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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)

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A Newly Confirmed Planet and 42 Additional Planet Candidates

PH2_moon

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 seo services 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.

Happy Holidays

Carnaby Street Lights

Image Credit: Steve Harris (swh) from Flickr http://www.flickr.com/photos/steveharris/5255090489/

Happy Holidays and Merry Northern Winter (and Southern Summer) Solstice from everyone on the Planets Hunters team.

In spirit of the holiday season, each day this month, the Zooniverse has revealed a new gift on the Zooniverse Advent Calendar. Two years ago, Planet Hunters was hiding behind one of the doors. This year there were several Planet Hunters themed surprises (including the background for the Advent Calendar which might look very familiar) :

In case you missed them:

Day 1: Zooniverse Publications Page – Including 3 Journal published/accepted Planet Hunters papers

Day 12: A Live Chat with members of the Science Team

Day 16: Planet Hunters Anniversary Poster composed of all of our volunteers names (can you find yours?)

And be sure to check out tomorrow as the last door opens on the Advent Calendar.

Wishing you a very Happy Holiday,Merry Solstice, and Happy New Year from us to you.

Happy 2nd Anniversary

2012 Poster Extract

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!

New Publications Page

With the start of December, it’s that time of year again. The Zooniverse Advent Calendar is back. Each day this month, a door opens and there’s a new surprise.  Planet Hunters was behind one of those doors two years ago.  On Day 1,  the door revealed the new Zooniverse publications page. There you will find all of the peer-reviewed and Journal accepted papers for Planet Hunters as well as the other projects that make up the Zooniverse. It’s been a busy year with our first paper which was accepted for publication in 2011 officially printed in  Monthly Notices of the Royal Astronomical Society in 2012,  2 more papers accepted (Schwamb et al. 2012 accepted and published in Astrophysical Journal; Lintott et al 2012 accepted to Astronomical Journal), and the PH1 paper submitted. You’ll see the PH1 paper isn’t listed there yet. That’s because it’s still in the peer-review process.  We’re the midst of responding to the referee’s report and resubmitting the paper to the Journal and the referee. We hope to have it accepted and listed there on the Publications page soon.

P.S. Thanks for all of your hard work to help make these publications happen. We can’t add thousands of names to the paper authorship, but we acknowledge your time, effort, and contribution to all of our publications on our authors page .We update the authors page each time a paper is accepted for publication. The link to the authors page is in the acknowledgements of every Planet Hunters paper.

P.P.S. The background image for the Zooniverse Advent Calendar might look very familiar.

Status of the PH1 Paper

We had submitted the PH1 paper to the Astrophysical Journal about a month ago and released the submitted draft on the public arXiv.org archive. What happened at that point is the paper was assigned an editor from the Journal. The editor selects a referee, a scientist in the field  and  one of our scientific peers, to read and critique the paper. We call this the peer review process. It may not be perfect, but the process is supposed to help ensure the quality of the science published. The referee has a different perspective than the authors and collaborators of the paper, and that new perspective can in many cases help improve a paper. In most cases, the referee has about a month to read the paper and write up a report assessing whether the paper is worthy of publication with comments and critiques on points and issues the referee believes should be addressed or included in the paper.

Last night, I received the email from the Journal with the referee’s report for the PH1 paper. The referee thinks the work does merit publication but has raised some good points and has questions that he or she would like to be addressed. Now our task is to respond to the referee’s feedback, concerns, and suggestions. We’ll make some revisions to the paper based on the input from the referee’s report, and resubmit to the Journal the paper and a formal response highlighting the changes we made and  addressing specifically each point raised by the referee. This will take probably a few weeks for us to complete. Once resubmitted, the referee will receive our response and revised draft and have another chance to comment and critique. We’ll  find out in another several weeks what the referee thinks of the revised draft. We’ll keep you updated on our progress.

