A Planet Hunters Review of the Kepler Transit Candidate List
The Kepler team uses automated routines, specifically the Transiting Planet Search (TPS) algorithm, to search for transit signals in the Kepler light curves. TPS triggers on many repeated transit-like features in the light curves dubbed Threshold Crossing Events or TCEs. TPS generates many many TCEs, much more than the number of real extrasolar planets. The majority are false detections, but a few are real transits due to orbiting exoplanets. A subset of the Kepler team examine the TCE list and whittles it down to make the KOI (Kepler Object of Interest) list. A handful of Kepler scientists review each TCE and data validation report, results from a series of checks and test to help rule out astrophysical false positives that might produce a transit-like signal such as blended background eclipsing binary. It takes many many months for this process. The current Kepler planet candidate list released in January was using Q1-8, but there are many more Quarters of Kepler data available.
The Kepler team has made all of their data products publicly available in the extended mission. In December, the Kepler team released the list of 18,406 TCEs found during a search of Quarters(Q) 1-12 data and the resulting reports produced by their data validation pipeline. These Q1-12 TCEs have yet to fully searched by the Kepler team, meaning there are likely discoveries waiting to be found.
For the past few months I’ve been working with Chris and Arfon to set up a Planet Hunters review of the TCE list. Today the review site is live, and we need your help to review these potential transit candidates and identify the ones that are likely due to real planets. We’re using a version of the round 2 review interface, we used before to vet planet candidates for my short period planets paper. For each TCE, you’ll be presented with a light curve (from the data validation report) that has been zoomed-in and folded on the period determined by TPS so that the repeat transits all line up on top of each other.
A good TCE candidate – The black data points all the actual measured Kepler data folded on the period identified by TPS. The blue diamonds represent an average of the folded data. The red line plotted is a model of the transit that TPS identified.
We are asking you to confirm that there is a visible transit in the light curve identified by TPS (“Is there a transit?”) and determine whether the red line matches the light curve (“Does the red line fit the data?”).
With the folded light curves we can see smaller planets, the rocky ones that are so hard for most of us to see in the regular light curves we show on the Planet Hunters website. There are other teams who are using the TCE list in their research and as targets for follow-up observations, but where I think we have an advantage is that we have the ability to review the entire TCE list, not just the rocky planet transits but also the Jupiter-sized and in between.
We’re not in a race with the Kepler team who am I sure are also vetting the current released list, but I believe what is unique to this project and Planet Hunters is the ability to review uniformly all the ~18,000 potential transit signals identified by TPS. The current versions of the Kepler KOI list currently has not gone back and reanalyzed all the previous planet candidates detected in previous TPS runs with the longer observational baseline. So we’ll have the first independent vetting of the Kepler Quarters 1-12 TCE catalog providing a uniform selected sample of planet candidates.
Each TCE will require 10 independent review before being retired. Once we’ve gotten through identifying what looks to be real transit candidates from the non-detections, I’ll apply some additional cuts based on the output from the Kepler validation pipeline (like how the consistent is the depth of the odd and even transits to rule out eclipsing binaries and pixel offsets in and out of transit that might indicate a blended background eclipsing binary is producing the signal) to come up with our very own Planet Hunters planet candidate list from the TCEs.
I think this project will result in a very interesting paper looking at the frequencies of super-Earth to Neptunes to Jupiter-sized planets in the Kepler field, and also serve as an efficiency estimate for the Kepler KOI vetting process. If it goes well, we may consider making this a more permanent fixture on Planet Hunters for future releases of the Kepler TCE list. My goal is to have the first results from the TCE review to show in a poster at Protostars and Planets VI conference in Heidelberg, Germany in July.
If you are interested in participating and helping out with this project, you can go to http://tcereview.planethunters.org/ where you can join in and characterize the TCEs. Please do read through the tutorial on the front page. It will guide you on what you should be doing, as well as show you some examples of non-detections and good TCE transit detections.
Thanks in advance,
~Meg
PH1 Paper Offically Accepted for Publication
Last October we announced the discovery of PH1 – a four star planetary system hosting a circumbinary planet (PH1b). The transits were spotted by volunteers Robert Gagliano and Kian Jek on Talk. I’m thrilled to announce that our paper “Planet Hunters: A Transiting Circumbinary Planet in a Quadruple Star System” has been officially accepted to Astrophysical Journal. Congratulations to all involved.
Now that the paper has been accepted and is in press, you can find the accepted manuscript online and added to the Zooniverse publications page (which has a total of 4 Planet Hunters in press/published papers based on your clicks). The official journal version will be published sometime in May.
PH1b is our first confirmed exoplanet discovery, a milestone for Planet Hunters. The 6.18 Earth radii planet orbits outside the 20-day orbit of an eclipsing binary consisting of an F dwarf ( 1.734 x the Radius of the Sun) and M dwarf ( 0.378 x the Radius of the Sun). For the planet, we find an upper mass limit of 169 Earth masses (0.531 Jupiter masses) at the 99.7% confidence level. With a radius and mass less than that of Jupiter, PH1b is a bona fide planet. Not all planet candidates can be confirmed as we could with PH1b. Since PH1b is orbiting an eclipsing binary, we could use the fact that there are no changes in the timing of the stellar eclipses due to the planet to constrain PH1b’s mass.
