Solar Atlases Research Articles

Maximization of Total Profit for Hybrid Hydro-Thermal-Wind-Solar Power Systems Considering Pumped Storage, Cascaded Systems, and Renewable Energy Uncertainty in a Real Zone, Vietnam

The study maximizes the total profit of a hybrid power system with cascaded hydropower plants, thermal power plants, pumped storage hydropower plants, and wind and solar power plants over one operation day, considering the uncertainty of wind speed and solar radiation. Wind speed and solar radiation in a specific zone in Vietnam are collected using the wind and solar global atlases, and the maximum data are then supposed to be 120% of the collection for uncertainty consideration. The metaheuristic algorithms, including the original Slime mould algorithm (SMA), Equilibrium optimizer, and improved Slime mould algorithm (ISMA), are implemented for the system. ISMA is a developed version of SMA that cancels old methods and proposes new methods of updating new solutions. In the first stage, the cascaded system with four hydropower plants is optimally operated by simulating two cases: simultaneous optimization and individual optimization. ISMA is better than EO and SMA for the two cases, and the results of ISMA from the simultaneous optimization reach greater energy than individual optimization by 154.8 MW, equivalent to 4.11% of the individual optimization. For the whole system, ISMA can reach a greater total profit than EO and SMA over one operating day by USD 6007.5 and USD 650.5, equivalent to 0.12% and 0.013%. The results indicate that the optimization operation of cascaded hydropower plants and hybrid power systems can reach a huge benefit in electricity sales

Egypt’s energy balance map: a geographical perspective

ABSTRACT This study aims to determine Egypt’s potential for energy sources, and the volume of potential energy production and consumption, balancing inputs, outputs and availability of energy. The study depends on analyzing the map of Egypt’s energy balance of non-renewable and renewable energy, including oil, gas, solar, and wind energy, using UN-Energy Balance of Egypt data and the global solar and wind atlases of Egypt. It demonstrates that in 2020 Egypt’s production of fossil fuels is 89.03% of the total energy production, while renewable energy production is only 10.97%. More specifically, fossil fuel consumption is 97.8% of the total consumed energy, while energy consumption from renewable sources is 2.2%. Therefore, this study recommends that further studies should be conducted to explore ‘hybrid’ energy sources to solve Egypt’s energy crisis and to preserve the environment through clean energy sources, such as using green hydrogen and working on reducing emissions from fossil fuels. It is also recommended that there is value in employing GIS and RS applications to estimate the potential of renewable energy across the map of Egypt, and to present this information to possible investors who could expand the development of clean energy sources.

The Environmental Feasibility of Decentralised Solar Ammonia.

Intense efforts have been devoted to developing green and blue centralised Haber-Bosch processes (gHB and bHB, respectively), but the feasibility of a decentralised and sustainable scheme has yet to be assessed. Here we reveal the conditions under which small-scale systems based on the electrocatalytic reduction of nitrogen (eN2R) powered by photovoltaic energy (NH3-leaf) could become a competitive technology in terms of environmental criteria. To this end, we calculated energy efficiency targets based on solar irradiation atlases to guide research in the incipient eN2R field. Even under this germinal state, the NH3-leaf technology would compete favourably in sunny locations relative to the business-as-usual production scenario. The disclosed sustainability potential of NH3-leaf makes it a strong ally of gHB toward a non-fossil ammonia production.

Predicting the suitability area of heath alliances over France using open-source data

While fine-scale maps of vegetation alliances are required for conservation, their distribution is usually known at broad scales. Open-access field and spatial data are increasingly available worldwide, but their contribution to modelling vegetation alliances remains to be assessed. This study aimed to map the suitability area of six heath alliances distributed along ecological gradients throughout France. We used 20 broad and local variables derived from WorldClim, the European Union DEM, SoilGrids, and the Global Wind and Solar Atlases that describe bioclimatic and environmental conditions. For each alliance, two nested MaxEnt models were calibrated and validated using archive field data: one at a broad scale (1000 × 1000 m) to define its bioclimatic area, and the second at a local scale (25 × 25 m) to predict its environmental area. The results showed complementarity of the variables used to discriminate the alliances, and the accuracy of spatial modelling at broad (AUC = 0.83–0.99) and local scales (AUC = 0.91–0.99). They also highlighted the gradients of continentality and temperature that differentiate the alliances. These new maps provide additional knowledge about alliance distribution areas and could support natural vegetation conservation at a national scale.

