Journal articles on the topic 'Full-spectral fitting'
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Cid Fernandes, Roberto. "On tests of full spectral fitting algorithms." Monthly Notices of the Royal Astronomical Society 480, no. 4 (August 7, 2018): 4480–88. http://dx.doi.org/10.1093/mnras/sty2012.
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Wilkinson, David M., Claudia Maraston, Daniel Goddard, Daniel Thomas, and Taniya Parikh. "firefly (Fitting IteRativEly For Likelihood analYsis): a full spectral fitting code." Monthly Notices of the Royal Astronomical Society 472, no. 4 (September 6, 2017): 4297–326. http://dx.doi.org/10.1093/mnras/stx2215.
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Wilkinson, David M., Claudia Maraston, Daniel Thomas, Lodovico Coccato, Rita Tojeiro, Michele Cappellari, Francesco Belfiore, et al. "P-MaNGA: full spectral fitting and stellar population maps from prototype observations." Monthly Notices of the Royal Astronomical Society 449, no. 1 (March 17, 2015): 328–60. http://dx.doi.org/10.1093/mnras/stv301.
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Ruiz-Lara, Tomás, M. A. Beasley, C. Gallart, J. Falcón-Barroso, G. Battaglia, E. Bernard, C. Brook, et al. "Full-spectral fitting techniques to characterise the stellar content of ultra diffuse galaxies." Proceedings of the International Astronomical Union 14, S344 (August 2018): 408–12. http://dx.doi.org/10.1017/s174392131800577x.
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AbstractUnderstanding the peculiar properties of Ultra Diffuse Galaxies (UDGs) via spectroscopic analysis is a challenging task that is now becoming feasible. The advent of 10m-class telescopes and high sensitivity instruments is enabling the gathering of high quality spectra even for the faintest systems. In addition, advances in the modelling of stellar populations, stellar libraries, and full-spectral fitting codes are allowing the recovery of the stellar content shaping those spectra with unprecedented reliability. In this contribution we report on the extensive tests we have carried out using the inversion code STECKMAP. The similarities between the Star Formation Histories (SFH) recovered from STECKMAP (applied to high-quality spectra) and deep Colour-Magnitude diagrams fitting (resolved stars) in two Local Group dwarf galaxies (LMC and LeoA) are remarkable, demonstrating the impressive performance of STECKMAP. We exploit the capabilities of STECKMAP and perform one of the most complete and reliable characterisations of the stellar component of UDGs to date using deep spectroscopic data. We measure radial and rotation velocities, SFHs and mean population parameters, such as ages and metallicities, for a sample of five UDG candidates in the Coma cluster. From the radial velocities, we confirm the Coma membership of these galaxies. We find that their rotation properties, if detected at all, are compatible with dwarf-like galaxies. The SFHs of the UDG are dominated by old (∼ 7 Gyr), metal-poor ([M/H] ∼ -1.1) and alpha-enhanced ([Mg/Fe]∼ 0.4) populations followed by a smooth or episodic decline which halted ∼ 2 Gyr ago, possibly a sign of cluster-induced quenching. We find no obvious correlation between individual SFH shapes and any UDG morphological properties. The recovered stellar properties for UDGs are similar to those found for DDO 44, a local UDG analogue resolved into stars. We conclude that the UDGs in our sample are extended dwarfs whose properties are likely the outcome of both internal processes, such as bursty SFHs and/or high-spin haloes, as well as environmental effects within the Coma cluster.
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Li Kaipeng, 李凯朋, 王济洲 Wang Jizhou, 王多书 Wang Duoshu, 王云飞 Wang Yunfei, and 董茂进 Dong Maojin. "Optical parameters measurement of infrared filter based on envelope-full spectral fitting inversion method." Infrared and Laser Engineering 48, no. 9 (2019): 913004. http://dx.doi.org/10.3788/irla201948.0913004.
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Lasche, George, Robert Coldwell, and Robert Metzger. "VRF (“Visual RobFit”) — nuclear spectral analysis with non-linear full-spectrum nuclide shape fitting." EPJ Web of Conferences 153 (2017): 01002. http://dx.doi.org/10.1051/epjconf/201715301002.
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Cezario, E., P. R. T. Coelho, A. Alves-Brito, D. A. Forbes, and J. P. Brodie. "Full spectral fitting of Milky Way and M 31 globular clusters: ages and metallicities." Astronomy & Astrophysics 549 (December 19, 2012): A60. http://dx.doi.org/10.1051/0004-6361/201220336.
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Katkov, Ivan Yu, and Igor V. Chilingarian. "Multi-component parametric inversion of galaxy kinematics and stellar populations using full spectral fitting." Proceedings of the International Astronomical Union 7, S284 (September 2011): 69–71. http://dx.doi.org/10.1017/s1743921312008770.
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AbstractThe stellar line-of-sight velocity distribution (LOSVD) can be strongly asymmetric in regions where the light contributions of both disc and bulge in spiral and lenticular galaxies are comparable. Existing techniques for the stellar kinematics analysis do not take into account the difference of disc and bulge stellar populations. Here we present a novel approach to the analysis of stellar kinematics and stellar populations. We use a two-component model of spectra where different stellar population components are convolved with pure Gaussian LOSVDs. For this model we present Monte-Carlo simulations demonstrating degeneracies between the parameters.
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Koleva, Mina, and Alexander Vazdekis. "Stellar population models in the UV: I. Characterisation of the New Generation Stellar Library." Proceedings of the International Astronomical Union 7, S284 (September 2011): 35–37. http://dx.doi.org/10.1017/s1743921312008678.
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AbstractWe have fully characterized the NGSL stellar spectral library, which allows us to open the UV stellar spectral range for stellar population studies. We have performed the necessary steps to prepare this library for its implementation in models synthesizing SEDs of stellar cluster and galaxy spectra. We have determined and homogenized the atmospheric parameters of the stars of this library with the aid of a full spectrum-fitting algorithm, using the MILES spectral library as a template. We also have characterized the resolution of this library and corrected systematic effects in the optical spectral range to achieve a precision of 10% of the dispersion.
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Scott, Nicholas. "Spatially resolved stellar populations with SAMI." Proceedings of the International Astronomical Union 10, S309 (July 2014): 343–44. http://dx.doi.org/10.1017/s1743921314010369.
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AbstractUsing data from the SAMI Galaxy Survey we measure azimuthally averaged stellar age and metallicity profiles for ∼ 500 galaxies, using both luminosity-weighted Lick indices and mass-weighted full spectral fitting. We find a weak trend for steeper (i.e. more negative) metallicity gradients in more massive galaxies, however, below stellar masses ∼ 1010.5 M⊙, the scatter in metallicity gradient increases dramatically.
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Gacic, Zoran, Branislav Mickovic, Luka Gacic, and Ilija Damjanovic. "New spectral templates for rhodopsin and porphyropsin visual pigments." Archives of Biological Sciences 71, no. 1 (2019): 103–10. http://dx.doi.org/10.2298/abs180822052g.
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A four-parameter model of spectral sensitivity curves was developed. Empirical equations were designed for A1- and A2-based visual pigments with the main ?-band maximum absorptions (?max) from 350 nm, near the ultraviolet, up to 635 nm in the far-red part of the spectrum. Subtraction of the ?-band from the full absorbance spectrum left a ??-band? described by a ?max-dependent Gaussian equation. Compatibility of our templates with A1- and A2-based spectra was tested on the electroretinographic (ERG-derived) scotopic action spectra recorded in dogfish shark, eel, Prussian carp and perch. To more precisely estimate the accuracy of our model, we compared it with widely used templates for visual pigments. There was almost no difference between the tested models in fitting the above-mentioned spectral data. One of the advantages of our model is that in the fitting of spectral sensitivity data it uses non-transformed wavelengths and the shape of the curve remains the same for a broad range of ?max values. Compared to multiparameter templates of other authors, our model was designed with fewer (four) parameters, which we believe can bring us closer to understanding the true nature of the absorption curve.
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Goudfrooij, Paul, and Randa S. Asa’d. "On the precision of full-spectrum fitting of simple stellar populations – II. The dependence on star cluster mass in the wavelength range 0.3–5.0 µm." Monthly Notices of the Royal Astronomical Society 501, no. 1 (December 3, 2020): 440–66. http://dx.doi.org/10.1093/mnras/staa3617.
