CO2 Absorption Band Research Articles

An improvement to the volcano-scan algorithm for atmospheric correction of CRISM and OMEGA spectral data

The observations of Mars by the CRISM and OMEGA hyperspectral imaging spectrometers require correction for photometric, atmospheric and thermal effects prior to the interpretation of possible mineralogical features in the spectra. Here, we report on a simple, yet non-trivial, adaptation to the commonly-used volcano-scan correction technique for atmospheric CO 2, which allows for the improved detection of minerals with intrinsic absorption bands at wavelengths between 1.9 and 2.1 μm. This volcano-scan technique removes the absorption bands of CO 2 by ensuring that the Lambert albedo is the same at two wavelengths: 1.890 and 2.011 μm, with the first wavelength outside the CO 2 gas bands and the second wavelength deep inside the CO 2 gas bands. Our adaptation to the volcano-scan technique moves the first wavelength from 1.890 μm to be instead within the gas bands at 1.980 μm, and for CRISM data, our adaptation shifts the second wavelength slightly, to 2.007 μm. We also report on our efforts to account for a slight ∼0.001 μm shift in wavelengths due to thermal effects in the CRISM instrument.

Simultaneous observations of the Martian atmosphere by Planetary Fourier Spectrometer on Mars Express and Miniature Thermal Emission Spectrometer on Mars Exploration Rover

In this study we present temperature profiles in the lower atmosphere of Mars from simultaneous observations performed by the Planetary Fourier Spectrometer (PFS) aboard the Mars Express spacecraft and the Miniature Thermal Emission Spectrometer (Mini‐TES) aboard the Mars Exploration Rovers. Thermal infrared spectra were collected in both the upward and downward looking geometries from the surface and from orbit, respectively. We used two sets of criteria to select PFS observations. These criteria took into account the location around the landing sites of the rovers, the local time (LT), and the solar longitude (Ls) corresponding to the Martian solar day (sol). The first set of criteria included PFS measurements carried out within ±1° in latitude and longitude, within 1 h in local time, and on the same sol. From the restricted set of measurements we conclude that the PFS data are consistent with the Mini‐TES data. The next set of criteria covered the area 5° × 5° around the landing sites, within 1 h in local time and within 9 sols. The latter criteria allow us to study the variation of parameters LT, distance, and Ls and their influence on changes of temperature profiles. This comparison for the group with relaxed criteria showed also that local time has strongest effect on temperature differences. The main purpose of this study is to confirm the validity of PFS temperature profiles close to the surface. Atmospheric temperatures below 5 km are retrieved from satellite measurements with a large uncertainty because of poor pieces of information in the wings of the CO2 absorption band at 667 cm−1. The Mini‐TES temperature profiles span atmospheric layers below 2 km. The good correspondence observed in a number of cases confirms the possibility of using PFS measurements to investigate the lower atmosphere.

Wavelength selection for quantum cascade lasers by cavity length

A systematic shift in spectral emission wavenumbers in quantum cascade lasers (QCLs) is observed over a variation in cavity lengths from 0.5 to 3 mm resulting in a gain peak shift ranging from 2404 to 2286 cm−1. Thereby, a wavelength selection range of 118 cm−1 is provided, which is sufficiently broad for selecting the laser emission across the entire CO2 absorption band at 2326 cm−1 (4.3 μm). In contrast to current QCL wavelength selection techniques, modifying the cavity length is a straightforward postprocessing procedure. Experimental evidence confirms that this frequency shift is due to a change in threshold voltage and applied electric field as a function of cavity length which is in agreement with the theory.

