Planet Hunters: An Online Community
The team at Possible including Elena Moffet and Tyler Brain made a short documentary exploring online communities from the perspective of the individuals who compose them. This included talking to people involved with Wikipedia and open source software developers. Our own Katy Maloney reflects on being a citizen scientist and part of the Planet Hunters community. You can watch the final product titled COLLECTIVE: An exploration of online community below:
Revising the PH1 Paper
I just wanted to give you all a quick update on the PH1 paper. We submitted the paper in October to a scientific journal, Astrophysical Journal. We got a few months ago feedback from the referee (another scientist in the field who reads the paper, gives to the editor his/her opinion on if the paper is worthy of publication, and many times raise issues or concerns he/she would like to see addressed before publication will be recommended). Recently, I’ve been working on finishing the response to the referee’s report. I have been making changes and edits to the text to address the specific concerns and questions raised by the referee. I think the changes make it a stronger paper. I sent the revised manuscript to the rest of the coauthors last night. I’m waiting for their comments and feedback. Hopefully in the next few weeks, we’ll have the paper resubmitted to the journal and referee. With any luck, hopefully the paper will be accepted soon after that. I’ll keep you updated on our progress.
Starspots and Transits
There was a great question about transits in response to my post about “What Factors Impact Transit Shape” so I thought I’d answer in a blog post.
Jean Tate asked:
Question: In the image of Venus transiting the Sun, there are sunspots. How common are sunspots on the Sun-like stars in the Kepler field? How do sunspots change the transit light curve? How are sunspots modeled?
Starspots are dark blotches on the surface of the star and are regions of intense magnetic activity. Their temperature are lower than the rest of the photosphere which gives them their dark appearance. These blemishes are transitory and last anywhere from hours to months. They are an indication of the magnetic activity of the star, and the Sun goes through an 11-year cycle where the number of starspots (or sunspots as we call them on the Sun) changes. The more active the Sun, the more sunspots visible on its surface.
If you viewed the transit of Venus last July, there were several sunspots on the surface of the Sun which you can see in the image below.
Transit of Venus – Image credit- Wikipedia – http://en.wikipedia.org/wiki/File:2012_Transit_of_Venus_from_SF.jpg – Venus is at the top right of the Sun’s disk. Other dark blotches are sunspots.
On the Sun we can actually spatially resolve the sunspots, but on other stars we can’t. So for Kepler that is monitoring stars thousands of light years away, we detect starspots through the light curve. As the star rotates, starspots will come in and out view causing changes in the star’s brightness. The pattern in the star’s light curve will repeat once per rotation period of the star. At the equator, the Sun rotates every 24.47 days much longer than the short few-tens of hours that a planet transit lasts.
Light curve likely showing star spot variation
If the transiting planet doesn’t cross over a starspot we get a fairly rounded U-shaped symmetric bottom to the transit as you can see below for a set of simulated planet transits.
Simulated planet transits including limb darkening of the star. For the plot I assume the star 0.8 times the radius of the Sun and the planets cross the center of the star
Because planet transits last a few to tens of hours and stars rotate over a period of days, you can think of the starspot as effectively stationary with the planet moving across it during the transit. The starspot is not as bright as the surrounding areas of the photosphere, so when the planet transits across that starspot the lightcurve gets a bit brighter than average and you don’t see a symmetric bottom to your transit. So you see a small positive bump in the transit lightcurve. In the observed transit shown below, the planet crosses a starspot during the second half of the transit.
Planet transit of Kepler-30c across a star spot Figure from Sanchis-Ojeda et al 2012. (http://arxiv.org/abs/1207.5804)
Planets transiting starspots can be extremely useful. Those transits have been recently used to measure the alignment of the planet’s orbit to the rotation axis of the star. In our Solar System, the planets are about 8 degrees off from being aligned with the Sun’s rotation axis, but other planetary systems are severely misaligned.
