Limb-darkening Effect Research Articles

ZPEKTR: A code for spectral synthesis of fast-rotating stars

Estimating the physical states of the surfaces of fast-rotating stars is challenging due to several intrinsic processes, which include radiative flux inhomogeneities on the photosphere induced by rotation and circumstellar signatures in their spectra. The analysis of their spectra ultimately requires the use of synthetic grids of spectra accounting for all these physical processes. In this paper, we present the `von ZeiPEl's code for gravity darKening specTRal synthesis' (ZPEKTR) code, which is designed to perform the spectral synthesis of fast-rotating stars, accounting for gravity darkening, limb-darkening effects in the continuum and geometrical deformation induced by fast rotation. We consider colatitudinal temperature and surface-gravity variations, assuming both the classical prescription developed by von Zeipel and the new formulation by Espinosa-Lara. The code runs either with a rectangular or a triangular mesh on the stellar surface. We compare the temperature and gravitational distribution as a function of the stellar latitude arising from both models. The line profiles of 4388, 4471, 4922, and 6678 produced with both formalisms are compared at three different rotation rates and illustrate differences in shape and central intensity. We also illustrate the fittings of 31 line spectra of classical Be stars averaged from the Be Stars Observation Survey (BeSOS) database and make a comparison among their apparent physical parameters and ages determined from plane-parallel non-local thermodynamical equilibrium (non-LTE) models and parameters determined from classical von Zeipel models, finding a displacement of more evolved objects towards the zero-age main sequence. We also compare the distributions of projected rotation velocities of these objects obtained with and without the inclusion of gravity-darkening effects with ZPEKTR. We observe a shift of the histogram of rotation velocities calculated accounting for effects of gravity darkening concerning rotation velocities obtained through the fittings with classical plane-parallel non-LTE models. We show that models that do not account for gravity darkening can underestimate the rotation velocity, because the stellar latitudes that contribute the higher velocities are those in the equator with the least radiative flux. We envisage near-future improvements to the code, such as the inclusion of differential rotation and treatment of tidal forces in binary stellar systems.

Correcting Exoplanet Transmission Spectra for Stellar Activity with an Optimized Retrieval Framework

The chromatic contamination that arises from photospheric heterogeneities, e.g., spots and faculae on the host star presents a significant noise source for exoplanet transmission spectra. If this contamination is not corrected for, it can introduce substantial bias in our analysis of the planetary atmosphere. We utilize two stellar models of differing complexity, StARPA (Stellar Activity Removal for Planetary Atmospheres) and ASteRA (Active Stellar Retrieval Algorithm), to explore the biases introduced by stellar contamination in retrieval under differing degrees of stellar activity. We use the retrieval framework TauREx3 and a grid of 27 synthetic, spot-contaminated transmission spectra to investigate potential biases and to determine how complex our stellar models must be in order to accurately extract the planetary parameters from transmission spectra. The input observation is generated using the more complex model (StARPA), in which the spot latitude is an additional, fixable parameter. This observation is then fed into a combined stellar-planetary retrieval, which contains a simplified stellar model (ASteRA). Our results confirm that the inclusion of stellar activity parameters in retrieval minimizes bias under all activity regimes considered. ASteRA performs very well under low-to-moderate activity conditions, retrieving the planetary parameters with a high degree of accuracy. For the most active cases, characterized by larger, higher-temperature contrast spots, some minor residual bias remains due to ASteRA neglecting the interplay between the spot and the limb-darkening effect. As a result of this, we find larger errors in retrieved planetary parameters for central spots (0°) and those found close to the limb (60°) than those at intermediate latitudes (30°).

Numerically studying the degeneracy problem in extreme finite-source microlensing events

