Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies. III.
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Spectroscopic Study of the Interaction between Small Molecules and Large Proteins1. IntroductionThe study of drug-protein interactions is of great importance in drug discovery and development. Understanding how small molecules interact with proteins at the molecular level is crucial for the design of new and more effective drugs. Spectroscopic techniques have proven to be valuable tools in the investigation of these interactions, providing det本人led information about the binding affinity, mode of binding, and structural changes that occur upon binding.2. Spectroscopic Techniques2.1. Fluorescence SpectroscopyFluorescence spectroscopy is widely used in the study of drug-protein interactions due to its high sensitivity and selectivity. By monitoring the changes in the fluorescence emission of either the drug or the protein upon binding, valuable information about the binding affinity and the binding site can be obt本人ned. Additionally, fluorescence quenching studies can provide insights into the proximity and accessibility of specific amino acid residues in the protein's binding site.2.2. UV-Visible SpectroscopyUV-Visible spectroscopy is another powerful tool for the investigation of drug-protein interactions. This technique can be used to monitor changes in the absorption spectra of either the drug or the protein upon binding, providing information about the binding affinity and the stoichiometry of the interaction. Moreover, UV-Visible spectroscopy can be used to study the conformational changes that occur in the protein upon binding to the drug.2.3. Circular Dichroism SpectroscopyCircular dichroism spectroscopy is widely used to investigate the secondary structure of proteins and to monitor conformational changes upon ligand binding. By analyzing the changes in the CD spectra of the protein in the presence of the drug, valuable information about the structural changes induced by the binding can be obt本人ned.2.4. Nuclear Magnetic Resonance SpectroscopyNMR spectroscopy is a powerful technique for the investigation of drug-protein interactions at the atomic level. By analyzing the chemical shifts and the NOE signals of the protein in thepresence of the drug, det本人led information about the binding site and the mode of binding can be obt本人ned. Additionally, NMR can provide insights into the dynamics of the protein upon binding to the drug.3. Applications3.1. Drug DiscoverySpectroscopic studies of drug-protein interactions play a crucial role in drug discovery, providing valuable information about the binding affinity, selectivity, and mode of action of potential drug candidates. By understanding how small molecules interact with their target proteins, researchers can design more potent and specific drugs with fewer side effects.3.2. Protein EngineeringSpectroscopic techniques can also be used to study the effects of mutations and modifications on the binding affinity and specificity of proteins. By analyzing the binding of small molecules to wild-type and mutant proteins, valuable insights into the structure-function relationship of proteins can be obt本人ned.3.3. Biophysical StudiesSpectroscopic studies of drug-protein interactions are also valuable for the characterization of protein-ligandplexes, providing insights into the thermodynamics and kinetics of the binding process. Additionally, these studies can be used to investigate the effects of environmental factors, such as pH, temperature, and ionic strength, on the stability and binding affinity of theplexes.4. Challenges and Future DirectionsWhile spectroscopic techniques have greatly contributed to our understanding of drug-protein interactions, there are still challenges that need to be addressed. For instance, the study of membrane proteins and protein-protein interactions using spectroscopic techniques rem本人ns challenging due to theplexity and heterogeneity of these systems. Additionally, the development of new spectroscopic methods and the integration of spectroscopy with other biophysical andputational approaches will further advance our understanding of drug-protein interactions.In conclusion, spectroscopic studies of drug-protein interactions have greatly contributed to our understanding of how small molecules interact with proteins at the molecular level. Byproviding det本人led information about the binding affinity, mode of binding, and structural changes that occur upon binding, spectroscopic techniques have be valuable tools in drug discovery, protein engineering, and biophysical studies. As technology continues to advance, spectroscopy will play an increasingly important role in the study of drug-protein interactions, leading to the development of more effective and targeted therapeutics.。
应用波谱学英文Applications of spectroscopySpectroscopy has a wide range of applications across various scientific disciplines. Some of the common applications of spectroscopy include:1. Chemistry: Spectroscopy is extensively used in chemistry for the identification and analysis of chemical compounds. It helps in determining the chemical composition, molecular structure, and functional groups present in a sample.2. Pharmaceuticals: Spectroscopic techniques are crucial in the drug discovery and development process. They are used for quality control, impurity analysis, and determining the stability of pharmaceutical products.3. Environmental science: Spectroscopy plays a vital role in environmental monitoring and assessment. It is used to evaluate air quality, analyze water pollutants, and identify harmful substances in soil samples.4. Biochemistry and molecular biology: Spectroscopy is employed in studying the structure, function, and dynamics of biological molecules like proteins, nucleic acids, and carbohydrates. Techniques such as UV-Visible spectroscopy, fluorescence spectroscopy, and circular dichroism spectroscopy are commonly used in this field.5. Material science: Spectroscopy helps in characterizing andstudying various materials and their properties. It is used to analyze the composition, crystal structure, and surface properties of materials such as metals, ceramics, polymers, and semiconductors.6. Astronomy: Spectroscopy is fundamental in studying the properties and composition of celestial objects. Astronomers use spectroscopic techniques to analyze the light emitted or absorbed by stars, galaxies, and other astronomical phenomena to determine their chemical composition, temperature, and motion.7. Forensics: Spectroscopic methods are employed in forensic science for the detection and analysis of trace evidence, such as drugs, explosives, and chemical residues. They are also used in analyzing questioned documents and for the identification of counterfeit or forged materials.8. Food science and agriculture: Spectroscopic techniques are used for analyzing food products, determining their quality, and detecting adulteration. They are also employed in agricultural research for monitoring plant health and analyzing soil fertility. These are just a few examples of the diverse applications of spectroscopy in various fields. Overall, spectroscopy is a powerful analytical tool that enables scientists to study and understand the properties and behavior of substances in a wide range of scientific domains.。
第29卷,第4期 光谱学与光谱分析Vol 129,No 14,pp1093-10992009年4月 Spectro sco py and Spectr al AnalysisA pril,2009羟基和超氧自由基的检测研究进展张 昊,任发政*中国农业大学食品科学与营养工程学院,教育部-北京市功能乳品实验室,北京 100083摘 要 活细胞在必需的新陈代谢过程中会产生自由基,越来越多的研究证据表明,这些自由基涉及到许多体内调控系统,然而一旦有过多的自由基生成便会氧化细胞脂膜、蛋白质、DN A 和酶,进而对细胞造成致命性的损伤。
此外,研究还表明许多疾病与自由基密切相关,例如,有研究报道海氏默症病人脑中生物分子的氧化损伤程度明显高于正常值,另外癌症可能也是DN A 受到氧化损伤的结果。
因此,测定自由基的方法就显得十分必需和重要。
文章重点对羟基和超氧自由基检测技术的发展情况进行了讨论,涉及的自由基检测技术主要有分光光度法、荧光法、化学发光法和电子自旋共振技术,并评价了各种方法的优缺点。
关键词 羟基自由基;超氧自由基;检测技术;评述中图分类号:O 65713 文献标识码:A DOI :1013964/j 1issn 11000-0593(2009)04-1093-07收稿日期:2007-11-28,修订日期:2008-03-06基金项目:国家/十一五0科技支撑项目(2006BAD05A16)资助作者简介:张 昊,1984年生,中国农业大学食品科学与营养工程学院硕士研究生 e -mail:david1hao@sina 1com*通讯联系人 e -mail:r enfaz heng@2631n et引 言羟基自由基(O H #)和超氧自由基(O 2-#)是生物体内活性氧代谢产生的物质,其中O 2-#经一系列反应最终会生成OH #,而OH #是一种氧化性很强的自由基,可以引发不饱和脂肪酸发生脂质过氧化反应,使糖类、蛋白质、核酸及脂类等发生氧化损伤。
