Multiplanet system imaged at HR 8799

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 6th February 2009, 10:42 pm

From http://www.tat.physik.uni-tuebingen.de/~fgp/Conf09/abstractbooklet.pdf

A dynamical analysis of the multiple planetary system of HR 8799

Abstract wrote:We perform a dynamical analysis of available observations gathered during imaging campaigns by Marois et al. (2008). The preliminary orbital solutions of this three-planet system involving massive objects of 10 Jupiter-masses each lead to strongly unstable configurations. Although the semimajor axes are large (about of 24, 36 and 68 AU, respectively), the planets are heavily interacting and their orbits are located in a zone spanned by numerous low-order mean motion resonances. Constraining the initial conditions by the available imaging observations and the requirement of dynamical stability (the Copernican Principle), we search for the long-term stable configurations, living at least for a time comparable with the parent star life-time (100 Myr). We also test a hypothesis of yet undetected fourth planet that could be hidden in the coronagraph images and that could stabilize the whole system.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 19th February 2009, 10:12 pm

Here's the paper about the HST 1998 detection.

HST/NICMOS detection of HR 8799 b in 1998
http://arxiv.org/abs/0902.3247

Abstract wrote:Three planets have been directly imaged around the young star HR 8799. The planets are 5-13 Mjup and orbit the star at projected separations of 24-68 AU. While the initial detection occurred in 2007, two of the planets were recovered in a re-analysis of data obtained in 2004. Here we present a detection of the furthest planet of that system, HR 8799 b, in archival HST/NICMOS data from 1998. The detection was made using the locally-optimized combination of images algorithm to construct, from a large set of HST/NICMOS images of different stars taken from the archive, an optimized reference point-spread function image used to subtract the light of the primary star from the images of HR 8799. This new approach improves the sensitivity to planets at small separations by a factor of ~10 compared to traditional roll deconvolution. The new detection provides an astrometry point 10 years before the most recent observations, and is consistent with a Keplerian circular orbit with a~70 AU and low orbital inclination. The new photometry point, in the F160W filter, is in good agreement with an atmosphere model with intermediate clouds and vertical stratification, and thus suggests the presence of significant water absorption in the planet's atmosphere. The success of the new approach used here highlights a path for the search and characterization of exoplanets with future space telescopes, such as the James Webb Space Telescope or a Terrestrial Planet Finder.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 11th March 2009, 8:07 pm

Looks like the planet was also imaged in 2002.

H band Image of a Planetary Companion around HR 8799 in 2002
http://arxiv.org/abs/0903.1919

Abstract wrote:The discovery of three planetary companions around HR 8799 (Marois et al. 2008) marked a significant epoch in direct imaging of extrasolar planets. Given the importance of this system, we re-analyzed H band images of HR 8799 obtained with the Subaru 36-elements adaptive optics (AO) in July 2002. The low-order AO imaging combined with the classical PSF-subtraction methods even revealed the extrasolar planet, HR 8799b. Our observations in 2002 confirmed that it has been orbiting HR 8799 in a counter-clockwise direction. The flux of HR 8799b was consistent with those in the later epochs within the uncertainty of 0.25 mag, further supporting the planetary mass estimate by Marois et al. (2008).

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 12th March 2009, 4:54 pm

Well things are starting to pop up out of the archives aren't they? HR 8799b, Beta Pictoris b...

A for archive, A for A-type star???
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 27th April 2009, 8:10 pm

This paper contemplates the hypothesis that the HR 8799 system is indeed ultimately unstable.

Is the HR 8799 extrasolar system destined for planetary scattering?
http://arxiv.org/abs/0904.4106

Abstract wrote:The recent discovery of a three-planet extrasolar system of HR 8799 by Marois et al. is a breakthrough in the field of the direct imaging. This great achievement raises questions on the formation and dynamical stability of the HR 8799 system, because Keplerian fits to astrometric data are strongly unstable during ~0.2Myr. We search for stable, self-consistent N-body orbits with the so called GAMP method that incorporates stability constraints into the optimization algorithm. Our searches reveal only small regions of stable motions in the phase space of three-planet, coplanar configurations. Most likely, if the planetary masses are in 10-Jupiter-mass range, they may be stable only if the planets are involved in two- or three-body mean motion resonances (MMRs). We found that 80% systems found by GAMP that survived 30Myr backwards integrations, eventually become unstable after 100Myr. It could mean that the HR 8799 system undergo a phase of planet-planet scattering. We test a hypothesis that the less certain detection of the innermost object is due to a blending effect. In such a case, two-planet best-fit systems are mostly stable, on quasi-circular orbits and close to the 5:2 MMR, resembling the Jupiter-Saturn pair.




