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Absorption Features (absorption + feature)
Kinds of Absorption Features Selected AbstractsSpectral reflectance-compositional properties of spinels and chromites: Implications for planetary remote sensing and geothermometryMETEORITICS & PLANETARY SCIENCE, Issue 4 2004Edward A. Cloutis These two groups of minerals are spectrally distinct, which relates largely to differences in the types of major cations present. Both exhibit a number of absorption features in the 0.3,26 ,m region that show systematic variations with composition and can be used to quantify or constrain certain compositional parameters, such as cation abundances, and site occupancies. For spinels, the best correlations exist between Fe2+ content and wavelength positions of the 0.46, 0.93, 2.8, Restrahelen, 12.3, 16.2, and 17.5 ,m absorption features, Al and Fe3+ content with the wavelength position of the 0.93 ,m absorption feature, and Cr content from the depth of the absorption band near 0.55 ,m. For chromites, the best correlations exist between Cr content and wavelength positions of the 0.49, 0.59, 2, 17.5, and 23 ,m absorption features, Fe2+ and Mg contents with the wavelength position of the 1.3 ,m absorption feature, and Al content with the wavelength position of the 2 ,m absorption feature. At shorter wavelengths, spinels and chromites are most readily distinguished by the wavelength position of the absorption band in the 2 ,m region (<2.1 ,m for spinels, >2.1 ,m for chromite), while at longer wavelengths, spectral differences are more pronounced. The importance of being able to derive compositional information for spinels and chromites from spectral analysis stems from the relationship between composition and petrogenetic conditions (pressure, temperature, oxygen fugacity) and the widespread presence of spinels and chromites in the inner solar system. When coupled with the ability to derive compositional information for mafic silicates from spectral analysis, this opens up the possibility of deriving petrogenetic information for remote spinel- and chromite-bearing targets from analysis of their reflectance spectra. [source] Observations of 433 Eros from 1.25 to 3.35 micronsMETEORITICS & PLANETARY SCIENCE, Issue 12 2001A. S. Rivkin As expected, Eros shows no evidence of an absorption feature >5% in the 3 ,m region, and is interpreted to have an anhydrous surface within observational uncertainties. Our observations in the JHK region agree with previous work by Chapman and Morrison (1976) and Murchie and Pieters (1996), but differ from the near-infrared spectrometer spectra reported by Clark et al. (2001). Our calculations indicate that thermal flux from Eros is not responsible for this mismatch. [source] Evolution of the 3.3-,m emission feature in the Red RectangleMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2003In-Ok Song ABSTRACT Medium-resolution infrared spectroscopic observations of the biconical Red Rectangle nebula in the region of the 3.3-,m unidentified infrared (UIR) emission band are reported. The data were recorded at UKIRT using CGS4 and have allowed the peak wavelength, width, profile and intensity of the 3.3-,m feature to be investigated as a function of offset from the central star HD 44179. Analysis of the profile of the feature along the north-western bicone interface shows an evolution from Type 2 to Type 1 in the classification of Tokunaga et al. The 3.3-,m band recorded on-star shows a close fit to a Lorentzian profile, possibly suggesting a single class of carriers. Subtraction of the Lorentzian fit to the on-star spectrum from the spectrum at each offset reveals a new ,3.28'-,m emission feature that grows in intensity relative to the main 3.3-,m band as a function of distance from the central star. The 3.28-,m emission band at large offset appears to correspond well in wavelength and FWHM with an absorption feature seen towards the Galactic Centre. [source] On the anomalous silicate absorption feature of the prototypical Seyfert 2 galaxy NGC 1068MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010M. Köhler ABSTRACT The first detection of the silicate absorption feature in Active Galactic Nuclei (AGNs) was made at 9.7 ,m for the prototypical Seyfert 2 galaxy NGC 1068 35 yr ago, indicating the presence of a large column of silicate dust in the line of sight to the nucleus. It is now well recognized that type 2 AGNs exhibit prominent silicate absorption bands, while