Measured Line Strengths Research Articles

Coarsely scannable comb-locked ECDL with fixed local oscillator for CRDS measurement of CO line strength

Coarsely scannable comb-locked ECDL with fixed local oscillator for CRDS measurement of CO line strength

Mg/Fe] and variable initial mass function: Revision of [α/Fe] for massive galaxies

Observations of nearby massive galaxies have revealed that they are older and richer in metals and magnesium than their low-mass counterparts. In particular, the overabundance of magnesium compared to iron, [Mg/Fe], is interpreted to reflect the short star formation history that the current massive galaxies underwent early in the Universe. We present a systematic revision of the [Mg/Fe] – velocity dispersion (σ) relation based on stacked spectra of early-type galaxies with a high signal-to-noise ratio from the Sloan Digital Sky Survey. Using the penalized pixel-fitting (pPXF) method and the MILES single stellar population models, we fit a wide optical wavelength range to measure the net α-abundance. The combination of pPXF and α-enhanced MILES models incorrectly leads to an apparently decreasing trend of [α/Fe] with velocity dispersion. We interpret this result as a consequence of variations in the individual abundances of the different α-elements. This warrants caution for a naive use of full spectral fitting algorithms paired with stellar population models that do not take individual elemental abundance variations into account, especially when deriving averaged quantities such as the mean [α/Fe] of a stellar population. In addition, and based on line-strength measurements, we quantify the impact of a non-universal initial mass function on the recovered abundance pattern of galaxies. In particular, we find that a simultaneous fit of the slope of the initial mass function and the [Mg/Fe] results in a shallower [Mg/Fe]–σ relation. Therefore, our results suggest that star formation in massive galaxies lasted longer than what has been reported previously, although it still occurred significantly faster than in the solar neighbourhood.

High-temperature line strength and line shape parameters measurements of Ar- and N2-perturbed CO2 lines near 4.18 µm in a shock tube

Line strengths and line shape parameters of Ar- and N2-perturbed CO2 R-branch transitions (82 ≤J″≤ 90) in the ν3 fundamental band were measured in a shock tube from 730 K to 2500 K and pressure below 1.13 atm using laser absorption spectroscopy (LAS). The retrieved absorption curves were fitted with the Voigt and the quadratic speed-dependent Voigt (qSDV) profiles to obtain the line strengths, broadening, and shift coefficients. Line strengths were compared to values in HITEMP, HITRAN2020, and Ames2021 databases, and the HITEMP shows the best agreement with the measured results. Ar- and N2-broadening and shift coefficients were regressed into the power law and the double power law form to study the temperature dependence of the targeted lines. The speed-dependence parameter aw was temperature-dependent. The J-dependence of the derived broadening and shift coefficients was discussed. The results of this work will aid the development of the absorption model in the far-wing region and the design of CO2 LAS sensors for high-temperature measurement.

Measurements of absolute line strength of the ν1 fundamental transitions of OH radical and rate coefficient of the reaction OH + H2O2 with mid-infrared two-color time-resolved dual-comb spectroscopy

Absolute line strengths of several transitions in the ν1 fundamental band of the hydroxyl radical (OH) have been measured by simultaneous determination of hydrogen peroxide (H2O2) and OH upon laser photolysis of H2O2. Based on the well-known quantum yield for the generation of OH radicals in the 248-nm photolysis of H2O2, the line strength of the OH radicals can be accurately derived by adopting the line strength of the well-characterized transitions of H2O2 and analyzing the difference absorbance time traces of H2O2 and OH obtained upon laser photolysis. Employing a synchronized two-color dual-comb spectrometer, we measured high-resolution time-resolved absorption spectra of H2O2 near 7.9 µm and the OH radical near 2.9 µm, simultaneously, under varied conditions. In addition to the studies of the line strengths of the selected H2O2 and OH transitions, the kinetics of the reaction between OH and H2O2 were investigated. A pressure-independent rate coefficient kOH+H2O2 was determined to be [1.97 (+0.10/−0.15)] × 10−12 cm3 molecule−1 s−1 at 296 K and compared with other experimental results. By carefully analyzing both high-resolution spectra and temporal absorbance profiles of H2O2 and OH, the uncertainty of the obtained OH line strengths can be achieved down to <10% in this work. Moreover, the proposed two-color time-resolved dual-comb spectroscopy provides a new approach for directly determining the line strengths of transient free radicals and holds promise for investigations on their self-reaction kinetics as well as radical–radical reactions.

