Spectral Fitting Technique Research Articles

Physical properties of z ~ 4 LBGs: differences between galaxies with and without Lyα emission

Aims. We analysed the physical properties of z ∼ 4 Lyman Break Galaxies observed in the GOODS-S survey, in order to investigate possible differences between galaxies where the Lyα is present in emission, and those where the line is absent or in absorption. Methods. The objects were selected from their optical color and then spectroscopically confirmed by Vanzella et al. (2005). From the public spectra we assessed the nature of the Lyα emission and divided the sample into galaxies with Lyα in emission and objects without a Lyα line (i.e. either absent or in absorption). We then used complete photometry, from U band to mid-infrared from the GOODS-MUSIC database, to study the observational properties of the galaxies, such as UV spectral slopes and optical to mid-infrared colors, and the possible differences between the two samples. Lastly, we used standard spectral fitting techniques to determine the physical properties of the galaxies, such as total stellar mass, stellar ages and so on, and again we looked at the possible differences between the two samples. Results. Our results indicate that LBG with Lyα in emission are on average a much younger and less massive population than the LBGs without Lyα emission. Both populations are forming stars very actively and are relatively dust free, although those with line emission seem to be even less dusty on average. We briefly discuss these results in the context of recent models for the evolution of Lyman break galaxies and Lyα emitters.

Enhanced edge Thomson scattering on MAST

A new edge Thomson scattering diagnostic has been implemented at MAST to complement an existing high spatial resolution ruby laser system and the high time sampling core Nd:YAG system. The Nd:YAG system comprises of four independently controllable lasers. Scattered light from these lasers is viewed at large scattering angle (153°) by a special optical arrangement in the new edge system. The Nd:YAG lasers are viewed at 16 contiguous spatial locations separated by ∼1cm each, located at the plasma outboard pedestal and scrape-off layer region. Here the use of a low f-number lens for the collection of a large solid angle of scattered light is particularly beneficial due to low plasma density (ne). The spectrum of scattered light is significantly broader at large scattering angles, allowing diagnosis of lower plasma temperatures (Te) while using the same spectrometer design as the core system. The four Nd:YAG lasers follow two separate slightly offset (<1∕3 of a spatial channel) optical paths through the vessel. This is useful when the lasers are used in burst mode for detailed edge studies of fast events such as ELMs. Polychromators have been designed to allow for both Raman and Rayleigh calibration. First results from this diagnostic are presented showing H-mode pedestal behavior. A novel spectral fitting technique has been devised and is applied to edge pedestal fitting.

XMM-Newton RGS spectra of four Seyfert 1 galaxies

AbstractUsing the spectral fitting technique we have studied the components contributing to the soft X-ray spectra of four AGN. The selected objects are the Seyfert 1 galaxies: HE 1143-1810, Mkn 110, CTS A08.12 and ESO 359-G19. The high-resolution X-ray spectra analysed were taken with the Reflection Grating Spectrometers on board the XMM-Newton satellite. In contrast to the results for other well-studied Seyfert 1 galaxies, we have found that the spectra of the four galaxies lack of significant absorption features. Hence, there are no signs of high-column-density partially-ionised absorbing material in the vicinity of the active nucleus in these galaxies.

Observations of upper tropospheric/lower stratospheric water vapor and its isotopes

Airborne observations of high‐resolution infrared absorption, recorded between 1978 and 2005, are used to retrieve column amounts of H216O, H217O, H218O and HDO. Observations span a wide range of years, seasons and latitudes, all made with essentially the same spectrometer system. A spectral optimal estimator fitting technique, SFIT2, has been used uniformly to analyze all the data. The latitudinal distributions of H216O, H217O and H218O are similar and much like those from other observations (e.g., SPARC (Kley et al., 2000)). The column of HDO above 13 km exhibits a distribution with latitude that is much less pronounced. From 1978 to 2005 the long‐term increase in the column of Northern Hemisphere H216O above 13 km is found to be 1.16 ± 0.4%/year, consistent with previous observations. HDO is found to decrease by about 0.4%/year during the same period. In low latitudes, from 35°S to 35°N, large depletions of HDO relative to H216O, δD (−460 ± 21‰), and H218O relative to H216O (−104 ± 47‰) are determined. δD shows an unexpected trend of enhanced depletion of about 5–6‰ per year for the period from 1978 to 2005.

