CN Molecular Bands Research Articles

High-resolution infrared spectroscopy of field Red Horizontal Branch stars

We obtained the surface abundances of more than 20 elements from H- and K-band observations of three Red Horizontal Branch (RHB) stars. High-resolution (R ≃ 45,000) infrared spectra were obtained using IGRINS (the Immersion Grating Infrared Spectrograph) on the 2.7 m Smith telescope at McDonald Observatory. IGRINS has the capacity of making simultaneous observations with a wavelength coverage of essentially the entire H and K-bands (1.5–2.4 μm). High S/N (>200) IGRINS data serve as a laboratory of molecular bands. A large number of OH, CO and CN molecular bands provided us invaluable information on the abundances of C, N and O, which can be altered as stars evolve from birth to death. OH bands confirmed and greatly strengthened the oxygen abundances previously measured from visible [O I] lines. Carbon and nitrogen abundances were determined from CO and CN molecular bands, respectively. IGRINS also made it possible to achieve more robust abundances of light elements such as Na, Mg, Al, and Si than obtained from their visible counterparts, and allowed S, P and K abundance determination mostly for the first time. Most importantly, we were able to detect 12C/13C isotopic ratios from the CO (2–0) and CO (3–1) band-heads present in the K-band, which give us important clues about the evolutionary status of the stars and mixing processes that take place in the interiors of these RHB He core-burning stars.

The benchmark halo giant HD 122563: CNO abundances revisited with three-dimensional hydrodynamic model stellar atmospheres

We present an abundance analysis of the low-metallicity benchmark red giant star HD 122563 based on realistic, state-of-the-art, high-resolution, three-dimensional (3D) model stellar atmospheres including non-grey radiative transfer through opacity binning with four, twelve, and 48 bins. The 48-bin 3D simulation reaches temperatures lower by ~ 300 - 500 K than the corresponding 1D model in the upper atmosphere. Small variations in the opacity binning, adopted line opacities, or chemical mixture can cool the photospheric layers by a further ~ 100 - 300 K and alter the effective temperature by ~ 100 K. A 3D local thermodynamic equilibrium (LTE) spectroscopic analysis of Fe I and Fe II lines gives discrepant results in terms of derived Fe abundance, which we ascribe to non-LTE effects and systematic errors on the stellar parameters. We also determine C, N, and O abundances by simultaneously fitting CH, OH, NH, and CN molecular bands and lines in the ultraviolet, visible, and infrared. We find a small positive 3D-1D abundance correction for carbon (+0.03 dex) and negative ones for nitrogen (-0.07 dex) and oxygen (-0.34 dex). From the analysis of the [O I] line at 6300.3 {\AA}, we derive a significantly higher oxygen abundance than from molecular lines (+0.46 dex in 3D and +0.15 dex in 1D). We rule out important OH photodissociation effects as possible explanation for the discrepancy and note that lowering the surface gravity would reduce the oxygen abundance difference between molecular and atomic indicators.

Scl-1013644: a CEMP-s star in the Sculptor dwarf spheroidal galaxy

Recent studies of the Milky Way and its satellites have paid special attention to the importance of carbon-enhanced metal-poor (CEMP) stars due to their involvement in Galactic formation history and their possible connection with the chemical elements originating in the first stellar generation. In an ongoing study of red giants in the Sculptor dwarf galaxy we have discovered a star with extremely strong CN and CH molecular bands. This star, Scl-1013644, has previously been identified by Geisler et al. (2005) as a star with an enrichment in the heavy elements. Spectrum synthesis has been used to derive the carbon, nitrogen and barium abundances for Scl-1013644. Our findings are [C/Fe] = +0.8, [N/Fe] = -0.3 and [Ba/Fe] = +2.1 with the latter result consistent with the value found by Geisler et al. (2005). These results reveal Scl-1013644 as a CEMP-s star, the third such star discovered in this dwarf galaxy.

LIMITATIONS OF CN AND CH MOLECULAR BAND STRENGTHS AT HIGH METALLICITIES: A CASE STUDY IN NGC 6791

ABSTRACT We present an analysis of the CN and CH molecular band strengths in NGC 6791 from low-resolution Sloan Extension for Galactic Understanding and Exploration spectra as a means to detect chemical variations in the cluster. NGC 6791 is a heavily studied open cluster (OC) due to its unique combination of old age, high mass, and high metallicity. These characteristics place NGC 6791 between the physical properties of most globular and OCs. Recent photometric and spectroscopic studies yield contradicting results, with some claiming to detect signs of multiple populations, as in globular clusters, while others do not. We do not find large spreads in the CN and CH band strength distributions that would suggest multiple populations. By pairing spectral synthesis with the measured CN values, we conclude that the maximum [N/Fe] variation in the cluster is 0.2 dex. Additionally, we find that the saturation of the CH band at high metallicities limits its usefulness in detecting multiple populations and determining C abundances.

