Monthly Archives: May 2006

Sonified

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Many systemic readers have not yet experienced the thrill of fitting planetary systems with the systemic console because the console fails to properly launch in their browser. The standard refrain for the last several months has been, “We’re working on it…”

Tomorrow, we’ll be releasing an upgraded version of the console in downloadable form. We’ve tested this version on Mac OSX, Windows, and Linux platforms, and we’ve gotten it to work on all three.

The downloadable version of the console will contain a number of new features, including a sonification button that brings up the following window:

console sonification controller

Sonification takes the N-body initial condition corresponding to the current positions of the console sliders and performs an integration of the equations of motion to produce a self-consistent radial velocity curve for the star. The radial velocity curve is then interpreted as an audio waveform and the resulting audio signal is written to the .wav format. You, the user, choose the duration of the integration and the audio frequency to which the innermost planet’s orbital frequency is mapped (440 Hertz, for example, corresponds to the A below middle C). A simple envelope function is also provided in order to avoid strange-sounding glitches associated with sharp turn-on and turn-off transients.

A single planet in a circular orbit produces a pure sine-wave tone. Very boring. The introduction of orbital eccentricity adds additional frequency content to the single-planet signal, and produces a variety of buzzing hornlike timbres, depending on the chosen values for the eccentricity and longitude of periastron. (For example, here are tones corresponding to keplerian orbits with [1] e=0.5, omega=90 deg; [2] e=0.9, omega=150 deg; and [3] e=0.9, omega=312 deg).

Hewitt, Conceptual Physics, p. 284

I scanned the above photo from my groovy 1974 edition of Conceptual Physics. Author Paul Hewitt is using a pipe to generate what looks to be a 420 Hz tone. The oscilliscope trace indicates that the pipe is producing both a fundamental frequency as well as a first overtone. A similar effect can be had with the console by adding an additional planet and sonifying the resulting radial velocity curve. For example, a quick fit to the 55 Cancri data-set generates a flute-like timbre that arises primarily from the near 3:1 commensurability of the orbits of the 14.65 and 44.3 day planets. Here’s a detail from the waveform:

55 Cancri Waveform

And here’s the .wav format audio file corresponding to the 55 Cancri fit.

Systems in 2:1 mean-motion resonances can generate some very weird audio waveforms. Oklo favorite GJ 876 was the first (and is still by far the best) example of a 2:1 resonant configuration. GJ 876’s audio signal, however, is pretty lackluster (the .wav file is here). This is because the system is so deeply in the resonance that the waveform has a nearly invariant long time-baseline structure. Much more interesting from an audio standpoint, are the newly discovered 2:1 resonant systems HD 128311 and HD 73526. With the console, one can work up a quick fit to the HD 128311 data set which has one 2:1 resonant argument in circulation and the other in libration.

a fit to the 128311 system

The long-term orbital motion is completely bizarre (as shown by this .mpeg animation) and the corresponding audio file [.wav file here] has a certain demented quality. The signal definitely evolves on longer timescales than shown in this snapshot of the fit:

waveform for hd 128311

Results-oriented planet hunters should definitely be asking, “Does sonification have any scientific utility?”

Maybe. I’ll be posting more fairly soon on why we think sonification might be useful, but here’s a straw-man example. Call up the data set for HD 37124 on the console. There are a lot of ways to get an acceptable orbital model for this system, including a panoply of far-out configurations like this one:

hd 37124 alternate orbital configuraton

The corresponding waveform looks like this:

hd 37124 alternate orbital fit

If we sonify the fit, we can literally hear the system going unstable (.wav file here). The question is, can a trained ear “hear” signs of instability well before the actual drama of collisions and ejections occurs?

observations of observations

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water glass on a placemat

About two weeks ago, I wrote a post about the Dexter application which is available from the ADS website. Dexter extracts digitized data from image files such as .gifs or .jpgs. We’ve been using it to extract radial velocity data sets for planets that have been published without accompanying radial velocity tables. Our goal is to soon have data sets for all of the planets published to date.

That’ll make oklo.org your site for one-stop shopping.

Eugenio will soon be posting a very interesting discussion of the technique and pitfalls of using Dexter to extract radial velocity data sets. In the meantime, I’ve added a sample dextered data set to the systemic console:

dextered selection for hd50499

The data set HD50499d contains velocities digitized from a figure in the California -Carnegie Planet Search Team’s recent ApJ paper, (entitled Five New Multicomponent Systems). This paper also contains the actual radial velocity data for HD 50499 in tabulated form. This actual data is available on the console by clicking HD50499 (i.e. without the “d” for Dexter).

