Context.
Directly imaged planets and substellar companions are key targets for the characterization of self-luminous atmospheres. Their photometric appearance at 4–5
μ
m is sensitive to the chemical ...composition and cloud content of their atmosphere.
Aims.
We aim to systematically characterize the atmospheres of directly imaged low-mass companions at 4–5
μ
m. We want to homogeneously process the data, provide robust flux measurements, and compile a photometric library at thermal wavelengths of these mostly young, low-gravity objects. In this way, we want to find trends related to their spectral type and surface gravity by comparing with isolated brown dwarfs and predictions from atmospheric models.
Methods.
We used the high-resolution, high-contrast capabilities of NACO at the Very Large Telescope (VLT) to directly image the companions of HIP 65426, PZ Tel, and HD 206893 in the NB4.05 and/or
M
′ filters. For the same targets, and additionally
β
Pic, we also analyzed six archival VLT/NACO datasets which were taken with the NB3.74,
L
′, NB4.05, and
M
′ filters. The data processing and photometric extraction of the companions was done with
PynPoint
while the
species
toolkit was used to further analyze and interpret the fluxes and colors.
Results.
We detect for the first time HIP 65426 b, PZ Tel B, and HD 206893 B in the NB4.05 filter, PZ Tel B and HD 206893 B in the
M
′ filter, and
β
Pic b in the NB3.74 filter. We provide calibrated magnitudes and fluxes with a careful analysis of the error budget, both for the new and archival datasets. The
L
′–NB4.05 and
L
′–
M
′ colors of the studied sample are all red while the NB4.05–
M
′ color is blue for
β
Pic b, gray for PZ Tel B, and red for HIP 65426 b and HD 206893 B (although typically with low significance). The absolute NB4.05 and
M
′ fluxes of our sample are all larger than those of field dwarfs with similar spectral types. Finally, the surface gravity of
β
Pic b has been constrained to log
g
= 4.17
−0.13
+0.10
dex from its photometry and dynamical mass.
Conclusions.
A red color at 3–4
μ
m and a blue color at 4–5
μ
m might be (partially) caused by H
2
O and CO absorption, respectively, which are expected to be the most dominant gaseous opacities in hot (
T
eff
≳ 1300 K) atmospheres. The red characteristics of
β
Pic b, HIP 65426 b, and HD 206893 B at 3–5
μ
m, as well as their higher fluxes in NB4.05 and
M
′ compared to field dwarfs, indicate that cloud densities are enhanced close to the photosphere as a result of their low surface gravity.
We report 13 high-precision light curves of eight transits of the exoplanet WASP-52 b, obtained by using four medium-class telescopes, through different filters, and adopting the defocussing ...technique. One transit was recorded simultaneously from two different observatories and another one from the same site but with two different instruments, including a multiband camera. Anomalies were clearly detected in five light curves and modelled as star-spots occulted by the planet during the transit events. We fitted the clean light curves with the JKTEBOP code, and those with the anomalies with the PRISM+GEMC codes in order to simultaneously model the photometric parameters of the transits and the position, size and contrast of each star-spot. We used these new light curves and some from the literature to revise the physical properties of the WASP-52 system. Star-spots with similar characteristics were detected in four transits over a period of 43 d. In the hypothesis that we are dealing with the same star-spot, periodically occulted by the transiting planet, we estimated the projected orbital obliquity of WASP-52 b to be ... = 3 Math Processing Error...8 plus or minus 8 Math Processing Error...4. We also determined the true orbital obliquity, ... = 20... plus or minus 50..., which is, although very uncertain, the first measurement of ... purely from star-spot crossings. We finally assembled an optical transmission spectrum of the planet and searched for variations of its radius as a function of wavelength. Our analysis suggests a flat transmission spectrum within the experimental uncertainties. (ProQuest: ... denotes formulae/symbols omitted.)
The WASP-98 planetary system represents a rare case of a hot Jupiter hosted by a metal-poor main-sequence star. We present a follow-up study of this system based on multiband photometry and ...high-resolution spectroscopy. Two new transit events of WASP-98 b were simultaneously observed in four passbands (g′, r′, i′, z′), using the telescope-defocusing technique, yielding eight high-precision light curves with point-to-point scatters of less than 1 mmag. We also collected three spectra of the parent star with a high-resolution spectrograph, which we used to remeasure its spectral characteristics, in particular its metallicity. We found this to be very low, Fe/H = −0.49 ± 0.10, but larger than was previously reported, Fe/H = −0.60 ± 0.19. We used these new photometric and spectroscopic data to refine the orbital and physical properties of this planetary system, finding that the stellar and planetary mass measurements are significantly larger than those in the discovery paper. In addition, the multiband light curves were used to construct an optical transmission spectrum of WASP-98 b and probe the characteristics of its atmosphere at the terminator. We measured a lower radius at z′ compared with the other three passbands. The maximum variation is between the r′ and z′ bands, has a confidence level of roughly 6σ and equates to 5.5 pressure scale heights. We compared this spectrum to theoretical models, investigating several possible types of atmospheres, including hazy, cloudy, cloud-free, and clear atmospheres with titanium and vanadium oxide opacities. We could not find a good fit to the observations, except in the extreme case of a clear atmosphere with TiO and VO opacities, in which the condensation of Ti and V was suppressed. As this case is unrealistic, our results suggest the presence of an additional optical-absorbing species in the atmosphere of WASP-98 b, of unknown chemical nature.
