Occultation Observations Research Articles

Radio Occultation Observations of the Solar Corona Over 1.60–1.86 R⊙: Faraday Rotation and Frequency Shift Analysis

AbstractThe study of coronal energy transport, central to the solar wind acceleration problem, relies upon accurate representation of magnetic fields and plasma electron densities. This information is difficult to obtain in middle‐to‐lower coronal regions that may contain complex magnetic structures. Faraday rotation (FR) solar radio occultation observations, which reveal line‐of‐sight (LOS) integrated product of the coronal magnetic field and electron density, can help characterize the coronal environment and constrain magnetic field strengths. Global magnetohydrodynamic (MHD) models use specified synoptic solar surface magnetograms and may be used to facilitate FR interpretation by estimating detailed magnetic field properties along the radio LOS. We present a hybrid FR analysis incorporating magnetic field solutions from an MHD coronal model, and an electron density radial profile conforming to radio frequency shift observations. The FR modeled by the hybrid method is compared to MErcury Surface, Space ENvironment, GEochemistry and Ranging spacecraft radio FR observations through a coronal region of low heliolatitudes and radial distance 1.60–1.86 R⊙ from the heliocenter, collected during a state of relative solar quiescence. The hybrid model reasonably reproduces the form, polarity, and magnitude of the observed FR. For this specific coronal region, the calculated radial profile of electron concentrations and varied magnetic field strengths indicate Alfvén wave speeds below 50 km/s close to the point of closest approach but near 400 km/s in adjacent regions along the sounding LOS. The new approach of combining MHD models with radio sounding observations supports study of MHD wave processes in the challenging middle‐coronal magneto‐ionic environment.

GNSS Radio Occultation Advances the Monitoring of Volcanic Clouds: The Case of the 2008 Kasatochi Eruption

The products of explosive volcanic eruptions, in particular, volcanic ash, can pose a severe hazard to, for example, international aviation. Detecting volcanic clouds and monitoring their dispersal is hence, the subject of intensive current research. However, the discrepancies between the different available methods lead to detected cloud altitude with significant uncertainties. Here we show the results of an algorithm developed explicitly for high vertical resolution detection of volcanic cloud altitude by using the Global Navigation Satellite System radio occultation (RO) observations. Analyzing the energetic Kasatochi eruption of August 2008 in a case study, we find the volcanic cloud altitudes detected with RO in good agreement (within ~1 km) with cloud altitude estimations from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar backscatter images in the 4 h range between RO and CALIOP acquisitions. The tracking by combined RO and imaging of the volcanic cloud evolution during the weeks after the eruption indicates a promising potential for operational global cloud altitude monitoring.

Tidal wind shear observed by meteor radar and comparison with sporadic E occurrence rates based on GPS radio occultation observations

Abstract. We analyze tidal (diurnal, semidiurnal, terdiurnal, quarterdiurnal) phases and related wind shear in the mesosphere/lower thermosphere as observed by meteor radar over Collm (51.3∘ N, 13.0∘ E). The wind shear phases are compared with those of sporadic E (Es) occurrence rates, which were derived from GPS radio occultation signal-to-noise ratio (SNR) profiles measured by the COSMIC/FORMOSAT-3 satellites. At middle latitudes Es are mainly produced by wind shear, which, in the presence of a horizontal component of the Earth's magnetic field, leads to ion convergence in the region where the wind shear is negative. Consequently, we find good correspondence between radar derived wind shear and Es phases for the semidiurnal, terdiurnal, and quarterdiurnal tidal components. The diurnal tidal wind shear, however, does not correspond to the Es diurnal signal.

TOI-150b and TOI-163b: two transiting hot Jupiters, one eccentric and one inflated, revealed by TESS near and at the edge of the JWST CVZ