ABSTRACT Most transit microlensing events due to very low mass lens objects suffer from extreme finite-source effects. While modelling their light curves, there is a known continuous degeneracy between their relevant lensing parameters, i.e. the source angular radius normalized to the angular Einstein radius ρ⋆, the Einstein crossing time tE, the lens impact parameter u0, the blending parameter, and the stellar apparent magnitude. In this work, I numerically study the origin of this degeneracy. I find that these light curves have five observational parameters (i.e. the baseline magnitude, the maximum deviation in the magnification factor, the full width at half-maximum $\rm {FWHM}=2 \mathit{ t}_{\rm {HM}}$, the deviation from a top-hat model, and the time of the maximum time derivative of microlensing light curves $T_{\rm {max}}=t_{\rm E}\sqrt{\rho _{\star }^{2}-u_{0}^{2}}$). For extreme finite-source microlensing events due to uniform source stars, we get tHM ≃ Tmax and the deviation from the top-hat model tends to zero, which both cause the known continuous degeneracy. When either ρ⋆ ≲ 10 or the limb-darkening effect is considerable, tHM and Tmax are two independent observational parameters. I use a numerical approach, i.e. random forests containing 100–120 decision trees, to study how these observational parameters are efficient in yielding the lensing parameters. These machine learning models find the mentioned five lensing parameters for finite-source microlensing events from uniform and limb-darkened source stars with the average R2-scores of 0.87 and 0.84, respectively. R2-score for evaluating the lens impact parameter gets worse on adding limb darkening, and for extracting the limb-darkening coefficient itself this score falls as low as 0.67.

Observation and feature measurements of cloud and haze in exoplanet atmosphere based on transmission spectra

Clouds and hazes are important components of exoplanet atmospheres. This paper generalizes features and applications of exoplanet clouds and hazes in transmission spectra. A transmission spectrum presents a planet atmosphere’s wavelength-dependent absorption ability of host star’s radiation during transit. Effective transit radius model is often adopted to explain the wavelength-dependent absorption. In spectrum processing, the effect of stellar limb darkening and star spots should be taken into consideration. Clouds and hazes change features of planet transmission spectrums considerably, e.g., clouds reduce or eliminate absorption features on all bands observed. Since hazes (with small sizes) produce Rayleigh scattering, their reduction in absorption depth is greater in optical band than in infrared band. As transmission spectrum provides limited data about exoplanet atmospheres, emission and reflection spectrum during secondary transit should receive more observation. JWST will perform well in all forms of atmospheric spectrum observation. Advanced knowledge about clouds and hazes will benefit the confine of exoplanet atmospheres’ chemical composition, biosignatures, meteorology as well as planet evolvement model. These results shed light on guiding further exploration of exoplanets and life possibilities on them.

A Low-mass, Pre-main-sequence Eclipsing Binary in the 40 Myr Columba Association—Fundamental Stellar Parameters and Modeling the Effect of Star Spots

Young eclipsing binaries (EBs) are powerful probes of early stellar evolution. Current models are unable to simultaneously reproduce the measured and derived properties that are accessible for EB systems (e.g., mass, radius, temperature, and luminosity). In this study we add a benchmark EB to the pre-main-sequence population with our characterization of TOI 450 (TIC 77951245). Using Gaia astrometry to identify its comoving, coeval companions, we confirm TOI 450 is a member of the ∼40 Myr Columba association. This eccentric (e = 0.2969), equal-mass (q = 1.000) system provides only one grazing eclipse. Despite this, our analysis achieves the precision of a double-eclipsing system by leveraging information in our high-resolution spectra to place priors on the surface-brightness and radius ratios. We also introduce a framework to include the effect of star spots on the observed eclipse depths. Multicolor eclipse light curves play a critical role in breaking degeneracies between the effects of star spots and limb-darkening. Including star spots reduces the derived radii by ∼2% from a unspotted model (>2σ) and inflates the formal uncertainty in accordance with our lack of knowledge regarding the starspot orientation. We derive masses of 0.1768( ± 0.0004) and 0.1767( ± 0.0003) M ⊙, and radii of 0.345(±0.006) and 0.346(±0.006) R ⊙ for the primary and secondary, respectively. We compare these measurements to multiple stellar evolution isochones, finding good agreement with the association age. The MESA MIST and SPOTS (f s = 0.17) isochrones perform the best across our comparisons, but detailed agreement depends heavily on the quantities being compared.

Wavelength-Dependent Solar Limb Darkening with Smartphones, Solar Projection, and SalsaJ

Solar limb darkening is a prominent feature seen in white images of the Sun: the brightness of the solar disk is greatest at the solar center and decreases radially outward towards the limb. White light images can be used to examine and even model limb darkening; however, the limb-darkening effect is, in fact, wavelength dependent. Limb darkening is more pronounced at the blue end of the spectrum and less at the red end. We discuss a relatively simple method to examine the wavelength-dependent nature of limb darkening using solar projection, smartphone imaging, and SalsaJ software.

