Context.
Clouds are ubiquitous in exoplanet atmospheres and they represent a challenge for the model interpretation of their spectra. When generating a large number of model spectra, complex cloud ...models often prove too costly numerically, whereas more efficient models may be overly simplified.
Aims.
We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach.
Methods.
We used our radiative transfer code petitRADTRANS for generating the spectra, which we coupled to the PyMultiNest tool. We added the effect of multiple scattering which is important for treating clouds. Two cloud model parameterizations are tested: the first incorporates the mixing and settling of condensates, the second simply parameterizes the functional form of the opacity.
Results.
In mock retrievals, using an inadequate cloud model may result in atmospheres that are more isothermal and less cloudy than the input. Applying our framework on observations of HR 8799e made with the GPI, SPHERE, and GRAVITY, we find a cloudy atmosphere governed by disequilibrium chemistry, confirming previous analyses. We retrieve that C/O = 0.60
−0.08
+0.07
. Other models have not yet produced a well constrained C/O value for this planet. The retrieved C/O values of both cloud models are consistent, while leading to different atmospheric structures: either cloudy or more isothermal and less cloudy. Fitting the observations with the self-consistent Exo-REM model leads to comparable results, without constraining C/O.
Conclusions.
With data from the most sensitive instruments, retrieval analyses of directly imaged planets are possible. The inferred C/O ratio of HR 8799e is independent of the cloud model and thus appears to be a robust. This C/O is consistent with stellar, which could indicate that the HR 8799e formed outside the CO
2
or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.
Context. Determining the chemical properties of the atmosphere of young forming gas giants might shed light on the location their formation occurred and the mechanisms involved. Aims. Our aim was to ...detect molecules in the atmosphere of the young forming companion PDS70 b by searching for atmospheric absorption features typical of substellar objects. Methods. We obtained medium-resolution (R ≈ 5075) spectra of the PDS70 planetary system with the SINFONI integral field spectrograph at the Very Large Telescope. We applied molecular mapping, based on cross-correlation with synthetic spectra, to identify signatures of molecular species in the atmosphere of the planet. Results. Although the planet emission is clearly detected when resampling the data to lower resolution, no molecular species could be identified with the cross-correlation technique. We estimated upper limits on the abundances of H2O, CO, and CH4 (log(Xmol) < −4.0, − 4.1, and − 4.9, respectively) assuming a clear atmosphere, and we explored the impact of clouds, which increase the upper limits by a factor of up to 0.7 dex. Assuming that the observations directly probe the planet’s atmosphere, we found a lack of molecular species compared to other directly imaged companions or field objects. Under the assumption that the planet atmosphere presents similar characteristics to other directly imaged planets, we conclude that a dusty environment surrounds the planet, effectively obscuring any feature generated in its atmosphere. We quantify the extinction necessary to impede the detection (AV ≈ 16−17 mag), pointing to the possibility of higher optical thickness than previously estimated from other studies. Finally, the non-detection of molecular species conflicts with atmospheric models previously proposed to describe the forming planet. Conclusions. To reveal how giant planets form a comprehensive approach that includes constraints from multiple techniques needs to be undertaken. Molecular mapping emerges as an alternative to more classical techniques like SED fitting. Specifically tuned atmospheric models are likely required to faithfully describe the atmospheres of forming protoplanets, and higher spectral resolution data may reveal molecular absorption lines despite the dusty environment enshrouding PDS70 b.
Many post-processing algorithms have been developed in order to better separate the signal of a companion from the bright light of the host star, but the effect of such algorithms on the shape of ...exoplanet spectra extracted from integral field spectrograph data is poorly understood. The resulting spectra are affected by noise that is correlated in wavelength space due to both optical and data processing effects. Within the framework of Bayesian atmospheric retrievals, we aim to understand how these correlations and other systematic effects impact the inferred physical parameters. We consider three algorithms (KLIP, PynPoint, and ANDROMEDA), optimising the choice of algorithmic parameters using a series of injection tests on archival SPHERE and GPI data of the HR 8799 system. The wavelength-dependent covariance matrix was calculated to provide a measure of instrumental and algorithmic systematics. We perform atmospheric retrievals using petit RADTRANS on optimally extracted spectra to measure how these data processing systematics influence the retrieved parameter distributions. The choice of data processing algorithm and parameters significantly impact the accuracy of retrieval results, with the mean posterior parameter bias ranging from 1 to 3
σ
from the true input parameters. Including the full covariance matrix in the likelihood improves the accuracy of the inferred parameters, and cannot be accounted for using ad hoc scaling parameters in the retrieval framework. Using the Bayesian information criterion and other statistical measures as heuristic goodness-of-fit metrics, the retrievals including the full covariance matrix are favoured when compared to using only the diagonal elements.
Context.