GASTLI Acuña, L.; Kreidberg, L.; Zhai, M. ...
Astronomy and astrophysics (Berlin),
08/2024, Volume:
688
Journal Article
Peer reviewed
The metal mass fractions of gas giants are a powerful tool for constraining their formation mechanisms and evolution. The metal content is inferred by comparing mass and radius measurements with ...interior structure and evolution models. In the midst of the JWST, CHEOPS, TESS, and the forthcoming PLATO era, we are at the brink of obtaining unprecedented precision in radius, age, and atmospheric metallicity measurements. To prepare for this wealth of data, we present the GAS gianT modeL for Interiors (GASTLI), an easy-to-use, publicly available Python package. The code is optimized to rapidly calculate mass-radius relations, and radius and luminosity thermal evolution curves for a variety of envelope compositions and core mass fractions. Its applicability spans planets with masses of 17 M ⊕ < M < 6 M Jup , and equilibrium temperatures of T eq < 1000 K. The interior model is stratified in a core composed of water and rock, and an envelope constituted by H/He and metals (water). The interior is coupled to a grid of self-consistent, cloud-free atmospheric models to determine the atmospheric and boundary interior temperature, as well as the contribution of the atmosphere to the total radius. We successfully validate GASTLI by comparing it to previous work and data of the gas giants of the Solar System and Neptune. We also test GASTLI on the Neptune-mass exoplanet HAT-P-26 b, finding a bulk metal mass fraction of between 0.60 and 0.78 and a core mass of 8.5–14.4 M ⊕ . Finally, we explore the impact of different equations of state and assumptions, such as C/O ratio and transit pressure, in the estimation of bulk metal mass fraction. These differences between interior models entail a change in radius of up to 2.5% for Jupiter-mass planets, but of more than 10% for Neptune-mass. These are equivalent to variations in core mass fraction of 0.07, or 0.10 in envelope metal mass fraction.
The circumstellar disk of PDS 70 hosts two forming planets, which are actively accreting gas from their environment. The physical and chemical characteristics of these planets remain ambiguous due to ...their unusual spectral appearance compared to more evolved objects. In this work, we report the first detection of PDS 70 b in the Br
α
and
M
′ filters with VLT/NACO, a tentative detection of PDS 70 c in Br
α
, and a reanalysis of archival NACO
L
′ and SPHERE
H
23 and
K
12 imaging data. The near side of the disk is also resolved with the Br
α
and
M
′ filters, indicating that scattered light is non-negligible at these wavelengths. The spectral energy distribution (SED) of PDS 70 b is well described by blackbody emission, for which we constrain the photospheric temperature and photospheric radius to
T
eff
= 1193 ± 20 K and
R
= 3.0 ± 0.2
R
J
. The relatively low bolometric luminosity, log(
L
∕
L
⊙
) = −3.79 ± 0.02, in combination with the large radius, is not compatible with standard structure models of fully convective objects. With predictions from such models, and adopting a recent estimate of the accretion rate, we derive a planetary mass and radius in the range of
M
p
≈ 0.5–1.5
M
J
and
R
p
≈ 1–2.5
R
J
, independently of the age and post-formation entropy of the planet. The blackbody emission, large photospheric radius, and the discrepancy between the photospheric and planetary radius suggests that infrared observations probe an extended, dusty environment around the planet, which obscures the view on its molecular composition. Therefore, the SED is expected to trace the reprocessed radiation from the interior of the planet and/or partially from the accretion shock. The photospheric radius lies deep within the Hill sphere of the planet, which implies that PDS 70 b not only accretes gas but is also continuously replenished by dust. Finally, we derive a rough upper limit on the temperature and radius of potential excess emission from a circumplanetary disk,
T
eff
≲ 256 K and
R
≲ 245
R
J
, but we do find weak evidence that the current data favors a model with a single blackbody component.
Ultra-hot Jupiters (UHJs) are gas giants with very high equilibrium temperatures. In recent years, multiple chemical species, including various atoms and ions, have been discovered in their ...atmospheres. Most of these observations have been performed with transmission spectroscopy, although UHJs are also ideal targets for emission spectroscopy due to their strong thermal radiation. We present high-resolution thermal emission spectroscopy of the transiting UHJ KELT-20b/MASCARA-2b. The observation was performed with the CARMENES spectrograph at orbital phases before and after the secondary eclipse. We detected atomic Fe using the cross-correlation technique. The detected Fe lines are in emission, which unambiguously indicates a temperature inversion on the dayside hemisphere. We furthermore retrieved the temperature structure with the detected Fe lines. The result shows that the atmosphere has a strong temperature inversion with a temperature of 4900 ± 700 K and a pressure of 10
−4.8
−1.1
+1.0
bar at the upper layer of the inversion. A joint retrieval of the CARMENES data and the TESS secondary eclipse data returns a temperature of 2550
−250
+150
K and a pressure of 10
−1.5
−0.6
+0.7
bar at the lower layer of the temperature inversion. The detection of such a strong temperature inversion is consistent with theoretical simulations that predict an inversion layer on the dayside of UHJs. The joint retrieval of the CARMENES and TESS data demonstrates the power of combing high-resolution emission spectroscopy with secondary eclipse photometry in characterizing atmospheric temperature structures.