Approach for determination of detonation performance and aluminum percentage of aluminized-based explosives by laser-induced breakdown spectroscopy.

Energetic materials containing aluminum powder are hazardous compounds, which have wide applications as propellants, explosives, and pyrotechnics. This work introduces a new method on the basis of the laser-induced breakdown spectroscopy technique in air and argon atmospheres to investigate determination of aluminum content and detonation performance of 1,3,5-trinitro-1,3,5-triazine (RDX)-based aluminized explosives. Plasma emission of aluminized RDX explosives are recorded where atomic lines of Al, C, H, N, and O, as well as molecular bands of AlO and CN are identified. The formation mechanism of AlO and CN molecular bands is affected by the aluminum percentage and oxygen content present in the composition and plasma. Relative intensity of the Al/O is used to determine detonation velocity and pressure of the RDX/Al samples. The released energy in the laser-induced plasma of aluminized RDX composition is related to the heat of explosion and percentage of aluminum.

A novel approach for investigation of chemical aging in composite propellants through laser-induced breakdown spectroscopy (LIBS)

Many methods have been developed in recent years for the analysis and evaluation of energetic materials. This work introduces a novel approach for the analysis and aging of solid composite propellants by laser-induced breakdown spectroscopy (LIBS). The results of the plasma spectrum were used to investigate the behavior of the aged samples. For this purpose, CN and AlO molecular bands of different samples were compared with each other. The samples were examined under inert argon atmosphere to study LIBS signal improvement. Some absent lines such as C and C2 swan bands were detected and reduction of air impact was carried out. Line intensity ratios of samples were changed for all samples during their aging. Differential scanning calorimetry (DSC) method was used to compare them with the output of LIBS’s technique. The results of LIBS and DSC methods show a similar trend in changing mechanical and thermal properties.

Identification of atomic lines and molecular bands of benzene and carbon disulfide liquids by using LIBS

Plasma emission of liquid benzene (C6H6) and carbon disulfide (CS2) have been studied by using the laser-induced breakdown spectroscopy (LIBS) technique in air. Atomic lines of carbon, hydrogen, sulfur, nitrogen, and oxygen and molecular emissions of CN and C2 have been identified. The formation mechanism of C2 and CN molecules has been discussed. The combustion process and high mole fraction of hydrogen in benzene caused a decreasing atomic line intensity of oxygen and an increasing atomic line intensity of hydrogen with respect to the CS2 and air. Additionally, more intense CN molecular bands and weak nitrogen atomic lines in the C6H6 spectrum compared to CS2 have been observed. Furthermore, molecular emissions of C2 have not been observed in the CS2 spectrum. The electron temperature and vibrational temperature have been calculated from the atomic lines and molecular band intensity, respectively. Finally, the validity of the local thermodynamic equilibrium (LTE) assumption in this experiment has been shown.

Emission Spectroscopy of Hypervelocity Impacts on Aluminum, Organic and High-Explosive Targets

Laboratory experiments of hypervelocity impacts on aluminum, nylon and high-explosive targets are presented. Spectral measurements of the impact flash are recorded, together with radiometric measurements to derive the temperature of the flash. Such experiments aim at demonstrating that the impact flash produced by a ballistic missile interception contains the spectral information required to identify the content of the intercepted missile. It is shown that the elements that are part of the aluminum projectile and/or aluminum target are successfully identified from the obtained spectra. For the case of a nylon/aluminum target organic molecular emission lines characteristic of CN and C2 are also identified. The CN molecular band is also observed for the case of a high-explosive target, although the detection of organic elements from such targets is more difficult than for nylon targets. In most cases, the temperature of the impact flash measured using the radiometer is in the range 2500 – 4000K, whereas a comparison between simulated and experimental spectra shows temperatures up to 9000K. Hence a conclusive impact flash temperature could not be obtained.