the silicate bands of type 1 AGNs appear in emission. More recently, using the Mid-Infrared Interferometric Instrument on the Very Large Telescope Interferometer, Jaffe et al. for the first time spatially resolved the parsec-sized dust torus around NGC 1068 and found that the 10 ,m silicate absorption feature of the innermost hot component exhibits an anomalous profile differing from that of the interstellar medium and that of common olivine-type silicate dust. While they ascribed the anomalous absorption profile to gehlenite (Ca2Al2SiO7, a calcium aluminium silicate species), we propose a physical dust model and argue that, although the presence of gehlenite is not ruled out, the anomalous absorption feature mainly arises from silicon carbide. [source] Spectroscopy of Hydrocarbon Grains toward the Galactic Center and Quintuplet ClusterASTRONOMISCHE NACHRICHTEN, Issue S1 2003J.E. Chiar Abstract Our view of the Galactic center (GC) is affected by extinction from both diffuse interstellar medium (ISM) dust and dense molecular clouds along the line of sight. The enormous visual extinction present toward the center of our Galaxy (,31 magnitudes) necessitates a study of the interstellar dust properties as well as an investigation into the distribution of the different dust components. We have built upon the historic spectroscopy of Willner et al. (1979), Butchart et al. (1986), and McFadzean et al. (1989) in order to investigate the distribution of these dust components across the GC field. Specifically, we employ spectroscopy in the 3 ,m region to investigate absorption features at 3.0 ,m and 3.4 ,m in lines of sight toward the GC central cluster and the Quintuplet cluster to the northeast. The 3.4 ,m feature is one of the primary spectral signatures of the organic component of interstellar dust and is, to date, only observed in the cold diffuse interstellar medium. The 3.0 ,m ice feature is carried by dense molecular cloud material, and can therefore be used to loosely trace the distribution of such material across the GC field. By obtaining spectra for multiple sightlines we have been able to deconvolve the diffuse ISM and dense molecular cloud components. Our study shows that differences exist in the spectra of relatively nearby lines of sight in the Galactic center central cluster. The depth of the 3.0 ,m water-ice feature varies by a factor of almost 5 across a 2 parsec (in projection) region, perhaps re.ecting the clumpy nature of the dense clouds. In addition, we found that the 3.4 ,m hydrocarbon feature varies in depth across the areas studied toward the central cluster, whereas the depth is relatively constant toward the Quintuplet cluster. This is likely a reflection of the distribution of extinction from the foreground diffuse ISM. Our ground-based and space-based spectroscopy reveals differences in absorption features in the 3 and 6 ,m regions between sightlines toward the GC central cluster and those toward the Quintuplet cluster. While the 3 ,m spectra of both regions show a broad absorption feature blueward of the 3.4 ,m absorption, only the Quintuplet spectra show a distinct absorption feature at 3.28 ,m. This feature is indicative of the presence of polycyclic aromatic hydrocarbons (PAHs) along the line of sight. The Quintuplet-proper sources have 6 ,m spectra that are markedly different than that of GC IRS 7 in the central cluster, and instead strongly resemble the spectra seen toward dusty late-type carbon-class (WC)Wolf-Rayet stars. This is the first hint of some spectroscopic similarity between the Quintuplet sources and dusty WC stars. [source] Mid-Infrared Imaging and Spectroscopic Observations of the Galactic Center with Subaru/COMICSASTRONOMISCHE NACHRICHTEN, Issue S1 2003Y. Okada Abstract We report the results of mid-infrared (7.8,m,13.2 ,m) high-spatial resolution imaging and spectroscopic observations of the Galactic center region with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope. The images clearly show bright infrared sources and small structures in the diffuse emission. The spectra of all the observed positions show the 9.7 ,m silicate absorption feature. After corrected for the empirically-derived extinction, the intrinsic spectra of the infrared sources show either strong silicate emission or absorption, while the intrinsic diffuse emission has a power-law type spectrum. This difference indicates a possibility of dust processing due to the interaction between the infrared sources and