Pairs Of Absorption Lines Research Articles

Probing Galactic variations in the fine-structure constant using solar twin stars: Systematic errors

ABSTRACT Sun-like stars are a new probe of variations in the fine-structure constant, α, via the solar twins approach: velocity separations of close pairs of absorption lines are compared between stars with very similar stellar parameters, i.e. effective temperature, metallicity, and surface gravity within 100 K, 0.1 dex, and 0.2 dex of the Sun’s values. Here, we assess possible systematic errors in this approach by analysing ≳10 000 archival exposures from the High-Accuracy Radial Velocity Planetary Searcher (HARPS) of 130 stars covering a much broader range of stellar parameters. We find that each transition pair’s separation shows broad, low-order variations with stellar parameters that can be accurately modelled, leaving only a small residual, intrinsic star-to-star scatter of 0–33 m s−1 (average ≈7 m s−1, ≈1 × 10−4 Å at 5000 Å). This limits the precision available from a single pair in a single star. We consider potential systematic errors from a range of instrumental and astrophysical sources (e.g. wavelength calibration, charge transfer inefficiency, stellar magnetic activity, line blending) and conclude that variations in elemental abundances, isotope ratios, and stellar rotational velocities may explain this star-to-star scatter. Finally, we find that the solar twins approach can be extended to solar analogues – within 300 K, 0.3 dex, and 0.4 dex of the Sun’s parameters – without significant additional systematic errors, allowing a much larger number of stars to be used as probes of variation in α, including at much larger distances.

Development of an infrared laser absorption sensor for non-intrusive gas temperature measurements

Energetic materials have extremely high volumetric and specific energy densities, making them attractive and important in combustion systems. To improve their combustion performance, reliable temperature acquirement method is highly demanded. A laser sensor was developed for in situ and quantitative measurements of gas temperature. Scanned-wavelength direct absorption spectroscopy was used for line-of-sight temperature measurements. Multiple H2O absorption features in the near-infrared combination band (v1+v3) and mid-infrared fundamental band (v3) were selected to establish four absorption line pairs with good temperature sensitivity. Three infrared distributed feedback lasers (DFB) were used to cover the selected absorption lines. The accuracy and uncertainty of the sensor were first numerically evaluated in a wide temperature range of 1000–3000 ​K under different Gaussian white noise levels (5–20%). A free-space optical setup was established to experimentally evaluate the sensor performance by measuring benchmark laminar premixed flames, which were compared with additional thermocouple measurements, chemical kinetic modeling and computational fluid dynamics simulations. The good performance of the current sensor indicates the potential of being used in non-intrusive, in-situ and quantitative diagnostics of the energetic materials combustion.

Effects of thermochemical non-uniformity on line-of-sight laser absorption thermometry in counterflow diffusion flames

In this work, the effects of thermochemical non-uniformity on line-of-sight (LOS) laser absorption thermometry in counterflow diffusion flame (CDF) was systematically investigated. Differences between the LOS-determined temperature and the true core flame temperature was quantified considering the coupled effects of thermal and gas concentration non-uniformities along the LOS. Experimentally validated computational fluid dynamics simulation was used to establish the flame thermochemical structure with wide ranges of non-uniformities that were subsequently used as test cases. Six absorption line pairs of H2O near 2.5 μm were selected to ensure sufficiently strong absorption and wide temperature sensitivity. The level of non-uniformity (Γ, an index to reflect the percentage of the non-uniform thermochemical region), core flame temperature (Tcore) and core species concentration (Xcore) were parametrically examined under various non-uniformity conditions (Γ = 5–80%, Tcore = 1200–2600 K, Xcore = 2–20%). In the presence of thermochemical non-uniformity, the LOS-determined temperature was consistently lower than the core flame temperature under typical CDF conditions. The temperature deviations were found to increase with the increase of Tcore and Γ; however, they remained unchanged when Xcore varied dramatically from 2% to 20%. Additionally, the thermal non-uniformity was observed to have a stronger impact on temperature deviations than the gas concentration non-uniformity does. Further studies in two representative CDFs with significant thermochemical gradients showed that the LOS measurement could lead not only to deviations in the core flame temperature but also has the risk of providing inaccurate peak temperature position and the axial distribution profile. The most significant deviations occurred in the region near the fuel nozzle sections. Finally, novel strategies were proposed to mitigate the temperature deviations to improve the accuracy of LOS thermometry.