Abstract We present the discovery of TYC9191-519-1b (TOI-150b, TIC 271893367) and HD271181b (TOI-163b, TIC 179317684), two hot Jupiters initially detected using 30-min cadence Transiting Exoplanet Survey Satellite (TESS) photometry from Sector 1 and thoroughly characterized through follow-up photometry (CHAT, Hazelwood, LCO/CTIO, El Sauce, TRAPPIST-S), high-resolution spectroscopy (FEROS, CORALIE), and speckle imaging (Gemini/DSSI), confirming the planetary nature of the two signals. A simultaneous joint fit of photometry and radial velocity using a new fitting package juliet reveals that TOI-150b is a $1.254\pm 0.016\ \rm {R}_ \rm{J}$, massive ($2.61^{+0.19}_{-0.12}\ \rm {M}_ \rm{J}$) hot Jupiter in a 5.857-d orbit, while TOI-163b is an inflated ($R_ \rm{P}$ = $1.478^{+0.022}_{-0.029} \,\mathrm{ R}_ \rm{J}$, $M_ \rm{P}$ = $1.219\pm 0.11 \, \rm{M}_ \rm{J}$) hot Jupiter on a P = 4.231-d orbit; both planets orbit F-type stars. A particularly interesting result is that TOI-150b shows an eccentric orbit ($e=0.262^{+0.045}_{-0.037}$), which is quite uncommon among hot Jupiters. We estimate that this is consistent, however, with the circularization time-scale, which is slightly larger than the age of the system. These two hot Jupiters are both prime candidates for further characterization – in particular, both are excellent candidates for determining spin-orbit alignments via the Rossiter–McLaughlin (RM) effect and for characterizing atmospheric thermal structures using secondary eclipse observations considering they are both located closely to the James Webb Space Telescope (JWST) Continuous Viewing Zone (CVZ).

Timing of PSR J2055+3829, an eclipsing black widow pulsar discovered with the Nançay Radio Telescope

We report on the timing observations of the millisecond pulsar PSR J2055+3829 originally discovered as part of the SPAN512 survey conducted with the Nançay Radio Telescope. The pulsar has a rotational period of 2.089 ms and is in a tight 3.1 h orbit around a very low mass (0.023 ≤ mc ≲ 0.053 M⊙, 90% c.l.) companion. Our 1.4 GHz observations reveal the presence of eclipses of the radio signal of the pulsar, caused by the outflow of material from the companion, for a few minutes around superior conjunction of the pulsar. The very low companion mass, the observation of radio eclipses, and the detection of time variations of the orbital period establish PSR J2055+3829 as a “black widow” (BW) pulsar. Inspection of the radio signal from the pulsar during ingress and egress phases shows that the eclipses in PSR J2055+3829 are asymmetric and variable, as is commonly observed in other similar systems. More generally, the orbital properties of the new pulsar are found to be very similar to those of other known eclipsing BW pulsars. No gamma-ray source has been detected at the location of the pulsar in recent Fermi-LAT source catalogs. We used the timing ephemeris to search ten years of Fermi Large Area Telescope (LAT) data for gamma-ray pulsations, but were unable to detect any. This non-detection could be a consequence of the large distance of the pulsar compared to those of known gamma-ray millisecond pulsars outside of globular clusters. We finally compared the mass functions of eclipsing and non-eclipsing BW pulsars and confirmed previous findings that eclipsing BWs have higher mass functions than their non-eclipsing counterparts. Larger inclinations could explain the higher mass functions of eclipsing BWs. On the other hand, the mass function distributions of Galactic disk and globular cluster BWs appear to be consistent, suggesting, despite the very different environments, the existence of common mechanisms taking place in the last stages of evolution of BWs.

Atmospheric Sounding from Fengyun-3C GPS Radio Occultation Observations: First Results and Validation

Carrying global positioning system (GPS) radio occultation (RO) receiver, Chinese meteorological satellite Fengyun-3C (FY-3C) was launched on September 23, 2013, which provides new observation data for observations and studies of weather and climate change. In this paper, the results of FY-3C GPS RO atmospheric sounding are presented for the first time, including high-order ionospheric correction, atmospheric parameters estimation, and evaluation by COSMIC and radiosonde observations as well as applications in estimating gravity wave activities. It is found that the effect of the ionospheric correction residual on the phase delay is below 20 mm, which has minimal impact on bending angle estimation and generates differences of about 1 K in the average temperature profile. The difference between FY-3C and COSMIC temperatures at all heights is within 1°C, and the tropopause temperature and height have a good consistency. Deviations from Radiosonde measurements are within 2°C, and the tropopause temperature and height results also have a strong consistency. Furthermore, global gravity wave potential energy is estimated from FY-3C GPS RO, exhibiting similar behavior to results derived from COSMIC radio occultation measurements. The mean value of the gravity wave potential energy near the equator is 10 J/kg and decreases toward the two poles while in the northern hemisphere, it is stronger than that in the southern hemisphere.

