systemic

A recent e-mail from Bruce Gary prompted me to pay a return visit the Exoplanet Transit Database (ETD) which is maintained by the variable star and exoplanet section of the Czech Astronomical Society. I came away both impressed and inspired. The ETD is really leveraging the large, fully global community of skilled small-telescope photometric observers.

There are hundreds of citizen scientists worldwide who have demonstrated the ability to obtain high-quality light curves of transiting extrasolar planets. I’ve developed many contacts with this cohort over the past decade through the Transitsearch.org project, and small-telescope observers played a large role in the discovery of the two longest-period transits, HD 17156b, and HD 80606b.

Once a particular planet has been found to transit, there is considerable scientific value in continued monitoring of the transits. Additional perturbing planets can cause the transit times to deviate slightly from strict periodicity, and a bona-fide case of such transit timing variations (TTVs)  has become something of a holy grail in the exoplanet community. A perturbing body will also produce changes in the depth and duration of transits as a consequence of changes in the orbital inclination relative to the line of sight. Moreover, for favorable cases, a large moon orbiting a transiting planet can produce TTVs detectable with a small telescope from the ground.

New transiting planets are being announced at a rate of roughly one per month. The flow of fresh transits continuously improves the odds that systems with detectable TTVs are in the catalog, but also makes it harder for any single observing group (e.g. the TLC project) to stay on top of all the opportunities.

The Exoplanet Transit Database maintains a catalog of all publicly available transit light curves. At present, there are 1113 data sets distributed over 58 transiting planets. The ETD site provides a facility for photometric observers to upload their data, and also provides online tools for observation scheduling and automated model fitting. Simply put, this is a groundbreaking resource for the community.

The ETD also provides concise summaries of the state of the data sets. Light curves are divided into five quality bins, depending on the noise level, the cadence, and the coverage of the photometry:

It’s interesting to go through the summary reports for each of the transiting planets. Here’s the current plot of predicted and observed transit times for Gliese 436b, the famously transiting hot Neptune:

The data show no hint of transit timing variations. (So what’s up with that e?)

In other cases, however, there are hints that either the best-fit orbital period needs adjustment, or that, more provocatively, the TTVs are already being observed. TrES-2 provides an intriguing example:

In sifting through the database, it looks like XO-1, CoRoT-1, Hat-P-2, OGLE-TR-10, OGLE-TR-132, OGLE-TR-182, TrES-1, TrES-3, and WASP-1 are all worthy of further scrutiny.

Over the past year, as a result of Stefano Meschiari’s efforts, the Systemic Console (latest version downloadable here) has been evolving quite quickly behind the scenes. Stefano and I are working on a paper which illustrates how the console can be used to solve the TTV inverse problem through the joint analysis of radial velocity and transit timing data. In the meantime, it’s worth pointing out that the ETD database lists transit midpoints in HJD for all of the cataloged light curves. These midpoints can easily be added to the .tds files that come packaged with the console.

Visitors to oklo.org may have noticed that the site was down for most of Sunday. I’d been neglecting to update my WordPress installation, which lead to a problem with the database, and a huge load spike for the server. Everything seems stable now, and I’m now flossin’ 2.8.4 inch rims.

In the relatively near future, I will be modernizing some aspects of the look and feel of the site, which will make it more discussion-friendly, and more smoothly slotted into the hum of the outside world. No need to worry, though. We’ll continue to roll ad-free.

I’ve updated the second systemic console tutorial which guides the user through the remarkable Upsilon Andromedae radial velocity data set. The back-end database is getting closer to its relaunch, and the systemic console (version 1.0.97) is freely available for download here.

Read on to work through the tutorial.

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The systemic backend will be offline for a period of time starting on Monday Aug. 03. We’re pulling our server from its current rack space. When it comes back on line, it be on the UCSC network. The database has been fully backed up, so despite the temporary unavailability, there’ll be no loss of data. The oklo.org web log will continue uninterrupted.

When we return, we have several goals in mind for the backend. First, there will be support. Several UCSC physics and computer engineering undergrads will be joining the systemic team, and will be focused on improving the backend and keeping it running smoothly. Due to time constraints, and despite best efforts, we just weren’t able to keep up with this ourselves. Second, the backend will maintain improved integration with the console as the console develops, and will be more focused on scientific tools rather than the web 2.0 social network aspect. Third, we’ll be introducing features geared toward the use of the console as an instructional tool in astronomy, physics and astrobiology classes.

i-Phone snapshot of Difference Engine #2.

The systemic console started life over five years ago as a web-based applet for analyzing radial velocity data. The original version was a collaboration between Aaron Wolf (then a UCSC Undergraduate, now a Caltech Grad Student) and myself, and the Java was coded in its entirety by Aaron. Our goal was to clarify the analysis of radial velocity data — the “fitting” of extrasolar planets — by providing an interactive graphical interface. The look and feel were inspired by sound-mixing boards, in particular, the ICON Digital Console built by Digidesign:

Over the intervening years, the console has expanded greatly in scope. Stefano Meschiari has taken over as lead software developer, and has directed the long-running evolution with considerable skill. The console has been adopted by planet-hunting groups world-wide, as well as by classroom instructors and by a large community of users from the public.

Tuesday’s post pointed to our new peer-reviewed article (Meschiari et al. 2009) that describes the algorithms under the console’s hood, and now that the code base has matured, we’re developing documentation that can serve the widely varying needs of our users. We also intend to return the systemic backend collaboration to the forefront of relevance. A great deal of very interesting work has been done by the backend users, and it can be leveraged.

As the first step, we’re updating and expanding the tutorials, which have been largely gathering dust since November 2005. Following the page break, the remainder of this post updates tutorial #1. If you’ve ever had interest in using the console, now’s the time to start…

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oklo.org is heading into its fifth year, and we’ve just hit something of a milestone: this is the 300th post. A great deal has been learned about extrasolar planets in the past half-decade, and I’ve found that participative reporting has been a great way to keep up with, and even, sometimes, to influence the course of events.

We’ve also just hit another big milestone with the release of the Systemic Console Paper. Our manuscript has just been accepted for publication in the peer-reviewed journal Publications of the Astronomical Society of the Pacific, and the article is now available on astro-ph.

In coming posts, we’ll be highlighting the many new features of the console, and we’ll be updating the now badly-out-of-date tutorials. If you are interested, then by all means download the latest “cutting edge” version, which is available on Stefano’s website.

And finally, if you use the console, and find it useful, please consider citing Meschiari et al. 2009 in your publications.