Lamb-dip saturated-absorption cavity ring-down rovibrational molecular spectroscopy in the near-infrared

The high-detection-sensitivity saturated-absorption cavity ring-down (SCAR) technique is extended to Lamb-dip spectroscopy of rovibrational molecular transitions in the near-infrared region. Frequency-comb-referenced sub-Doppler saturation measurements, performed on the acetylene ( ν 1 + ν 3 + ν 4 ← ν 4 ) R(14)e line at 6562 cm − 1 , are analyzed by a SCAR global line profile fitting routine, based on a specially developed theoretical model. Compared to a conventional cavity ring-down evaluation, our approach yields dip profiles with a linewidth freed from saturation broadening effects, reduced by 40%, and a signal-to-noise ratio increased by 90%. Ultimately, an overall (statistical and systematic) fractional uncertainty as low as 7 × 10 − 12 is achieved for the absolute line-center frequency. At the same time, our method is also able to accurately infer the linear (non-saturated) behavior of the gas absorption, providing Lamb-dip-based line strength measurements with a relative uncertainty of 0.5%.

Measurement of temperature-dependent line parameters of ammonia transitions near 1103 cm−1

Accurate knowledge of the line parameters of ammonia (NH3) transitions is important for developing precise laser-based NH3 sensors. We report the measurement of line-strengths and temperature-dependent broadening coefficients of NH3 with N2, air, Ar, and CO2 for six transitions in the ν2 fundamental band near 1103 cm−1. The absorption feature contributed by the target transitions is of particular interest for combustion emission applications due to its strong absorbance and the minimal spectral interference from other species such as H2O, CO2, and NOX. In this work, we measured NH3 absorption spectra with different collisional partners at the temperature range of 296–573 K using a quantum cascade laser. Spectroscopic parameters were determined by conducting multi-line fitting of the measured spectra using the Galatry lineshape function due to the evident line narrowing effect. Our study will aid the development of mid-infrared NH3 sensors particularly for high-temperature applications.

Forward and back: kinematics of the Palomar 5 tidal tails

ABSTRACTThe tidal tails of Palomar 5 (Pal 5) have been the focus of many spectroscopic studies in an attempt to identify individual stars lying along the stream and characterize their kinematics. The well-studied trailing tail has been explored out to a distance of 15○ from the cluster centre, while less than 4° have been examined along the leading tail. In this paper, we present results of a spectroscopic study of two fields along the leading tail that we have observed with the AAOmega spectrograph on the Anglo-Australian telescope. One of these fields lies roughly 7○ along the leading tail, beyond what has been previously been explored spectroscopically. Combining our measurements of kinematics and line strengths with Pan-STARRS1 photometric data and Gaia EDR3 astrometry, we adopt a probabilistic approach to identify 16 stars with a high probability of belonging to the Pal 5 stream. Eight of these stars lie in the outermost field and their sky positions confirm the presence of ‘fanning’ in the leading arm. We also revisit previously published radial velocity studies and incorporate Gaia EDR3 astrometry to remove interloping field stars. With a final sample of 109 bona fide Pal 5 cluster and tidal stream stars, we characterize the 3D kinematics along the the full extent of the system. We provide this catalogue for future modeling work.

Diode laser measurements of high-temperature line strength and self-broadening coefficient of carbon dioxide near 2.0 μm

A tunable diode laser combined with a self-made heated static cell was used to measure the high-resolution absorption spectra of ten strong lines of carbon dioxide belonging to the 20012 ← 00001 band near 2.0 μm in the temperature range of 296 K to 1100 K. Using the Voigt profile of the measured direct absorption spectrum and the line strength, self-broadening coefficient and temperature dependent exponent of the ten lines were determined. The measured spectral line strength and self-broadening coefficients of 12C16O2 were compared well with the available values listed in the HITEMP/HITRAN database. The uncertainties and primary error sources in the determination of those parameters were discussed respectively. The temperature dependence exponents of self-broadening coefficients were compared with the calculated values obtained from HITEMP2010. We found that there was not a monotonic relationbetween the temperature exponent n and the J values, which was different with the result reported in the previous papers.

