Secondary Eclipse Research Articles

Fundamental challenges to remote sensing of exo-earths

ABSTRACT Inferring the climate and surface conditions of terrestrial exoplanets in the habitable zone is a major goal for the field of exoplanet science. This pursuit will require both statistical analyses of the population of habitable planets as well as in-depth analyses of the climates of individual planets. Given the close relationship between habitability and surface liquid water, it is important to ask whether the fraction of a planet’s surface where water can be a liquid, χhab, can be inferred from observations. We have produced a diverse bank of 1874 3D climate models and computed the full-phase reflectance and emission spectrum for each model to investigate whether surface climate inference is feasible with high-quality direct imaging or secondary eclipse spectroscopy. These models represent the outcome of approximately 200 000 total simulated years of climate and over 50 000 CPU-hours, and the roughly 100 GB model bank and its associated spectra are being made publicly available for community use. We find that there are correlations between spectra and χhab that will permit statistical approaches. However, spectral degeneracies in the climate observables produced by our model bank indicate that inference of individual climates is likely to be model-dependent, and inference will likely be impossible without exhaustive explorations of the climate parameter space. The diversity of potential climates on habitable planets therefore poses fundamental challenges to remote sensing efforts targeting exo-Earths.

A New Detached Binary USNO-B1.0 1421-0485411 with the Secondary Component having Large Albedo

Abstract USNO-B1.0 1421-0485411 is an eclipsing binary system newly discovered in the Yunnan-Hong Kong wide-field photometric survey. Its orbital period is 1.295 days. Based on the V- and R-band photometric data collected at Kunming 1.0 m telescope and spectroscopic data observed at Lijiang 2.4 m telescope, we used the Wilson-Devinney program to determine the physical parameters of the binary system. The results show that the mass and radius are 2.21 M ⊙ and 1.70 R ⊙ for the A0V primary component, and 2.11 M ⊙ and 1.77 R ⊙ for the A4–5V secondary one. The observed light curves show higher shoulders around the secondary eclipse, which can originate from hot spots, circumstellar materials, abnormal albedo of the secondary component, etc. Through analyzing and modeling, a quite large albedo (∼1.89) of the secondary component was considered to be the most possible reason for this phenomenon. The position of the two components on the H-R diagram implies that the binary is in main-sequence stage.

CHEOPS geometric albedo of the hot Jupiter HD 209458 b

We report the detection of the secondary eclipse of the hot Jupiter HD 209458 b in optical/visible light using the CHEOPS space telescope. Our measurement of 20.4−3.3+3.2 parts per million translates into a geometric albedo of Ag = 0.096 ± 0.016. The previously estimated dayside temperature of about 1500 K implies that our geometric albedo measurement consists predominantly of reflected starlight and is largely uncontaminated by thermal emission. This makes the present result one of the most robust measurements of Ag for any exoplanet. Our calculations of the bandpass-integrated geometric albedo demonstrate that the measured value of Ag is consistent with a cloud-free atmosphere, where starlight is reflected via Rayleigh scattering by hydrogen molecules, and the water and sodium abundances are consistent with stellar metallicity. We predict that the bandpass-integrated TESS geometric albedo is too faint to detect and that a phase curve of HD 209458 b observed by CHEOPS would have a distinct shape associated with Rayleigh scattering if the atmosphere is indeed cloud free.