The Road to Characterizing PH1: Stellar Evolution Models

Today we have a guest post from Willie Torres. Willie is an astronomer the Harvard-Smithsonian Center for  Astrophysics (Cambridge, MA), and member of the Kepler team. His work for Kepler includes the statistical “validation” of transiting planet  candidates that cannot be confirmed in the usual way, that is, by  measuring their mass and showing that it is small enough to be a planet. He also works on determining fundamental parameters of stars in eclipsing or astrometric binaries, for testing models of stellar evolution.

Transiting circumbinary planets are interesting because they show us that planets can form in environments that are very different from our Solar System. Instead of being a single star, the central object is actually a pair of stars orbiting each other, and in these systems the planet can occasionally pass in front of one or even both stars, producing transit signals. For circumbinary planets such as those the Kepler Mission has announced (Kepler-16, Kepler-34, Kepler-35, Kepler-38, and most recently Kepler-47), the orbit of the two stars is such that they eclipse each other periodically, and these typically deep eclipses are what calls attention to them in the first place, in the light curves produced by Kepler.  The neat thing about these transiting circumbinary systems is that they can also provide a wealth of information about the stars that is normally not available in regular transiting planet systems with a single host star. Two important stellar properties one can often measure are the masses and radii, from knowledge of the orbit of the stars around each other.

Masses and radii can of course also be determined in favorable eclipsing systems that don’t have planets, but when there is a transiting circumbinary planet, it’s even better. This is not hard to understand: as the planet passes in front of one or both stars, it is actually chasing a moving target because the two stars are revolving around each other. Each time the planet transits, the stars are in a different place in their orbit. This means that by measuring the precise times of these transits, we are actually mapping the orbit of the binary in a different way than would normally be done for a regular eclipsing binary. This provides extra information about the motion of the stars, and in particular it constrains the ratio of the masses between the two stars very well. It also helps to determine their sizes. Combining this with additional observations such as radial velocities measured from spectra of one or both stars, their masses and radii can be measured to high precision.

Astronomers care about the masses and radii of stars because these measurements allow them to test their models of how stars form and evolve. Theorists have come up with a fairly detailed prescription for how a star of a given mass and chemical composition changes its properties (radius, temperature, luminosity, etc.) as time goes by. But without real observations against which to check those predictions, we can’t be sure they’re right. This is important because astronomers often use those same models to infer properties of single stars that are much more difficult to measure directly. Or they may be interested in knowing the age of a star, which also relies on theoretical models. As it turns out, observations have shown that models for low mass stars (such as the cool M dwarfs) are not quite right: real stars tend to be a little bit larger and cooler than the models predict.

Circumbinary planets in which the eclipsing binary at the center contains an M dwarf are particularly interesting, because they allow us to test theory in this problematic low-mass regime.  That happens to be the case for the recent exciting Planet Hunters discovery of KIC 4862625.  The primary component in the eclipsing binary is an F star of about 1.3 solar masses, and the secondary is an mid M dwarf a little under 0.4 solar masses. They orbit each other every 20 days. The circumbinary planet goes around every 138 days.  With other colleagues I’ve been working on determining the stellar properties of both stars as accurately as possible, and comparing them with several sets of stellar evolution models (since models are not all created equal). For getting the stellar properties we use not only high-quality spectra taken with the 10-meter Keck telescope in Hawaii, but also results from a very sophisticated modeling of the Kepler light curve that can reproduce all the binary eclipses as well as the transits of the circumbinary planet nearly perfectly. This tells us that we at least understand the dynamics of the system pretty well (i.e., how all the objects move).

But there are always complications. In this case, we took a high-resolution image of the system and discovered that there’s another star right next to eclipsing binary that (we realize now) is introducing contamination in the Kepler light curve. It’s only about 0.7 arcsec away from the eclipsing binary, and we believe it is physically associated.  But wait, there’s more!  The images show that this companion is actually a close binary itself!  At the time of this writing we are still trying to figure out exactly how much extra light these new objects are contributing to the Kepler photometry, so that we can take that into account in order not to bias the measured properties of the eclipsing binary stars, or of the circumbinary planet.