With the acceptance of the paper, we have asked that PH1b be added to the NASA Exoplanet Archive (NExSci)’s list of confirmed exoplanets . NExSci has taken on the role of being the keeper of the list of confirmed exoplanet discoveries. In addition, PH1b has bestowed the Kepler # that was saved for us in October. PH1b has been given officially a Kepler designation of Kepler-64b and added to the list of planets in the Kepler field. You can find out more about what the criteria for obtaining a Kepler # is here.
In the list of confirmed planets, the planet is referred to as PH1b (you might notice an extra space – that should be revised in an update to the NASA Exoplanet Archive). I like to think of the Kepler # as icing on the cake. We’ll still refer to the planet as PH1b. Kepler-64b will be an alternate designation and used in the catalog of planets in the Kepler field (PH1b will be listed as an alternative designation). The full data page for PH1b on the NASA Exoplanet Archive can be found here
For those who are wondering what the NASA Exoplanet Archive is, Rachel Akeson, Deputy Director of NexSci and Project Scientist for the NASA Exoplanet Archive, explains below:
The NASA Exoplanet Archive is an online astronomical exoplanet and stellar catalog and data service provided to the astronomical community to assist in the search for and characterization of exoplanets and their host stars.
Current data content and tools include:
- Interactive tables of confirmed planets, Kepler Objects of Interest (which includes the planet candidates), Kepler Threshold Crossing Events, stellar parameters for all Kepler targets in Q1-12 and a list of Kepler confirmed planet names and aliases.
- Overview pages with all available data for each confirmed planet and Kepler Object of Interest
- Tools to view, normalize, phase and calculate periodograms for light curves, particularly those from Kepler and CoRoT
- Transit predictions for all known transiting planets and Kepler Objects of Interest
- URL-based access to all table data
The archive is available at http://exoplanetarchive.ipac.caltech.edu/index.html and includes links to documentation for all these services.
More about the Discovery of PH2-b
The project’s second confirmed planet, PH2-b (a Jupiter-sized gas giant planet orbiting a Sun-like star), was discovered by several members of the PH community who classified the light curve and then posted the candidate on Talk. A volunteer-organized effort took this from a possible repeat of transits to a likely candidate that was then passed to the Science Team and subsequently validated as a real bona fided planet. Volunteer rafcioo28 who was the first person to mark a transit in Q4. Mike Chopin was the second and the one to first post on the Talk page about the transit in February of last year. Hans Martin Schwengeler went to look at the rest of the publicly released Kepler data months later spotting the other transits. Together rafcioo28, Mike, and Hans with the help of Abe Hoekstra, Tom Jacobs, Kian Jek, Daryll LaCourse have discovered Planet Hunters’ 2nd confirmed planet PH2-b. I’ve asked Mike and Hans (rafcioo28 we haven’t been able to contact thus far) write a bit about their thoughts on the discovery.
Artistic rendition is a hybrid photo-illustration, showing a sunset view
from the perspective of an imagined Earthlike moon orbiting the giant planet, PH2 b. Image Credit: H. Giguere, M. Giguere/Yale University
Mike Chopin
At school, at the age of fourteen, I did a project on atomic (particle) physics which gained me a grade 1 CSE. The following year I studied and passed my Physics exam which was interesting for my school since that was a subject not on the school curriculum. After leaving school, I studied OND Engineering at Kingston Polytechnic although I only completed my first year since I longed to go travelling. My wanderlust got the better of me and I joined a shipping line as a Navigating Cadet Officer. I suppose it’s easy to see why astronomy has fascinated me since knowing about stars was part of my navigation syllabus.
My childhood hero was, and still is, Captain James Cook a man I consider to be the greatest explorer of all time. I consider myself fortunate to have visited many places this great navigator charted. In 2012 his observation of the transit of Venus in 1769 was commemorated at Venus Point in Tahiti. Although I wasn’t there for 2012, I did get to Venus Point a couple of years earlier. Like Cook, I spent some time in the Navy and have a passion for boats especially under sail. I have two complete circumnavigations under my belt; the first by sea (unfortunately via the Panama Canal and not Cape Horn) the second was by air, island hopping my way across the Pacific. I have now visited ninety six countries and hope that it won’t be too long before I join the Travellers’ Century Club.
Latterly, I was employed by Lloyds TSB (Registrars) as a project officer with my principal role as the sole technical writer writing context sensitive help for software, on-line documentation, trouble-shooting guides for the IT department and interactive eLearning modules. Following redundancy, I went freelance as a writer and have had a couple of small contracts both as a writer and as a data manager.
I am delighted to have been involved with the discovery of an exoplanet, a planet orbiting a distant sun. From the outset, I enjoyed the thrill of analysing the light signals recorded and posted on the planethunters.org website. This website invites ordinary people to take part in analysis of vast amounts of data. Often called ‘Citizen Science’ this excellent website provides clear tutorials to enable the amateur to partake in this worthwhile research project.
