Spectroscopy of the HR 8799 system

VLT Captures First Direct Spectrum of an Exoplanet

http://www.eso.org/public/news/eso1002/

(assuming HR8799c is an exoplanet)

A link to the paper is provided at the end of the press release.

Moving further into the era of exoplanetary characterisation. This system is also valuable as there are multiple, presumably roughly coeval planets: wonder if there are going to be significant differences in the spectra. Also good to get data on planets in a different range of irradiation than the hot Jupiters which have been the best characterised planets up to now.

(I would think it is rather difficult to argue against HR 8799 c being a planet given the configuration of the entire system.)

Lazarus wrote:

(I would think it is rather difficult to argue against HR 8799 c being a planet given the configuration of the entire system.)

Yes, quite true. Just teasing a little
A common origin based on a protoplanetary disc is more likely.

Less methane and more carbon monoxide than expected?

Here's the paper.

Spatially resolved spectroscopy of the exoplanet HR 8799 c
http://arxiv.org/abs/1001.2017

Abstract wrote:

HR 8799 is a multi-planet system detected in direct imaging, with three companions known so far. Here, we present spatially resolved VLT/NACO 3.88--4.10 micron spectroscopy of the middle planet, HR 8799 c, which has an estimated mass of ~10 Mjup, temperature of ~1100 K and projected separation of 38 AU. The spectrum shows some differences in the continuum from existing theoretical models, particularly longwards of 4 microns, implying that detailed cloud structure or non-equilibrium conditions may play an important role in the physics of young exoplanetary atmospheres.

Now this is interesting guys.
By studying a triple planetary system that resembles a scaled-up
version of our own Sun’s family of planets, astronomers have been able
to obtain the first direct spectrum — the “chemical fingerprint” — of a planet orbiting a distant star ,
thus bringing new insights into the planet's formation and composition.
The result represents a milestone in the search for life elsewhere in
the Universe.

Already discussed in this thread.

Edit (Aug 20, 2010): Threads merged.

ops...anyway,that one was on the exoplanetary news and discoveries,
this one is for discussing the issue scientifically.

Near-Infrared Spectroscopy of the Extrasolar Planet HR 8799 b
http://arxiv.org/abs/1008.4582

Abstract wrote:

We present 2.12-2.23 um high contrast integral field spectroscopy of the extrasolar planet HR 8799 b. Our observations were obtained with OSIRIS on the Keck II telescope and sample the 2.2 um CH4 feature, which is useful for spectral classification and as a temperature diagnostic for ultracool objects. The spectrum of HR 8799 b is relatively featureless, with little or no methane absorption, and does not exhibit the strong CH4 seen in T dwarfs of similar absolute magnitudes. Overall, we find that HR 8799 b has a spectral type consistent with L5-T2, although its SED is atypical compared to most field objects. We fit the 2.2 um spectrum and the infrared SED using the Hubeny & Burrows, Burrows et al., and Ames-Dusty model atmosphere grids, which incorporate nonequilibrium chemistry, non-solar metallicities, and clear and cloudy variants. No models agree with all of the data, but those with intermediate clouds produce significantly better fits. The largest discrepancy occurs in the J-band, which is highly suppressed in HR 8799 b. The best-fitting effective temperatures range from 1300-1700 K with radii between ~0.3-0.5 RJup. These values are inconsistent with evolutionary model-derived values of 800-900 K and 1.1-1.3 RJup based on the luminosity of HR 8799 b and the age of HR 8799, a discrepancy that probably results from imperfect atmospheric models or the limited range of physical parameters covered by the models. The low temperature inferred from evolutionary models indicates that HR 8799 b is ~400 K cooler than field L/T transition objects, providing further evidence that the L/T transition is gravity-dependent. With an unusually dusty photosphere, an exceptionally low luminosity for its spectral type, and hints of extreme secondary physical parameters, HR 8799 b appears to be unlike any class of field brown dwarf currently known.

Well that is weird, definitely poking some holes into theoretical models of such objects, and given the masses are determined from these models, it raises the question of just how far they can be trusted.

(Incidentally it might be worth merging this with the two threads on the spectrum of HR 8799 c?)

