CH Lines Research Articles

Abundances of neutron-capture elements in G 24-25

The differences between the neutron-capture element abundances of halo stars are important to our understanding of the nucleosynthesis of elements heavier than the iron group. We present a detailed abundance analysis of carbon and twelve neutron-capture elements from Sr up to Pb for a peculiar halo star G24-25 with [Fe/H] = -1.4 in order to probe its origin. The equivalent widths of unblended lines are measured from high resolution NOT/FIES spectra and used to derive abundances based on Kurucz model atmospheres. In the case of CH, Pr, Eu, Gd, and Pb lines, the abundances are derived by fitting synthetic profiles to the observed spectra. Abundance analyses are performed both relative to the Sun and to a normal halo star G16-20 that has similar stellar parameters as G24-25. We find that G24-25 is a halo subgiant star with an unseen component. It has large overabundances of carbon and heavy s-process elements and mild overabundances of Eu and light s-process elements. This abundance distribution is consistent with that of a typical CH giant. The abundance pattern can be explained by mass transfer from a former asymptotic giant branch component, which is now a white dwarf.

Spectral and spatial fluctuations of cosmic microwave background radiation. RATAN-600 radio telescope observations with a Fourier spectral analyzer

The “circumpolar survey” technique allowed us to achieve a rather high antenna temperature sensitivity of 0.5 mK at 6 cm on a fixed antenna with a relatively narrow frequency resolution band (600 kHz) and an angular resolution of 45″ × 7′. Starting from 2007 we use a Fourier spectral analyzer with a survey band 10 times broader than that of previous observations. This upgrade allowed us to rapidly perform repeated test observations, which confirmed the power-law nature and the frequency structure of spatial spectra in two strips in the vicinity of the celestial pole in the 4′–16′ interval of angular periods. These observations also showed that the Galactic CH molecular line that was by chance captured in our survey strip (Λ-doubling of rotational transition) has nothing to do with the emission spectra we obtained. The angular pattern of emission in two main lines of Λ-doubling (4847.84 and 4870.12 MHz) is absolutely different, whereas there is practically no maser amplification in the CH line to explain this fact. Our observations also confirm the H110 α line (4874.157 MHz), which forms in the tenuous ionized Galactic hydrogen at such relatively high latitudes. Other features of the spatial spectra also appear to be quite real, although their interpretation remains unclear and requires further studies.

U-Band Wavelength References Based on Photonic Bandgap Fiber Technology

In this paper, we surveyed potential wavelength references in U-band wavelength region. The hollow-core photonic bandgap fiber (PBGF) filled with methane (CH4) gas is used as a gas cell. The experimental results clearly indicate that the weak absorption lines of methane can be used as U-band wavelength division multiplexing (WDM) channel references due to the long interaction path length provided by PBGF. The absorption lines of CH4 are useful as wavelength references in the 1625-1700 nm region. In addition, we have measured the pressure broadening and the wavelength stability of absorption lines, and find that absorption lines are particularly insensitive to external perturbation. This technique is useful for wavelength calibration of components of communication system, or as monitor the wavelength of the channels. It may be implemented in next-generation WDM communication systems.

The spectrum of comet C/2009 R1 (McNaught) in 4140–5240 Å wavelength region

The spectroscopic observations of comet C/2009 R1 (McNaught) were carried out with the 2m Zeiss-RCC Telescope of Pik Terskol Observatory operated by the International Center for Astronomical and Medico-Ecological Research (Ukraine, Russia). The Multi Mode Cassegrain spectrometer was used to obtain spectra of moderate spectral resolving power with a wavelength coverage from 4140 to 5240Å. The spectrum is characterized by the extremely low continuum level and strong molecular features. 192 emission lines of C2, CN, CH, NH2, CO+, and CH+ have been identified by the comparison of the observed and theoretical spectra of the molecules. The ratios of the gas production rates of Q(C2)/Q(CN)=1.32, Q(CH)/Q(CN)=0.49, and Q(NH2)/Q(CN)=0.81 were derived using a Haser model.