In its simplest form, when an exoplanet passes between our line of sight and its sun, there is a reduction in the amount of light that we receive. This effect can be seen if we plot the light output from this star against time. While trying to analyse the data, I would try to imagine the planet transiting its sun, if it was a large planet and close to its sun would it cut more light than if it had been a small planet and a giant sun? Does it have a high reflectivity (albedo) and is it inclined to its ecliptic and if so, would it add or reduce the amount of light recorded. If distant suns had multiple planets with systems similar to our own solar system, then would it be possible to identify additional planets. It was with all these ideas in mind that I began my quest for the exoplanets.
Sometimes, the pattern appeared to be too random to be able to distinguish a planet and at others, beautiful patterns could be seen as if generated by an oscilloscope, these it would seem were possible candidates for a binary star and so these were recorded also. Now and again, a pattern would emerge which would make you sit up and take notice. Using the sliders on the screen, I would drag out the ‘x’ scale to magnify a section of the screen where I was certain a transit was occurring and then I would check to see whether there was a second transit which may indicate its periodicity. It was during such an event that I found, what is recently been called, PH2-b. With, what at time was simply a planetary candidate; I posted a note to see if any of my fellow planet hunters had seen what I had seen.
Carl Sagan spoke of the ‘Pale Blue Dot’, the Earth as seen from Voyager 1 in the distant reaches of space, how exciting would it be if spectral analysis revealed this planet to have water and an atmosphere, another ‘Pale Blue dot’, now that would be truly remarkable.
Hans Martin Schwengeler
I’m a regular user (zoo3hans) on PH, more or less from the beginning two years ago. My name is Hans Martin Schwengeler and I live near Basel in Switzerland. I’m 54 years old, I’m married and we have two children. I’m a mathematician and work as a computer professional. I like to advance Science in general and Astronomy in particular. I did work a few years at the Astronomical Institute of the University of Basel (before it got closed because they decided to save some money…), mainly on Cepheids and the Hubble Constant (together with Prof. G.A. Tammann). Nowadays I’m very interested in exoplanets and spend every free minute on PH.
I’ve always been interested in stars, planets and the universe in general. So when I studied Mathematics at the ETH in Zurich it was natural to choose Astronomy as a second discipline. After working a few years on a Statistics research program (based on the Kalman Filter) I managed to get a job at the Astronomical Institute of the University of Basel (Switzerland) as a system manager. There I could work part time on research programs, mainly on Cepheids to determine the Hubble Constant (together with G.A.Tammann and Allan Sandage). I did this with the image processing software ESO-MIDAS, where we analyzed images taken by the ESO New Technology Telescope (NTT) or the Hubble Space Telescope (HST). I also used a program (written in Fortran-77) called superperiod to find the periods of the variable stars found in the galaxy images and see if they could be cepheids with periods between 2 and 100 days. With the Cepheid period-luminosity relationship we were then able to determine the distance of the Cepheid and the host-galaxy.
As soon as Michel Mayor and Didier Queloz detected the planet around 51 Pegasi, I was drawn in into exoplanets. I followed every single announcement of the detection of a new exoplanet on Exoplanet.eu and arXiv.org and elsewhere. So when I first took notice of the Planet Hunters project, I joined immediately. In the meantime the Astronomical Institute has been closed down (on monetary reasons) and I was working as a systems engineer at the Federal Office for Information Technologies and Telecommunications in Bern. I did not have anymore the tools needed to analyze light curves and so on. I also had to realize that to detect a planet transit in a Kepler light curve is not so easy as I first thought (except for the very big Jupiter-like ones). The learning curve was rather steep. Fortunately some fellow hunters had already gathered some very good insight and also some useful tools. So after some months I think I accumulated enough experience to do some real work here on PH.
So when I got the light curve for KID 12735740 I thought it looks very nice and might be a real planetary transit. Kian Jek had already commented on it favorably. The transit shape is more like an “U” instead of a “V”, the transit depth and duration is compatible with a 1.1 R_Jupiter planet with a period around 282.6 days. We can check this with Kian’s very good Planetary Calculator. The first thing I then usually do, is to have a look at the sky view and then post this image to the PH Talk pages for others to have a look too My second step is then to download the FITS files from MAST (using the very good tools from http://www.kianjin.com/kepler/detrend.tar.gz ), detrend the curve roughly and view it by eye first (often using the program ggobi for this purpose). I upload the light curve also to PH if it looks interesting. Thirdly I may do a periodogram to find the period if a good period seems to be present (and upload it as well of course).
In the case of KID 12735740 I think all looks very good for a real planet candidate. Not much would be possible without the help of others, especially Kian Jek (aka kianjin) is invaluable here at PH. He compiles very good lists of “good candidates” or EB lists. I also find the other lists of “good Q2 candidates (non Kepler favorites)” (or Q3, Q4, etc. lists) very helpful in finding candidates and discuss them in more detail. It’s otherwise rather difficult to keep track of all the interesting cases on PH Talk. Kian does also the best detrending jobs, contamination vector determination, fitting of transit parameters, and more. nighthawk_black does perfect Keppix analysis, troyw has his amazing AKO service, capella, JKD, ajebson, gccgg, Tom128 and many other are very helpful too.So very often we work together here at PH as a good team.
In order to discriminate between real transits and instrumental or processing artifacts, I add comments to the “consolidated list of glitches” in the Science section on the PH Talk site. I collected a few bright and quiet and constant stars over the last few months / years exactly for this purpose. When I see a dip on one light curve and the same feature is also present on the other light curves, then it’s very likely a glitch.
