featureless band of points.
If you look closely at the light curve data for these quiet stars, you will see light gray error bars associated with each data point. In any physical measurement, the error bar simply captures our ignorance about the true value of the measurement. In the Kepler light curves, the brightness is represented as a discrete dot, however, any and all points along an error bar are equally correct values for that particular brightness measurement.
In the quiet light curves above, should any of those low points be flagged as possible transits? Probably not. A deviant point or two can still just be noise. A true transit event should have a series of low brightness points that last for the time it takes the planet to cross in front of its stars (i.e., a few to several hours, represented by a few to several data points). Low dips that repeat are also good indicators of a transit, however some of the most exciting transits (from planets in wider, more habitable orbits) will only occur once per month (for example, a true analog of our Earth would just transit once per year).
The quiet light curves above may seem like duds, but they are an extremely important aspect of research for this project. Stars that do not vary in brightness are particularly important objects for exoplanet searches with other techniques. The work that you’re doing will feed into our understanding for the next generation instruments and space missions that could be built to detect planets.
Happy Holidays to All! Debra Fischer
Planet Hunters 