Fraunhofer Lines Research Articles

Collisional line profiles of rubidium and cesium perturbed by helium and molecular hydrogen

Previous calculations of the far wings of the potassium and sodium doublets in a unified-line shape semi-classical theory have been used recently to improve theoretical modeling of synthetic spectra of brown dwarfs. However the comparison with observations shows missing opacity in the 0.85 to 1.1 μ m range. Contributions of other alkalis such as Rb I and Cs I may resolve this problem. We present new theoretical calculations of the line profiles of these two alkalis perturbed by helium and molecular hydrogen.

Photometric and spectroscopic variability of the pre-main sequence star V1184 Tauri (CB 34V)

We present recent results from optical photometric and spectroscopic observations of the pre-main sequence star V1184 Tau (CB 34V). The star is associated with the Bok globule CB 34 and was considered as a FUOR candidate in previous studies. Our photometric data obtained from October 2000 to April 2003 show that the stellar brightness varies with an amplitude of about 0.m 5 (I ), but from August 2003 the photometric behavior of the star has changed dramatically. Three deep brightness minima (ΔI ∼ 4m.2) were observed during the past two years. The analysis of available photometric data suggests that V1184 Tau shows two types of variability produced (1) by rotation of large cool spotted surface and (2) by occultation from circumstellar clouds of dust or from features of a circumstellar disk. The behavior of the V – I index indicates that the star becomes redder towards minimum light, but from a certain turning point (V ∼ 18m.2) it gets bluer and is fading further. Five medium dispersion optical spectra of V1184 Tau were obtained in the period 2001–2004. Signi.cant changes in the profile and strength of the emission lines in the spectrum of V1184 Tau were found. During minimum light the equivalent width of the Hα emission line increases from 4 A to 9 A. The [O I] lines (λλ 6003, 6363 A) are also seen in emission while the sodium doublet keeps its absorption strength and equivalent width. The possibility to reconstruct the historical light curve of V1184 Tau using photographical plate archives is brie.y discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photospheric physical conditions before a two-ribbon solar flare

We present preliminary results of the study of the photospheric physical conditions about 30 minutes before the 2N/M2 two-ribbon solar flare. The soft X-ray enhancement, brightening and microwave bursts occured prior to the flare. We demonstrate the semiempirical models of the preflaring photosphere fot two kernels of the future flare. These models derived from the inversion reproduce the spectral observations in seven Fraunhofer lines. The models consist of two atmospheres: the magnetic flux tube and its nonmagnetic surroundings. The inferred models show strong changes of the photospheric physical conditions in the preflare phase. The preheating was found in the flux tube. Upward motions of the surrounding photospheric material were revealed. Significant discrepancies of the flux-tube temperature and density are found for two sites of the future flare. The inner kernel located near the filament was cooler in the photosphere than the outer kernel.

Fluorescence sensing techniques for vegetation assessment

Active fluorescence (F) sensing systems have long been suggested as a means to identify species composition and determine physiological status of plants. Passive F systems for large-scale remote assessment of vegetation will undoubtedly rely on solar-induced F (SIF), and this information could potentially be obtained from the Fraunhofer line depth (FLD) principle. However, understanding the relationships between the information and knowledge gained from active and passive systems remains to be addressed. Here we present an approach in which actively induced F spectral data are used to simulate and project the magnitude of SIF that can be expected from near-ground observations within selected solar Fraunhofer line regions. Comparisons among vegetative species and nitrogen (N) supply treatments were made with three F approaches: the passive FLD principle applied to telluric oxygen (O2) bands from field-acquired canopy reflectance spectra, simulated SIF from actively induced laboratory emission spectra of leaves at a series of solar Fraunhofer lines ranging from 422 to 758 nm, and examination of two dual-F excitation algorithms developed from laboratory data. From these analyses we infer that SIF from whole-plant canopies can be simulated by use of laboratory data from active systems on individual leaves and that SIF has application for the large-scale assessment of vegetation.