CH abundance gradient in TMC-1

We observed the 9-cm Lambda-doubling lines of CH along the dense filament of TMC-1. The CH column densities were compared with the total H2 column densities derived using the 2MASS NIR data and previously published SCUBA maps and with OH column densities derived using previous observations with Effelsberg. We also modelled the chemical evolution of TMC-1 adopting physical conditions typical of dark clouds using the UMIST Database for Astrochemistry gas-phase reaction network to aid the interpretation of the observed OH/CH abundance ratios. The CH column density has a clear peak in the vicinity of the cyanopolyyne maximum of TMC-1. The fractional CH abundance relative to H2 increases steadily from the northwestern end of the filament where it lies around 1.0e-8, to the southeast where it reaches a value of 2.0e-8. The OH and CH column densities are well correlated, and we obtained OH/CH abundance ratios of ~ 16 - 20. These values are clearly larger than what has been measured recently in diffuse interstellar gas and is likely to be related to C to CO conversion at higher densities. The good correlation between CH and OH can be explained by similar production and destruction pathways. We suggest that the observed CH and OH abundance gradients are mainly due to enhanced abundances in a low-density envelope which becomes more prominent in the southeastern part and seems to continue beyond the dense filament. An extensive envelope probably signifies an early stage of dynamical evolution, and conforms with the detection of a large CH abundance in the southeastern part of the cloud. The implied presence of other simple forms of carbon in the gas phase provides a natural explanation for the observation of "early-type" molecules in this region.

Fast and sensitive time-multiplexed gas sensing of multiple lines using a miniature telecom diode laser between 1529 nm and 1565 nm

High-sensitive multi-species detection around 1550 nm using a modulated grating Y-branch, MG-Y, diode laser tunable between 1529 nm and 1565 nm is presented. The MG-Y diode laser is based on the Vernier effect of two modulated gratings, and exhibits quasi-continuous tuning over 36 nm. Multi-species detection is achieved by fast sequential scanning of single absorption lines of CH4, CO, C2H2, and CO2 distributed over the tuning range of the diode laser. The laser wavelength is scanned about 10 GHz around each absorption line for 5 ms and this is followed by a discrete large jump in operating wavelength to the next line.The MG-Y diode laser has a good repeatability in output frequency between sequential scan segments (<10 MHz) enabling averaging of the scans. The setup employs digital wavelength modulation spectroscopy, dWMS, with Fourier-based WMS retrieval, applicable through the use of data acquisition cards and coherent sampling.Absorbance sensitivity using 2f-WMS signals of 7×10−7 in 30 s (all precisions in this paper are at the 1σ level) is demonstrated for sensing of four gases and 2×10−7 when only one gas is detected. Corresponding numbers for 0.5 s of averaging are 4×10−6 and 1×10−6.

The Zeeman effect and hyperfine interactions in J = 1–0 transitions of CH+ and its isotopologues

The J = 1-0 transitions of (12)CH(+), (13)CH(+), and (12)CD(+) in the ground X(1)Σ(+) state have been unambiguously identified by using an extended negative glow discharge as an ion source. Unexpectedly large Zeeman splittings have been observed, and the (13)CH(+) line exhibits nuclear spin-rotation hyperfine splitting in addition to the Zeeman effect. The nuclear spin-rotation coupling constant was determined to be 1.087(50) MHz for the (13)C species. The rotational g-factor is found to be -7.65(29), in terms of the nuclear magneton for the J = 1 and v = 0 state, more than an order of magnitude larger than values for typical diamagnetic closed shell molecules. These larger than usual magnetic interactions for a (1)Σ molecule are caused by the large rotational energy and relatively small excitation energy of the excited A(1)Π state. The effective g-factor and the spin-rotation coupling constant obtained by ab initio calculations agree very well with the experimentally determined values.

Remotely operable compact instruments for measuring atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; column densities at surface monitoring sites

Abstract. Remotely operable compact instruments for measuring atmospheric CO2 and CH4 column densities were developed in two independent systems: one utilizing a grating-based desktop optical spectrum analyzer (OSA) with a resolution enough to resolve rotational lines of CO2 and CH4 in the regions of 1565–1585 and 1674–1682 nm, respectively; the other is an application of an optical fiber Fabry-Perot interferometer (FFPI) to obtain the CO2 column density. Direct sunlight was collimated via a small telescope installed on a portable sun tracker and then transmitted through an optical fiber into the OSA or the FFPI for optical analysis. The near infrared spectra of the OSA were retrieved by a least squares spectral fitting algorithm. The CO2 and CH4 column densities deduced were in excellent agreement with those measured by a Fourier transform spectrometer with high resolution. The rovibronic lines in the wavelength region of 1570–1575 nm were analyzed by the FFPI. The I0 and I values in the Beer-Lambert law equation to obtain CO2 column density were deduced by modulating temperature of the FFPI, which offered column CO2 with the statistical error less than 0.2% for six hours measurement.