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.
Context.
Temperate terrestrial exoplanets are likely to be common objects, but their discovery and characterization is very challenging because of the small intrinsic signal compared to that of their ...host star. Various concepts for optimized space missions to overcome these challenges are currently being studied. The Large Interferometer For Exoplanets (LIFE) initiative focuses on the development of a spacebased mid-infrared (MIR) nulling interferometer probing the thermal emission of a large sample of exoplanets.
Aims.
This study derives the minimum requirements for the signal-to-noise ratio (
S
/
N
), the spectral resolution (
R
), and the wavelength coverage for the LIFE mission concept. Using an Earth-twin exoplanet as a reference case, we quantify how well planetary and atmospheric properties can be derived from its MIR thermal emission spectrum as a function of the wavelength range,
S/N,
and
R
.
Methods.
We combined a cloud-free 1D atmospheric radiative transfer model, a noise model for observations with the LIFE interferometer, and the nested sampling algorithm for Bayesian parameter inference to retrieve planetary and atmospheric properties. We simulated observations of an Earth-twin exoplanet orbiting a G2V star at 10 pc from the Sun with different levels of exozodiacal dust emissions. We investigated a grid of wavelength ranges (3–20 μm, 4–18.5 μm, and 6–17 μm),
S/Ns
(5, 10, 15, and 20 determined at a wavelength of 11.2 μm), and
R
s (20, 35, 50, and 100).
Results.
We find that H
2
O, CO
2
, and O
3
are detectable if
S/N ≥
10 (uncertainty ≤ ± 1.0 dex). We find upper limits for N
2
O (abundance ≲10
−3
). In conrtrast, CO, N
2
, and O
2
are unconstrained. The lower limits for a CH
4
detection are
R
= 50 and
S
/
N
= 10. Our retrieval framework correctly determines the exoplanet’s radius (uncertainty ≤ ± 10%), surface temperature (uncertainty ≤ ± 20 K), and surface pressure (uncertainty ≤ ± 0.5 dex) in all cloud-free retrieval analyses. Based on our current assumptions, the observation time required to reach the specified
S/N
for an Earth-twin at 10 pc when conservatively assuming a total instrument throughput of 5% amounts to ≈6−7 weeks with four 2m apertures.
Conclusions.
We provide first order estimates for the minimum technical requirements for LIFE via the retrieval study of an Earth-twin exoplanet. We conclude that a minimum wavelength coverage of 4–18.5 μm, an
R
of 50, and an
S/N
of at least 10 is required. With the current assumptions, the atmospheric characterization of several Earth-like exoplanets at a distance of 10 pc and within a reasonable amount of observing time will require apertures ≥ 2m.
Context. This paper continues a series in which we predict the main observable characteristics of exoplanets based on their formation. In Paper I we described our global planet formation and ...evolution model that is based on the core accretion paradigm. In Paper II we studied the planetary mass-radius relationship with population syntheses. Aims. In this paper we present an extensive study of the statistics of planetary luminosities during both formation and evolution. Our results can be compared with individual directly imaged extrasolar (proto)planets and with statistical results from surveys. Methods. We calculated three populations of synthetic planets assuming different efficiencies of the accretional heating by gas and planetesimals during formation. We describe the temporal evolution of the planetary mass-luminosity relation. We investigate the relative importance of the shock and internal luminosity during formation, and predict a statistical version of the post-formation mass vs. entropy “tuning fork” diagram. Because the calculations now include deuterium burning we also update the planetary mass-radius relationship in time. Results. We find significant overlap between the high post-formation luminosities of planets forming with hot and cold gas accretion because of the core-mass effect. Variations in the individual formation histories of planets can still lead to a factor 5 to 20 spread in the post-formation luminosity at a given mass. However, if the gas accretional heating and planetesimal accretion rate during the runaway phase is unknown, the post-formation luminosity may exhibit a spread of as much as 2–3 orders of magnitude at a fixed mass. As a key result we predict a flat log-luminosity distribution for giant planets, and a steep increase towards lower luminosities due to the higher occurrence rate of low-mass (M ≲ 10–40 M⊕) planets. Future surveys may detect this upturn. Conclusions. Our results indicate that during formation an estimation of the planetary mass may be possible for cold gas accretion if the planetary gas accretion rate can be estimated. If it is unknown whether the planet still accretes gas, the spread in total luminosity (internal + accretional) at a given mass may be as large as two orders of magnitude, therefore inhibiting the mass estimation. Due to the core-mass effect even planets which underwent cold accretion can have large post-formation entropies and luminosities, such that alternative formation scenarios such as gravitational instabilities do not need to be invoked. Once the number of self-luminous exoplanets with known ages and luminosities increases, the resulting luminosity distributions may be compared with our predictions.
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