DI Herculis Revisited: Starspots, Gravity Darkening, and 3D Obliquities

Abstract DI Herculis is an eclipsing binary famous for a longstanding disagreement between theory and observation of the apsidal precession rate, which was resolved when both stars were found to be severely misaligned with the orbit. We used data from the Transiting Exoplanet Survey Satellite (TESS) to refine our knowledge of the stellar obliquities and sharpen the comparison between the observed and theoretical precession rates. The TESS data show variations with a 1.07 day period, which we interpret as rotational modulation from starspots on the primary star. This interpretation is supported by the detection of photometric anomalies during primary eclipses consistent with starspot crossings. The secondary eclipse light curve shows a repeatable asymmetry that we interpret as an effect of gravity darkening. By combining the TESS data with previously obtained data, we determined the three-dimensional spin directions of both stars. Using this information, the updated value of the theoretical apsidal precession rate (including the effects of tides, rotation, and general relativity) is 1.35 − 0.50 + 0.58 arcsec cycle−1. The updated value of the observed rate (after including new TESS eclipse times) is 1.41 − 0.28 + 0.39 arcsec cycle−1. Given the agreement between the observed and theoretical values, we fitted all the relevant data simultaneously, assuming the theory is correct. This allowed us to place tighter constraints on the stellar obliquities, which are 75 − 3 + 3 and 80 − 3 + 3 degrees for the primary and secondary stars, respectively.

Detection of iron emission lines and a temperature inversion on the dayside of the ultra-hot Jupiter KELT-20b

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.

ProbingKepler’s hottest small planets via homogeneous search and analysis of optical secondary eclipses and phase variations

Context.High-precision photometry can lead to the detection of secondary eclipses and phase variations of highly irradiated planets.Aims.We performed a homogeneous search and analysis of optical occultations and phase variations of the most favorable ultra-short-period (USP) (P< 1 days) sub-Neptunes (Rp< 4R⊕), observed byKeplerand K2, with the aim to better understand their nature.Methods.We first selected 16Keplerand K2 USP sub-Neptunes based on the expected occultation signal. We filtered out stellar variability in theKeplerlight curves, using a sliding linear fitting and, when required, a more sophisticated approach based on a Gaussian process regression. In the case of the detection of secondary eclipse or phase variation with a confidence level higher than 2σ, we simultaneously modeled the primary transit, secondary eclipse, and phase variations in a Bayesian framework, by using information from previous studies and knowledge of theGaiaparallaxes. We further derived constraints on the geometric albedo as a function of the planet’s brightness temperature.Results.We confirm the optical secondary eclipses for Kepler-10b (13σ), Kepler-78b (9.5σ), and K2-141b (6.9σ), with marginal evidence for K2-312b (2.2σ). We report new detections for K2-106b (3.3σ), K2-131b (3.2σ), Kepler-407b (3.0σ), and hints for K2-229b (2.5σ). For all targets, with the exception of K2-229b and K2-312b, we also find phase curve variations with a confidence level higher than 2σ.Conclusions.Two USP planets, namely Kepler-10b and Kepler-78b, show non-negligible nightside emission. This questions the scenario of magma-ocean worlds with inefficient heat redistribution to the nightside for both planets. Due to the youth of the Kepler-78 system and the small planetary orbital separation, the planet may still retain a collisional secondary atmosphere capable of conducting heat from the day to the nightside. Instead, the presence of an outgassing magma ocean on the dayside and the low high-energy irradiation of the old host star may have enabled Kepler-10b to build up and retain a recently formed collisional secondary atmosphere. The magma-world scenario may instead apply to K2-141b and K2-131b.

