Category Archives: systemic faq

information and updates specific to systemic

The mu Arae four

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flowerstalk

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With the verdict in on Pluto, we here at oklo.org will have to revert to sober, scientifically rigorous posts on extrasolar planetary systems to keep our readership and ad rates up. And as soon as I can figure out how to make WordPress launch those “swing for the fences” pop-ups from our site, we’ll be increasing our revenue stream even more.

American Scientist has just published my article on planet formation and extrasolar planets in their September/October issue. The article wraps up with a description of the systemic console, and the systemic collaborative research project. If you’re an American Scientist reader visiting oklo.org for the first time, welcome aboard!

Several posts back, I put up a brief description of the immediate goals of the Systemic collaboration:

The Systemic collaboration is proceeding in three steps. In the first step, which is ongoing, we’ve been gathering all of the radial velocity data that have been published for known planet-bearing stars. These data sets are included in the downloadable systemic console, and the systemic back-end allows participants to upload their own planetary fits to this data. We want to use the data to create a uniform catalog of known planetary systems.

In the second and third phases of the systemic project, we’ll be studying synthetic data sets that have been produced using our own algorithms. “Systemic Jr.” will launch at the beginning of September, and will contain 100 synthetic data sets, four of which will be special challenge systems. The Systemic Challenge, sponsored by Sky and Telescope will be explained in more detail, and will be available at a link on their website. The challenge systems will be released on September 3, 10, 17, and 24, along with a specific set of contest rules. The first person to crack each of these systems will recieve a paperback edition of the Millennium Star Atlas (a $149.95 value). In order to prepare for the contests, go ahead and download a copy of the systemic console, and work through tutorials one, two, and three. A full technical manual for the console is in the works, and will be ready for download quite soon.

Later this Fall, when Systemic Jr. wraps up, we’ll launch the full Systemic simulation. A lot more on this will be posted in the weeks ahead. Our overall goal is to obtain an improved statistical characterization of the galactic planetary census.

The most interesting serious-planet news from the past week has been the paper by the Geneva Extrasolar Planet Search Team that releases an updated radial velocity data set for the nearby solar-type star Mu Arae (also known as HD 160691). As discussed in this post, the console can be used to quickly uncover and characterize the orbits of the four planets that have been announced for the system.

The mu Arae system is remarkable because the two middle planets (with periods P~300 days, planet “d”, and P~640 days, planet “b”) experience strong mutual gravitational interactions during the 5-year time period that the system has been observed. The presence of strong interactions indicates that a model for the system built from independant Keplerian orbits cannot provide a fully realistic fit to the system. In order to build a fully self-consistent fit, one must find an N-body model. The systemic console has this ability, which is enabled whenever the “integrate” box is checked.

N-body integrations are much more time-consuming to compute than simple evaluations of Keplerian fitting functions. The performance of the console thus slows down considerably when integration is enabled. (Note also, that this post now becomes a bit technical. If it sounds like gibberish, you can either skim the next few paragraphs, or, better yet, work through the tutorials on the use of the console.)

Continue reading →

Roll your own.

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succulent

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The October 2006 issue of Sky and Telescope is just hitting the stands. It contains a feature article — Virtual Planet Sleuths — on the usage of the console and the Systemic collaborative project. If you’ve read the Sky and Telescope article, and are a first-time visitor to oklo.org, welcome aboard!

The Systemic collaboration is proceeding in three steps. In the first step, which is ongoing, we’ve been gathering all of the radial velocity data that have been published for known planet-bearing stars. These data sets are included in the downloadable systemic console, and the systemic back-end allows participants to upload their own planetary fits to this data. We want to use the data to create a uniform catalog of known planetary systems.

In the second and third phases of the systemic project, we’ll be studying synthetic data sets that have been produced using our own algorithms. “Systemic Jr.” will launch at the beginning of September, and will contain 100 synthetic data sets, four of which will be special challenge systems. The Systemic Challenge, sponsored by Sky and Telescope will be explained in more detail, and will be available at a link on their website. The challenge systems will be released on September 3, 10, 17, and 24, along with a specific set of contest rules. The first person to crack each of these systems will recieve a paperback edition of the Millennium Star Atlas (a $149.95 value).