AGN-starburst connection in NGC 7582: Gemini near-infrared spectrograph integral field unit observations

We analyse two-dimensional near-infrared K-band spectra from the inner 660 × 315 pc 2 of the Seyfert galaxy NGC 7582 obtained with the Gemini near-infrared spectrograph integral field unit at a spatial resolution of ≈50 pc and spectral resolving power R ≈ 5900. The nucleus harbours an unresolved source well reproduced by a blackbody of temperature T ≈ 1050 K, which we attribute to emission by circumnuclear dust located closer than 25 pc from the nucleus, with a total mass of ≈3 × 10 −3 M� . Surrounding the nucleus, we observe a ring of active star formation, apparently in the Galactic plane, with a radius of ≈190 pc, an age of ≈5 Myr and a total mass of ionized gas of ≈3 × 10 6 M� . The radiation of the young stars in the ring accounts for at least 80 per cent of the ionization observed in the Brγ emitting gas, the remaining being due to the radiation emitted by the active nucleus. The stellar kinematics was derived using the CO absorption band at 2.29 μm and reveals: (i) a distorted rotation pattern in the radial velocity field with kinematic centre apparently displaced from the nuclear source by a few tens of parsec; (ii) a high-velocity dispersion in the bulge of σ ∗ = 170 km s −1 and (iii) a partial ring of σ ∗ = 50 km s −1 , located close to the Brγ emitting ring, but displaced by ≈50 pc towards the nucleus, interpreted as due to stars formed from cold gas in a previous burst of star formation. The kinematics of the ionized gas shows a similar rotation pattern to that of the stars, plus a blueshifted component with velocities ≥ 100 km s −1 interpreted as due to an outflow along the ionization cone, which was partially covered by our observations. The mass outflow rate in the ionized gas was estimated as u

Atmospheric Circulation of Hot Jupiters: Three‐dimensional Circulation Models of HD 209458b and HD 189733b with Simplified Forcing

We present global, three-dimensional numerical simulations of the atmospheric circulation on HD 209458b and HD 189733b and calculate the infrared spectra and light curves predicted by these simulations, which we compare with available observations. Radiative heating/cooling is parameterized with a simplified Newtonian relaxation scheme. Our simulations develop day-night temperature contrasts that vary strongly with pressure. At low pressure (<10 mbar), air flows from the substellar point toward the antistellar point, both along the equator and over the poles. At deeper levels, the flow develops an eastward equatorial jet with speeds of 3-4 km s−1, with weaker westward flows at high latitudes. This basic flow pattern is robust to variations in model resolution, gravity, radiative time constant, and initial temperature structure. Nightside spectra show deep absorption bands of H2O, CO, and/or CH4, whereas on the dayside these absorption bands flatten out or even flip into emission. This results from the strong effect of dynamics on the vertical temperature-pressure structure; the temperature decreases strongly with altitude on the nightside but becomes almost isothermal on the dayside. In Spitzer bandpasses, our predicted planet-to-star flux ratios vary by a factor of ~2-10 with orbital phase, depending on the wavelength and chemistry. For HD 189733b, where a detailed 8 μm light curve has been obtained, we correctly produce the observed phase offset of the flux maximum, but we do not explain the flux minimum and we overpredict the total flux variation. This discrepancy likely results from the simplifications inherent in the Newtonian relaxation scheme and provides motivation for incorporating realistic radiative transfer in future studies.

Radial Velocities of Stars in the Galactic Center

We present results from K-band slit scan observations of a ~20'' × 20'' region of the Galactic center (GC) in two separate epochs more than 5 years apart. The high-resolution (R = λ/Δ λ ≥ 14,000) observations allow the most accurate radial velocity and acceleration measurements of the stars in the central parsec of the Galaxy. Detected stars can be divided into three groups based on the CO absorption band heads at ~2.2935 μm and the He II lines at ~2.0581 and ~2.112, 2.113 μm: cool, narrow-line hot, and broad-line hot. The radial velocities of the cool, late-type stars have approximately a symmetrical distribution with its center at ~–7.8 ± 10.3 km s−1 and a standard deviation ~113.7 ± 10.3 km s−1. Although our statistics are dominated by the brightest stars, we estimate a central black hole mass of (3.9 ± 1.1) × 106 M☉, consistent with current estimates from complete orbits of individual stars. Our surface density profile and the velocity dispersion of the late-type stars support the existence of a low-density region at the Galactic center suggested by earlier observations. Many hot, early-type stars show radial velocity changes higher than maximum values allowed by pure circular orbital motions around a central massive object, suggesting that the motions of these stars greatly deviate from circular orbital motions around the Galactic center. The correlation between the radial velocities of the early-type He I stars and their declination offsets from Sagittarius A* suggests that a systematic rotation is present for the early-type population. No figure rotation around the Galactic center for the late-type stars is supported by the new observations.