Spatially Resolved Modeling of Optical Albedos for a Sample of Six Hot Jupiters

Abstract Optical secondary eclipse measurements made by Kepler reveal a diverse set of geometric albedos for hot Jupiters with equilibrium temperatures between 1550 and 1700 K. The presence or absence of high-altitude condensates, such as Mg2SiO4, Fe, Al2O3, and TiO2, can significantly alter optical albedos, but these clouds are expected to be confined to localized regions in the atmospheres of these tidally locked planets. Here, we present 3D general circulation models and corresponding cloud and albedo maps for six hot Jupiters with measured optical albedos in this temperature range. We find that the observed optical albedos of K2-31b and K2-107b are best matched by either cloud-free models or models with relatively compact cloud layers, while Kepler-8b’s and Kepler-17b’s optical albedos can be matched by moderately extended (f sed = 0.1) parametric cloud models. HATS-11b has a high optical albedo, corresponding to models with bright Mg2SiO4 clouds extending to very low pressures (f sed = 0.03). We are unable to reproduce Kepler-7b’s high albedo, as our models predict that the dayside will be dominated by dark Al2O3 clouds at most longitudes. We compare our parametric cloud model with a microphysical cloud model. We find that even after accounting for the 3D thermal structure, no single cloud model can explain the full range of observed albedos within the sample. We conclude that a better knowledge of the vertical mixing profiles, cloud radiative feedback, cloud condensate properties, and atmospheric metallicities is needed in order to explain the unexpected diversity of albedos in this temperature range.

An Eccentric Brown Dwarf Eclipsing an M dwarf

Abstract We report the discovery of an M = 67 ± 2M J brown dwarf transiting the early M dwarf TOI-2119 on an eccentric orbit (e = 0.3362 ± 0.0005) at an orbital period of 7.200861 ± 0.000005 days. We confirm the brown dwarf nature of the transiting companion using a combination of ground-based and space-based photometry and high-precision velocimetry from the Habitable-zone Planet Finder. Detection of the secondary eclipse with TESS photometry enables a precise determination of the eccentricity and reveals the brown dwarf has a brightness temperature of 2100 ± 80 K, a value which is consistent with an early L dwarf. TOI-2119 is one of the most eccentric known brown dwarfs with P < 10 days, possibly due to the long circularization timescales for an object orbiting an M dwarf. We assess the prospects for determining the obliquity of the host star to probe formation scenarios and the possibility of additional companions in the system using Gaia EDR3 and our radial velocities.

A Scaling for Atmospheric Heat Redistribution on Tidally Locked Rocky Planets

Abstract Atmospheric heat redistribution shapes the remote appearance of rocky exoplanets, but there is currently no easy way to predict a planet’s heat redistribution from its physical properties. This paper proposes an analytical scaling theory for the heat redistribution on tidally locked rocky exoplanets. The main parameters of the scaling are a planet’s equilibrium temperature, surface pressure, and broadband longwave optical thickness. The scaling compares favorably against idealized general circulation model simulations of TRAPPIST-1b, GJ1132b, and LHS 3844b. For these planets, heat redistribution generally becomes efficient, and a planet’s observable thermal phase curve and secondary eclipse start to deviate significantly from that of a bare rock, once surface pressure exceeds  ( 1 ) bar. The scaling additionally points to planetary scenarios for which heat transport can be notably more or less efficient, such as H2 and CO atmospheres or hot lava ocean worlds. The results thus bridge the gap between theory and imminent observations with the James Webb Space Telescope. They can also be used to parameterize the effect of 3D atmospheric dynamics in 1D models, thereby improving the self-consistency of such models.

Extended use of the Ariel Core Survey Data

The Ariel mission will execute an ambitious survey to measure transit and / or secondary eclipse spectra of the atmospheres of about 1000 exoplanets. I outline here some possible scientific applications of the exquisite Ariel Core Survey data, beyond the science for which they are primarily designed.

Mapping the Pressure-dependent Day–Night Temperature Contrast of a Strongly Irradiated Atmosphere with HST Spectroscopic Phase Curve