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Inorganic Chemistr无机化学与核化学Chem Res Chinese U Chemical Research In Chinese Universi化学综合Chinese Chem Lett Chinese Chemical Letters化学综合Dokl Chem Doklady Chemistry化学综合Main Group Met Chem Main Group Metal Chemistry无机化学与核化学Main Group Met Chem Main Group Metal Chemistry有机化学Chem Unserer Zeit Chemie In Unserer Zeit化学综合Prog React Kinet Mec Progress In Reaction Kinetics And Mec物理化学J Indian Chem Soc Journal Of The Indian Chemical Societ化学综合Lc Gc N Am Lc Gc North America分析化学Bunseki Kagaku Bunseki Kagaku分析化学Rev Chim-Bucharest Revista De Chimie工程:化工Rev Chim-Bucharest Revista De Chimie化学综合Polym Sci Ser B+Polymer Science Series B高分子科学Indian J Heterocy Ch Indian Journal Of Heterocyclic Chemis有机化学Chem Ind-London Chemistry & Industry应用化学Oxid Commun Oxidation Communications化学综合Rev Roum Chim Revue Roumaine De Chimie化学综合Russ J Appl Chem+Russian Journal Of Applied Chemistry应用化学Asian J Chem Asian Journal Of Chemistry化学综合B Chem Soc Ethiopia Bulletin Of The Chemical Society Of Et化学综合Afinidad Afinidad化学综合J Autom Method Manag J ournal Of Automated Methods & Man分析化学J Autom Method Manag J ournal Of Automated Methods & Man仪器仪表Kobunshi Ronbunshu Kobunshi Ronbunshu高分子科学J Chem Soc Pakistan Journal Of The Chemical Society Of Pa化学综合J Chem Res-S Journal Of Chemical Research-S化学综合Actual Chimique Actualite Chimique化学综合Russ J Phys Chem B+Russian Journal Of Physical Chemistry物理:原子、分子和化学物理Chem Phys Carbon Chemistry And Physics Of Carbon物理化学Chem Phys Carbon Chemistry And Physics Of Carbon能源与燃料Chem Phys Carbon Chemistry And Physics Of Carbon工程:化工J Appl Crystallogr Journal Of Applied Crystallography晶体学Acta Crystallogr B Acta Crystallographica Section B-Struc晶体学Acta Crystallogr A Acta Crystallographica Section A晶体学J Cryst Growth Journal Of Crystal Growth晶体学Liq Cryst Liquid Crystals晶体学Cryst Res Technol Crystal Research And Technology晶体学Acta Crystallogr C Acta Crystallographica Section C-Cryst晶体学Mol Cryst Liq Cryst Molecular Crystals And Liquid Crystal晶体学Acta Crystallogr E Acta Crystallographica Section E-Struc晶体学Crystallogr Rep+Crystallography Reports晶体学Z Krist-New Cryst St Zeitschrift Fur Kristallographie-New C晶体学小类名称(英文)小类分区大类分区2008年影响因子2007年影响因子2006年影响因子2008年平均影响因子Chemistry, Multidisciplinary 1123.59222.75726.05424.13433Chemistry, Multidisciplinary 1112.17616.21417.11315.16767Polymer Science 1116.81912.80914.81814.81533Chemistry, Multidisciplinary 1117.41913.08213.6914.73033Chemistry, Organic 1116.73311.92910.69213.118Chemistry, Physical 1114.6889.43911.2511.79233Chemistry, Physical 1112.80811.9239.30411.345Physics, Condensed Matter 1112.80811.9239.30411.345Chemistry, Multidisciplinary 1110.87910.03110.23210.38067Chemistry, Inorganic & Nuclear 1110.5668.5688.8159.316333Chemistry, Medicinal 117.457.6678.8898.002Chemistry, Organic 117.457.6678.8898.002Biochemistry & Molecular Biolo 217.457.6678.8898.002Chemistry, Physical 11 4.8127.66711.257.909667Chemistry, Multidisciplinary 218.0917.8857.6967.890667Chemistry, Physical 11 5.625 6.3339.2227.06Chemistry, Physical 21 6.8928.121 6.0367.016333Chemistry, Physical 21 5.36 5.7317.32 6.137Polymer Science 12 6.802 5.93 4.284 5.672Chemistry, Analytical 12 5.712 5.287 5.646 5.548333Chemistry, Multidisciplinary 22 5.27 6.394 4.789 5.484333Chemistry, Analytical 12 5.485 5.827 5.068 5.46Chemistry, Multidisciplinary 22 5.454 5.33 5.015 5.266333Chemistry, Applied 12 5.619 4.977 4.762 5.119333Chemistry, Organic 12 5.619 4.977 4.762 5.119333Chemistry, Multidisciplinary 22 5.34 5.141 4.521 5.000667Chemistry, Inorganic & Nuclear 12 3.571 4.176 6.85 4.865667Chemistry, Organic 22 3.571 4.176 6.85 4.865667Chemistry, Organic 22 5.128 4.802 4.659 4.863Chemistry, Physical 22 5.493 4.354 4.63 4.825667Chemistry, Physical 22 4.6045 4.731 4.778333Chemistry, Multidisciplinary 22 4.542 4.836 4.192 4.523333Chemistry, Physical 22 6.511 4.041 2.893 4.481667Chemistry, Inorganic & Nuclear 22 6.511 4.041 2.893 4.481667Chemistry, Inorganic & Nuclear 22 4.214 4.6 3.792 4.202Crystallography 12 4.215 4.046 4.339 4.2Materials Science, Multidisciplin22 4.215 4.046 4.339 4.2Chemistry, Multidisciplinary 22 4.215 4.046 4.339 4.2Chemistry, Multidisciplinary 22 4.19700 4.197Chemistry, Multidisciplinary 32 3.39 4.297 4.893 4.193333Chemistry, Physical 22 4.189 4.086 4.115 4.13Chemistry, Multidisciplinary 32 4.274 4.308 3.627 4.069667Chemistry, Physical32 5.333 3.074 3.79 4.065667 Chemistry, Inorganic & Nuclear22 4.147 4.123 3.911 4.060333 Chemistry, Physical32 4.097 4.009 3.902 4.002667 Polymer Science22 4.146 4.169 3.664 3.993 Chemistry, Organic22 4.146 4.169 3.664 3.993 Biochemistry & Molecular Biolo32 4.146 4.169 3.664 3.993 Chemistry, Organic22 3.952 3.959 3.79 3.900333 Chemistry, Inorganic & Nuclear22 3.815 3.833 3.632 3.76 Chemistry, Organic22 3.815 3.833 3.632 3.76 Chemistry, Analytical22 3.756 3.641 3.554 3.650333 Biochemical Research Methods22 3.756 3.641 3.554 3.650333 Chemistry, Analytical22 4.028 3.269 3.63 3.642333 Spectroscopy22 4.028 3.269 3.63 3.642333 Polymer Science22 3.821 3.529 3.405 3.585 Crystallography22 3.535 3.468 3.729 3.577333 Chemistry, Multidisciplinary32 3.535 3.468 3.729 3.577333 Physics, Atomic, Molecular & C12 3.636 3.502 3.449 3.529 Chemistry, Physical32 3.636 3.502 3.449 3.529 Chemistry, Analytical22 3.761 3.553 3.198 3.504 Chemistry, Organic22 3.184 3.961 3.232 3.459 Physics, Atomic, Molecular & C22 4.064 3.343 2.892 3.433 Chemistry, Physical32 4.064 3.343 2.892 3.433 Chemistry, Inorganic & Nuclear22 3.6 3.325 3.303 3.409333 Biochemistry & Molecular Biolo32 3.6 3.325 3.303 3.409333 Materials Science, Multidisciplin22 3.39600 3.396 Chemistry, Physical32 3.39600 3.396 Nanoscience & Nanotechnology32 3.39600 3.396 Chemistry, Analytical22 3.181 3.664 3.307 3.384 Spectroscopy22 3.181 3.664 3.307 3.384 Chemistry, Physical32 3.181 3.664 3.307 3.384 Computer Science, Information 12 3.643 2.986 3.423 3.350667 Computer Science, Interdisciplin22 3.643 2.986 3.423 3.350667 Chemistry, Multidisciplinary32 3.643 2.986 3.423 3.350667 Chemistry, Inorganic & Nuclear22 3.58 3.212 3.012 3.268 Chemistry, Multidisciplinary33 3.477 2.641 3.583 3.233667 Chemistry, Organic23 3.55 3.167 2.874 3.197 Chemistry, Analytical23 3.206 3.374 2.81 3.13 Chemistry, Applied13 3.011 3.154 3.153 3.106 Chemistry, Multidisciplinary33 3.011 3.154 3.153 3.106 Chemistry, Medicinal33 3.011 3.154 3.153 3.106 Chemistry, Analytical23 3.146 3.186 2.894 3.075333 Polymer Science23 3.331 3.065 2.773 3.056333 Environmental Sciences23 3.19 3.166 2.63 2.995333Chemistry, Physical33 3.19 3.166 2.63 2.995333 Spectroscopy23 2.94 3.062 2.945 2.982333 Biophysics33 2.94 3.062 2.945 2.982333 Chemistry, Organic33 2.94 3.062 2.945 2.982333 Chemistry, Physical33 2.424 3.333 3.083 2.946667 Chemistry, Multidisciplinary33 2.424 3.333 3.083 2.946667 Physics, Multidisciplinary33 2.424 3.333 3.083 2.946667 Physics, Atomic, Molecular & C23 2.871 2.918 3.047 2.945333 Chemistry, Physical33 2.871 2.918 3.047 2.945333 Chemistry, Analytical23 3.328 2.867 2.591 2.928667 Biochemical Research Methods33 3.328 2.867 2.591 2.928667 Oceanography23 2.977 3.085 2.663 2.908333 Chemistry, Multidisciplinary33 2.977 3.085 2.663 2.908333 Chemistry, Organic33 3.016 2.914 2.769 2.899667 Chemistry, Organic33 2.897 2.869 2.817 2.861 Chemistry, Organic33 2.61 2.8443 2.818 Chemistry, Analytical23 2.772 2.971 2.68 2.807667 Spectroscopy33 2.772 2.971 2.68 2.807667 Chemistry, Analytical23 2.901 2.949 2.444 2.764667 Electrochemistry33 2.901 2.949 2.444 2.764667 Chemistry, Organic33 2.659 2.763 2.838 2.753333 Chemistry, Multidisciplinary33 2.942 2.651 2.647 2.746667 Chemistry, Analytical33 3.5 2.973 1.656 2.709667 Chemistry, Inorganic & Nuclear332 2.1184 2.706 Mathematics, Interdisciplinary A13 3.5 2.582 2.693333 Computer Science, Interdisciplin23 3.5 2.582 2.693333 Chemistry, Multidisciplinary33 3.5 2.582 2.693333 Chemistry, Physical33 2.814 2.707 2.511 2.677333 Chemistry, Inorganic & Nuclear33 2.694 2.597 2.704 2.665 Engineering, Chemical13 3.004 2.764 2.148 2.638667 Chemistry, Applied23 3.004 2.764 2.148 2.638667 Chemistry, Physical33 3.004 2.764 2.148 2.638667 Chemistry, Analytical33 2.746 2.632 2.535 2.637667 Chemistry, Physical33 2.796 2.634 2.468 2.632667 Chemistry, Inorganic & Nuclear33 2.796 2.634 2.468 2.632667 Chemistry, Organic33 2.796 2.634 2.468 2.632667 Chemistry, Organic33 2.538 2.615 2.509 2.554 Materials Science, Multidisciplin23 2.555 2.21 2.796 2.520333 Chemistry, Applied23 2.555 2.21 2.796 2.520333 Chemistry, Physical33 2.555 2.21 2.796 2.520333 Nanoscience & Nanotechnology33 2.555 2.21 2.796 2.520333 Chemistry, Physical33 1.833 2.6673 2.5 Chemistry, Organic33 1.833 2.6673 2.5。
Devices (CCD) Arrays and Photo Diode (PD) Arrays, enabled the production of low cost scanners, CCD cameras etc. The same CCD and PDA detectors are now used in the Avantes line of spectrometers, enabling fast scanning of the spectrum, wit-hout the need of a moving grating.Thanks to the need for fiber optics in the communication technology, low absorption silica fibers have been developed. Similar fibers can be used as measurement fibers to transport light from the sample to the optical bench of the spectrome-ter. The easy coupling of fibers allows a modular build-up of a system that consists of light source, sampling accessories and fiber optic spectrometer.Advantages of fiber optic spectroscopy are the modularity and flexibility of the system. The speed of measurement allows in-line analysis, and the use of low-cost commonly used detectors enable a complete low cost Avantes spectrometer system.Optical spectroscopy is a technique for measuring light intensity in the UV-, VIS-, NIR- and IR-region. Spectroscopic measurements are being used in many different applications, such as color measurement, concentration determination of chemical components or electromagnetic radiation analysis. For more elaborate application information and setups, please see further the Application chapter at the end of this catalog.A spectroscopic instrument generally consists of entrance slit, collimator, a dispersive element, such as a grating or prism, focusing optics and detector. In