Creation of Turkey's Solar Exergy Potantial Atlas (SEXPATR)

In this study, Turkey's annual and monthly solar exergy potential atlases (SEXPATR) in ArcGIS software has been created by calculating exergy of solar radiation values for all provinces in Turkey (MJ/m2yr). Annual solar radiation exergy values for Turkey 4346,67 MJ/m2yr and 5613,68 MJ/m2yr calculated and the average annual solar radiation exergy amount was set at 5034,37 MJ/m2yr. The highest value was determined for Karaman province and the lowest value for Bartın province. The average monthly solar radiation exergy value was determined as 160,25 MJ/m2months in average at the lowest December and 665,06 MJ/m2months in July at the highest. The annual exergy / energy ratio was calculated between 92,95% and 94,17%, with an annual average value of 93,39%.

The IAG Solar Flux Atlas: Telluric Correction with a Semiempirical Model

Abstract Observations of the Sun as a star have been key to guiding models of stellar atmospheres and additionally provide useful insights on the effects of granulation and stellar activity on radial velocity measurements. Most high-resolution solar atlases contain telluric lines that span the optical and limit the spectral regions useful for analysis. We present here a telluric-corrected solar atlas covering 0.5–1.0 μm derived from solar spectra taken with a Fourier transform spectrograph at the Institut für Astrophysik, Göttingen. This atlas is the highest-resolution spectrum with a wavelength calibration precise to ±10 m s−1 across this 500 nm spectral window. We find that the atlas matches to within 3% of the telluric-corrected Kitt Peak atlas in regions containing telluric absorption weaker than 50% in transmission. The telluric component of the spectral data is fit with a semiempirical model composed of Lorentz profiles initialized to the High-resolution Transmission Molecular Absorption Database (HITRAN) parameters for each absorption feature. Comparisons between the best-fit telluric parameters describing the Lorentz profile for each absorption feature and the original HITRAN values in general show excellent agreement considering the effects atmospheric pressure and temperature have on our final parameters. However, we identify a small subset of absorption features with larger offsets relative to the cataloged line parameters. We make our final solar atlas available online. We additionally make available the telluric spectra extracted from the data that, given the high resolution of the spectrum, would be useful for studying the time evolution of telluric line shapes and their impact on Doppler measurements.

Accurate effective temperature from Hα profiles

Context. The determination of stellar effective temperature (Teff) in F, G, and K stars using Hα profile fitting is a quite remarkable and powerful tool because it does not depend on reddening and is only slightly sensitive to other atmospheric parameters. Nevertheless, this technique is not frequently used because of the complex procedure needed to recover the profile of broad lines in echelle spectra. As a consequence, tests performed on different models have sometimes provided ambiguous results. Aims. The main aim of this work is to test the ability of the Hα profile fitting technique to derive Teff. We also aim to improve the applicability of this technique to echelle spectra and to test how well 1D + LTE models perform on a variety of F–K stars. We also apply the technique to HARPS spectra and test the reliability and the stability of the HARPS response over several years using the Sun. Methods. We have developed a normalization method for recovering undistorted Hα profiles and we have first applied it to spectra acquired with the single-order Coudé instrument (resolution R = 45 000) at do Pico dos Dias Observatory to avoid the problem of blaze correction. The continuum location around Hα is optimised using an iterative procedure, where the identification of minute telluric features is performed. A set of spectra was acquired with the MUSICOS echelle spectrograph (R = 40 000) to independently validate the normalization method. The accuracy of the method and of the 1D + LTE model is determined using Coudé/HARPS/MUSICOS spectra of the Sun and Coudé-only spectra of a sample of ten Gaia Benchmark Stars with Teff determined from interferometric measurements. HARPS, Coudé, and MUSICOS spectra are used to determine Teff of 43 sample stars. Results. We find that a proper choice of spectral windows of fits plus the identification of telluric features allow for a very careful normalization of the spectra and produce reliable Hα profiles. We also find that the most used solar atlases cannot be used as templates for Hα temperature diagnostics without renormalization. The comparison with the Sun shows that Hα profiles from 1D + LTE models underestimate the solar Teff by 28 K. We find the same agreement between Hα and interferometry and between Hα and Infrared Flux Method: a shallow dependency on metallicity according to the relation Teff = TeffHα − 159[Fe/H] + 28 K within the metallicity range − 0.70 to + 0.40 dex. The comparison with the Infrared Flux Method shows a scatter of 59 K dominated by photometric errors (52 K). In order to investigate the origin of this dependency, we analyzed spectra from 3D models and found that they produce hotter temperatures, and that their use largely improves the agreement with the interferometric and Infrared Flux Method measurements. Finally, we find HARPS spectra to be fully suitable for Hα profile temperature diagnostics; they are perfectly compatible with the Coudé spectra, and lead to the same Teff for the Sun as that found when analysing HARPS spectra over a timespan of more than 7 yr.