Try using the console to fit to both the actual data and the Dextered data. You should find that for this particular system, the fits are nearly the same. In this case, Dexter did a very good job of extracting the velocities.

fit to the hd50499 radial velocity data set

The HD 50499 system clearly harbors at least two satellites. One of them has a very long period, considerably longer than 10,000 days. The way to get the console to fit this system is to fix the outer planet period at 10,000 days, while minimizing on the other orbital parameters.

Approach

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Nevada Test Site 1957

Priscilla, Nevada Test Site, 1957 (US National Archives, see Michael Light’s 100 Suns)

Today was a bright spring day in California, and now, as I write, the night air coming through the window is drunken, redolent with the scent of a million flowers.

Spring is also arriving on HD 80606 b, but with devastating ferocity. This morning, HD 80606 b’s parent star, which resembles our Sun in intrinsic size and brightness, subtended more than two degrees as it rose above the horizon. It loomed, angry and white, with more than four times the angular size of a full moon. It grew perceptibly larger as the day wore on. Above the vortical scream of the cloud tops, it was scores of degrees warmer today than yesterday.

Last Friday, HD 80606 b fell through the imaginary boundary given by the size of Mercury’s orbit. Midsummer — HD 80606 b’s periastron passage — will occur on Friday of this week. At this moment, the planet will plunge to within 6 stellar radii, and the furnace of the stellar surface will stretch across 19 degrees of sky.

80606 position today

Five days later, on its way back out to apastron, the planet will perforate the plane containing the line of sight to the Earth. At this moment, there’s a possibility (a 1.7% possibility to be exact) that a transit can be observed.

a selection from the current transit table

Varkaus

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Varkaus

Image source: NASA Visible Earth

For most people, a mention of Finland brings to mind snow, lakes, conifers, Nokia and Linus Torvalds. Here at oklo.org, however, we hear Finland and we think of top-drawer amateur astronomers. In 2000, the Finn Arto Oksanen was the first amateur to observe the HD 209458 b transit. More recently, both Oksanen and countryman Pertti Paakkonen have contributed a number of observations of TrES-1 and other stars to transitsearch.org. Finnish IP addresses are consistently among the top traffic generators on the Systemic Console.

Now, Veli-Pekka Hentunen and the Warkauden Kassiopeia ry (the Astronomical Association of Varkaus) join the ranks, with a fine observation of last week’s TrES-1 planetary transit. Their lightcurve, shown just below, was obtained with a Meade 12-inch LX200 telescope and a cooled SBIG ST8-XME CCD camera:

April 30, 2006 TrES-1 Transit Photometry

The photometry shows a tantalizing hint of the starspot activity that is known to characterize TrES-1. A more detailed analysis will be needed to see whether the small in-transit bump has statistical significance. As discussed in a previous post, HST has shown that starspot activity on TrES-1 can produce stange-looking features in the light curve:

transit of TrES-1 obtained with HST

Hentunen and his colleagues have constructed a very impressive facility at a dark (and from the look of things cold) site in the Finnish interior. Information in English regarding both their observatory and their scientific work can be found at the Taurus Hill Observatory Website.

varkaus observatory

Taurus Hill Observatory

Hentunen and friends will be able to kick back and take it easy for the next few months because it doesn’t really get dark at their location during the Summer. In the Winter, however, when the weather is clear, they’ll have the opportunity to make long-duration time-series photometric observations of stars near the polar cap. For example, they’ll be in awesome position to snag oklo.org favorite HD 80606 (+50 deg declination) during its Dec. 26, 2006 transit opportunity.

tilt shift

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When it comes to planetary systems, our own eclectic gathering of eight (or nine, or ten) planets is by far and away the best characterized and best understood. We’ve flung space probes past all of the planets in the solar system, and we’ve directly, physically, probed four of them (in addition to two major satellites). We know their orbits to stunning, uncanny precision. We have actual pieces of Vesta and Mars under minute scrutiny in our laboratories. We have coffee table books overflowing with detailed photographs our our home worlds.

a detailed view of a surface feature on a life-bearing habitable planet

I can step right outside my door and photograph the surface details of a habitable terrestrial planet.

Sadly, we don’t have anything rembling this wealth of detail when it comes to extrasolar planets. Most of our information is encapsulated in the tables of radial velocity measurements accessible to the Systemic Console. Much of what I write about in these posts, and indeed, most of what we can infer about these distant worlds, must be squeezed from sparse columns of times, velocities, and velocity uncertainty estimates.