The Medium Resolution Spectrometer (MRS) of the Mid-Infrared Instrument (MIRI) on board the
James Webb
Space Telescope (JWST) will give access to mid-infrared (mid-IR) spectra (5–28 microns) ...while retaining spatial information. With the unparalleled sensitivity of JWST and the MIRI detectors, the MRS has the potential to revolutionise our understanding of giant exoplanet atmospheres.
Aims.
Molecular mapping is a promising detection and characterisation technique used to study the spectra of directly imaged exoplanets. We aim to examine the feasibility and application of this technique to MRS observations.
Methods.
We used the instrument simulator
MIRISIM
to create mock observations of resolved star and exoplanet systems. As an input for the simulator, we used stellar and planet parameters from literature, with the planet spectrum being modelled with the radiative transfer code
petitRADTRANS
. After processing the raw data with the JWST pipeline, we high pass filter the data to account for the stellar point spread function, and used a forward modelling approach to detect the companions and constrain the chemical composition of their atmospheres through their molecular signatures.
Results.
We identified limiting factors in spectroscopic characterisation of directly imaged exoplanets with the MRS and simulated observations of two representative systems, HR8799 and GJ504. In both systems, we could detect the presence of multiple molecules that were present in the input model of their atmospheres. We used two different approaches with single molecule forward models, used in literature, that are sensitive to detecting mainly H2O, CO, CH4, and NH3, and a log-likelihood ratio test that uses full atmosphere forward models and is sensitive to a larger number of less dominant molecular species.
Conclusions.
We show that the MIRI MRS can be used to characterise widely separated giant exoplanets in the mid-IR using molecular mapping. Such observations would provide invaluable information for the chemical composition of the atmosphere, complementing other JWST observing modes, as well as ground-based observations.
Molecular mapping of the PDS70 system Cugno, G.; Patapis, P.; Stolker, T. ...
Astronomy and astrophysics (Berlin),
9/2021, Letnik:
653
Journal Article
Recenzirano
Context.
Determining the chemical properties of the atmosphere of young forming gas giants might shed light on the location their formation occurred and the mechanisms involved.
Aims.
Our aim was to ...detect molecules in the atmosphere of the young forming companion PDS70 b by searching for atmospheric absorption features typical of substellar objects.
Methods.
We obtained medium-resolution (
R
≈ 5075) spectra of the PDS70 planetary system with the SINFONI integral field spectrograph at the Very Large Telescope. We applied molecular mapping, based on cross-correlation with synthetic spectra, to identify signatures of molecular species in the atmosphere of the planet.
Results.
Although the planet emission is clearly detected when resampling the data to lower resolution, no molecular species could be identified with the cross-correlation technique. We estimated upper limits on the abundances of H
2
O, CO, and CH
4
(log(
X
mol
) < −4.0, − 4.1, and − 4.9, respectively) assuming a clear atmosphere, and we explored the impact of clouds, which increase the upper limits by a factor of up to 0.7 dex. Assuming that the observations directly probe the planet’s atmosphere, we found a lack of molecular species compared to other directly imaged companions or field objects. Under the assumption that the planet atmosphere presents similar characteristics to other directly imaged planets, we conclude that a dusty environment surrounds the planet, effectively obscuring any feature generated in its atmosphere. We quantify the extinction necessary to impede the detection (
A
V
≈ 16−17 mag), pointing to the possibility of higher optical thickness than previously estimated from other studies. Finally, the non-detection of molecular species conflicts with atmospheric models previously proposed to describe the forming planet.
Conclusions.
To reveal how giant planets form a comprehensive approach that includes constraints from multiple techniques needs to be undertaken. Molecular mapping emerges as an alternative to more classical techniques like SED fitting. Specifically tuned atmospheric models are likely required to faithfully describe the atmospheres of forming protoplanets, and higher spectral resolution data may reveal molecular absorption lines despite the dusty environment enshrouding PDS70 b.
It has been proposed that the distinct formation and evolutionary pathways of exoplanets and brown dwarfs may affect the chemical and isotopic content of their atmospheres. Recent work has indeed ...shown differences in the $ C/^ C $ isotope ratio, which have provisionally been attributed to the top-down formation of brown dwarfs and the core accretion pathway of super-Jupiters. The ESO SupJup Survey is aimed at disentangling the formation pathways of isolated brown dwarfs and planetary-mass companions using chemical and isotopic tracers. The survey utilises high-resolution spectroscopy with the recently upgraded CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES$^+$) at the Very Large Telescope, covering a total of 49 targets. Here, we present the first results of this survey: an atmospheric characterisation of DENIS J0255-4700, an isolated brown dwarf near the L-T transition. We analysed its observed CRIRES$^+$ K-band spectrum using an atmospheric retrieval framework in which the radiative transfer code petitRADTRANS was coupled with the PyMultiNest sampling algorithm. Gaussian processes were employed to model inter-pixel correlations. In addition, we adopted an updated parameterisation of the pressure-temperature profile. Abundances of CO, H$_2$O, CH$_4$, and NH$_3$ were retrieved for this fast-rotating L-dwarf. The ExoMol H$_2$O line list provides a significantly better fit than that of HITEMP. A free-chemistry retrieval is strongly favoured over equilibrium chemistry, caused by an under-abundance of CH$_4$. The free-chemistry retrieval constrains a super-solar $ C/O $-ratio of sim \,$0.68$ and a solar metallicity. We find tentative evidence (sim \,$3 for the presence of 13CO, with a constraint on the isotopologue ratio of $ CO/^ CO $ and a lower limit of gtrsim \,$97$, which suggests a depletion of $ C $ compared to the local interstellar medium ($ C/^ C sim$\,$68$). High-resolution, high signal-to-noise K-band spectra provide an excellent means of constraining the chemistry and isotopic content of sub-stellar objects, which is the main objective of the ESO SupJup Survey.