Coronal Plasma Characterization via Coordinated Infrared and Extreme Ultraviolet Observations of a Total Solar Eclipse

Abstract We present coordinated coronal observations of the 2017 August 21 total solar eclipse with the Extreme-ultraviolet Imaging Spectrometer (EIS) and the Airborne Infrared Spectrometer (AIR-Spec). These instruments provide an unprecedented view of the solar corona in two disparate wavelength regimes, the extreme ultraviolet (EUV) and the near- to mid-infrared (IR), opening new pathways for characterizing the complex coronal plasma environment. During totality, AIR-Spec sampled coronal IR spectra near the equatorial west limb, detecting strong sources of Mg viii, S xi, Si ix, and Si x in two passbands encompassing 1.4–4 μm. We apply an intensity-ratio diagnostic to a strong resonant Fe xii line pair arising from the coordinated EIS observations. This results in a high-resolution map of electron density throughout the shared EIS/AIR-Spec field of view. Electron density measurements allow us to produce a similar map of plasma temperature using emission measure (EM) loci analysis as applied to 27 EIS emission lines, providing temperatures of 106.12 ± 103.5 K along the limb and 106.19 ± 103.5 K at about 100″ outward. Applying EM loci analysis to AIR-Spec IR spectra coadded over two 31″ wide ranges centered at two locations, 30″ and 100″ from the limb, produces temperatures consistent with the EIS data, albeit suffering from moderate uncertainties. Regardless, we demonstrate that EUV spectral data are valuable constraints to coronal IR emission models, and will be powerful supplements for future IR solar observatories, particularly DKIST.

Validation of the HITRAN 2016 and GEISA 2015 line lists using ACE-FTS solar occultation observations

The ExoMars Trace Gas Orbiter (TGO) began its nominal science phase at Mars in April 2018, following releases of editions to two major spectroscopic line lists: GEISA 2015 (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), and HITRAN 2016 (High Resolution Transmission). This work evaluates both line lists over the spectral region between 2325–4350 cm−1 using terrestrial solar occultation observations made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). This spectral region is targeted on Mars by two complementary solar occultation instruments on TGO that will monitor temperature and pressure, aerosols, the abundance of CO2, CO, H2O, HDO, CH4, and other undetected trace gases. Major updates to GEISA 2015 and HITRAN 2016, with respect to previous editions, have been focused on CO2 absorption features in support of Earth-observing missions to monitor greenhouse. Since CO2 is the dominant absorber on Mars, making up 96.5% of the atmosphere, validating the updated line lists is critically important before their deployment for ExoMars. We report that updated CO2 parameters make significant improvements to spectral fits made when using both line lists. Several updates to H2O lines in both line lists also show improvement. The primary difference we observe between the two line lists comes from O3 absorption features near 3850 cm−1 and from several CH4 absorption lines in the regions 2800–3200 cm−1 and 4000–4300 cm−1. Because of these differences, we find that using HITRAN 2016 tends to result in better spectral fits, especially below 30 km, than using GEISA 2015 in this spectral region. Differences are strongly reduced with increasing altitude ( > 40 km) as pressure and gas abundance falls off. It was also discovered that several new errors in both new editions of GEISA and HITRAN were introduced since the HITRAN 2012.

Role of Latent Heating Vertical Distribution in the Formation of the Tropical Cold Trap

AbstractThis study examines the role of latent heating (LH) vertical distribution in tropical tropopause layer (TTL) cooling and upper‐tropospheric warming associated with equatorial wave responses using LH from the Tropical Rainfall Measurement Mission and temperature from radio occultation observations. We distinguish the effects of convective and stratiform LH in tropical convection on temperature in the upper troposphere and lower stratosphere. Cross‐spectral analysis of time series of temperature and LH shows that stratiform LH exhibits higher coherence with temperature throughout most of the upper troposphere and lower stratosphere, especially in the equatorial Rossby wave response. Coherence between total LH and temperature tends to increase with the altitude of heating. Highest coherences occur almost exclusively at time scales of the Madden‐Julian Oscillation, suggesting the importance of mesoscale convective activity in TTL cooling and subsequent dehydration processes. These results demonstrate that TTL and upper‐tropospheric temperature perturbations depend on the vertical distribution of LH and that stratiform LH release has strong relationship with the formation of the horseshoe‐shaped cold trap over the Maritime Continent and West Pacific.

