Multiplanet system imaged at HR 8799

Heh... someone's pointed out something which is not about Hubble that's also extremely interesting, perhaps more so...

(Unfortunately it's probably still embargoed too, until later today it looks like)

Hi!

The news is released: http://www.keckobservatory.org/article.php?id=228

There are 3 new exoplanets discoverd around the star HR8799. The masses are 10, 9 and 6 M_jup and the semimajor axis are 24, 37 and 67 AU.

Bye!

Hmmm... the article in question does not appear on the list of press releases yet, so not sure if it counts as officially released yet.

And also I guess we should split the non-Hubble news out of this thread? Has been done.

http://www.keckobservatory.org/article.php?id=228

Jaw dropping! Unbelievable even! Very, very, VERY COOL!

Wonder if the motion of the star is at all prepurbed by the planets they have imaged. If the motion of the star is preturbed then they could model for the presence of other planets also...

I thought the post above (x2) mine meant that the discovery was released???

Well it is released now (it appears on the W. M. Keck Observatory website's list of press releases), however at the time Michael Johne posted the link, the release was not accessible from the main part of the website he linked to. Therefore it probably shouldn't have been considered "released" until it appeared properly.

It's always fun when you find such things that should probably not be available, however there are certain ethical details with posting the details of such findings before they have been generally released.

Could this also have anything to do with the Hubble's announcement a couple of days ago? Something along the lines of it confirming the discovery?

No, it's an independent (and very much welcome) discovery.

Now this one will pose problems for planet formation theories... these planets are located quite a way out from the region expected to form Jovians, are very massive and orbit a very young star. One planet at such distances might be scattering, but a system of them makes things very interesting indeed.

There must be an efficient mechanism for getting material out that far. Or perhaps the protoplanetary disks are more massive than believed?

Apparently the announcement has been taken down from the Keck site.

Well the embargo is now definitely over: http://www.gemini.edu/threeplanetspr

Plus the details are up on EPE: http://exoplanet.eu/star.php?st=HR+8799

Dudes, forgive the silly thread, but this is really a great discovery. If confirmed. As well as the discovery of "Fomalhaut b" via imaging.

This system is consistent with the observation that planets around stars more massive than the Sun do not have the metallicity dependence for forming giant planets: iron abundance is only 34% solar.

I'm not sure what's going on. What happened to HR 8799 d? The new, bluer image shows only b and c.

Here's the original image.

What'cha talking about.
"d" is in the bottom right corner of the central blur
http://www.keckobservatory.org/images/article_pictures/231_403.jpg

Yeah, the Gemini telescope image does not show planet d: looks like it's hidden behind the occulter.

(Note also the orbital motion for planet d is not shown - it was only detected in the Keck image)

Lazarus wrote:

Yeah, the Gemini telescope image does not show planet d: looks like it's hidden behind the occulter.

(Note also the orbital motion for planet d is not shown - it was only detected in the Keck image)

Hmm. In the image Marasama just posted, d's orbital motion is marked by an arrow.

FOXNews: "First Direct Images of Planets Around Other Stars". Lots of first images so far. 2M1207 b, 1RXS ... b, etc.

I guess that was added later to be consistent with the planets - according to the discovery paper, planet d was only observed in 2008, so not sure if any statistically-significant orbital motion has been observed.

Lazarus wrote:

not sure if any statistically-significant orbital motion has been observed.

I first thought that, too. But found this in the paper.

The Paper wrote:

HR 8799d was first detected in the July 2008 data set. The two months of available proper motion measurements are sufficient to confirm that it is bound to the star at the ~6 sigma level. The available data is also consistent with a counter-clockwise orbital motion of 42 ±27 mas/year (1.65 AU/year). For a semi-major axis of 24 AU, the orbital period is 100 years and the expected orbital motion is 1.57 AU/year (40 mas/year).

Here's the paper on arXiv.

Direct Imaging of Multiple Planets Orbiting the Star HR 8799
http://arxiv.org/abs/0811.2606

C. Marois et al. wrote:

Direct imaging of exoplanetary systems is a powerful technique that can reveal Jupiter-like planets in wide orbits, can enable detailed characterization of planetary atmospheres, and is a key step towards imaging Earth-like planets. Imaging detections are challenging due to the combined effect of small angular separation and large luminosity contrast between a planet and its host star. High-contrast observations with the Keck and Gemini telescopes have revealed three planets orbiting the star HR 8799, with projected separations of 24, 38, and 68 astronomical units. Multi-epoch data show counter-clockwise orbital motion for all three imaged planets. The low luminosity of the companions and the estimated age of the system imply planetary masses between 5 and 13 times that of Jupiter. This system resembles a scaled-up version of the outer portion of our Solar System.

Looks like the HR 8799 system would be unstable unless the planets are far lower mass than believed (unlikely), or in resonance.

Stability of the directly imaged multiplanet system HR 8799: resonance and masses
http://arxiv.org/abs/0812.0011

Abstract wrote:

A new era of directly imaged extrasolar planets has produced a three-planet system (Marois et al. 2008), where the masses of the planets have been estimated by untested cooling models. We point out that the nominal circular, face-on orbits of the planets lead to a dynamical instability in ~1e5 yr, a factor of at least 100 shorter than the estimated age of the star. Relaxing the face-on assumption, but still requiring circular orbits while fitting the observed positions, makes the problem even worse. Keeping the nominal orbits, but reducing the planetary masses, allows stability only for unreasonably small (<~ 2 MJup) planetary masses. A suite of numerical integrations shows the system can only survive until now if the inner two planets have a 2:1 commensurability between their periods, avoiding close encounters with each other through this resonance. This resonance implies the inner planet is eccentric (e>0.04) and that its current velocity is smaller than the nominal circular orbit, which can be confirmed with several more years of observations. That the resonance has lasted until now, in spite of the perturbations of the outer planet, leads to a limit <~10 MJup on the masses of the outer two planets. This constraint rules out certain versions of the core accretion hypothesis, and favors hot-start cooling models. If the outer two planets are also engaged in a 2:1 mean-motion resonance, which is consistent with the current data, the system could last until now even if the planets have masses of ~20 MJup.

A 1:2:4 resonance? Somewhat like the Io/Europa/Ganymede system, but scaled up (lots)...

Newscientist reports that the outermost planet has been detected in 10-year-old HST data.


http://www.newscientist.com/article/mg20126934.400-exoplanet-spotted-in-hubble-archive.html

Well that should help further constrain the orbits, which is good. As to the matter of other planets lurking in the archives, I wonder if the putative planet around Vega's been spotted already...