Quantum cascade laser measurements of CH4 linestrength and temperature-dependent self-broadening and narrowing parameters at 7.16 µm

Absorption lineshapes for 10 CH4 transitions in the v2 and v4 band were measured at high-resolution in a thermodynamically-controlled optical cell using a quantum cascade laser near 7.16 µm. Linestrength, self-broadening, -narrowing, pressure-shift coefficients and their temperature dependence were recorded over a temperature and pressure range of 290–1050 K and 3–80 kPa, respectively. Voigt, Rautian, speed-dependent Voigt profiles were least-squares fit to the measured absorption spectra to determine the best-fit lineshape parameters. Significant collisional-narrowing and speed-dependent effects were observed but no line mixing behaviour was found in pure CH4 at the experimental conditions. The self-pressure-shift coefficients were found to change signs from negative to positive with increasing temperature and the Frost's formula fit well their temperature dependence for the studied transitions. The measured spectra provided tests of the CH4 line lists near 1397 cm−1 released in HITEMP 2020 and the recorded spectroscopic parameters compared well with the values in the database. Several weak transitions excluded from the HITEMP database were observed at elevated temperatures with the line positions given here. The analyses of uncertainties in all the measured spectroscopic parameters were also demonstrated in this work.

Structure, first-principles calculations and yellow spectral properties of Dy3+: CaLaGa3O7 single crystal

High optical quality Dy3+-doped CaLaGa3O7 (abbreviated as Dy: CLGO below) crystal was grown successfully by the Czochralski technique along the (0 0 1) orientation. The lattice parameters of the as-grown crystal were obtained by Rietveld refinement to its XRD pattern. The electronic structures including band structure and density of state (DOS) were calculated by using first-principles calculations based on density functional theory (DFT). The spectroscopic characteristics of Dy: CLGO are investigated, with special attention to the yellow emission that could be pumped directly by the rapidly developed blue GaN LD. Based on the Judd-Ofelt (J-O) theory, the intensity parameters from the measured line strengths were determined. The J-O parameters were used to predict radiative transition probabilities, radiative lifetime and branching ratios for various excited levels of the Dy: CLGO crystal. The absorption cross-sections of Dy: CLGO at 453 nm are calculated to be 0.14 × 10−20 cm2 and 0.11 × 10−20 cm2 for π- and σ-polarizations, respectively. Meanwhile, Dy: CLGO exhibits strong yellow emission at 574 nm corresponding to the transition 4F9/2 → 6H13/2 with stimulated emission cross-sections of 3.88 × 10−21 cm2 and 3.42 × 10−21 cm2 for π- and σ-polarizations, respectively. The relatively long fluorescence lifetime (565 μs) indicates a high laser efficiency of the crystal. All results suggest that Dy: CLGO crystal could be a promising candidate for yellow laser at 574 nm pumped by blue GaN LD.

Towards a high resolution view of infrared line formation

Observing in the infrared has many benefits, such as seeing through the interstellar dust in the galaxy, easier use of adaptive optics, and better flux ratios for direct observations of exoplanets. Before the infrared spectral range can be utilised for highly accurate stellar spectroscopy there is a need for a better understanding of both stellar modelling and the atomic physics that go into forming spectral lines. In this thesis I aim to evaluate to what extent abundances derived from infrared spectra agree with optical values, and which aspects of the line formation cause eventual discrepancies. The aspects investigated in this study are: macroturbulence determination; astrophysical linestrengths; NLTE corrections; and hyperfine structure splitting of atomic energy levels. For this purpose I have analysed H band (1.49 to 1.80 $\mu m$) spectra of 34 K giants, taken with the spectrometer IGRINS. The elemental abundances derived from these infrared spectra are benchmarked against results from high resolution optical spectra of the same stars. This study uses stellar parameters derived from the same optical spectra, as techniques for determining them from infrared spectra are still being developed. My results for the elemental abundances of C, Na, Mg, Ca, Ti, V, Cr, Co, Ni, Cu and Ce show good agreement with the optical values. Significant differences are seen in the abundances of Al, Si, Mn and Nd. I have also measured the abundances of P, S, K and Zn, elements which lack optical benchmark values. No measurements have been possible for Ge and Rb. Different factors affecting the analysis have been studied in more detail. I show that the method used for determining macroturbulence is an important factor in abundance determination, especially for stars with supersolar metallicity. The lack of accurate measurements of spectral linestrength is addressed in the thesis by my astrophysical measurements of the quantity, using a method developed in the thesis that accounts for the relative strengths of fine and hyperfine structure lines. For elements with NLTE corrections from Amarsi et al. (2020) I show how these corrections improve the agreement between optical and infrared results. For elements with data on the hyperfine structure splitting of the energy levels, I have assessed the impact of including the additional transitions, showing the importance of doing so.