Novel and efficient cobalt encapsulated SBA-15 catalysts for the selective oxidation of cyclohexane

Co-SBA-15 catalysts were synthesized by direct synthesis and post-synthetic impregnation methods at two different loadings of Co viz., 1.2 and 2 wt%. The structure of SBA-15 was found to remain intact even after the incorporation of Co in either of the two methods of catalyst preparation, which was confirmed by low-angle XRD. The existence of Co 2+ species were confirmed by characteristic absorption bands of Co in the UV–vis spectra and XPS results. The encapsulation of Co in SBA-15 was found to be highly advantageous in yielding significant amounts of the desired products viz., cyclohexanone and cyclohexanol in the oxidation of cyclohexane in liquid phase without using any solvent under moderate pressure of O 2 at 433 K. The catalysts showed high turn over numbers towards the oxidation of cyclohexane to cyclohexanone and 2%CoSYN (2 wt% Co-SBA-15) catalyst showed a maximum of 9.4% conversion of cyclohexane and 78% selectivity towards the formation of cyclohexanone.

Sulphuric acid and Pt treatment of the photocatalytically active titanium dioxide

The study focuses on preparation, surface sites characterization and catalytic activity testing of pure (TiO 2), sulfated (TiO 2-S), loaded with 1 wt% Pt (TiO 2-Pt) and platinized/sulfated (TiO 2-Pt-S) high surface area anatase TiO 2 (100% anatase, 340 m 2/g). Sulfation was performed in 4 M H 2SO 4 solution and was not followed by a high temperature calcination. TEM images reveal the formation of a 3 Å amorphous layer over TiO 2 and TiO 2-Pt surface after their sulfation. Infrared spectrum of TiO 2-S contains additional absorption bands at 1235, 1333 and 1378 cm −1 that are assigned to S O stretch and distorted adsorbed SO 4 2 − vibrations. Low temperature CO adsorption and organic species adsorption from heptane solutions was performed for characterization of surface sites. TiO 2-S showed 3–5 cm −1 shift of adsorbed CO absorption band compared to initial TiO 2. The quantity of adsorbed CO increased by a factor of 1.5 for TiO 2-S indicating the increase of the quantity of surface Lewis sites. Sulfation also resulted in disappearance of OH groups having absorption band at 3690 cm −1 that was attributed to substitution by monodentate and bidentate sulfates. Four bases and two acids with different p K were used as probes in solution titration revealing that the quantity of different acid sites in TiO 2-S increases 1.07–2.17 times. Unexpectedly the quantity of acid and base sites in TiO 2-Pt-S decreases relatively to other catalysts studied. Catalytic activity of the samples in acetone deep photooxidation was measured as a function of acetone vapor concentration in a flow-circulating reactor. All dependences are well described by the one site Langmuir–Hinshelwood kinetic model. The maximum oxidation rate was similar for all samples and was observed at acetone concentration above 1500 ppm. However, in the range of low acetone concentration the activity of TiO 2-Pt-S was about triple of pure TiO 2 activity. The high activity of sulfated/platinized and sulfated TiO 2 is due to the much increased acetone adsorption constant.

Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity

We examine the spectra and infrared colors of the cool methane-dominated atmospheres at Teff < 1400 K expected for gas giant planets. We couple these spectral calculations to an updated version of the Marley et al. (2007) giant planet thermal evolution models that include formation by core accretion-gas capture. These relatively cool young can be 1-6 magnitudes fainter than predicted by standard cooling tracks that include a traditional initial condition, which may provide a diagnostic of formation. If correct, this would make true Jupiter-like planets much more difficult to detect at ages than previously thought. Since Jupiter and Saturn are of distinctly super-solar composition, we examine emitted spectra for model planets at both solar metallicity and a metallicity of 5 times solar. These metal-enhanced Jupiters have lower pressure photospheres than field brown dwarfs of the same effective temperatures arising from both lower surface gravities and enhanced atmospheric opacity. We highlight several diagnostics for enhanced metallicity. A stronger CO absorption band at 4.5 $\mu$m for the warmest objects is predicted. At all temperatures, enhanced flux in $K$ band is expected due to reduced collisional induced absorption by H$_2$. This leads to correspondingly redder near infrared colors, which are redder than solar metallicity models with the same surface gravity by up to 0.7 in $J-K$ and 1.5 in $H-K$. Molecular absorption band depths increase as well, most significantly for the coolest objects. We also qualitatively assess the changes to emitted spectra due to nonequilibrium chemistry.