A search for interstellar anthracene towards the Perseus anomalous microwave emission region

We report the discovery of a new broad interstellar (or circumstellar) band at 7088.8 +- 2.0 \AA coincident to within the measurement uncertainties with the strongest band of the anthracene cation (C$_{14}$H$_{10}$$^+$) as measured in gas-phase laboratory spectroscopy at low temperatures (Sukhorukov et al.2004). The band is detected in the line of sight of star Cernis 52, a likely member of the very young star cluster IC 348, and is probably associated with cold absorbing material in a intervening molecular cloud of the Perseus star forming region where various experiments have recently detected anomalous microwave emission. From the measured intensity and available oscillator strength we find a column density of N$_{an^+}$= 1.1(+-0.4) x 10$^{13}$ cm$^{-2}$ implying that ~0.008% of the carbon in the cloud could be in the form of C$_{14}$H$_{10}$$^+$. A similar abundance has been recently claimed for the naphthalene cation (Iglesias-Groth et al. 2008) in this cloud. This is the first location outside the Solar System where specific PAHs are identified. We report observations of interstellar lines of CH and CH$^+$ that support a rather high column density for these species and for molecular hydrogen. The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 \AA suggests the presence of a ``zeta'' type cloud in the line of sight (consistent with steep far-UV extinction and high molecular content). The presence of PAH cations and other related hydrogenated carbon molecules which are likely to occur in this type of clouds reinforce the suggestion that electric dipole radiation from fast spinning PAHs is responsible of the anomalous microwave emission detected toward Perseus.

Herschel-SPIRE FTS spectroscopy of the carbon-rich objects AFGL 2688, AFGL 618, and NGC 7027

We present far-infrared and submillimetre spectra of three carbon-rich evolved objects, AFGL 2688, AFGL 618 and NGC 7027. The spectra were obtained with the SPIRE Fourier transform spectrometer on board the Herschel Space Observatory, and cover wavelengths from 195-670 um, a region of the electromagnetic spectrum hitherto difficult to study in detail. The far infrared spectra of these objects are rich and complex, and we measure over 150 lines in each object. Lines due to 18 different species are detected. We determine physical conditions from observations of the rotational lines of several molecules, and present initial large velocity gradient models for AFGL 618. We detect water in AFGL 2688 for the first time, and confirm its presence in AFGL 618 in both ortho and para forms. In addition, we report the detection of the J=1-0 line of CH+ in NGC 7027.

Where is the warm H2? A search for H2emission from disks around Herbig Ae/Be stars

Mid-IR emission lines of H2 are useful probes to determine the mass of warm gas present in the surface layers of disks. Numerous observations of Herbig Ae/Be stars (HAeBes) have been performed, but only 2 detections of mid-IR H2 toward HD97048 and AB Aur have been reported. We aim at tracing the warm gas in the disks of 5 HAeBes with gas-rich environments and physical characteristics close to those of AB Aur and HD97048, to discuss whether the detections toward these 2 objects are suggestive of peculiar conditions for the gas. We search for the H2 S(1) emission line at 17.035 \mu\m with VISIR, and complemented by CH molecule observations with UVES. We gather the H2 measurements from the literature to put the new results in context and search for a correlation with some disk properties. None of the 5 VISIR targets shows evidence for H2 emission. From the 3sigma upper limits on the integrated line fluxes we constrain the amount of optically thin warm gas to be less than 1.4 M_Jup in the disk surface layers. There are now 20 HAeBes observed with VISIR and TEXES instruments to search for warm H2, but only two detections (HD97048 and AB Aur) were made so far. We find that the two stars with detected warm H2 show at the same time high 30/13 \mu\m flux ratios and large PAH line fluxes at 8.6 and 11.3 \mu\m compared to the bulk of observed HAeBes and have emission CO lines detected at 4.7 \mu\m. We detect the CH 4300.3A absorption line toward both HD97048 and AB Aur with UVES. The CH to H2 abundance ratios that this would imply if it were to arise from the same component as well as the radial velocity of the CH lines both suggest that CH arises from a surrounding envelope, while the detected H2 would reside in the disk. The two detections of the S(1) line in the disks of HD97048 and AB Aur suggest either peculiar physical conditions or a particular stage of evolution.