Abstract Many brown dwarfs are on ultrashort-period and tidally locked orbits around white dwarf hosts. Because of these small orbital separations, the brown dwarfs are irradiated at levels similar to hot Jupiters. Yet, they are easier to observe than hot Jupiters because white dwarfs are fainter than main-sequence stars at near-infrared wavelengths. Irradiated brown dwarfs are, therefore, ideal hot Jupiter analogs for studying the atmospheric response under strong irradiation and fast rotation. We present the 1.1–1.67 μm spectroscopic phase curve of the irradiated brown dwarf (SDSS1411-B) in the SDSS J141126.20 + 200911.1 brown dwarf–white dwarf binary with the near-infrared G141 grism of the Hubble Space Telescope Wide Field Camera 3. SDSS1411-B is a 50M Jup brown dwarf with an irradiation temperature of 1300 K and has an orbital period of 2.02864 hr. Our best-fit model suggests a phase-curve amplitude of 1.4% and places an upper limit of 11° for the phase offset from the secondary eclipse. After fitting the white dwarf spectrum, we extract the phase-resolved brown dwarf emission spectra. We report a highly wavelength-dependent day–night spectral variation, with a water-band flux variation of about 360% ± 70% and a comparatively small J-band flux variation of 37% ± 2%. By combining the atmospheric modeling results and the day–night brightness temperature variations, we derive a pressure-dependent temperature contrast. We discuss the difference in the spectral features of SDSS1411-B and hot Jupiter WASP-43b, as well as the lower-than-predicted day–night temperature contrast of J4111-BD. Our study provides the high-precision observational constraints on the atmospheric structures of an irradiated brown dwarf at different orbital phases.

The Emission Spectrum of the Hot Jupiter WASP-79b from HST/WFC3

Abstract Here we present a thermal emission spectrum of WASP-79b, obtained via Hubble Space Telescope Wide Field Camera 3 G141 observations as part of the PanCET program. As we did not observe the ingress or egress of WASP-79b’s secondary eclipse, we consider two scenarios: a fixed mid-eclipse time based on the expected occurrence time, and a mid-eclipse time as a free parameter. In both scenarios, we can measure thermal emission from WASP-79b from 1.1 to 1.7 μm at 2.4σ confidence consistent with a 1900 K brightness temperature for the planet. We combine our observations with Spitzer dayside photometry (3.6 and 4.5 μm) and compare these observations to a grid of atmospheric forward models that span a range of metallicities, carbon-to-oxygen ratios, and recirculation factors. Given the strength of the planetary emission and the precision of our measurements, we found a wide range of forward models to be consistent with our data. The best-match equilibrium model suggests that WASP-79b’s dayside has a solar metallicity and carbon-to-oxygen ratio, alongside a recirculation factor of 0.75. Models including significant H− opacity provide the best match to WASP-79b’s emission spectrum near 1.58 μm. However, models featuring high-temperature cloud species—formed via vigorous vertical mixing and low sedimentation efficiencies—with little day-to-night energy transport also match WASP-79b’s emission spectrum. Given the broad range of equilibrium chemistry, disequilibrium chemistry, and cloudy atmospheric models consistent with our observations of WASP-79b’s dayside emission, further observations will be necessary to constrain WASP-79b’s dayside atmospheric properties.

TOI-1431b/MASCARA-5b: A Highly Irradiated Ultrahot Jupiter Orbiting One of the Hottest and Brightest Known Exoplanet Host Stars