I think the PH project is a great contribution to Science. I’d like to thank all fellow PH hunters for their help and also to Meg.
Kind regards,
Hans Martin Schwengeler (aka zoo3hans)
—
In addition to Mike, Hans, and rafcioo28, several others get a tip of the hat for marking transits in the discovery light curve for PH2: Sean Flanagan, Anand, and Jaroslav Pešek. Congratulations to you as well.
A Newly Confirmed Planet and 42 Additional Planet Candidates Part 2
For our latest planet candidates paper, there were many volunteers who helped identify these potential transits on Talk. To thank all of them for their hard work and effort, their contributions are individually acknowledged here. A few people stood out organizing a significant follow-up effort on their own working to sort these potential candidates identified on Talk into a list of potential planet candidates. This included looking for repeat transits and performing checks to rule out potential false positives. To acknowledge their effort, the science asked Abe Hoekstra, Tom Jacobs, Kian Jek, Daryll LaCourse, and Hans Martin Schwengeler to be co-authors on the paper. I’ve asked them each write a bit about this experience and about being part of Planet Hunters.
Abe Hoekstra
I am from the Netherlands and am fifty years of age. In the past I used to be a teacher. Astronomy has always been a hobby of mine, I am what they call an armchair astronomer. I couldn’t pursue a career in astronomy as I am very bad at maths and physics. Early 2011 I got my first laptop and I subscribed to the NASA Newsletter. When I was reading up on exoplanets, I came across Planet Hunters. I am very glad I can make a contribution to astronomy, however small.
When I heard my name was going to be mentioned on the Planet Hunter Planet Candidates paper, I was quite surprised, excited and very honoured. I have been so busy with eclipsing binaries, variable stars, dwarf novae and checking out dozens and dozens of collections of fellow planet hunters, that I almost forgot I made some contributions with respect to finding planetary transits.I had to check the candidates on the list to see where I made those contributions. I found one candidate that I may have discovered first, shortly after I started here in February 2012, and another where I was among he first to spot a transit. I also helped in finding repeats of transit features, by checking out NASA’s Exoplanet Archive (NEA). I definitely remember two candidates I found in other planet hunters’ collections in November.Finding a transit feature and/or repeat is very exciting. It doesn’t stop there. I am among those planet hunters that regularly check stars on Sky View and the NEA. Other hunters are very experienced in doing contamination checks, determining the length and depths of transits, and also determining the period of a planet.That is what I like about Planet Hunters. There is a great sense of community and cooperation here. I hope a lot of planet hunters get a mention in the paper. A great deal of hard work has gone into finding these planet candidates, and finding your name up there is very rewarding.Let’s hope we can add a few more candidates to the list in 2013!
Tom Jacobs
I am a graduate of the University of Washington with a non science degree in Business Administration and later commissioned as an officer in the U.S. Navy. Currently, I reside in Bellevue, Washington with my family and work as an employment consultant for workers with developmental disabilities going on 17 years. I have always been a treasure hunter and consider Planet Hunters a great way to find planet and other unique star treasures and learn some astrophysics through immersion along the way.
It is a great honor to be part of this planet candidate discovery paper as a Planet Hunters’ citizen scientist. Nothing occurs in a vacuum at Planet Hunters. If not for all your hard work in classifying light curves and posting your finds on Talk, most likely these planet gems would have slipped away unnoticed. You all deserve as much credit as those mentioned in the science paper. It is all about teamwork and diligent pursuit in analyzing the Kepler light curves. We are collectively demonstrating what the incredible pattern recognition of the human mind can accomplish that challenges the high powered state of the art computer algorithms and we are having fun while doing it.
Kian Jek
I have been fascinated by the stars ever since my uncle handed me a copy of a book by H. A. Rey when I was 10 years old. It wasn’t until much later when I had children of my own that I realized that Rey also wrote the Curious George books. I guess I must have been a geek since then because the other things going on that grabbed my attention were the Apollo moon landings and the original Star Trek series.
I used to spend hours with a tiny 2-inch telescope at night looking for the Messier objects, not knowing that it was almost impossible to see them all with an aperture that small – I was hung up on M1 for a long time! It was astronomy got me hooked on science but by the time I went to college I was sidetracked by an interest in DNA and I went on to get a degree in molecular genetics at Cambridge in the UK. One of my biggest thrills while studying there was being able to use a 180-year old 12-in refractor, the Northumberland telescope (http://www.ast.cam.ac.uk/about/northumberland.telescope) during freezing winter mornings. You had to open and rotate the observatory dome using a hand-crank! At last I managed to see the Crab Nebula for the first time. It was, of course, not as impressive as the photographs in the books.
After my studies, I was again sidelined by another passion, I spent the next 20 years or so in a career in computers, ending up as a founder of an Internet service provider during the start of the dot-com craze in 1995. In December 2010 I rekindled my long-lost affair with astronomy by volunteering on Planethunters.org. I am very sure it was in December very near the beginning of the project because I remember working through Christmas Day 2010 writing a javascript planetary calculator.