Occultation observations of Saturn's rings with Cassini VIMS

We describe the prediction, design, execution and calibration of stellar and solar occultation observations of Saturn's rings by the Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini spacecraft. Particular attention is paid to the technique developed for onboard acquisition of the stellar target and to the geometric and photometric calibration of the data. Examples of both stellar and solar occultation data are presented, highlighting several aspects of the data as well as the different occultation geometries encountered during Cassini's 13-year orbital tour. Complete catalogs of ring stellar and solar occultations observed by Cassini-VIMS are presented, as a guide to the standard data sets which have been delivered to the Planetary Data System's Ring Moon Systems Node (Hedman and Nicholson, 2019b).

Retrieval of Chemical Abundances in Titan's Upper Atmosphere From Cassini UVIS Observations With Pointing Motion

AbstractCassini/Ultraviolet Imaging Spectrograph (UVIS) Far‐UV observations of stellar occultations at Titan are well suited for probing its atmospheric composition and structure. However, due to instrument pointing motion, only 5 out of tens of observations have been analyzed. We present an innovative retrieval method that corrects for the effect of pointing motion by forward modeling the Cassini/UVIS instrument response function with the pointing motion value obtained from the SPICE C‐kernel along the spectral dimension. To illustrate the methodology, an occultation observation made during flyby T52 is analyzed, when the Cassini spacecraft had insufficient attitude control. A high‐resolution stellar model and an instrument response simulator that includes the position of the point source on the detector are used for the analysis of the pointing motion. The Markov chain Monte Carlo method is used to retrieve the line‐of‐sight abundance profiles of eleven species (CH4, C2H2, C2H4, C2H6, HCN, C4H2, C6N2, C6H6, haze, HC3N, and C2N2) in the spectral vector fitting process. We obtain tight constraints on all of the species aside from C2H6, C2N2, and C6N2, for which we only retrieved upper limits. This is the first time that the T52 occultation was used to derive abundances of major hydrocarbon and nitrile species in Titan's upper and middle atmosphere, as pointing motion prohibited prior analysis. With this new method, nearly all of the occultations obtained over the entire Cassini mission could yield reliable profiles of atmospheric composition, allowing exploration of Titan's upper atmosphere over seasons, latitudes, and longitudes.

An emission spectrum for WASP-121b measured across the 0.8–1.1 μm wavelength range using the Hubble Space Telescope

Abstract WASP-121b is a transiting gas giant exoplanet orbiting close to its Roche limit, with an inflated radius nearly double that of Jupiter and a dayside temperature comparable to a late M dwarf photosphere. Secondary eclipse observations covering the 1.1–$1.6\, \mu{\rm m}$ wavelength range have revealed an atmospheric thermal inversion on the dayside hemisphere, likely caused by high-altitude absorption at optical wavelengths. Here we present secondary eclipse observations made with the Hubble Space Telescope Wide Field Camera 3 spectrograph that extend the wavelength coverage from $1.1\, \mu{\rm m}$ down to $0.8\, \mu{\rm m}$. To determine the atmospheric properties from the measured eclipse spectrum, we performed a retrieval analysis assuming chemical equilibrium, with the effects of thermal dissociation and ionization included. Our best-fitting model provides a good fit to the data with reduced $\chi ^2_\nu =1.04$. The data diverge from a blackbody spectrum and instead exhibit emission due to H− shortward of $1.1\, \mu{\rm m}$. The best-fitting model does not reproduce a previously reported bump in the spectrum at $1.25\,\mu{\rm m}$, possibly indicating this feature is a statistical fluctuation in the data rather than a VO emission band as had been tentatively suggested. We estimate an atmospheric metallicity of $[{\rm M}/{\rm H}]= {1.09}_{-0.69}^{+0.57}$, and fit for the carbon and oxygen abundances separately, obtaining $[{\rm C}/{\rm H}]= {-0.29}_{-0.48}^{+0.61}$ and $[{\rm O}/{\rm H}]= {0.18}_{-0.60}^{+0.64}$. The corresponding carbon-to-oxygen ratio is ${\rm C/O} = 0.49_{-0.37}^{+0.65}$, which encompasses the solar value of 0.54, but has a large uncertainty.