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ABSTRACT In this second paper of a series on the accuracy and precision of the determination of age and metallicity of simple stellar populations (SSPs) by means of the full-spectrum fitting technique, we study the influence of star cluster mass through stochastic fluctuations of the number of stars near the top of the stellar mass function, which dominate the flux in certain wavelength regimes depending on the age. We consider SSP models based on the Padova isochrones, spanning the age range $7.0 \le \mbox{log(age/yr}) \le 10.1$. Simulated spectra of star clusters in the mass range 104 ≤ M/M⊙ < 106 are compared with SSP model spectra to determine best-fitting ages and metallicities using a full-spectrum fitting routine in four wavelength regimes: the blue optical (0.35–0.70 µm), the red optical (0.6–1.0 µm), the near-infrared (near-IR; 1.0–2.5 µm), and the mid-IR (2.5–5.0 µm). We compare the power of each wavelength regime in terms of both the overall precision of age and metallicity determination and its dependence on cluster mass. We also study the relevance of spectral resolution in this context by utilizing two different spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR regime in terms of identifying young massive clusters in dusty star-forming regions in distant galaxies. The spectra of the simulated star clusters and SSPs are made available online to enable follow-up studies by the community.
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Bak, Juseon, Xiong Liu, Robert Spurr, Kai Yang, Caroline R. Nowlan, Christopher Chan Miller, Gonzalo Gonzalez Abad, and Kelly Chance. "Radiative transfer acceleration based on the principal component analysis and lookup table of corrections: optimization and application to UV ozone profile retrievals." Atmospheric Measurement Techniques 14, no. 4 (April 7, 2021): 2659–72. http://dx.doi.org/10.5194/amt-14-2659-2021.
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Abstract. In this work, we apply a principal component analysis (PCA)-based approach combined with lookup tables (LUTs) of corrections to accelerate the Vector Linearized Discrete Ordinate Radiative Transfer (VLIDORT) model used in the retrieval of ozone profiles from backscattered ultraviolet (UV) measurements by the Ozone Monitoring Instrument (OMI). The spectral binning scheme, which determines the accuracy and efficiency of the PCA-RT performance, is thoroughly optimized over the spectral range 265 to 360 nm with the assumption of a Rayleigh-scattering atmosphere above a Lambertian surface. The high level of accuracy (∼ 0.03 %) is achieved from fast-PCA calculations of full radiances. In this approach, computationally expensive full multiple scattering (MS) calculations are limited to a small set of PCA-derived optical states, while fast single scattering and two-stream MS calculations are performed, for every spectral point. The number of calls to the full MS model is only 51 in the application to OMI ozone profile retrievals with the fitting window of 270–330 nm where the RT model should be called at fine intervals (∼ 0.03 nm with ∼ 2000 wavelengths) to simulate OMI measurements (spectral resolution: 0.4–0.6 nm). LUT corrections are implemented to accelerate the online RT model due to the reduction of the number of streams (discrete ordinates) from 8 to 4, while improving the accuracy at the level attainable from simulations using a vector model with 12 streams and 72 layers. Overall, we speed up our OMI retrieval by a factor of 3.3 over the previous version, which has already been significantly sped up over line-by-line calculations due to various RT approximations. Improved treatments for RT approximation errors using LUT corrections improve spectral fitting (2 %–5 %) and hence retrieval errors, especially for tropospheric ozone by up to ∼ 10 %; the remaining errors due to the forward model errors are within 5 % in the troposphere and 3 % in the stratosphere.
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Lonoce, I., C. Maraston, D. Thomas, M. Longhetti, T. Parikh, P. Guarnieri, and J. Comparat. "Stellar population properties of individual massive early-type galaxies at 1.4 < z < 2." Monthly Notices of the Royal Astronomical Society 492, no. 1 (December 10, 2019): 326–51. http://dx.doi.org/10.1093/mnras/stz3404.
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ABSTRACT We analyse publicly available, individual spectra of four massive ($M\gt 10^{11}\, \mathrm{M}_{\odot }$) early-type galaxies with redshifts in the range 1.4 ≤ z ≤ 2 to determine their stellar content, extending our previous work up to z ∼ 2. The wide wavelength range of the VLT/X-Shooter spectroscopic data in the UV–Optical–NIR arms along with the availability of spectro-photometry allows us to explore different techniques to obtain the stellar population properties, namely through age/metallicity-sensitive spectral indices, full spectral fitting, and broad-band photometric fitting. Moreover, together with the widely used optical Lick indices, we consider further indices in the UV rest frame, and demonstrate that UV indices significantly help the accuracy of the resulting population parameters. We find galaxy ages ranging from 0.2 to 4 Gyr, where the oldest galaxy is found at the lowest redshift, with an excellent agreement between ages determined via indices, full spectral fitting, or broad-band colours. These ages are in perfect agreement with ages of local galaxies at the same velocity dispersion when we assume pure passive evolution. Total metallicities derived from indices show some scatter (between less than half-solar to very high values, [Z/H] ∼ 0.6). We speculate on possible mechanisms explaining these values, but given the sample size and low S/N of the spectra no conclusion can be made. Indices in the UV rest frame generally lead to similar conclusions as optical indices. For the oldest galaxy (4 Gyr), we show that its UV indices can only be explained by stellar population models including a UV contribution from old stellar populations, suggesting that old, UV bright populations start to inhabit mature galaxies of a few Gyr of age. This is the highest redshift (z ∼ 1.4) detection of the UV upturn up to date.
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Brosch, Joseph K., Ziwei Wu, Carolyn G. Begley, Tobin A. Driscoll, and Richard J. Braun. "Blink characterization using curve fitting and clustering algorithms." Modeling and Artificial Intelligence in Ophthalmology 1, no. 3 (June 19, 2017): 60–81. http://dx.doi.org/10.35119/maio.v1i3.38.
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The motion of the upper eyelid during blinking can be important in identifying possible diseases and syndromes that affect the eye. Hypothesized lid motion functions are fit to the dynamic position of the center of the upper lid under four experimentally controlled conditions in a pilot study. The coefficients of these nonlinear fits are used to classify blinks. Agglomerative hierarchical and spectral clustering were used to attempt an automatic distinction between partial and full blinks as well as between normal and abnormal blinks. Results for both approaches are similar when the input data is suitably normalized. Clustering finds outlying blinks that do not fit the model functions for lid motion well and that differ from the majority of blinks in our sample; however, those blinks may not be outliers based on easily observed data such as blink amplitude and duration. This type of analysis has potential for studying blink dynamics under normal and pathological conditions, but more work is needed with larger sets of data from blinks.
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Liu, Xinjie, Liangyun Liu, Su Zhang, and Xianfeng Zhou. "New Spectral Fitting Method for Full-Spectrum Solar-Induced Chlorophyll Fluorescence Retrieval Based on Principal Components Analysis." Remote Sensing 7, no. 8 (August 18, 2015): 10626–45. http://dx.doi.org/10.3390/rs70810626.
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Martins, Lucimara P. "Recovering the star formation history of galaxies through spectral fitting: Current challenges." Proceedings of the International Astronomical Union 15, S359 (March 2020): 386–90. http://dx.doi.org/10.1017/s1743921320001647.
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AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.
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Minty, Brian R. S. "Multichannel models for the estimation of radon background in airborne gamma‐ray spectrometry." GEOPHYSICS 63, no. 6 (November 1998): 1986–96. http://dx.doi.org/10.1190/1.1444492.
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Adequate background correction is a crucial step in processing airborne gamma‐ray spectrometric data because any errors are amplified during subsequent processing procedures. Two multichannel models for the estimation of atmospheric radon background are proposed. The spectral‐ratio method uses the relative heights of uranium (U) series photopeaks to estimate the contribution of atmospheric radon to observed spectra. The full‐spectrum method estimates the atmospheric radon contribution through the weighted least‐squares fitting of potassium (K), U, thorium (Th), and radon component spectra to the observed spectra. Both the spectral‐ratio and full‐spectrum methods are adequately calibrated through the estimation of component spectra from calibration experiments on the ground using radioactive calibration sources and wood to simulate the attenuation of gamma rays by air. The simulated heights used in these calibrations must be mapped onto real heights through calibration flights over an airborne calibration range. The spectral‐ratio method is also adequately calibrated using a heuristic calibration procedure. An iterative minimization method is used to find the optimum values of the calibration constants such that the radon background over suitable calibration lines is best removed.