Synthesis and evaluation of new chiral nonracemic C2-symmetric and unsymmetric 2,2′-bipyridyl ligands

The synthesis of a series of chiral nonracemic and C2-symmetric 2,2'-bipyridyl ligands (R = Me, i-Pr and Ph) as well as the syntheses of the corresponding unsymmetric 2,2'-bipyridyl ligands (R = Me and Ph) is described. These bipyridyl ligands were prepared, in a notably direct and modular fashion, from the readily available and corresponding 2-chloropyridine acetals (R = Me, i-Pr and Ph). The bipyridyl ligands were evaluated in copper(I)-catalyzed cyclopropanation reactions of styrene with the ethyl and t-butyl esters of diazoacetic acid. The stereoselectivities, as well as the yields of the cyclopropanation reactions, were dependant on the ratio of the bipyridyl ligands and copper triflate that was employed. The best result was obtained in the asymmetric cyclopropanation reaction of styrene and tert-butyl diazoacetate with the C2-symmetric bipyridyl ligand (R = i-Pr). This afforded the corresponding trans-cyclopropane in good diastereoselectivity (4 : 1) and in moderate enantioselectivity (44% ee). The X-ray structure determination of a complex formed between the C2-symmetric 2,2'-bipyridyl ligand (R = Ph) and copper(I) chloride showed that two bipyridyl ligands had coordinated to the copper(I) ion. This information, along with the results of a series of cyclopropanation reactions and NMR data, led to the conclusion that the 2,2'-bipyridyl ligands had the propensity to form catalytically inactive bis-ligated copper(I) species in solution that were in equilibrium with catalytically active copper(i) triflate and the desired mono-ligated copper(I) species. Moreover, it was observed that the complex of the bipyridyl ligand (R = Ph) and copper(I) chloride had a particularly large optical rotation (sodium D-line). The maximum positive optical rotation was subsequently found to be +1.1 x 10(4) at 304 nm and the maximum negative optical rotation was -1.3 x 10(4) at 329 nm.

Detecting Photosynthesis Fluorescence under Natural Sunlight Based on Fraunhofer Line

Detecting Photosynthesis Fluorescence under Natural Sunlight Based on Fraunhofer Line

A DVD Spectroscope: A Simple, High-Resolution Classroom Spectroscope

A new, simple, inexpensive spectroscope for classroom experiments, a DVD spectroscope, is described and some emission spectra observed with the spectroscope are presented. This spectroscope is made with a sheet of cardboard, or an empty box, and a digital versatile disk (DVD). The quality of the spectra is much improved compared to that obtained by compact disk (CD) spectroscopes and DVD spectroscopes reported earlier. The resolution of this spectroscope is high enough to distinctly resolve the two yellow spectral lines of mercury at 577 and 579 nm. One can also observe clearly many Fraunhofer lines in the sunlight spectrum. Photographs of spectra are easily taken with a digital camera. Such images can be displayed on a monitor in real time, which helps students understand what is observed in the spectroscope.

Variability of the mesospheric nightglow sodium D2/D1 ratio

Measurements of the intensity ratio of the 589.0/589.6 nm sodium doublet in the terrestrial nightglow over an 8‐year period, involving >300 separate determinations, have established that it is variable, the value RD = I(D2)/I(D1) lying between 1.2 and 1.8. Sky spectra from the Keck I telescope with the High‐Resolution Échelle Spectrometer (HIRES) échelle spectrograph and the Keck II telescope with the Échellette Spectrograph and Imager (ESI) échelle spectrograph were used in this analysis. The result contrasts with the accepted view, from earlier measurements at midlatitude, that the ratio is 2.0, as expected on statistical grounds. The lack of dependence of the ratio on viewing elevation angle, and hence Na slant column, allows self‐absorption to be ruled out as a cause of the variability. The data suggest a semiannual oscillation in the ratio, maximum at the equinoxes and minimum at the solstices. Airborne measurements over the North Atlantic (40°–50°N) in 2002 show an even larger range in the nightglow ratio and no correlation with the upper mesospheric temperature determined from the OH 6–2 bands. A laboratory study confirms that the ratio does not depend on temperature; however, it is shown to be sensitive to the [O]/[O2] ratio. It is therefore postulated that the variable ratio arises from a competition between O reacting with NaO(A3Σ+), produced from the reaction of Na with O3, to yield D‐line emission with a D2/D1 ratio greater than about 2.0, and quenching by O2 to produce NaO(X2Π), possibly with vibrational excitation, which then reacts with O to produce emission with a ratio of less than 1.3.