Cloud properties from Atmospheric Infrared Sounder and evaluation with Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations

The Atmospheric Infrared Sounder (AIRS) onboard the NASA Aqua satellite was primarily designed to provide atmospheric temperature and water vapor profiles, and the high spectral resolution of this instrument also allows the retrieval of cloud properties (especially cirrus). We present a retrieval of cloud pressure and effective emissivity, based on a weighted χ2 method using channels around the 15‐micron CO2 absorption band. The cloud property retrieval is applied to all data, and tests based on the retrieved parameters determine cloud amount in a second step. Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), launched as part of the A‐Train in 2006, made it possible to evaluate the AIRS retrieved cloud height by comparing it to the height of maximum backscatter and of the “apparent middle” of the highest cloud layer determined by CALIPSO. The retrieved cloud height of about 66% (80%) of AIRS high (low) clouds lies within 1.5 km of the apparent middle of the CALIPSO cloud layers. Comparing cloud pressures shows an agreement in cloud height of 72% (59%) for high (low) clouds within 75 hPa. Keeping in mind that (1) low clouds are geometrically thinner (less than 1 km) than high clouds (in general between 1.5 and 3 km), (2) high clouds are also much more heterogeneous, and (3) CALIPSO only samples a small fraction of the AIRS footprint, the comparison is very encouraging. Zonal averages of high‐, midlevel‐, and low‐cloud amount are compared to those of other data sets for January and July. Compared to our cloud retrieval, distributions of cloud pressure provided by AIRS L2 data reveal a strong bias toward lower pressures for low clouds.

Dust aerosols above the south polar cap of Mars as seen by OMEGA

The time evolution of atmospheric dust at high southern latitudes on Mars has been determined using observations of the south seasonal cap acquired in the near infrared (1–2.65 μm) by OMEGA/Mars Express in 2005. Observations at different solar zenith angles and one EPF sequence demonstrate that the reflectance in the 2.64 μm saturated absorption band of the surface CO 2 ice is mainly due to the light scattered by aerosols above most places of the seasonal cap. We have mapped the total optical depth of dust aerosols in the near-IR above the south seasonal cap of Mars from mid-spring to early summer with a time resolution ranging from one day to one week and a spatial resolution of a few kilometers. The optical depth above the south perennial cap is determined on a longer time range covering southern spring and summer. A constant set of optical properties of dust aerosols is consistent with OMEGA observations during the analyzed period. Strong variations of the optical depth are observed over small horizontal and temporal scales, corresponding in part to moving dust clouds. The late summer peak in dust opacity observed by Opportunity in 2005 propagated to the south pole contrarily to that observed in mid spring. This may be linked to evidence for dust scavenging by water ice-rich clouds circulating at high southern latitudes at this season.

Mapping of molecular gas inflow towards the Seyfert nucleus of NGC 4051 using Gemini NIFS