Ozone observations by the Gas and Aerosol Measurement Sensor during SOLVE II

Abstract. The Gas and Aerosol Measurement Sensor (GAMS) was deployed aboard the NASA DC-8 aircraft during the second SAGE III Ozone Loss and Validation Experiment (SOLVE II). GAMS acquired line-of-sight (LOS) direct solar irradiance spectra during the sunlit portions of ten science flights of the DC-8 between 12 January and 4 February 2003. Differential line-of-sight (DLOS) optical depth spectra are produced from the GAMS raw solar irradiance spectra. Then, DLOS ozone number densities are retrieved from the GAMS spectra using a multiple linear regression spectral fitting technique. Both the DLOS optical depth spectra and retrieved ozone data are compared with coincident measurements from two other solar instruments aboard the DC-8 platform to demonstrate the robustness and stability of the GAMS data. The GAMS ozone measurements are then utilized to evaluate the quality of the Wulf band ozone cross sections, a critical component of the SAGE III aerosol, water vapor, and temperature/pressure retrievals. Results suggest the ozone cross section compilation of Shettle and Anderson currently used operationally in SAGE III data processing may be in error by as much as 10–20% in the Wulf bands, and their lack of reported temperature dependence is a significant deficiency. A second, more recent, cross section database compiled for the SCIAMACHY satellite mission appears to be of much better quality in the Wulf bands, but still may have errors as large as 5% near the Wulf band absorption peaks, which is slightly larger than their stated uncertainty. Additional laboratory measurements of the Wulf band cross sections should be pursued to further reduce their uncertainty and better quantify their temperature dependence.

A compact broadband cavity enhanced absorption spectrometer for detection of atmospheric NO2 using light emitting diodes

A compact and low power detector has been developed for the in situ measurement of atmospheric NO(2) using broadband cavity enhanced absorption spectroscopy. Absorption by the O(2)-O(2) collisional pair was used to determine the cavity mirror reflectivity, thus enabling the retrieval of absolute absorber concentrations by differential spectral fitting techniques. Quantitative amounts of ambient NO(2) (between 3 and 32 parts per billion) were retrieved from spectra recorded in the presence of ambient aerosol with statistical uncertainties approaching 100 ppt for a 60 s averaging period. The instrument's response was compared to that of a commercial chemiluminescence detector and was found to agree to within 6%.

Column ozone and aerosol optical properties retrieved from direct solar irradiance measurements during SOLVE II

Abstract. Direct observation of the Sun at large solar zenith angles during the second SAGE III Ozone Loss and Validation Experiment (SOLVE II)/Validation of International Satellites and study of Ozone Loss (VINTERSOL) campaign by several instruments provided a rich dataset for the retrieval and analysis of line-of-sight column composition, intercomparison, and measurement validation. A flexible, multi-species spectral fitting technique is presented and applied to spectral solar irradiance measurements made by the NCAR Direct beam Irradiance Atmospheric Spectrometer (DIAS) on-board the NASA DC-8. The approach allows for the independent retrieval of O3, O2·O2, and aerosol optical properties, by constraining Rayleigh extinction. We examine the 19 January 2003 and 6 February 2003 flights and find very good agreement of O3 and O2·O2 retrievals with forward-modeling calculations, even at large solar zenith angles, where refraction is important. Intercomparisons of retrieved ozone and aerosol optical thickness with results from the Ames Airborne Tracking Sunphotometer (AATS-14) are summarized.

Broadband cavity enhanced absorption spectroscopy using light emitting diodes

A broadband variant of cavity enhanced absorption spectroscopy has been demonstrated at visible wavelengths using red and green light emitting diodes. The broadband CEAS spectrum of a mixture of molecular oxygen and water vapour has been recorded with a bandwidth of 60 nm centred at 675 nm. Quantitative amounts of three atmospherically important absorbers (NO 3, NO 2 and I 2) have also been retrieved from broadband CEAS spectra of laboratory samples at high dilution using spectral fitting techniques adapted from differential optical absorption spectroscopy.