their surrounding medium or a different origin of the dust grains surrounding the sources from those in the diffuse region. [source] The Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Ralf Mauer Abstract The charge transport in pristine poly(3-hexylthiophene) (P3HT) films and in photovoltaic blends of P3HT with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is investigated to study the influence of charge-carrier transport on photovoltaic efficiency. The field- and temperature dependence of the charge-carrier mobility in P3HT of three different regioregularities, namely, regiorandom, regioregular with medium regioregularity, and regioregular with very high regioregularity are investigated by the time-of-flight technique. While medium and very high regioregularity polymers show the typical absorption features of ordered lamellar structures of P3HT in the solid state even without previous annealing, films of regiorandom P3HT are very disordered as indicated by their broad and featureless absorption. This structural difference in the solid state coincides with partially non-dispersive transport and hole mobilities µh of around 10,4 and 10,5,cm2 V,1 s,1 for the high and medium regioregularity P3HT, respectively, and a slow and dispersive charge transport for the regiorandom P3HT. Upon blending the regioregular polymers with PCBM, the hole mobilities are typically reduced by one order of magnitude, but they do not significantly change upon additional post-spincasting annealing. Only in the case of P3HT with high regioregularity are the electron mobilities similar to the hole mobilities and the charge transport is, thus, balanced. Nonetheless, devices prepared from both materials exhibit similar power conversion efficiencies of 2.5%, indicating that very high regioregularity may not substantially improve order and charge-carrier transport in P3HT:PCBM and does not lead to significant improvements in the power-conversion efficiency of photovoltaic devices. [source] CF3CH(ONO)CF3: Synthesis, IR spectrum, and use as OH radical source for kinetic and mechanistic studiesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2003M. P. Sulbaek Andersen The synthesis, IR spectrum, and first-principles characterization of CF3CH(ONO)CF3 as well as its use as an OH radical source in kinetic and mechanistic studies are reported. CF3CH(ONO)CF3 exists in two conformers corresponding to rotation about the RCONO bond. The more prevalent trans conformer accounts for the prominent IR absorption features at frequencies (cm,1) of 1766 (NO stretch), 1302, 1210, and 1119 (CF stretches), and 761 (ONO bend); the cis conformer contributes a number of distinct weaker features. CF3CH(ONO)CF3 was readily photolyzed using fluorescent blacklamps to generate CF3C(O)CF3 and, by implication, OH radicals in 100% yield. CF3CH(ONO)CF3 photolysis is a convenient source of OH radicals in the studies of the yields of CO, CO2, HCHO, and HC(O)OH products which can be difficult to measure using more conventional OH radical sources (e.g., CH3ONO photolysis). CF3CH(ONO)CF3 photolysis was used to measure k(OH + C2H4)/k(OH + C3H6) = 0.29 ± 0.01 and to establish upper limits of 16 and 6% for the molar yields of CO and HC(O)OH from the reaction of OH radicals with benzene in 700 Torr of air at 296 K. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 159,165, 2003 [source] Calibration of spectra from dispersive XAS beamlinesJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2006M. P. Ruffoni The DXAS Calibration computer program provides a quantitative and automated solution to the problem of calibrating spectra from dispersive XAS beamlines. Such spectra, obtained in arbitrary energy units, are calibrated with respect to the absorption features of a supplied reference spectrum, which has been obtained under similar conditions on a calibrated beamline. In addition to basic energy coordinate transformation parameters, DXAS Calibration supplies instrument corrections to compensate for mismatches in instrument response functions between the dispersive and reference beamlines. [source] Spectral properties of angritesMETEORITICS & PLANETARY SCIENCE, Issue 8 2006T. H. Burbine Almost all angrites (e.g., D'Orbigny, Lewis Cliff [LEW] 86010, and Sahara 99555) are composed predominately of anorthite, Al-Ti diopside-hedenbergite, and Ca-rich olivine, except for the type specimen, Angra dos Reis, which is composed almost entirely of Al-Ti diopside-hedenbergite. D'Orbigny, LEW 