Multiplanet system imaged at HR 8799

> The HR 8799 photometry is much nearer to visible, with wavelengths on the order of 2 - 3 µm. I'm having some difficulty finding images of Saturn in the wavelengths that the HR 8799 planets were imaged in, so even if ignore the IR luminosity contrast between Saturn and the HR 8799 planets, it still isn't clear what contribution the rings would have.

I found this:

hogewash.files.wordpress.com/2012/12/saturn_in_ir.jpg

"This image was assembled from data collected in near-infrared wavelengths of light by the Cassini spacecraft. Blue indicates sunlight reflected at a wavelength of 2 µm, green to indicate sunlight reflected at 3 µm, and red to indicate thermal emission from the planet at 5 µm. Saturn’s rings reflect sunlight at 2 µm, but not at 3 or 5 µm, so they appear deep blue. Saturn’s high altitude haze reflects sunlight at both 2 and 3 µm, and so it appears green to blue-green. The heat emissions from the interior of Saturn are only seen at the 5 µm wavelength in the data; they appear red."

A Combined Subaru/VLT/MMT 1--5 Micron Study of Planets Orbiting HR 8799: Implications for Atmospheric Properties, Masses, and Formation
http://arxiv.org/abs/1101.1973

See section 3.1.2:

Quote :

To summarize, all three HR 8799 planets – especially HR 8799 b – have near-IR colors that cannot be easily understood within the field L/T dwarf sequence. They are consistently red and underluminous at Y and J, indicating that the 1–1.25 µm portion of their SEDs are suppressed in flux. The HR 8799 planets also lie well outside the loci of standard atmosphere models used to interpret the physical properties of L/T dwarfs. Thus, the HR 8799 planet atmospheres are not simply ’scaled down’ (in mass) versions of the atmospheres of field brown dwarfs defining the L/T dwarf sequence.

Not sure how that fits in with your rings idea?

Lazarus wrote:

Not sure how that fits in with your rings idea?

To me it looks like all papers so far say "we have hard time interpreting the spectra" and "we estimated planet sizes/masses based on observed luminosity and they do not make sense - they are too massive to be stable in these orbits".

Also, these are one of the very few giant planets we know today which are far away from their star - much farther that the frost line.

That, and looking at Saturn's photos, made me say "aha, they might be looking at significantly more than only *planet's* emissions"!

I by no means claim that I'm sure the rings are there. It's just an idea. I am not qualifed enough, by far, to test it.

What are the possible reflection spectra of such rings? Are they icy? Rocky?
How large they can be? (It's unlikely our Saturn has the largest possible rings)
What if there are "super-Enceladus" or "super-Io" satellites throwing humongous amounts of ice, sulfur etc particles in volcanic plumes up and into rings? Our Io and Enceladus are ~4 billion years old and they still do it.

Quote :

To me it looks like all papers so far say "we have hard time interpreting the spectra" and "we estimated planet sizes/masses based on observed luminosity and they do not make sense - they are too massive to be stable in these orbits".

A major issue is the uncertainty in the age of the system. We've got models that basically say that a planet of M mass and A age at D distance should have appear a certain brightness. We compare that to what we observe and our estimates of the age and distance to crank out a mass. But there's considerable uncertainty over the stellar age. If HR 8799 is older, like say 1 Gyr, then the planets need to be much more massive to explain their luminosity. This cases the instability issues. However if, as some have suggested, the star is 30 Myr old or so, then the masses go down and the system stabilises.

I do understand your idea about the rings and it's not a bad idea, though. We just don't know the age of the system well enough to confidently say what the masses are (but I do think the consensus recently has converged on the 30 Myr age and lower masses for the planets).

Heading for disaster maybe?

Effects of a planetesimal debris disk on stability scenarios for the extrasolar planetary system HR 8799
http://arxiv.org/abs/1301.2004

An exterior debris disk of about the mass of Neptune would disrupt any stabilising resonance on a timescale of 2–6 Myr.

HR 8799 f
http://exoplanet.eu/catalog/hr_8799_f/

Mass: 7 M_J

Sirius_Alpha wrote:

HR 8799 f
http://exoplanet.eu/catalog/hr_8799_f/

Mass: 7 M_J

I just looked rapidly at the paper, i cant find any reference to a new planet.

Seriously, how many superjovians does one system need?!

I suppose the system is younger than 30 milions years and massess of planets are in range 0.3-2 jupiter mass

This system is such a freak of nature...

Disappeared again.

