Multiplanet system imaged at HR 8799

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Re: Multiplanet system imaged at HR 8799

Post by exofever on 3rd November 2010, 9:24 am

Sirius_Alpha wrote: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.

Nice improvement of the Angular Differential Imaging. The old image does not look fit for additional discoveries.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 22nd November 2010, 9:10 pm

Images of a fourth planet orbiting HR 8799
http://arxiv.org/abs/1011.4918

High-contrast near-infrared imaging of the nearby star HR 8799 has shown three giant planets. Such images were possible due to the wide orbits (> 25 AU) and youth (< 100 Myr) of the imaged planets, which are still hot and bright as they radiate away gravitational energy acquired during their formation. A major area of contention in the extrasolar planet community is whether outer planets (> 10 AU) more massive than Jupiter form via one-step gravitational instabilities or, rather, via a two-step process involving accretion of a core followed by accumulation of a massive outer envelope composed primarily of hydrogen and helium. Here we report the presence of a fourth planet, interior to and about the same mass as the other three. The system, with this additional planet, represents a challenge for current planet formation models as none of them can explain the in situ formation of all four planets. With its four young giant planets and known cold/warm debris belts, the HR 8799 planetary system is a unique laboratory to study the formation and evolution of giant planets at wide > 10 AU separations.


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Re: Multiplanet system imaged at HR 8799

Post by Borislav on 23rd November 2010, 5:22 am

Beautiful picture Smile
The embargo is canceled?

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 23rd November 2010, 1:42 pm

Well this time the authors have definitely uploaded to a public website, rather than the case where an embargoed abstract was accidentally left in a publically-visible state.

Definitely nice to see this one: closer-in planets complete their orbits faster, which will certainly help in refining the fairly uncertain orbital parameters.
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 6th July 2011, 9:05 pm

M-band Imaging of the HR 8799 Planetary System Using an Innovative LOCI-based Background Subtraction Technique
http://arxiv.org/abs/1107.0967

Multi-wavelength observations/spectroscopy of exoplanetary atmospheres are the basis of the emerging exciting field of comparative exoplanetology. The HR 8799 planetary system is an ideal laboratory to study our current knowledge gap between massive field brown dwarfs and the cold 5-Gyr old Solar system planets. The HR 8799 planets have so far been imaged at J- to L-band, with only upper limits available at M-band. We present here deep high-contrast Keck II adaptive optics M-band observations that show the imaging detection of 3 of the 4 currently known HR 8799 planets. Such detections were made possible due to the development of an innovative LOCI-based background subtraction scheme that is 3 times more efficient than a classical median background subtraction for Keck II AO data, representing a gain in telescope time of up to a factor of 9. These M-band detections extend the broad band photometric coverage out to about 5 microns and provide access to the strong CO fundamental absorption band at 4.5microns. The new M-band photometry shows that the HR 8799 planets are located near the L/T-type dwarf transition, similar to what was found by other studies. We also confirm that the best atmospheric fits are consistent with low surface gravity, dusty and non-equilibrium CO/CH4 chemistry models.

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Re: Multiplanet system imaged at HR 8799

Post by jyril on 6th October 2011, 9:45 am

Astronomers Find Elusive Planets in Decade-Old Hubble Data

In a painstaking re-analysis of Hubble Space Telescope images from 1998, astronomers have found visual evidence for two extrasolar planets that went undetected back then.

Finding these hidden gems in the Hubble archive gives astronomers an invaluable time machine for comparing much earlier planet orbital motion data to more recent observations. It also demonstrates a novel approach for planet hunting in archival Hubble data.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 6th October 2011, 8:50 pm

Quite exciting. Looks like the 1:2:4 resonance is holding up. With the recent confirmation of the KOI-730 planets, I wonder if the e planet plays a part in this resonance as well.

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 8th January 2012, 4:08 am

Further suggestions for lower planetary masses at HR 8799
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 13th March 2012, 8:13 pm

Large Binocular Telescope first light images are of the HR 8799 planetary system.



First Light LBT AO Images of HR 8799 bcde at 1.65 and 3.3 Microns: New Discrepancies between Young Planets and Old Brown Dwarfs
http://arxiv.org/abs/1203.2615

As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3$ micron photometry of the innermost planet (for the first time) and put strong upper-limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 microns compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find that removing CH4 to fit the 3.3 micron photometry increases the predicted L' (3.8 microns) flux enough that it is inconsistent with observations. In an effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability.