Determination of Diffused Irradiation from Horizontal Global Irradiation - Study for the City of Curitiba

Abstract Understanding the solar radiation values ​​in the surface is important for the development of solar energy projects, obtaining through radiometers installed in certain places or publications as in solar energy atlases. Typically, solar or weather stations do not have sensors to measure diffuse irradiation due to high investment and the need for constant maintenance. This paper presents methods for the determination of diffuse irradiation from surface measured data of global horizontal irradiation in the city of Curitiba, obtained through pyranometers installed at the Federal University of Technology – Parana (UTFPR) headquarters and from Curitiba-A807 National Institute of Meteorology (INMET) station. Two models are presented for the estimation of the monthly mean daily diffuse irradiation, based on the studies of Liu and Jordan (1960) and Page (1961). Finally, these data were compared with those presented by the Solar Energy Atlas - Parana, verifying the percentage differences presented. It was observed that the model elaborated by Page presented better results in the diffuse radiation estimates when compared to the values ​​presented by the Parana Atlas, with an average variation of -1.39% and -1.55%, for data from INMET and UTFPR respectively.

PEPSI deep spectra

Context. Full-disk solar flux spectra can be directly compared to stellar spectra and thereby serve as our most important reference source for, for example stellar chemical abundances, magnetic activity phenomena, radial-velocity signatures or global pulsations. Aim. As part of the first Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) key-science project, we aim to provide well-exposed and average-combined (viz. deep) high-resolution spectra of representative stellar targets. Such deep spectra contain an overwhelming amount of information, typically much more than what could be analyzed and discussed within a single publication. Therefore, these spectra will be made available in form of (electronic) atlases. The first star in this series of papers is our Sun. It also acts as a system-performance cornerstone. Methods. The Sun was monitored with PEPSI at the Large Binocular Telescope (LBT). Instead of the LBT we used a small robotic solar disk integration (SDI) telescope. The deep spectra in this paper are the results of combining up to ≈100 consecutive exposures per wavelength setting and are compared with other solar flux atlases. Results. Our software for the optimal data extraction and reduction of PEPSI spectra is described and verified with the solar data. Three deep solar flux spectra with a spectral resolution of up to 270 000, a continuous wavelength coverage from 383 nm to 914 nm, and a photon signal to noise ratio (S/N) of between 2000–8000:1 depending on wavelength are presented. Additionally, a time-series of 996 high-cadence spectra in one cross disperser is used to search for intrinsic solar modulations. The wavelength calibration based on Th-Ar exposures and simultaneous Fabry–Pérot combs enables an absolute wavelength solution within 10 m s−1 (rms) with respect to the HARPS laser-comb solar atlas and a relative rms of 1.2 m s−1 for one day. For science demonstration, we redetermined the disk-average solar Li abundance to 1.09 ± 0.04 dex on the basis of 3D NLTE model atmospheres. We detected disk-averaged p-mode RV oscillations with a full amplitude of 47 cm s−1 at 5.5 min. Conclusions. Comparisons with two solar FTS atlases, as well as with the HARPS solar atlas, validate the PEPSI data product. Now, PEPSI/SDI solar-flux spectra are being taken with a sampling of one deep spectrum per day, and are supposed to continue a full magnetic cycle of the Sun.

