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Simulated Transits

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

  1. 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.

  2. 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.

Happy Hunting,

~Meg Schwamb

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