Hydraulic and photosynthetic responses of big sagebrush to the 2017 total solar eclipse

The total solar eclipse of August 21, 2017 created a path of totality ~115 km in width across the United States. While eclipse observations have shown distinct responses in animal behavior often emulating nocturnal behavior, the influence of eclipses on plant physiology are less understood. We investigated physiological perturbations due to rapid changes of sunlight and air temperature in big sagebrush (Artemisia tridentata ssp. vaseyana), a desert shrub common within the path of eclipse totality. Leaf gas exchange, water potential, and chlorophyll a fluorescence were monitored during the eclipse and compared to responses obtained the day before in absence of the eclipse. On the day of the eclipse, air temperature decreased by 6.4 °C, coupled with a 1.0 kPa drop in vapor pressure deficit having a 9-minute lag following totality. Using chlorophyll a fluorescence measurements, we found photosynthetic efficiency of photosystem II (Fv’/Fm’) recovered to near dark acclimated state (i.e., 87%), but the short duration of darkness did not allow for complete recovery. Gas exchange data and a simple light response model were used to estimate a 14% reduction in carbon assimilation for one day over sagebrush dominated areas within the path of totality for the Western United States.

Analysis of synchronism and response velocity in instrumental assemblies for the observation of stellar occultations

Currently the stellar occultation technique is one of the most effective methods for observing minor bodies of the Solar System. Due to the collaborative nature of these observations, precise synchronization and short response times are necessary in instrumental assemblies. This paper presents the development of a methodology that allows for the evaluation of the temporal performance of the detectors used in the observation of stellar occultations. The software “TimesCCam” was developed, which, when being photographed by astronomical cameras, graphically represents the parameters of exposure time, dead time, and jitter referenced to UTC. The process of alignment and focus is obtained, thanks to a structure built with movement in the three axes. The methodology was applied in the evaluation of STF-8300M, ST-2000XM and QHY174M-GPS cameras, using different driver software, synchronization methods, and exposure times. In real exposure times, insignificant variations were identified. Dependency was found between the dead times and the configurations used for the CCD cameras, and it was determined that the dead time and its instability in the ST-2000XM camera prevent its use for the observation of stellar occultations. The results show that the STF-8300M camera is convenient for the observation of asteroid occultations, while the QHY174M-GPS camera given its dead time and synchronization, is suitable for the observation of occultations by trans-Neptunian objects.

Influence of ENSO and MJO on the zonal structure of tropical tropopause inversion layer using high-resolution temperature profiles retrieved from COSMIC GPS Radio Occultation

Abstract. Using COSMIC GPS Radio Occultation (RO) observations from January 2007 to December 2016, we retrieved temperature profiles with the height resolution of about 0.1 km in the upper troposphere and lower stratosphere (UTLS). We investigated the distribution of static stability (N2) and the zonal structure of the tropopause inversion layer (TIL) in the tropics, where a large change in the temperature gradient occurs associated with sharp variations in N2. We show the variations in the mean N2 profiles in coordinates relative to the cold-point tropopause (CPT). A very thin (<1 km) layer is found with average maximum N2 in the range of 11.0–12.0×10-4 s−2. The mean and standard deviation of TIL sharpness, defined as the difference between the maximum N2 (max⁡N2) and minimum N2 (min⁡N2) within ±1 km of the CPT, is (10.5±3.7)×10-4 s−2. The max⁡N2 is typically located within 0.5 km above CPT. We focused on the variation in TIL sharpness in two longitude regions, 90–150∘ E (Maritime Continent; MC) and 170–230∘ E (Pacific Ocean; PO), with different land–sea distribution. Seasonal variations in TIL sharpness and thickness were related to the deep convective activity represented by low outgoing longwave radiation (OLR) during the Australian and Asian monsoons. The deviation from the mean sharpness (sharpness anomaly) was out of phase with the OLR anomaly in both the MC and PO. The correlation between the sharpness anomaly over the MC and PO and the sea surface temperature (SST) Niño 3.4 index was −0.66 and +0.88, respectively. During La Niña (SST Niño 3.4 <-0.5 K) in the MC and El Niño (SST Niño 3.4 >+0.5 K) in the PO, warmer SSTs in the MC and PO produce more active deep convection that tends to force the air upward to the tropopause layer and increase the temperature gradient there. The intraseasonal variation in sharpness anomaly during slow and fast episodes of the Madden–Julian Oscillation (MJO) demonstrates that eastward propagation of the positive sharpness anomaly is associated with organized deep convection. Deep convection during MJO will tend to decrease N2 below CPT and increase N2 above CPT, thus enlarging the TIL sharpness. Convective activity in the tropics is a major control on variations in tropopause sharpness at intraseasonal to interannual timescales.