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Martín, S., J. Martín-Pintado, C. Blanco-Sánchez, V. M. Rivilla, A. Rodríguez-Franco, and F. Rico-Villas. "Spectral Line Identification and Modelling (SLIM) in the MAdrid Data CUBe Analysis (MADCUBA) package." Astronomy & Astrophysics 631 (November 2019): A159. http://dx.doi.org/10.1051/0004-6361/201936144.
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Context. The increase in bandwidth and sensitivity of state-of-the-art radio observatories is providing a wealth of molecular data from nearby star-forming regions up to high-z galaxies. Analysing large data sets of spectral cubes requires efficient and user-friendly tools optimised for astronomers with a wide range of backgrounds. Aims. In this paper we present the detailed formalism at the core of Spectral Line Identification and Modelling (SLIM) within the MAdrid Data CUBe Analysis (MADCUBA) package and their main data-handling functionalities. These tools have been developed to visualise, analyse, and model large spectroscopic data cubes. Methods. We present the highly interactive on-the-fly visualisation and modelling tools of MADCUBA and SLIM, which includes a stand-alone spectroscopic database. The parameters stored therein are used to solve the full radiative transfer equation under local thermodynamic equilibrium (LTE). The SLIM package provides tools to generate synthetic LTE model spectra based on input physical parameters of column density, excitation temperature, velocity, line width, and source size. It also provides an automatic fitting algorithm to obtain the physical parameters (with their associated errors) better fitting the observations. Synthetic spectra can be overlayed in the data cubes/spectra to ease the task of multi-molecular line identification and modelling. Results. We present the Java-based MADCUBA and its internal module SLIM packages which provide all the necessary tools for manipulation and analysis of spectroscopic data cubes. We describe in detail the spectroscopic fitting equations and make use of this tool to explore the breaking conditions and implicit errors of commonly used approximations in the literature. Conclusions. Easy-to-use tools like MADCUBA allow users to derive physical information from spectroscopic data without the need for simple approximations. The SLIM tool allows the full radiative transfer equation to be used, and to interactively explore the space of physical parameters and associated uncertainties from observational data.
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Durden, S. L., M. A. Fischman, R. A. Johnson, A. J. Chu, M. N. Jourdan, and S. Tanelli. "An FPGA-Based Doppler Processor for a Spaceborne Precipitation Radar." Journal of Atmospheric and Oceanic Technology 24, no. 10 (October 1, 2007): 1811–15. http://dx.doi.org/10.1175/jtech2086.1.
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Abstract Measurement of precipitation Doppler velocity by spaceborne radar is complicated by the large velocity of the satellite platform. Even if successive pulses are well correlated, the velocity measurement may be biased if the precipitation target does not uniformly fill the radar footprint. It has been previously shown that the bias in such situations can be reduced if full spectral processing is used. The authors present a processor based on field-programmable gate array (FPGA) technology that can be used for spectral processing of data acquired by future spaceborne precipitation radars. The requirements for and design of the Doppler processor are addressed. Simulation and laboratory test results show that the processor can meet real-time constraints while easily fitting in a single FPGA.
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Yuan, Fang-Ting, Shiyin Shen, Lei Hao, and Maria Argudo Fernandez. "Star formation history of the galaxy merger Mrk848 with SDSS-IV MaNGA." Proceedings of the International Astronomical Union 11, S321 (March 2016): 304. http://dx.doi.org/10.1017/s1743921316008978.
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AbstractWith the 3D data of SDSS-IV MaNGA (Bundy et al. 2015) spectra and multi-wavelength SED modeling, we expect to have a better understanding of the distribution of dust, gas and star formation of galaxy mergers. For a case study of the merging galaxy Mrk848, we use both UV-to-IR broadband SED and the MaNGA integral field spectroscopy to obtain its star formation histories at the tail and core regions. From the SED fitting and full spectral fitting, we find that the star formation in the tail regions are affected by the interaction earlier than the core regions. The core regions show apparently two times of star formation and a strong burst within 500Myr, indicating the recent star formation is triggered by the interaction. The star formation histories derived from these two methods are basically consistent.
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Wei, Jin-Nan, Zi-Ke Liu, Jun-Jie Wei, Bin-Bin Zhang, and Xue-Feng Wu. "Exploring Anisotropic Lorentz Invariance Violation from the Spectral-Lag Transitions of Gamma-Ray Bursts." Universe 8, no. 10 (October 6, 2022): 519. http://dx.doi.org/10.3390/universe8100519.
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The observed spectral lags of gamma-ray bursts (GRBs) have been widely used to explore possible violations of Lorentz invariance. However, these studies were generally performed by concentrating on the rough time lag of a single highest-energy photon and ignoring the intrinsic time lag at the source. A new way to test nonbirefringent Lorentz-violating effects has been proposed by analyzing the multi-photon spectral-lag behavior of a GRB that displays a positive-to-negative transition. This method gives both a plausible description of the intrinsic energy-dependent time lag and comparatively robust constraints on Lorentz-violating effects. In this work, we conduct a systematic search for Lorentz-violating photon dispersion from the spectral-lag transition features of 32 GRBs. By fitting the spectral-lag data of these 32 GRBs, we place constraints on a variety of isotropic and anisotropic Lorentz-violating coefficients with mass dimension d=6 and 8. While our dispersion constraints are not competitive with existing bounds, they have the promise to complement the full coefficient space.
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Springett, R., J. Newman, M. Cope, and D. T. Delpy. "Oxygen dependency and precision of cytochrome oxidase signal from full spectral NIRS of the piglet brain." American Journal of Physiology-Heart and Circulatory Physiology 279, no. 5 (November 1, 2000): H2202—H2209. http://dx.doi.org/10.1152/ajpheart.2000.279.5.h2202.
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Oxidation changes of the copper A (CuA) center of cytochrome oxidase in the brain were measured during brief anoxic swings at both normocapnia and hypercapnia (arterial Pco 2 ≈55 mmHg). Hypercapnia increased total hemoglobin from 37.5 ± 9.1 to 50.8 ± 12.9 μmol/l (means ± SD; n = 7), increased mean cerebral saturation (SmcO2 ) from 65 ± 4 to 77 ± 3%, and oxidized CuA by 0.43 ± 0.23 μmol/l. During the onset of anoxia, there were no significant changes in the CuA oxidation state until SmcO2 had fallen to 43 ± 5 and 21 ± 6% at normocapnia and hypercapnia, respectively, and the maximum reduction during anoxia was not significantly different at hypercapnia (1.49 ± 0.40 μmol/l) compared with normocapnia (1.53 ± 0.44 μmol/l). Residuals of the least squares fitting algorithm used to convert near-infrared spectra to concentrations are presented and shown to be small compared with the component of attenuation attributed to the CuAsignal. From these observations, we conclude that there is minimal interference between the hemoglobin and CuA signals in this model, the CuA oxidation state is independent of cerebral oxygenation at normoxia, and the oxidation after hypercapnia is not the result of increased cerebral oxygenation.
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Wu, X., X. Zhang, and H. Lin. "SUPERPIXEL BASED FACTOR ANALYSIS AND TARGET TRANSFORMATION METHOD FOR MARTIAN MINERALS DETECTION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3 (April 30, 2018): 1901–6. http://dx.doi.org/10.5194/isprs-archives-xlii-3-1901-2018.
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The Factor analysis and target transformation (FATT) is an effective method to test for the presence of particular mineral on Martian surface. It has been used both in thermal infrared (Thermal Emission Spectrometer, TES) and near-infrared (Compact Reconnaissance Imaging Spectrometer for Mars, CRISM) hyperspectral data. FATT derived a set of orthogonal eigenvectors from a mixed system and typically selected first 10 eigenvectors to least square fit the library mineral spectra. However, minerals present only in a limited pixels will be ignored because its weak spectral features compared with full image signatures. Here, we proposed a superpixel based FATT method to detect the mineral distributions on Mars. The simple linear iterative clustering (SLIC) algorithm was used to partition the CRISM image into multiple connected image regions with spectral homogeneous to enhance the weak signatures by increasing their proportion in a mixed system. A least square fitting was used in target transformation and performed to each region iteratively. Finally, the distribution of the specific minerals in image was obtained, where fitting residual less than a threshold represent presence and otherwise absence. We validate our method by identifying carbonates in a well analysed CRISM image in Nili Fossae on Mars. Our experimental results indicate that the proposed method work well both in simulated and real data sets.