86010, and Sahara 99555 also have spectral properties very different from Angra dos Reis. These newly measured angrites all have broad absorption features centered near 1 ,m with very weak to absent absorption bands at ,2 ,m, which is characteristic of some clinopyroxenes. The spectrum of Angra dos Reis has the characteristic 1 and 2 ,m features due to pyroxene. One asteroid, 3819 Robinson, has similar spectral properties to the newly measured angrites in the visible wavelength region, but does not appear to spectrally match these angrites in the near-infrared. [source] Spectral reflectance-compositional properties of spinels and chromites: Implications for planetary remote sensing and geothermometryMETEORITICS & PLANETARY SCIENCE, Issue 4 2004Edward A. Cloutis These two groups of minerals are spectrally distinct, which relates largely to differences in the types of major cations present. Both exhibit a number of absorption features in the 0.3,26 ,m region that show systematic variations with composition and can be used to quantify or constrain certain compositional parameters, such as cation abundances, and site occupancies. For spinels, the best correlations exist between Fe2+ content and wavelength positions of the 0.46, 0.93, 2.8, Restrahelen, 12.3, 16.2, and 17.5 ,m absorption features, Al and Fe3+ content with the wavelength position of the 0.93 ,m absorption feature, and Cr content from the depth of the absorption band near 0.55 ,m. For chromites, the best correlations exist between Cr content and wavelength positions of the 0.49, 0.59, 2, 17.5, and 23 ,m absorption features, Fe2+ and Mg contents with the wavelength position of the 1.3 ,m absorption feature, and Al content with the wavelength position of the 2 ,m absorption feature. At shorter wavelengths, spinels and chromites are most readily distinguished by the wavelength position of the absorption band in the 2 ,m region (<2.1 ,m for spinels, >2.1 ,m for chromite), while at longer wavelengths, spectral differences are more pronounced. The importance of being able to derive compositional information for spinels and chromites from spectral analysis stems from the relationship between composition and petrogenetic conditions (pressure, temperature, oxygen fugacity) and the widespread presence of spinels and chromites in the inner solar system. When coupled with the ability to derive compositional information for mafic silicates from spectral analysis, this opens up the possibility of deriving petrogenetic information for remote spinel- and chromite-bearing targets from analysis of their reflectance spectra. [source] A catalogue of absorption lines in eight Hubble Space Telescope/STIS E230M 1.0 < z < 1.7 quasar spectra,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007N. Milutinovi ABSTRACT We have produced a catalogue of line identifications and equivalent width measurements for all absorption features in eight ultraviolet echelle quasar spectra. These spectra were selected as having the highest signal-to-noise ratio among the Hubble Space Telescope/STIS spectra obtained with the E230M grating. We identify 56 metal-line systems towards the eight quasars, and present plots of detected transitions, aligned in velocity space. We found that about 1/4,1/3 of the features in the Ly, forest region, redward of the incidence of the Ly, forest, are metal lines. High-ionization transitions are common. At the redshift range we study, z < 1.7, we see both O vi and C iv in 88,90 per cent of the metal-line systems for which the spectra cover the expected wavelength. Si iii is seen in 58 per cent, while low-ionization absorption in C ii, Si ii and/or Al ii is detected in 50 per cent of the systems for which they are covered. This catalogue will facilitate future studies of the Ly, forest and of metal-line systems of various types. [source] Early-type stars observed in the ESO UVES Paranal Observatory Project , I. Interstellar Na i UV, Ti ii and Ca ii K observations,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006I. Hunter ABSTRACT We present an analysis of interstellar Na i (,air= 3302.37 and 3302.98 Å), Ti ii(,air= 3383.76 Å) and Ca ii K (,air= 3933.66 Å) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project, at a spectral resolution of 3.75 km s,1 and with mean signal-to-noise ratios per pixel of 260, 300 and 430 for the Na i, Ti ii and Ca ii observations, respectively. Interstellar features were detected in all but one of the Ti ii sightlines and all of the