a monochromator system there is normally also an exit slit, and only a narrow portion of the spectrum is projected on a one-element detector. In monochromators the entrance and exit slits are in a fixed position and can be changed in width. Rotating the grating scans the spectrum.Development of micro-electronics during the 90’s in the field of multi-element optical detectors, such as Charged Coupledmetrical Czerny-Turner design (figure 1).Light enters the optical bench through a standardSMA905 connector and is collimated by a spherical mirror. A plane grating diffracts the collimated light; a second spherical mirror focuses the resulting diffracted light. An image of the spectrum is projected onto a 1-dimensional linear detector array.installed configurations, depending on the intended application. The choice of these components such as the diffraction grating, entrance slit, order sorting filter, and detector coating have a strong influence on system specifications. Sensitivity, resolution, bandwidth and stray light are further discussed in the following paragraphs.Introduction Fiber Optic SpectroscopySpectrometersinfo@ • S p e c t r o m e t e r s •info@Biomedical Technology Chemistry Colorimetry Food Technology Inline Process Control Radiometry Thinfilm AnalysisHow to configure a spectrometer for your application?For optimal UV sensitivity we recommend the back-thinned UV sensitive CCD detector, as implemented in the AvaSpec-2048x14.For the different detector types the photometric sensitivity is given in table 4, the spectral sensitivity for each detector is depicted in figure 5.b. Chemometric SensitivityTo detect two absorbance values, close to each other with maximum sensitivity you need a high Signal to Noise (S/N) performance. The detector with best S/N performance is the 2048x14 pixel back-thinned CCD detector, next to the 256/1024 CMOS detector in the AvaSpec-256/1024. The S/N performance can also be enhanced by averaging over multiple spectra.4. Timing and SpeedThe data capture process is inherently fast with detector arrays and no moving parts. However there is an optimal detector for each application. For fast response applications, we recommend to use the AvaSpec- USB2 platform spectrometers. When datatransfer time is critical we recommend to select a small amount of pixels to be transferred with the UBS2 interface. Data transfer time can be enhanced by selecting the pixel range of interest to be transmitted to the PC; in general the AvaSpec-128 may be considered as the fastest spectrometer with more than 8000 scans per second.The above parameters are the most important in choosing the right spectrometer configuration, please contact our application engi-neers to optimize and fine-tune the system to your needs. On the next page you will find a quick reference table 1 for most common applications, for a more elaborate explanation and configurations, please refer to the applications section in the back of this catalog.In addition we have introduced in this catalog application icons, that will help you to find the right products and accessories for your applications.In the modular AvaSpec design a number of choices have to be made on several optical components and options, depending on the application you want to use the spectrometer for.This section should give you some guidance on how to choose the right grating, slit, detector and other options, installed in the AvaSpec.1. Wavelength RangeIn the determination for the optimal configuration of a spectrometer system the wavelength range is the first important parameter that defines the grating choice. If you are looking for a wide wavelength range, we recommend to take an A-type (300 lines/mm) or B-type (600 lines/mm) grating (see Grating selection table in the spectrometer product section). The other important component is the detector choice, Avantes offers 9 different detector types with each different sensitivity curves (see figure 5). For UV applications the new 2048x14 pixel back-thinned CCD detector, the 256/1024 pixel CMOS detectors or DUV- enhanced 2048 or 3648 pixel CCD detectors may be selected. For the NIR range 3 different InGaAs detectors are available.If you want to combine a wide range with a high resolu-tion, a multiple channel spectrometer may be the best choice.2. Optical ResolutionIf you desire a high optical resolution we recommend to pick a grating that has 1200 or more lines/mm (C,D,E or F types) in combination with a narrow slit and a detector with 2048 or 3648 pixels, for example 10 µm slit for the best resolution on the AvaSpec-2048 (see Resolution table in the spectrometer product section)3. SensitivityTalking about sensitivity, it is very important to distinguish between photometric sensitivity (How much light do I need for a detectable signal?) and chemometric sensitivity (What absorbance difference level can still be detected?) a. Photometric SensitivityIn order to achieve the most sensitive spectrometer in for example Fluorescence or Raman applications we recommend the 2048 pixel CCD detector, as in the AvaSpec-2048. Further we recommend the use of a DCL-UV/VIS detector collection lens, a relatively wide slit (100µm or wider) or no slit and an A type grating. For an A-type grating (300 lines/mm) the light dispersion is minimal, so it has the highest sensitivity of the grating types. Optionally the Thermo-electric cooling of the CCD detector (see product section AvaSpec-2048-TEC, page 30) may be chosen to minimize noise and increase dynamicrange at long integration times (60 seconds).Table 1 Quick reference guide for spectrometer configurationApplication AvaSpec- Grating WL range (nm) Coating SlitFWHM DCL OSF OSCtype Resolution (nm)Biomedical 2048 NB 500-1000 - 50 1.2 - 475 -Chemometry 1024 UA 200-1100 - 50 2.0 - - OSC-UA 128 VA 360-780 - 100 6.4 X/- - -Color 256 VA 360-780 - 50 3.2 - - -2048 BB 360-780 - 200 4.1 X/- - -Fluorescence 2048 VA 350-1100 - 200 8.0 X - OSC Fruit-sugar 128 IA 800-1100 - 50 5.4 X 600 -Gemology 2048 VA 350-1100 - 25 1.4 X - OSC High 2048 VD 600-700 - 10 0.07 - 550 -resolution 3648 VD 600-700 - 10 0.05 - 550 -High UV- 2048x14UC200-450-2002.0---Sensitivity Irradiance 2048 UA 200-1100 DUV 50 2.8 X/- - OSC-UA Laserdiode 2048 NC 700-800 - 10 0.1 - 600 -LED 2048 VA 350-1100 - 25 1.4 X/- - OSC LIBS 2048FT UE 200-300 DUV 10 0.09 - - - 2048USB2 UE 200-300 DUV 10 0.09 - - -Raman 2048TEC NC 780-930 - 25 0.2 X 600 -Thin Films 2048 UA 200-1100 DUV - 4.1 X - OSC-UA UV/VIS/NIR 2048 UA 200-1100 DUV 25 1.4 X/- - OSC-UA 2048x14UA200-1100 - 25 1.4 - - OSC-UA NIR NIR256-1.7 NIRA 900-1750 - 50 5.0 - 1000 - NIR256-2.2 NIRZ 1200-2200 - 50 10.0 - 1000 -NIR256-2.5 NIRY1000-2500-5015.0-1000-info@ • Spectrometers9S p e c t r o m e t e r s • info@For each spectrometer type, a grating selection table is shown in the Spectrometer Platforms section. Table 2 illustrates how to read the grating selection table. The spectral range to select in Table 2 depends on the starting wavelength of the grating Please select Spectral range band-width from the useable Wavelength range, for example: grating UE (200-315nm)*the spectral range depends on the starting wavelength of the grating; the higher the wave-length, the smaller the range.For example grating UE (510-580 nm)The order code is defined by 2 letters: the first is the Blaze (U= 250/300nm or UV for holo-graphic, B=400nm, V=500nm or VIS for holo-graphic, N=750nm, I=1000nm) and the second the nr of lines/mm (Z=150, A=300, B=600, C=1200, D=1800, E=2400, F=3600 lines/mm)Spectrometersinfo@ •Figure 2 Grating Efficiency Curves 300 Lines/mm Gratings600 Lines/mm Gratings1200 Lines/mm Gratings 1800 Lines/mm Gratings2400 Lines/mm Gratings3600 Lines/mm GratingsSpectrometers •info@Figure 3 Grating Dispersion Curves300 Lines/mm Gratings600 Lines/mm Gratings1200 Lines/mm Gratings1800 Lines/mm Gratings2400 Lines/mm Gratings3600 Lines/mm Gratingsinfo@ •SpectrometersThe optical resolution is defined as the minimum difference in wavelength that can be separated by the spectrometer. For separation of two spectral lines it is necessary to image them at least 2 array-pixels apart. Because the grating determines how far different wavelengths are separated (dispersed) at the detector array, it is an important variable for the resolution.The other important parameter is the width of the light beam entering the spectrometer. This is basically the instal-led fixed entrance slit in the spectrometer, or the fiber core diameter when no slit is installed.The slits can be installed with following dimensions: 10, 25 or 50 x 1000 µm high or 100, 200 or 500 µm x 2000 µm high. Its image on the detector array for a given wavelength will cover a number of pixels. For two spectral lines to be separated, it is now necessary that they be dispersed over at least this image size plus one pixel. When large core fibers are used the resoluti-on can be improved by a slit of smaller size than the fiber core. This effectively reduces the width of the entering light beam. The influence of the chosen grating and the effective width of the light beam (fiber core or entrance slit) are shown in the