PH1 : A planet in a four-star system

A family portrait of the PH1 planetary system: The newly discovered planet is depicted in this artist's rendition transiting the larger of the two eclipsing stars it orbits. Off in the distance, well beyond the planet orbit, resides a second pair of stars bound to the planetary system. Image Credit: Haven Giguere/Yale.

Image credit: Haven Giguere/Yale

Today we’re pleased to announce the discovery of the first confirmed planet discovered by Planet Hunters, and it’s a fabulous and unusual world. Labelled ‘Planet Hunters 1’ (or PH1) in a paper released today and submitted to the Astrophysical Journal, it is the first planet in a four-star system. It is a circumbinary planet – one which orbits a double star – and our follow-up observations indicate that there is a second pair of stars approximately 90 billion miles (1000 Astronomical Units) away which are gravitationally bound to the system.

This is much closer than the nearest stars are to the Sun, so anyone viewing the sky from PH1 would have a spectacular view of all four stars. More importantly, this amazing system will help us understand how and where planets can form – producing a stable planet in a system where four different stars are moving about can’t be easy. This is the seventh circumbinary planet, and the first to be in a quadruple system.

The planet itself has a radius a little more than 6 times that of Earth, making it a little bigger than Neptune. It’s mass is harder to pin down (and being in such a complicated system didn’t help), but we have a definite limit that means it must be no more than half that of Jupiter – so this is definitely a planet.

A huge amount of work went into this discovery (as well as a fair bit of observing time on the Keck and other telescopes), but a lot of the credit should be pointed at the Planet Hunters who made the discovery. It was Kian Jek and Robert Gagliano, working together on Talk that made the initial discovery; there’s a post from them on exactly what happened up already. The paper also credits Hans Martin Schwengeler, Dr. Johann Sejpka, and Arvin Joseff Tan all of whom flagged one or more of the transits before the paper was published! This is great news for us and we’re sure there are more planets hiding in data, both at the main interface and over on Talk. For today, though, we can celebrate the arrival of Planet Hunters 1!

Chris

PS We’ve announced discoveries before, of course – as well as being the first four-star planetary system, this is the first where we’ve been able to obtain not only transit information but follow up with radial velocity measurements, detecting the wobbles of the parent stars as well as the dips in light seen when the planet moves in front of them. This is the gold standard for planet discovery, and so this is officially a planet, not just a planet candidate.

PPS The paper, of course, still has to be refereed. We’ll keep you updated here as that process goes on, but as Meg is presenting the details of the system at the annual Division of Planetary Sciences meeting right now we thought you’d want to know the news as soon as possible. There will be more posts about exactly how PH1 was tracked down later in the week, so watch this space. In the meantime, you might prefer version of the paper, which has been annotated with the ScienceWISE tool in order to help explain some of the more technical language.

Assessing the Kepler Inventory of Short Period Planets

You might remember that I’ve been working on a systematic search of the Q1 light curves to examine the frequencies of large planets (> 2 R⊕ -Earth radii) on orbits less than 15 days. I’m happy to announce that my paper titled “Planet Hunters: Assessing the Kepler Inventory of Short Period Planets” has just been accepted to Astrophysical Journal. The paper is available on-line here if you’d like to read it (warning: it’s quite long coming in at 22 pages of single spaced text, 13 figures, and 8 tables!), but I’ll give the highlights below.

We wanted to see for Q1 light curves, how well we could find planets and what might be left remaining there to be found compared to the known Kepler sample of planets. I think this important because Planet Hunters can serve as a separate estimate of the planet abundance and Kepler detection efficiency. I decided first to concentrate the search of planets with periods less than 15 days so that I was certain there would be at least two transits visible in the Q1 light curve. I thought it might be harder for us to identify transits if there was only one dip, so I thought it would be a good idea to start where there were at least transits.

To figure out which of the light curves had transits, I developed an algorithm to combine the multiple classifications for each light curve (for Q1 on average 10 people classified each ~33 day Kepler light curve) by developing a weighting scheme based on the majority vote.  What the weights are doing is really just helping me pay  a bit more attention to those that are a bit more sensitive at finding transits when combining the results from everyone who classified that light curve. The weighting scheme makes us more sensitive to transits than if I just took the majority vote for each light curve and helps to decrease the false positives. Below is the distribution of user weights for Q1 classifiers.