First Mid‐Infrared Spectrum of a Faint High‐ z Galaxy: Observations of CFRS 14.1157 with the Infrared Spectrograph on the Spitzer Space Telescope

The unprecedented sensitivity of the Infrared Spectrograph on the Spitzer Space Telescope allows for the first time the measurement of mid-infrared spectra from 14 to 38 μm of faint high-z galaxies. This unique capability is demonstrated with observations of sources having 16 μm fluxes of 3.6 mJy (CFRS 14.1157) and 0.35 mJy (CFRS 14.9025). A spectral-fitting technique is illustrated that determines the redshift by fitting emission and absorption features characteristic of nearby galaxies to the spectrum of an unknown source. For CFRS 14.1157, the measured redshift is z = 1.00 ± 0.20, in agreement with the published result of z = 1.15. The spectrum is dominated by emission from an active galactic nucleus, similar to the nucleus of NGC 1068, rather than a typical starburst with strong polycyclic aromatic hydrocarbon emission like M82. Such spectra will be crucial in characterizing the nature of newly discovered distant galaxies, which are too faint for optical follow-up.

Temperature determination via STJ optical spectroscopy

ESA's Superconducting Tunnel Junction (STJ) optical photon-counting camera (S-Cam2) incorporates an array of pixels with intrinsic energy sensitivity. Using the spectral fitting technique common in X-ray astronomy, we fit black bodies to nine stellar spectra, ranging from cool flare stars to hot white dwarfs. The measured temperatures are consistent with literature values at the expected level of accuracy based on the predicted gain stability of the instrument. Having also demonstrated that systematic eects due to count rate are likely to be small, we then proceed to apply the temperature determination method to four cataclysmic variable (CV) binary systems. In three cases we measure the temperature of the accretion stream, while in the fourth we measure the temperature of the white dwarf. The results are discussed in the context of existing CV results. We conclude by outlining the prospects for future versions of S-Cam.

Nitrogen broadening and shift coefficients in the 4.2–4.5-μm bands of CO 2

In this study we report the first high-resolution measurements of pressure broadening and pressure-induced shift coefficients due to nitrogen for rovibrational transitions in the ν 3 band of 13 C 16 O 2 . N 2 broadening and shift coefficients of ν 3 12 C 16 O 2 transitions were also measured. In addition, nitrogen-broadening coefficients for many transitions in the ν 3+ ν 2− ν 2 hot band of 13 C 16 O 2 as well as the ν 3 band of 13 C 16 O 18 O were also determined. The results were obtained by analyzing five high-resolution ( 0.0028 cm −1 ) room temperature laboratory absorption spectra with a multispectrum nonlinear least-squares spectral fitting technique. The data were recorded with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory on Kitt Peak using a 4.08 cm sample cell, total pressures up to 470 Torr , and a 90% 13 C -enriched CO 2 sample. For the pressure-broadened spectra the 13 C 16 O 2 volume-mixing ratios were⩽0.5%. Similar to broadening coefficients, the measured pressure shift coefficients were also found to be transition dependent. However, the shift coefficients were different in the P and R branch lines with the same rotational quantum number, J. The measured nitrogen-broadening coefficients range from 0.0960 to 0.0643 cm −1 atm −1 at 296 K . The measured shift coefficients were all negative and varied between 0 and −0.0036 cm −1 atm −1 . The results obtained are compared with other values reported in the literature.

Principal Component Analysis Approach for Modeling Sulfur K-XANES Spectra of Humic Acids

Quantitative application of x-ray absorption near edge structure (XANES) spectroscopy to soils and other geochemical systems requires a determination of the proportions of multiple chemical species that contribute to the measured spectrum. Two common approaches to fitting XANES spectra are spectral deconvolution and least-squares linear combination fitting (LCF). The objective of this research was to evaluate principal component analysis (PCA) coupled with target transformation to model S K-XANES spectra of humic acid samples, and to compare the results with least-squares LCF. Principal component analysis provided a statistical basis for choosing the number of standard species to include in the fitting model. Target transformation identified which standards were statistically more likely to explain the spectra of the humic acid samples. The selected standards and the scaling coefficients obtained by the PCA approach deviated by ≤6 mol% from results obtained by performing LCF using a large number of binary, ternary, and quaternary combinations of seven S standards. Because no energy shift is allowed in the PCA approach, fitting may be refined, when appropriate, by using afterwards a least-squares method that includes energy offset parameters. Statistical ranking of the most likely standard spectra contributing to the unknown spectra enhanced LCF by reducing the analysis to a smaller set of standard spectra. The PCA approach is a valuable complement to other spectral fitting techniques as it provides statistical criteria that improve insight to the data, and lead to a more objective approach to fitting.

Principal Component Analysis Approach for Modeling Sulfur K‐XANES Spectra of Humic Acids

Quantitative application of x‐ray absorption near edge structure (XANES) spectroscopy to soils and other geochemical systems requires a determination of the proportions of multiple chemical species that contribute to the measured spectrum. Two common approaches to fitting XANES spectra are spectral deconvolution and least‐squares linear combination fitting (LCF). The objective of this research was to evaluate principal component analysis (PCA) coupled with target transformation to model S K‐XANES spectra of humic acid samples, and to compare the results with least‐squares LCF. Principal component analysis provided a statistical basis for choosing the number of standard species to include in the fitting model. Target transformation identified which standards were statistically more likely to explain the spectra of the humic acid samples. The selected standards and the scaling coefficients obtained by the PCA approach deviated by ≤6 mol% from results obtained by performing LCF using a large number of binary, ternary, and quaternary combinations of seven S standards. Because no energy shift is allowed in the PCA approach, fitting may be refined, when appropriate, by using afterwards a least‐squares method that includes energy offset parameters. Statistical ranking of the most likely standard spectra contributing to the unknown spectra enhanced LCF by reducing the analysis to a smaller set of standard spectra. The PCA approach is a valuable complement to other spectral fitting techniques as it provides statistical criteria that improve insight to the data, and lead to a more objective approach to fitting.

On a possible cause of discrepancy between Yohkoh and SMM calcium abundance determinations in flares

We have investigated problems concerning the discrepancy between estimates of absolute calcium abundances (A Ca) in solar flares as derived from soft X-ray high resolution spectra as obtained from Yohkoh and Solar Maximum Mission ( SMM) Bragg spectrometers. The analysis of these spectra allows for determination of absolute calcium abundance since both Ca xix resonance line and neighbouring continuum are reliably measured in these experiments. The abundance determinations are possible by means of fitting the synthetic spectra to the observed ones. In previous work, we attributed part (around 50%) of the observed disagreement to a possible instrumental problem in Yohkoh. In the present research, we consider in more details possible causes of the other part of the discrepancy. We first investigate whether the estimates of (A Ca) depend substantially on the extension of the observed short wavelength wing of the Ca xix resonance line. This problem is important in the case of the analysis of Yohkoh spectra, since the extension of the spectrum towards the short wavelengths depends on the position of the flare along North—South direction on the Sun. After verifying the robustness of results of the spectral fitting technique, we have considered possible physical scenario which may cause the observed discrepancy. The hypothesis tested was that the Ca abundance in flares is correlated with brightness in the source — namely that it is a few times higher in the centre of the source (flaring kernel) than outside. We have found that postulated model may account for a part of the noted discrepancy as the SMM spectrometer has been equipped with the 6 × 6 arcmin collimator and no collimator has been used on Yohkoh.

Design and implementation of a rapid-mixer flow cell for time-resolved infrared microspectroscopy

A rapid mixer for the analysis of reactions in the millisecond and submillisecond time domains by Fourier-transform infrared microspectroscopy has been constructed. The cell was tested by examination of cytochrome-c folding kinetics. The device allows collection of full infrared spectral data on millisecond and faster time scales subsequent to chemical jump reaction initiation. The data quality is sufficiently good such that spectral fitting techniques could be applied to analysis of the data. Thus, this method provides an advantage over kinetic measurements at single wavelengths using infrared laser or diode sources, particularly where band overlap exists.

New and refined constraints on three‐dimensional Earth structure from normal modes below 3 mHz

We present the results of generalized spectral fitting (GSF) regressions which estimate normal mode structure coefficients for the observable spheroidal and toroidal free oscillation multiplets below 3 mHz. The size, accuracy, and precision of our new catalogue of modal constraints make it a powerful new tool for assessing and refining three‐dimensional Earth models. The estimates include more than 3100 coefficients for 90 multiplets and 25 pairs of coupled multiplets, including several deep mantle overtones previously obscured by fundamental modes. The coefficients constrain mantle structures of both even and odd spherical harmonic degrees, through degree 12 in some cases. Improvements in accuracy and precision have been achieved with three innovations: the development of GSF, an enhancement of the established spectral fitting technique which incorporates both Coriolis and structural coupling between multiplets; the application of GSF to an edited, high signal‐to‐noise and geographically diverse data set of more than 4500 seismograms from 33 high moment earthquakes; and the assignment of coefficient uncertainties using a Monte Carlo method to simulate the effects of seismic noise, theoretical errors, and coefficient covariances. The results of GSF are assessed by examining the internal consistency of estimated coefficients and through comparisons with recent mantle models. The new catalogue of structure coefficients and uncertainties is available as an electronic supplement to this paper and through the University of Colorado internet site.

Trace element analyses of fertilizers and soil amendments by axial‐view inductively‐coupled plasma atomic emission spectrophotometry

The application of fertilizers and other amendments, including urban and industrial wastes, to agricultural lands is of some concern due to the possibility of soil pollution by heavy metals and, ultimately, deterioration of the environment. Easy, rapid, and safe analytical procedures are therefore required to assess the potential hazard of applying these materials to soils. The objective of this study was to evaluate the potential of axial‐view inductively‐coupled plasma atomic emission (ICP‐AES) for the determination of 17 elements of environmental significance in HNO3 and HF digests of selected fertilizers and soil amendments. Reliable results were obtained for silver (Ag), barium (Ba), beryllium (Be), cadmium (Cd), and nickel (Ni). The arsenic (As), manganese (Mn) and vanadium (V) analyses were virtually problem free in samples containing low to moderate amounts of chromium (Cr), Ni, and titanium (Ti). Bismuth (Bi), selenium (Se), and thallium (Tl) could not be determined due to spectral interferences and cobalt (Co), Cr, copper (Cu), lead (Pb), antimony (Sb), and zinc (Zn) results were of intermediate quality. Correction of spectral interferences using the multi‐component spectral fitting (MSF) technique was only partially useful for Co and Pb and not necessary or beneficial for other analytes. Axial‐view ICP‐AES is a suitable tool for the routine analyses of trace elements in fertilizers and soil amendments, and its scope could be extended to more analytes provided that more detailed interference studies are carried out. The use of the interelement correction technique (IEC), which was not tested in this study, might be helpful in correcting spectral interferences. The analyte detection limits ranged from <0.7 to 17 μg L‐1.

Real-time spectroscopic ellipsometry monitoring of Si1−xGex/Si epitaxial growth

Real-time spectroscopic ellipsometry has been used to monitor oxide desorption and Si1−xGex/Si multilayer growth. A database of dielectric function spectra at the growth temperature has been determined for x=0.07, 0.11, 0.15. Real-time data obtained during growth have been analyzed using spectral fitting techniques to determine composition at selected growth times, and by using time-dependent data to determine optical constants and growth rates. The pseudosubstrate approximation has been used to determine layer parameters from the growing surface and information on interface widths obtained.

Spectroscopic study of the seasonal variation of carbon monoxide vertical distribution above Kitt Peak

A method to retrieve elements of the carbon monoxide (CO) vertical distribution from ground‐based high‐resolution infrared solar spectra has been developed. The method is based on the fact that the total column amount retrieved by nonlinear least squares spectral fitting techniques depends on the shape of the assumed a priori profile and this dependence is a function of the absorption line intensity and the lower state energy of the transition. Four CO lines between 2057 and 2159 cm−1 have been selected and the method has been tested on synthetic spectra. The CO total column content and average concentrations in two atmospheric layers (surface to 400 mbar and 400 mbar to the top of the atmosphere) can be retrieved with precisions of about 1% and less than 10%, respectively. Solar spectra recorded at Kitt Peak from 1982 to 1993 have been analyzed. The CO total column and the average concentration in the two layers show an asymmetrical seasonal cycle with extreme values of (1.1–2.1) × 1018 molecules cm−2, (50–80) parts per billion by volume (ppbv) in the top layer and (80–160) ppbv in the bottom layer, and precisions of 1, 3, and 6%, respectively; a spring maximum and late summer minimum are observed.

Infrared spectroscopic measurements of the ethane (C 2H 6) total column abundance above Mauna Loa, Hawaii—seasonal variations

About 200 i.r. solar spectra recorded at 0.01 cm -1 resolution on 71 days between November 1991 and July 1993 at the Network for the Detection of Stratospheric Change (NDSC) station at Mauna Loa, Hawaii (latitude 19.53°N, longitude 155.58°W, elevation 3.459 km) have been analyzed with a nonlinear least-squares spectral fitting technique to study temporal variations in the total column of atmospheric ethane (C 2H 6) above the site. The results were derived from the analysis of the unresolved v 7 band P Q 3 subbranch at 2976.8 cm -1. A distinct seasonal cycle is observed with a factor of 2 variation, a maximum total column of 1.16×10 16mol·cm -2 at the end of winter, and a minimum total column of 0.53×10 16mol·cm -2 at the end of summer. Our measurements are compared with previous observations and model predictions.