Later this Fall, when Systemic Jr. wraps up, we’ll launch the full Systemic simulation. A lot more on this will be posted in the weeks ahead. Our overall goal is to obtain an improved statistical characterization of the galactic planetary census.

In the Sky and Telescope article, I made a rather bold claim that by using the console, it’s possible to find an as-yet unannounced planet around more than a dozen different stars. The 55 Cancri data set, for example, is an excellent place for aspiring planet hunters to try their hand.

The feasibility of detecting planets in the published data sets was illustrated dramatically over the past week. On August 14th, Krzysztof Gozdziewski, Andrzej Maciejewski, and Cezary Migaszewski posted a preprint on astro-ph which describes their detection of a fourth — then unknown and then unconfirmed — planet orbiting HD 160691 (also known as mu Ara). They detected the planet using their own software, which has a similar set of capabilities to the systemic console, and they used the dataset provided by the recent Butler et al. 2006 catalog paper. They found an orbital period of P~307 days for the planet, a nearly circular orbit, and a mass of 0.5 Jupiter Masses.

Today, on astro-ph, the Geneva Radial Velocity Search team published a paper with an updated set of radial velocities of HD 160691 which were obtained with the HARPS instrument at La Silla. In the abstract of their paper, they write: “We present the discovery of mu Ara d, a new planet on an almost circular 310-days period and with a mass of 0.52 Jupiter Masses”.

So there you go, folks! The planets are in the data sets. You just need to download the console, fire it up, get a good fit, and submit it to the Systemic back-end.

[Note: It’s not clear what (if any) “credit” Gozdziewski et al. will get for their discovery. I don’t want to proffer an opinion on who should get credit in a case like this, mainly because I really don’t care. The Systemic backend includes a public-record chronological list of submitted fits for each radial velocity data set. If you turn up a planetary configuration that later gets confirmed by one of the radial velocity teams, you’ll get the personal satisfaction of knowing you knew about the planet first. What you almost certainly won’t get, however, is official credit for the discovery, or the right to name the planet, etc., etc.

For the synthetic planets in phases 2 and 3 of the Systemic collaboration, however, the discoverers will receive official credit, and they will have the right to name the planets if they choose to do so.]

Synthesis

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The Dragon at the Kurama Shrine

Potentially the most interesting feature on the downloadable systemic console is the “sonify button”, which integrates the model planetary system specified by the state of the console sliders and produces a .wav format CD-quality audio file of the resulting radial velocity waveform. Not interested in planets? The console is a stand-alone non-linear digital synthesizer. It’s capable of producing strange, remarkable, musically useful sounds. They merely need to be located within the uncountable infinity of solutions to the gravitational N-body problem.

First, use the console to build an interesting multi-planet system (for this purpose, there’s no need to try to fit whatever data is in the window.) Then click the sonify button. This brings up a dialogue window which enables the user to make several specifications for the sound file that is produced.

console sonify dialogue box

The most important user-specified parameter is the frequency onto which the orbital period of the shortest-period planet on the console is mapped. If, for example, the innermost planet has a period of 365.25 days, then a 440 Hz map will play 440 years worth of evolution in one second. (440 Hz corresponds to the A below middle C.) Mapping the radial velocity curve onto a high-frequency note extends the total number of orbits that go into the sample, and thus increases the integration time required to produce the sample. You can also specify the length of the sample, and you can exert simple control over the attack and decay rate of the envelope for the overall waveform.

Once you’ve produced the soundfile, it appears in the “soundClips” subdirectory within the systemic parent directory. Both of these directories are automatically created when you download and expand the console — see the instruction set for the downloadable console for more details. With a Macintosh, you get the best results if you play the sample right from the folder. i-Tunes seems to want to convert the samples to .mp3 format in a manner that introduces audible noise, and we’re not yet sure how to resolve this issue.

To the extent that planets orbit independently of one another, the console behaves like a simple additive synthesizer, in which the individual Kepler waveforms add to form a composite sound. Much more interesting, is the situation when planets experience significant gravitational interaction, leading, for example, to resonance and to nonlinear instability (here are examples, 1, 2, from the resources page of both types of waveforms). Close encounters provide discontinuities between individual blocks of sound that resemble the results of granular synthesis.