tables at the product information. In Table 3 the typical reso-lution can be found for the AvaSpec-2048. Please note that for the higher lines/mm gratings the pixel dispersion varies along the wavelength range and gets better towards the lon-ger wavelengths (see also Figure 3). The best resolution can always be found for the longest wavelengths. The resolution in this table is defined as F(ull) W(idth) H(alf) M(aximum), which is defined as the width in nm of the peak at 50% of the maximum intensity (see Figure 4).Graphs with information about the pixel dispersion can be found in the gratings section as well, so you can optimally determine the right grating and resolution for your specific application.In combination with a DCL-detector collection lens or thick fibers the actual FWHM value can be 10-20% higher than the value in the table. For best resolution small fibers and no DCLFigure 4 Full Width Half MaximumHow to select optimal Optical Resolution?Slit size (µm)Grating (lines/mm) 10 25 50 100 200 500 300 0.8 1.4 2.4 4.3 8.0 20.0600 0.4 0.7 1.2 2.1 4.1 10.01200 0.1-0.2* 0.2-0.3* 0.4-0.6* 0.7-1.0* 1.4-2.0* 3.3-4.8*1800 0.07-0.12* 0.12-0.21* 0.2-0.36* 0.4-0.7* 0.7-1.4* 1.7-3.3*2400 0.05-0.09* 0.08-0.15* 0.14-0.25* 0.3-0.5* 0.5-0.9* 1.2-2.2*36000.04-0.06*0.07-0.10*0.11-0.16*0.2-0.3*0.4-0.6*0.9-1.4**depends on the starting wavelength of the grating; the higher the wavelength, the bigger the dispersion and the better the resolutionTable 3 Resolution (FWHM in nm) for the AvaSpec-2048Installed Slit in SMA AdapterS p e c t r o m e t e r s •info@The AvaSpec spectrometers can be equipped with several types of detector arrays. Presently we offer silicon-based CCD, back-thinned CCD, CMOS and Photo Diode Arrays for the 200-1100 nm range. A complete overview is given in the next sec-tion “Sensitivity” in table 4. For the NIR range (1000-2500nm) InGaAs arrays are implemented.CCD Detectors (AvaSpec-2048/3648)The Charged Coupled Device (CCD) detector stores the charge, dissipated as photons strike the photoactive surface. At the end of a controlled time-interval (integration time), the remaining charge is transferred to a buffer and then this signal is being transferred to the AD converter. CCD detectors are naturally integrating and therefore have an enormous dynamic range, only limited by the dark (thermal) current and the speed of the AD converter. The 3648 pixel CCD has an integrated electronic shutter function, so an integration time of 10µsec can be achieved.+ Advantages for the CCD detector are many pixels (2048 or 3648), high sensitivity and high speed.- Main disadvantage is the lower S/N ratio.UV enhancementFor applications below 350 nm with the AvaSpec-2048/3648 a special DUV-detector coating is required. The uncoated CCD-response below 350 nm is very poor; the DUV lumo-gen coating enhances the detector response in the region 150-350nm. The DUV coating has a very fast decay time, typ. in ns range and is therefore useful for fast trigger LIBS applications.Back-thinned CCD Detectors (AvaSpec-2048x14)For applications requiring high quantum efficiency in the UV (200-350nm) and NIR (900-1160nm) range, combined with good S/N and a wide dynamic range, the new back-thinned CCD detector may be the right choice. The detector is an area detector of 2048x14 pixels, for which the vertical 14 pixels are binned (electronically added together) to have more sensiti-vity and a better S/N performance. + A dvantage of the back-thinned CCD detector is the good UV and NIR sensitivity, combined with good S/N and dynamic range- Disadvantage is the relative high costPhoto Diode Arrays (AvaSpec-128)A silicon photodiode array consists of a linear array of mul-tiple photo diode elements, for the AvaSpec-128 this is 128 pixels. Each pixel consists of a P/N junction with a positively doped P region and a negatively doped N region. When light enters the photodiode, electrons will become excited and output an electrical signal. Most photodiode arrays have anDetector Arraysintegrated signal processing circuit with readout/integration amplifier on the same chip.+ Advantages for the Photodiode detector are high NIR sensitivity and high speed.- Disadvantages are limited amount of pixels and no UV response.CMOS linear image sensors (AvaSpec-256/1024)These so called CMOS linear image sensors have a lower charge to voltage conversion efficiency than CCD array sensors and are therefore less light sensitive, but have a much better signal to noise ratio.The CMOS detectors have a higher conversion gain than NMOS detectors and also have a clamp circuit added to the internal readout circuit to suppress noise to a low level.+ Advantages for the CMOS detectors are good S/N ratio and good UV sensitivity.- Disadvantages are the low readout speed, low sensitivity, and relative high cost (1024 pixels).InGaAs linear image sensors (AvaSpec-NIR256)The InGaAs linear image sensors deliver high sensitivity in the NIR wavelength range. The detector consists of a charge ampli-fier array with CMOS transistors, a shift register and timing generator. 3 versions of detectors are available:• 256 pixel non-cooled InGaAs detector for the 900-1750nm useable range • 256 pixel 2-stage cooled Extended InGaAs detector for the 1000-2200nm range • 256 pixel 2-stage cooled Extended InGaAs detector for the1000-2500nm rangeDifferent Detector ArraysSensitivityThe sensitivity of a detector pixel at a certain wavelength is defined as the detector electrical output per unit of radia-tion energy (photons) incident to that pixel. With a given A/D converter this can be expressed as the number of counts per mJ of incident radiation.The relation between light energy entering the optical bench and the amount hitting a single detector pixel depends on the optical bench configuration. The efficiency curve of the grating used, the size of the input fiber or slit, the mirror performance and the use of a Detector Collection Lens are the main parameters. With a given set-up it is possible to do measurements over about 6-7 decades of irradiance levels. Some standard detector specifications can be found in Table 4 detector specifications. Optionally a cylindrical Detector Collection Lens (DCL) can be mounted directly on the detec-tor array. The quartz lens (DCL-UV for AvaSpec-2048/3648) will increase the system sensitivity by a factor of 3-5, depen-ding on the fiber diameter used.In Table 4 the overall sensitivity is given for the detector types currently used in the UV/VIS AvaSpec spectrometers as output in counts per ms integration time for a 16-bit AD converter. To compare the different detector arrays we have assumed an optical bench with 600 lines/mm grating and no DCL. The entrance of the bench is an 8 µm core diameter fiber, con-nected to a standard AvaLight-HAL halogen light source. This is equivalent to ca. 1 µWatt light energy input.In table 5 the specification is given for the NIR spectrometers, in figure 5 and figure 6 the spectral response curve for the dif-ferent detector types are depicted.info@ •SpectrometersTable 4 Detector specifications (based on a 16-bit AD converter)Detector TAOS 128 HAM256 HAM1024 SONY2048 TOSHIBA3648 HAM2048x14Type Photo diode array CMOS linear array CMOS linear array CCD linear array CCD linear array Back-thinnedCCD Array # Pixels, pitch 128, 63.5 µm 256, 25 µm 1024, 25 µm 2048, 14 µm 3648, 8 µm 2048x14, 14 µmpixel width x 55.5 x 63.5 25 x 500 25 x 500 14 x 56 8 x 200 14x14 (totalheight (µm)height 196 µm)pixel well depth 250,000 4,000,000 4,000,000 40,000 120,000 250,000(electrons)Sensitivity 100 22 22 240 160 200V/lx.sSensitivity 100 440 440 40 60 50Photons/count@600nmSensitivity 4000 120 120 20,000 14,000 16,000(AvaLight-HAL, (AvaSpec-128) (AvaSpec-256) (AvaSpec-1024) (AvaSpec-2048) (AvaSpec-3648) (Avaspec 2048x14)8 µm fiber)in counts/µW perms integration timePeak wavelength 750 nm 500 nm 500 nm 500 nm 550 nm 650 nmSignal/Noise 500:1 2000 :1 2000 :1 200 :1 350 :1 500:1Dark noise 60 28 60 35 35 50(counts RMS)Dynamic Range 1000 2500 2500 2000 2000 1300PRNU**± 4% ± 3% ±3% ± 5% ± 5% ± 3%Wavelength range 360-1100 200-1000 200-1000 200*-1100 200*-1100 200-1160(nm)Frequency 2 MHz 500 kHz 500 kHz 2 MHz 1 MHz 1.5 MHz* DUV coated** Photo Response Non-Uniformity = max difference between output of pixels when uniformly illuminated, divided by average signalS p e c t r o m e t e r s • info@Figure 5 Detector Spectral sensitivity curves Table 5 NIR Detector SpecificationsDetectorNIR256-1.7 NIR256-2.2NIR256-2.5TypeLinear InGaAs array Linear InGaAs array Linear InGaAs arraywith 2 stage TE cooling with 2 stage TE cooling # Pixels, pitch 256, 50 µm 256, 50 µm 256, 50 µm pixel width x 50 x 50050 x 500 50 x 500height (µm)Pixel well depth 16,000,000 1,500,000 1,500,000(electrons)Sensitivity 350250200(AvaLight-HAL, 8 µm fiber)in counts/µW per ms integration timePeak wavelength 1550 nm 2000 nm 2300 nmSignal/Noise 4000:1 1200 :1 1200 :1Dark noise 12 40 40 (counts RMS)Dynamic Range 5000 1600 1600PRNU** ± 5% ± 5% ± 5%Defective pixels 012 12(max)Wavelength range 900-1750 1000-2200 1000-2500 (nm)Frequency500 kHz500 kHz500 kHz** Photo Response Non-Uniformity = max