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Sioris, Christopher E., Landon A. Rieger, Nicholas D. Lloyd, Adam E. Bourassa, Chris Z. Roth, Douglas A. Degenstein, Claude Camy-Peyret, et al. "Improved OSIRIS NO<sub>2</sub> retrieval algorithm: description and validation." Atmospheric Measurement Techniques 10, no. 3 (March 21, 2017): 1155–68. http://dx.doi.org/10.5194/amt-10-1155-2017.
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Abstract. A new retrieval algorithm for OSIRIS (Optical Spectrograph and Infrared Imager System) nitrogen dioxide (NO2) profiles is described and validated. The algorithm relies on spectral fitting to obtain slant column densities of NO2, followed by inversion using an algebraic reconstruction technique and the SaskTran spherical radiative transfer model (RTM) to obtain vertical profiles of local number density. The validation covers different latitudes (tropical to polar), years (2002–2012), all seasons (winter, spring, summer, and autumn), different concentrations of nitrogen dioxide (from denoxified polar vortex to polar summer), a range of solar zenith angles (68.6–90.5°), and altitudes between 10.5 and 39 km, thereby covering the full retrieval range of a typical OSIRIS NO2 profile. The use of a larger spectral fitting window than used in previous retrievals reduces retrieval uncertainties and the scatter in the retrieved profiles due to noisy radiances. Improvements are also demonstrated through the validation in terms of bias reduction at 15–17 km relative to the OSIRIS operational v3.0 algorithm. The diurnal variation of NO2 along the line of sight is included in a fully spherical multiple scattering RTM for the first time. Using this forward model with built-in photochemistry, the scatter of the differences relative to the correlative balloon NO2 profile data is reduced.
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Krepelka, Pavel, Iveta Hynstova, Roman Pytel, Fernando Pérez-Rodríguez, Jean-Michel Roger, and Petr Drexler. "Curve fitting in Fourier transform near infrared spectroscopy used for the analysis of bacterial cells." Journal of Near Infrared Spectroscopy 25, no. 3 (May 2, 2017): 151–64. http://dx.doi.org/10.1177/0967033517705032.
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Infrared spectroscopy is a prominent molecular technique for bacterial analysis. Within its context, near infrared spectroscopy in particular brings benefits over other vibrational approaches; these advantages include, for example, lower sensitivity to water, high penetration depth and low cost. However, near infrared spectroscopy is not popular within microbiology, because the spectra of organic samples are difficult to interpret. We propose a comparison of spectral curve-fitting methods, namely, techniques that facilitate the interpretation of most peaks, simplify the spectra and improve the prediction of bacterial species from the relevant near infrared spectra. The performances of three common curve-fitting algorithms and the technique based on the differential evolution were compared via a synthesized experimental spectrum. Utilizing the obtained results, the spectra of three different bacterial species were curve fit by optimized algorithm. The proposed algorithm decomposed the spectra to specific absorption peaks, whose parameters were estimated via the differential evolution approach initialized through Levenberg-Marquardt optimization; subsequently, the spectra were classified with conventional procedures and using the parameters of the revealed peaks. On a limited data set, the correct classification rate computed by partial least squares discriminant analysis was 95%. When we employed the peak parameters for the classification, the rate corresponded to 91.7%. According to the Gaussian formula, the parameters comprise the spectral peak position, amplitude and width. The most important peaks for bacterial discrimination were identified by analysis of variance and interpreted as N–H stretching bonds in proteins, cis bonds and CH2 absorption in fatty acids. We examined some aspects of the behaviour of standard curve-fitting algorithms and proposed differential evolution to optimize the fitting process. Based on the correct use of these algorithms, the near infrared spectra of bacteria can be interpreted and the full potential of near infrared spectroscopy in microbiology exploited.
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Ruiz-Lara, T., C. Gallart, M. Beasley, M. Monelli, E. J. Bernard, G. Battaglia, P. Sánchez-Blázquez, E. Florido, I. Pérez, and I. Martín-Navarro. "Integrated-light analyses vs. colour-magnitude diagrams." Astronomy & Astrophysics 617 (September 2018): A18. http://dx.doi.org/10.1051/0004-6361/201732398.
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Context. Most of our knowledge of the stellar component of galaxies is based on the analysis of distant systems and comes from integrated light data. It is important to test whether the results of the star formation histories (SFH) obtained with standard full-spectrum fitting methods are in agreement with those obtained through colour-magnitude diagram (CMD) fitting (usually considered the most reliable approach). Aims. We compare SFHs recovered from the two techniques in Leo A, a Local Group dwarf galaxy most of whose stars formed during the last 8 Gyrs. This complements our previous findings in a field in the Large Magellanic Cloud bar, where star formation has been in progress since early epochs at varying rates. Methods. We have used GTC/OSIRIS in long-slit mode to obtain a high-quality integrated light spectrum by scanning a selected region within Leo A, for which a CMD reaching the old main sequence turn-off (oMSTO) is available from HST. We compared the SFH obtained from the two datasets, using state-of-art methods of integrated light (STECKMAP) and resolved stellar population analysis. In the case of the CMD, we computed the SFH both from a deep CMD (observed with HST/ACS) and from a shallower CMD (archival data from HST/WFPC2). Results. The agreement between the SFHs recovered from the oMSTO CMD and from full spectrum fitting is remarkable, particularly regarding the time evolution of the star formation rate. The overall extremely low metallicity of Leo A is recovered up to the last 2 Gyrs when some discrepancies appear. A relatively high metallicity found for the youngest stars from the integrated data is a recurring feature that might indicate that the current models or synthesis codes should be revised, but that can be significantly mitigated using a more restrictive metallicity range. We thoroughly inspect the robustness of both approaches separately, finding that the subtle differences between them are inherent to the methods themselves. The SFH recovered from the shallow CMD also presents differences with the other two. Conclusions. Modern full-spectral fitting codes are able to recover both average constant SFHs (LMC case) and SFHs with a dominant fraction of young stellar populations. The analysis of high S/N spectra seems to provide more reliable SFH estimates than that of CMDs not reaching the oMSTO. The comparison presented in this paper needs to be repeated for predominantly old systems, thus assessing the performance of full-spectrum fitting for a full range of SFHs.
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Petzler, Anita, J. R. Dawson, and Mark Wardle. "Amoeba: Automated Molecular Excitation Bayesian Line-fitting Algorithm." Astrophysical Journal 923, no. 2 (December 1, 2021): 261. http://dx.doi.org/10.3847/1538-4357/ac2f42.
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Abstract The hyperfine transitions of the ground-rotational state of the hydroxyl radical (OH) have emerged as a versatile tracer of the diffuse molecular interstellar medium. We present a novel automated Gaussian decomposition algorithm designed specifically for the analysis of the paired on-source and off-source optical depth and emission spectra of these OH transitions. In contrast to existing automated Gaussian decomposition algorithms, Amoeba (Automated Molecular Excitation Bayesian line-fitting Algorithm) employs a Bayesian approach to model selection, fitting all four optical-depth and four emission spectra simultaneously. Amoeba assumes that a given spectral feature can be described by a single centroid velocity and full width at half maximum, with peak values in the individual optical-depth and emission spectra then described uniquely by the column density in each of the four levels of the ground-rotational state, thus naturally including the real physical constraints on these parameters. Additionally, the Bayesian approach includes informed priors on individual parameters that the user can modify to suit different data sets. Here we describe Amoeba and establish its validity and reliability in identifying and fitting synthetic spectra with known (but hidden) parameters, finding that the code performs very well in a series of practical tests. Amoeba’s core algorithm could be adapted to the analysis of other species with multiple transitions interconnecting shared levels (e.g., the 700 MHz lines of the first excited rotational state of CH). Users are encouraged to adapt and modify Amoeba to suit their own use cases.
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Tsuchikawa, T., H. Kaneda, S. Oyabu, T. Kokusho, H. Kobayashi, and Y. Toba. "Spitzer/IRS Full Spectral Modeling to Characterize Mineralogical Properties of Silicate Dust in Heavily Obscured AGNs." Astrophysical Journal 941, no. 1 (December 1, 2022): 50. http://dx.doi.org/10.3847/1538-4357/ac9b23.