Lazarus wrote:

(Incidentally it might be worth merging this with the two threads on the spectrum of HR 8799 c?)

That's a great idea

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

Quote :

We present new 1--1.25 $\mu m$ (z and J band) Subaru/IRCS and 2 $\mu m$ (K band) VLT/NaCo data for HR 8799 and a rereduction of the 3--5 $\mu m$ MMT/Clio data first presented by citet{Hinz2010}. Our VLT/NaCo data yields a detection of a fourth planet at a projected separation of $\sim$ 15 AU -- "HR 8799e". We also report new, albeit weak detections of HR 8799b at 1.03 $\mu m$ and 3.3 $\mu m$. Empirical comparisons to field brown dwarfs show that at least HR 8799b and HR8799c, and possibly HR 8799d, have near-to-mid IR colors/magnitudes significantly discrepant from the L/T dwarf sequence. Standard cloud deck atmosphere models appropriate for brown dwarfs provide only (marginally) statistically meaningful fits to HR 8799b and c for unphysically small radii. Models with thicker cloud layers not present in brown dwarfs reproduce the planets' SEDs far more accurately and without the need for rescaling the planets' radii. Our preliminary modeling suggests that HR 8799b has log(g) = 4--4.5, T$_{eff}$ = 900K, while HR 8799c, d, and (by inference) e have log(g) = 4--4.5, T$_{eff}$ = 1000--1200K. Combining results from planet evolution models and new dynamical stability limits implies that the masses of HR 8799b, c, d, and e are 6--7 M$_{J}$, 7--10 M$_{J}$, 7--10 M$_{J}$ and 7--10 M$_{J}$. 'Patchy" cloud prescriptions may provide even better fits to the data and may lower the estimated surface gravities and masses. Finally, contrary to some recent claims, forming the HR 8799 planets by core accretion is still plausible, although such systems are likely rare.

Best of all, it was possible to confirm the fourth planet. Keck and VLT telescopes is the best telescops for photographing.

Wonder if the HR 8799 planets are sufficiently different from brown dwarfs to warrant a new spectral type (Y?). The bit about core accretion is interesting, wouldn't be surprised if this debate goes on for a while...

More modelling, seems that thick clouds (thicker than those on typical brown dwarfs) might be to blame for the weird spectra.

Furthermore the spectral type sequence L/T may not be so useful for planets...

Quote :

Therefore, our analysis predicts that the near-IR SEDs of many soon-to-be imaged planets will not track the L/T dwarf sequence. Rather, like the HR 8799 planets and 2M1207b, they will track a distinguishable “planet locus” following an extension of the L dwarf sequence, diverging from the L/T dwarf sequence for field brown dwarfs at the L/T transition, and extending to systematically fainter and redder color-magnitude positions.

Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b
http://arxiv.org/abs/1103.3895

Quote :

Using the integral field spectrograph OSIRIS, on the Keck II telescope, broad near-infrared H and K-band spectra of the young exoplanet HR8799b have been obtained. In addition, six new narrow-band photometric measurements have been taken across the H and K bands. These data are combined with previously published photometry for an analysis of the planet's atmospheric properties. Thick photospheric dust cloud opacity is invoked to explain the planet's red near-IR colors and relatively smooth near-IR spectrum. Strong water absorption is detected, indicating a Hydrogen-rich atmosphere. Only weak CH4 absorption is detected at K band, indicating efficient vertical mixing and a disequilibrium CO/CH4 ratio at photospheric depths. The H-band spectrum has a distinct triangular shape consistent with low surface gravity. New giant planet atmosphere models are compared to these data with best fitting bulk parameters, Teff = 1100K +- 100 and log(g) = 3.5 +-0.5 (for solar composition). Given the observed luminosity, log(Lobs/Lsun) ~ -5.1, these values correspond to a radius of 0.75 Rjup (+0.17, -0.12) and mass ~ 0.72 Mjup (+2.6,-0.6) -- strikingly inconsistent with interior/evolution models. Enhanced metallicity (up to ~ 10 times that of the Sun) along with thick clouds and non-equilibrium chemistry are likely required to reproduce the complete ensemble of spectroscopic and photometric data and the low effective temperatures (< 1000K) required by the evolution models.

Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy
http://arxiv.org/abs/1303.2627

Quote :

We obtained spectra, in the wavelength range \lambda = 995 - 1769 nm, of all four known planets orbiting the star HR 8799. Using the suite of instrumentation known as Project 1640 on the Palomar 5-m Hale Telescope, we acquired data at two epochs. This allowed for multiple imaging detections of the companions and multiple extractions of low-resolution (R ~ 35) spectra. Data reduction employed two different methods of speckle suppression and spectrum extraction, both yielding results that agree. The spectra do not directly correspond to those of any known objects, although similarities with L and T-dwarfs are present, as well as some characteristics similar to planets such as Saturn. We tentatively identify the presence of CH_4 along with NH_3 and/or C_2H_2, and possibly CO_2 or HCN in varying amounts in each component of the system. Other studies suggested red colors for these faint companions, and our data confirm those observations. Cloudy models, based on previous photometric observations, may provide the best explanation for the new data presented here. Notable in our data is that these presumably co-eval objects of similar luminosity have significantly different spectra; the diversity of planets may be greater than previously thought. The techniques and methods employed in this paper represent a new capability to observe and rapidly characterize exoplanetary systems in a routine manner over a broad range of planet masses and separations. These are the first simultaneous spectroscopic observations of multiple planets in a planetary system other than our own.

Quote :

Notable in our data is that these presumably co-eval objects of similar luminosity have significantly different spectra; the diversity of planets may be greater than previously thought.

Makes you wonder how well we should expect the class I-V system of Sudarsky et al. (2000) to hold up, once giant planets in the relevant distance ranges are observed.

I expect surprises.

The C/O ratio has been determined for HR 8799 c. The atmospheric C/O is consistent with core accretion formation.

Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
http://arxiv.org/abs/1303.3280

First optical interferometric detection of an exoplanet, HR 8799 e

GRAVITY instrument breaks new ground in exoplanet imaging
https://www.eso.org/public/news/eso1905/

Quote :

This is the first time that optical interferometry has been used to reveal details of an exoplanet, and the new technique furnished an exquisitely detailed spectrum of unprecedented quality — ten times more detailed than earlier observations. The team’s measurements were able to reveal the composition of HR8799e’s atmosphere  — which contained some surprises.

“Our analysis showed that HR8799e has an atmosphere containing far more carbon monoxide than methane — something not expected from equilibrium chemistry,” explains team leader Sylvestre Lacour researcher CNRS at the Observatoire de Paris - PSL and the Max Planck Institute for Extraterrestrial Physics. “We can best explain this surprising result with high vertical winds within the atmosphere preventing the carbon monoxide from reacting with hydrogen to form methane.”

The team found that the atmosphere also contains clouds of iron and silicate dust. When combined with the excess of carbon monoxide, this suggests that HR8799e’s atmosphere is engaged in an enormous and violent storm.

“Our observations suggest a ball of gas illuminated from the interior, with rays of warm light swirling through stormy patches of dark clouds,” elaborates Lacour. “Convection moves around the clouds of silicate and iron particles, which disaggregate and rain down into the interior. This paints a picture of a dynamic atmosphere of a giant exoplanet at birth, undergoing complex physical and chemical processes.”

From the paper's abstract:

Quote :

The GRAVITY astrometric measurement disfavors perfectly coplanar stable orbital solutions. A small adjustment of a few degrees to
the orbital inclination of HR 8799 e can resolve the tension, implying that the orbits are close to, but not strictly coplanar. The spectrum, with a signal-to-noise ratio of ≈5 per spectral channel, is compatible with a late-type L brown dwarf. Using Exo-REM synthetic spectra, we derive a temperature of 1150 ± 50 K and a surface gravity of 10^4.3±0.3cm s2. This corresponds to a radius of 1.17+0.13−0.11 RJup and a mass of 10+7−4 MJup, which is an independent confirmation of mass estimates from evolutionary models. Our results demonstrate the power of interferometry for the direct detection and spectroscopic study of exoplanets at close angular separations from their stars.