The Solar-flux Third Granulation Signature

Abstract The velocity shifts of spectral lines as a function of line strength, so-called the third signature of granulation, are investigated using three published solar-flux atlases. We use flux atlases because we wish to treat the Sun as a star, against which stellar observations can be compared and judged. The atlases are critiqued and compared to the lower-resolution observations taken with the Elginfield stellar spectrograph. Third-signature plots are constructed for the 6020–6340 Å region. No dependence on excitation potential or wavelength is found over this wavelength span. The shape of the plots from the three solar atlases is essentially the same, with rms line-core velocity differences of 30–35 m s−1. High-resolution atlas data are degraded to the level of the Elginfield spectrograph and compared to direct observations taken with that spectrograph. The line-core velocities show good agreement, with rms differences of 38 m s−1. A new standard curve is derived and compared with the previously published one. Only small differences in shape are found, but a significant (+97 m s−1) change in the zero point is indicated. The bisector of the Fe i 6253 line is mapped onto the third-signature plots and flux deficits are derived, which measure the granule/lane flux imbalance. The lower spectral resolution lowers the flux deficit area slightly and moves the peak of the deficit 0.3–0.5 km s−1 toward higher velocities. These differences, while significant, are not large compared to measurement errors for stellar data.

Uncertainties in the solar photospheric oxygen abundance

The purpose of this work is to better understand the confidence limits of the photospheric solar oxygen abundance derived from three-dimensional models using the forbidden [OI] line at 6300 \AA , including correlations with other parameters involved. We worked with a three-dimensional empirical model and two solar intensity atlases. We employed Bayesian inference as a tool to determine the most probable value for the solar oxygen abundance given the model chosen. We considered a number of error sources, such as uncertainties in the continuum derivation, in the wavelength calibration and in the abundance/strength of Ni. Our results shows correlations between the effects of several parameters employed in the derivation. The Bayesian analysis provides robust confidence limits taking into account all of these factors in a rigorous manner. We obtain that, given the empirical three-dimensional model and the atlas observations employed here, the most probable value for the solar oxygen abundance is $\log(\epsilon_O) = 8.86\pm0.04$. However, we note that this uncertainty does not consider possible sources of systematic errors due to the model choice.

The HERMES solar atlas and the spectroscopic analysis of the seismic solar analogue KIC 3241581

Solar-analog stars provide an excellent opportunity to study the Sun's evolution, i.e. the changes with time in stellar structure, activity, or rotation for solar-like stars. The unparalleled photometric data from the NASA space telescope Kepler allows us to study and characterise solar-like stars through asteroseismology. We aim to spectroscopically investigate the fundamental parameter and chromospheric activity of solar analogues and twins, based on observations obtained with the HERMES spectrograph and combine them with asteroseismology. Therefore, we need to build a solar atlas for the spectrograph, to provide accurate calibrations of the spectroscopically determined abundances of solar and late type stars observed with this instrument and thus perform differential spectral comparisons. We acquire high-resolution and high signal-to-noise spectroscopy to construct three solar reference spectra by observing the reflected light of Vesta and Victoria asteroids and Europa (100<S/N<450) with the \Hermes spectrograph. We then observe the Kepler solar analog KIC3241581 (S/N~170). We constructed three solar spectrum atlases from 385 to 900 nm obtained with the Hermes spectrograph from observations of two bright asteroids and Europa. A comparison between our solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent agreement. KIC3241581 was found to be a long-periodic binary system. The fundamental parameter for the stellar primary component are Teff=5689+/-11K, logg=4.385+/-0.005, [Fe/H]=+0.22+/-0.01, being in agreement with the published global seismic values confirming its status of solar analogue. KIC 3241581 is a metal rich solar analogue with a solar-like activity level in a binary system of unknown period. The chromospheric activity level is compatible to the solar magnetic activity.

