Abstract
We present model constraints on the atmospheric structure of HD 106906 b, a planetary-mass companion orbiting at a ∼700 au projected separation around a 15 Myr old stellar binary, using the ...APOLLO retrieval code on spectral data spanning 1.1–2.5
μ
m. C/O ratios can provide evidence for companion formation pathways, as such pathways are ambiguous both at wide separations and at star-to-companion mass ratios in the overlap between the distributions of planets and brown dwarfs. We benchmark our code against an existing retrieval of the field L dwarf 2MASSW J2224–0158, returning a C/O ratio consistent with previous fits to the same
JHK
s
data, but disagreeing in the thermal structure, cloud properties, and atmospheric scale height. For HD 106906 b, we retrieve C/O
=
0.53
−
0.25
+
0.15
, consistent with the C/O ratios expected for HD 106906's stellar association and therefore consistent with a stellar-like formation for the companion. We find abundances of H
2
O and CO near chemical equilibrium values for a solar metallicity but a surface gravity lower than expected, as well as a thermal profile with sharp transitions in the temperature gradient. Despite high signal-to-noise ratio and spectral resolution, more accurate constraints necessitate data across a broader wavelength range. This work serves as preparation for subsequent retrievals in the era of JWST, as JWST's spectral range provides a promising opportunity to resolve difficulties in fitting low-gravity L dwarfs and also underscores the need for simultaneous comparative retrievals on L-dwarf companions with multiple retrieval codes.
A key hypothesis in the field of exoplanet atmospheres is the trend of atmospheric thermal structure with planetary equilibrium temperature. We explore this trend and report here the first ...statistical detection of a transition in the near-infrared atmospheric emission between hot and ultra-hot Jupiters. We measure this transition using secondary eclipse observations and interpret this phenomenon as changes in atmospheric properties, and more specifically in terms of transition from non-inverted to inverted thermal profiles. We examine a sample of 78 hot Jupiters with secondary eclipse measurements at 3.6 and 4.5 μ m measured with Spitzer Infrared Array Camera. We calculate the planetary brightness temperatures using PHOENIX models to correct for the stellar flux. We measure the deviation of the data from the blackbody, which we define as the difference between the observed 4.5 μ m eclipse depth and that expected at this wavelength based on the brightness temperature measured at 3.6 μ m. We study how the deviation between 3.6 and 4.5 μ m changes with theoretical predictions with equilibrium temperature and incoming stellar irradiation. We reveal a clear transition in the observed emission spectra of the hot Jupiter population at 1660 ± 100 K in the zero albedo, full redistribution equilibrium temperature. We find the hotter exoplanets have even hotter daysides at 4.5 μ m compared to 3.6 μ m, which manifests as an exponential increase in the emitted power of the planets with stellar insolation. We propose that the measured transition is a result of seeing carbon monoxide in emission due to the formation of temperature inversions in the atmospheres of the hottest planets. These thermal inversions could be caused by the presence of atomic and molecular species with high opacities in the optical and/or the lack of cooling species. Our findings are in remarkable agreement with a new grid of 1D radiative and convective models varying metallicity, carbon to oxygen ratio (C/O), surface gravity, and stellar effective temperature. We find that the population of hot Jupiters statistically disfavors high C/O planets (C/O ≥ 0.85).
We present model constraints on the atmospheric structure of HD 106906 b, a planetary-mass companion orbiting at a ~700 AU projected separation around a 15 Myr-old stellar binary, using the APOLLO ...retrieval code on spectral data spanning 1.1-2.5 \(\mu\)m. C/O ratios can provide evidence for companion formation pathways, as such pathways are ambiguous both at wide separations and at star-to-companion mass ratios in the overlap between the distributions of planets and brown dwarfs. We benchmark our code against an existing retrieval of the field L dwarf 2M2224-0158, returning a C/O ratio consistent with previous fits to the same JHKs data, but disagreeing in the thermal structure, cloud properties, and atmospheric scale height. For HD 106906 b, we retrieve C/O \(=0.53^{+0.15}_{-0.25}\), consistent with the C/O ratios expected for HD 106906's stellar association and therefore consistent with a stellar-like formation for the companion. We find abundances of H\(_2\)O and CO near chemical equilibrium values for a solar metallicity, but a surface gravity lower than expected, as well as a thermal profile with sharp transitions in the temperature gradient. Despite high signal-to-noise and spectral resolution, more accurate constraints necessitate data across a broader wavelength range. This work serves as preparation for subsequent retrievals in the era of JWST, as JWST's spectral range provides a promising opportunity to resolve difficulties in fitting low-gravity L dwarfs, and also underscores the need for simultaneous comparative retrievals on L dwarf companions with multiple retrieval codes.