Continue reading →

Where we’re at

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banana leaf

The systemic collaboration website has now been on the air for six months. Traffic has been increasingly steadily. By the end of April, oklo.org has been averaging 250 visitors a day, with a total of 1661 unique “real” visitors for the month. (This brings to mind a philosophical question: if a tree falls in a forest, and only robots, worms, or replies with special HTTP status codes comment, did it make a sound?)

april showers

The Systemic Team is enthusiastic about a number of improvements that will be coming on line very soon. Here’s a rundown of what to look for during May:

1. Aaron Wolf is putting the finishing touches on the next release of the systemic console. The updated version will have a number of subtle improvements to the existing controls, and will have several completely new features, including a sonification utility and a folding window. Sonification allows the user to create a .wav format audio file of the radial velocity waveform produced by a given configuration of planets orbiting a star:

console sonification controller

As we’ll discuss in future posts, the ability to “listen” to dynamical systems provides a startlingly effective and completely novel way to evaluate the long-term orbital stability of a hypothesized system of planets. For example, when a configuration of planets is stable, one generally gets a sound with a steady timbre: [example 1.5 MB .wav file corresponding to a stable planetary system].

On the other hand, when a configuration of planets is unstable, the radial velocity waveform of the star can get pretty crazy, which can lead to an inifinite variety of very weird sounds: [example 0.5 MB .wav file corresponding to a dynamically unstable planetary system].

2. Stefano Meschiari, who will be transferring as a graduate student to the UCSC graduate program this Fall (yes!), has developed a PHP-based collaborative environment for the systemic project. Think flickr, think myspace, think the Extrasolar Planets Encyclopedia, think seti@home, and think effective scientific collaboration all rolled into one. I’m not kidding, folks, it’s amazing.

G.I. No

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planet formation is not yet in focus

In a comment on yesterday’s core-accretion post, a reader anticipated that all is not hunky-dory with the core-accretion scenario for the formation of the gas giant planets in our solar system, and asked if is there any support for Alan Boss’ disk instability model. In the Boss model (described here by Alan, see also the buff 137-strong citation list) gas giant planets condense directly out of the protostellar disk as the result of gravitational instability in the disk.

The handy thing about an extrasolar planet web log is that you can express your opinions on the formation of extrasolar planets. In my opinion, there are a number of very serious difficulties with the hypothesis that gravitational instability is the dominant mechanism for giant planet formation. Here are three:

(1) In order to have gravitational instability work in the manner shown in the fragmentation simulations, you need to start with an axisymmetric disk that has a sufficiently low value for the Toomre Q parameter. That is, in order for the initial conditions in the successful Boss simulations to be valid, a growing protostellar disk needs to remain completely stable with respect to low-level non-axisymmetric disturbances until BOOM, it reaches a threshold Q value where it is prone to spiral instabilities that exponentiate on a near-orbital timescale.

In reality, I think that a growing (or alternately, a cooling) protostellar disk will be prone to low-level spiral disturbances that steadily transport mass inward and angular momentum outward, allowing the disk to avoid ever reaching the state where instabitilies can grow on an orbital timescale. (For a bulked-up version of this argument, see the papers (one and two) that I wrote with Vladimir Korchagin and Fred Adams on this issue).

(2) The core accretion model provides a very natural explanation for both the planet-metallicity correlation, as well as the paucity of Jovian-mass planets found in orbit around low-mass M type stars. The gravitational instability model predicts that the incidence of Jovian-mass planets should be independant of both the stellar metallicity and the parent star mass.

(3) There’s simply no way that the gravitational instability model can produce the 72 Earth Masses of heavy elements in HD 149026 b. (See this paper for a thorough discussion).

To be fair, there are also some thorny problems associated with core-accretion. In the next few posts of the giant planet formation series [1, 2, 3, 4 and 5] that we’ve been running, I’ll describe these in more detail.

Planet Orbiting a Brown Dwarf

Photo credit: ESO (VLT/NACO)

Another important point to stress is that Alan’s simulations certainly aren’t in error in the sense of being computationally wrong. It’s just that I don’t agree with the generic validity of the initial conditions. Indeed, I do think that gravitational instability sometimes plays a role in giant planet formation. The best example is probably the 5 Jupiter-mass companion to the brown dwarf 2M1207 discovered by Chauvin et al. last year. (The ESO press release on this system is here.) I see no way in which the core-accretion process could have made any headway at 55 AU in this particular system.

Finally, GJ 876, which is by far the best RV-characterized extrasolar planetary system, provides a tough challenge to both the gravitational instability and the core-accretion theories. The inner 7.5 Earth Mass planet in the GJ 876 system is almost certainly an accreted protoplanetary core (regardless of whether it formed in-situ, or migrated from a larger radius). It would be nearly impossible to form lil’ D via gravitational instability. The outer two planets, on the other hand, contain more than three Jupiters worth of mass, and stand in embarrassing conflict with the notion that core-accretion process is difficult to carry through to Jovian-mass completion in red-dwarf protostellar disks.

I would very much like the 411 on what went down in GJ 876’s protostellar disk.