Archive for May, 2008

Worlds worlds worlds

May 25th, 2008 3 comments

On Friday, I flew back from the Boston IAU meeting, still buzzing with excitement. On Saturday, I woke up with what might best be described as a transit-induced hangover (an entirely distinct condition from transit fever). I’d basically allowed all my professorial responsibilities to slide for a week. On my desk is a mountain of work, a preliminary exam to assemble, and a horrifying backlog of e-mail.

Ahh, but like an exotic sports car bought on credit, it was worth it. The meeting was amazing, certainly the most exciting conference that I’ve ever attended. Big ups to the organizers! Planetary transits are no longer the big deal of the future. They’re the big deal of the right here right now. Spitzer, Epoxi, MOST, HST and CoRoT are firing on all cylinders. The ground-based surveys are delivering bizarre worlds by the dozen. And we’re clearly in the midst of very rapid improvement of our understanding of the atmospheres and interiors of the planets that are being discovered.

From a long-term perspective, the conference’s biggest news was probably provided by the Geneva group, in the form of Christophe Lovis’ presentation on Tuesday afternoon. In his 15-minute talk to a packed auditorium, Lovis covered a lot of ground. I scrambled to take notes. My reconstructed summary (hopefully without major errors) runs like this:

The HARPS planet survey of solar-type stars contains ~400 non-active, slowly rotating FGK dwarfs. Observations with the 3.6-meter telescope have been ongoing since 2004, and over time, their emphasis has been progressively narrowed to focus on stars that harbor low-amplitude radial velocity variations with RMS residuals in the 0.5-2.0 m/s range. The current observing strategy is to obtain a nightly multiple-shot composite velocity of an in-play candidate during block campaigns that run for 7-10 nights.

During the first few minutes, Lovis reviewed the current status of the published results. The Mu Arae planets (including the hot Neptune on the 9.6-day orbit, see here and here) are all present and accounted for. The HD 69830 triple-Neptune data set (see here, here and here) now contains twice as many velocities, with virtually no changes to the masses and orbits of the three known planets. Long-term scatter in the HD 69830 data set is at the ~90 cm/sec level, indicating either the effect of residual stellar jitter, or perhaps the presence of additional as-yet uncharacterized bodies.

He then announced that there are currently forty-five additional candidate planets with Msin(i)<30 Earth masses, P<50 days and acceptable orbital solutions. And that’s not counting candidates orbiting red dwarfs.

He then began to highlight specific systems. To say that planets were flying thick and fast is an understatement. Here’s the verbatim text that I managed to type out while simultaneously attempting to focus on the talk:

Rumor has it that some of these systems will be officially unveiled at the upcoming Nantes meeting on Super Earths. Odds-on, with 45 candidates in play, we’ll soon be hearing about a transiting planet with a mass of order ten times Earth’s. I won’t be at the Nantes meeting, but the stands will be harboring agents of the Oklo Corporation.

The talk finished with an overview of the statistics of the warm Neptune population. Most strikingly, a full 80% of the candidates appear to belong to multiple planet systems, but cases of low-order mean motion resonance seem to be rare [as predicted –Ed.] . There is a concentration of these planets near the 10-day orbital period, and the mass function is growing toward lower masses. Significant eccentricities seem to be the rule. And finally, I think it was mentioned that the planet-metallicity correlation is weaker for the warm Neptunes than for the population of higher-mass planets.

Seems like core accretion is standing the test of time.

Note on the images: Gaspar Bakos (of HAT fame) had the cool idea of machining metal models for the planets of known radius which are correct in terms of relative size, and which have the actual density of their namesakes. HAT-P-6, for example, is constructed from a hollow aluminum shell, and with a density of ~0.6 gm/cc it would float like a boat. HAT-P-2b, on the other hand, which packs 8.6 Jupiter masses into less than a Jovian radius, has the density of lead and (not coincidently) is made out of lead. It’s startling to pick it up. CoRoT-Exo-3b, which was announced at the meeting, has a mass of twenty Jovian masses, and a radius just less than Jupiter. I guess that one will have to be made from Osmium.

Earth, at ~5.5 gm/cc, on the other hand, can be readily manufactured from a variety of different alloys.

Categories: detection Tags:

A Field Guide to the Spitzer Observations

May 18th, 2008 8 comments

Jonathan Fortney
has the office next to mine at UCSC, and so we’re always talking about the Spitzer observations of extrasolar planets. The Spitzer Space Telescope has proved to be an extraordinary platform for observing planets in the near infrared, and during the past year, the number of published and planned observations has really been growing rapidly.