The strongest 2-planet mean-motion resonances occur when the pair of planets share a common period and engage in a one-to-one resonant motion. There are a variety of different one-to-one resonances, including binary planet orbits (e.g. Earth and Moon), trojan configurations, and generalizations of retrograde satellite orbits. In this last catefgory, one can have two planets with the same semi-major axis, but with different eccentricities. If one starts the planets in the following configuration, then the motion is dynamically stable, and evolves in a complicated way over time.

evolution of eccentric 1:1 resonance

The motion leads to an interesting audio wave-form, in which you can hear the system cycling between configurations in which both planets are modestly eccentric and configurations in which one orbit is nearly circular while the other one is highly eccentric. As a specific example, set the console to the following configuration: P1=P2=10 days, M1=M2=0.3 Mjup, MA1=180., MA2=190., e1=0.9, e2=0.1, long1=0.0, long2=0.0. If you increase MA2 to about 225 degrees while keeping the other parameters fixed, you’ll hear the system go unstable.

Evolving, high-eccentricity orbits tend to have an insect-like quality, which brings to mind the 1986 album, The Insect Musicians, by Greame Revell (formerly of SPK). From the album jacket:

For the two years 1984-85, Graeme Revell travelled from Australia to Europe, to Africa, Indonesia and North America recording and negotiating copyrights of insect sound recordings. It took another full year sampling and metamorphosing some fourty sounds thus gathered using the Fairlight Computer Musical Instrument, to produce this record. The only sounds used are those of insects, altered digitally and combined into a unique orchestra of instruments, an orchestra of strange and delicate timbres, music of natural rhythm and texture.

extraterrestrial

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thistle against a white background

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We’re working hard to keep the systemic project moving forward.

Eugenio, as of July 14th, has compiled and documented all of the published radial velocity data sets, and has been designing and developing the “KeckTAC” code, which will be a workhorse for systemic’s next phase. The published datasets are all available on the systemic systems catalog. Aaron has stripped the console down to its component parts, and he’s rebuilding it with new features, faster algorithms and a sleekly expandable architecture. Stefano has been tweaking the systemic backend [sign up and get fittin’, y’all -ed.], and will be arriving at UCSC in the Fall to do his Ph.D. research. We’re hoping that part of his thesis will be a statistical analysis of the final results of the 100,000 star systemic simulation.

When I was in graduate school, I spent a lot of time doing research on brown dwarfs (objects between 13 and 75 Jupiter masses that lie in the mass range between giant planets and red dwarf stars). At that time, circa 1992, no bona-fide brown dwarfs had actually been found, but the prospects for detecting them seemed reasonably good. My friend Todd Henry, who was a graduate student at the University of Arizona, and who was hunting for brown dwarfs using the speckle method, told me something that stuck in my mind.

“Face it, Greg,” he said, “the reason you’re interested in brown dwarfs is not because you’re interested in Brown Dwarfs — the reason you’re interested in brown dwarfs is because you’re really interested in planets, and brown dwarfs are just one stop away on the line.”

He was right.

A similar logic might apply today, “The reason I’m interested in giant planets is not because I’m really interested in Giant Planets — the reason I’m interested in giant planets is because I’m really interested in habitable terrestrial planets, and giant planets are one stop away on the line.”

Good Librations

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Janus and Epimetheus

Janus and Epimetheus Source: JPL

Last week, I wrote a post about the negative heat capacity of self-gravitating systems. I never cease to find it remarkable that if you drain energy out of a system that is held together by its own gravity (such as a giant planet, or a cluster of stars), then that system gets hotter. There really is such a thing as a free lunch, brought to you courtesy of the attractive gravitational force.

A collection of bodies orbiting a larger body is a self-gravitating system, and therefore will also display a negative heat capacity. We illustrated this with the idea of a satellite running through a cloud of dust. Friction between the satellite and the dust heats both bodies up, and they radiate energy away to space. The satellite simultaneously spirals into an orbit with higher velocity, and hence a higher kinetic energy, or temperature.

A family of orbital trajectories known as horseshoe orbits present a riff on this basic principle. A horseshoe orbit occurs when two bodies, with slightly different orbital periods, start off in near-circular orbits on opposite sides of a large central mass. The body with the shorter orbital period eventually attempts to overtake the body with the longer orbital period.