LBT observations of the HR 8799 planetary system: First detection of HR8799e in H band
http://arxiv.org/abs/1203.2735

We have performed H and Ks band observations of the planetary system around HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES Camera. The excellent instrument performance (Strehl ratios up to 80% in H band) enabled detection the inner planet HR8799e in the H band for the first time. The H and Ks magnitudes of HR8799e are similar to those of planets c and d, with planet e slightly brighter. Therefore, HR8799e is likely slightly more massive than c and d. We also explored possible orbital configurations and their orbital stability. We confirm that the orbits of planets b, c and e are consistent with being circular and coplanar; planet d should have either an orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c. Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion resonances with c and d, while coplanar and circular orbits are allowed for a 5:2 resonance. The analysis of dynamical stability shows that the system is highly unstable or chaotic when planetary masses of about 5 MJup for b and 7 MJup for the other planets are adopted. Significant regions of dynamical stability for timescales of tens of Myr are found when adopting planetary masses of about 3.5, 5, 5, and 5 Mjup for HR 8799 b, c, d, and e respectively. These masses are below the current estimates based on the stellar age (30 Myr) and theoretical models of substellar objects.

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 14th March 2012, 7:12 pm

Still many possible orbital solutions, though given the high mutual inclinations in some of them (50 degrees between d and e in the all-circular 1:2:4:8 resonance!), some may be more plausible than others. 5:2 between d and e allows for much greater degrees of coplanarity, especially if small eccentricities are involved.
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 30th May 2012, 8:23 pm

Masses, Radii, and Cloud Properties of the HR 8799 Planets
http://arxiv.org/abs/1205.6488

The near-infrared colors of the planets directly imaged around the A star HR 8799 are much redder than most field brown dwarfs of the same effective temperature. Previous theoretical studies of these objects have concluded that the atmospheres of planets b, c, and d are unusually cloudy or have unusual cloud properties. Most studies have also found that the inferred radii of some or all of the planets disagree with expectations of standard giant planet evolution models. Here we compare the available data to the predictions of our own set of atmospheric and evolution models that have been extensively tested against observations of field L and T dwarfs, including the reddest L dwarfs. Unlike almost all previous studies we require mutually consistent choices for effective temperature, gravity, cloud properties, and planetary radius. This procedure thus yields plausible values for the masses, effective temperatures, and cloud properties of all three planets. We find that the cloud properties of the HR 8799 planets are not unusual but rather follow previously recognized trends, including a gravity dependence on the temperature of the L to T spectral transition--some reasons for which we discuss. We find the inferred mass of planet b is highly sensitive to whether or not we include the H and K band spectrum in our analysis. Solutions for planets c and d are consistent with the generally accepted constraints on the age of the primary star and orbital dynamics. We also confirm that, like in L and T dwarfs and solar system giant planets, non-equilibrium chemistry driven by atmospheric mixing is also important for these objects. Given the preponderance of data suggesting that the L to T spectral type transition is gravity dependent, we present an exploratory evolution calculation that accounts for this effect. Finally we recompute the the bolometric luminosity of all three planets.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 4th June 2012, 9:17 pm

Direct Detection and Orbit Analysis of the Exoplanets HR 8799 bcd from Archival 2005 Keck/NIRC2 Data
http://arxiv.org/abs/1206.0483

We present previously unpublished July 2005 $H$-band coronagraphic data of the young, planet-hosting star HR 8799 from the newly-released Keck/NIRC2 archive. Despite poor observing conditions, we image three of the planetary companions (HR 8799 bcd), two of them (HR 8799 bc) without advanced image processing. Comparing these data with previously published 1998-2011 astrometry and that from re-reduced October 2010 Keck data constrains the orbits of the planets. Analyzing the planets' astrometry separately, HR 8799 d's orbit is likely inclined at least 25$^\circ$ from face-on and the others may be on in inclined orbits. For semimajor axis ratios consistent with a 4:2:1 mean-motion resonance, our analysis yields precise values for HR 8799 bcd's orbital parameters and strictly constrains the planets' eccentricities to be less than 0.18--0.3. However, we find no acceptable orbital solutions with this resonance that place the planets in face-on orbits; HR 8799 d shows the largest deviation from such orbits. Moreover, few orbits make HR 8799 d coplanar with b and c, whereas dynamical stability analyses used to constrain the planets' masses typically assume coplanar and/or face-on orbits. This paper illustrates the significant science gain enabled with the release of the NIRC2 archive.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 2nd October 2012, 8:23 pm