Analytic model for photometric variation due to starspots on a differentially rotating star

Abstract We present an analytic model of the light-curve variation for stars with non-evolving starspots on a differentially rotating surface. The Fourier coefficients of the harmonics of the rotation period are expressed in terms of the latitude of the spot, ℓs, and the observer’s line-of-sight direction, ℓo, including the limb-darkening effect. We generate different realizations of multi-spots according to the model, and perform mock observations of the resulting light-curve modulations. We discuss to what extent one can recover the properties of the spots and the parameters for the differential rotation law from the periodogram analysis. Although our analytical model neglects the evolution of spots on the stellar surface (dynamical motion, creation, and annihilation), it provides a basic framework to interpret the photometric variation of stars, in particular from the existing Kepler data and the future space-born mission. It is also applicable to photometric modulations induced by rotation of various astronomical objects.

Empirical Limb-darkening Coefficients and Transit Parameters of Known Exoplanets from TESS

Although the main goal of the Transiting Exoplanet Survey Satellite (TESS) is to search for new transiting exoplanets, its data can also be used to study already-known systems in further detail. The TESS bandpass is particularly interesting to study the limb-darkening effect of the stellar host that is imprinted in transit light curves, as the widely used phoenix and atlas stellar models predict different limb-darkening profiles. Here we study this effect by fitting the transit light curves of 176 known exoplanetary systems observed by TESS, which allows us to extract empirical limb-darkening coefficients (LDCs) for the widely used quadratic law but also updated transit parameters (including ephemeride refinements) as a by-product. Comparing our empirically obtained LDCs with theoretical predictions, we find significant offsets when using tabulated TESS LDCs. Specifically, the u 2 coefficients obtained using phoenix models show the largest discrepancies depending on the method used to derive them, with offsets that can reach up to Δu 2 ≈ 0.2, on average. Most of those average offsets disappear, however, if one uses the SPAM algorithm introduced by Howarth to calculate the LDCs instead. Our results suggest, however, that for stars cooler than about 5000 K, no methodology is good enough to explain the limb-darkening effect; we observe a sharp deviation between measured and predicted LDCs on both quadratic LDCs of order Δu 1, Δu 2 ≈ 0.2 for those cool stars. We recommend caution when assuming LDCs as perfectly known, in particular for these cooler stars when analyzing TESS transit light curves.

Measurements of limb-darkening effect and solar radiation during the partial solar eclipse of 21 June 2020 at Varanasi

Measurements of limb-darkening effect and solar radiation during the partial solar eclipse of 21 June 2020 at Varanasi

The strange case of Na I in the atmosphere of HD 209458 b

Aims. We aim to investigate the origin of the discrepant results reported in the literature about the presence of Na I in the atmosphere of HD 209458 b, based on low- and high-resolution transmission spectroscopy. Methods. We generated synthetic planetary atmosphere models and we compared them with the transmission light curves and spectra observed in previous studies. Our models account for the stellar limb-darkening and Rossiter-McLaughlin (RM) effects, and contemplate various possible scenarios for the planetary atmosphere. Results. We reconciled the discrepant results by identifying a range of planetary atmospheres that are consistent with previous low- and high-resolution spectroscopic observations. Either both datasets are interpreted as consistent with a total absence of Na I in the planetary atmosphere (with Hubble Space Telescope data being affected by limb darkening), or the terminator temperature of HD 209458 b has to have an upper limit of about 1000 K. In particular, we find that 1D transmission spectra with lower-than-equilibrium temperatures can also explain the previously reported detection of absorption signal at low resolution due to differential transit depth in adjacent bands, while the cores of the Na I D lines may be masked by the strong RM signal seen at high resolution. We also rule out high-altitude clouds, which would otherwise mask the absorption signal at low resolution, as the source of the discrepancies. Conclusions. This work highlights the synergies between different observing techniques, specifically low- and high-resolution spectroscopy, to fully characterise transiting exoplanet systems.

Correcting the effect of stellar spots on ARIEL transmission spectra – II. The limb-darkening effect

ABSTRACT This paper is part of an effort to correct the transmission spectra of a transiting planet orbiting an active star. In Paper I (Cracchiolo, Micela & Peres 2020), we have demonstrated a methodology to minimize the potential bias induced by unocculted star spots on the transmission spectrum, assuming a spot model parametrized by filling factor and temperature. In this work, we introduce the limb-darkening effect, therefore the position of the spot in the stellar disc and the impact parameter of the transiting planet now play a key role. The method is tested on simulations of planetary transits of three representative kinds of planetary systems, at ARIEL resolution. We find that a realistic treatment of the limb darkening is required to reliably estimate both the spots parameters and the transmission spectrum of the transiting planet. Furthermore, we show that the influence of the spots on the retrieval of the planetary transmission spectrum is significant for spots close to the centre of the star, covering a fraction greater than 0.05 and with a temperature contrast greater than $500\, {\rm K}$, and that for these cases our method can confidently extract the transmission spectrum and the impact parameter of the transiting planet for both cases of occulted and not occulted spots, provided that we have an accurate characterization of the stellar parameters and a reliable simulator of the instrument performances.