The IAG solar flux atlas: Accurate wavelengths and absolute convective blueshift in standard solar spectra

We present a new solar flux atlas with the aim to understand wavelength precision and accuracy in solar benchmark data. The atlas covers the wavelength range 405--2300 nm and was observed at the Institut f\"ur Astrophysik, G\"ottingen (IAG) with a Fourier Transform Spectrograph. In contrast to other FTS atlases, the entire visible wavelength range was observed simultaneously using only one spectrograph setting. We compare the wavelength solution of the new atlas to the Kitt Peak solar flux atlases and to the HARPS frequency-comb calibrated solar atlas. Comparison reveals systematics in the two Kitt Peak FTS atlases resulting from their wavelength scale construction, and shows consistency between the IAG and the HARPS atlas. We conclude that the IAG atlas is precise and accurate on the order of $\pm 10$ m s$^{-1}$ in the wavelength range 405--1065 nm while the Kitt Peak atlases show deviations as large as several ten to 100 m s$^{-1}$. We determine absolute convective blueshift across the spectrum from the IAG atlas and report slight differences relative to results from the Kitt Peak atlas that we attribute to the differences between wavelength scales. We conclude that benchmark solar data with accurate wavelength solution are crucial to better understand the effect of convection on stellar RV measurements, which is one of the main limitations of Doppler spectroscopy at m s$^{-1}$ precision.

Community-scale assessment of rooftop-mounted solar energy potential with meteorological, atlas, and GIS data: a case study of Guelph, Ontario (Canada)

Forward-thinking governments recognize that local renewable resource use is crucial to the resilience of communities and are developing and implementing community energy plans (CEPs). Guelph, Ontario, (Canada) included solar energy in its CEP, but the question of resource potential remained. The primary goal of this work was the assessment of Guelph’s solar energy potential with arrays of grid-tied, rooftop-mounted photovoltaic (PV) and hot-water (HW) panels. This work relies on atlas and meteorological data with insolation modeling to evaluate the solar resource and incorporates geographic information system data for rooftop area quantification. The assessment applies the performance characteristics of commercially available PV and HW panels and systems to estimate the upper-limit potential for electricity and hot-water production. The modeling results closely matched the values provided by two solar resource atlases for multiple orientations and time periods. Extensive modeling led to the development of sunflower diagrams, radial plots representing the variation of insolation on planar surfaces with orientation and inclination. The optimum orientation for annual beam and sky-diffuse insolation occurred at 18° east of south with a slope of 30°. Deviation from the optimum by 15° resulted in losses of less than 5%. Assuming horizontal rooftops, Guelph could provide 1,496 GWh of electricity or 5,360 GWh[e] of heat, over 90% or twice the respective demands for 2005. Including the variation of rooftop orientation and inclination, Guelph could achieve 2,950 GWh of electricity or 10,580 GWh[e] of heat, approaching double and quadruple the respective 2005 demands.

Na I spectra in the 1.4–14 micron range: transitions and oscillator strengths involving f-, g-, and h-states

Context. Compared with the visible and ultraviolet ranges, fewer atomic and ionic lines are available in the infrared spectral region. Atlases of stellar spectra often provide only a short list of identified lines, and modern laboratory-based spectral features for wavelengths longer than 1 micron are not available for most elements. For the efficient use of the growing capabilities of infrared (IR) astronomy, detailed spectroscopical information on atomic line features in the IR region is needed. Aims. Parts of the infrared stellar (e.g., solar) spectra in the 1200–1800 cm-1 (5.6–8 μ m) range have never been observed from the ground because of heavy contamination of the spectrum by telluric absorption lines. Such an infrared spectrum represents a great challenge for laboratory observations of new, unknown infrared atomic transitions involving the atomic levels with high orbital momentum and their comparison with the available spectra. Methods. The vapors of excited Na i atoms are produced during the ablation of the salt (sodium iodide, Na i) targets by a high-repetition rate (1.0 kHz) pulsed nanosecond ArF laser ExciStar S-Industrial V2.0 1000, pulse length 12 ns, λ = 193 nm, output energy of 15 mJ, fluence about 2–20 J/cm2 inside a vacuum chamber (average pressure 10-2 Torr). The time-resolved emission spectrum of the neutral atomic potassium (Na i) was recorded in the 700–7000 cm-1 region using the Fourier transform infrared spectroscopy technique with a resolution of 0.02 cm-1 . The f -values calculated in the quantum-defect theory approximation are presented for the transitions involving the reported Na i levels. Results. This study reports precision laboratory measurements for 26 Na i lines in the range of 700–7000 cm-1 (14–1.4 μ m), including 20 lines not measured previously in the laboratory. This results in newly observed 7h, 6h, and 6g levels, and improved energy determination for ten previously known levels. The doublet structure of the 4f level has been observed for the first time. For transitions between the observed levels, we report calculated f -values that agree reasonably well with experiment.Conclusions. The recorded Na i line features agree with the data from the available solar spectrum atlases. The energy values of Na i 4s, 4p, 5p, 6p, 4f, 5f, and 5g levels extracted from our spectra have lower uncertainties as compared to the values reported several decades ago, but the latter values slightly differ from ours.