CHARA has been used to measure the star's angular diameter, constraining its age, and thus the mass of its companions, suggesting that they are indeed planetary.
http://arxiv.org/abs/1210.0556

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 3rd October 2012, 1:30 pm

I am going to assume that the use of "Gyr" in the abstract is an error of factor 1000 because the star being substantially older than the universe is not entirely plausible Smile
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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 3rd October 2012, 3:16 pm

Yeah, I'm sure they meant Myr. Laughing

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Re: Multiplanet system imaged at HR 8799

Post by Borislav on 26th December 2012, 2:03 pm

Possible?

http://www.noao.edu/perl/abstract?2011B-0310

Abstract: Four planets have been directly imaged around HR 8799. A new analysis of our recent 2009-2010 Keck Lp-band observations shows a new candidate planet "f" (7 MJup for 30 Myr). We propose to confirm this candidate planet by observing HR 8799 with Altair/NIRI at Lp-band. The Gemini unique queue scheduling is required to perform this research given that several HR 8799 transits with decent seeing are required to confirm this candidate. If confirmed, the existence of planet f will (1) lower planet mass upper limits obtained from a system dynamical stability analysis, (2) better constraint the mass-luminosity evolutionary model predictions and (3) complicate the system formation scenario by adding an additional planet in the core accretion formation region located close (< 35 AU) to the star.

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Re: Multiplanet system imaged at HR 8799

Post by Edasich on 26th December 2012, 2:48 pm

Why not?
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Re: Multiplanet system imaged at HR 8799

Post by Stalker on 27th December 2012, 2:56 am

I dont understand, the "f" planet is transiting?

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 27th December 2012, 10:24 am

I believe they meant to imply observations of the target in the sky, not transits of the planet across the star.

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Re: Multiplanet system imaged at HR 8799

Post by Led_Zep on 30th December 2012, 5:38 pm

The AAS 221 th meeting is coming soon (06-10 january)

This abstract is listed as embarged -- Sirius Alpha
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Re: Multiplanet system imaged at HR 8799

Post by Den on 2nd January 2013, 5:34 am

Lazarus wrote:These planets are ... very massive and orbit a very young star.

*Every* giant planet in solar system has rings - and that's after 4.5 billion years of continual depletion of ring material.

Young (0.5 Gy or less) Jovians are likely to have *large* rings - after all, they recently formed by *accreting material*.

I would hazard to guess that these mass estimates are so big because they do not account for possible rings.

A similar, but even more extreme situation seems to be in Fomalhaut - we *should not be able to see Fomalhaut b at all*, no matter how massive it is - unless it has a large halo or ring of material aroung it (which it should have, as it clears out that humongous debris ring).

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 2nd January 2013, 9:16 am

Den wrote:Young (0.5 Gy or less) Jovians are likely to have *large* rings - after all, they recently formed by *accreting material*.

I would hazard to guess that these mass estimates are so big because they do not account for possible rings.
Remember we're viewing these planets in infrared. I would expect a massive ring system to be icy in composition at this distance from the star. If they were hot enough to make a significant contribution to the observed brightness of the "planet," then I would not expect them to survive long.

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Re: Multiplanet system imaged at HR 8799

Post by Den on 2nd January 2013, 12:12 pm

Quickly googled an IR image of Saturn:

enleuk.files.wordpress.com/2009/12/ir_mirsi_03oct28291.gif

As you see, the rings contribution is huge.

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Re: Multiplanet system imaged at HR 8799

Post by Sirius_Alpha on 2nd January 2013, 1:01 pm

Saturn isn't exactly a warm planet itself. It's my understanding that these giant planets around HR 8799 are cranking out orders of magnitude more IR light than Saturn. Both due to their much higher mass, and much younger age.

A much more important point, the images of Saturn you link to are more mid-infrared, with wavelengths that are pretty long. The HR 8799 photometry is much nearer to visible, with wavelengths on the order of 2 - 3 Ám. 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.


Last edited by Sirius_Alpha on 28th February 2013, 2:30 pm; edited 1 time in total (Reason for editing : Spelling)

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Re: Multiplanet system imaged at HR 8799

Post by Lazarus on 2nd January 2013, 5:52 pm

The spectrum of Fomalhaut b indicates that what we are seeing is reflected or scattered starlight, which does indeed indicate that it is probably a dust cloud - the central object (if there is one) has not yet been detected.

This does not seem to be the case for the spectra of the HR 8799 planets. As far as I am aware both HR 8799 c and HR 8799 b have had their spectra observed and there does not seem to be evidence for reflected starlight.
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