Limb-darkening effect of source stars in gravitational microlensing observations in different filters

Spherical property of stars means that the flux received from different parts of their surface is not uniform and less than its center at the edges. Thus, the edges appear darker than the center of the star; this is called the limb-darkening effect. The amount of the limb-darkening effect depends on the stellar atmosphere, stellar temperature, gravity and metallicity. In this paper, we offer a method to better characterize the source stars in high-magnification microlensing events. In high-magnification microlensing events in which the lens is transiting the source surface, the non-uniformity of the stellar flux and the magnification factor as a function of the lens location can both cause the stellar color changes with time. Measuring the stellar color while lens is crossing the source surface will offer additional information regarding the dependence of the limb-darkening parameters on the wave length and hence, the stellar atmosphere parameters and the source star parameters.

Retraction: Revised instellation patterns for close-in exoplanets

The distribution of instellation at the top of a planet's atmosphere or surface is usually calculated using the inverse-square law of radiation. This is based on the assumption that the host star is far enough to be considered a point-sized Lambertian source. This assumption, which works well for the solar system planets and most exoplanets, must be revised for close-in exoplanets. The objective of this work is to derive accurate instellation patterns for close-in exoplanets, for which the effects of the spherical shape of the star must be taken into account. First an analytical formula of the insolation as a function of latitude was derived, taking the star and the planet as 3-D bodies, and incorporating the limb darkening effects of the star. Then numerical techniques were used to compute the distribution of the insolation on close-in planets as a function of latitude for a wide range of stellar and planetary properties.There are significant deviations in instellation values and their distribution on close-in exoplanets, due in similar proportions to the physical size of the star and stellar limb-darkening effects. The insolation at the susbtellar point is always higher -- by as much as 21% for known exoplanets -- than the standard calculation. The substellar longitude of the terminator can significantly extend on the nightside, from 90 degrees up to 110 degrees for known exoplanets.

Homogenization of Geostationary Infrared Imager Channels for Cold Cloud Studies Using Megha-Tropiques/ScaRaB

Infrared (IR) observations from the fleet of multiagencies meteorological geostationary satellites have a great potential to support scientific and operational investigations at a quasi-global scale. In particular, such a data record, defined as the GEOring data set, is well suited to document the tropical convective systems life cycles by applying cloud tracking algorithms. Yet, this GEOring data set is far from being homogeneous, preventing the realization of its potential. A number of sources of inhomogeneities are identified ranging from spatiotemporal resolutions to spectral characteristics of the IR channels and calibration methodologies. While previous efforts have attempted to correct such issues, the adjustment of the cold part of the IR spectrum remains unfit for cold cloud studies. Here, a processing method is introduced to minimize the inhomogeneities against a reference observational data set from the Scanner for Radiation Budget (ScaRaB) instrument onboard the Megha-Tropiques satellite. The method relies on the collocations between the geostationary observations and the reference. The techniques exhibit significant sensitivity to the selection of the relevant pairs of observations requiring a dedicated filtering of the data. A second effort is then proposed to account for the limb-darkening effect and a method is developed to correct the brightness temperature (BT) dependence on the geostationary viewing zenith angle (VZA). Overall, results show a residual after the processing of 0 K between any of the geostationary data and the ScaRaB reference. The final calibrated and limb-adjusted IR observations are then homogeneous for cold BT lower than 240 K with a standard deviation lower than 1.5 K throughout the GEOring.