Sounding of Titan’s atmosphere at submillimeter wavelengths from an orbiting spacecraft

An investigation of the capabilities and science goals of a submillimeter-wave heterodyne sounder onboard a Titan orbiter is presented. Based on a model of Titan’s submillimeter spectrum, and including realistic instrumental performances, we show that passive limb observations of Titan’s submillimeter radiation would bring novel and unique information on the dynamical and chemical state of Titan’s atmosphere, particularly in the so far poorly probed 500–900 km region. The 300–360, 540–660 and 1080–1280 GHz spectral ranges appear especially promising, and could be explored with an instrument equipped with a tunable local oscillator system. Vertical temperature profiles can be determined up to ∼1200 km using rotational lines of CH 4, CO, and HCN. Winds can be measured over the 200–1200 km altitude range with an accuracy of 3–5 m/s from Doppler shift measurements of any strong optically thin line. Numerous molecular species are accessible, including H 2O, NH 3, CH 3C 2H, CH 2NH, and several nitriles (HC 3N, HC 5N, CH 3CN, and C 2H 3CN). Many of them are expected to be detectable in a large fraction of the atmosphere and in some cases at all levels, providing an observational link between stratospheric and thermospheric chemistry. Isotopic variants of some of these species can also be measured, providing new measurements of H, C, N, and O isotopic ratios. Mapping of the thermal, wind, and composition fields, best achieved from a polar orbit and with an articulated antenna, would provide a new view of the couplings between chemistry and dynamics over an extended altitude range of Titan’s atmosphere. Additional science goals at Saturn and Enceladus are briefly discussed.

Infrared Spectra of12CF2═12CH2and12CF2═13CH2, Quantum-Chemical Calculations of Anharmonicity, and Analyses of Resonances

Infrared spectra obtained in gas and liquid argon phases are reported for (12)CF(2) horizontal line(12)CH(2) and (12)CF(2) horizontal line(13)CH(2). These spectra firmly establish the positions of nu(3)(A(1)) and nu(6)(A(2)) for both isotopomers. Using anharmonicity constants from MP2 calculations, Fermi resonances affecting nu(1)(A(1)), nu(2)(A(1)), nu(3), and nu(8)(B(1)) are analyzed. Deperturbed fundamental frequencies from these analyses are used in conjunction with unaffected fundamentals and ab initio anharmonicity data to predict all 12 "observed" harmonic frequencies. A Darling-Dennison type resonance between 2nu(6) and nu(11) + nu(12) is diagnosed, the calculation of which from ab initio data requires modification of the existing second-order treatment of such constants, where Fermi resonance type terms are also present. Predictions are made of many overtone and combination band frequencies, aiding assignment of observed spectra. From the isolated CH stretching frequency obtained here of 3125.4 cm(-1), the C-H equilibrium bond length is predicted to be 1.0762(11) A.

High-resolution 3-μm spectra of Jupiter: Latitudinal spectral variations influenced by molecules, clouds, and haze

We present latitudinally-resolved high-resolution ( R = 37,000) pole-to-pole spectra of Jupiter in various narrow longitudinal ranges, in spectral intervals covering roughly half of the spectral range 2.86–3.53 μm. We have analyzed the data with the aid of synthetic spectra generated from a model jovian atmosphere that included lines of CH 4, CH 3D, NH 3, C 2H 2, C 2H 6, PH 3, and HCN, as well as clouds and haze. Numerous spectral features of many of these molecular species are present and are individually identified for the first time, as are many lines of H 3 + and a few unidentified spectral features. In both polar regions the 2.86–3.10-μm continuum is more than 10 times weaker than in spectra at lower latitudes, implying that in this wavelength range the single-scattering albedos of polar haze particles are very low. In contrast, the 3.24–3.53 μm the weak polar and equatorial continua are of comparable intensity. We derive vertical distributions of NH 3, C 2H 2 and C 2H 6, and find that the mixing ratios of NH 3 and C 2H 6 show little variation between equatorial and polar regions. However, the mixing ratios of C 2H 2 in the northern and southern polar regions are ∼6 and ∼3 times, respectively, less than those in the equatorial regions. The derived mixing ratio curves of C 2H 2 and C 2H 6 extend up to the 10 −6 bar level, a significantly higher altitude than most previous results in the literature. Further ground-based observations covering other longitudes are needed to test if these mixing ratios are representative values for the equatorial and polar regions.

Doppler splitting in diffuse interstellar bands

We demonstrate evident Doppler splitting in the profiles of many narrow diffuse interstellar bands (DIBs). Their components are compared with those of atomic and molecular lines of interstellar origin. It is shown that it is likely that the species that shares both wavelength shifts and strength ratios of the Doppler components seen in the DIB profiles is the CH radical. Because of this profile resemblance, it is recommended that CH lines can be used to shift spectra to the rest velocity frame for interstellar features, especially to determine the DIB rest wavelengths on the basis of the CH line at 4300.3132 A in the spectrum of HD 147889. Our results strongly support a molecular origin of diffuse bands.