Sensitive detection of atmospheric N2O isotopomers using a quantum cascade laser based spectrometer

Stable isotope analytical techniques have a crucial role to play in the study of atmospheric pollutant and trace gas sources, sinks and transport processes. Quantum cascade laser absorption spectroscopy (QCLAS) allows the site-selective and high-precision analysis of many isotopic species at trace levels, yet not sensitive enough for atmospheric N2O mixing ratios. In this study, a quantum cascade laser based spectrometer combining with a liquid nitrogen-free preconcentration unit was developed to demonstrate the applicability of high sensitivity and high precision measurement of atmospheric N2O isotopomers. Primary laboratory tests have been performed for simultaneous determination of the mixing ratios of the most abundant nitrous oxide isotopic species: 14N15N16O, 15N14N16O and 14N216O. The experiment results showed that site-selective 15N/14N can be measured with the precision of 0.59‰ with an optimal averaging time of 258 s at 100 ppm. Details of spectral absorption line pairs selection and N2O adsorption/desorption processes are also discussed.

Influence of Line Pair Selection on Flame Tomography Using Infrared Absorption Spectroscopy.

We report the influence of absorption line selection on the tomographic results for high-temperature flames by numerical and experimental methods. Different combinations of infrared H2O absorption transitions are utilized with the Tikhonov-regularized Abel inversion to reconstruct the radial distribution of temperature and H2O concentration in a flat flame. It is shown that besides using the mathematical algorithm such as regularization, selecting a line pair with a large Δ E″ (>1390 cm-1) also reduces the reconstruction uncertainty at 300-2000 K. In this study, a proper selection of absorption line pairs reduces the reconstruction uncertainty by 25% at the same level of noise. The line pair of H2O transitions at 4029.524 cm-1 and 4030.729 cm-1 is recommended for the tomography of high-temperature flames at 1000-3000 K, whereas the line pair of 7185.597 cm-1 and 7444.352 cm-1 can be used at 300-1000 K.

A Novel Multi-Pass Cell System for Measurements of Methane Carbon Isotopes Using a Near-Infrared Tunable Diode Laser

A novel multi-pass cell laser absorption spectrometer to measure δ13C diluted with nitrogen using a 1.658 μm nearinfrared distributed-feedback laser was developed. The system temperature and pressure were measured with an accuracy of ±11 mK and ±3.2 Pa, respectively. The spectrometer is small, reliable, and compact. To minimize the temperature effect in absorbance ratio measurements, we used two appropriate absorption line pairs with nearly the same temperature dependences. The absorption spectrometer demonstrated high precision (a repetitive precision (reproducibility) of ~0.9‰ (1σ) is obtained at 300 ppmv methane concentrations). This concentration ratio is adequate for most CH4 source characterization studies.

LINE-DEPTH RATIOS INH-BAND SPECTRA TO DETERMINE EFFECTIVE TEMPERATURES OF G- AND K-TYPE GIANTS AND SUPERGIANTS

The stellar effective temperature is the fundamental parameter of stellar atmospheres. It characterizes the spectra and plays an essential role in chemical abundance analysis. Previous optical studies have shown that line-depth ratios (LDRs) are good indicators of the effective temperature. Essentially, the ratios of absorption lines with different excitation potentials can be used as temperature scales. The most important advantage of LDRs is their robustness against interstellar reddening and extinction. Furthermore, the scales are constructed and calibrated empirically by observables. Although this method is well-established for optical spectra, we require infrared high-resolution spectroscopy to access the most obscured stars in the Galactic disk and thereby understand the Milky Way's structure and evolution in the innermost region. This study newly derives the temperature scales from the LDRs in infrared spectra. We explored LDRs in the high-resolution H-band spectra (1.4–1.8 μm) of well-known stars in the solar neighborhood obtained with Subaru/infrared camera and spectrograph. We found nine pairs of absorption lines whose LDRs allow us to determine the temperatures of G- and K-type giants/supergiants to an accuracy of ~60 K. Checking the dependency of our scales on stellar parameters, we found that our developed temperature scales may slightly bias the estimates for low-metal stars, [Fe/H] < dex.