Abridged A key hypothesis in the field of exoplanet atmospheres is the trend of atmospheric thermal structure with planetary equilibrium temperature. We explore this trend and report here the first ...statistical detection of a transition in the near-infrared (NIR) atmospheric emission between hot and ultra-hot Jupiters. We measure this transition using secondary eclipse observations and interpret this phenomenon as changes in atmospheric properties, and more specifically in terms of transition from non-inverted to inverted thermal profiles. We examine a sample of 78 hot Jupiters with secondary eclipse measurements at 3.6 {\mu}m and 4.5 {\mu}m measured with Spitzer Infrared Array Camera (IRAC). We measure the deviation of the data from the blackbody, which we define as the difference between the observed 4.5 {\mu}m eclipse depth and that expected at this wavelength based on the brightness temperature measured at 3.6 {\mu}m. We study how the deviation between 3.6 and 4.5 {\mu}m changes with theoretical predictions with equilibrium temperature and incoming stellar irradiation. We reveal a clear transition in the observed emission spectra of the hot Jupiter population at 1660 +/- 100 K in the zero albedo, full redistribution equilibrium temperature. We find the hotter exoplanets have even hotter daysides at 4.5 {\mu}m compared to 3.6 {\mu}m, which manifests as an exponential increase in the emitted power of the planets with stellar insolation. We propose that the measured transition is a result of seeing carbon monoxide in emission due to the formation of temperature inversions in the atmospheres of the hottest planets. These thermal inversions could be caused by the presence of atomic and molecular species with high opacities in the optical and/or the lack of cooling species. We find that the population of hot Jupiters statistically disfavors high C/O planets (C/O>= 0.85).
Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG) was organized to study the effect of stellar contamination on space-based transmission spectroscopy, a ...method for studying exoplanetary atmospheres by measuring the wavelength-dependent radius of a planet as it transits its star. Transmission spectroscopy relies on a precise understanding of the spectrum of the star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and chromospheres with inhomogeneities like spots, faculae, plages, granules, and flares. This SAG brought together an interdisciplinary team of more than 100 scientists, with observers and theorists from the heliophysics, stellar astrophysics, planetary science, and exoplanetary atmosphere research communities, to study the current research needs that can be addressed in this context to make the most of transit studies from current NASA facilities like HST and JWST. The analysis produced 14 findings, which fall into three Science Themes encompassing (1) how the Sun is used as our best laboratory to calibrate our understanding of stellar heterogeneities ("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun extend our knowledge of heterogeneities ("Surface Heterogeneities of Other Stars") and (3) how to incorporate information gathered for the Sun and other stars into transit studies ("Mapping Stellar Knowledge to Transit Studies"). In this invited review, we largely reproduce the final report of SAG21 as a contribution to the peer-reviewed literature.
Uranus and Neptune are the archetypes of "ice giants", a class of planets that may be among the most common in the Galaxy. They hold the keys to understand the atmospheric dynamics and structure of ...planets with hydrogen atmospheres inside and outside the solar system; however, they are also the last unexplored planets of the Solar System. Their atmospheres are active and storms are believed to be fueled by methane condensation which is both extremely abundant and occurs at low optical depth. This means that mapping temperature and methane abundance as a function of position and depth will inform us on how convection organizes in an atmosphere with no surface and condensates that are heavier than the surrounding air, a general feature of giant planets. Owing to the spatial and temporal variability of these atmospheres, an orbiter is required. A probe would provide a reference atmospheric profile to lift ambiguities inherent to remote observations. It would also measure the abundances of noble gases which can be used to reconstruct the history of planet formation in the Solar System. Finally, mapping the planets' gravity and magnetic fields will be essential to constrain their global composition, atmospheric dynamics, structure and evolution. An exploration of Uranus or Neptune will be essential to understand these planets and will also be key to constrain and analyze data obtained at Jupiter, Saturn, and for numerous exoplanets with hydrogen atmospheres.