We present 2D stellar and gaseous kinematics of the inner ∼130× 180 pc 2 of the Narrow-Line Seyfert 1 galaxy NGC 4051 at a sampling of 4.5 pc, from near-infrared K-band spectroscopic observations obtained with the Gemini's Near-infrared Integral Field Spectrograph (NIFS) operating with the ALTAIR adaptive optics module. We have used the CO absorption band heads around 2.3 μm to obtain the stellar kinematics which show the turnover of the rotation curve at only ≈55 pc from the nucleus, revealing a highly concentrated gravitational potential. The stellar velocity dispersion of the bulge is ≈60 km s -1 - implying on a nuclear black hole mass of ≈10 6 M ⊙ - within which patches of lower velocity dispersion suggest the presence of regions of more recent star formation. From measurements of the emission-line profiles we have constructed 2D maps for the flux distributions, line ratios, radial velocities and gas velocity dispersions for the H 2 , H II and [Ca VIII] emitting gas. Each emission-line samples a distinct kinematics. The Bry emission-line shows no rotation as well as no blueshifts or redshifts in excess of 30 km s -1 , and is thus not restricted to the galaxy plane. The [Ca VIII] coronal region is compact but resolved, extending over the inner 75 pc. It shows the highest blueshifts - of up to -250 km s -1 , and the highest velocity dispersions, interpreted as due to outflows from the active nucleus, supporting an origin close to the nucleus. Subtraction of the stellar velocity field from the gaseous velocity field has allowed us to isolate non-circular motions observed in the H 2 emitting gas. The most conspicuous kinematic structures are two nuclear spiral arms - one observed in blueshift in the far side of the galaxy (to the north-east), and the other observed in redshift in the near side of the galaxy (to the south-west). We interpret these structures as inflows towards the nucleus, a result similar to those of previous studies in which we have found streaming motions along nuclear spirals in ionized gas using optical Integral Filed Unit (IFU) observations. We have calculated the mass inflow rate along the nuclear spiral arms, obtaining M H2 ≈ 4 x 10 -5 M ⊙ yr -1 , a value ∼100 times smaller than the accretion rate necessary to power the active nucleus. This can be understood as due to the fact that we are only seeing the hot 'skin' (the H 2 emitting gas) of the total mass inflow rate, which is probably dominated by cold molecular gas. From the H 2 emission-line ratios we conclude that X-ray heating can account for the observed emission, but the H 2 λ2.1218 μm/Br y line ratio suggests some contribution from shocks in localized regions close to the compact radio jet.

Spectral properties of gaseous biomarkers and choice of the optimal analytical line at interference of the spectra of detected gases

A method for comparative investigation of the absorption line properties at interference of vibration-rotation bands of the detected and interfering gases is proposed. This method is intended for highly sensitive analysis of complex gas mixtures when measurement of absorption in a weak analytical line is hindered by a stronger, closely located interfering line. Disappearance of the analytical line extrema in the spectrum studied is proposed as an assessment criterion. The concentration ratio of the analytical and interfering gases under this condition could be used for quantitative analysis and comparison of the properties. This criterion can be applied to the first and second derivatives of the absorption spectra. To demonstrate the potential of the approach proposed, it was applied to the NO and NH3 lines that are promising for monitoring the contents of these compounds in atmospheric and exhaled air. The interference of the absorption bands of H2O, CO2, and several gaseous biomarkers was analyzed in the near-IR spectral region using the HITRAN2000 database. It was demonstrated that the problem of the vibration-rotation band interference for detected and interfering gases is aggravated in this spectral region. This aggravation is caused not only by the decrease in the absolute band intensity for overtones and combination bands of the molecular vibrations but also by the relative increase in the absorption in H2O lines and high density of CO2 lines in the near-IR spectral region.

Band profiles and band strengths in mixed H2O:CO ices

Context. Laboratory spectroscopic research plays a key role in the identification and analysis of interstellar ices and their structure. To date, a number of molecules have been positively identified in interstellar ices, either as pure, mixed or layered ice structures. Aims. Previous laboratory studies on H2O:CO ices have employed a “mix and match” principle and describe qualitatively how absorption bands behave for different physical conditions. The aim of this study is to quantitatively characterize the absorption bands of solid CO and H2O, both pure and in their binary mixtures, as a function of partner concentration and temperature. Methods. Laboratory measurements based on Fourier transform infrared transmission spectroscopy are performed on binary mixtures of H2O and CO ranging from 1:4 to 4:1. Results. A quantitative analysis of the band profiles and band strengths of H2O in CO ice, and vice versa, is presented and interpreted in terms of two models. The results show that a mutual interaction takes place between the two species in the solid, which alters the band positions and band strengths. It is found that the band strengths of the H2O bulk stretch, bending and libration vibrational bands decrease linearly by a factor of up to 2 when the CO concentration is increased from 0 to 80%. By contrast, the band strength of the free OH stretch increases linearly. The results are compared to a recently performed quantitative study on H2O:CO2 ice mixtures. It is shown that for mixing ratios of 1:0.5 H2O:X and higher, the H2O bending mode offers a good tracer to distinguish between CO2 or CO in H2O ice. Additionally, it is found that the band strength of the CO fundamental remains constant when the water concentration is increased in the ice. The integrated absorbance of the 2152 cm −1 CO feature, with respect to the total integrated CO absorption feature, is found to be a good indicator of the degree of mixing of CO in the H2O:CO laboratory ice system. From the change in the H2O absorption band strength in laboratory ices upon mixing we conclude that astronomical water ice column densities on various lines of sight can be underestimated by up to 25% if significant amounts of CO and CO2 are mixed in.