It’s been two years since the Planet Hunters was initiated and I’m so proud to be a part of its community. We’ve come quite a long way since those early days in December 2010. Back then very few amateur volunteers like ourselves really knew much about exoplanet transit photometry and we were marking every dip in flux as a transit (I guess many people still do!) and we thought that going beyond 5000 classifications was a big deal – there is even a forum topic devoted to this! I won’t mention who he is because he might be embarrassed but he is one of the co-authors and among my most prolific collaborators – he has done over 100,000 classifications!
Since 2010 then we’ve learned much about determining what is and isn’t a planet candidate. We discovered that 99% of transit events weren’t even due to planets. Most of the time they were glitches and even if they were real, they turned out to be false positives, e.g eclipsing binaries (EBs) or contamination due to background blends. I recall being so frustrated by demonstrating that so many of these were EBs that I started a secondary effort to collect what we called unlisted EBs – these were EBs not identified by Kepler’s EB expert Andrej Prsa.
But over the two years we learned how to separate a good PC from a false positive. We learned how to use a periodogram and phase plots, what were pixel centroid shifts, how to analyze TPFs, how to pull down Skyview and UKIRT images and how to model a transit light curve accurately.
Although I was named in the PH-1 discovery paper, and as exciting as that discovery is, I feel that was just happenstance. My more important contribution to the Planet Hunters initiative has been in collecting, compiling and curating the efforts of the community – In the last two years the Planet Hunters have turned up a lot of potential PCs that seemed to me to be real, and by applying all the methods and techniques mentioned above I eliminated all those that failed the tests. We were disappointed a few times when many of these discoveries were overtaken by events. I recall that the list was pared down from over 50 PCs down to 20 when the February 2012 Kepler paper was released (Batalha et al 2012). But I realized that if over 30 of our independent discoveries were real PCs, that fact alone vindicated our efforts. Slowly that list went up to beyond 30 and then reached 40 PCs. In May 2012, another paper by the Princeton team (Huang et al, 2012) took out another chunk of our PCs, but we continued to persevere and by the time the data releases of July and October came around, we had even more PCs to consider. I spent the last quarter of this year rounding these up and characterizing them.
I would not have been able to do this with the help and contribution of the community. I’ve been very privileged to work with some of the smartest and dedicated citizen scientists on this site. I tried my best to follow up on every e-mail and private message you sent me – please keep them coming!
Daryll LaCourse
I’m a Canadian aerospace machinist and amateur astronomer living in the Pacific Northwest. I prefer working with Kepler data to backyard stargazing as heavy clouds and rain can’t interfere with the former.
I am very pleased to see the release of the fifth Planet Hunters discovery paper and the addition of PH2b to the family of confirmed exoplanets. Every volunteer that has participated in the Planet Hunters project thus far has played an important role in the efforts that led to the identification and consolidation of this latest candidate list, which includes a stunning array of potential habitable zone prospects. It is impressively difficult to confirm that a Kepler candidate is a bona fide exoplanet rather than a false positive; thanks to the meticulous follow up work of Ji Wang and the rest of the PH Science team we can say with confidence that these 43 candidates are very likely the real deal.
It has been a privilege to work with so many talented individuals on PH Talk as these discoveries were sifted from the many thousands of highlighted light curves. The tenacity and resourcefulness of the PH volunteers can’t be understated or underestimated, and I look forward to what we will find in 2013 as the extended mission progresses. There are already new targets of interest popping up on the radar for the team to pursue, and the single/double transit candidates (some of which are mentioned in the new paper) hint at a hidden population of long period exoplanets that have yet to fully reveal themselves to us. How will our own solar system eventually fit into this widening hierarchy of possible arrangements and configurations? How common are exoplanets within the habitable zones of Sun-like stars? These questions may not be resolved quickly, but the discovery of every new candidate brings us closer to definitive answers. Experts in the field have speculated that the first true Earth analog candidate may be found this year, which will be a very exciting and historic milestone. I don’t think it is a huge stretch of the imagination to consider that with some sharp eyed luck, it may even be found by one of you!
Hans Martin Schwengeler
I’m a regular user (zoo3hans) on PH, more or less from the beginning two years ago. My name is Hans Martin Schwengeler and I live near Basel in Switzerland. I’m 54 years old, I’m married and we have two children. I’m a mathematician and work as a computer professional. I like to advance Science in general and Astronomy in particular. I did work a few years at the Astronomical Institute of the University of Basel (before it got closed because they decided to save some money…), mainly on Cepheids and the Hubble Constant (together with Prof. G.A. Tammann). Nowadays I’m very interested in exoplanets and spend every free minute on PH.
I’m pleased to hear that I’m going to be mentioned as a co-author of the PH Habitable Zone (HZ) candidates paper. My motivation to participate in the PH project is not really to “name” a planet or such a silly thing, but to advance Science in general and Astronomy in particular. Probably I’m just a curious fellow, although I’ve got named “a cold precise German” on PH Talk by someone (actually I’m Swiss).