If the planetary system is aligned with the star’s rotation axis, then the planet transit path is a chord that always crosses over the starspot when it is in view, so you will see many of the planet transits having the signature of a starspot crossing. Because the star is also rotating between transits, the starspot will be likely be in a different place on the star’s disk the next time the planet comes around so you will see the timing of the bump change from transit to transit. If the orbit is misaligned, then only when the starspot is in a position crossing the planet’s transit chord across the star’s surface will there be a positive bump in the transit lightcurve. So the next several transits the planet has extremely low chances of being timed such that the starspot is in the same position on the star’s disk for the event to repeat. So you should see no starspot signal in subsequent transits. You can see this effect below in the figure from Sanchis-Ojeda et al 2012.
Figure from Sanchis-Ojeda et al 2012 (http://arxiv.org/abs/1211.2002)
What factors impact transit shape
I’m rewriting the simulation code I use for making simulated transits and injecting them into Kepler light curves from a program language called IDL to python. I’m working on a new paper idea and project with Planet Hunters so I thought now would be the perfect to time to make the coding switch. The actual part of the code that computers the shape of the transit comes from publicly available code written by another astronomer, Ian Crossfield (if you want to play with the code you can find it here).
I’ve been doing some simple tests to make sure the code works and thought that it would be worth using the test output as a great way to talk about a few things that affect the transits that you see in the Kepler light curves on the Planet Hunters website.
Ratio of the size of the planet to the size of the star:
The transit depth is the ratio of the surface area of the star’s disk blocked out by the planet’s disk. So the transit depth is the square of the planet radius divided by the star’s radius. The majority of Kepler stars are similar in size to the Sun or a bit bigger or smaller, so in general the bigger the planet the bigger the transit you see.
Below is the ideal transits you’d see for a series of planet radii assuming the star was perfectly quiet and is uniformly bright. For the plot below I assume the star 0.8 times the radius of the Sun and the planets cross the center of the star. 
These transits are very boxy – In real life they won’t look like this at least not on the ingress and egress (the edges of the transit). That’s because the a star is not a uniformly illuminated disk. It is darker at the edges than it is at the center. We call this limb darkening. What is happening is that you are seeing into different layers of the Sun depending on how far from the center of the disk. So the center is hotter layers and therefore brighter than the edges. You can see the effect when looking at the Sun shown below during the transit of Venus.
Transit of Venus – Image credit- Wikipedia – http://en.wikipedia.org/wiki/File:2012_Transit_of_Venus_from_SF.jpg – You can see the limb darkening is quite apparent. The edges of the sun are darker than the center.
Limb darkening changes mostly the edges of the transit making them softer and rounder less box like. If we account for limb darkening for the same planet transits shown in the previous plot, they now look look this:
Simulated planet transits including limb darkening of the star. For the plot I assume the star 0.8 times the radius of the Sun and the planets cross the center of the star
You can see the transits are more U-shaped like we see in the Planet Hunters interface. Now the plot is very zoomed in, it shows 3x the star’s radius on either side, but if you zoomed in on Planet Hunters this is what you’ll see for a spotted transit if the planet is very large and the transit depth is pretty large compared to the measurement noise of Kepler.
Another factor to account for is the impact parameter. You can think of the planet’s transit across the star in the x- direction and think of the impact parameter as the y project coordinate of the transit. In essence you can think of as the impact parameter (b) as how close in the y direction is planet to the center of the star’s disk.
Transit schematic from Winn 2011 – http://arxiv.org/abs/1001.2010v3
Changing the impact parameter changes the duration of the transit. If we assume no limb darkening and a uniformly illuminated stellar disk this is what you would see:
Larger b higher from the center of the star the planet crosses. Transits of a 10 Earth radii (Jupiter-sized planet) with varying impact parameters and no limb darkening assuming a 0.8 x Solar radius star
Now if we add in limb darkening we get:
Larger b higher from the center of the star the planet crosses. Transits of a 10 Earth radii (Jupiter-sized planet) with varying impact parameters with limb darkening assuming a 0.8 x Solar radius star
You can see for the highest impact parameter (where the planet is crossing very close to the edge of the star) the transit looks pretty V-shaped like an eclipsing binary eclipse when we account for limb darkening. This is why if you see a V-shaped transit we typically think it’s most likely not a planet transit because the vast majority of times the planet transits will be U-shaped with a flatish bottom. You also see the depths on the bottom change slightly. This is because they are not all crossing the very center of the star which is the brightest point anymore.
One other factor that will effect the shape will be the duration of the transit which depends on the orbital period of the planet and the eccentricity of the orbit, but for all of these plots I’m plotting in the X-axis in terms of the size of the star.