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Abstract Mid-infrared silicate dust bands observed in heavily obscured active galactic nuclei (AGNs) include information on the mineralogical properties of silicate dust. We aim to investigate the mineralogical picture of the circumnuclear region of heavily obscured AGNs to reveal obscured AGN activities through the picture. In our previous study, we investigated the properties of silicate dust in heavily obscured AGNs, focusing on the mineralogical composition and the crystallinity with Spitzer/IRS 5.3–12 μm spectra. In this study, we model the full-range Spitzer/IRS 5–30 μm spectra of 98 heavily obscured AGNs using a one-dimensional radiative transfer calculation with four dust species in order to evaluate wider ranges of the properties of silicate dust more reliably. Comparing fitting results between four dust models with different sizes and porosities, 95 out of the 98 galaxies prefer a porous silicate dust model without micron-sized large grains. The pyroxene mass fraction and the crystallinity are overall consistent with—but significantly different from—the previous results for the individual galaxies. The pyroxene-poor composition, small dust size, and high porosity are similar to newly formed dust around mass-loss stars as seen in our Galaxy, which presumably originates from the recent circumnuclear starburst activity. The high crystallinity on average suggests dust processing induced by AGN activities.
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Natoli, C. R., M. Benfatto, S. Della Longa, and K. Hatada. "X-ray absorption spectroscopy: state-of-the-art analysis." Journal of Synchrotron Radiation 10, no. 1 (December 24, 2002): 26–42. http://dx.doi.org/10.1107/s0909049502017247.
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State-of-the-art techniques for analysing X-ray absorption spectra are reviewed, with an eye to biological applications. Recent attempts to perform full spectral fitting of the XANES energy region and beyond for the purpose of structural analysis have met with encouraging success. The present paper analyses the theoretical motivations behind this success and indicates routes for future improvements. The theoretical background is not entirely new, although the point of view is, and some sections and appendices present material that the authors believe has never been published before. The aim of this paper is to provide a theoretical analysis that is as self-contained as possible.
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Bak, Juseon, Xiong Liu, Kang Sun, Kelly Chance, and Jae-Hwan Kim. "Linearization of the effect of slit function changes for improving Ozone Monitoring Instrument ozone profile retrievals." Atmospheric Measurement Techniques 12, no. 7 (July 11, 2019): 3777–88. http://dx.doi.org/10.5194/amt-12-3777-2019.
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Abstract. We introduce a method that accounts for errors caused by the slit function in an optimal-estimation-based spectral fitting process to improve ozone profile retrievals from the Ozone Monitoring Instrument (OMI) ultraviolet measurements (270–330 nm). Previously, a slit function was parameterized as a standard Gaussian by fitting the full width at half maximum (FWHM) of the slit function from climatological OMI solar irradiances. This cannot account for the temporal variation in slit function in irradiance, the intra-orbit changes due to thermally induced change and scene inhomogeneity, and potential differences in the slit functions of irradiance and radiance measurements. As a result, radiance simulation errors may be induced due to convolving reference spectra with incorrect slit functions. To better represent the shape of the slit functions, we implement a more generic super Gaussian slit function with two free parameters (slit width and shape factor); it becomes standard Gaussian when the shape factor is fixed to be 2. The effects of errors in slit function parameters on radiance spectra, referred to as pseudo absorbers (PAs), are linearized by convolving high-resolution cross sections or simulated radiances with the partial derivatives of the slit function with respect to the slit parameters. The PAs are included in the spectral fitting scaled by fitting coefficients that are iteratively adjusted as elements of the state vector along with ozone and other fitting parameters. The fitting coefficients vary with cross-track and along-track pixels and show sensitivity to heterogeneous scenes. The PA spectrum is quite similar in the Hartley band below 310 nm for both standard and super Gaussians, but is more distinctly structured in the Huggins band above 310 nm with the use of super Gaussian slit functions. Finally, we demonstrate that some spikes of fitting residuals are slightly smoothed by accounting for the slit function errors. Comparisons with ozonesondes demonstrate noticeable improvements when using PAs for both standard and super Gaussians, especially for reducing the systematic biases in the tropics and midlatitudes (mean biases of tropospheric column ozone reduced from -1.4∼0.7 to 0.0∼0.4 DU) and reducing the standard deviations of tropospheric ozone column differences at high latitudes (by 1 DU for the super Gaussian). Including PAs also makes the retrievals consistent between standard and super Gaussians. This study corroborates the slit function differences between radiance and irradiance, demonstrating that it is important to account for such differences in the ozone profile retrievals.
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Jiménez-Domínguez, H., S. CRuz-Jiménez, and A. Cabral-Prieto. "New Simple Method to Analyze Mildly Gaussian-Convolved Lorentzian Lines with the Aid of DISPA Data." Applied Spectroscopy 51, no. 1 (January 1997): 37–42. http://dx.doi.org/10.1366/0003702971938948.
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A new and simple method, not based on numerical fitting, to analyze mildly Gaussian-convolved Lorentzian isolated nonoverlapped lines in any spectroscopy, with the aid of DISPA (DISPersion vs. Absorption) data, is presented. The method is based on a model of the dispersion line which is obtained by taking the Hilbert transform of a previously published approximate expression for the absorption Voigt profile. The resulting DISPA pair is valid in the interval α, where α is a parameter that measures the relative Lorentzian (ΓL) and Gaussian (ΓG) full width at half-maximum (FWHM) contributions to the Voigt profile. As an example of an application of the method, a deconvolution of the potassium–ammonium solution electron paramagnetic resonance (EPR) line is performed. This deconvolution produces the Lorentzian and Gaussian contributions to the line. The deconvolution operation is done after obtaining a list of DISPA values for this line. The resulting values of the Lorentzian and Gaussian FWHMs are then compared with those obtained after deconvolving the line by fitting the spectral data with both the exact and approximate expressions for the Voigt profile. The method may be used in any spectroscopy in which the spectral lines are not overlapped and can be represented by Voigtians with a small Gaussian component and with a very low degree of asymmetry.
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Yuan, Yanhua O., and Frederik J. Simons. "Multiscale adjoint waveform-difference tomography using wavelets." GEOPHYSICS 79, no. 3 (May 1, 2014): WA79—WA95. http://dx.doi.org/10.1190/geo2013-0383.1.
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Full-waveform seismic inversions based on minimizing the distance between observed and predicted seismograms are, in principle, able to yield better-resolved earth models than those minimizing misfits derived from traveltimes alone. Adjoint-based methods provide an efficient way of calculating the gradient of the misfit function via a sequence of forward-modeling steps, which, using spectral-element codes, can be carried out in realistically complex media. Convergence and stability of full-waveform-difference adjoint schemes are greatly improved when data and synthetics are progressively presented to the algorithms in a constructive multiscale approximation using a (bi)orthogonal wavelet transform. Wavelets provide the nonredundant spectral decomposition that paves the way for the inversion to proceed successively from long-wavelength fitting to detailed exploration of the phases in the seismogram. The choice of wavelet class and type, the initial depth of the multiscale decomposition, and the minimization algorithms used at every level continue to play crucial roles in our procedure, but adequate choices can be made that test successfully on 2C elastic seismograms generated in toy models, as well as in the industry-standard 2D Marmousi model. Although for simplicity our inversion ignored surface waves by prior tapering and filtered removal, those also appeared to be very well matched in the final model.
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da Cunha, Elisabete. "Panchromatic star formation rate indicators and their uncertainties." Proceedings of the International Astronomical Union 11, A29B (August 2015): 184–85. http://dx.doi.org/10.1017/s1743921316004816.
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AbstractThe star formation rate (SFR) is a fundamental property of galaxies and it is crucial to understand the build-up of their stellar content, their chemical evolution, and energetic feedback. The SFR of galaxies is typically obtained by observing the emission by young stellar populations directly in the ultraviolet, the optical nebular line emission from gas ionized by newly-formed massive stars, the reprocessed emission by dust in the infrared range, or by combining observations at different wavelengths and fitting the full spectral energy distributions of galaxies. In this brief review we describe the assumptions, advantages and limitations of different SFR indicators, and we discuss the most promising SFR indicators for high-redshift studies.
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Thompson, Richard B., and Peter S. Allen. "The role of the N-acetylaspartate multiplet in the quantification of brain metabolites." Biochemistry and Cell Biology 76, no. 2-3 (May 1, 1998): 497–502. http://dx.doi.org/10.1139/o98-065.
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N-Acetylaspartate, whose methyl singlet is the primary magnetic resonance marker of neuronal dysfunction, also gives rise to a sequence-dependent, strongly coupled multiplet that overlaps the resonances of several other metabolites. Results are presented in this paper of a full numerical calculation of the response of the strongly coupled aspartate multiplet of N-acetylaspartate to a PRESS pulse sequence employing practical slice-selective pulses. These calculations, confirmed by experiments on phantoms, demonstrate the ability to predict the dependence of the response of strongly coupled spins on pulse design, as well as on interpulse evolutions, thereby facilitating a more rigorous comparison of the use of spectral fitting routines employed to extract metabolite concentrations on different instruments.Key words: magnetic resonance spectroscopy, N-acetylaspartate, NAA, brain, quantification, PRESS.