difference between output of pixels when uniformly illuminated, divided by average signalFigure 6 NIR Detector Sensitivity CurvesSpectrometers Stray light is radiation of the wrong wavelength that activatesa signal at a detector element. Sources of stray light can be:• Ambient light• Scattering light from imperfect optical components orreflections of non-optical components• Order overlapEncasing the spectrometer in a light tight housing eliminatesambient stray light.When working at the detection limit of the spectrometersystem, the stray light level from the optical bench, gratingand focusing mirrors will determine the ultimate limit ofdetection. Most gratings used are holographic gratings,known for their low level of stray light. Stray light measure-ments are being carried out with a laser light, shining into theoptical bench and measuring light intensity at pixels far awayfrom the laser projected beam. Other methods use a halogenlight source and long pass- or band pass filters.Typical stray light performance is <0.05 % at 600 nm; <0.10% at 435 nm; <0.10 % at 250 nm.Second order effects, which can play an important role forgratings with low groove frequency and therefore a widewavelength range, are usually caused by the grating 2ndorder diffracted beam. The effects of these higher orders canoften be ignored, but sometimes need to be taken care of.The strategy is to limit the light to the region of the spectra,where order overlap is not possible. Second order effectscan be filtered out, using a permanently installed long-passoptical filter in the SMA entrance connector or an order sor-ting coating on a window in front of the detector. The ordersorting coatings on the window typically have one long passfilter (590nm) or 2 long pass filters (350 nm and 590 nm),depending on the type and range of the selected grating.In Table 6 a wide range of optical filters for installation in theoptical bench can be found. The use of following long-passfilters is recommended: OSF-475 for grating NB and NC, OSF-515/550 for grating NB and OSF-600 for grating IB.In addition to the order sorting coatings we implement partialDUV coatings on Sony 2048 and Toshiba 3648 detectors toavoid second order effects from UV response and to enhancesensitivity and decrease noise in the Visible range.This partial DUV coating is done automatically for the follo-wing grating types:• UA for 200-1100 nm, DUV400, only first 400 pixelscoated• UB for 200-700 nm, DUV800, only first 800 pixelscoatedStray Light and Second Order EffectsTable 6 Filters installed in the AvaSpec spectrometer seriesOSF-385Permanently installed 1 mm order sorting filter @ 371 nmOSF-475 Permanently installed 1 mm order sorting filter @ 466 nmOSF-515 Permanently installed 1 mm order sorting filter @ 506 nmOSF-550 Permanently installed 1 mm order sorting filter @ 541 nmOSF-600 Permanently installed 1 mm order sorting filter @ 591 nmOSC Order sorting coating with 590nm long pass filter for VA, BB (>350 nm) and VB gratingsin AvaSpec-1024/2048/3648/2048x14OSC-UA Order sorting coating with 350 and 590nm longpass filter for UA gratingsin AvaSpec-1024/2048/3648/2048x14OSC-UB Order sorting coating with 350 and 590nm longpass filter for UB or BB (<350 nm) gratingsin AvaSpec-1024/2048/3648/2048x14Order Sorting Window in holderinfo@ • Product name Electronics Optical bench Detector Housing AvaSpec-128 AS-161 with USB AvaBench-45, allgratings 360-1100 nm TAOS 128AvaSpec-128-USB2 AS-5216 with USB2AvaSpec-256 AS-161 with USB AvaBench-45, allgratings 200-1100 nm HAM 256AvaSpec-256-USB2 AS-5216 with USB2AvaSpec-1024 AS-161 with USB AvaBench-75, allgratings 200-1100 nm HAM 1024AvaSpec-1024-USB2 AS-5216 with USB2AvaSpec-2048 AS-161 with USB AvaBench-75, allgratings 200-1100 nm Sony 2048AvaSpec-2048-USB2 AS-5216 with USB2AvaSpec-3648-USB2 AS-5216 with USB2 AvaBench-75, Toshiba 3648all gratings 200-1100 nmAvaSpec-2048x14-USB2 AS-5216 with USB2 AvaBench-75, HAM 2048x14all gratings 200-1160 nmAvaSpec-NIR256-1.7 AS-5216 with USB2 AvaBench-50, HAM NIR256-1.7grating 900-1750 nmAvaSpec-NIR256-2.2 AS-5216 with USB2 AvaBench-50, HAM NIR256-2.2grating 1000-2200 nmAvaSpec-NIR256-2.5 AS-5216 with USB2 AvaBench-50, HAM NIR256-2.5grating 1000-2500 nmAvaSpec-xxx-2 AS-161 with USB, 2 channels AvaBench-45/75, all TAOS 128xxx = 102/256/1024/ gratings 200-1100 nm HAM 256/10242048 or Sony 2048AvaSpec Multichannel AS-161 with USB1 or AvaBench-45/75, All detectorsas Desktop AS-5216 with USB2 all gratings 200-1100 nmor Rackmount17S p e c t r o m e t e r s • info@。
红外光谱的英文书籍There are several English books on infrared spectroscopy that provide comprehensive and detailed information on the subject. In this article, we will explore some popular books in the field, discussing their content, formatting, and overall presentation. By the end, you will have a better understanding of the available options for studying infrared spectroscopy through English books.1. "Infrared and Raman Spectroscopy: Principles and Spectral Interpretation" by Peter LarkinPeter Larkin's book "Infrared and Raman Spectroscopy: Principles and Spectral Interpretation" is a widely recognized book in the field of vibrational spectroscopy. It covers both infrared and Raman spectroscopy, making it a valuable resource for researchers, students, and professionals.The book is structured logically, starting with the basics and gradually progressing to more advanced topics. It includes extensive explanations of spectroscopic principles, instrumentation, and data interpretation. The chapters are well-organized and utilize clear figures and diagrams to enhance understanding. The author also provides numerous real-world examples and case studies, aiding readers in the practical application of infrared spectroscopy.2. "Introduction to Infrared and Raman Spectroscopy" by N. B. Colthup, L. H. Daly, and S. E. Wiberley"Introduction to Infrared and Raman Spectroscopy" is a classic textbook authored by N. B. Colthup, L. H. Daly, and S. E. Wiberley. It serves as an excellent introduction to the principles of infrared and Raman spectroscopy.The book covers the theory and practice of infrared and Raman spectroscopy, as well as the necessary knowledge of quantum mechanics and group theory. The content is presented in a concise and understandable manner, supported by numerous examples and problems for self-assessment. The authors also provide an extensive range of spectra for reference, allowing readers to compare and identify various functional groups.3. "Infrared Spectroscopy: Fundamentals and Applications" by BarbaraH. StuartBarbara H. Stuart's "Infrared Spectroscopy: Fundamentals and Applications" offers a comprehensive overview of infrared spectroscopy, focusing on its practical applications in various scientific fields.The book begins with an introduction to the basic principles of infrared spectroscopy and instrumentations. It then delves into the applications of infrared spectroscopy in organic and inorganic chemistry, materials science, environmental analysis, and more. Each chapter includes detailed explanations, key concepts, and examples to assist readers in grasping the fundamentals and applying them to real-life scenarios.4. "Infrared Spectroscopy: Theory, Developments and Applications" edited by A. Gauglitz and T. Vo-DinhFor readers interested in more advanced topics, "Infrared Spectroscopy: Theory, Developments and Applications" edited by A. Gauglitz and T. Vo-Dinh is an excellent choice. This book consolidates the latest advancements in infrared spectroscopy, providing a comprehensive reference for researchers and experts in the field.The book covers topics such as Fourier transform infrared spectroscopy, near-infrared spectroscopy, and emerging techniques. It includes contributions from multiple authors, each specializing in different areas of infrared spectroscopy. This collective effort ensures a broad range of perspectives and expertise, making it an invaluable resource for those looking to expand their knowledge in the field.Conclusion:In conclusion, there are several English books available that cover various aspects of infrared spectroscopy. From introductory texts to advanced reference materials, these books provide a wealth of information for individuals interested in the subject. Depending on the specific focus and level of expertise required, researchers, students, and professionals will find one or more of these books suitable for their needs.。