Disk dissipation timescale of pre-main sequence stars in Taurus

Abstract We present the results of an age determination study of pre-main sequence stars in the Taurus star-forming region. The ages of 10 single stars with masses of 0.5–1.1 M⊙ were derived from the surface gravities, estimated from high-resolution optical and near-infrared spectroscopy. The equivalent width ratios of nearby absorption line pairs were employed for the surface gravity diagnostic, which directly reflects the parameters of the stellar atmosphere without any veiling correction. From a comparison of determined ages and near-infrared color excesses such as J − H, J − K, and J − L, the inner disk lifetime of the young stars with 0.5–1.1 M⊙ in Taurus is estimated to be 3–4 Myr.

Impact of atmospheric state uncertainties on retrieved XCO2columns from laser differential absorption spectroscopy measurements

This work assesses the impact of uncertainties in atmospheric state knowledge on retrievals of carbon dioxide column amounts (XCO2) from laser differential absorption spectroscopy (LAS) measurements. LAS estimates of XCO2 columns are normally derived not only from differential absorption observations but also from measured or prior knowledge of atmospheric state that includes temperature, moisture, and pressure along the viewing path. In the case of global space-based monitoring systems, it is often difficult if not impossible to provide collocated in situ measurements of atmospheric state for all observations, so retrievals often rely on collocated remote-sensed data or values derived from numerical weather prediction (NWP) models to describe the atmospheric state. A radiative transfer-based simulation framework, combined with representative global upper-air observations and matched NWP profiles, was used to assess the impact of model differences on estimates of column CO2 and O2 concentrations. These analyses focus on characterizing these errors for LAS measurements of CO2 in the 1.57-μm region and of O2 in the 1.27-μm region. The results provide a set of signal-to-noise metrics that characterize the errors in retrieved values associated with uncertainties in atmospheric state and provide a method for selecting optimal differential absorption line pairs to minimize the impact of these noise terms.

Spectrometric monitoring of atmospheric carbon tetrafluoride (CF&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;) above the Jungfraujoch station since 1989: evidence of continued increase but at a slowing rate

Abstract. The long-term evolution of the vertical column abundance of carbon tetrafluoride (CF4) above the high-altitude Jungfraujoch station (Swiss Alps, 46.5° N, 8.0° E, 3580 m a.s.l.) has been derived from the spectrometric analysis of Fourier transform infrared solar spectra recorded at that site between 1989 and 2012. The investigation is based on a multi-microwindow approach, two encompassing pairs of absorption lines belonging to the R-branch of the strong ν3 band of CF4 centered at 1283 cm−1, and two additional ones to optimally account for weak but overlapping HNO3 interferences. The analysis reveals a steady accumulation of the very long-lived CF4 above the Jungfraujoch at mean rates of (1.38 ± 0.11) × 1013 molec cm−2 yr−1 from 1989 to 1997, and (0.98 ± 0.02) × 1013 molec cm−2 yr−1 from 1998 to 2012, which correspond to linear growth rates of 1.71 ± 0.14 and 1.04 ± 0.02% yr−1 respectively referenced to 1989 and 1998. Related global CF4 anthropogenic emissions required to sustain these mean increases correspond to 15.8 ± 1.3 and 11.1 ± 0.2 Gg yr−1 over the above specified time intervals. Findings reported here are compared and discussed with respect to relevant northern mid-latitude results obtained remotely from space and balloons as well as in situ at the ground, including new gas chromatography mass spectrometry measurements performed at the Jungfraujoch since 2010.