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Mandel, Kaisey S., Stephen Thorp, Gautham Narayan, Andrew S. Friedman, and Arturo Avelino. "A hierarchical Bayesian SED model for Type Ia supernovae in the optical to near-infrared." Monthly Notices of the Royal Astronomical Society 510, no. 3 (December 2, 2021): 3939–66. http://dx.doi.org/10.1093/mnras/stab3496.
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ABSTRACT While conventional Type Ia supernova (SN Ia) cosmology analyses rely primarily on rest-frame optical light curves to determine distances, SNe Ia are excellent standard candles in near-infrared (NIR) light, which is significantly less sensitive to dust extinction. An SN Ia spectral energy distribution (SED) model capable of fitting rest-frame NIR observations is necessary to fully leverage current and future SN Ia data sets from ground- and space-based telescopes including HST, LSST, JWST, and RST. We construct a hierarchical Bayesian model for SN Ia SEDs, continuous over time and wavelength, from the optical to NIR (B through H, or $0.35{-}1.8\, \mu$m). We model the SED as a combination of physically distinct host galaxy dust and intrinsic spectral components. The distribution of intrinsic SEDs over time and wavelength is modelled with probabilistic functional principal components and the covariance of residual functions. We train the model on a nearby sample of 79 SNe Ia with joint optical and NIR light curves by sampling the global posterior distribution over dust and intrinsic latent variables, SED components and population hyperparameters. Photometric distances of SNe Ia with NIR data near maximum obtain a total RMS error of 0.10 mag with our BayeSN model, compared to 0.13–0.14 mag with SALT2 and SNooPy for the same sample. Jointly fitting the optical and NIR data of the full sample up to moderate reddening (host E(B − V) < 0.4) for a global host dust law, we find RV = 2.9 ± 0.2, consistent with the Milky Way average.
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Zhang, Xiangyue, Xiaoyu Cheng, Tianru Xue, and Yueming Wang. "Linear Spatial Misregistration Detection and Correction Based on Spectral Unmixing for FAHI Hyperspectral Imagery." Sensors 22, no. 24 (December 16, 2022): 9932. http://dx.doi.org/10.3390/s22249932.
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In push-broom hyperspectral imaging systems, the sensor rotation to the optical plane leads to linear spatial misregistration (LSM) in hyperspectral images (HSIs). To compensate for hardware defects through software, this paper develops four methods to detect LSM in HSIs. Different from traditional methods for grayscale images, the method of fitting the sum of abundance (FSAM) and the method of searching for equal abundance (SEAM) are achieved by hyperspectral unmixing for a selected rectangular transition areas containing an edge, which makes good use of spatial and spectral information. The method based on line detection for band-interleaved-by-line (BIL) images (LDBM) and the method based on the Fourier transform of BIL images (FTBM) aim to characterize the slope of line structure in BIL images and get rid of the dependence on scene and wavelength. A full strategy is detailed from aspects of data selection, LSM detection, and image correction. The full spectrum airborne hyperspectral imager (FAHI) is China’s new generation push-broom scanner. The HSIs obtained by FAHI are tested and analyzed. Experiments on simulation data compare the four proposed methods with traditional methods and prove that FSAM outperforms other methods in terms of accuracy and stability. In experiments on real data, the application of the full strategy on FAHI verifies its effectiveness. This work not only provides reference for other push-broom imagers with similar problems, but also helps to reduce the requirement for hardware calibration.
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Davison, Thomas A., Harald Kuntschner, Bernd Husemann, Mark A. Norris, Julianne J. Dalcanton, Alessandra De Rosa, Pierre-Alain Duc, Stefano Bianchi, Pedro R. Capelo, and Cristian Vignali. "Old and new major mergers in the SOSIMPLE galaxy, NGC 7135." Monthly Notices of the Royal Astronomical Society 502, no. 2 (January 21, 2021): 2296–307. http://dx.doi.org/10.1093/mnras/stab162.
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ABSTRACT The simultaneous advancement of high resolution integral field unit spectroscopy and robust full-spectral fitting codes now make it possible to examine spatially resolved kinematic, chemical composition, and star-formation history from nearby galaxies. We take new MUSE data from the snapshot optical spectroscopic imaging of mergers and pairs for legacy Exploration (SOSIMPLE) survey to examine NGC 7135. With counter-rotation of gas, disrupted kinematics and asymmetric chemical distribution, NGC 7135 is consistent with an ongoing merger. Though well hidden by the current merger, we are able to distinguish stars originating from an older merger, occurring 6–10 Gyr ago. We further find a gradient in ex-situ material with galactocentric radius, with the accreted fraction rising from 0 per cent in the galaxy centre, to ∼7 per cent within 0.6 effective radii.
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Barkley, M. P., U. Frieß, and P. S. Monks. "Measuring atmospheric CO<sub>2</sub> from space using Full Spectral Initiation (FSI) WFM-DOAS." Atmospheric Chemistry and Physics Discussions 6, no. 2 (April 10, 2006): 2765–807. http://dx.doi.org/10.5194/acpd-6-2765-2006.
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Abstract. Satellite measurements of atmospheric CO2 concentrations are a rapidly evolving area of scientific research which can help reduce the uncertainties in the global carbon cycle fluxes and provide insight into surface sources and sinks. One of the emerging CO2 measurement techniques is a relatively new retrieval algorithm called Weighting Function Modified Differential Optical Absorption Spectroscopy (WFM-DOAS) that has been developed by Buchwitz et al. (2000). This algorithm is designed to measure the total columns of CO2 (and other greenhouse gases) through the application to spectral measurements in the near infrared (NIR), made by the SCIAMACHY instrument on-board ENVISAT. The algorithm itself is based on fitting the logarithm of a model reference spectrum and its derivatives to the logarithm of the ratio of a measured nadir radiance and solar irradiance spectrum. In this work, a detailed error assessment of this technique has been conducted and it has been found necessary to include suitable a priori information within the retrieval in order to minimize the errors on the retrieved CO2 columns. Hence, a new CO2 retrieval algorithm called Full Spectral Initiation (FSI) WFM-DOAS has been developed which generates a reference spectrum for each individual SCIAMACHY observation using the known properties of the atmosphere and surface at the time of the measurement. Initial retrievals over Siberia during the summer of 2003 show that the measured CO2 columns are not biased from the input a priori data and that whilst the monthly averaged CO2 distributions contain a high degree of variability, they also contain significant spatial features.
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Barkley, M. P., U. Frieß, and P. S. Monks. "Measuring atmospheric CO<sub>2</sub> from space using Full Spectral Initiation (FSI) WFM-DOAS." Atmospheric Chemistry and Physics 6, no. 11 (August 30, 2006): 3517–34. http://dx.doi.org/10.5194/acp-6-3517-2006.
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Abstract. Satellite measurements of atmospheric CO2 concentrations are a rapidly evolving area of scientific research which can help reduce the uncertainties in the global carbon cycle fluxes and provide insight into surface sources and sinks. One of the emerging CO2 measurement techniques is a relatively new retrieval algorithm called Weighting Function Modified Differential Optical Absorption Spectroscopy (WFM-DOAS) that has been developed by Buchwitz et al. (2000). This algorithm is designed to measure the total columns of CO2 (and other greenhouse gases) through the application to spectral measurements in the near infrared (NIR), made by the SCIAMACHY instrument on-board ENVISAT. The algorithm itself is based on fitting the logarithm of a model reference spectrum and its derivatives to the logarithm of the ratio of a measured nadir radiance and solar irradiance spectrum. In this work, a detailed error assessment of this technique has been conducted and it has been found necessary to include suitable a priori information within the retrieval in order to minimize the errors on the retrieved CO2 columns. Hence, a more flexible implementation of the retrieval technique, called Full Spectral Initiation (FSI) WFM-DOAS, has been developed which generates a reference spectrum for each individual SCIAMACHY observation using the estimated properties of the atmosphere and surface at the time of the measurement. Initial retrievals over Siberia during the summer of 2003 show that the measured CO2 columns are not biased from the input a priori data and that whilst the monthly averaged CO2 distributions contain a high degree of variability, they also contain interesting spatial features.