Dust and gas in the central region of NGC 1316 (Fornax A)

Context. The early-type galaxy NGC 1316, associated with the radio source Fornax A, hosts about 107 M⊙ of dust within a central radius of 5 kpc. These prominent dust structures are believed to have an external origin, which is also a popular interpretation for other dusty early-type galaxies. Moreover, it has been long known that ionised gas is present in NGC 1316, but to date there has been a lack of detailed investigation. Aims. Our aim is to understand the nature of ionised gas and dust in NGC 1316 and to offer an interpretation for the origin of the dust. Methods. We use archival Hubble Space Telescope/Advanced Camera for Surveys data to construct colour maps that delineate the dust pattern in detail, and we compare these data with maps constructed with data from the Multi Unit Spectroscopic Explorer (MUSE) instrument of the Very Large Telescope at the European Southern Observatory. Twelve MUSE pointings in wide field mode form a mosaic of the central 3.3 × 2.4 arcmin2. We use the tool PyParadise to fit the stellar population. We use the residual emission lines and the residual interstellar absorption NaI D-lines, and we measure line strengths, the velocity field, and the velocity dispersion field. Results. The emission lines resemble low-ionisation nuclear emission-line region lines, with [NII] being the strongest line everywhere. Ionising sources are plausibly the post-asymptotic giant branch stars of the old or intermediate-age stellar population. There is a striking match between the dust structures, ionised gas, and atomic gas distributions, the last of which is manifested by interstellar absorption residuals of the stellar NaI D-lines. In the dust-free regions, the interstellar NaI D-lines appear in emission, which is indicative of a galactic wind. The velocity field of the ionised gas (and thus of the dust) is characterised by small-scale turbulent movements that indicate short lifetimes. At the very centre, a bipolar velocity field of the ionised gas is observed, which we interpret as an outflow. The low-velocity part is associated with dust. We identify a strongly inclined gaseous dusty disc along the major axis of NGC 1316. A straight beam of ionised gas with a length of about 4 kpc emanates from the centre. Conclusions. The dust in NGC 1316 has different origins. Our findings are strongly suggestive of a dusty outflow that is curved along the line-of-sight. Nuclear outflows may be important dust-producing machines in galaxies. Another dusty gaseous component forms a disc that we identify as the predecessor of a central dust lane.

Transition Strength Measurements to Guide Magic Wavelength Selection in Optically Trapped Molecules.

Optical trapping of molecules with long coherence times is crucial for many protocols in quantum information and metrology. However, the factors that limit the lifetimes of the trapped molecules remain elusive and require improved understanding of the underlying molecular structure. Here we show that measurements of vibronic line strengths in weakly and deeply bound ^{88}Sr_{2} molecules, combined with abinitio calculations, allow for unambiguous identification of vibrational quantum numbers. This, in turn, enables the construction of refined excited potential energy curves, informing the selection of magic wavelengths that facilitate long vibrational coherence. We demonstrate Rabi oscillations between far-separated vibrational states that persist for nearly 100ms.

Measurements of line strengths for NO2 near 6.2 μm using a quantum cascade laser spectrometer

A high-resolution quantum cascade spectrometer was developed to study nitrogen dioxide (NO2) line intensities near 6.2 μm. The spectral region ranging from 1629.7 cm−1 to 1632.5 cm−1, which is suitable for the in situ laser sensing of trace NO2 in the atmosphere, was investigated using a thermoelectrically cooled continuous-wave distributed feed-back quantum cascade laser. Forty-three lines of nitrogen dioxide were experimentally studied within the pressure region ranging between 0 and 90 mbar. The measured intensities were thoroughly compared to the latest HITRAN16 database, a good agreement within ±3% was obtained for most of the established lines.