Qualitative evaluation of maternal milk and commercial infant formulas via LIBS

This study focuses on the use of laser-induced breakdown spectroscopy (LIBS) for the evaluation of the nutrients in maternal milk and some commercially available infant formulas. The results of such evaluation are vital for adequate and healthy feeding for babies during lactation period. Laser-induced breakdown spectroscopy offers special advantages in comparison to the other conventional analytical techniques. Specifically, LIBS is a straightforward technique that can be used in situ to provide qualitative analytical information in few minutes for the samples under investigation without preparation processes. The samples studied in the current work were maternal milk samples collected during the first 3 months of lactation (not colostrum milk) and samples from six different types of commercially available infant formulas. The samples' elemental composition has been compared with respect to the relative abundance of the elements of nutrition importance, namely Mg, Ca, Na, and Fe using their spectral emission lines in the relevant LIBS spectra. In addition, CN and C2 molecular emission bands in the same spectra have been studied as indicators of proteins content in the samples. The obtained analytical results demonstrate the higher elemental contents of the maternal milk compared with the commercial formulas samples. Similar results have been obtained as for the proteins content. It has been also shown that calcium and proteins have similar relative concentration trends in the studied samples. This work demonstrates the feasibility of adopting LIBS as a fast, safe, less costly technique evaluating qualitatively the nutrients content of both maternal and commercial milk samples.

Carbon-enhanced metal-poor stars: the most pristine objects?

Carbon-enhanced metal poor stars (CEMP) form a significant proportion of the metal-poor stars, their origin is not well understood. Three very metal-poor C-rich turnoff stars were selected from the SDSS survey, observed with the ESO VLT (UVES) to precisely determine the element abundances. In turnoff stars (unlike giants) the carbon abundance has not been affected by mixing with deep layers and is therefore easier to interpret. The analysis was performed with 1D LTE static model atmospheres. When available, non-LTE corrections were applied to the classical LTE abundances. The 3D effects on the CH and CN molecular bands were computed using hydrodynamical simulations of the stellar atmosphere (CO5BOLD) and are found to be very important. To facilitate a comparison with previous results, only 1D abundances are used in the discussion. The abundances (or upper limits) of the elements enable us to place these stars in different CEMP classes. The carbon abundances confirm the existence of a plateau at A(C)= 8.25 for [Fe/H] \geq -3.4. The most metal-poor stars ([Fe/H] < -3.4) have significantly lower carbon abundances, suggesting a lower plateau at A(C) \approx 6.5. Detailed analyses of a larger sample of very low metallicity carbon-rich stars are required to confirm (or refute) this possible second plateau and specify the behavior of the CEMP stars at very low metallicity.

G0404 プラズマジェット中のケイ素系耐熱材料周りの放射測定(GS4 粒子流・プラズマ)

In order to investigate the characteristics of radiation around Si-based heat-resistant materials in air plasma freejets, radiation measurements were performed at the three positions around ablating silicon carbide test piece in the air plasma freejets, namely just upstream point of the tip of the ablating test piece, side point just off the surface of the test piece, and a point in the ablation gas at a distance from the flow axis. In each point, characteristic continuum radiation, atomic Si lines, OH molecular bands, and CN molecular bands were observed in common.

ANALYSIS OF THE CN AND CH MOLECULAR BAND STRENGTHS IN STARS OF THE OPEN CLUSTER NGC 6791

Low resolution SDSS/SEGUE spectra have been used to study the behavior of the strengths of the CN and CH molecular bands in stars at different evolutionary stages of the open cluster NGC 6791. We find a significant spread in the strengths of the CN bands, more than twice that expected from the uncertainties, although the bimodalities observed in globular clusters are not clearly observed here. This behavior, is observed not only among red clump objects but also in unevolved stars such as those in the main sequence and lower red giant branch. In contrast, not all the stars studied show significant scatter in their CH strengths.

Accumulation of air in polymeric materials investigated by laser-induced breakdown spectroscopy

We report on spectroscopic analyses of plasmas produced by laser irradiation of nitrogen-free and nitrogen-containing polymer materials. Ultraviolet laser pulses of 5 ns duration and 4 mJ energy were focused onto the samples with a fluence of about 20 Jcm−2. The plasma emission was analyzed with an Echelle spectrometer equipped with a gated detector. Comparing the spectra recorded during ablation in air and argon, it is shown that the spectral line emission of atomic nitrogen originates from the excitation of the ambient air, whereas the CN molecular bands are essentially emitted from the ablation plume. Furthermore, the measurements demonstrate an additional contribution of nitrogen emission from the air molecules accumulated in the polymer. Storage under vacuum over a duration of the order of one day leads to the release of the absorbed air. As a consequence of the air absorption, the measurement of elemental composition of polymers via laser-induced breakdown spectroscopy is particularly difficult. Here, we quantify the atmospheric contribution to the plume emission during polymer analysis.