Abstract We present the discovery of a highly irradiated and moderately inflated ultrahot Jupiter, TOI-1431b/MASCARA-5 b (HD 201033b), first detected by NASA’s Transiting Exoplanet Survey Satellite mission (TESS) and the Multi-site All-Sky Camera (MASCARA). The signal was established to be of planetary origin through radial velocity measurements obtained using SONG, SOPHIE, FIES, NRES, and EXPRES, which show a reflex motion of K = 294.1 ± 1.1 m s−1. A joint analysis of the TESS and ground-based photometry and radial velocity measurements reveals that TOI-1431b has a mass of M p = 3.12 ± 0.18 M J (990 ± 60 M ⊕), an inflated radius of R p = 1.49 ± 0.05 R J (16.7 ± 0.6 R ⊕), and an orbital period of P = 2.650237 ± 0.000003 days. Analysis of the spectral energy distribution of the host star reveals that the planet orbits a bright (V = 8.049 mag) and young ( 0.29 − 0.19 + 0.32 Gyr) Am type star with T eff = 7690 − 250 + 400 K, resulting in a highly irradiated planet with an incident flux of 〈 F 〉 = 7.24 − 0.64 + 0.68 × 109 erg s−1 cm−2 ( 5300 − 470 + 500 S ⊕ ) and an equilibrium temperature of T eq = 2370 ± 70 K. TESS photometry also reveals a secondary eclipse with a depth of 127 − 5 + 4 ppm as well as the full phase curve of the planet’s thermal emission in the red-optical. This has allowed us to measure the dayside and nightside temperature of its atmosphere as T day = 3004 ± 64 K and T night = 2583 ± 63 K, the second hottest measured nightside temperature. The planet’s low day/night temperature contrast (∼420 K) suggests very efficient heat transport between the dayside and nightside hemispheres. Given the host star brightness and estimated secondary eclipse depth of ∼1000 ppm in the K band, the secondary eclipse is potentially detectable at near-IR wavelengths with ground-based facilities, and the planet is ideal for intensive atmospheric characterization through transmission and emission spectroscopy from space missions such as the James Webb Space Telescope and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey.

First investigation of eclipsing binary KIC 9026766: analysis of light curve and periodic changes

We investigate a short-period W UMa binary KIC 9026766 with an orbital period of 0.2721278d in the Kepler field of view. By applying an automated q-search for the folded light curve and producing a synthetic light curve for this object based on the PHOEBE code, we calculate the fundamental stellar parameters. We also analyze the O − C curve of the primary minima. The orbital period changes can be attributed to the combination of an upward quadratic function and light-travel time effect (LTTE) due to a possible third body with a minimum mass of 0.029 M ⊙ and an orbital period of 972.5866 ±0.0041d. The relative luminosity of the primary and secondary eclipses (Min I − Min II) is calculated. The periodogram of the residuals of the LTTE and Min I − Min II show peaks with the same period of 0.8566d. The background effect of two nearby stars on our target is the possible reason for this signal. By considering the amplitudes and periods of the remaining signals in the O − C curve of minima, spot motion is possible.

Why is it So Hot in Here? Exploring Population Trends in Spitzer Thermal Emission Observations of Hot Jupiters Using Planet-specific, Self-consistent Atmospheric Models

Abstract Thermal emission has now been observed from dozens of exoplanet atmospheres, opening the gateway to population-level characterization. Here, we provide theoretical explanations for observed trends in Spitzer IRAC channel 1 (3.6 μm) and channel 2 (4.5 μm) photometric eclipse depths (EDs) across a population of 34 hot Jupiters. We apply planet-specific, self-consistent atmospheric models, spanning a range of recirculation factors, metallicities, and C/O ratios, to probe the information content of Spitzer secondary eclipse observations across the hot-Jupiter population. We show that most hot Jupiters are inconsistent with blackbodies from Spitzer observations alone. We demonstrate that the majority of hot Jupiters are consistent with low-energy redistribution between the dayside and nightside (hotter dayside than expected with efficient recirculation). We also see that high-equilibrium temperature planets (T eq ≥ 1800 K) favor inefficient recirculation in comparison to the low temperature planets. Our planet-specific models do not reveal any definitive population trends in metallicity and C/O ratio with current data precision, but more than 59% of our sample size is consistent with the C/O ratio ≤ 1 and 35% are consistent with whole range (0.35 ≤ C/O ≤ 1.5). We also find that for most of the planets in our sample, 3.6 and 4.5 μm model EDs lie within ±1σ of the observed EDs. Intriguingly, few hot Jupiters exhibit greater thermal emission than predicted by the hottest atmospheric models (lowest recirculation) in our grid. Future spectroscopic observations of thermal emission from hot Jupiters with the James Webb Space Telescope will be necessary to robustly identify population trends in chemical compositions with its increased spectral resolution, range, and data precision.