Distribution of Q1 Planet Hunters user weights binned in 0.5 bins

Using the user weights, I am able to give each light curve a ‘transit’ score (the sum of the user weights who marked a transit box divided by the sum of the user weights for everyone who classified the light curve). To narrow the list from 150,000 light curves, I picked those light curves that had ‘transit’ scores greater than 0.5 as my initial list of candidates. I applied several additional cuts to widdle down the list (you can read all about those details in the paper). That left about 3000 light curves and approximately 4000 simulations to go through. So to identify those that had at least two transits in them, we turned to a second round of review where light curves were presented in a separate interface and volunteers were asked whether they could see at least two transits (ignoring the depths being the same or not) in the light curve and asked to answer either asked to answer ‘yes’, ‘no’ or ‘maybe’ to the question. Those light curves where the majority of classifiers said ‘yes’ were moved on to review by the science team.  A big thank you to everyone helped out with the Round 2 review; your efforts are acknowledged here. As always we acknowledge all those who contribute to Planet Hunters science on our authors page.

At the end of the search after removing all the known planet candidates and transit false positives known before February 2012, there were 7 light curves that have transit-like events but not on the original Kepler candidates list published back in 2011 that used  only Quarters 1 and 2. I show example transits from each of these 7 light curves in the Figure below. One of these light curves turns out to be one of the candidates from our first paper and another one was part of our co-discoveries with the Kepler team.  Even those these 7 light curves weren’t found in the first Kepler candidate releases, they now have been found in the latest iteration of the Kepler candidate list released earlier this year, where they’ve used an updated and improved versions of their detection and data validation pipelines. So what that shows is that the Kepler detection and validation processes has indeed gotten better, but there’s more that we can say.

Zoom-in of selected transits for each set of transit identified visible in short period candi- date light curves remaining after Round 2 review and visual inspection. Visually the science team could identify two separate sets of repeating transits in the mutli-planet KIC 8240797, 9729691, and 11551692 based on the user drawn boxes We note that the snapshot of KIC 8240797 contains two independent transit events.

Now that we know what new things we found, and that there wasn’t anything more than the 7 candidates that are now KOIs on the latest Kepler candidate list, we can look at what that says for the completeness of the short period planet inventory. Using the simulations that you’ve helped classify, I was able to look at how good Planet Hunters is at detecting planets of different sizes on orbits less than 15 days.  I randomly selected about 7000 light curves that at the time weren’t known to have transiting planets or were not eclipsing binaries and inject synthetic transits into them for varying planet radii (ranging from 2- 15 R⊕) and periods less than 15 days.  The simulations are really important because one completed I could see what which of the simulations made it to the end of my candiate pipeline and which ones didn’t.  Having the results from those classifications really made the heart of the paper, because we could show independent of the Kepler planet candidates and detection and validation processes, what we were sensitive to.

Efficiency recovery rate for simulated planet transits with orbital periods between 0.5 and 15 days and radii between 2 and 15 R⊕.

What was striking to me, was our detection efficiency is basically independent of orbital period and that whether there were 2 or 15 transits in the light curve, they were just as easily identified. I think this bodes well for us being just as sensitive to single transit events (I’m starting to work on testing that now). Although performance drops rapidly for smaller radii, ≥ 4 R⊕ Planet Hunters is ≥ 85% efficient at identifying transit signals for planets with periods less than 15 days for the Kepler sample of target stars. For 2-3 R⊕ planets, the recovery rate for < 15 day orbits drops to 40%. I compared to the Kepler planet candidates and found similar results (which is a good check).

Our high recovery rate of both ≥4 R⊕ simulations and Kepler planet candidates and the lack of additional candidates not recovered by the improved Kepler detection and data validation routines and procedures suggests the Kepler inventory of ≥4 R⊕ short period planets is nearly complete!