As the short-period body catches up with the long-period body, an attractive gravitational force is exerted between the pair. This force pulls the short-period body forward, and pulls the long-period body back. That is, the gravitational interaction leads to an exchange which drains orbital energy from the long-period (leading) body, and gives energy to the short-period (trailing) body. This exchange causes the bodies to swap orbital periods. The long-period body gets a shorter period, and the short-period body gets a longer period. In a frame that rotates with the average orbital velocity of the pair, the two bodies eventually come in to contact again on the opposite side of the star, and the process is repeated. Again and again in an mindlessly delicate cycle.

dynamics of the horseshoe orbit

The orbital trajectory in the above figure is lifted and adapted from a paper in the Astronomical Journal that I wrote with John Chambers. In that paper, we studied a number of weird co-orbital planetary configurations, and speculated that they might eventually be observed using the radial velocity method. If you can’t fit a particular data set with the console, the horseshoe configuration is always a good thing to check.

In our own solar system, there are two small Saturnian moons, Janus and Epimetheus, which are caught in a horseshoe-like orbit. The splash picture for today’s post shows a Cassini photograph of these moons taken near the time during which they exchange periods.

One of the most useful features of systemic console is its ability to sonify radial velocity waveforms. The soundfiles are produced by making a full integration of the equations of motion, hence all of the nonlinear gravitational interactions between the bodies are incorporated into the sound. When the console is used as a nonlinear digital synthesizer, the horseshoe orbits provide a method for producing amplitude modulation of a tone. To see how this works, launch the downloadable console, and set up the following system (just ignore the radial velocity data, since we’re not interested in fitting, but rather just in waveform generation):

console for a horseshoe orbit

That is, set up two 0.2 Jupiter mass planets with mean anomalies of 0 and 180 degrees. Make the period of one planet 10.1 days, and the other 10.0 days. For simplicity, keep the eccentricities at zero. Clicking the integration box shows the resulting radial velocity waveform. When the planets are on opposite sides of the star, their radial velocity influences on the star cancel. When they are on the same side of the star, their radial velocity influences are additive. This gives an overall modulation envelope on top of the fundamental ~10.05 day period. Use the sonify button to create a 220 hz tone out of this system:

sonifier

Here’s a link to the resulting .wav file. The amplitude modulation (or tremolo) can clearly be heard.

Try building some more complex sounds by nesting horseshoe orbits, and using unequal masses. If you get something cool, e-mail me at laughlin ucolick edu.

cleanse, fold, and manipulate

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Thanks to everyone who has created an account on the systemic backend, downloaded the console, and submitted fits to the HD 69830 data sets. It’s gratifying to see the collaborative effort coming together. We’re starting to get a better understanding of which aspects of the HD 69830 data set seem secure, and which aspects are uncertain.

That outer planet seems to me to be leaning toward the latter category.

For example, I just had a look at data set #17 for HD 69830. Guided first by the console’s periodogram and then by the console’s residuals periodogram, I worked up a two planet fit to the data. I kept the orbits of the resulting 8.66 and 31.7 day planets circular. In the absence of strong planet-planet gravitational interactions or resonant disk migration, I don’t see a clear rationale for assigning non-circular orbits unless the data really demands it.

The residuals periodogram of the 2-planet fit above has peaks near 200 and 400 days. The 200 day peak is a little higher, and indeed, corresponds to the outermost planet announced in the Nature paper published last week.

Use the folding window to look at the case for the 200 day planet. Try updating the period in tiny increments, and watch the data congeal into a relatively sinusoidal pattern. The third planet in the published fit is based on this configuration:

The 400 day data also looks good (although the power is not quite as high). Notice, too, that the phase coverage near 400 days is not as good. This is due both to the limited time baseline of the whole data set, as well as to the fact that the star can be observed only when it is not too near the Sun in the sky.

Apparently, the Las Vegas bookies are giving 3:1 odds in favor of the 200 day planet being correct. That said, however, the 400 day planet rounds out a very nice all-circular fit to the data.

Divide and conquer.

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Hats off to everyone who’s downloaded the console, logged into the backend, and submitted fits for the HD 69830 data sets. The process now seems to be working smoothly, but we need more users. Don’t be shy! We won’t make fun of you if you turn in high-chi-square fits.

First, a follow-up note to yesterday’s post: Some of our original HD 69830-based data files did not have all their radial velocities listed in time-ascending order. This caused the periodogram generator to fail when asked to analyze these data sets. If you downloaded the console yesterday, please download a fresh copy. The version on the site now has the correctly bundled data files.