Ceres’ sunlight atlas

Context. Astronomical research dealing with accurate radial velocity measurements need reliable astronomical standards to calibrate the spectrographs and to assess possible systematics. Stellar radial velocity standards offer a reference at the level of a few hundred m s −1 and are not adequate for most present needs. Aims. We aim to show that sunlight reflected by asteroids is a fairly accessible way to record a high-resolution solar spectrum from the whole disk, which can therefore be used as a radial velocity standard and can improve the uncertainties of solar line positions. Methods. We used solar light reflected by the asteroid Ceres observed with HARPS to measure solar lines’ wavelengths. Results. We provide a new solar atlas with 491 line wavelengths in the range 540−690 nm and 222 lines in the range 400−410 nm obtained from reflected solar spectrum of Ceres. These measurements are consistent with those of Allende Prieto & Garcia Lopez (1998b) based on FTS solar atlases but with a factor 3 higher precision. Conclusions. This atlas provides a benchmark for wavelength calibration to check radial velocity accuracy down to 44 m s −1 locally and a few m s −1 globally. The asteroid-based technique could provide a new way to track radial velocity shifts with solar activity cycle, as well as to derive convective shifts suitable for comparison with theoretical atmospheric models. It could also be used to study radial velocity deviations in spectrographs such as those recently detected in HIRES and UVES. Dedicated HARPS observations of other asteroids could improve present results substantially and these investigations have been solicited.

The solar photospheric abundance of carbon

<i>Context. <i/>The analysis of the solar spectra using hydrodynamical simulations, with a specific selection of lines, atomic data, and method for computing deviations from local thermodynamical equilibrium, has led to a downward revision of the solar metallicity, <i>Z<i/>. We are using the latest simulations computed with the CO5BOLD code to reassess the solar chemical composition. Our previous analyses of the key elements, oxygen and nitrogen, have not confirmed any extreme downward revision of <i>Z<i/>, as derived in other works based on hydrodynamical models.<i>Aims. <i/>We determine the solar photospheric carbon abundance with a radiation-hydrodynamical CO5BOLD model and compute the departures from local thermodynamical equilibrium by using the Kiel code.<i>Methods. <i/>We measured equivalent widths of atomic lines on high-resolution, high signal-to-noise ratio solar atlases of disc-centre intensity and integrated disc flux. These equivalent widths were analysed with our latest solar 3D hydrodynamical simulation computed with CO5BOLD. Deviations from local thermodynamic equilibrium we computed in 1D with the Kiel code, using the average temperature structure of the hydrodynamical simulation as a background model.<i>Results. <i/>Our recommended value for the solar carbon abundance relies on 98 independent measurements of observed lines and is <i>A<i/>(C)=8.50 <i>±<i/> 0.06. The quoted error is the sum of statistical and systematic errors. Combined with our recent results for the solar oxygen and nitrogen abundances, this implies a solar metallicity of <i>Z<i/> = 0.0154 and <i>Z<i/>/<i>X<i/> = 0.0211.<i>Conclusions. <i/>Our analysis implies a solar carbon abundance that is about 0.1 dex higher than what was found in previous analyses based on different 3D hydrodynamical computations. The difference is partly driven by our equivalent width measurements (we measure, on average, larger equivalent widths than the other work based on a 3D model), in part because of the different properties of the hydrodynamical simulations and the spectrum synthesis code. The solar metallicity we obtain from the CO5BOLD analyses is in slightly better agreement with the constraints of helioseismology than the previous 3D abundance results.