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Li, Can, Nickolay A. Krotkov, Simon Carn, Yan Zhang, Robert J. D. Spurr, and Joanna Joiner. "New-generation NASA Aura Ozone Monitoring Instrument (OMI) volcanic SO<sub>2</sub> dataset: algorithm description, initial results, and continuation with the Suomi-NPP Ozone Mapping and Profiler Suite (OMPS)." Atmospheric Measurement Techniques 10, no. 2 (February 6, 2017): 445–58. http://dx.doi.org/10.5194/amt-10-445-2017.
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Abstract. Since the fall of 2004, the Ozone Monitoring Instrument (OMI) has been providing global monitoring of volcanic SO2 emissions, helping to understand their climate impacts and to mitigate aviation hazards. Here we introduce a new-generation OMI volcanic SO2 dataset based on a principal component analysis (PCA) retrieval technique. To reduce retrieval noise and artifacts as seen in the current operational linear fit (LF) algorithm, the new algorithm, OMSO2VOLCANO, uses characteristic features extracted directly from OMI radiances in the spectral fitting, thereby helping to minimize interferences from various geophysical processes (e.g., O3 absorption) and measurement details (e.g., wavelength shift). To solve the problem of low bias for large SO2 total columns in the LF product, the OMSO2VOLCANO algorithm employs a table lookup approach to estimate SO2 Jacobians (i.e., the instrument sensitivity to a perturbation in the SO2 column amount) and iteratively adjusts the spectral fitting window to exclude shorter wavelengths where the SO2 absorption signals are saturated. To first order, the effects of clouds and aerosols are accounted for using a simple Lambertian equivalent reflectivity approach. As with the LF algorithm, OMSO2VOLCANO provides total column retrievals based on a set of predefined SO2 profiles from the lower troposphere to the lower stratosphere, including a new profile peaked at 13 km for plumes in the upper troposphere. Examples given in this study indicate that the new dataset shows significant improvement over the LF product, with at least 50 % reduction in retrieval noise over the remote Pacific. For large eruptions such as Kasatochi in 2008 (∼ 1700 kt total SO2) and Sierra Negra in 2005 (> 1100 DU maximum SO2), OMSO2VOLCANO generally agrees well with other algorithms that also utilize the full spectral content of satellite measurements, while the LF algorithm tends to underestimate SO2. We also demonstrate that, despite the coarser spatial and spectral resolution of the Suomi National Polar-orbiting Partnership (Suomi-NPP) Ozone Mapping and Profiler Suite (OMPS) instrument, application of the new PCA algorithm to OMPS data produces highly consistent retrievals between OMI and OMPS. The new PCA algorithm is therefore capable of continuing the volcanic SO2 data record well into the future using current and future hyperspectral UV satellite instruments.
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Ataee, Mohammad Sadegh, Yasser Maghsoudi, Hooman Latifi, and Farhad Fadaie. "Improving Estimation Accuracy of Growing Stock by Multi-Frequency SAR and Multi-Spectral Data over Iran’s Heterogeneously-Structured Broadleaf Hyrcanian Forests." Forests 10, no. 8 (July 29, 2019): 641. http://dx.doi.org/10.3390/f10080641.
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Via providing various ecosystem services, the old-growth Hyrcanian forests play a crucial role in the environment and anthropogenic aspects of Iran and beyond. The amount of growing stock volume (GSV) is a forest biophysical parameter with great importance in issues like economy, environmental protection, and adaptation to climate change. Thus, accurate and unbiased estimation of GSV is also crucial to be pursued across the Hyrcanian. Our goal was to investigate the potential of ALOS-2 and Sentinel-1’s polarimetric features in combination with Sentinel-2 multi-spectral features for the GSV estimation in a portion of heterogeneously-structured and mountainous Hyrcanian forests. We used five different kernels by the support vector regression (nu-SVR) for the GSV estimation. Because each kernel differently models the parameters, we separately selected features for each kernel by a binary genetic algorithm (GA). We simultaneously optimized R2 and RMSE in a suggested GA fitness function. We calculated R2, RMSE to evaluate the models. We additionally calculated the standard deviation of validation metrics to estimate the model’s stability. Also for models over-fitting or under-fitting analysis, we used mean difference (MD) index. The results suggested the use of polynomial kernel as the final model. Despite multiple methodical challenges raised from the composition and structure of the study site, we conclude that the combined use of polarimetric features (both dual and full) with spectral bands and indices can improve the GSV estimation over mixed broadleaf forests. This was partially supported by the use of proposed evaluation criterion within the GA, which helped to avoid the curse of dimensionality for the applied SVR and lowest over estimation or under estimation.
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Prichard, Laura J., Sam P. Vaughan, and Roger L. Davies. "Unravelling the origin of the counter-rotating core in IC 1459 with KMOS and MUSE." Monthly Notices of the Royal Astronomical Society 488, no. 2 (May 17, 2019): 1679–94. http://dx.doi.org/10.1093/mnras/stz1191.
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ABSTRACT The massive early-type galaxy IC 1459 is a slowly rotating galaxy that exhibits a rapidly counter-rotating kinematically decoupled core (KDC, RKDC ≈ 5 arcsec ≈ 0.1Re). To investigate the origin of its KDC, we coupled large data mosaics from the near-infrared and optical integral field unit instruments K-band Multi-Object Spectrograph (KMOS) and Multi-Unit Spectroscopic Explorer (MUSE), respectively. We studied IC 1459’s stellar populations and, for the first time for a KDC, the spatially resolved initial mass function (IMF). We used full-spectral-fitting to fit the stellar populations and IMF simultaneously, and an alternative spectral-fitting method that does not assume a star formation history (SFH; although does not constrain the IMF) for comparison. When no SFH is assumed, we derived a negative metallicity gradient for IC 1459 that could be driven by a distinct metal-poor population in the outer regions of the galaxy, and a radially constant old stellar age. We found a radially constant bottom-heavy IMF out to ${\sim }\frac {1}{3}R_{\rm e}$. The radially flat IMF and age extend beyond the counter-rotating core. We detected high-velocity dispersion along the galaxy’s major axis. Our results potentially add weight to findings from orbital modelling of other KDCs that the core is not a distinct population of stars but in fact two smooth co-spatial counter-rotating populations. No clear picture of formation explains the observational results of IC 1459, but we propose it could have included a gas-rich intense period of star formation at early times, perhaps with counter-rotating accreting cold streams, followed by dry and gas-rich mergers through to the present day.
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Feldmeier-Krause, A., W. Kerzendorf, T. Do, F. Nogueras-Lara, N. Neumayer, C. J. Walcher, A. Seth, et al. "Asymmetric spatial distribution of subsolar metallicity stars in the Milky Way nuclear star cluster." Monthly Notices of the Royal Astronomical Society 494, no. 1 (March 30, 2020): 396–410. http://dx.doi.org/10.1093/mnras/staa703.
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ABSTRACT We present stellar metallicity measurements of more than 600 late-type stars in the central 10 pc of the Galactic Centre. Together with our previously published KMOS data, this data set allows us to investigate, for the first time, spatial variations of the nuclear star cluster’s metallicity distribution. Using the integral-field spectrograph KMOS (VLT), we observed almost half of the area enclosed by the nuclear star cluster’s effective radius. We extract spectra at medium spectral resolution and apply full spectral fitting utilizing the PHOENIX library of synthetic stellar spectra. The stellar metallicities range from [M/H] = −1.25 dex to [M/H] > +0.3 dex, with most of the stars having supersolar metallicity. We are able to measure an anisotropy of the stellar metallicity distribution. In the Galactic north, the portion of subsolar metallicity stars with [M/H] < 0.0 dex is more than twice as high as in the Galactic south. One possible explanation for different fractions of subsolar metallicity stars in different parts of the cluster is a recent merger event. We propose to test this hypothesis with high-resolution spectroscopy and by combining the metallicity information with kinematic data.
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Teimoorinia, Hossen, Finn Archinuk, Joanna Woo, Sara Shishehchi, and Asa F. L. Bluck. "Mapping the Diversity of Galaxy Spectra with Deep Unsupervised Machine Learning." Astronomical Journal 163, no. 2 (January 18, 2022): 71. http://dx.doi.org/10.3847/1538-3881/ac4039.