Haumea’s Shape, Composition, and Internal Structure

We have calculated the figure of equilibrium of a rapidly rotating, differentiated body to determine the shape, structure, and composition of the dwarf planet Haumea. Previous studies of Haumea's light curve have suggested Haumea is a uniform triaxial ellipsoid consistent with a Jacobi ellipsoid with axes $\approx 960 \times 774 \times 513$ km, and bulk density $\approx 2600 \, {\rm kg} \, {\rm m}^{-3}$. In contrast, observations of a recent stellar occultation by Haumea indicate its axes are $\approx 1161 \times 852 \times 523$ km and its bulk density $\approx 1885 \, {\rm kg} \, {\rm m}^{-3}$; these results suggest that Haumea cannot be a fluid in hydrostatic equilibrium and must be partially supported by interparticle forces. We have written a code to reconcile these contradictory results and to determine if Haumea is in fact a fluid in hydrostatic equilibrium. The code calculates the equilibrium shape, density, and ice crust thickness of a differentiated Haumea after imposing (semi-) axes lengths $a$ and $b$. We find Haumea is consistent with a differentiated triaxial ellipsoid fluid in hydrostatic equilibrium with axes of best fit $a$ = 1050 km, $b$ = 840 km, and $c$ = 537 km. This solution for Haumea has $\rho_{\rm avg} = 2018 \, {\rm kg} \, {\rm m}^{-3}$, $\rho_{\rm core} = 2680 \, {\rm kg} \, {\rm m}^{-3}$, and core axes $a_{\rm c} = 883$ km, $b_{\rm c} = 723$ km, and $c_{\rm c}=470$ km, which equates to an ice mantle comprising $\sim 17\%$ of Haumea's volume and ranging from 67 to 167 km in thickness. The thick ice crust we infer allows for Haumea's collisional family to represent only a small fraction of Haumea's pre-collisional ice crust. For a wide range of parameters, the core density we calculate for Haumea suggests that today the core is composed of hydrated silicates and likely underwent serpentinization in the past.

The Two-Parts Step-by-Step Ionospheric Assimilation Based on Ground-Based/Spaceborne Observations and Its Verification

This study introduced a Kalman filtering assimilation model that considers the DCB errors of GPS/LEO satellites and GNSS stations. The assimilation results and reliability were verified by various types of data, such as ionMap, ionosonde, ISR, and the EDP of ionPrf from COSMIC. The following analyses were carried out. Assimilating the measured ground-based/spaceborne ionospheric observation data from DOY 010, 2008 and DOY 089, 2012 revealed that the introduction of GPS/LEO satellite and GPS station DCB errors can effectively suppress the STEC observation errors caused by the single-layer hypothesis. Furthermore, the top of the ionosphere contributes 2.8 TECU (approximately 10–20% of the STEC) of electrons during the ionospheric quiet period, greatly influencing the ionospheric assimilation at altitudes of 100–800 km. The assimilation results also show that, after subtracting the influence of the top of the ionosphere, the ionospheric deviation during the quiet period improved from 1.645 TECU to 1.464 TECU; when the ionosphere was active, the standard deviation was improved from 4.408 TECU to 3.536 TECU. The IRI-Imp model introduced by Wu et al. and the IRI (2007) model were used as background fields to compare the effects of COSMIC occultation observation data on the ionospheric assimilation process. Upon comparison, the occultation data introduced by the improved model showed the greatest improvement in the vertical structure of the ionosphere; additionally, the assimilation process reused the horizontal structure information of the occultation data, and the assimilation result (IRI-Imp-Assi) was the most ideal. Due to the lack of an occultation data correction, the IRI2007 model was relatively more prone to errors. With the strategy of the IRI-Imp-Assi model, the introduction of occultation data caused a more significant reduction in the error between the assimilation model with the IRI model as the background field and the ionMap.