On the nature of the single eclipse per 80d orbit of the H-rich luminous WN star WR22

ABSTRACT WR22 = HD 92740 is a bright (V = 6.4 mag), intrinsically luminous, double-line WN7h + O9III-V binary exhibiting one sharp 8 per cent deep eclipse near periastron in its elliptical (e = 0.6) 80-day orbit, when the WR-star passes in front of the O star, with no secondary eclipse. We apply two models (L96, A13) to probe the optical space-based light curves from BRITE-Constellation, including three separate, complete eclipses, that show increased (o-c) scatter compared to the rest of the observations outside the eclipses, likely due to O-star light encountering WR wind-clumps. L96 is a simple atmospheric-eclipse model, often applied to close WR + O binaries, where the O-star is considered a point-source. A13 considers a finite-disk O-star and allows for atmospheric, photospheric and reflection components to the eclipse, permitting a better characterization of its shape through a more physically realistic description of the structures for both stars in WR22. Nevertheless, A13 is still susceptible to uncertainties in the luminosity of the O-star before unique values for the orbital inclination and WR mass-loss rate can be estimated. We present solutions for the two extremes of the O-star, O9V and O9III. As photometry alone cannot allow us to discriminate between these, we compared our results to the spectral models found in the literature and determined the correct solution to be O9V. Our best-fitting A13 Model 1 gives i = 83.5 ± 0.4°, with $\dot{M}_{\rm WR} = (1.86 \pm 0.2) \times 10^{-5} \dot{M}_{\odot }/yr$. The flux ratio in the red BRITE band in this model is FO/FWR = 0.064 ± 0.002.

TOI-2109: An Ultrahot Gas Giant on a 16 hr Orbit

Abstract We report the discovery of an ultrahot Jupiter with an extremely short orbital period of 0.67247414 ± 0.00000028 days (∼16 hr). The 1.347 ± 0.047 R Jup planet, initially identified by the Transiting Exoplanet Survey Satellite (TESS) mission, orbits TOI-2109 (TIC 392476080)—a T eff ∼ 6500 K F-type star with a mass of 1.447 ± 0.077 M ☉, a radius of 1.698 ± 0.060 R ☉, and a rotational velocity of v sin i * = 81.9 ± 1.7 km s−1. The planetary nature of TOI-2109b was confirmed through radial-velocity measurements, which yielded a planet mass of 5.02 ± 0.75 M Jup. Analysis of the Doppler shadow in spectroscopic transit observations indicates a well-aligned system, with a sky-projected obliquity of λ = 1.°7 ± 1.°7. From the TESS full-orbit light curve, we measured a secondary eclipse depth of 731 ± 46 ppm, as well as phase-curve variations from the planet’s longitudinal brightness modulation and ellipsoidal distortion of the host star. Combining the TESS-band occultation measurement with a K s -band secondary eclipse depth (2012 ± 80 ppm) derived from ground-based observations, we find that the dayside emission of TOI-2109b is consistent with a brightness temperature of 3631 ± 69 K, making it the second hottest exoplanet hitherto discovered. By virtue of its extreme irradiation and strong planet–star gravitational interaction, TOI-2109b is an exceptionally promising target for intensive follow-up studies using current and near-future telescope facilities to probe for orbital decay, detect tidally driven atmospheric escape, and assess the impacts of H2 dissociation and recombination on the global heat transport.