Increasingly, with the flood of data, I’ve been finding that I have trouble keeping mental track of all the photometric observations of all the planets that Spitzer has produced. Let’s see, was Tres-1 observed in primary eclipse? Did someone get a 24-micron time series for HD 149026? And so on.

So Jonathan and I decided to put together a poster that aggregates the observations (that we know of) that have either been completed, or which have been scheduled. The relevant information for each campaign includes the star-planet system, the bandpass, and the duration and phase of the observation. We wanted the information for each system to be presented in a consistent manner, in which the orbits, the stars, and the planets are all shown to scale (and at a uniform scale from system to system). As an example, here’s the diagram for HD 189733:

In putting the poster together, we were struck by the variety of different observational programs that have been carried out. Some of the diagrams, furthermore, with text removed, have a delicate insect-like quality.

(The figure just above shows Bryce Croll’s planned 8-micron observations of fave HD 17156b. Croll’s campaign will attempt to measure the pseudo-synchronous rotation period of the planet.)

I’m going to Boston next week to attend the IAU transit meeting, and so I printed out a copy of the poster to put up at the meeting:

Here’s a link to the Illustrator file and the .pdf version. Full size, it’s two feet wide and three feet tall. Going forward, I’ll update the files as new observations come in.

Categories: detection Tags:

ars magna

May 13th, 2008 42 comments

“Getting scooped” is an ongoing occupational hazard for astronomers. An interesting idea pops into your head, or a significant peak starts to emerge in a periodogram, and you drop everything to do an analysis and write up your idea or discovery for submission. If your idea seems to work, and as your story takes shape on paper, it occurs to you that there are plenty of other colleagues who could easily have latched on to what you’ve just done. After all, there are only so many nearby red dwarfs in the sky!

The invention of the telescope at the beginning of the seventeenth century led to very rapid progress in astronomy, and because telescopes are relatively straightforward to make once the principle is understood, astronomers suddenly faced heightened competition, and with it, the ever-unnerving possibility of getting scooped.

Anagrams were brought into use as a method of protecting one’s priority of discovery while simultaneously keeping a discovery under wraps in order to obtain further verification. Galileo was an early adopter of anagrams. After observing Saturn, he circulated the following jumble of letters:

s m a i s m r m i l m e p o e t a l e u m i b u n e n u g t t a u i r a s

When he was ready to announce that Saturn has a very unusual shape when seen through his small telescope, he revealed that the letters in the anagram can be rearranged to read, Altissimum planetam tergeminum observavi, or “I have observed the highest planet tri-form.”

Galileo’s telescope wasn’t powerful enough to allow him to decode what he was actually seeing when he observed Saturn. The true configuration as a ringed planet was first understood by Christiaan Huygens, who, in 1656, with the publication of the discovery of Titan in De Saturni luna observatio nova, also circulated an anagram to protect his claim to discovery:

a a a a a a a c c c c c d e e e e e h i i i i i i i l l l l m m n n n n n n n n n o o o o p p q r r s t t t t t u u u u u.

In 1659, Huygens revealed that the anagram can be decoded to read, Annulo cingitur, tenui, plano, nusquam cohaerente, ad eclipticam inclinato, or “It is surrounded by a thin flat ring, nowhere touching, and inclined to the ecliptic.”

The most appealing anagrams rearrange the true sentence into a satisfyingly oblique haiku-like clue. In connection with his discovery of the phases of Venus, Galileo issued an anagram that read, Haec immatura a me iam frustra leguntur, or “These immature ones have already been read in vain by me.” When properly reconstructed, the letters reveal that, Cynthiae figuras aemulatur Mater Amorum, or “The Mother of Loves [i.e. Venus] imitates the figures of Cynthia [i.e. the moon]”.

So, in service to this venerable tradition, but without adhering to the hoary custom of couching everything in Latin, let me just say that,

Huge Applet, Unsearchable Terrestrials!

Note that according to the wikipedia,

The disadvantage of computer anagram solvers, especially when applied to multi-word anagrams, is that they usually have no understanding of the meaning of the words they are manipulating. They are therefore usually poor at filtering out meaningful or appropriate anagrams from large numbers of nonsensical word combinations.

Categories: worlds Tags: