Band Area Ratio Research Articles

Physical and dynamical properties of the unusual V-type asteroid (2579) Spartacus

Context.Asteroid (2579) Spartacus is a small V-type object located in the inner main belt. This object shows spectral characteristics unusual for typical Vestoids, which may indicate an origin deeper than average within Vesta or an origin from an altogether different parent body.Aims.Our main goal is to study the origin of Spartacus. We derive the spin of Spartacus and a convex shape model of Spartacus in order to increase the knowledge of the body’s physical properties. The rotational parameters are then used to investigate dynamical evolution of the object as well as to distinguish regions sampled by spectral observations to determine whether its surface displays heterogeneity.Methods.We collected lightcurves available from the literature (oppositions of 2009, 2012) and obtained additional photometric observations at various telescopes in 2016, 2017, and 2018. We used the lightcurve inversion method to derive a spin and convex shape model. We have collected spectral observations over two rotational periods of Spartacus and determined its spectral parameters using the modified Gaussian model (MGM). We then dynamically integrated the orbital elements of Spartacus, taking into account existing information, including its thermal properties, size and the derived spin axis orientation.Results.We find two models for (2579) Spartacus: (a)λ= 312° ± 5°,β= −57° ± 5° and (b)λ= 113° ± 5°,β= −60° ± 5° both retrograde. We find that the drift direction for Spartacus is consistent with separation from Vesta, and after a backward integration of 1 Gyr the asteroid reaches the boundary of the family. We did not observe spectral variations with rotation, thus the body most likely has a homogeneous surface. Additionally, new spectral analysis indicates that the 1.0 and 2.0μm band centers are within ranges that are typical for Vestoids while the area ratio of these bands is about half that of typical Vestoids.Conclusions.The asteroid (2579) Spartacus is in retrograde rotation and has a drift direction consistent with an origin from Vesta. The revised spectral band centers are within ranges typical for Vestoids, while band area ratio (BAR) is unusually low compared to that of other V-types. The dynamical model shows that the asteroid could have migrated to its current location from the edges of the Vesta family within 1 Gyr, but an origin from an earlier impact on Vesta could also be plausible.

A simple and rapid Fourier transform infrared method for the determination of the degree of acetyl substitution of cellulose nanocrystals

The application of cellulose nanocrystal (CNC) is limited by the rich hydroxyl groups on its surface. It can be promoted by acetylation. The degree of acetyl substitution of CNC is a key index to evaluate its performance. In this paper, a series of acetylated CNC with different degrees of substitution (DS) were prepared by acetylation with acetic anhydride and were analyzed by means of Fourier transform infrared spectroscopy (FTIR). The absorbance ratio (AR) of the band at ~ 1745 cm−1 to the one at 1164 cm−1 was applied to determine the DS. An excellent linear relationship with a correlation coefficient $$ R^{2} \ge 0.994 $$ between AR and the referenced DS from 1H NMR was established. The regression equations, both based on band area ratio and band height ratio, can be directly applied to any FTIR instruments. The proposed method is simple, rapid and universal and can also be applied to determine the DS of any other cellulose derivatives.

Spectral properties and mineral compositions of acapulcoite–lodranite clan meteorites: Establishing S‐type asteroid–meteorite connections

AbstractExcept for asteroid sample return missions, measurements of the spectral properties of both meteorites and asteroids offer the best possibility of linking meteorite groups with their parent asteroid(s). Visible plus near‐infrared spectra reveal distinguishing absorption features controlled mainly by the Fe2+ contents and modal abundances of olivine and pyroxene. Meteorite samples provide relationships between spectra and mineralogy. These relationships are useful for estimating the olivine and pyroxene mineralogy of stony (S‐type) asteroid surfaces. Using a suite of 10 samples of the acapulcoite–lodranite clan (ALC), we have developed new correlations between spectral parameters and mafic mineral compositions for partially melted asteroids. A well‐defined relationship exists between Band II center and ferrosilite (Fs) content of orthopyroxene. Furthermore, because Fs in orthopyroxene and fayalite (Fa) content in olivine are well correlated in these meteorites, the derived Fs content can be used to estimate Fa of the coexisting olivine. We derive new equations for determining the mafic silicate compositions of partially melted S‐type asteroid parent bodies. Stony meteorite spectra have previously been used to delineate meteorite analog spectral zones in Band I versus band area ratio (BAR) parameter space for the establishment of asteroid–meteorite connections with S‐type asteroids. However, the spectral parameters of the partially melted ALC overlap with those of ordinary (H) chondrites in this parameter space. We find that Band I versus Band II center parameter space reveals a clear distinction between the ALC and the H chondrites. This work allows the distinction of S‐type asteroids as nebular (ordinary chondrites) or geologically processed (primitive achondrites).

Hydrothermal Transformation of Inorganic and Biogenic Silica as Studied Using in Situ Hydrothermal Infrared Microspectroscopy.

Infrared (IR) spectral changes with time of biogenic and inorganic silica have been examined using in situ IR micro-spectroscopy by using an original hydrothermal diamond cell. Centric diatoms (diameters = 100-350 µm) and silica gels (C-300, Wako Chemicals) were heated at 125-185 ℃ range with a pressure of 3 MPa. Decreases of 950 cm-1 (Si-OH) peak heights could be fitted by a combination of exponential and linear decreases (y = A1 exp (-k1t) - k0 t + A0). The first-order rate constants k1 [s-1] for Si-OH decreases of diatoms and silica gels are similar but the activation energy was lower for diatoms (61 kJċmol-1 < 106 kJċmol-1). The first-order rate constants k1 [s-1] for Si-OH decreases of diatoms and silica gels are much faster than reported hydrothermal transformation rates of silica (Opal A to Opal CT and Opal CT to quartz). These results indicate that the exponential Si-OH decreases observed in biogenic and inorganic silica during hydrothermal reactions are considered to correspond to dehydration-condensation reactions in the amorphous states (Si-OH + HO-Si → Si-O-Si). In fact, band area ratios 1220 cm-1/1120 cm-1 increased exponentially indicating more bridging of Si-O-Si. On the other hand, the linear decreases of Si-OH of silica gels (k0 [s-1]) were considered to be due to dissolution of silica. By using the grain size and density of silica gels, the zero-order dissolution rate constants k0* [molċm-2ċs-1] were calculated from k0 [s-1]. The obtained dissolution rates k0* are larger than reported values for silica glass and quartz. The zero-order dissolution rates k0 [s-1] for diatoms are similar to those for silica gels but with a lower activation energy (32 kJċmol-1 < 60 kJċmol-1). The smaller activation energy values for diatoms than silica gels both for the first and zero-order decrease rates of Si-OH might indicate catalytic effects of organic components bound to biogenic silica for the dehydration-condensation reaction and dissolution. The present in situ hydrothermal IR micro-spectroscopy is useful for characterizing transformation of amorphous materials including inorganic-organic composites.

Organic Matter Maturity Profile of a Well Case Study by Combination of Raman Spectroscopy and Principal Component Analysis–Partial Least Squares Regression (PCA–PLS) Chemometric Methods

Raman spectroscopy is largely informative about organic matter (OM) chemical composition and structure and can therefore be applied to evaluate the thermal maturity of coals, carbonaceous materials and kerogens, i.e., their degree of evolution during burial heating. The evaluation of OM maturity is commonly performed by band-fitting followed by the measure of suitable spectral parameters (typically band separations and area ratios). However, this procedure can introduce some subjectivity both in the number and line-shape of the fitting bands and in the definition and selection of the most meaningful spectroscopic parameters. Here, a principal component analysis–partial least squares regression (PCA–PLS) chemometric approach for the treatment of spectra is presented, that is intrinsically unaffected by such arbitrariness. In fact, the total spectrum is analyzed in order to extract the spectroscopic ranges of maximum variance in a multivariate approach. In addition, being automated, the treatment is well-su...

Remote spectral–compositional analysis of basalt mineralogy at Hansteen‐Billy, Moon

AbstractThe Hansteen‐Billy region of the Moon lying toward the southwest edge of Oceanus Procellarum is characterized by emplacement of three different aged basaltic units viz. INm, Im, and Em. The present study primarily utilizes high‐resolution Chandrayaan‐I, Moon Mineralogy Mapper (M3) data clipped at ~2.5 μm for mineral analysis of these units. The spectra of all the three regions show two prominent absorption bands. Spectral analysis characterizes the earliest INm basalts as low‐Ca pyroxenes with large band area ratios (BAR) and nearly similar B‐I and B‐II strength. The Em and Im basalts are Ca and high‐Ca pyroxenes, respectively, with relatively less BAR values and more B‐II/B‐I strength. The relative content of their spectra after olivine correction appears to be dominated by pyroxene. The obtained results have been used for estimation of the compositional characteristics of pyroxenes from laboratory‐based calibration equations. The pyroxene composition for INm basalts indicates their pigeonitic affinity, whereas the Im and Em basalts is close to augite. The estimated temperature of crystallization suggests that basalts in this region evolved at higher temperature and are preserved in a metastable condition due to quick cooling. Furthermore, the area is characterized by increase in concentration of both the Fe and Ti with age as assessed from Clementine mineral map. The obtained results have been discussed in relation with source of the magma.

Coal macromolecular structural characteristic and its influence on coalbed methane adsorption

In order to investigate the effect of coalification on coal macromolecular structure, the combination of Raman spectroscopy and low-pressure N2 gas adsorption (LP-N2GA) was adopted to explore the chemical and physical characteristics of selected samples ranging from bituminous C to anthracite. Raman structural parameters, including band position, band area ratio (AD1/AG) and band position difference (G-D1) of G band and D1 band were derived from curve-fitting analysis. Methane adsorption properties of these samples were measured, and correlations between these Raman parameters and coalbed methane adsorption capacity (VL) were also established. The results indicate that D1 band generally shifts to the lower wavenumbers decreasing from 1365 cm−1 to 1339 cm−1, while G band shifts to higher wavenumbers ranging from 1578 cm−1 to 1609 cm−1 with increasing coal rank. The values of G-D1 increase, but the band area ratio (AD1/AG) declines with the increase of Ro. Pore parameters, including the BET SSA and pore volume, show a polynomial relationship with G-D1, but a reduction for AD1/AG. The increase of graphitization and the order degree of aromatic structures in coal can enhance the porosity in coal. The evolution of coal macromolecular has significant impact on methane adsorption, which displays a U-shape correlation with Raman parameters. Coalbed methane adsorption is not only related to the physical structures, but also to the chemical characteristics, which should be taken into account in practice.

Toxicity impact of fenvalerate on the gill tissue of Oreochromis mossambicus with respect to biochemical changes utilizing FTIR and principal component analysis.

The use of pesticides in agriculture can make their way into the earth and wash into the amphibian system causing ecological stress. This study aims to understand the changes occurring in gill tissues as a result of fenvalerate exposure using Fourier-transform infrared spectroscopy. The intensity ratio of the selected bands I1545/I1657, I2924/I2853, and I1045/I1545 measures changes in proteins, lipids, and carbohydrates. Curve-fitting analysis was performed in the selected band region to analyze the quantitative changes of proteins, lipids, and carbohydrates. The band area ratio of CH3/asCH2+ sCH2 shows the absence of a long chain of fatty acids due to fenvalerate treatment. The band area ratio of asCH2/sCH2 increases for higher sublethal concentrations, which shows the lower disorder of lipid acyl chain flexibility. A decrease in lipids was found in lower sublethal concentrations. The secondary structure of proteins affirms β sheet development. Carbohydrate metabolism of gill tissues demonstrates a decrease in glycogen contents. A further decrease in glycogen content and an increase in lactic acid were observed when presented to a fenvalerate concentration. PCA plots indicate distinct variations among the biochemical parameters of the gill tissues. This study provides a quantitative examination of assessing pesticide toxicity in aquatic environments.

Do L chondrites come from the Gefion family?

Ordinary chondrites (H, L, and LL chondrites) are the most common type of meteorites comprising 80 per cent of the meteorites that fall on Earth. The source region of these meteorites in the main asteroid belt has been a basis of considerable debate in the small bodies community. L chondrites have been proposed to come from the Gefion asteroid family, based on dynamical models. We present results from our observational campaign to verify a link between the Gefion asteroid family and L chondrite meteorites. Near-infrared spectra of Gefion family asteroids (1839) Ragazza, (2373) Immo, (2386) Nikonov, (2521) Heidi, and (3860) Plovdiv were obtained at the NASA Infrared Telescope Facility (IRTF). Spectral band parameters including band centres and the band area ratio were measured from each spectrum and used to constrain the composition of these asteroids. Based on our results, we found that some members of the Gefion family have surface composition similar to that of H chondrites, primitive achondrites, and basaltic achondrites. No evidence was found for L chondrites among the Gefion family members in our small sample study. The diversity of compositional types observed in the Gefion asteroid family suggests that the original parent body might be partially differentiated or that the three asteroids with non-ordinary chondrite compositions might be interlopers.

Study on effects of ash on the evolution of physical and chemical structures of char during CO2 gasification

In this paper, the gasification reactivities of four types of Chinese coal were studied, each with different ash content and coal rank. Of the 4 coal types, 2 were HCl-washed and demineralized to investigate the effects of ash removal (for both dealkalization and demineralization) on coal gasification. The effects of ash on the evolution of physical and chemical structure were further studied using scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDX), N2 absorption and FT-Raman techniques. The results show that the initial gasification rate of raw chars is twice as high as the HCl-washed and ash-free chars. The gasification rate of ash-free char significantly increases with the increase in carbon conversion and surpasses the gasification rate of raw char when carbon conversion is higher than 50%. Moreover, the specific surface area of ash-free char significantly increases with carbon conversion, resulting in the significant increase in the gasification rate. Whereas the specific surface areas of raw char and HCl-washed char both decrease during high-conversion stages. The FT-Raman analysis shows that the ash-free char band area ratios AD3/AG and AD4/AG are lower than those of raw char at the initial gasification stage; this results in the initial gasification rate decrease of ash-free chars. In addition, the ash-free char band area ratio AG/Aall is smaller than that of raw char in the high conversion stages.

Laser Techniques on Acoustically Levitated Droplets

This work reports the results of an experimental study where laser techniques are applied to acoustically levitated droplets of trehalose aqueous solutions in order to perform spectroscopic analyses as a function of concentration and to test the theoretical diameter law. The study of such systems is important in order to better understand the behaviour of trehalose-synthesizing extremophiles that live in extreme environments. In particular, it will be shown how acoustic levitation, combined with optical spectroscopic instruments allows to explore a wide concentration range and to test the validity of the diameter law as a function of levitation lag time, i.e. the D2 vs t law. On this purpose a direct diameter monitoring by a video camera and a laser pointer was first performed; then the diameter was also evaluated by an indirect measure through an OH/CH band area ratio analysis of collected Raman and Infrared spectra. It clearly emerges that D2 vs t follows a linear trend for about 20 minutes, reaching then a plateau at longer time. This result shows how trehalose is able to avoid total water evaporation, this property being essential for the surviving of organisms under extreme environmental conditions.

A New Chemometric Approach for Automatic Identification of Microplastics from Environmental Compartments Based on FT-IR Spectroscopy.

One key step studying interactions of microplastics with our ecological system is to identify plastics within environmental samples. Aging processes and surface contamination especially with biofilms impede this characterization. A complex and time-consuming cleaning procedure is a common solution for this problem. However, it implies an artificial change of sample composition with a risk of losing important information or even damaging microplastic particles. In the present work, we introduce a new chemometric approach to identify heavily weathered and contaminated microplastics without any cleaning. The main idea of this concept is based on an automated curve fitting of most relevant vibrational bands to calculate a highly characteristic fingerprint that contains all vibrational band area ratios. This new data set will be used to estimate the similarity of samples and reference standards for identification. A total of 300 individual naturally weathered plastic particles were measured with Fourier transformation infrared spectroscopy in attenuated total reflection mode (FT-IR ATR) and identified successfully with the new method. To that end, all samples were compared with a selection of common reference plastics and bio polymers. As it turns out, the accuracy of identification rises significantly from 76% by means of conventional library searching algorithms to 96% by identifying microplastics with our new method. Therefore, the new approach can be a useful tool to compare and describe similarities of FT-IR spectra of microplastics, which may improve further research studies on this topic.

In Situ Raman Spectroscopy Study on Catalytic Pyrolysis of a Bituminous Coal

How different catalysts would affect the evolution of char structure with increasing temperature during the pyrolysis of coal is fundamentally important for the clean utilization of coal. In this study, we applied in situ Raman spectroscopy and a fixed-bed reactor to characterize the evolution of char structure and product gas formation behavior. The results showed that the formation curves of the main gases presented two stages and the catalyst enhanced the pyrolysis significantly. The Raman spectra were fitted with a combination of four Lorentzian bands (D1, D2, D4, G) and one Gaussian band (D3) in the first-order region. Spectral parameters, such as band position, full widths at half-maximum (FWHM), and band area ratio, were used to characterize char structure. The D1 and G band FWHM and band area ratios ID1/IG, ID3/IG, and ID4/IG increased with increasing temperature, while the D1 and G band positions and IG/IAll decreased, indicating a decrease in the ordering of the char structure. The addition of c...

Char structure dependence on formation enthalpy of parent coal

The aim of this work was to investigate char structure dependency on parent coal rank expressed by the formation enthalpy. For this purpose, a detailed characterization of eleven char samples obtained under the same pyrolysis conditions was performed. The porous structure was investigated in terms of micro-, meso- and macropores by employing nitrogen adsorption at 77K, carbon dioxide adsorption at 273K and mercury intrusion porosimetry. In order to assess both the carbon crystalline structure and degree of structure organization, the X-ray diffraction and Raman spectroscopy techniques were employed as well. The found correlations revealed a strong linear dependency of aromaticity index and char rank parameters from the formation enthalpy of parent coal. Other char parameters, like micropore and macropore surface area, average crystalline sizes and band area ratio from Raman spectroscopy demonstrate weaker correlation but still the results suggest a valid relationship with formation enthalpy of parent coal.

Fourier Transform Infrared Imaging analysis of dental pulp inflammatory diseases

Fourier Transform Infrared microspectroscopy let characterize the macromolecular composition and distribution of tissues and cells, by studying the interaction between infrared radiation and matter. Therefore, we hypothesize to exploit this analytical tool in the analysis of inflamed pulps, to detect the different biochemical features related to various degrees of inflammation. IR maps of 13 irreversible and 12 hyperplastic pulpitis, together with 10 normal pulps, were acquired, compared with histological findings and submitted to multivariate (HCA, PCA, SIMCA) and statistical (one-way ANOVA) analysis. The fit of convoluted bands let calculate meaningful band area ratios (means±s.d., P<0.05). The infrared imaging analysis pin-pointed higher amounts of water and lower quantities of type I collagen in all inflamed pulps. Specific vibrational markers were defined for irreversible pulpitis (Lipids/Total Biomass, PhII/Total Biomass, CH2 /CH3 , and Ty/AII) and hyperplastic ones (OH/Total Biomass, Collagen/Total Biomass, and CH3 Collagen/Total Biomass). The study confirmed that FTIR microspectroscopy let discriminate tissues' biological features. The infrared imaging analysis evidenced, in inflamed pulps, alterations in tissues' structure and composition. Changes in lipid metabolism, increasing amounts of tyrosine, and the occurrence of phosphorylative processes were highlighted in irreversible pulpitis, while high amounts of water and low quantities of type I collagen were detected in hyperplastic samples.

Effects of steam and CO2 on the characteristics of chars during devolatilization in oxy-steam combustion process

Oxy-steam combustion is considered as one of promising technologies for the next generation oxy-fuel combustion, in which coal mainly burns in O2/H2O atmosphere. This work aims to investigate the devolatilization characteristics of coal in oxy-steam combustion and clarify the potential effects of steam and CO2 on the char characteristics. Chars of a Chinese lignite were prepared in a fixed-bed reactor at 1050°C under various steam/CO2/N2 atmospheres and characterized by a FT-IR/Raman spectrometer and thermogravimetric analyzer. The results indicate the char yield during devolatilization in oxy-steam combustion was lower than that in N2 atmosphere, and the steam gasification reaction played the key role. The high concentration of steam would significantly accelerate the condensation of aromatic rings in the char, and more condensed char would form during devolatilization in oxy-steam combustion compared to that in N2 atmosphere. CO2 in high concentration of steam had little effects on the char yields but it could participate in the cross-linking reactions on the char surface and partly reduce the condensation of the chars during devolatilization. Steam and CO2 gasification reactions can not only speed up the consumption of the original O-containing functional groups in the coal but also bring some additional O-containing functional groups in the char. The reactivity of the char formed during devolatilization in oxy-steam combustion was lower than that in N2. A good linear relationship between the Raman band area ratio I(Gr+Vl+Vr)/ID and char reactivity confirmed the decrease of the char reactivity was mainly attributed to the condensation of the char.

Embryo viability indexing using Raman spectroscopy of spent culture media

ABSTRACTEmbryo viability quantification is an important topic for in vitro fertilization researchers. This study suggests Raman spectroscopy as a candidate method to find an objective measure of embryo viability. Raman spectra of 31 spent embryo culture samples (16 nonpregnant, 15 pregnant) from 31 patients were analyzed with band component analysis. The band area ratio of 902 to 943 cm−1 was found to be the most discriminatory. These bands are related to glutamine, glycine, proline, aspartic acid, and valine. According to the pregnancy outcome the sensitivity and specificity of Raman analysis were found to be 93% and 77%, respectively.

Individual and combined toxic effect of nickel and chromium on biochemical constituents in E. coli using FTIR spectroscopy and Principle component analysis

Ni and Cr are ubiquitous pollutants in the aquatic environments. These heavy metals elicit toxicities to aquatic organisms including microbes. In this study, interaction of the two heavy metals on the toxicity in Escherichia coli (E. coli) was studied using FTIR spectroscopy. The binding of Ni(II) to E. coli was stronger than that for Cr(VI). Cr exhibited antagonistic effects in the presence of Ni in E. coli. FTIR analysis showed a decrease in lipid content in the presence of Ni and not for Cr. Further, a decrease in band area was observed in the region of 3000–2800cm−1 and at ~1455cm−1 due to a decrease in fatty acids and lipid molecules. The band area ratio of lipid was used to monitor the changes in fatty acids due to metal toxicity. Principle component method helps to discriminates the results between control and metal toxicities in E. coli from the FTIR data. The study shows the importance of metal interaction and its toxicity on E. coli.

Raman Spectroscopy of Graphene Molecules: Size Dependent and Reaction Time Studies

Graphene molecules, nanostructures with fascinating optical and electronic properties, also referred to as graphene quantum dots, have attracted significant interest for a number of applications, including photovoltaics, electrochromic, and bio-sensing.[1],[2],[3],[4] Raman spectroscopy is a non-destructive, powerful technique, commonly used to characterize graphitic materials and investigate the doping level, the number of layers, edge-type, and the presence/type of defects. Even though, Raman studies of large-area graphene, as well as, nano-graphene sheets, with lateral dimensions larger than ∼3 nm, have been previously reported, an investigation of structures with well-controlled dimensions below 2 nm has been lacking. Raman spectroscopy can be employed to gain important insights on the structure of well-defined graphene, by studying the dependence of the Raman spectral features on the edge-type and the level of defects present on graphene molecules. In this study, we present a detailed Raman analysis of graphene molecules with synthetically controlled lateral dimensions between 0.76-1.39 nm, which correspond to structures with 16-79 ordered carbon rings. Graphene molecules with armchair edges and controlled lateral dimensions smaller than 2 nm were synthesized utilizing a new synthetic approach. [3.4] The samples were excited using laser light at discrete wavelengths (405 nm and 532 nm), and their Raman spectral features, including integrated band area ratios and peak positions, were systematically investigated. Our studies indicated that the integrated area ratios of D and G bands (AD/AG) increase with the size of the molecules. These results are in good agreement with the findings of the Raman studies of structures larger than 2 nm, generated via ion-bombardment.[5]The D and G band positions were also found to depend on the size of the graphene molecules. Additionally, we observed that the intensities of the higher-order bands (e.g., 2D, D+G, and 2G), increase for both wavelengths, as the size of the graphene molecules increases. To elucidate the effect of synthesis conditions on the structure of graphene molecule, we varied the reaction time and probed the crystallinity of the resulting graphene molecules. The integrated area band ratios and the band positions of the graphene molecules (with 79 and 48 carbon rings) were strongly dependent on the reaction time. These results demonstrate the suitability of Raman spectroscopy as a useful diagnostic tool for structural characterization and reaction dynamics of graphene molecules smaller than 2 nm, which is currently missing from the studies of larger graphene structures generated via ion-bombardment or other techniques. [1] S. H. Jin et al., ACSNano, 7 (2), 1239-1245, 2013. [2] H. Razmin et al., Biosensors and Bioelectronics, 41, 498-504, 2013. [3] Z. Ji et al., ACS Appl. Mater. Interfaces, 6, 20473-20478, 2014. [4] Z. Ji et al., ACSNano, 9 (4), 4043-4049, 2015. [5] L. G. Cancado et al., Nano Lett. 11, 3190-3196, 2011.

The Red Edge Problem in asteroid band parameter analysis

AbstractNear‐infrared reflectance spectra of S‐type asteroids contain two absorptions at 1 and 2 μm (band I and II) that are diagnostic of mineralogy. A parameterization of these two bands is frequently employed to determine the mineralogy of S(IV) asteroids through the use of ordinary chondrite calibration equations that link the mineralogy to band parameters. The most widely used calibration study uses a Band II terminal wavelength point (red edge) at 2.50 μm. However, due to the limitations of the NIR detectors on prominent telescopes used in asteroid research, spectral data for asteroids are typically only reliable out to 2.45 μm. We refer to this discrepancy as “The Red Edge Problem.” In this report, we evaluate the associated errors for measured band area ratios (BAR = Area BII/BI) and calculated relative abundance measurements. We find that the Red Edge Problem is often not the dominant source of error for the observationally limited red edge set at 2.45 μm, but it frequently is for a red edge set at 2.40 μm. The error, however, is one sided and therefore systematic. As such, we provide equations to adjust measured BARs to values with a different red edge definition. We also provide new ol/(ol+px) calibration equations for red edges set at 2.40 and 2.45 μm.