I think we have a few very good cases of fine planet candidates collected over the last two years, a few of them even in the HZ of their host stars. Kian Jek (kinjin) has made a good list, many other PH users have also contributed a lot to our collaborative effort. I try to classify as many stars as possible, and also to comment on promising cases, or comment avoiding glitches and other bad features. To examine a promising star, it needs a lot of time. First I just look at the light curve and try to let my brain do the pattern recognition. I actually believe it might indeed be superior to computer algorithms to discriminate between real transits and just glitches or processing artifacts. In my experience it only works down to about 2.0 R_Earth planets, below this border size they cannot be detected anymore just by eye without prior detrending of the light curve. Second I do therefore download the FITS files from MAST and detrend roughly the light curve. Further inspection of the whole Q0-Q13 detrended light curve often reveals already if it might be an interesting case or not. If I suspect a regular signal (i.e. a well defined period) is present in the data, then I try a periodogram to see if the potential transit looks symmetrical, U-shaped and so on. Also important is to check the sky view. We are dealing with stars on the sky after all.A bit frustratingly often it’s just contamination by a nearby background star. Of course I post all findings to the PH Talk pages, so others can profit from the work done so far, and to get their opinion about the case.
Although I have classified over 30000 stars so far, even I select sometimes
a glitch for a transit. It’s not an easy “game”, but rather addictive I think. I also like the teamwork aspect of the PH community. It’s great to get help from the
“specialists” out there who can do contamination vector determination, Keppix series analysis, transit curve fitting and much more. I’d like to thank them all for their great help. I thank also Meg for her great effort to vet more promising exoplanet candidates. PH is a great project!
Yours,
Hans Martin Schwengeler (aka zoo3hans)
A Newly Confirmed Planet and 42 Additional Planet Candidates
Artistic rendition of a sunset view
from the perspective of an imagined Earth-like moon orbiting the giant planet, PH2 b. Image Credit: H. Giguere, M. Giguere/Yale University
We are pleased to announce the discovery and confirmation of our second confirmed planet : PH2 b-a Jupiter-size planet in the habitable zone of a star like the Sun-by the Planet Hunter project. The paper has already been submitted to the Astrophysical Journal and has been made public via arxiv.org.
The estimated surface temperature of 46 degrees Celsius is right for there to be liquid water, but it is extremely unlikely that life exists on PH2 b because it is a gas planet like our Jupiter, and thus there is no solid surface or liquid environment for life to thrive. In order to study this interesting system, we used the HIRES spectrograph and NIRC2 adaptive optics system on the Keck telescopes in Hawaii to obtain both high resolution spectrum and high spatial-resolution images. The observations help us to rule out possible scenarios for false positive detections and give us a measured confidence level of more than 99.9% that PH2 b is a bona-fide planet rather than just an illusion.
In the meantime, we also announce the discoveries of 31 long-period planet candidates with periods more than 100 days, including 15 candidates located in the habitable zones of their host stars. The candidate list is a joint effort between the volunteer Planet Hunters, and the science team. Each individual planet candidate was identified and then discussed on Talk by Planet Hunters. Several dedicated Planet Hunters collected information on candidates and carried out light curve modeling and initial vetting for false positives. The science team then decided the priority of each target on the candidate list and conducted follow-up observations.
Although most of these planets are large, like Neptune or Jupiter in our own Solar System, these discoveries increase the sample size of long-period planet candidates by more than 30% and almost double the number of known gas giant planet candidates in the habitable zone. In the future, we may find moons around these planet candidates (just like Pandora around Polyphemus in the movie Avatar) that allows life to survive and evolve under a habitable temperature.
In addition to the 31 long-period planet candidates, we announce a watch list for 9 further planet candidates which have only 2 transits observed. They do not currently meet the three-transit criteria of being a planet candidate set by the Kepler team. However, the Planet Hunters were able to pull them out and a future third transit would greatly increase the probability of them being real, allowing us to promote them into the full candidate list.
Lots of our candidates appear on a recent list published by the Kepler team (Tenenbaum et al. 2012) of possible transit signals, but it’s good to see they have now passed the additional tests to be planet candidates (not all of the Tenenbaum objects are real planet candidates; there are plenty of false positives). 6 candidates on our list were somehow missing in that list, all of which have periods of more than 240 day. This is an indication that we, the Planet Hunters, are effective in detecting long-period planet candidates. Heading into the future, we have reason to believe that more long-period planets and potentially habitable planets can be discovered by us. Go Planet Hunters, go hunting planets!
Ji Wang
Ji is a post-doctoral associate in the department of Astronomy at the Yale University, and the lead author on the latest Planet Hunters paper. Before assuming his current position, he attended college at the University of Science and Technology of China and obtained his Ph.D. at the University of Florida. The roll of honour for planet hunters who contributed to these discoveries is here.
The Planet Characterizer
Today we have a guest post from Seth Redfield. Seth is an Assistant Professor at Wesleyan University in Middletown, CT. Before Wesleyan, he was a postdoc in Austin, TX, and a graduate student in Boulder, CO. He is an avid hiker, and an oboe player (with a degree from the New England Conservatory of Music in Boston), but these days spends any free time with his kids (4 and 1 years old) and sleeping.