Role of the impact parameter in exoplanet transmission spectroscopy

Context. Transmission spectroscopy is a promising tool for the atmospheric characterization of transiting exoplanets. Because the planetary signal is faint, discrepancies have been reported regarding individual targets. Aims. We investigate the dependence of the estimated transmission spectrum on deviations of the orbital parameters of the star-planet system that are due to the limb-darkening effects of the host star. We describe how the uncertainty on the orbital parameters translates into an uncertainty on the planetary spectral slope. Methods. We created synthetic transit light curves in seven different wavelength bands, from the near-ultraviolet to the near-infrared, and fit them with transit models parameterized by fixed deviating values of the impact parameter b. First, we performed a qualitative study to illustrate the effect by presenting the changes in the transmission spectrum slope with different deviations of b. Then, we quantified these variations by creating an error envelope (for centrally transiting, off-center, and grazing systems) based on a derived typical uncertainty on b from the literature. Finally, we compared the variations in the transmission spectra for different spectral types of host stars. Results. Our simulations show a wavelength-dependent offset that is more pronounced at the blue wavelengths where the limb-darkening effect is stronger. This offset introduces a slope in the planetary transmission spectrum that becomes steeper with increasing b values. Variations of b by positive or negative values within its uncertainty interval introduce positive or negative slopes, thus the formation of an error envelope. The amplitude from blue optical to near-infrared wavelength for a typical uncertainty on b corresponds to one atmospheric pressure scale height and more. This impact parameter degeneracy is confirmed for different host types; K stars present prominently steeper slopes, while M stars indicate features at the blue wavelengths. Conclusions. We demonstrate that transmission spectra can be hard to interpret, basically because of the limitations in defining a precise impact parameter value for a transiting exoplanet. This consequently limits a characterization of its atmosphere.

Accurate 3-D radiative transfer simulation of spectral solar irradiance during the total solar eclipse of 21 August 2017

Abstract. We calculate the variation of spectral solar irradiance in the umbral shadow of the total solar eclipse of 21 August 2017 and compare it to observations. Starting from the Sun's and Moon's positions, we derive a realistic profile of the lunar shadow at the top of the atmosphere, including the effect of solar limb darkening. Subsequently, the Monte Carlo model MYSTIC (Monte Carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres) is used to simulate the transfer of solar radiation through the Earth's atmosphere. Among the effects taken into account are the atmospheric state (pressure, temperature), concentrations of major gas constituents and the curvature of the Earth, as well as the reflectance and elevation of the surrounding area. We apply the model to the total solar eclipse on 21 August 2017 at a position located in Oregon, USA, where irradiance observations were performed for wavelengths between 306 and 1020 nm. The influence of the surface reflectance, the ozone profile, the mountains surrounding the observer and aerosol is investigated. An increased sensitivity during totality is found for the reflectance, aerosol and topography, compared to non-eclipse conditions. During the eclipse, the irradiance at the surface not only depends on the total ozone column (TOC) but also on the vertical ozone distribution, which in general complicates derivations of the TOC from spectral surface irradiance. The findings are related to an analysis of the prevailing photon path and its difference compared to non-eclipse conditions. Using the most realistic estimate for each parameter, the model is compared to the irradiance observations. During totality, the relative difference between model and observations is less than 10 % in the spectral range from 400 to 1020 nm. Slightly larger deviations occur in the ultraviolet range below 400 and at 665 nm.

Solar sailing near the Sun: A comparison study between point-like and spherical-like Sun models

A study on the behavior of flat and spherical solar sails near the Sun is performed for two Sun models, a point-like model and a spherical-like model. The study is carried on by taking into account two prominent effects near the Sun, Poynting-Robertson effect for high velocities and variation in solar disk intensity. Limb darkening effect has been applied as a model for the variation in solar disk intensity over the wavelength λ∈[302.5,997.5]nm. Acceleration equations for absorption and specular reflection has been developed analytically for spherical sails and flat sails at normal orientation for the spherical model with limb darkening and Poynting-Robertson effect. As a result of the spherical Sun model, in general, escape trajectories show a large decrease in solar sail speed and overall distance in comparison with the point model. Furthermore, for heliocentric bound orbits, large degradation in radial distance over the period of the solar sail mission is found, accompanied with trajectory oscillation. Between the two solar sail configurations, at close encounter to the Sun, the optimal choice is dependent on the possible values of reflectivity and absorptivity.