Influence of biological degradation and environmental effects on the interpretation of archeological bone samples with laser-induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) has emerged in the past decade as a very promising technique for the analysis and characterization of a broad variety of objects of cultural heritage especially bio-archeological samples such as calcified tissues namely teeth and bones. The most important advantages of LIBS from the archeological point of view are its quasi nondestructive nature and its potential for performing in situ measurements. In the present work human calcified tissue samples of recent and archeological bones have been studied via the LIBS technique. The old samples were from three different ancient Egyptian dynasties representing the middle kingdom (1980–1630 BC), the 2nd intermediate period (1630–1539/23 BC) and the pre-Roman period (664 BC). Elements normally used to study dietary habits such as strontium, barium, aluminium and lead were analyzed in the obtained LIBS spectra and the interferences of postmortem or diagenic effects due to the burial place were investigated viaLIBS analysis of soil samples taken from the same locations where the archeological bones have been buried. The obtained results have demonstrated evidently that conclusions about dietary habits must take into account postmortem effects such as biological degradation and environmental leaching (especially from the surrounding soil). Study of CN and C2 molecular bands in the obtained LIBS spectra of the bones revealed that these bands have strong intensities in recent bones spectra contrary to the archaeological ones. This is attributed to the degradation of the tissues and has been confirmed by following up calcium to phosphorus ratios in different bone samples.

Spectroscopic characterization of rovibrational temperatures in atmospheric pressure He∕CH4 plasmas

Atmospheric pressure of helium (He) and methane (CH4) mixture discharge characteristics are investigated using emission spectroscopic methods. Plasmas are produced in a radio frequency capacitively coupled device at atmospheric pressure in the ambient air. Without the CH4 gas introduced in the plasma, the emission spectrum exhibits typical helium discharge characteristics showing helium atomic lines with nitrogen molecular bands and oxygen atomic lines resulting from air impurities. Addition of a small amount (&amp;lt;1%) of CH4 to the supplied He results in the emission of CN (B2∑+-X2∑+: violet system) and CH (A2Δ-X2∏: 430nm system) molecular bands. Analyzing the CN and CH diatomic molecular emission spectra, the vibrational temperature (Tvib) and rotational temperature (Trot) are simultaneously obtained. As input power levels are raised from 20Wto200W, Tvib and Trot are increased from 4230Kto6310K and from 340K to500K, respectively. On the contrary, increasing the CH4 amount brings about the decrease of both temperatures because CH4 is harder to ionize than He. The emission intensities of CN and CH radicals, which are important in plasma processing, are also changed along with the temperature variation. From the results, the atmospheric pressure plasma shows strong nonequilibrium discharge properties, which may be effectively utilized for thermal damage free material treatments.

Characterization of a microwave microstrip helium plasma with gas-phase sample introduction for the optical emission spectrometric determination of bromine, chlorine, sulfur and carbon using a miniaturized optical fiber spectrometer

Continuous flow generation of Br 2, Cl 2 and H 2S coupled to a low-power 2.45 GHz microwave microstrip He plasma exiting from a capillary gas channel in a micro-fabricated sapphire wafer with microstrip lines has been used for the optical emission spectrometric determination of Br, Cl and S using a miniaturized optical fiber CCD spectrometer. Under optimized conditions, detection limits (3σ) of 330, 190 and 220 μg l − 1 for Br, Cl and S, respectively, under the use of the Br II 478.5 nm, Cl I 439.0 nm and S I 469.0 nm lines were obtained and the calibration curves were found to be linear over 2 orders of magnitude. In addition, when introducing CO 2 and using the rotational line of the CN molecular band at 385.7 nm the detection limit for C was 4.6 μg l − 1 . The procedure developed was found to be free from interferences from a number of metal cations and non-metal anions. Only the presence of CO 3 2− and CN − was found to cause severe spectral interferences as strong CN and C 2 molecular bands occurred as a result of an introduction of co-generated CO 2 and HCN into the plasma. With the procedure described Br, Cl and S could be determined at a concentration level of 10–30 mg l − 1 with accuracy and precision better than 2%.