This paper investigates the possibility of more companions to HR 8799.


A Search for Wide Companions to the Extrasolar Planetary System HR 8799
http://arxiv.org/abs/0904.3936
Abstract wrote:The extrasolar planetary system around HR 8799 is the first multiplanet system ever imaged. It is also, by a wide margin, the highest mass system with >27 Jupiters of planetary mass past 25 AU. This is a remarkable system with no analogue with any other known planetary system. In the first part of this paper we investigate the nature of two faint objects imaged near the system. These objects are considerably fainter (H=20.4, and 21.6 mag) and more distant (projected separations of 612, and 534 AU) than the three known planetary companions b, c, and d (68-24 AU). It is possible that these two objects could be lower mass planets (of mass ~5 and ~3 Jupiters) that have been scattered to wider orbits. We make the first direct comparison of newly reduced archival Gemini adaptive optics images to archival HST/NICMOS images. With nearly a decade between these epochs we can accurately assess the proper motion nature of each candidate companion. We find that both objects are unbound to HR 8799 and are background. We estimate that HR 8799 has no companions of H<22 from ~5-15 arcsec. Any scattered giant planets in the HR 8799 system are >600 AU or less than 3 Jupiters in mass. In the second part of this paper we carry out a search for wider common proper motion objects. While we identify no bound companions to HR 8799, our search yields 16 objects within 1 degree in the NOMAD catalog and POSS DSS images with similar (+/-20 mas/yr) proper motions to HR 8799, three of which warrant follow-up observations.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 29th May 2009, 8:40 am

Inner asteroid belt at 10 AU reported here.

A possible architecture of the planetary system HR 8799

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 29th May 2009, 1:12 pm

Starting to look like ye olde familiare Sol-system type planetary system architecture, but on a much larger scale: gas giants in wide, low eccentricity orbits with inner and outer planetesimal belts.

Wonder if there are any terrestrials in the inner system.
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 29th May 2009, 1:51 pm

Would be terribly difficult to detect terrestrial planets. For now, direct imaging of them would be out of the question, from what it seems, detected the innermost gas planet was hard enough.

Radial velocity is out of the question as well with a near face-on inclination providing a low signal, and and a heavily jittery surface to drown it out.

Could astrometry be the key?

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 29th May 2009, 2:28 pm

Star's quite massive and far away. Quick back-of-the-envelope calculation suggests the wobble would be far too small to measure for Earth mass planets.
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 29th May 2009, 4:35 pm

Far too small to measure for what? Current technology? Or SIM (and/or its derivatives)? or... ?

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 29th May 2009, 5:22 pm

Considering an Earth-mass planet in the HZ (at roughly 2.2 AU)

Star mass is 1.5 solar masses, so radius of the reflex orbit = m/(M+m) * d is 660 km. For reference the radius of the star is 930,000 km.

Since the star is located at a distance of 39 parsecs, the full amplitude of the astrometric wobble is 0.2 microarcseconds...
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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 16th September 2009, 2:07 pm

More on the HR 8799 debris disc. Three components: an inner warm belt at 6-15 AU, an outer disc at 90-300 AU, and a halo at 300-1000 AU. This halo suggests the outer parts of the disc are dynamically active. A similar phenomenon is observed at Vega.

Two papers on the formation of the HR 8799 planets... conclusion is that it is probably gravitational instability.
The Runts of the Litter: Why planets formed through gravitational instability can only be failed binary stars
The Formation Mechanism of Gas Giants on Wide Orbits

Amusingly enough given the title of the first, the second one contains the following...
However, several lines of observational evidence show that HR 8799 and Fomalhaut are not simply binary or multiple stars with high mass ratios:
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 6th October 2009, 8:58 pm

Pre-Discovery 2007 Image of the HR 8799 Planetary System
http://arxiv.org/abs/0910.0915