Secondary eclipse of the hot Jupiter WASP-121b at 2 μm

Ground-based observations of the secondary eclipse in the 2MASS K band are presented for the hot Jupiter WASP-121b. These are the first occultation observations of an extrasolar planet that were carried out with an instrument attached to a 1 m class telescope (the SMARTS 1.3 m). We find a highly significant eclipse depth of (0.228 ± 0.023)%. Together with other planet atmosphere measurements, including the Hubble Space Telescope near-infrared emission spectrum, current data support more involved atmosphere models with species producing emission and absorption features, rather than simple smooth blackbody emission. Analysis of the time difference between the primary and secondary eclipses and the durations of these events yields an eccentricity of e = 0.0207 ± 0.0153, which is consistent with the earlier estimates of low or zero eccentricity, but with a smaller error. Comparing the observed occultation depth in the K band with the one derived under the assumption of zero Bond albedo and full heat redistribution, we find that WASP-121b has a deeper observed occultation depth than predicted. Together with the sample of 31 systems with K-band occultation data, this observation lends further support to the idea of inefficient heat transport between the day and night sides for most of the hot Jupiters.

The EBLM Project

Measurements of the physical properties of stars at the lower end of the main sequence are scarce. In this context we report masses, radii and surface gravities of ten very-low-mass stars in eclipsing binary systems, with orbital periods of the order of several days. The objects probe the stellar mass-radius relation in the fully convective regime, M⋆ ≲ 0.35 M⊙, down to the hydrogen burning mass-limit, MHB ∼ 0.07 M⊙. The stars were detected by the WASP survey for transiting extra-solar planets, as low-mass, eclipsing companions orbiting more massive, F- and G-type host stars. We use eclipse observations of the host stars, performed with the TRAPPIST, Leonhard Euler and SPECULOOS telescopes, and radial velocities of the host stars obtained with the CORALIE spectrograph, to determine the physical properties of the low-mass companions. Surface gravities of the low-mass companions are derived from the eclipse and orbital parameters of each system. Spectroscopic measurements of the host star effective temperature and metallicity are used to infer the host star mass and age from stellar evolution models for solar-type stars. Masses and radii of the low-mass companions are then derived from the eclipse and orbital parameters of the binary systems. The objects are compared to stellar evolution models for low-mass stars, to test for an effect of the stellar metallicity and orbital period on the radius of low-mass stars in close binary systems. Measurements are found to be in good agreement with stellar evolution models; a systematic inflation of the radius of low-mass stars with respect to model predictions is limited to 1.6 ± 1.2%, in the fully convective low-mass regime. The sample of ten objects indicates a scaling of the radius of low-mass stars with the host star metallicity. No correlation between stellar radii and the orbital periods of the binary systems is determined. A combined analysis with thirteen comparable objects from the literature is consistent with this result.

The Influence of Host Star Spectral Type on Ultra-hot Jupiter Atmospheres

Abstract Ultra-hot Jupiters are the most highly irradiated gas giant planets, with equilibrium temperatures from 2000 to over 4000 K. Ultra-hot Jupiters are amenable to characterization due to their high temperatures, inflated radii, and short periods, but their atmospheres are atypical for planets in that the photosphere possesses large concentrations of atoms and ions relative to molecules. Here we evaluate how the atmospheres of these planets respond to irradiation by stars of different spectral type. We find that ultra-hot Jupiters exhibit temperature inversions that are sensitive to the spectral type of the host star. The slope and temperature range across the inversion both increase as the host star effective temperature increases due to enhanced absorption at short wavelengths and low pressures. The steep temperature inversions in ultra-hot Jupiters around hot stars result in increased thermal dissociation and ionization compared to similar planets around cooler stars. The resulting increase in H− opacity leads to a transit spectrum that has muted absorption features. The emission spectrum, however, exhibits a large contrast in brightness temperature, a signature that will be detectable with both secondary eclipse observations and high-dispersion spectroscopy. We also find that the departures from local thermodynamic equilibrium in the stellar atmosphere can affect the degree of heating caused by atomic metals in the planet’s upper atmosphere. Additionally, we further quantify the significance of heating by different opacity sources in ultra-hot Jupiter atmospheres.