Spectral signature of native CN bonds for bacterium detection and identification using femtosecond laser-induced breakdown spectroscopy

A sample of Escherichia coli has been analyzed by laser-induced breakdown spectroscopy (LIBS) using femtosecond pulses. The spectrum shows strong CN molecular bands due to the direct ablation of native CN molecular bonds from the bacteria in contrast with weak atomic lines from carbon. The native nature of the observed CN bonds is supported by the kinetic behavior of the CN band head which rapidly decays with a time constant of 94 ns, while for a pure graphite sample the CN band head increases with a delay of 450 ns due to recombination with the ambient air. Moreover, about hundred resolved lines belonging to 12 atomic or molecular species are recorded, providing a valuable spectral signature to identify the bacterium.

CH stars at high Galactic latitudes

In the present work we report on several CH stars identified in a sample of Faint High Latitude Carbon stars from Hamburg survey and discuss their medium resolution spectra covering a wavelength range 4000 - 6800 \AA . Estimation of the depths of bands (1,0) $^{12}$C$^{12}$C ${\lambda}$4737 and (1,0) $^{12}$C$^{13}$C ${\lambda}$4744 in these stars indicate isotopic ratio $^{12}$C/$^{13}$C ${\sim}$ 3, except for a few exceptions; these ratios are consistent with existing theories of CH stars evolution. The stars of Hamburg survey, a total of 403 objects were reported to be carbon star candidates with strong C$_{2}$ and CN molecular bands. In the first phase of observation, we have acquired spectra of ninety one objects. Inspection of the objects spectra show fifty one objects with C$_{2}$ molecular bands in their spectra of which thirteen stars have low flux below about 4300 \AA . Twenty five objects show weak or moderate CH and CN bands, twelve objects show weak but detectable CH bands in their spectra and there are three objects which do not show any molecular bands due to C$_{2}$, CN or CH in their spectra. Objects with C$_{2}$ molecular bands and with good signals bluewards of 4300 \AA which show prominent CH bands in their spectra are potential candidate CH stars. Thirty five such candidates are found in the present sample of ninty one objects observed so far. The set of CH stars identified could be the targets of subsequent observation at high resolution for a detail and comprehensive analysis for understanding their role in early Galactic chemical evolution.

CN variations in NGC 7006

Rotationally induced mixing with subsequent dredge-up of nucleosynthesized material is discussed as a second parameter of the horizontal branch morphology in globular clusters. CNO abundances have been proposed as tracers of the dredge up of processed material. \ngc is a prominent example of a second parameter GC: Its HB morphology is too red for its metallicity. We present spectroscopic measurements of CN molecular band strengths S(3839) and CH band CH(4300) strengths for 12 giants in \ngc to test rotationally-driven mixing as a second parameter in this cluster. Our observations reveal (i) a scatter in star-to-star CN absorption strengths with the same amplitude as seen in other GCs of the same metallicity, but different HB morphologies; (ii) a possible continuous distribution of CN absorption strength with a preference for CN-enriched stars, and (iii) a possible weak radial gradient in the number ratio of CN-strong and CN-weak stars. We argue against the hypothesis that CN-variations are directly correlated with the second parameter effect of the HB morphology. However, the small sample of stars measured in \ngc prevents us from drawing firm conclusions. Finally, we identify one star of our sample as a foreground dwarf carbon star.

An Abundance Analysis of the New Carbon‐rich Proto–Planetary Nebula IRAS 06530−0213

In this paper we present a study of the proto-planetary nebula (PPN) IRAS 06530-0213 based on low- and high-resolution spectra. The low-resolution spectrum shows that the star is an F5 supergiant with molecular C2 and C3 and enhanced s-process lines. From the high-resolution spectra, the following atmospheric parameters were determined: Teff = 6900 K, log g = 1.0, and ξt = 4.5. Abundance analysis shows that IRAS 06530-0213 is metal-poor ([Fe/H] = -0.9) and overabundant in carbon ([C/Fe] = 1.3), nitrogen ([N/Fe] = 1.0), and s-process elements ([s-process/Fe] = 1.9), indicating asymptotic giant branch (AGB) nucleosynthesis and deep convective mixing. From the analysis of circumstellar C2 and CN molecular bands in the spectrum of IRAS 06530-0213, an envelope expansion velocity of Vexp = 14 ± 1 km s-1 was determined, a typical value for post-AGB stars. Also typical of PPNs is the double-peaked spectral energy distribution. The properties of both the photosphere and circumstellar envelope suggest that IRAS 06530-0213 is unambiguously a low-mass, carbon-rich PPN. For comparison purposes, new, high-resolution spectra of the well-known PPN HD 56126 (IRAS 07134+1005) were also analyzed and compared with previous results.