Ca ii sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, H i column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the Na i column density as an indicator of that for H i. In general, we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium (ISM) and also that the Ti ii/Ca ii ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general ISM conditions of the Galactic disc. [source] The effect of condensates on the characterization of transiting planet atmospheres with transmission spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005Jonathan J. Fortney ABSTRACT Through a simple physical argument we show that the slant optical depth through the atmosphere of a ,hot Jupiter' planet is ,35,90 times greater than the normal optical depth. This not unexpected result has direct consequences for the method of transmission spectroscopy for characterizing the atmospheres of transiting giant planets. The atmospheres of these planets likely contain minor condensates and hazes, which at normal viewing geometry have negligible optical depth, but at slant viewing geometry have appreciable optical depth that can obscure absorption features of gaseous atmospheric species. We identify several possible condensates. We predict that this is a general masking mechanism for all planets, not just for HD 209458b, and will lead to weaker than expected or undetected absorption features. Constraints on an atmosphere from transmission spectroscopy are not the same as constraints on an atmosphere at normal viewing geometry. [source] The mass of the white dwarf in the recurrent nova U ScorpiiMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001T.D. Thoroughgood We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi-amplitude of the primary star was found to be from the motion of the wings of the He ii,4686-Å emission line. By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be . From these parameters, we obtain a mass of for the white dwarf primary star and a mass of for the secondary star. The radius of the secondary is calculated to be , confirming that it is evolved. The inclination of the system is calculated to be , consistent with the deep eclipse seen in the light-curves. The helium emission lines are double-peaked, with the blueshifted regions of the disc being eclipsed prior to the redshifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within ,700 000 yr. [source] Extreme-ultraviolet laser metrology of O i transitionsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008T. I. Ivanov ABSTRACT Some 16 transitions in atomic oxygen originating from its 3P ground state were measured using a tunable narrow-band extreme-ultraviolet laser source, with an unprecedented accuracy of ,,/,= 8 × 10,8. The results are relevant for comparisons with spectral absorption features observed in the line of sight of quasars, in order to test a possible variation of the fine-structure constant , on a cosmological time-scale. [source] Probing dark matter, galaxies and the expansion history of the Universe with Ly, in absorption and emissionASTRONOMISCHE NACHRICHTEN, Issue 5 2010M.G. Haehnelt Abstract Ly, radiation is an important diagnostic tool in a wide range of astrophysical environments. I will first describe here how measurements of the matter power spectrum on small scales from Ly, forest data constrain the mass of dark matter particles. I then will report on an ambitious program of searching for very faint spatially extended Ly, emission at z , 3 which has led to the discovery of a new population of faint Ly, emitters which I will argue should be identified with the long searched for host galaxies of damped Ly, absorbers. Finally, I will discuss the possibility of measuring the redshift drift of Ly, absorption features and therefore the change of the expansion rate of the Universe in real time with the ultra-stable high-resolution spectrograph CODEX proposed for the E-ELT (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] V5116 Sgr: A disc-ecipsed SSS post-outburst nova?,ASTRONOMISCHE NACHRICHTEN, Issue 2 2010G. Sala Abstract Nova V5116 Sgr 2005 No. 2, discovered on 2005 July 4, was observed with XMM-Newton in March 2007, 20 months after the optical outburst. The X-ray spectrum showed that the nova had evolved to a pure supersoft X-ray source, indicative of residual H-burning on top of the white dwarf. The X-ray light-curve shows abrupt decreases and increases of the flux by a factor 8 with a periodicity of 2.97 h, consistent