A 3D-NLTE study of the 670 nm solar lithium feature

AbstractWe derive the 3D-NLTE lithium abundance in the solar photosphere from the Lii line at 670 nm as measured in several solar atlases. The Li abundance is obtained from line profile fitting with 1D/3D-LTE/3D-NLTE synthetic spectra, considering several possibilities for the atomic parameters of the lines blending the Li feature. The 670 nm spectral region shows considerable differences in the two available disc-centre solar atlases, while the two integrated disc spectra are very similar. We obtain A(Li)3D–NLTE = 1.03. The 1D-LTE abundance is 0.07 dex smaller. The line-lists giving the best fit for the Sun may fail for other stars, while some line-lists fail to reproduce the solar profile satisfactorily. We need a better knowledge of the atomic parameters of the lines blending the Li feature in order to be able to reproduce both the solar spectrum and the spectra of other stars. An improved line-list is also required to derive reliable estimates of the isotopic Li ratio in solar-metallicity stars.

Oxygen lines in solar granulation

Context: There is a lively debate about the solar oxygen abundance and the role of 3D models in its recent downward revision. The models have been tested using high resolution solar atlases. Further testing can be done using centre-to-limb variations. Aims: Using high quality observations of oxygen lines across the solar surface we seek to test if the 3D and 1D models reproduce their observed centre-to-limb variation (CLV). In particular we seek to assess whether the 3D model is appropriate to derive the solar oxygen abundance. Methods: We use our recent observations of OI 777 nm, OI 615.81 nm, [OI] 630.03 nm and nine lines of other elements for five viewing angles 0.2<mu<1 of the quiet solar disk. We compare them with the predicted line profiles from the 3D and 1D models computed using the most up-to-date line formation codes, line data and allowing for departures of LTE. The CLV of the OI 777 nm lines is also used to obtain an empirical correction for the poorly known efficiency of the inelastic collisions with H. Results: The 3D model generally reproduces the CLV observations of the lines very well, particularly the oxygen lines. From the OI 777 nm lines we find that the classical Drawin recipe slightly overestimates H collisions. The limb observations of the OI 615.82 nm line allow us to identify a previously unknown contribution of molecules for this line, prevalent at the solar limb. A detailed treatment of the [OI] 630.03 nm line shows that the 3D modeling provides an excellent agreement with the observations. The derived oxygen abundances with the 3D model are 8.68 (OI 777 nm), 8.66 ([OI] 630.03 nm) and 8.62 (OI 615.82 nm). Conclusions: These additional tests have reinforced the trustworthiness of the 3D model and line formation for abundance analyses.

Our changing atmosphere: Evidence based on long-term infrared solar observations at the Jungfraujoch since 1950

The Institute of Astrophysics of the University of Liège has been present at the High Altitude Research Station Jungfraujoch, Switzerland, since the late 1940s, to perform spectrometric solar observations under dry and weakly polluted high-mountain conditions. Several solar atlases of photometric quality, extending altogether from the near-ultra-violet to the middle-infrared, were produced between 1956 and 1994, first with grating spectrometers then with Fourier transform instruments. During the early 1970s, scientific concerns emerged about atmospheric composition changes likely to set in as a consequence of the growing usage of nitrogen-containing agricultural fertilisers and the industrial production of chlorine-bearing compounds such as the chlorofluorocarbons and hydro-chlorofluorocarbons. Resulting releases to the atmosphere with ensuing photolysis in the stratosphere and catalytic depletion of the protective ozone layer prompted a worldwide consortium of chemical manufacturing companies to solicit the Liège group to help in clarifying these concerns by undertaking specific observations with its existing Jungfraujoch instrumentation. The following pages evoke the main steps that led from quasi full sun-oriented studies to priority investigations of the Earth's atmosphere, in support of both the Montreal and the Kyoto Protocols.