New Features on the Source Pages and Other Updates
With the Kepler extended mission in full swing, we have added some new data to the source pages to help your investigations. If you don’t know what a source page is, it’s where we show all the light curve data for a given Kepler target that we have uploaded on the Planet Hunters website as you would see it in the main classification interface. We show roughly 30 day light curve segments in the main Planet Hunters classification interface, so on the source pages you can peruse the other light curve sections. In addition the source page is the place where you can get the Kepler ID of your favorite star and look up other information about the Kepler source.
You can get to the source pages by clicking on the “Examine Star” link (see below) on any Talk light curve page.
The source pages now include some new links to reflect some of the new data on Kepler stars now available. At the top of each source page you’ll see several links: Add to Favorites – Download Data – Kepler Archive – Kepler TPS – UKIRT DB
Download Data: The Download Data link will download to your harddrive a csv file of all the light curve data we have uploaded for that star.
Kepler Archive: The Kepler Archive link will take you to a Kepler Catalog Search which outputs the Kepler id of the star, it’s position on the sky (right ascension and declination), magnitude, colors, etc.
***New Features***
The Kepler TPS: In the Kepler Extended Mission, the Kepler team is now releasing their list of Transit Crossing Events (TCEs) from their main Transiting Planet Search (TPS) code. A TCE from TPS is not a planet candidate. It’s a possible series of linked transits, identified by TPS that has hit the criteria for being considered a detection. There’s a lot of work needed to go from TCE to planet candidate. TPS detects may thousands upon thousands of TCEs and most of these are false positives. So lots of other checks have to be made to validate the possible transit detection to a planet candidate. For the Quarter 1-12 run of TPS there are over 18,000 TCEs. The TCE list has not been vetted by the Kepler team. Probably only a few thousand are actually real. Provided by the Kepler team is the data validation report for each TCE. This is the output from their data validation pipeline of some tests to assess whether the TCE may be a real planet candidate. (You can learn more about the TCEs and other data products provided in the Kepler Extended Mission here.) The Kepler TCE link will search the TCE list and report back if there was a hit on the TCE list with some info about the properties of the detection, which you can then further investigate on the NExSci website. If there are columns names and nothing else when you click the Kepler TPS link that means the source is not on the TCE list.
UKIRT DB Link: The Kepler pixels are rather large. Each pixel in a Kepler image is 4 arcseconds. The typical photometric aperture radius for a Kepler target star is 6 arcseconds, and all the photons collected by the CCD within that radius are assumed to come from the target star and summed to make the Kepler light curve you see. With such a wide aperture, stellar contamination and photometric blends are a concern. Adding linearly, the contribution of extra light decreases from other stars within the Kepler aperture causes the observed transit depths to be shallower than they really are. Accurately estimating the size of the transiting planet requires knowledge of the additional stars contributing to the Kepler light curve to correct for this effect. Also knowing there are additional stars in the Kepler photometric aperture is important because it can help identify that a Kepler source;s light curve is being contaminating by a nearby star that is an eclipsing binary. By clicking on the UKIRT DB link, you get a search reporting back UKIRT J band (near infrared) images of the Kepler star from the WFCAM Science Archive. The typical pixel scale is 0.8-0.9 arcseconds per pixel, which allows us to zoom in within a few arcseconds of the Kepler target. (Thanks to Mike Read from the WFCAM Science Archive for helping set this up and to Phil Lucas for generously letting us link to the data in this way).
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Other updates to the site include updating the lists of known eclipsing binaries, false positives, and Kepler planet candidates. The Kepler team last week released their list of planet candidates and false positives from analysis and vetting using data from Q1-Q8. The Talk labels have been updated to reflect this. The eclipsing binary list comes from the July 2012, since that’s the last static list to be released.
