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Web 2.0

September 6th, 2006

fenceposts at ucsc

Hey ya’ll, there’s a whole lotta fittin’ goin on out there in the back 40.

Seriously, though. We’re really seeing a great response from users who are contributing their efforts. Nearly 200 people have registered on the back-end during the past few days, and over 750 different radial velocity fits have been uploaded. Hopefully we’ll see that work continue to flow in, and everyone has been showing admirable patience as we smooth out the inevitable rough spots which began to show up as soon as we had a surge of real users on the site.

If you’re arriving by way of the Sky and Telescope article, you’ll notice that the full universe of 100,000 synthetic stars is not yet listed on the systemic backend. During September, we’re still carrying out the first phase of our planned research effort, which consists of accumulating a wide variety of fits to the full collection of actual, published radial velocity data sets. Very soon, we will have accumulated enough fits to be able to present a dynamic, interactive catalog of candidate planets. A query-based dynamically generated planetary catalog will allow a variety of very interesting questions to be answered. For instance, by how much can one deflate the famous eccentricity-period diagram, while still demanding a prespecified goodness-of-fit for all of the candidate planets?

generated at exoplanet.eu

At the moment, such questions are hard to answer, because (other than here at oklo) there is no consolidated repository of radial velocity data and associated self-consistent fits.

In order to make dynamically generated planet catalogs scientifically useful, we’re going to have to provide several more tools to the users. As I mentioned yesterday, the console will soon be multi-threaded, which will make it easier to use for high-performance work. In the interim, however, you can have the console print a stream of diagnostic messages by launching it from the command line. For example, on linux or OSX architectures, open a terminal (shell), cd to the systemic directory, and type java -jar systemic.jar at the prompt . The diagnostics provide a running update of the progress of the console as it produces fits to the data set.

We’ll also soon be providing a long-term integration window that will allow users to verify that their model systems are dynamically stable. It’s alarmingly easy to find multiple-planet fits to radial velocity data sets that have low values for the reduced chi-square statistic, but in which the planets experience dynamical disasters (collisions, ejections, close encounters, etc.) on a time scale that is short in comparison to the known age of the parent star. Indeed, most of the candidate stars in the back-end catalog are more than 2 billion years old. Young stars tend to be rapidly rotating, which broadens their absorption lines and makes radial velocity measurements less accurate. Rapidly rotating stars also tend to have elevated levels of magnetically driven chromospheric activity, which adds additional noise to the velocity estimates.

And finally, the console needs to provide error estimates on the orbital parameters that it generates. This is best done using the so-called bootstrap method, which we’ll discuss in an upcoming post.

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  1. andy
    September 6th, 2006 at 22:15 | #1

    Might be interesting to have a few simulated fits for our solar system in there as well.

  2. greg
    September 6th, 2006 at 23:50 | #2

    Definitely… Our solar system will be represented in a number of different observing strategies and cadences.


  3. Eugenio
    September 8th, 2006 at 00:35 | #3

    Under Windows XP, you can also run the console from the command line as stated in the directions posted
    for using the downloadable console. Thus, under all three operating systems, you can get an indication of progress by watching all the diagnostics scroll by. Note that among this output, you can see the parameters change and chisq drop as the minimization algorithm does its job.

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