a r X i v :a s t r o -p h /0306167v 1 9 J u n 2003Astronomy &Astrophysics manuscript no.(will be inserted by hand later)Spectroscopic and photometric studies of low-metallicitystar-forming dwarf galaxies.III.SBS 1415+437N.G.Guseva 1,P.Papaderos 2,Y.I.Izotov 1,R.F.Green 3,K.J.Fricke 2,T.X.Thuan 4,and K.G.Noeske 21Main Astronomical Observatory,Ukrainian National Academy of Sciences,Zabolotnoho 27,Kyiv 03680,Ukraine 2Universit¨a ts–Sternwarte,Geismarlandstraße 11,D–37083G¨o ttingen,Germany 3National Optical Astronomy Observatory,Tucson,AZ 85726,USA4Astronomy Department,University of Virginia,Charlottesville,VA 22903,USAReceived;AcceptedAbstract.We present a detailed optical spectroscopic and B ,V ,I ,H αphotometric study of the metal-deficient cometary blue compact dwarf (BCD)galaxy SBS 1415+437.We derive an oxygen abundance 12+log(O/H)=7.61±0.01and 7.62±0.03(Z =Z ⊙/20)⋆in the two brightest H ii regions,among the lowest in BCDs.The helium mass fractions in these regions are Y =0.246±0.003and 0.243±0.010.Four techniques based on the equivalent widths of the hydrogen emission and absorption lines,the spectral energy distribution and the colours of the galaxy are used to put constraints on the age of the stellar population in the low-surface-brightness (LSB)component of the galaxy,assuming two limiting cases of star formation (SF),the case of an instantaneous burst and that of a continuous SF with a constant or a variable star formation rate (SFR).The spectroscopic and photometric data for different regions of the LSB component are well reproduced by a young stellar population with an age t ≤250Myr,assuming a small extinction in the range A V =0–0.6mag.Assuming no extinction,we find that the upper limit for the mass of the old stellar population,formed between 2.5Gyr and 10Gyr,is not greater than ∼(1/20–1)of that of the stellar population formed during the last ∼250Myr.Depending on the region considered,this also implies that the SFR in the most recent SF period must be 20to 1000times greater than the SFR at ages >∼2.5Gyr.We compare the photometric and spectroscopic properties of SBS 1415+437with those of a sample of 26low-metallicity dwarf irregular and BCD galaxies.We show that there is a clear trend for the stellar LSB component of lower-metallicity galaxies to be bluer.This trend cannot be explained only by metallicity effects.There must be also a change in the age of the stellar populations.The most metal-deficient galaxies have also smaller luminosity-weighted ages.Key words.galaxies:abundances —galaxies:dwarf —galaxies:evolution —galaxies:compact —galaxies:starburst —galaxies:stellar content —galaxies:individual (SBS 1415+437)1.IntroductionSince its discovery as a metal-deficient blue compact dwarf (BCD)galaxy (Thuan,Izotov &Lipovetsky 1995),SBS 1415+437(≡CG 389)has been considered as a probable nearby young dwarf galaxy.Situated at a distance D =11.4Mpc it was classified by Thuan,Izotov &Foltz (1999)as a cometary BCD with a very bright supergiant H ii region at the SW tip of the galaxy.From 4m Kitt Peak National Observatory (KPNO)telescope spectra,Thuan et al.(1995)first derived an oxygen abundance of 12+log(O/H)=7.51±0.01in SBS 1415+437placing the galaxy among the most metal-deficient BCDs ter,Izotov &Thuan (1998,1999)derived from the same spectrum 12+log(O/H)=2N.G.Guseva et al.spectral energy distributions(SED)in the optical range,they concluded that SBS1415+437is a truly young galaxythat did not start to form stars until∼100Myr ago.However,the V and I images used by Thuan et al.(1999)were not deep enough for the detection of old red giantbranch(RGB)stars in the CMD.Furthermore,they con-sidered an instantaneous burst model which gives only alower limit to the age of the stellar population in SBS1415+437.In this paper we combine new spectroscopic and photo-metric data with previous observations to derive elementalabundances and to better constrain the age of the stellarpopulation in SBS1415+437.For the latter task we usefour different techniques of age determination and con-sider different star formation(SF)histories.The paperis organized as follows.In Sect.2we describe the obser-vations and data reduction.The photometric propertiesof SBS1415+437are described in Sect.3.We derive inSect.4the chemical abundances in the two brightest H iiregions.In Sect.5we discuss the properties of the stel-lar populations in SBS1415+437and compare them withthose in other low-metallicity dwarf galaxies.Finally,Sect.6summarises the main conclusions of this study.2.Observations and data reduction2.1.PhotometryNarrow-band images of SBS1415+437in the Hαline atλ6563˚A through a passband with a full width at half max-imum(FWHM)of74˚A,and in the adjacent continuum atλ6477˚A through a passband with FWHM=72˚A wereobtained with the Kitt Peak12.1m telescope on April22,1999during a photometric night.The telescope wasequipped with a Tektronix1024×1024CCD detectoroperating at a gain of3e−ADU−1,giving an instrumen-tal scale of0.′′305pixel−1andfield of view of5′.The totalexposures of50min in the Hαline and40min in the adja-cent continuum bluewards of Hαwere split up into5and4subexposures,slightly offset with respect to each other forremoval of cosmic particle hits and bad pixels.The pointspread function has a FWHM of2.′′2.Bias andflat–fieldframes were obtained during the same night.The standardstars Feige34and HZ44were observed in bothfilters dur-ing the same night at several airmasses for absolutefluxcalibration.Another broad-band B image(15min)of SBS1415+437was obtained on March9,1997under pho-tometric conditions,with the CAFOS focal reducer at-tached to the 2.2m telescope of the German-SpanishAstronomical Center,Calar Alto2,Spain.CAFOS was3IRAF is the Image Reduction and Analysis Facility dis-tributed by the National Optical Astronomy Observatory,which is operated by the AURA under cooperative agreementwith the NSF.4Munich Image Data Analysis System,provided by theEuropean Southern Observatory(ESO).Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies.III.SBS 1415+4373Fig.2.Continuum-subtracted H αimage of SBS 1415+437with superposed H αcontinuum isophotes.Regions with nebular emission are labeled e 1,e 2and e 4.The faint region e 3with H βand H αemission lines in its spectrum is not seen in the H αimage.CCD detector.The 2′′×300′′slit was centered on the brightest H ii region e 1(slit 2in Fig.1)with position angle P.A.=48◦so as to include the second brightest H ii region e 2to the SW of region e 1.We used the KPC-10A grating in first order and a GG 375order separation filter.The spatial scale along the slit was 0.′′69pixel −1and the spec-tral resolution ∼7˚A (FWHM).The spectra were obtained at an airmass 1.27.The total exposure time of 60minutes was broken up into 3subexposures.No correction for at-mospheric refraction was made because of the small air-mass during the observations.Two Kitt Peak spectropho-tometric standard stars were observed for flux calibration.For wavelength calibration,He-Ne-Ar comparison spectra were obtained after each exposure.The data reduction was performed with the IRAF software package.This includes bias–subtraction,flat–field correction,cosmic-ray removal,wavelength calibra-tion,night sky background subtraction,correction for at-mospheric extinction and absolute flux calibration of the two–dimensional spectrum.For abundance determination,one-dimensional spec-tra of regions e 1and e 2were extracted within apertures of 2′′×4.′′6and 2′′×4.′′0,respectively.In addition,we extracted spectra of the low-surface-brightness (LSB)re-Fig.3.(a )Surface brightness profiles (SBPs)of SBS 1415+437in V and I (filled and open circles,respectively),derived from HST /WFPC2data.A linear fit to the VSBP in the radius interval 4′′≤R ∗<∼13′′is shown by the upper solid-grey line.Both SBPs reveal a significant slopechange for R ∗>∼13′′.Filled squares show the ground-based B SBP,shifted vertically by 0.5mag.In addition to theexponential intensity slope at radii 4′′≤R ∗<∼13′′,thisprofile reveals for R ∗>∼16′′an outer exponential regime with an α∼0.27kpc (lower solid-grey line).The residu-als after subtraction of the outer exponential distribution from the B SBP are shown by crosses.(b )(V −I )colour profile of SBS 1415+437,computed from subtraction of the SBPs in (a ).A strong colour gradient γ+=2.5mag kpc −1is derived for radii smaller than the effective radius r eff(inner fit).The (V −I )colour of 0.4–0.5mag for larger radii is nearly constant with a γ+<0.2mag kpc −parison of the B and V SBPs implies a B −V color ∼0.2mag in the radius range 13′′≤R ∗≤16′′.gions a 3and a 4with strong hydrogen Balmer absorption lines,and of region e 3with H αand H βin emission (Fig.1).We also used the two-dimensional MMT spectrum ob-tained by Thuan et al.(1999)with the slit oriented at P.A.=22◦(slit 1in Fig.1).We extracted one-dimensional spectra of the LSB regions a 1and a 2within apertures of 1.′′5×3.′′4and 1.′′5×13.′′2,respectively (Fig.1).These spectra show strong hydrogen Balmer absorption lines.4N.G.Guseva etal.Fig.4.The KPNO4m telescope spectra of the brightest H ii regions e1and e2with the identified emission lines.The lower spectra in(a)and(b)are the observed spectra downscaled by factors of50and30,respectively.The selected LSB regions are listed in Tables3and4with their positions and spatial extents.Origins are setat the center of the brightest region e1(Fig.1,2).Thespectra of the LSB regions are used to study the stellarpopulations and to constrain the age of the oldest starswhich contribute to the light of these regions.3.Photometric propertiesIt is seen from the continuum-subtracted Hαimages(Fig.2)that star-forming activity in SBS1415+437is primarilyoccurring in regions e1and e2,with some additional faintHαemission present in region e4.However,the availablenarrow-band data are not deep enough for tracing faintHαemission in other regions of the LSB component,suchas in regions a1,a3and e3where Hαand Hβhave beendetected spectroscopically(Table3).The latter fact sug-gests that some low-level SF may be present at variouslocations within the LSB component.The photometric properties of the stellar LSB compo-nent of SBS1415+437werefirst investigated by Thuanet al.