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Abstract Modern spectroscopic surveys of galaxies such as MaNGA consist of millions of diverse spectra covering different regions of thousands of galaxies. We propose and implement a deep unsupervised machine-learning method to summarize the entire diversity of MaNGA spectra onto a 15 × 15 map (DESOM-1), where neighboring points on the map represent similar spectra. We demonstrate our method as an alternative to conventional full spectral fitting for deriving physical quantities and full probability distributions much more efficiently than traditional resource-intensive Bayesian methods. Since spectra are grouped by similarity, the distribution of spectra onto the map for a single galaxy, i.e., its “fingerprint,” reveals the presence of distinct stellar populations within the galaxy, indicating smoother or episodic star formation histories. We further map the diversity of galaxy fingerprints onto a second map (DESOM-2). Using galaxy images and independent measures of galaxy morphology, we confirm that galaxies with similar fingerprints have similar morphologies and inclination angles. Since morphological information was not used in the mapping algorithm, relating galaxy morphology to the star formation histories encoded in the fingerprints is one example of how the DESOM maps can be used to make scientific inferences.
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Arentsen, Anke, Philippe Prugniel, Anais Gonneau, Ariane Lançon, Scott Trager, Reynier Peletier, Mariya Lyubenova, et al. "Stellar atmospheric parameters for 754 spectra from the X-shooter Spectral Library." Astronomy & Astrophysics 627 (July 2019): A138. http://dx.doi.org/10.1051/0004-6361/201834273.
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Context. The X-shooter Spectral Library (XSL) is an empirical stellar library at medium spectral resolution covering the wavelength range from 3000 Å to 24 800 Å. This library aims to provide a benchmark for stellar population studies. Aims. In this work, we present a uniform set of stellar atmospheric parameters, effective temperatures, surface gravities, and iron abundances for 754 spectra of 616 XSL stars. Methods. We used the full-spectrum fitting package ULySS with the empirical MILES library as reference to fit the ultraviolet-blue (UVB) and visible (VIS) spectra. We tested the internal consistency and we compared our results with compilations from the literature. Results. The stars cover a range of effective temperature 2900 < Teff < 38 000 K, surface gravity 0 < logg < 5.7, and iron abundance −2.5 < [Fe/H] < +1.0, with a couple of stars extending down to [Fe/H] = −3.9. The precisions of the measurements for the G- and K-type stars are 0.9%, 0.14, and 0.06 in Teff, logg, and [Fe/H], respectively. For the cool giants with logg < 1, the precisions are 2.1%, 0.21, and 0.22, and for the other cool stars these values are 1%, 0.14, and 0.10. For the hotter stars (Teff > 6500 K), these values are 2.6%, 0.20, and 0.10 for the three parameters.
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Kawamura, Tenyo, Magnus Axelsson, Chris Done, and Tadayuki Takahashi. "A full spectral-timing model to map the accretion flow in black hole binaries: the low/hard state of MAXI J1820+070." Monthly Notices of the Royal Astronomical Society 511, no. 1 (January 13, 2022): 536–52. http://dx.doi.org/10.1093/mnras/stac045.
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ABSTRACT The nature and geometry of the accretion flow in the low/hard state of black hole binaries is currently controversial. While most properties are generally explained in the truncated disc/hot inner flow model, the detection of a broad residual around the iron line argues for strong relativistic effects from an untruncated disc. Since spectral fitting alone is somewhat degenerate, we combine it with the additional information in the fast X-ray variability and perform a full spectral-timing analysis for NICER and NuSTAR data on a bright low/hard state of MAXI J1820+070. We model the variability with propagating mass accretion rate fluctuations by combining two separate current insights: that the hot flow is spectrally inhomogeneous, and that there is a discontinuous jump in viscous time-scale between the hot flow and variable disc. Our model naturally gives the double-humped shape of the power spectra, and the increasing high-frequency variability with energy in the second hump. Including reflection and reprocessing from a disc truncated at a few tens of gravitational radii quantitatively reproduces the switch in the lag-frequency spectra, from hard lagging soft at low frequencies (propagation through the variable flow) to the soft lagging hard at the high frequencies (reverberation from the hard X-ray continuum illuminating the disc). The viscous time-scale of the hot flow is derived from the model, and we show how this can be used to observationally test ideas about the origin of the jet.
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Yousefi, Mastoureh, Seyed Hassan Tabatabaei, Reyhaneh Rikhtehgaran, Amin Beiranvand Pour, and Biswajeet Pradhan. "Application of Dirichlet Process and Support Vector Machine Techniques for Mapping Alteration Zones Associated with Porphyry Copper Deposit Using ASTER Remote Sensing Imagery." Minerals 11, no. 11 (November 6, 2021): 1235. http://dx.doi.org/10.3390/min11111235.
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The application of machine learning (ML) algorithms for processing remote sensing data is momentous, particularly for mapping hydrothermal alteration zones associated with porphyry copper deposits. The unsupervised Dirichlet Process (DP) and the supervised Support Vector Machine (SVM) techniques can be executed for mapping hydrothermal alteration zones associated with porphyry copper deposits. The main objective of this investigation is to practice an algorithm that can accurately model the best training data as input for supervised methods such as SVM. For this purpose, the Zefreh porphyry copper deposit located in the Urumieh-Dokhtar Magmatic Arc (UDMA) of central Iran was selected and used as training data. Initially, using ASTER data, different alteration zones of the Zefreh porphyry copper deposit were detected by Band Ratio, Relative Band Depth (RBD), Linear Spectral Unmixing (LSU), Spectral Feature Fitting (SFF), and Orthogonal Subspace Projection (OSP) techniques. Then, using the DP method, the exact extent of each alteration was determined. Finally, the detected alterations were used as training data to identify similar alteration zones in full scene of ASTER using SVM and Spectral Angle Mapper (SAM) methods. Several high potential zones were identified in the study area. Field surveys and laboratory analysis were used to validate the image processing results. This investigation demonstrates that the application of the SVM algorithm for mapping hydrothermal alteration zones associated with porphyry copper deposits is broadly applicable to ASTER data and can be used for prospectivity mapping in many metallogenic provinces around the world.
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Zhang, Yanjun, Otso Peräkylä, Chao Yan, Liine Heikkinen, Mikko Äijälä, Kaspar R. Daellenbach, Qiaozhi Zha, et al. "A novel approach for simple statistical analysis of high-resolution mass spectra." Atmospheric Measurement Techniques 12, no. 7 (July 11, 2019): 3761–76. http://dx.doi.org/10.5194/amt-12-3761-2019.
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Abstract. Recent advancements in atmospheric mass spectrometry provide huge amounts of new information but at the same time present considerable challenges for the data analysts. High-resolution (HR) peak identification and separation can be effort- and time-consuming yet still tricky and inaccurate due to the complexity of overlapping peaks, especially at larger mass-to-charge ratios. This study presents a simple and novel method, mass spectral binning combined with positive matrix factorization (binPMF), to address these problems. Different from unit mass resolution (UMR) analysis or HR peak fitting, which represent the routine data analysis approaches for mass spectrometry datasets, binPMF divides the mass spectra into small bins and takes advantage of the positive matrix factorization's (PMF) strength in separating different sources or processes based on different temporal patterns. In this study, we applied the novel approach to both ambient and synthetic datasets to evaluate its performance. It not only succeeded in separating overlapping ions but was found to be sensitive to subtle variations as well. Being fast and reliable, binPMF has no requirement for a priori peak information and can save much time and effort from conventional HR peak fitting, while still utilizing nearly the full potential of HR mass spectra. In addition, we identify several future improvements and applications for binPMF and believe it will become a powerful approach in the data analysis of mass spectra.
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Gaikwad, Prakash, Michael Rauch, Martin G. Haehnelt, Ewald Puchwein, James S. Bolton, Laura C. Keating, Girish Kulkarni, et al. "Probing the thermal state of the intergalactic medium at z > 5 with the transmission spikes in high-resolution Ly α forest spectra." Monthly Notices of the Royal Astronomical Society 494, no. 4 (April 9, 2020): 5091–109. http://dx.doi.org/10.1093/mnras/staa907.
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ABSTRACT We compare a sample of five high-resolution, high S/N Ly α forest spectra of bright 6 < z < ∼6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z > 5 with those obtained from mock absorption spectra from the Sherwoodand Sherwood–Relics simulation suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile-fitting procedure for the inverted transmitted flux, 1 − F, similar to the widely used Voigt profile fitting of the transmitted flux F at lower redshifts, to characterize the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8 km s−1) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T0 caused by spatial fluctuations in the temperature–density relation.