Abstract wrote:We present a pre-discovery H-band image of the HR 8799 planetary system that reveals all three planets in August 2007. The data were obtained with the Keck adaptive optics system, using angular differential imaging and a coronagraph. We confirm the physical association of all three planets, including HR 8799d, which had only been detected in 2008 images taken two months apart, and whose association with HR 8799 was least secure until now. We confirm that the planets are 2-3 mag fainter than field brown dwarfs of comparable near-infrared colors. We note that similar under-luminosity is characteristic of young substellar objects at the L/T spectral type transition, and is likely due to enhanced dust content and non-equilibrium CO/CH_4 chemistry in their atmospheres. Finally, we place an upper limit of 18 mag per square arc second on the >120 AU H-band dust-scattered light from the HR 8799 debris disk. The upper limit on the integrated scattered light flux is 1e-4 times the photospheric level, 24 times fainter than the debris ring around HR 4796A.

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 7th October 2009, 3:56 pm

That's going to have implications for the stability calculations: one of the suggestions for ensuring the system is stable over the age of the star is that HR 8799d is not associated with the system/spurious detection. That doesn't work any more...
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Re: Multiplanet system imaged at HR 8799

Post by Stalker on 9th October 2009, 1:25 am

I assume that the hypothesis of brown dwarfs for planets c and d is moved aside. I think that such a young brown dwarf would be of spectral type M, not L/T
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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 9th October 2009, 5:38 pm

Well it depends on the mass of the brown dwarf: at the low end of the mass range they cool quite quickly (especially since such objects do not fuse lithium). According to this comparison, various models allow for quite high masses.

On the other hand the configuration of the system (a non-hierarchical system with low-eccentricity orbits, with inner and outer debris belts) argues against the brown dwarf classification, even if some of these objects are in the deuterium-fusion regime. There are several discoveries which suggest the high mass tail of the planetary distribution includes objects that fuse deuterium at some point in their life cycle, while the low-mass tail of the stellar (brown dwarf) distribution includes objects which do not undergo internal fusion at all.
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 4th November 2009, 6:14 pm

Spitzer observations of the disk at HR 8799. Apparently it's "a bit of a mess."
http://www.jpl.nasa.gov/news/features.cfm?feature=2349

A large halo is observed a little over 2000 AU. Probably scattered from further in by those planets.


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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 4th November 2009, 6:40 pm

More details of this are in the arXiv paper I linked upthread (0909.2687). Nice to see a press release for the architecture of a planetary system.
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Re: Multiplanet system imaged at HR 8799

Post by Stalker on 5th November 2009, 1:56 am

Looks like the Oort Cloud?
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 5th November 2009, 9:48 am

Probably on a much smaller and denser scale. I'm not entirely sure about this, so correct me if I'm wrong. The Oort cloud is expected to extend out several tens of thousands of AU. While HR 8799 may have such an Oort cloud, it's probably far too faint to detect, and what we are seeing is the protoplanetary disk that has been scattered outward. Perhaps given sufficient time, the planets will scatter much of what we see further out, adding to HR 8799's Oort cloud and subtracting from the visible disk.

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Re: Multiplanet system imaged at HR 8799

Post by Stalker on 5th November 2009, 1:50 pm

Sirius_Alpha wrote:Probably on a much smaller and denser scale. I'm not entirely sure about this, so correct me if I'm wrong. The Oort cloud is expected to extend out several tens of thousands of AU. While HR 8799 may have such an Oort cloud, it's probably far too faint to detect, and what we are seeing is the protoplanetary disk that has been scattered outward. Perhaps given sufficient time, the planets will scatter much of what we see further out, adding to HR 8799's Oort cloud and subtracting from the visible disk.

this looks like therefore rather the scattered disc (Éris and co.) and in the cloud of Hills (Sedna...)
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 2nd November 2010, 3:16 pm

Embargoed


Last edited by Sirius_Alpha on 2nd November 2010, 9:35 pm; edited 1 time in total

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Re: Multiplanet system imaged at HR 8799

Post by Edasich on 2nd November 2010, 4:16 pm

Planet counter does not work so well. Who knows how much "hidden" planets Schneider is hiding us? *lol* Laughing
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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 2nd November 2010, 4:24 pm

This is under embargo. The relevant source was briefly available but was later removed. EPE probably updated during the time this was still online.
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Re: Multiplanet system imaged at HR 8799

Post by Edasich on 2nd November 2010, 4:30 pm

Uhmm... tricky thing if we're dealing with embargo Neutral
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