To date, I have working on studying known exoplanets rather than finding them. Instead of a “planet hunter”, you could call me a “planet characterizer” (which doesn’t have quite the same ring to it). Perhaps the most well-studied planet, and one of my personal favorites, is HD189733b. This is because it is a transiting exoplanet, orbiting one of the brightest stars that we know has a planet. The fact that it transits, allows us to use spectroscopy of the starlight from HD189733 while the planet is transiting to look for wavelength-dependent effects that reveal interesting properties of the planet. For example, we can measure the composition, temperature, and even wind speeds in the atmosphere of the planet. The fact that HD189733b orbits a bright star, makes all these measurements “easier”, meaning that they are still incredibly difficult and require careful observations using the world’s largest and most sophisticated telescopes, but nonetheless are possible.
Because transiting planets are so useful, I follow with excitement all the searches of transiting planets, hoping they will find one around a bright, nearby star. However, the strategy for searching is directly at odds with finding one around a bright star. In order to find the rare planetary system that is edge-on, and therefore transits, one must observe many tens of thousands of stars. Bright stars tend to wash out large sections of our detectors and make it difficult to see the multitude of fainter stars around them. For this reason, all the searches largely avoid the bright stars.
Indeed, HD189733b was not discovered first by its transit, but by the radial velocity method of observing the host star orbit the center of mass of the system. It is for this reason, that I feel that the planets that will become household names, meaning the planets whose names will be known by school kids around the world, have yet to be discovered. These will be small, Earth-like planets, for which we can just barely detect using the radial velocity method, but which will also transit a bright host star and thereby make it possible for us to probe the characteristics of the planetary atmosphere.
So, as this young field of exoplanet research matures, I see this clear synergy between the detection of exoplanets and characterization of those exoplanets. Obviously, exoplanets must be detected in order to be characterized. The handful of exoplanet atmosphere detections to-date have uncovered a diverse collection of atmospheres that appear to be influenced by a myriad of planetary and stellar phenomena (such as planetary composition, stellar flares, etc). So, the characterization of exoplanets motivates us to find more exoplanets with new and extreme properties. I feel like we are at a similar point to astronomers 150 years ago when spectroscopic observations of stars were being made for the first time. Every discovered exoplanet is amazing, but it is likely that the planets we are talking about now will not be the planets we will be obsessing over in twenty years.
One final note, is that the brightest stars being observed by Kepler are almost as bright as HD189733, so let me take this opportunity to make a plug for searching the brightest stars in the Kepler field. Anything found to be transiting those stars will certainly be of interest to the “planet characterizers” out there.
Happy 2nd Anniversary
It’s been two years since everyone embarked on the Planet Hunters adventure. To celebrate we’ve created another anniversary poster, featuring the names of all the participants. You can download it here (warning that’s a 20 MB file) or a slightly smaller one here (6 MB).
As you know may know, Planet Hunters is now producing science! We already have three papers published and online -with more to come. You can see these and all the Zooniverse publications at http://zooniverse.org/publications. Happy Anniversary everyone!
Live Chat at 3pm GMT Today
Later today (3PM GMT / 9am CST) we’ll be holding a Google+ Hangout on Air to talk about Planet Hunters science and news. The video feed will be shown here and you’ll also be able to find us find us on the Zooniverse Google+ Page.
If you have questions for the Planet Hunters team you can ask them, either by leaving a comment here on the blog or by tweeting us @planethunters.
PS. To celebrate Planet Hunters turning 2 we’ve created another anniversary poster, featuring the names of all the participants.
Turning Planetary Systems on Their Heads (Gently)
Today we have a guest post from Nate Kaib. Nate is a postdoctoral researcher at Northwestern University. In terms of research, his main interests lie in using computers to model the orbital dynamics of exoplanets as well as the small bodies of the solar system. He’s written numerous papers on the evolution of comet orbits within our own solar system and how they can be used as a tool to constrain the solar system’s history. More recently Nate has gotten interested in the evolution of planetary systems residing in binary star systems.
In a select number of exoplanet systems, astronomers have successfully measured the inclinations between the stellar equators of parent stars and the orbital planes of the planets found around these stars. This is done by measuring something called the Rossiter-McLaughlin effect, which is a subtle change in the Doppler shift of a star’s light that occurs during a planetary transit (see wikipedia for a brief overview). Based on models of star and planetary system formation we would expect all of these inclinations to be near zero since the star and planetary system form out of the same spinning, collapsing gas cloud. Indeed, our Sun is only inclined about 7 degrees with respect to the Earth’s orbit.
Surprisingly, however, groups led by Amaury Triaud and Josh Winn have found that many planet orbits are highly inclined to the equators of their host stars. In fact, some are even retrograde, meaning the planet orbits the star in the opposite direction that the star spins. Explaining these results has presented a major problem for theorists, but several promising mechanisms have been proposed. Most of them assume that all planetary systems initially form with the star’s spin and planetary orbits aligned. However, later dynamical processes alter the planetary orbits. These include planets scattering off one another during orbital instabilities as well as Kozai resonances, which is where a distant massive perturber such as a giant planet or binary star excites both the inclination and eccentricity of an inner planet.