NH<sub>3</sub> aliasing absorption spectra at 1103.4 cm<sup>–1</sup> based on continuous quantum cascade laser

Due to the important role of NH<sub>3</sub> in atmospheric aerosol chemistry, rapid and accurate inversion of ammonia concentration is very important for environmental issues. In this paper, a 9.05 μm continuous quantum cascade laser (QCL) is used as the light source at room temperature, and the scanned-wavelength direct-absorption tunable diode laser absorption spectroscopy (TDLAS) is used to study the spectral characteristics of the QCL at 1103.4 cm<sup>–1</sup>. A low-pressure experimental platform based on two-level temperature control was designed to measure the six aliasing absorption lines of ammonia at 1103.4 cm<sup>–1</sup>. The broadening of spectral line becomes smaller under the condition of reducing the pressure, and the aliasing spectra are separated. The line strength of each absorption line is calculated, and the measurement uncertainty is further analyzed. A method for accurate inversion of single-spectrum gas concentration by low-pressure separation was proposed for severely aliased spectra, and experimental verification was performed. By comparing the results with the HITRAN database, it is concluded that the experimental measured line strength of ammonia gas at 1103.4 cm<sup>–1</sup> has a deviation from the database of . The uncertainty of the line intensity measurement is mainly related to the separation and extraction of aliasing absorbance, which is about 2.42%–8.92%. The deviation between the inversion concentration and the actual value under the condition of extreme low pressure is between 1% and 3%, while the calculated deviation of the line intensity value in the 2.71%–4.71% HITRAN database is about 3% to 5%. The results above indicate that the experimental data are reliable. The non-separative aliasing spectral line method is used to invert the concentration at normal pressure, and the low-pressure separated single spectral line method is used to invert the concentration at low pressure. The results of the two are compared. The analysis results show that the low-pressure separation single-spectrum spectral line inversion concentration value has smaller deviation and higher accuracy from the original concentration. The study of this method provides reference for future inversion of gas concentrations inversion in the atmospheric environment and other fields.

Measurement of nitric oxide from cigarette burning using TDLAS based on quantum cascade laser

Nitric oxide (NO) is an important product released by cigarette burning with significantly negative effects to both environment and human health, but it is hard to be measured in-situ in the process of burning. In this paper, we report a tunable diode laser absorption spectroscopy (TDLAS) set-up using a quantum cascade laser emitting at 5.24 μm to continuously determine the emitted NO mass in cigarette smoke during burning. Wavelength modulation spectroscopy was applied to improve the detection sensitivity and robustness of the measurement system. A simple single-pass gas cell with a volume of 28 cm3 was used to record the absorption spectra, and then the mass of NO was derived based on the measured line strength. Allan variance analysis demonstrated that the limit of detection of system reached 28 ppb over 180 s integration time. Due to the low effective volume, the rise time and the fall time were rapid with 3 s and 6 s, respectively. An adaptive Kalman filter was used to reduce the noise on the concentration measurement. As a result, the measurement precision is improved by a factor of 4.5. For accurate determination the total NO mass, the emissions of mainstream (MS) and sidestream (SS) of a burning cigarette were individually measured at the same continuous flow rate. The recorded results of three types of cigarettes revealed that the NO mass emitted in the MS is correlated with the sampling flow rate, while the NO mass emitted by the same cigarette in the SS is hardly influenced by at different smoke flow rates. And different cigarette types with identical physical dimensions emit approximately equivalent mass of NO. This work provides a promising method for determining the mass of emitted NO and other compositions of cigarettes smoke.

Accurate measurements of line strengths and air-broadening coefficients in methane around 1.66 µm using cavity ring down spectroscopy

Accurate measurements of line strengths and air-broadening coefficients for 10 lines of 12CH4 mostly from the band (2ν2 + ν3) and 2 lines of 13CH4 from the band (2ν3) around 1.66 µm were performed using cavity ring down spectroscopy. Spectra of mixtures of 12CH4 in air and 13CH4 in air with well-defined mole fractions of methane were recorded at pressures between 10 and 90 mbar at 296 K. The values of the line strength for 12CH4 and 13CH4 lines were obtained with the uncertainty 1% and 2%, respectively. The uncertainties of the values of the air-broadening coefficient varied from 2 to 5% depending on the line. The values of the line strength and air-broadening coefficient for two methane isotopes obtained in this work were compared with the corresponding values from different experimental studies, as well as with the data given in HITRAN 2016 database.