Two newly identified eclipsing binaries in open cluster NGC 3532

ABSTRACT We present light-curve analyses of two newly identified detached eclipsing binaries, namely HD 96609 and HD 303734, in the region of the richly populated open cluster NGC 3532. HD 96609 is composed of two main sequence stars (B9-A0V + A2V) with masses and radii of M1 = 2.66 ± 0.02 M⊙, M2 = 1.84 ± 0.01 M⊙, R1 = 2.740 ± 0.006 R⊙, and R2 = 1.697 ± 0.005 R⊙. The positions of the components on logM − logR plane suggest log(age/yr) 8.55, corresponding 350 ± 40 Myr of age, which agrees with the 300 ± 100 Myr age of NGC 3532 estimated in previous studies. We find the distance of HD 96609 as 460 ± 17 pc, which is consistent with the $484^{+35}_{-30}$ pc distance of NGC 3532, estimated from Gaia parallaxes. HD 303734 is an interesting totally eclipsing binary with a quite shallow secondary eclipse. Using photometric properties of the system in conjunction with theoretical calibrations, we estimate that HD 303734 consists of A6V + K3V components. HD 96609 and HD 303734 are the second and third eclipsing binaries discovered in the region of NGC 3532, after the first one, GV Car.

TOI-1518b: A Misaligned Ultra-hot Jupiter with Iron in Its Atmosphere

Abstract We present the discovery of TOI-1518b—an ultra-hot Jupiter orbiting a bright star (V = 8.95). The transiting planet is confirmed using high-resolution optical transmission spectra from EXPRES. It is inflated, with R p = 1.875 ± 0.053 R J, and exhibits several interesting properties, including a misaligned orbit ( 240.34 − 0.98 + 0.93 degrees) and nearly grazing transit ( b = 0.9036 − 0.0053 + 0.0061 ). The planet orbits a fast-rotating F0 host star (T eff ≃ 7300 K) in 1.9 days and experiences intense irradiation. Notably, the TESS data show a clear secondary eclipse with a depth of 364 ± 28 ppm and a significant phase-curve signal, from which we obtain a relative day–night planetary flux difference of roughly 320 ppm and a 5.2σ detection of ellipsoidal distortion on the host star. Prompted by recent detections of atomic and ionized species in ultra-hot Jupiter atmospheres, we conduct an atmospheric cross-correlation analysis. We detect neutral iron (5.2σ), at K p = 157 − 44 + 68 km s−1 and V sys = − 16 − 4 + 2 , adding another object to the small sample of highly irradiated gas-giant planets with Fe detections in transmission. Detections so far favor particularly inflated gas giants with radii ≳1.78 R J, which may be due to observational bias. With an equilibrium temperature of T eq = 2492 ± 38 K and a measured dayside brightness temperature of 3237 ± 59 K (assuming zero geometric albedo), TOI-1518b is a promising candidate for future emission spectroscopy to probe for a thermal inversion.

Retrieving Exoplanet Atmospheres Using Planetary Infrared Excess: Prospects for the Night Side of WASP-43 b and Other Hot Jupiters

Abstract To increase the sample size of future atmospheric characterization efforts, we build on the planetary infrared excess (PIE) technique that has been proposed as a means to detect and characterize the thermal spectra of transiting and non-transiting exoplanets using sufficiently broad wavelength coverage to uniquely constrain the stellar and planetary spectral components from spatially unresolved observations. We performed simultaneous retrievals of stellar and planetary spectra for the archetypal planet WASP-43b in its original configuration and a non-transiting configuration to determine the efficacy of the PIE technique for characterizing the planet’s night-side atmospheric thermal structure and composition using typical out-of-transit JWST observations. We found that using PIE with JWST should enable the stellar and planetary spectra to be disentangled with no degeneracies seen between the two flux sources, thus allowing robust constraints on the planet’s night-side thermal structure and water abundance to be retrieved. The broad wavelength coverage achieved by combining spectra from NIRISS, NIRSpec, and MIRI enables PIE retrievals that are within 10% of the precision attained using traditional secondary eclipse measurements, although mid-IR observations with MIRI alone may face up to 3.5× lower precision on the planet’s irradiation temperature. For non-transiting planets with unconstrained radius priors, we were able to identify and break the degeneracy between planet radius and irradiation temperature using data that resolved the peak of both the stellar and planetary spectra, thus potentially increasing the number of planets amenable to atmospheric characterization with JWST and other future mission concepts.