(1999)using HST/WFPC2V and I images.Theseauthorsfit the surface brightness profiles(SBPs)of SBS1415+437with an exponential distribution in the radiusrange4′′≤R∗<∼13′′with a scale lengthα=5.′′4(≈0.3kpc).However,their study was limited by the fact thatthe HST images do not include the outermost NE part ofthe LSB component.Furthermore,the SBPs in Thuan etSpectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies.III.SBS1415+4375 al.(1999)reach only a surface brightness levelµ∼24.5mag arcsec−2.It is known,however,that the star-formingcomponent may contribute to the optical BCD emissionto fainter surface brightness levels(see e.g.Papaderos etal.2002and references therein).A comparatively youngstellar population has been observed in the inner part ofthe LSB component of other cometary BCDs,several hun-dred pc away from the brightest H ii region(Noeske et al.2000;Guseva et al.2001;Fricke et al.2001).Thereforedeeper images are needed to study the outer parts of theLSB component in SBS1415+437.Note that the SBPs by Thuan et al.(1999)show inthe outermost part(13′′<∼R∗<∼16′′,or24<∼µV<∼24.5)a steeper exponential intensity decrease than the one ob-served at intermediate intensity levels.This slope change,not discussed in Thuan et al.(1999),is found indepen-dently by us in the HST/WFPC2SBPs derived with themethod iv of Papaderos et al.(2002)and ellipsefittingto the visible part of the LSB component.While the lat-ter method extends surface photometry out to larger radii(R∗∼22′′),it is subject to large uncertainties becausethe NE part of the LSB component withµ>∼24.5V magarcsec−2(R∗>∼16′′)lies outside the HST/WFPC2field of view.Additionally,the outermost LSB isophotes show considerable deviations from ellipticity.To study the surface brightness distribution at large radii we use the ground-based Calar Alto B image.Despite the poor spatial resolution this image allows us to study the entire LSB component out to its Holmberg radius.The change in the exponential slope for13′′<∼R∗<∼16′′is con-firmed from the ground-based B SBP.At large radii,how-ever,this SBP reveals aflatter,outer exponential regime with a scale lengthαfairly comparable to that previously obtained at intermediate intensity levels from HST data (upper thick-grey line in Fig.3a).Fromfitting an expo-nential model to the B SBP for R∗≥16′′(lower thick-grey line in Fig.3a)we obtain a central surface brightness µE,0=21.37B mag arcsec−2and a scale lengthα=0.27 kpc.Note,however,that the inner exponential profile stud-ied by Thuan et al.(1999)is>∼0.3mag brighter than the outer one,which suggests that more than1/4of the emis-sion associated with this profile originates from the part of the LSB component between regions e1and a2.The present data provide no compelling evidence for a large age difference between the stellar population which dominates within the inner exponential regime discussed in Thuan et al.(1999)and that responsible for the outer-most LSB emission(i.e.for R∗>16′′).The(V−I)profile reveals a strongcolour gradient(γ+=2.5mag kpc−1;inner solid-grey line in Fig.3b)within the inner5′′,or roughly the V band effective radius(r eff=5.′′6)of SBS1415+437. At larger radii,however,linearfits to the(V−I)pro-file yield,depending on whether they are error-weighted or not,a gradient not exceeding0.1and0.2mag kpc−1, parable values are also found from sub-traction of the exponentialfits in V and I(Fig.3a)in the radius range r eff≤R∗≤13′′(Fig.3b,solid-grey line at intermediate radii).4.Chemical abundancesIn this section we derive the elemental abundances of re-gions e1and e2using the Kitt Peak4m telescope observa-tions.Their spectra with strong emission lines are shown in Fig.4.The observed(F(λ))and extinction-corrected(I(λ)) emission linefluxes relative to the Hβemission linefluxes, their equivalent widths EW,the extinction coefficients C(Hβ),the observedfluxes of the Hβemission line,and the equivalent widths of the hydrogen absorption lines for regions e1and e2are shown in Table1.Despite the dif-ferences in aperture(2′′×4.′′6for the Kitt Peak4m data, 1.′′5×5′′and1.′′5×0.′′6for the MMT data from Thuan et al.1999),the relativefluxes of the emission lines for region e1are in agreement within the errors with those derived by Thuan et al.(1999).parison of the elemental abundance ratios,ob-tained for the brightest H ii regions e1(large squares)and e2(small squares)with data for other BCDs(open circles).The physical conditions and heavy element abun-dances in regions e1and e2were derived following Izotov et al.(1994,1997a)and Thuan et al.(1995).The electron temperatures T e(O iii),T e(S iii),T e(O ii)for the high-, intermediate-and low-ionization regions respectively,the6N.G.Guseva et al.Table1.Observed(F(λ))and extinction-corrected(I(λ))fluxes and equivalent widths(EW)of emission lines in the H ii regions e1and e2.region e1region e2λ0(˚A)Ion F(λ)/F(Hβ)I(λ)/I(Hβ)EW(˚A)F(λ)/F(Hβ)I(λ)/I(Hβ)EW(˚A)a in units10−14erg s−1cm−2.electron number densities N e(S ii),ionization correction factors(ICF),and ionic and total heavy element abun-dances are shown in Table2for both regions.The oxygen abundance12+log(O/H)=7.61±0.01(Z⊙/20)and heavy element abundance ratios for region e1are in good agreement with those derived by Thuan et al.(1999).The oxygen abundance12+log(O/H)=7.62±0.03and heavy element abundance ratios in region e2are consistent with those for region e1within the errors.In Figure5we compare the heavy element abundance ratios in the two brightest regions of SBS1415+437with data for a sample of low-metallicity BCDs.The Ne/O,S/O,Ar/O and[O/Fe]abundance ratios for the compar-ison sample are taken from Izotov&Thuan(1999),while the Cl/O abundance ratios are collected from Izotov& Thuan(1998)and Izotov et al.(1997a).The heavy element abundance ratios for regions e1(large squares)and e2 (small squares)are in good agreement with those for other BCDs.Note,that the Cl/O ratio does not show any sig-nificant increase with increasing oxygen abundance.This conclusion is strengthened by the observations of Esteban et al.(1998,1999a,1999b)who derived log(Cl/O)in the range from–3.28to–3.47for high-metallicity H ii regions in Orion,M17and M8with12+log(O/H)=8.60,8.50Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies.III.SBS 1415+4377Fig.6.The blue part of the MMT spectrum of region a 1with labeled emission and absorption lines.and 8.60,respectively.For comparison,log(Cl/O)=–3.37is derived for the Sun (Anders &Grevesse 1989).The high brightness of regions e 1and e 2allows for a reliable determination of the 4He abundance.Nine He i emission lines are detected in the spectrum of region e 1(Table 1).Two of them,He i λ3889and λ4713,are blended with other lines.Six He i lines are detected in region e 2.The five brightest He i λ3889,λ4471,λ5876,λ6678,λ7065emission lines are used to correct their fluxes for collisional and fluorescent enhancement.This is done by minimizing the deviations of the corrected He i line flux ratios from the recombination ratios,through vary-ing the electron number density in the He +zone and the optical depth in the He i λ3889emission line.The flux of this line was preliminarily corrected for the contribution of the H i λ3889emission line,according to prescriptions of Izotov et al.(1994,1997a).Helium abundances He +/H +,derived from the corrected He i λ4471,λ5876,λ6678line fluxes and their weighted mean are listed in Table 2.The abundance He +2/H +is added to He +/H +for region e 1,as He ii λ4686is present in its spectrum.Note the lower He abundance derived from the He i λ4471flux which is most likely due to significant underlying stellar He i λ4471ab-sorption.The effect of underlying absorption for the other He i emission lines used in the He abundance determina-tion is much smaller,as they have much larger equivalent widths compared to the He i λ4471emission line (Table 1).The mean 4He mass fractions Y =0.246±0.003and 0.243±0.010in regions e 1and e 2(Table 2)are consistent with the values derived for SBS 1415+437by Izotov &Thuan (1998)and Thuan et al.