Remote sensing of surface pressure on Mars with the Mars Express/OMEGA spectrometer: 2. Meteorological maps

Surface pressure measurements help to achieve a better understanding of the main dynamical phenomena occurring in the atmosphere of a planet. The use of the Mars Express OMEGA visible and near‐IR imaging spectrometer allows us to tentatively perform an unprecedented remote sensing measurement of Martian surface pressure. OMEGA reflectances in the CO2 absorption band at 2 μm are used to retrieve a hydrostatic estimation of surface pressure (see companion paper by Forget et al. (2007)) with a precision sufficient to draw maps of this field and thus analyze meteorological events in the Martian atmosphere. Prior to any meteorological analysis, OMEGA observations have to pass quality controls on insolation and albedo conditions, atmosphere dust opacity, and occurrence of water ice clouds and frosts. For the selected observations, registration shifts with the MOLA reference are corrected. “Sea‐level” surface pressure reduction is then carried out in order to remove the topographical component of the surface pressure field. Three main phenomena are observed in the resulting OMEGA surface pressure maps: horizontal pressure gradients, atmospheric oscillations, and pressure perturbations in the vicinity of topographical obstacles. The observed pressure oscillations are identified as possible signatures of phenomena such as inertia‐gravity waves or convective rolls. The pressure perturbations detected around the Martian hills and craters may be the signatures of complex interactions between an incoming flow and topographical obstacles. Highly idealized mesoscale simulations using the WRF model enable a preliminary study of these complex interactions, but more realistic mesoscale simulations are necessary. The maps provide valuable insights for future synoptic and mesoscale modeling, which will in turn help in the interpretation of observations.

Remote sensing of surface pressure on Mars with the Mars Express/OMEGA spectrometer: 1. Retrieval method

Observing and analyzing the variations of pressure on the surface of a planet is essential to understand the dynamics of its atmosphere. On Mars the absorption by atmospheric CO2 of the solar light reflected on the surface allows us to measure the surface pressure by remote sensing. We use the imaging spectrometer OMEGA aboard Mars Express, which provides an excellent signal to noise ratio and the ability to produce maps of surface pressure with a resolution ranging from 400 m to a few kilometers. Surface pressure is measured by fitting spectra of the CO2 absorption band centered at 2 μm. To process the hundreds of thousands of pixels present in each OMEGA image, we have developed a fast and accurate algorithm based on a line‐by‐line radiative transfer model which includes scattering and absorption by dust aerosols. In each pixel the temperature profile, the dust opacity, and the surface spectrum are carefully determined from the OMEGA data set or from other sources to maximize the accuracy of the retrieval. We estimate the 1‐σ relative error to be around 7 Pa in bright regions and about 10 Pa in darker regions, with a possible systematic bias on the absolute pressure lower than 30 Pa (4%). The method is first tested by comparing an OMEGA pressure retrieval obtained over the Viking Lander 1 (VL1) landing site with in situ measurements recorded 30 years ago by the VL1 barometer. The retrievals are further validated using a surface pressure predictor which combines the VL1 pressure records with the MOLA topography and meteorological pressure gradients simulated with a General Circulation Model. A good agreement is obtained. In particular, OMEGA is able to monitor the seasonal variations of the surface pressure in Isidis Planitia. Such a tool can be applied to detect meteorological phenomena, as described by Spiga et al. (2007).