New Planet Hunters Co-discoveries

When I posted with news of our second paper’s submission last week I mentioned that the new paper from the Kepler team included a section on Planet Hunters.

Neptune-sized worlds may be the most common in the Universe

The section (7.4, since you’re asking) is fabulous, mentioning the ‘remarkable enthusiasm’ of Planet Hunters volunteers, who are not only have the ‘opportunity to experience the scientific method but also the possibility of experiencing the gratification of discovery’.

There should be a whole lot of gratification around, because as well as our own candidates the paper included details of several co-discoveries, where nine of Kepler’s planet candidates were independently identified by our volunteers. The following Planet Hunters thus can claim to have officially discovered planet candidates. In each case, the names in bold were the first to identify a transit in a particular light curve – congratulations to all involved.

KIC 5864975

pina1234, Mary Corfield, Frank Barnet, Derrick Martinez, Vince Brytus, Darin Ragozzine (!), Gary Butler, Robert Casey, Krishna Babu, ‘shutterbug’, Hein Min Tun, Juan Albornoz, Gerald R. Green, Robert Spiker, Natalie Van Cleef

KIC 11875734

Robert Gagliano (who was on the list for the recently announced candidates too), Malcolm Lambert, Di Miceli Gaetano, Hitesh Patel, Robert Rozanski, Penn Gwenn, Jari Paakkonen, ‘maya’, John Mackereth, ‘zocker’, Dominick Dennis, Carl-Johan Wikman, ‘chulej’, Oleg Tsybulskyi

KIC 8160953

Frank Barnet, John Robinson, ‘colinjdavis’, Jari Paakkonen, Carl Davidson, Bruno Mauguin, Jan Bernard, Lee Chapman, Hans Martin Schwengeler, ‘Aurelhun’, Pablo Barroso Rodriguez, Julie Donnell, Dani Iannarelli, Peter Kool, Simon Humphreys, Chris Price, Alan Bowler, Jeff Mack, Rafal Konkol

KIC 6504954

Patrick Gruber, Malcolm Wain, Andrew Young, Steve Harris, ‘planet10’, Juha Lindqvist, Navid Baraty, ‘ahora’, Julia Fedyakina, John Harper, Pablo Barroso Rodriguez, Sue Wilson, Mathew Hadfield, John Ord, Bob Chau, Calum Patterson, Matthew Connolly

KIC 7761918

Breeann Phillips, Abe Hoekstra, ‘ozanne’, Daniel Speir, ‘komandantmirko’, Daryll LaCourse, Daniel Getler, Gene Cumberland, Dave Skillman, Tony Hoffman, Joe Johnson, ‘Tem’, Steve Stav, Daniel Meyersohn, Frederico Centeno Selbach, Mark Riggs

KIC 3326377

‘ronalde000’, Bob Leask, ‘oneironautics’, Bartömiej Jaracz, Priscilla Nowajewski, ‘lolodec’, Michael Ware, Larry Melanson, Victor Gabriel Bibeo, ‘AtheistRamblings’, Stuart Lynn (!), Abe Hoekstra, Andrew Rose, ‘dalwhinnie’, Loic Petitpas

KIC 6268648

‘snark’, Fiona Wynn, Ilya Karpeev, Lily Lau, ‘nargatte’, Kristian U. Saetre, Lubomir Stiak, D Le Clercq, Jeremy Garrett, Lee Martin, Verena Resch, Robert Fletcher, Jason Muir, Nick Amsel, Michael Kavanagh, Anthony Goddard, Tom Hartfil-Allgood, Shannon McLaughlin, ‘Natframpton’, Peter Unitt, Steve House, Paul Wightman, Pooja Rathod, Simon Stockwell, Jenny Satelle, Owain Dewi Hughes, Richard Hopkins, Adam Bunce, Simon Gardiner, ‘snorrelo’, Thomas McGauran, ‘tom0366’, ‘Chippywheetoes’, Ben Galley, Kirsty McMonagle, Rich Haines, Adam Derdzikowski, ‘pat’, Mark Halstead