The published radial velocity data sets consist of lists of times (in Julian Days), radial velocities (relative to an average baseline velocity), and uncertainty estimates for each velocity. These uncertainty estimates give an indication of how much imprecision is introduced at the telescope and by the measurement process itself. An additional source of velocity error, generally referred to as stellar jitter, is not contained in the published uncertainty estimates. Stellar jitter is produced by various processes that are occurring on the star itself. For example, at any given moment in time, there may be a larger portion of the stellar surface upwelling than downwelling, leading to a slight, temporary, net negative radial velocity. It has generally been assumed that for a Solar-type star, stellar jitter contributes roughly 3-5 meters per second of radial velocity error, and it is certainly true that stars somewhat more massive than the Sun (Upsilon Andromedae, for example) display close to 10 meters per second of intrinsic jitter.

Recently, however, as the radial velocity observational techniques have improved, it has become clear that some stars — low mass stars in particular — can have very small intrinsic jitter. Eugenio’s analysis of the GJ 876 radial velocities indicate that the jitter in that case is almost certainly less than 2-3 meters per second. HD 69830, however, seems to be in another category altogether. The published three-planet fit suggests that the star has considerably less than 1 meter per second intrinsic jitter. If this is indeed the case, and if there are a sizeable number of stars that are as quiet as HD 69830 seems to be, then it’s clear that high-cadence observations using the RV method are destined to eventually uncover potentially habitable planets, and likely sooner, rather than later. That’s a big deal.

The twenty alternate data sets for HD 69830 have been constructed to help us test whether the stellar jitter is really as small as the fit to the actual data suggests. Some of the synthetic data sets have been produced by adopting a model in which the stellar jitter is higher than 1 m/s. It should not be possible to find fully correct chi-square ~ 1 fits to these jittery data sets. In other words if we do find chi-square ~ 1 fits to these sets, then we’ve got a strong suggestion that overfitting might be occuring in the chi-square ~ 1 fits to the real data.

I’ll wrap up today with a set of screenshots showing how the backend environment operates. The best way to learn how it works, however, is to login and start using it. It’s quite self-explanatory.

After you’ve uploaded a fit from your own computer, you’ll get a response page that looks like this if the upload was successful:

Make sure that your fit file is appended with the suffix “.fit” before you upload it.

If you click on “view systems”, you’ll see a list of all the systems that have been added to the console thus far. All of the fits that have been uploaded by the systemic collaboration can be accessed from this catalog page. As of tonight, most of the systems have not yet been fitted…

Clicking on a system name brings up the corresponding system data page. There’s quite a bit of information available:

If you click on the icon next to a particular fit:

Then information about the planetary system corresponding to that fit is displayed:

Let’s see some activity! These planets won’t fit themselves…

Time for work!

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I think we’ve finally got the pieces in place. Its time to really push the collaborative aspect of the systemic project. (1) Aaron’s downloadable console has been tested, updated, and is known to work on Mac, Linux, and Windows platforms. (2) Stefano’s systemic back-end collaborative space is tested and working. (3) Eugenio and Paul are standing by and ready to provide technical support. (4) We’ve got nearly 400 unique users visiting oklo.org every day, and (5) with HD 69830, we have an extremely interesting new system to subject to the analytical and computational power of the distributed oklo community.

The questions to be answered are (1) is the published HD 69830 fit unique? and (2) can we get an independent estimation of the errors?

To get an initial analysis of these questions, I’d like to invite (and encourage!) the oklo community to use the console and the back-end environment to obtain a wide variety of fits to a new set of 21 radial velocity datasets. These data have been uploaded onto the web-based console, and they are also packaged into an updated version of the downloadable console. The data sets include the published HD 69830 data, along with 10 bootstrapped datasets, and 10 model-based synthetic data sets. I’ll write much more about bootstrapping and synthetic data sets in upcoming posts. For the time being, we’re simply interested in finding a variety of fits to these data.

The rest of this post will take the form of a brief tutorial to get you going. We really need as many people as possible to participate in this effort.

First, download the console onto your computer. The link to the downloadable console on the right menu bar gives download instructions. If you’re using a non-US English character set on a Windows machine, you will need to switch to the US English set. (We’ll have a fix in for this shortly.) Launch the console on your computer.