(1999).They are also con-sistent with the primordial 4He mass fraction Y p =0.244±0.002,derived by extrapolating the Y vs O/H linear regression to O/H =0(Izotov &Thuan 1998),or to Y p =0.245±0.002derived from spectroscopic observations of the two most metal-deficient BCDs known,I Zw 18and SBS 0335–052(Izotov et al.1999).Table 2.Element abundances in regions e 1and e 2.Valueregion e 1region e 2a ICF is the ionization correction factor.b[O/Fe]≡log (O/Fe)–log (O/Fe)⊙.5.Age of the stellar population in the LSB regionsWe consider next the spectroscopic and photometric prop-erties of the LSB regions labeled a 1,a 2(slit position 1in Fig.1)and a 3,e 3,a 4(slit position 2),to constrain the age of the stellar populations contributing to the light in those regions.H αand H βemission lines are present in re-gions a 1,a 3and e 3while H γand H δabsorption lines are8N.G.Guseva et al.detected in the spectra of all regions except for region e3. This allows us to derive the age of the stellar population using four methods,based on:(1)the time evolution of equivalent widths(EW)of hydrogen emission lines,(2) the time evolution of EW s of hydrogen absorption lines, (3)the comparison of the observed and theoretical spec-tral energy distributions,and(4)the broad-band colours. The requirement of consistency of the ages determined from the reddening-insensitive methods1and2and from the reddening-sensitive methods3and4allows to simul-taneously derive the extinction coefficient and constrain the SF history(Guseva et al.2001,2003a,2003b).We measured thefluxes and equivalent widths of the Hαand Hβemission lines and the Hγand Hδabsorption lines in the spectra of the LSB regions,and list them in Tables3and4.Because the Hβemission line is narrower than the absorption line in these regions and does notfill the absorption component,itsflux was measured using the continuum level at the bottom of the absorption line. This level was chosen by visually interpolating from the absorption line wings to the center of the line.The extinction coefficient C(Hβ)in those regions is derived from the Hα/Hβflux ratio.We adopt the theo-retical recombination Hα/Hβflux ratio of2.8,which is typical for hot low-metallicity H ii regions.No correction for the absorption line equivalent widths has been made. The extinction coefficients C(Hβ)are shown in Table3.Hydrogen absorption lines are seen in the spectra of all regions labeled in Fig.1except for the brightest H ii regions e1and e2and the LSB region e3.The blue part of the spectrum of region a1with hydrogen absorption and emission lines is shown in Fig.6.Table4lists the equiva-lent widths with their errors of the Hγand Hδabsorption lines measured in the wavelength intervals or“windows”of Bica&Alloin(1986).The errors include the errors in thefitting of line profiles with Gaussians and the noise dis-persion in the continuum.A careful placement of the con-tinuum level is very important for deriving accurate EW s. For this purpose,we choose points in the spectrum free of nebular and stellar lines,which were thenfitted by cu-bic splines.The uncertainties were estimated from several different measurements of the equivalent widths of hydro-gen absorption lines with independent continuumfittings. They are of the same order as the errors in Table4.5.1.Age calibrationThe calibration of the age of stellar populations using the equivalent widths of the Hαand Hβnebular emis-sion lines,those of the Hγand Hδstellar absorption lines and the spectral energy distributions is discussed in detail in Guseva et al.(2001,2003a,2003b).Here we only briefly describe these calibrations.5.1.1.Balmer emission linesThe temporal evolution of the Hαand Hβemission line equivalent widths depends on the star formation history. We consider here the two limiting cases of instantaneous burst and continuous star formation models.The equiv-alent widths for the instantaneous burst model with a heavy element mass fraction Z⊙/20are calculated using the galactic evolution code PEGASE.2(Fioc&Rocca-Volmerange1997).The dependence of the Hαemission line equivalent width on time is shown in Fig.6a of Guseva et al.(2003b)by the thick solid line.These models are ap-propriate for regions e1and e2with strong emission lines. The equivalent widths of Balmer emission lines in region e1(EW(Hα)=998˚A and EW(Hβ)=166˚A)and region e2(EW(Hα)=872˚A and EW(Hβ)=134˚A)correspond to an instantaneous burst age of4Myr.However,for the LSB regions,models with continu-ous star formation are more appropriate.For these mod-els we adopt a constant star formation rate(SFR)within the time interval from t i when star formation starts to t f when it stops.Time is zero now and increases to the past.The equivalent widths of hydrogen emission lines and SEDs for a set of instantaneous burst models(Fioc& Rocca-Volmerange1997)are used to calculate the tempo-ral evolution of EW s for continuous SF with a constant SFR.The temporal dependence of the equivalent widths of the Hαemission line is shown in Fig.6a of Guseva et al.(2003b)for different t i and t f.5.1.2.Stellar Balmer absorption linesAnother way to derive the age of a stellar population is to use the relation between the Hδand Hγabsorption line equivalent widths and age,derived by Gonz´a lez Delgado, Leitherer&Heckman(1999).Their instantaneous burst models predict a steady increase of the equivalent widths with age from1Myr to1Gyr.However,they did not ex-tend the calculations for ages>∼1Gyr when the equivalent widths of the absorption lines decrease with age(Bica& Alloin1986).Hence,each value of the hydrogen absorp-tion line equivalent width corresponds to two values of the age,<∼1Gyr and>∼1Gyr.This ambiguity can be resolved with the use of other age constraints discussed in this paper.Furthermore,the models by Gonz´a lez Delgado et al. (1999)probably overestimate the equivalent widths of the absorption lines at ages∼1Gyr(Guseva et al.2003b). Therefore,in the age range from1Myr to16.5Gyr in-stead of the calibration by Gonz´a lez Delgado et al.(1999) we use an empirical calibration of the hydrogen absorption line equivalent widths versus age by Bica&Alloin(1986). This calibration is based on the integrated spectra of63 open and globular stellar clusters with known ages,metal-licities and reddenings which can be used as templates for stellar populations formed in an instantaneous burst.For consistency we use the same wavelength intervals or“win-Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies.III.SBS1415+4379 Table3.Fluxes,equivalent widths of the Hαand Hβemission lines and the extinction coefficients C(Hβ)in the LSB regions.Telescope Region Distance a Aperture b F(Hα)c F(Hβ)c EW(Hα)d EW(Hβ)d C(Hβ)4m f a312.6 2.0×7.6 4.88±0.39 1.88±0.2932.81±2.327.72±1.010.0±0.04 e318.4 2.0×2.8 3.69±0.17 1.19±0.14109.80±1.4116.57±0.690.04±0.06a422.6 2.0×2.8...............MMT d a110.7 1.5×3.4–5.53±0.22–4.92±0.23a229.5 1.5×13.2–8.89±0.53–6.07±0.41a distance in arcsec from the brightest H ii region e1.b aperture size x×y,where x is the slit width and y the size along the slit in arcsec.c in˚A.d slit orientation with position angle P.A.=22◦.e slit orientation with position angle P.A.=48◦.dows”for Hγand Hδflux measurements as Bica&Alloin (1986)(λ4318–4364˚A andλ4082–4124˚A,respectively).The behaviour of the empirical Hδabsorption line equivalent width with the age for an instantaneous burst (Bica&Alloin1986)is shown in Fig.6b of Guseva et al. (2003b)by the thick solid line.The temporal evolution of the Hγand Hδabsorption line equivalent widths in the case of continuous SF is calculated similarly to that of the Hαand Hβemission line equivalent widths described in the section5.1.1.More specifically,we use the empirical equivalent widths of hy-drogen absorption lines(Bica&Alloin1986)and SEDs for instantaneous bursts(Fioc&Rocca-Volmerange1997)to calculate the temporal evolution of EW s in the case of continuous SF with constant SFR.The results are shown in Fig.6b of Guseva et al.(2003b)for SF with different t i and t f.5.1.3.Spectral energy distributionThe shape of the spectrum reflects the properties of the stellar population.However,it is also dependent on the reddening.A precise determination of the extinction can be done only for the two brightest H ii regions e1and e2which possess many strong hydrogen emission lines (Table1).We derived an extinction coefficient C(Hβ)=0 in these regions.In the LSB regions a1,a3and e3,only Hαand Hβemission lines are present.The extinction coeffi-cients obtained from the Hα/Hβflux ratio in these regions are small(Table3).However,they are more uncertain as compared to the ones in regions e1and e2because of the weakness of the emission lines and significant contribution of the stellar absorption lines.Hαand Hβemission lines are not detected in the other LSB regions.Therefore,the observed SED cannot directly give information on the age, but should be used together with the methods discussed in Sect.5.1.1and5.1.2for simultaneous determination of the age and interstellar extinction.We used the galactic evolution code PEGASE.2(Fioc &Rocca-Volmerange1997)to produce a grid of theoreti-cal SEDs for an instantaneous burst of star formation with ages ranging between0and10Gyr,and a heavy element mass fraction of Z=Z⊙/20.The SEDs for continuous SF in the time interval between t i ago and t f ago are derived by integration of instantaneous burst SEDs.5.2.Ages of the stellar populations in the LSB regions In this section we derive self-consistently the ages of the stellar populations in the LSB regions using:1)the equiv-alent widths of emission lines,2)the equivalent widths of absorption lines,3)the SEDs and4)the colours.For this we adopt a continuous SF scenario with constant or variable SFR.In the latter case we consider a sim-plified scenario with two time intervals of SF,which we call young and old,with different SFRs.To quantify。