Multiple mean motion resonances in the HR 8799 planetary system
http://arxiv.org/abs/1308.6462

Quote :

HR 8799 is a nearby star located at 39.4 pc and hosting at least four ~10 Jupiter-mass giant planets in wide orbits between ~15 au and ~70 au with orbital periods between 50 yr and ~500 yr. The formation of all HR 8799 planets in situ is a challenge for the planet formation theory. A key for this question is the current dynamical state of the system, which is uncertain due to limited astrocentric data covering small orbital arcs. We construct a self-consistent orbital model of the HR 8799 system assuming a fast common migration of the planets that have been formed in wider orbits. Our results suggest that HR 8799 planets are involved in a very robust, double Laplace mean motion resonance, 1e:2d:4c:8b MMR. This architecture of quasi-circular orbits is coplanar with the stellar equator and inclined by ~25 deg to the sky plane. Our new model perfectly matches current astrometry and mass estimates from astrophysical evolution models of substellar objects. The multiple MMR system is rigorously stable for time not shorter than the age of the star ~160 Myr, and survives for at least 1 Gyr unless significant perturbations to the N-body dynamics are present. We also predict four well bounded configurations in the parameter space involving the fifth, yet unseen hypothetical innermost planet. This a few Jupiter-mass giant planet may orbit the star at ~9.7 au, or ~7.5 au distance. Such orbits extend the MMR chain to triple Laplace resonance 1f:2e:4d:8c:16b MMR or to 1f:3e:6d:12c:24b MMR, respectively. Our findings may establish strong border conditions for the system formation and its early history.

So, HR 8799 f is from there.

There's nothing quite like the EPE dealing with hypothetical planets.

In other news, can we all just take a moment to look at how amazing figure 4 is?



It's definitely very interesting to see a system with a Laplace+1 resonance at work, even as only brief arcs on their ~50:100:200:400-year orbits.

Quote :

Moreover, a close inspection of panels in Fig. 6 for planets b, c, and d reveals that the dynamic model fits the measurements even better than the first terms of the Gibbs functions, particularly at the earliest HST images. This is suggestive for a noticeable deviations of the N-body orbits from their Keplerian first and second order approximations.

So even over the relatively short timespan (relative to the orbital periods) of the observations, non-Keplerian effects are already potentially visible? If so, that's pretty impressive.

EPE is listing 941 planets but I can't find anything. Is perhaps the planet count related to "HR 8799 f"?

I couldn't figure it out either. Maybe PH1 is the new planet? I already had all the planets in my notes that they listed were updated on 30 Aug 2013.

What a mess these recent EPE updates...  

Deep Thermal Infrared Imaging of HR 8799 bcde: New Atmospheric Constraints and Limits on a Fifth Planet
http://arxiv.org/abs/1409.5134

No evidence for an HR 8799 f yet.

Ingraham et al. "Gemini Planet Imager Spectroscopy of the HR 8799 planets c and d"
http://arxiv.org/abs/1409.5456

Among other things, some evidence that d may be warmer than c. (Given these planets are dominated by internal heating, planet d lying closer to the star is probably not much to do with it)

Reconnaissance of the HR 8799 Exosolar System II: Astrometry and Orbital Motion
http://arxiv.org/abs/1409.6388

Quote :

We present an analysis of the orbital motion of the four sub-stellar objects orbiting HR8799. Our study relies on the published astrometric history of this system augmented with an epoch obtained with the Project 1640 coronagraph + Integral Field Spectrograph (IFS) installed at the Palomar Hale telescope. We first focus on the intricacies associated with astrometric estimation using the combination of an Extreme Adaptive Optics system (PALM-3000), a coronagraph and an IFS. We introduce two new algorithms. The first one retrieves the stellar focal plane position when the star is occulted by a coronagraphic stop. The second one yields precise astrometric and spectro-photometric estimates of faint point sources even when they are initially buried in the speckle noise. The second part of our paper is devoted to studying orbital motion in this system. In order to complement the orbital architectures discussed in the literature, we determine an ensemble of likely Keplerian orbits for HR8799bcde, using a Bayesian analysis with maximally vague priors regarding the overall configuration of the system. While the astrometric history is currently too scarce to formally rule out coplanarity, HR8799d appears to be misaligned with respect to the most likely planes of HR8799bce orbits. This misalignment is sufficient to question the strictly coplanar assumption made by various authors when identifying a Laplace resonance as a potential architecture. Finally, we establish a high likelihood that HR8799de have dynamical masses below 13 M_Jup using a loose dynamical survival argument based on geometric close encounters. We illustrate how future dynamical analyses will further constrain dynamical masses in the entire system.

Another investigation of HR 8799 astrometry:

Maire et al. "The LEECH Exoplanet Imaging Survey. Further constraints on the planet architecture of the HR 8799 system"
http://arxiv.org/abs/1412.6989

Seems to favour the 1:2:4:8 resonance, and puts limits on planets near the 2:1 and 3:1 resonances with the innermost planet e.

http://www.gemini.edu/node/12314

THE GEMINI PLANET IMAGER PRODUCES STUNNING OBSERVATIONS IN ITS FIRST YEAR

Press release with images of HR 8799 and HR 4796A

http://www.astrobio.net/topic/deep-space/new-planets/astronomers-probe-inner-region-of-young-star-and-its-planets/

Observations of a Survey called LEECH by the LBT (Large Binocular Telescope)

SPHERE results for the HR 8799 planets

Zurlo et al. "First light of the VLT planet finder SPHERE. III. New spectrophotometry and astrometry of the HR8799 exoplanetary system"
http://arxiv.org/abs/1511.04083

There are generally two choices made for astrometric orbit fitting for HR 8799 - either circular + non-coplanar, or eccentric + coplanar. This paper goes with the former option.

Bonnefoy et al. "First light of the VLT planet finder SPHERE. IV. Physical and chemical properties of the planets around HR8799"
http://arxiv.org/abs/1511.04082