Note that the console application, “systemic.jar” is contained in a directory (folder) that contains several subdirectories. These subdirectories are named “datafiles”, “fits”, and “soundClips”:

When the console is running, select one of the HD69830 data sets from the system menu, and obtain a fit. Once you’ve got the fit, use the “save” button (a new feature of the downloadable console) to save the fit in the “fits” directory. Use the suffix “.fit”, as shown below:

Next, point your web-browser to the systemic back-end. The full url is: http://www.oklo.org/php/login.php

You’ll see the login page. Register as a new user. Once you’re logged in, the environment is designed to be as self-explanatory as possible. In particular, you can upload your fit from your computer, and compare it with other users’ fits to the same system. Go ahead and explore! The back-end contains a number of very interesting features, which we’ll look at in the next post.

backend

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Bertinoro, AGN and galaxy

Hey all! This is Stefano, one of the Systemic team members. I’m an MSc astrophysics student at the University of Bologna, Italy, and will be transferring to the beautiful city of Santa Cruz next year to start working on PhD.

I just came back this evening (18 pm on the West coast) from the National School of Astronomy, Bertinoro, where I’ve been sent to last week. It takes place in an old little city, surrounded by walls and dominated by a castle. The castle has bedrooms and seminar rooms with frescoes and red carpets. I was sleeping IN the castle, when I woke up I could see the green planes of the pianura padana extending for acres and acres, and little rocky houses of farmers. The city is famous for its wine. Galla Placidia, daughter of the Roman emperor Theodosius, drinking a glass of the sweet white wine albana purportedly said to the wine “sei degna di berti in oro” (you deserve to be drank in a golden glass), from which the name of the city “Bertinoro” comes. The city itself is full of little places to drink wine (the amazing Sangiovese) and other kinds of alcoholic beverages, which of course we visited often, more than once a night! Whoever thinks scientists are grey, sad people should have come to one of these crazy nights.
That said, it was my first astrophysics school, and I felt so young and unexperienced! Everyone was working on their PhD, and was brilliant, accomplished, and just plain cool — at least to my eyes. I was feeling really out of place in the midst of these amazing minds talking about galaxies and AGNs citing models and theory with apparent ease.

Thankfully I soon realized that these scientifical “hierarchies” don’t really stop you to have your say and give your, even small, contribution! And anyone, from a last-year student like me to the famous astrophysicist, is collaborating in an amazing community to help develop our knowledge of where we are and what’s been before us.
The astronomer Edwin Hubble
All this to introduce the systemic Backend. The systemic Backend lets you have your say in the field of extrasolar planets!

Thanks to the systemic console, you can fit radial velocity data taken by real astronomers and as easily as possible try to discover the evidence of unseen planets around distant stars. And it doesn’t matter if you’re an astronomer, an high school student or an astrophile out of budget for a telescope: if your findings are consistent with the data and explains the observations better than before, you’ve done it!

The systemic backend lets you share your results with other enthusiastic people, showcase your results and interact with your fellow colleagues, just as you would do on a myspace-like network. You can upload the fits saved from the console online from your account, and have other people enthusiastically comment or bash your findings. You might be doing real astrophysics, while knowing other people.

Try out the beta version of the system now, help us iron the bugs and the improvements to make!

The systemic console and backend will be part of a bigger picture — Greg will be talking about it in a future post.

More soon,
Ste

downloadable console now available

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chain link fence

The systemic team is pleased to announce the release of an updated systemic console. Thanks to Aaron Wolf for coding it into reality, and to Eugenio Rivera for troubleshooting the platform-specific installation issues.

Downloadable Console: systemic.zip

The new version of the console has been successfully tested on multiple Mac, Windows, and Linux machines. Specific download instructions and Java information for the three different platforms are available on our new downloads page.

We’re very interested in feedback from users. If you are able to download the console, or if you have problems, please register as a user and let us know via the comment space for this post. We need as much specific information as possible regarding your version of Java and your operating system.

Finally, if you are using a Windows-based browser, and you do not see the following links on the sidebar to the right:

screenshot of systemic on safari

You may have to scroll all the way down to the bottom of the window to see the links.

Thanks, and have fun fitting!

— The Systemic Team