Planet Hunter Kian awarded the Chambliss Prize
Congratulations to Planet Hunter Kian Jek, who just received the Chambliss Amateur Achievement Award! This is the premiere award for amateur astronomers presented by the American Astronomical Society – and we think it is highly deserved. Many of you know Kian, who works tirelessly on the site and to a large part is responsible for the dramatic success of Planet Hunters. He not only plays a leading role in hunting down planets, but has been responsible as well for much of the work on variable stars that the project has produced. This award is a suitable acknowledgement of his contributions, and we hope it also serves as recognition for all of the Planet Hunters by the American Astronomical Society. When solicited for a comment on the 42 new candidates in the latest Planet Hunters paper, co-author Kian (his third paper!) wrote:
“As someone who grew up with the Apollo moon landings, whose childhood imagination was fired by Kubrick’s 2001 and the original Star Trek, I never had any doubt that planets around other stars existed and that one day we would discover them. But I never dreamed that we would find them in my lifetime, let alone being involved in their discovery. Although there are over 700 discovered since 1996, each new planet opens another door to a strange alien world, some of them we could not even imagine could exist. Planethunters is an exciting project that allows citizens and scientists participate in pushing the final frontier ever slightly further.”
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 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.
AAS Meeting in Long Beach California
Tomorrow I’m heading to sunny southern California. I’m heading to the American Astronomical Society’s (AAS) 221st meeting in Long Beach, California. Right before the meeting in Long Beach on January 5th and 6th, I will also be attending the National Science Foundation’s Astronomy & Astrophysics Postdoctoral Fellows Symposium. At both I’ll be talking about Planet Hunters. Also Stuart Lynn from the Adler Planetarium and the Zooniverse development team, one of the chief architects behind Planet Hunters, is going to be at the NSF symposium as well. Stuart’s going to be participating in the Novel Approaches to Public Outreach panel. I’m sure he’ll be talking all things Planet Hunters and Zooniverse at the symposium. Science team member Kevin Schawinski will also be attending the AAS meeting as well.
I’m giving my AAS talk on January 9th in the morning exoplanet session. My title is Planet Hunters in the Kepler Extended Mission. I’ll be talking about the discovery of PH1 and where the project is moving in the Kepler extended mission in addition to presenting some of new preliminary results from the science team. If you’re on twitter you can follow the conference live. Many of the astronomers attending (including me) will be using #AAS221 and for the NSF Symposium we’ll be using #AAPF13
A Newly Spotted RR Lyrae Star
Although Kepler was designed to find extrasolar planets, the Kepler light curves with their high temporal cadence and measurement precision is a rich data set for studying stellar astrophysics. Although the main goal of Planet Hunters is to search for new extrasolar planets, the Talk discussion tool was designed to enable volunteers to be able to identify other types of potentially interesting variable stars and oddball light curves that we weren’t necessarily looking for with the main classification interface.
With so many eyes looking through the light curves for 160,000 stars on the website, we’re bound to find an interesting star or two, and we have. Planet Hunters has helped discover a new RR Lyrae variable star. This is the second one spotted by Planet Hunters. Just like the first (which was spotted a year ago), this one was spotted by the keen eyes of our volunteers on Talk. It was reported to the Science Team, and Chris contacted the Kepler folks who study these sorts of thing, and it looks like it is indeed a new find. Congratulations to all involved. The RR Lyrae discovery is actually not the Kepler target star, but is nearby and contributing light into the photometric aperture, contaminating the actual Kepler star’s light curve with it’s changing brightness.
RR Lyrae’s are a special type of variable star. The radial pulsations cause the star to expand and contract producing observed changes in the star’s luminosity and subsequently the observed light curve. The American Association of Variable Star Observers (AAVSO) has a nice writeup describing the history and properties of RR Lyraes. Because the pulsations are supposedly simple radial expansion, these stars are often used as standard candles for measuring distances. But there is still a lot to learn about these stars. In particular, the underlying cause of Blazhko modulation, a periodic amplitude and/or phase variation of the pulsations with a period of typically 10-100x the typical pulsation period, that some of the RR Lyraes undergo is still an open question in stellar astrophysics.
This class of variable stars is named for the prototype star, RR Lyrae, first identified to exhibit these oscillations and observed patterns of variation. The original RR Lyrae just so happens to be in the Kepler field as KIC 7198959. There are currently about 40 known RR Lyrae stars in the Kepler field, so this is indeed a rare find. This new find will subsequently be studied by the Kepler Cepheid & RR Lyrae Working Group, and hopefully eventually be included in publication featuring all RR Lyrae stars identified in the Kepler field.
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