Galaxy Populations in Massive z = 0.2–0.9 Clusters. I. Analysis of Spectroscopy

Abstract We present an analysis of stellar populations in passive galaxies in seven massive X-ray clusters at z = 0.19–0.89. Based on absorption-line strengths measured from our high signal-to-noise spectra, the data support primarily passive evolution of the galaxies. We use the scaling relations between velocity dispersions and the absorption-line strengths to determine representative mean line strengths for the clusters. From the age determinations based on the line strengths (and stellar population models), we find a formation redshift of . Based on line strength measurements from high signal-to-noise composite spectra of our data, we establish the relations between velocity dispersions, ages, metallicities [M/H], and abundance ratios [α/Fe] as a function of redshift. The [M/H]–velocity dispersion and [α/Fe]–velocity dispersion relations are steep and tight. The age–velocity dispersion relation is flat, with zero-point changes reflecting passive evolution. The scatter in all three parameters is within 0.08–0.15 dex at fixed velocity dispersions, indicating a large degree of synchronization in the evolution of the galaxies. We find an indication of cluster-to-cluster differences in metallicities and abundance ratios. However, variations in stellar populations with the cluster environment can only account for a very small fraction of the intrinsic scatter in the scaling relations. Thus, within these very massive clusters, the main driver of the properties of the stellar populations in passive galaxies appears to be the galaxy velocity dispersion.

Line strength measurements and relative isotopic ratio 13C/12C measurements in carbon dioxide using cavity ring down spectroscopy

Accurate intensity measurements were performed for several lines of the two main isotopologues of carbon dioxide, using cavity ring down spectroscopy. Absorption spectra of the R52e line at 6112.8902 cm-1 (30014←00001 band) of 12CO2 and the P6e line at 6114.8580 cm−1 (30013←00001 band) of 13CO2 were recorded at pressures between 15 and 50 mbar at 298 K. Line shape analysis shows that Galatry profile, taking into account Dicke narrowing of spectral lines, better describes the measured spectra at all pressures than the Voigt profile. The values of Dicke narrowing parameter for both lines were found to be significantly smaller than those predicted based on the mass diffusion constant. The values of the line strength for R52e line of 12CO2 and P6e line of 13CO2 were determined with an uncertainty of 0.5%. These values were found to be in good agreement with the corresponding data available in literature, in particular with the most recent ab initio calculations. The results of relative isotopic ratio 13CO2/12CO2 measurements are also presented in pure carbon dioxide samples and in 400 µmol/mol carbon dioxide in air samples, using cavity ring down spectroscopy.

Measurement of line strengths in the à 2A’ ← [formula omitted]2A” transition of HO2 and DO2

The absorption spectrum of the à 2A’ ← X˜2A” 000–000 band of HO2 and DO2 radicals has been measured in the range 6941–7077 cm−1 with a resolution of around 0.005 cm−1. HO2 and DO2 radicals were generated from the reaction of Cl-atoms with CH3OH and CD3OD, respectively, whereby Cl-atoms were generated by pulsed photolysis of (COCl)2 at 248 nm. One time-resolved absorption curve was measured by cw-Cavity Ring Down Spectroscopy (cw-CRDS) for each wavelength. The relative absorption coefficient for each wavelength was then obtained from the ring down time τ, extrapolated to t = 0 s with respect to the photolysis pulse, and the ring down time τ0 before the photolysis pulse. Absolute absorption coefficients were quantified for several selected lines relative to a well characterized absorption line of HO2 at 6638.21 cm−1 by a second cw-CRDS absorption path. The maximum absorption cross section at 50 Torr Helium was for HO2 the transition N Ka Kc J = 11 0 11 11.5 ← 11 1 11 11.5 with σ7000.28 cm−1 = 2.12 × 10−19 cm2 and for DO2 the doublet transition N Ka Kc J = 18 1 18 18.5 ← 18 0 18 18.5 and 18 1 18 17.5 ← 18 0 18 17.5 with σ7019.83 cm−1 = 2.97 × 10−19 cm2. The full spectrum has been very well reproduced by employing spectroscopic data from earlier works.