The highly inflated giant planet WASP-174b

Context. The transiting exoplanetary system WASP-174 was reported to be composed by a main-sequence F star (V = 11.8 mag) and a giant planet, WASP-174b (orbital period Porb = 4.23 days). However only an upper limit was placed on the planet mass (<1.3 MJup), and a highly uncertain planetary radius (0.7−1.7 RJup) was determined. Aims. We aim to better characterise both the star and the planet and precisely measure their orbital and physical parameters. Methods. In order to constrain the mass of the planet, we obtained new measurements of the radial velocity of the star and joined them with those from the discovery paper. Photometric data from the HATSouth survey and new multi-band, high-quality (precision reached up to 0.37 mmag) photometric follow-up observations of transit events were acquired and analysed for getting accurate photometric parameters. We fit the model to all the observations, including data from the TESS space telescope, in two different modes: incorporating the stellar isochrones into the fit, and using an empirical method to get the stellar parameters. The two modes resulted to be consistent with each other to within 2σ. Results. We confirm the grazing nature of the WASP-174b transits with a confidence level greater than 5σ, which is also corroborated by simultaneously observing the transit through four optical bands and noting how the transit depth changes due to the limb-darkening effect. We estimate that ≈76% of the disk of the planet actually eclipses the parent star at mid-transit of its transit events. We find that WASP-174b is a highly-inflated hot giant planet with a mass of Mp = 0.330 ± 0.091 MJup and a radius of Rp = 1.435 ± 0.050 RJup, and is therefore a good target for transmission-spectroscopy observations. With a density of ρp = 0.135 ± 0.042 g cm−3, it is amongst the lowest-density planets ever discovered with precisely measured mass and radius.

Unveiling Uranus: A Difference in Dark Spots Compared to Neptune

We searched for discrete dark features on Uranus at wavelengths near 467 nm and 547 nm, using Hubble Space Telescope data spanning 2014–2022 from the OPAL program (Simon et al. 2015). We unveil subtle cloud features by subtracting a rotationally-averaged mean image from each individual exposure to remove limb-darkening effects. In these wavelength bands, we can rule out the presence of any dark spots with contrasts darker than 1.4% at 467 nm and 1.2% at 547 nm. Dark spots with contrast similar to those seen before on Neptune (Wong et al. 2022) and Uranus (Hammel et al. 2009) would easily have been detected using our approach. Overall, our results suggest that the occurrence rate of dark spots on Uranus is less than one per 11 years, or at least 2—3 times less frequent than on Neptune (Hsu et al. 2019).

Measurements of spectral irradiance during the solar eclipse of 21 August 2017: reassessment of the effect of solar limb darkening and of changes in total ozone

Abstract. Measurements of spectral irradiance between 306 and 1020 nm were performed with a GUVis-3511 multi-channel filter radiometer at Smith Rock State Park, Oregon, during the total solar eclipse of 21 August 2017. The radiometer was equipped with a shadowband, allowing the separation of the global (sun and sky) and direct components of solar radiation. Data were used to study the wavelength-dependent changes in solar irradiance at Earth's surface. Results were compared with theoretical predictions using three different parameterizations of the solar limb darkening (LD) effect, which describes the change in the solar spectrum from the Sun's center to its limb. Results indicate that the LD parameterization that has been most widely used during the last 15 years underestimates the LD effect, in particular at UV wavelengths. The two alternative parameterizations are based on two independent sets of observations from the McMath–Pierce solar telescope. When these parameterizations are used, the observed and theoretical LD effects agree to within 4 % for wavelengths larger than 400 nm and occultation of the solar disk of up to 97.8 %. Maximum deviations for wavelengths between 315 and 340 nm are 7 %. These somewhat larger differences compared to the visible range may be explained with varying aerosol conditions during the period of observations. The aerosol optical depth (AOD) and its wavelength dependence was calculated from measurements of direct irradiance. When corrected for the LD effect, the AOD decreases over the period of the eclipse: from 0.41 to 0.34 at 319 nm and from 0.05 to 0.04 at 1018 nm. These results show that AODs can be accurately calculated during an eclipse if the LD effect is corrected. The total ozone column (TOC) was derived from measurements of global irradiance at 306 and 340 nm. Without correction for the LD effect, the retrieved TOC increases by 20 DU between the first and second contact of the eclipse. With LD correction, the TOC remains constant to within natural variability (±2.6 DU or ±0.9 % between first and second contact and ±1.0 DU or ±0.3 % between third and fourth contact). In contrast to results of observations from earlier solar eclipses, no fluctuations in TOC were observed that could be unambiguously attributed to gravity waves, which can be triggered by the supersonic speed of the Moon's shadow across the atmosphere. Furthermore, systematic changes in the ratio of direct and global irradiance that could be attributed to the solar eclipse were not observed, in agreement with results of three-dimensional (3-D) radiative transfer (RT) models. Our results advance the understanding of the effects of solar LD on the spectral irradiance at Earth's surface, the variations in ozone during an eclipse, and the partitioning of solar radiation in direct and diffuse components.