Science and Progress: Short Period Planets in Q1
Chris Lintott (Zookeeper Chris) and I wanted to give an update on what the team is working on and some of the changes made to the PH site to help us answer the question we are tackling right now. We used very simple cuts and visual inspection to come up with a preliminary list of planet candidates that John has discussed in an earlier post. We’ve been brainstorming on how to combine the results from all the multiple user classifications (about 10 users looking at each lightcurve) to tease out every transit in the database of over 2.0 million classifications. We are working hard on more sophisticated algorithms and techniques to take all your Q1 classifications and transit boxes and extract transits and planet candidates.
After starting to look at your classifications and results from the simulated transits, Chris and I think an interesting question to look at is what are the abundances of planets on short period orbits (less than 15 days ) in the Q1 data. The Kepler team is doing something similar and it will be very interesting to compare the two results. As an initial step we are only looking at planets bigger than 2 Earth radii so only gas and ice giants because the transits are more pronounced than the smaller rocky planets. Less than 2 Earth radii will be much harder to detect, so we first we want to develop the analysis tools and then we’ll come back to the less than 2 Earth radii planets later.
With just the transit discoveries alone we can’t answer this question. This is because we don’t know how complete the sample is. If we found 120 Neptune-sized planets for example, we can’t say anything about their abundance compared to Jupiter-sized planets, since we don’t know how many we might have missed in the data set. This is where the synthetic transits we insert into the interface play an important role. If users flag 100% of the Jupiter-sized simulations with orbital periods shorter than 15 days, but only 50% of the Neptune-sized synthetic transits, then we know that the number of transiting Neptunes in the real light curves is a factor of two larger than what we found. With this completeness estimate we can debias our sample and begin to understand the spectrum of solar systems providing crucial context for own solar system.
We find that we need higher numbers and finer resolution in period and radii for the synthetic lightcurves to do this analysis. Starting today, mixed in with the Q2 data, we will be showing newly generated synthetic Q1 lightcurves specifically made for this task. As always with the simulated transits ,we will identify the simulated transit points in red after you’ve classified the star and will mark the lightcurve as simulated data in Talk . With the results from these synthetics we can better tweak our analysis tools for extracting transits from your classifications as well as get sufficient numbers to calculate the short period planet detection efficiency for Planet Hunters. The new synthetics won’t be the only non-Q2 lightcurves you see. We also have about 5800 additional lightcurves from Q1 that were released by the Kepler team on Feb 1st,. Now that the Q2 data upload is complete, these have now been introduced into the database and we’ll be showing these mixed in the classify interface as well as a small subset of the Q1 data previously looked at to examine how classifications have changed over time since December.
Chris and I have are aiming to have the bulk of the analysis complete before October, so we can present the results at the joint meeting of the European Planetary Science Congress (EPSC) and the American Astronomical Society Division for Planetary Sciences (DPS) meeting being held in Nantes, France, in October. We will keep you posted on our progress and results as time goes on. Abstracts are due in May, and so we need to start work now to be able to have results for the Nantes meeting. With your help, we think this will lead to a very interesting paper.
In this blog post, we wanted to focus on the simulated transits you’ve been seeing and why they’re important to the project, as well as answer some of the questions regarding them.
One of the goal of Planet Hunters is to explore the diversity of the terrestrial and giant planet populations and begin to understand the spectrum of solar systems providing crucial context for own solar system. How many Jupiter sized planets are out there? How many Neptune-sized? How many Earth-sized? are solar systems like ours common? These questions are fundamental to understanding how planets form and evolve.
With just the planet discoveries alone you can’t answer these questions because you don’t know how complete the sample is. This is because you don’t know how sensitive to detecting planets of different types the project is, particularly since this is a new way to look for planets that has never been done before. If we found one earth-sized planet for example. We can’t say anything about their abundance compared to gas giant planets, since we don’t know how many we might have missed in the data set -that’s where the simulated transits come in.
We added Kepler lightcurves into the PH interface with simulated transits, spanning the range of exoplanet radii and orbital periods, to test which kinds of transiting planets can be detected with Planet Hunters to assess the fraction of missed planets. If users flag 100% of the Jupiter-sized planets with orbital periods shorter than 30 days, but only 50% of the Neptune-size planets with orbital periods shorter than 30 days, then we know that the number of transiting Neptunes in the real light curves is a factor of two larger than what has been flagged. This provides a powerful statement about the fraction of transiting planets that could only be made with the Planet Hunter collective.
It might seem like we’re testing you or trying to train you to identify transits , but we’re really testing the project. This is a really vital part of the project, with these simulated transits we can answer these really interesting and fundamental questions about how solar systems and planets form.
Some of the simulated planets like large Jupiter-sized planets will be really easy to spot while others will be near impossible to identify especially for the extremely small planets, but don’t be discouraged if you didn’t find the simulated transit. That’s okay, that’s part of the experiment. We don’t know what Planet Hunters we will be able to detect so we have to look at the look at range of possible planet radii and orbits. Can we find 1.2 Earth radii planets? 1.6? and how does incompleteness change in this critical range of radius? How much worse does detectability get when there is just 1 transit instead of 3?- with the simulated transits we will be able to answer these questions. With this information we can then start putting a picture together of the abundance and variety of solar systems.
We will always identify the simulated transit points in red after you’ve classified the star and will mark the lightcurve as simulated data in Talk. The reason we don’t identify the simulated data first, is that if you knew the lightcurve had simulated events you might look at it differently. To be able to use the data from the simulated transits accurately, we need them to be examined in exactly the same conditions as the real lightcurves.
Users on PH Talk have said that for some of the simulated transits the red points are in the wrong spot. The points we are marking for the simulated transits are correct. There are two reasons why it might look like the points are wrong
- The lightcurve have really a small and distat planet injected, and the flux drop caused by this planet would be so small it doesn’t look any different than the normal lightcurve. Right now we’re working to display the radius and period of the simulated transit signal injected, once you’ve classified it, so you can identify this for yourself.
- The star is an eclipsing binary or already has a transit signal from a larger planet than the one we injected into the lightcurve, since we don’t know beforehand which of the lightcurves in the Kepler data set have transiting planets or stars. These simulated events and your classifications for them are still useful because it gives us estimates for multiplanet system and how sensitive we could detect an additional transiting planet.
We know there were a few glitches we needed to work out with the simulated lightcurves that were making them conspicuous, we’ve fixed those, and the zoom works for the simulated lightcurves. We’ve also dialed back how frequently a user will see a simulated lightcurve. We’ll post some examples of the simulated transits in the next blog post.