These previously proposed mechanisms imply that highly inclined planet have all gone through at least one major disruptive instability. This would then seem to preclude well-ordered multi-planet systems similar to our own solar system from having planetary orbits that are highly inclined with respect to their star’s equator. In a recent paper, however, we showed that an additional mechanism exists to alter planetary orbital inclinations, rigid body precession. Unlike the other mechanisms, this one will only act in well-ordered tightly packed systems of multiple planets (like our own). The other key ingredient is that there must also be a distant binary star in the system. In this configuration, the binary star’s gravity tugs slightly on the planetary system. These perturbations are very weak but add up over time. If only one planet is present in the system, then the Kozai resonance mentioned above will usually be activated. However, if more than one planet is present, then the self-gravity of the planets cause them to evolve in a coherent manner. They remain on nearly circular orbits, and their mutual inclinations all remain low. Instead, the plane of the entire planetary system begins to tip over relative to the star. (How far it tips over depends on the exact orbit of the binary star.)
As a proof-of-concept, we demonstrated in a recent paper that such rigid body precession is likely ongoing in one very well-known planetary system, 55 Cancri. This system consists of 5 planets on roughly circular orbits. In addition, there is a small star orbiting the entire system at 1000 AU. Because this star takes at least 10000 years to make one orbit, we do not know its true orbit. To characterize its potential effect, we therefore ran hundreds of computer simulations modelling its effects on the planets for many different plausible binary orbits. The final results indicate that the star causes this rigid body precession most of the time, and we found that the most likely angle between the planet orbits now and their original plane is a little over 60 degrees. Thus, in addition to flipping over planetary orbits by more violent processes, it may be possible to do it gently and wind up with planetary systems like our own that are highly inclined to their host star.
To better understand rigid body precession, below is a movie (click on the image to view the movie) made from one of our simulations. In this movie, the white orbits are the two outermost planets of 55 Cancri. (The binary star is not shown since it is 200 times further away.) The green arrow marks the initial orientation of the planetary orbits, while the red arrows marks the instantaneous orientation. This evolution shown in this particular movie takes place over 50 million years, but other simulations require billions of years for similar types of evolution to occur (depending on the exact binary orbit).
Click on image to view a movie of the orbits precessing
Growing Planets Around Binary Stars
Today we have a guest post from Stefano Meschiari. Stefano is a postdoctoral researcher at the University of Texas at Austin. He works on planet formation in binary environments and planet detection through radial velocities and transits. He developed the Systemic software as a tool for scientists and citizens to analyze radial velocity data. His hobbies include cooking, clumsy puppeteering and all things pop culture. You can read more about his research here
The discovery of PH1, together with all the other circumbinary planets identified by Kepler, provides theorists with an incredibly important clue on how planets form in binary environments. The clue is that these planets, rather than being mere sci-fi tropes, are actually detected in Nature! Their existance is all the more remarkable when we consider that all the planets detected so far (including PH1) orbit rather close to the central binary; so close, in fact, that they almost straddle the region of dynamical instability (inside which a planet would eventually be either ejected or collide with one of the stars). The fact that these planets successfully formed and survived to be observed by us indicates that the process of planet formation must either be very robust to the dynamical perturbations from the central binary (if the planet formed near its current location), or have happened in a less disturbed region (with subsequent migration to the current location).
Planet formation in tight binaries has long been the subject of a number of studies in the scientific literature; indeed, both our closest neighbor, Alpha Centauri, and the system hosting one of the first detected planets (with a tentative detection dating back to 1988!), Gamma Cephei, are examples of tight binaries where planet formation is significantly hindered. The discovery of the first circumbinary planet, Kepler-16, reignited interest in the topic, and I (together with a number of other teams) have been performing numerical simulations that model planet formation, in an attempt to better understand the physical processes at play.
Binary systems represent a stringent test for planet formation theories, since the environment can be highly disturbed by the presence of multiple stellar components. Computer simulations show that the planetesimal stage is the most vulnerable to disruption, becoming a “bottleneck”. This bottleneck is primarily caused by the interplay between the gravitational perturbations of the binary (which raise the eccentricities of planetesimals) and the aerodynamic drag from a protoplanetary gas disk (which acts to misalign the planetesimal orbits). The latter misalignment raises the velocities at which planetesimals collide, such that instead of growing into larger objects, they get destroyed. The reason why the alignment of the orbits is crucial is easy to understand: imagine the collision between two cars on two contiguous lanes, versus that of two cars colliding at an angle. The latter collision will be much more violent, as there will be an additional velocity component perpendicular to the motion of either cars. The end result is that, in the simplest models, planet formation can only proceed far enough from the central binary (in the case of Kepler-16, outside 4 AUs).
The implication is that circumbinary planets might only be able to form far enough from the central binary (how “far” depends on the properties of the central binary), and subsequently migrate to their current observed location. This picture, while attractive, might be too simplistic to capture the full complexity of planet formation in this environment. More realistic models will need to include a number of physical ingredients (such as the dynamical evolution of the gas disk), which are usually neglected for the sake of computational expediency but could potentially play a big role in determining how and where circumbinary planets were formed. For instance, my models indicate that even small perturbations from turbulence in the disk can make the disk hostile to planet formation by perturbing planetesimal alignment. Comprehensive (and computationally expensive!) simulations of planet formation in the binary environment are still ongoing: they might reveal further roadblocks, or uncover “sweet spots” in the range of physical parameters where planet formation can proceed. As the census of circumbinary planets continues to grow thanks to the efforts of scientists and volunteers, it will provide a larger sample of planets to inform and constrain our models.