Global solar Doppler velocity determination with the GOLF/SoHO instrument

The Global Oscillation at Low Frequencies (GOLF) experiment is a resonant scattering spectrophotometer on board the Solar and Heliospheric Observatory (SoHO) mission, originally designed to measure the disk-integrated solar oscillations of the Sun. This instrument was designed in a relative photometric mode involving both wings of the neutral sodium doublet (D1 at λ 5896 and D2 at λ 5890 A). However, a “one-wing” photometric mode has been selected to ensure 100% continuity in the measurements after a problem in the polarization mechanisms. Thus the velocity is obtained from only two points on the same wing of the lines. This operating configuration imposes tighter constraints on the stability of the instrument with a higher sensitivity to instrumental variations. In this paper we discuss the evolution of the instrument during the last 8 years in space and the corrections applied to the measured counting rates due to known instrumental effects. We also describe a scaling procedure to obtain the variation of the Doppler velocity based on our knowledge of the sodium profile slope and we compare it to previous velocity estimations.

Measuring the thickness of clear freshwater ice using geometric optics and a spectrometer

An instrument 1 1 Patent pending. which exploits geometric optics was devised to measure the thickness of slabs of optically transparent material such as Plexiglas or freshwater ice using a high-intensity light source. The apparatus consisting of a prism, a micrometer single-axis translation stage, and an optical spectrometer measures the spatial span between two chosen Fraunhofer line wavelengths in the prism-refracted visible spectrum reflected through the test slab. This span was found to be proportional to slab thickness. Measurements were made on various thicknesses of Plexiglas sheets ranging from 8 to 49 mm thick as well as nearly-bubble-free macrocrystalline freshwater ice in the thicknesses ranging from 28 to 53 mm thick. Results indicated a linear relationship between spectral span and slab thickness. This device may be suitable for detecting and measuring point-location ice thickness on aircraft wings, as well as for other industrial and research purposes.

Detecting solar-induced chlorophyll fluorescence from field radiance spectra based on the Fraunhofer line principle

It is difficult to quantify the amount of chlorophyll fluorescence emitted by a leaf or canopy under natural sunlight because the reflected light obscures the fluorescence signal. In this study, two diurnal experiments were conducted on winter wheat (Triticum aestivum L.) and Japan Creeper (Parthenocissus tricuspidata) to detect the solar-induced chlorophyll fluorescence from field radiance spectra. In the separation of the fluorescence emissive signal from canopy radiance spectrum based on Fraunhofer lines, two Fraunhofer lines of the terrestrial oxygen absorption at 688 and 760 nm were observed in the radiance spectra by an Analytical Spectral Devices FieldSpec Pro NIR spectrometer, which largely overlaps the chlorophyll fluorescence emission spectrum of leaves. Therefore, Fraunhofer lines at 688 and 760 nm were selected to detect the emissive fluorescence. The diurnal changes of chlorophyll fluorescence in the two experiments were primarily affected by the diurnal changes of photosynthetically available radiation (PAR). The correlation coefficients (R/sup 2/) were greater than 0.9 for all the relationships between PAR and the solar-induced fluorescence of winter wheat and Japan Creeper at 688 and 760 nm based on Fraunhofer line-depth (FLD), suggesting that the solar-induced fluorescence could closely track the changes of PAR and chlorophyll fluorescence. The relative solar-induced fluorescence based on FLD was negatively related to Fv/Fm measured by an OS1-FL modulated chlorophyll fluorometer. The correlation coefficients (R/sup 2/) were 0.97 at 688 nm and 0.99 at 760 nm for winter wheat, and 0.79 at 688 nm and 0.78 at 760 nm for Japan Creeper. These results demonstrate that the solar-induced fluorescence from plant canopies can be detected from field radiance spectra based on the Fraunhofer line principle.

Multiple elastic and inelastic light scattering in the Earth's atmosphere: a doubling-adding method to include rotational Raman scattering by air

An accurate description of multiple scattering is essential in atmospheric radiative transfer modeling of ultraviolet and visible light in the Earth's atmosphere. Part of this multiply scattered radiation is inelastically scattered due to rotational Raman scattering by air. The distribution of the inelastically scattered light leads to filling-in of Fraunhofer lines, and to filling-in of absorption features of atmospheric constituents. This complicates the interpretation of satellite measurements of backscattered sunlight. Several atmospheric radiative transfer models consider multiple elastic scattering, but allow only one order of inelastic Raman scattering. In this paper, we investigate the validity of this approximation by taking also multiple inelastic scattering into account. We present an extension of the doubling-adding method which for the first time accounts for both multiple elastic and multiple inelastic scattering of light. Numerical implementation of this method shows that, in simulations of reflected light by a model atmosphere, multiple inelastic scattering contributes about 0.5% to the total intensity around 325 nm and about 0.2% around 395 nm . At the center of the Fraunhofer lines and in the Huggins ozone absorption bands this contribution is generally larger. For a simulated measurement by a typical space-borne spectrometer with 0.2 nm instrumental resolution, the observed contribution is about 0.6% at the Ca II K and H lines, located at 393.48 and 396.97 nm , respectively. At the 325 nm Huggins ozone absorption feature this contribution due to multiple inelastic scattering is also about 0.6%.