Vapour phase Fourier transform infrared spectrometric determination of l-cysteine and l-cystine

A novel and selective procedure for the determination of l-cysteine and l-cystine based on vapour-generation Fourier transform infrared spectrometry is described. Potassium iodate solution was injected into a glass vessel containing l-cysteine and/or l-cystine. The evolved CO was swept by a stream of nitrogen to an infrared gas cell. The vapour phase FTIR spectra were continuously recorded, as a function of time, between 2240 and 2000 cm −1, which includes the CO absorption band. The maximum absorbance at 2170 cm −1 was selected as a measurement criterion. The calibration curve was linear over the range 6–300 mg L −1. The method provided a limit of detection of 2 mg L −1 of l-cysteine, a throughput of 12 samples h −1 and an R.S.D. of 1.76% for five independent analyses of a 75 mg L −1 l-cysteine solution. For the measurement of l-cysteine and l-cystine separately, after measuring total concentration of l-cysteine and l-cystine, l-cysteine was masked with p-benzoquinone at a pH of 3 and individual l-cystine was determined. The amount of l-cysteine was obtained by difference. The method was applied to the determination of l-cysteine and l-cystine in pharmaceutical and urine samples. Results obtained for real samples compared well with those obtained by a reference spectrometric method.

Dynamical Nighttime Fog/Low Stratus Detection Based on Meteosat SEVIRI Data: A Feasibility Study

Automated detection of fog and low stratus in nighttime satellite data has been implemented on the basis of numerous satellite systems in past decades. Commonly, differences in small-droplet emissivities at 11μm and 3.9μm are utilized. With Meteosat SEVIRI, however, this method cannot be applied with a fixed threshold due to instrument design: The 3.9μm band is exceptionally wide and overlaps with the 4μm CO2 absorption band. Therefore, the emissivity difference varies with the length of the slant atmospheric column between sensor and object. To account for this effect, the new technique presented in this paper is based on the dynamical extraction of emissivity difference thresholds for different satellite viewing zenith angles. In this way, varying concentrations of CO2 and column depths are accounted for. The new scheme is exemplified in a plausibility study and shown to provide reliable results.

The supermassive black hole in NGC 4486a detected with SINFONI at the Very Large Telescope

The near-infrared (IR) integral field spectrograph SINFONI at the European Southern Observatory Very Large Telescope opens a new window for the study of central supermassive black holes. With a near-IR spatial resolution similar to Hubble Space Telescope optical and the ability to penetrate dust, it provides the possibility to explore the low-mass end of the M•‐σ relation ( σ< 120 km s −1 ) where so far very few black hole masses were measured with stellar dynamics. With SINFONI, we observed the central region of the low-luminosity elliptical galaxy NGC 4486a at a spatial resolution of ≈0.1 arcsec in the K band. The stellar kinematics were measured with a maximum penalized likelihood method considering the region around the CO absorption band heads. We determined a black hole mass of M• = (1.25 +0.75 −0.79) × 10 7 M� (90 per cent confidence limit) using the Schwarzschild orbit superposition method including the full two-dimensional spatial information. This mass agrees with the predictions of the M•‐σ relation, strengthening its validity at the lower σ end.

Physisorption of CO 2 on non-ice materials relevant to icy satellites

CO 2 is known to adsorb onto clay and other minerals when a significant atmospheric pressure is present. We have found that CO 2 can also adsorb onto some clays when the CO 2 partial pressure is effectively zero under ultra-high vacuum (UHV) if cooled to the surface temperatures of the icy satellites of Jupiter and Saturn. The strength of adsorption and the spectral characteristics of the adsorbed CO 2 infrared (IR) ν 3 absorption band near 4.25 μm depend on the composition and temperature of the adsorbent. CO 2 remains adsorbed onto the clay mineral montmorillonite for > 10 s of min when exposed to a vacuum of ∼ 1 × 10 −8 Torr at ∼ 125 K . CO 2 does not adsorb onto serpentine, goethite, or palagonite under these conditions. A small amount may adsorb onto kaolinite. When heated above 150 K under vacuum, the CO 2 desorbs from the montmorillonite within a few minutes. The ν 3 absorption band of CO 2 adsorbed onto montmorillonite at 125 K is similar to that of the CO 2 detected on the saturnian and Galilean satellites and is markedly different from CO 2 adsorbed onto montmorillonite at room temperature. We infer the adsorption process is physisorption and postulate that this mechanism may explain the presence and spectral characteristics of the CO 2 detected in the surfaces of these outer satellites.