with the possible orbital period of the system. The EPIC spectra are well fit with an ONe white dwarf atmosphere model, with the same temperature both in the low and the high flux periods. This rules out an intrinsic variation of the X-ray source as the origin of the flux changes, and points to a possible partial eclipse as the origin of the variable light curve. The RGS high resolution spectra support this scenario showing a number of emission features in the low flux state, which either disappear or change into absorption features in the high flux state. A new XMM-Newton observation in March 2009 shows the SSS had turned off and V51 16 Sgr had evolved into a weaker and harder X-ray source (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The evolution of spheroidal galaxies in different environmentsASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009A. Fritz Abstract We analyse the kinematic and chemical evolution of 203 distant spheroidal (elliptical and S0) galaxies at 0.2 < z < 0.8 which are located in different environments (rich clusters, low-mass clusters and in the field). VLT/FORS and CAHA/MOSCA spectra with intermediate-resolution have been acquired to measure the internal kinematics and stellar populations of the galaxies. From HST/ACS and WFPC2 imaging, surface brightness profiles and structural parameters were derived for half of the galaxy sample. The scaling relations of the Faber-Jackson relation and Kormendy relation as well as the Fundamental Plane indicate a moderate evolution for the whole galaxy population in each density regime. In all environments, S0 galaxies show a faster evolution than elliptical galaxies. For the cluster galaxies a slight radial dependence of the evolution out to one virial radius is found. Dividing the samples with respect to their mass, a mass dependent evolution with a stronger evolution of lower-mass galaxies (M < 2 × 1011 M,) is detected. Evidence for recent star formation is provided by blue colours and weak [OII] emission or strong H, absorption features in the spectra. The results are consistent with a down-sizing formation scenario which is independent from the environment of the galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Estimating black hole masses in young radio sources using CFHT spectroscopyASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009M.F. Gu Abstract The correlation between black hole masses and stellar velocity dispersions provides an efficient method to determine the masses of black holes in active galaxies. We obtained optical spectra of a Compact-Steep-Spectrum (CSS) galaxy 4C +29.70, using the Canada-France-Hawaii Telescope (CFHT) equipped with OSIS, in 2003 August 6. Several stellar absorption features, such asMg I (5175 Å), Ca E band (5269 Å) and Na D (5890 Å), were detected in the spectra. The stellar velocity dispersion, ,, of the host galaxy, measured from absorption features is ,250 km s,1. If 4C +29.70 follows the MBH - , relation established for nearby galaxies, then its central black hole has a mass of ,3.3 × 108 M,. In combination with the black hole masses of seven GPS galaxies in Snellen et al. (2003), we find that the average black hole mass of these eight young radio sources is smaller than that of the Bettoni et al. (2003) sample of extended radio galaxies. This may indicate that young radio sources are likely at the early evolutionary stage of radio galaxies, at which the central black holes may still undergo rapid growth. However, this needs further investigations (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Searching for the missing baryons in theWarm-Hot Intergalactic MediumASTRONOMISCHE NACHRICHTEN, Issue 2 2008X. Barcons Abstract At low redshift (z < 2), almost half of the baryons in the Universe are not found in bound structures like galaxies and clusters and therefore most likely reside in a Warm-Hot Intergalactic Medium (WHIM), as predicted by simulations. Attempts to detect WHIM filaments at cosmological distances in absorption towards bright background sources have yielded controversial results that I review here. I argue that a secure detection of absorption features by the WHIM is at the limit of the XMM-Newton capabilities, but feasible. A proper characterisation of the whole WHIM belongs to the realm of future X-ray missions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectroscopy of Hydrocarbon Grains toward the Galactic Center and Quintuplet ClusterASTRONOMISCHE NACHRICHTEN, Issue