The work in this thesis can be split into three areas. In the first, inelastic electron tunnelling spectroscopy (IETS) is used to investigate resistive and bias polarity dependent effects on ...vibrational mode energy in metal - aluminium oxide - metal tunnel junctions. It is shown that even when four point-probe techniques are used the ratio of width to thickness of the electrodes used in IET junctions has an effect on both the breadth and position of spectral lines. A simple treatment based upon work done by Giaever allows for such effects to be corrected. Work done on top metal and polarity effects in undoped IET junctions investigated the effect on the position of the 450 meV mode on reversing the applied bias. The investigation revealed that any dependence on the nature of the top-metal electrode was outside the accuracy of the work. Calculation of q/e for the hydroxyl group on alumina within the tunnel junction has been extended to include other electrode materials. A new and exciting facility within the university provided the impetus for the second area of work. A class 100 clean room housing a Langmuir Blodgett (LB) trough offered the opportunity to produce metal - insulator - Langmuir Blodgett film - metal tunnel junctions. It was realised at the outset that IETS using LB films would be difficult, previous workers had tried using a home-made tank with only limited success. However, the added sophistication of the new tank did not improve matters as was hoped. Although the results were disappointing, only a few junctions had resistances low enough to be usable in the spectrometer, the investigation produced some of the very few IET specra using junctions doped with LB films. The results also revealed the important role that imperfections and pin-holes play in the tunnelling process. The last area used IETS to investigate two commercially important and interesting polymers, hydrogels and polymeric electrolytes. Hydrogel have many applications in the field of implants, prosthetic, and cosmetics and have been studied and developed for many years. Polymeric electrolytes have many commercial applications especially in the field of solid-state batteries and conducting polymers. The way in which hydrogels swell as they absorb water is important, as is the way they adsorb onto a surface and much work has been done to investigate these characteristics using bulk samples. The study done by this group is the first to investigate the swelling and adsorption behaviour of a monolayer of the hydrogel poly 2-hydroxylethyl methacrylate. The results from both investigations indicate that ester cleavage occurs in p-HEMA and that water incorporated within a hydrogel has a limited structure with the first layer being thinner than the second and subsequent layers.
The work in this thesis can be split into three areas. In the first, inelastic electron tunnelling spectroscopy (IETS) is used to investigate resistive and bias polarity dependent effects on ...vibrational mode energy in metal - aluminium oxide - metal tunnel junctions. It is shown that even when four point-probe techniques are used the ratio of width to thickness of the electrodes used in IET junctions has an effect on both the breadth and position of spectral lines. A simple treatment based upon work done by Giaever allows for such effects to be corrected. Work done on top metal and polarity effects in undoped IET junctions investigated the effect on the position of the 450 meV mode on reversing the applied bias. The investigation revealed that any dependence on the nature of the top-metal electrode was outside the accuracy of the work. Calculation of q/e for the hydroxyl group on alumina within the tunnel junction has been extended to include other electrode materials. A new and exciting facility within the university provided the impetus for the second area of work. A class 100 clean room housing a Langmuir Blodgett (LB) trough offered the opportunity to produce metal - insulator - Langmuir Blodgett film - metal tunnel junctions. It was realised at the outset that IETS using LB films would be difficult, previous workers had tried using a home-made tank with only limited success. However, the added sophistication of the new tank did not improve matters as was hoped. Although the results were disappointing, only a few junctions had resistances low enough to be usable in the spectrometer, the investigation produced some of the very few IET specra using junctions doped with LB films. The results also revealed the important role that imperfections and pin-holes play in the tunnelling process. The last area used IETS to investigate two commercially important and interesting polymers, hydrogels and polymeric electrolytes. Hydrogel have many applications in the field of implants, prosthetic, and cosmetics and have been studied and developed for many years. Polymeric electrolytes have many commercial applications especially in the field of solid-state batteries and conducting polymers. The way in which hydrogels swell as they absorb water is important, as is the way they adsorb onto a surface and much work has been done to investigate these characteristics using bulk samples. The study done by this group is the first to investigate the swelling and adsorption behaviour of a monolayer of the hydrogel poly 2-hydroxylethyl methacrylate. The results from both investigations indicate that ester cleavage occurs in p-HEMA and that water incorporated within a hydrogel has a limited structure with the first layer being thinner than the second and subsequent layers.
A unit cell in which three isomers are in an L configuration and one is in a D configuration is inherently asymmetrical. For LDLL mixtures of amino acids with identical chemical structures (apart ...from chirality), the inter- and intramolecular interactions observed from the 13C CP/MAS NMR spectra are even larger than those which have been observed with mixtures of diastereoisomers in the solid state. This occurs even though the chemical composition of these molecular clusters consists only of nearest neighbor enantiomers. Because D and L isomers have identical chemical shifts, changes in chemical shift and peak intensities of these asymmetrical solid mixtures cannot be unambiguously assigned to either the D or one of the L isomers. In LLDL mixtures of amino acids in which half is L isomers and the other half is DL isomers, the NMR spectra clearly depend upon which amino acid contains the D isomer. Any further structural interpretation of these molecular clusters is equivocal without assigning chemical shifts to the D isomer (or alternatively designated the R, - or + isomer). Both more rigorous mathematical analysis and new NMR experiments are required which link interactions at chiral centers with NMR spectra of LLDL mixtures in the solid state.
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