Abstract
We present
K
-band interferometric observations of the PDS 70 protoplanets along with their host star using VLTI/GRAVITY. We obtained
K
-band spectra and 100
μ
as precision astrometry of ...both PDS 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. Rejecting unstable orbits, we found a nonzero eccentricity for PDS 70 b of 0.17 ± 0.06, a near-circular orbit for PDS 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. Enforcing dynamical stability, we obtained a 95% upper limit on the mass of PDS 70 b of 10
M
Jup
, while the mass of PDS 70 c was unconstrained. The GRAVITY
K
-band spectra rules out pure blackbody models for the photospheres of both planets. Instead, the models with the most support from the data are planetary atmospheres that are dusty, but the nature of the dust is unclear. Any circumplanetary dust around these planets is not well constrained by the planets’ 1–5
μ
m spectral energy distributions (SEDs) and requires longer wavelength data to probe with SED analysis. However with VLTI/GRAVITY, we made the first observations of a circumplanetary environment with sub-astronomical-unit spatial resolution, placing an upper limit of 0.3 au on the size of a bright disk around PDS 70 b.
Context.
Methods used to detect giant exoplanets can be broadly divided into two categories: indirect and direct. Indirect methods are more sensitive to planets with a small orbital period, whereas ...direct detection is more sensitive to planets orbiting at a large distance from their host star. This dichotomy makes it difficult to combine the two techniques on a single target at once.
Aims.
Simultaneous measurements made by direct and indirect techniques offer the possibility of determining the mass and luminosity of planets and a method of testing formation models. Here, we aim to show how long-baseline interferometric observations guided by radial-velocity can be used in such a way.
Methods.
We observed the recently-discovered giant planet
β
Pictoris c with GRAVITY, mounted on the Very Large Telescope Interferometer.
Results.
This study constitutes the first direct confirmation of a planet discovered through radial velocity. We find that the planet has a temperature of
T
= 1250 ± 50 K and a dynamical mass of
M
= 8.2 ± 0.8
M
Jup
. At 18.5 ± 2.5 Myr, this puts
β
Pic c close to a ‘hot start’ track, which is usually associated with formation via disk instability. Conversely, the planet orbits at a distance of 2.7 au, which is too close for disk instability to occur. The low apparent magnitude (
M
K
= 14.3 ± 0.1) favours a core accretion scenario.
Conclusions.
We suggest that this apparent contradiction is a sign of hot core accretion, for example, due to the mass of the planetary core or the existence of a high-temperature accretion shock during formation.
Aims.
We aim to demonstrate that the presence and mass of an exoplanet can now be effectively derived from the astrometry of another exoplanet.
Methods.
We combined previous astrometry of
β
Pictoris ...b with a new set of observations from the GRAVITY interferometer. The orbital motion of
β
Pictoris b is fit using Markov chain Monte Carlo simulations in Jacobi coordinates. The inner planet,
β
Pictoris c, was also reobserved at a separation of 96 mas, confirming the previous orbital estimations.
Results.
From the astrometry of planet b only, we can (i) detect the presence of
β
Pictoris c and (ii) constrain its mass to 10.04
−3.10
+4.53
M
Jup
. If one adds the astrometry of
β
Pictoris c, the mass is narrowed down to 9.15
−1.06
+1.08
M
Jup
. The inclusion of radial velocity measurements does not affect the orbital parameters significantly, but it does slightly decrease the mass estimate to 8.89
−0.75
+0.75
M
Jup
. With a semimajor axis of 2.68 ± 0.02 au, a period of 1221 ± 15 days, and an eccentricity of 0.32 ± 0.02, the orbital parameters of
β
Pictoris c are now constrained as precisely as those of
β
Pictoris b. The orbital configuration is compatible with a high-order mean-motion resonance (7:1). The impact of the resonance on the planets’ dynamics would then be negligible with respect to the secular perturbations, which might have played an important role in the eccentricity excitation of the outer planet.
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