S1 2003J.E. Chiar Abstract Our view of the Galactic center (GC) is affected by extinction from both diffuse interstellar medium (ISM) dust and dense molecular clouds along the line of sight. The enormous visual extinction present toward the center of our Galaxy (,31 magnitudes) necessitates a study of the interstellar dust properties as well as an investigation into the distribution of the different dust components. We have built upon the historic spectroscopy of Willner et al. (1979), Butchart et al. (1986), and McFadzean et al. (1989) in order to investigate the distribution of these dust components across the GC field. Specifically, we employ spectroscopy in the 3 ,m region to investigate absorption features at 3.0 ,m and 3.4 ,m in lines of sight toward the GC central cluster and the Quintuplet cluster to the northeast. The 3.4 ,m feature is one of the primary spectral signatures of the organic component of interstellar dust and is, to date, only observed in the cold diffuse interstellar medium. The 3.0 ,m ice feature is carried by dense molecular cloud material, and can therefore be used to loosely trace the distribution of such material across the GC field. By obtaining spectra for multiple sightlines we have been able to deconvolve the diffuse ISM and dense molecular cloud components. Our study shows that differences exist in the spectra of relatively nearby lines of sight in the Galactic center central cluster. The depth of the 3.0 ,m water-ice feature varies by a factor of almost 5 across a 2 parsec (in projection) region, perhaps re.ecting the clumpy nature of the dense clouds. In addition, we found that the 3.4 ,m hydrocarbon feature varies in depth across the areas studied toward the central cluster, whereas the depth is relatively constant toward the Quintuplet cluster. This is likely a reflection of the distribution of extinction from the foreground diffuse ISM. Our ground-based and space-based spectroscopy reveals differences in absorption features in the 3 and 6 ,m regions between sightlines toward the GC central cluster and those toward the Quintuplet cluster. While the 3 ,m spectra of both regions show a broad absorption feature blueward of the 3.4 ,m absorption, only the Quintuplet spectra show a distinct absorption feature at 3.28 ,m. This feature is indicative of the presence of polycyclic aromatic hydrocarbons (PAHs) along the line of sight. The Quintuplet-proper sources have 6 ,m spectra that are markedly different than that of GC IRS 7 in the central cluster, and instead strongly resemble the spectra seen toward dusty late-type carbon-class (WC)Wolf-Rayet stars. This is the first hint of some spectroscopic similarity between the Quintuplet sources and dusty WC stars. [source] Influence of the Protonic State of an Imidazole-Containing Ligand on the Electrochemical and Photophysical Properties of a Ruthenium(II),Polypyridine-Type ComplexCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2007Annamaria Quaranta Dr. Abstract The synthesis and characterisation of [Ru(bpy)2(PhenImHPh)]2+ where PhenImHPh represents the 2-(3,5-di- tert -butylphenyl)imidazo[4,5- f][1,10]phenanthroline ligand are described. The compounds issued from the three different protonic states of the imidazole ring [Ru(bpy)2(PhenImPh)]+ (I), [Ru(bpy)2(PhenImHPh)]2+ (II) and [Ru(bpy)2(PhenImH2Ph)]3+ (III) were isolated and spectroscopically characterised. The X-ray structures of [Ru(bpy)2(PhenImPh)](PF6),H2O,6,MeOH, [Ru(bpy)2(PhenImHPh)](NO3)2,H2O,3,MeOH and [Ru(bpy)2(PhenImH2Ph)](PF6)3, 5,H2O are reported. Electrochemical data obtained on these complexes indicate almost no potential shift for the RuIII/II redox couple. Therefore a Coulombic effect between the imidazole ring and the metal centre can be ruled out. The monooxidised forms of I and II have been characterised by EPR spectroscopy and are reminiscent of the presence of a radical species. The emission properties of the parent compound [Ru(bpy)2(PhenImHPh)]2+ were studied as a function of pH and both the lifetimes and intensities decreased upon deprotonation. Photophysical properties, investigated in the absence and presence of an electron acceptor (methylviologen), were distinctly different for the three compounds. Transient absorption features indicate that unique excited states are involved. Theoretical data obtained from DFT calculations in water on the three protonic forms are presented and discussed in the light of the experimental results. [source] | |||||||||||||