Fraunhofer Effect Atomic Absorption Spectrometry

The dark lines in the solar spectrum were discovered by Wollaston and cataloged by Fraunhofer in the early days of the 19th century. Some years later, Kirchhoff explained the appearance of the dark lines: the sun was acting as a continuum light source and metals in the ground state in its atmosphere were absorbing characteristic narrow regions of the spectrum. This discovery eventually spawned atomic absorption spectrometry, which became a routine technique for chemical analysis in the mid-20th century. Laboratory-based atomic absorption spectrometers differ from the original observation of the Fraunhofer lines because they have always employed a separate light source and atomizer. This article describes a novel atomic absorption device that employs a single source, the tungsten coil, as both the generator of continuum radiation and the atomizer of the analytes. A 25-microL aliquot of sample is placed on the tungsten filament removed from a commercially available 150-W light bulb. The solution is dried and ashed by applying low currents to the coil in a three-step procedure. Full power is then applied to the coil for a brief period. During this time, the coil produces white light, which may be absorbed by any metals present in the atomization cloud produced by the sample. A high-resolution spectrometer with a charge-coupled device detector monitors the emission spectrum of the coil, which includes the dark lines from the metals. Detection limits are reported for seven elements: 5 pg of Ca (422.7 nm); 2 ng of Co (352.7 nm); 200 pg of Cr (425.4 nm); 7 pg of Sr (460.7 nm); 100 pg of Yb (398.8 nm); 500 pg of Mn (403.1 nm); and 500 pg of K (404.4 nm). Simultaneous multielement analyses are possible within a 4-nm spectral window. The relative standard deviations for the seven metals are below 8% for all metals except for Ca (10.7%), which was present in the blank at measurable levels. Analysis of a standard reference material (drinking water) resulted in a mean percent recovery of 91%. This report attempts to give an historical perspective on the development of a novel atomic spectrometer based on the Fraunhofer effect.

Heliocentric Dependence of Sodium Emission of Comet Hale‐Bopp (C/1995O1)

A sequential spectroscopic observation of comet C/1995 O1 (Hale-Bopp) was performed from 1996 September to 1997 May. After the first positive detection in early 1997 February, the development of the neutral sodium emission was monitored during about 4 months around the perihelion passage. The ratio of the sodium D-line emission relative to the continuum emission strength varied with the days from perihelion. The sodium D-line emission was weak relative to the continuum near the perihelion because of the Swings effect. We corrected the Swings effect, the phase angle dependence of continuum emission, and the differences in geocentric distance. We found that the corrected sodium-to-continuum ratio varied with the dependence of r-k; k = 5-6, r denotes a heliocentric distance of the comet. Our result supports the hypothesis of thermal desorption of sodium atoms from dust grains.

Spectral-angular characteristics of scattered radiation under pumping near the D 1 and D 2 lines of the Na atom

The dependence of the form of the scattering spectra on different detunings of the pump wavelength from the sodium doublet D-lines has been investigated. The spectral-angular characteristics of three-photon scattered radiation have been obtained. It has been shown that the composition of the scattered-radiation spectrum strongly depends on the pump radiation power density and the concentration of sodium atoms. Our investigations of the spectral-angular characteristics of the radiation scattered by sodium vapors have revealed new regularities in the generated radiation spectrum.