HIGH-RESOLUTION CH OBSERVATIONS OF TWO TRANSLUCENT MOLECULAR CLOUDS

We present high-resolution (13 × 16) observations of the CH 2Π1/2 (F = 1-1) emission line at 3335 MHz in two high-latitude translucent clouds, MBM 3 and 40. At the assumed cloud distances, the angular resolution corresponds to ~0.05 pc, nearly an order of magnitude better than previous studies. Comparisons of the CH emission with previously obtained CO(1-0) data are difficult to interpret: the CO and CH line emission correlates in MBM 40 but not in MBM 3. In both clouds, there is a spatial offset in the peak emission, and perhaps in velocity for MBM 40. The difference in emission characteristics for the two tracers are noticeable in these two nearby clouds because of the high spatial resolution. Since both CH and CO are deemed to be reliable tracers of H2, our results indicate that more care should be taken when using one of these tracers to determine the mass of a nearby molecular cloud.

Determination of the electron temperature by optical emission spectroscopy in a 13.56 MHz dusty methane plasma: Influence of the power

Optical emission spectroscopy is applied to the study of a radiofrequency (13.56 MHz) discharge in methane used to obtain hydrogenated carbon films and particles. The methane dissociation allows the creation of species in the plasma bulk as H2, H, and CH. The emission lines of these species are studied as a function of time and of incident rf power. The electron temperature is determined from the two line radiance ratio method and the corona balance model using the Balmer lines (Hα, Hβ, and Hγ). The incident rf power enhancement in the range 40–120 W leads to the increase in the emission line intensities as the electron temperature decreases. The temporal variations of CH and hydrogen emission lines, of the dc self-bias voltage, and of the electron temperature are correlated both with the particle behavior and growth in the plasma, and with the coating that grows onto the powered electrode.

Broadband wavelength conversion based on apodized χ^(2) grating

We achieved apodization in a quasi-phase-matched (QPM) wavelength converter by changing the duty cycle of a χ(2) grating. The new design yields a large bandwidth and a flat phase-matching response with high conversion efficiency. Widely tunable 3-μm-band difference frequency generation was realized using an apodized QPM LiNbO3 ridge waveguide. We also demonstrated the simultaneous detection of the absorption lines of CH4 and C2H4 and obtained a broadband absorption spectrum of over 100 nm using the widely tunable source.

Vibration−Rotation Energy Pattern in Acetylene:13CH12CH up to 10 120 cm−1

All 18,219 vibration-rotation absorption lines of (13)CH(12)CH published in the literature, accessing substates up to 9400 cm(-1) and including some newly assigned, were simultaneously fitted to J-dependent Hamiltonian matrices exploiting the well-known vibrational polyad or cluster block-diagonalization, in terms of the pseudo quantum numbers N(s) = v(1) + v(2) + v(3) and N(r) = 5v(1) + 3v(2) + 5v(3) + v(4) + v(5), also accounting for k = l(4) + l(5) parity and e/f symmetry properties. Some 1761 of these lines were excluded from the fit, corresponding either to blended lines, for about 30% of them, or probably to lines perturbed by Coriolis for the remaining ones. The dimensionless standard deviation of the fit is 1.10, and 317 vibration-rotation parameters are determined. These results significantly extend those of a previous report considering levels below only 6750 cm(-1) [Fayt, A.; et al. J. Chem. Phys. 2007, 126, 114303]. Unexpected problems are reported when inserting in the global fit the information available on higher-energy polyads, extending from 9300 to 10 120 cm(-1). They are tentatively interpreted as resulting from a combination of the relative evolution of the two effective bending frequencies and long-range interpolyad low-order anharmonic resonances. The complete database, made of 18,865 vibration-rotation lines accessing levels up to 10 120 cm(-1), is made available as Supporting Information.

Terahertz time-domain spectroscopy of high-pressure flames

Laser spectroscopy in the visible and near infrared is widely used as a diagnostic tool for combustion devices, but this approach is difficult at high pressures within a sooty flame itself. High soot concentrations render flames opaque to visible light, but they remain transparent to far-infrared or terahertz (THz) radiation. The first far-infrared absorption spectra, to the best of our knowledge, of sooty, non-premixed, ethylene high-pressure flames covering the region of 0.2–2.5 THz is presented. A specially designed high-pressure burner which is optically accessible to THz radiation has been built allowing flame transmission measurements up to pressures of 1.6 MPa. Calculations of the theoretical combustion species absorption spectra in the 0.2–3 THz range have shown that almost all the observable features arise from H2O. A few OH (1.84 and 2.51 THz), CH (2.58 THz), and NH3 (1.77 and 2.95 THz) absorption lines are also observable in principle. A large number of H2O absorption lines are observed in the ground vibrational in a laminar non-premixed, sooty flame (ethylene) at pressures up to 1.6 MPa.