New Measurements of the Motion of the Zodiacal Dust

Using the Wisconsin Hα Mapper (WHAM), we have measured at high spectral resolution and high signal-to-noise ratio the profile of the scattered solar Mg I λ5184 Fraunhofer line in the zodiacal light. The observations were carried out toward 49 directions that sampled the ecliptic equator from solar elongations of 48° (evening sky) to 334° (morning sky) plus observations near +47° and +90° ecliptic latitude. The spectra show a clear prograde kinematic signature that is inconsistent with dust confined to the ecliptic plane and in circular orbits influenced only by the Sun's gravity. In particular, the broadened widths of the profiles, together with large amplitude variations in the centroid velocity with elongation angle, indicate that a significant population of dust is on eccentric orbits. In addition, the wide, flat-bottomed line profile toward the ecliptic pole indicates a broad distribution of orbital inclinations extending up to about 30°-40° with respect to the ecliptic plane. The absence of pronounced asymmetries in the shape of the profiles limits the retrograde population to less than 10% of the prograde population, and also places constraints on the scattering phase function of the particles. These results do not show the radial outflow or evening-morning velocity amplitude asymmetry reported in some earlier investigations. The reduction of the spectra included the discovery and removal of extremely faint, unidentified terrestrial emission lines that contaminate and distort the underlying Mg I profile. This atmospheric emission is too weak to have been seen in earlier, lower signal-to-noise ratio observations, but it probably affected the line centroid measurements of previous investigations.

Performance capabilities of middle-atmosphere temperature lidars: comparison of Na, Fe, K, Ca, Ca+, and Rayleigh systems.

The measurement accuracies of modern resonance fluorescence and Rayleigh temperature lidars are limited primarily by photon noise. The narrowband three-frequency fluorescence technique is shown to perform within a few decibels of the theoretical optimum at night for both temperature and wind observations. These systems also exhibit good performance during the day because the fluorescence wavelengths of Na, Fe, K, Ca, and Ca+ all correspond to strong solar Fraunhofer lines, where sky brightness is attenuated by a factor of 5 or more. Whereas Na systems achieve the highest signal-to-noise ratios for mesopause region observations (80-105 km), the three-frequency Fe system is attractive because it performs well as both a fluorescence and a Rayleigh lidar throughout the middle atmosphere at approximately 25-110 km.

Comparison of defocusing and fractional Fourier transform in spectroholographic storage.

In spectroholographic storage systems the defocusing method is often used for spectrum uniformity and quality improvement of recorded information. The same purpose is served by the fractional Fourier transform (FRFT) storage system. To simplify the numerical analysis, we derive the expressions of the Fraunhofer spectrum and the reconstructed image at the detected plane (CCD) for both cases instead of using the Fresnel spectrum and the FRFT spectrum. The recording aperture, spectrum uniformity, and reconstructed information of both systems are investigated. A numerical comparison is also presented.

Line strength factors for E,F1Σ+g(v′ = 0, J′ = J′′) – X1Σ+g (v′′, J′′) (2 + 1) REMPI transitions in molecular hydrogen

Experimentally and theoretically determined line strengths are presented for E,F1Σ+g(v′ = 0, J′ = J′′) – X1Σ+g (v′′, J′′) (2 + 1) REMPI transitions in H2, HD, and D2. The experimental technique employs a hot filament source of internally excited hydrogen that allows experimental determination of line strengths for the low rotational states of highly excited vibrational manifolds (v′′ ≤ 4). The line strengths are found to depend only weakly on J′′ for the states measured here, and theoretical results indicate that the line strengths depend strongly on v′′. These values are combined with previously measured and calculated line strengths for these transitions (K.-D. Rinnen, M.A. Buntine, D.A.V. Kliner, R.N. Zare, and W.M. Huo. J. Chem. Phys. 95, 214 (1991)), resulting in a more complete compilation of REMPI line strengths for molecular hydrogen. Key words: hydrogen, spectroscopy, REMPI, line strength, multiphoton.

A new instrument for passive remote sensing1. Measurements of sunlight-induced chlorophyll fluorescence

Abstract Under natural sunlight illumination, the chlorophyll fluorescence emitted by the vegetation represents less than 3% of the reflected light in the near infrared part of the spectrum. This small amount is difficult to quantify except at certain wavelengths, where the solar spectrum is attenuated (Fraunhofer lines). An instrument measuring the in-filling of the atmospheric oxygen absorption band at 760 nm by chlorophyll fluorescence has been designed and constructed at the “Laboratoire pour l'Utilisation du Rayonnement Electromagnetique” in Orsay, France. The system was calibrated against a pulsed fluorimeter (FIPAM), especially developed for monitoring chlorophyll fluorescence at distance. The penetration of diuron, a herbicide acting on photosynthesis, was monitored by the passive instrument for several days on a corn canopy. A good agreement was found between gas exchange and variable chlorophyll fluorescence at the canopy level and variable fluorescence at the leaf level. The potential application of the passive chlorophyll fluorescence measurements for long range vegetation remote sensing is discussed.