Magellan Spectroscopy of the Galaxy Cluster RX J1347.5−1145: Redshift Estimates for the Gravitationally Lensed Arcs

We present imaging and spectroscopic observations of the gravitationally lensed arcs in the field of RX J1347.5-1145, the most X-ray luminous galaxy cluster known. Based on the detection of the [O II] λ3727 emission line, we confirm that the redshift of one of the arcs is z = 0.806. Its color and [O II] line strength are consistent with those of distant, actively star-forming galaxies. In a second arc, we tentatively identify a pair of absorption lines superposed on a red continuum; the lines are consistent with Ca II λ3933 (K) and Ca II λ3968 (H) at z = 0.785. We detected a faint blue continuum in two additional arcs, but no spectral line features could be measured. We establish lower limits to their redshifts based on the absence of [O II] emission, which we argue should be present and detectable in these objects. Redshifts are also given for a number of galaxies in the field of the cluster.

Discovery of the Galaxy Proximity Effect and Implications for Measurements of the Ionizing Background Radiation at Low Redshifts

We present an analysis of galaxy and quasi-stellar object (QSO) absorption line pairs toward 24 QSOs at redshifts between z ≈ 0.2 and 1 in an effort to establish the relationship between galaxies and absorption lines in physical proximity to QSOs. We demonstrate the existence of a galaxy proximity effect, in that galaxies in the vicinities of QSOs do not show the same incidence and extent of gaseous envelopes as galaxies far from QSOs. We show that the galaxy proximity effect exists to galaxy-QSO velocity separations of 3000 km s-1, much larger than the size of a typical cluster (1000 km s-1); i.e., it is more comparable to the scale of the sphere of influence of QSO ionizing radiation rather than the scale of galaxy-QSO clustering. This indicates that the QSO ionizing radiation rather than some dynamical effect from the cluster environment is responsible for the galaxy proximity effect. We combine previous findings that (1) many or most Lyα absorption lines arise in extended galaxy envelopes, and (2) galaxies cluster around QSOs to show that the magnitude of the Lyα forest proximity effect is underestimated. Consequently, determinations of the UV ionizing background intensity using the proximity effect are likely overestimated. We use the galaxy-QSO cross-correlation function measured from our data to estimate the magnitude of this overestimate and find that it could be as high as a factor of 20 at z 1. This can have strong implications for models of the origin and evolution of the ionizing background and may indicate that QSOs produce sufficient ionizing flux at all redshifts to account for the entire background radiation field.

Effects of absorptivity due to fish on transmission loss in shallow water

Absorption losses at the resonance frequencies of sardines, 1.3 kHz (18 dB) at night, 1.7 kHz (15 dB) during the day and 2.7 kHz (35 dB) at dawn, were observed at a range of 12 km at a shallow water site in the Gulf of Lion in September of 1995. These observations were made during Modal Lion, a multidisciplinary experiment, which was designed to isolate absorptivity due to fish from other effects on long range propagation. Systematic changes in the resonance frequency of dispersed sardines were consistent with concurrent echo sounder observations of the vertical migration of sardines at twilight. Comparison of transmission loss measurements with a numerical sound propagation model that incorporates absorption layers in the water column permitted estimation of the average absorption coefficient, depth and thickness of absorption layers. Depths and thickness of layers estimated from sound propagation measurements were in good agreement with echo sounder data. Measured resonance frequencies, f0, of dispersed fish were in good agreement with theoretical computations based on measured swim bladder dimensions. The measured resonance frequency of sardines in schools, which were at a depth of about 65 m, was about 0.6 times the resonance frequency of dispersed sardines. The observed frequency shift is consistent with an analytical equation of the fundamental resonance frequency of a “cloud” of bubbles, an average separation between fish in schools of about 0.8 fish lengths and 5×103 fish per school. These estimates are consistent with previously published estimates of these parameters. The resonance frequencies of other absorption lines are consistent with the hypothesis that absorptivity due to sardines generally manifests itself in pairs of absorption lines, which correspond to the resonance frequencies of an ensemble of individual sardines, and the resonance frequencies of an ensemble of schools. Matching of theoretical calculations with inferences of the absorption coefficient permitted estimation of the average number of dispersed sardines per unit volume, which also consistent with previously published estimates. The results presented here suggest the possibility of long term tomographic mapping of fish parameters over large areas using broadband transmission loss measurements.

Selection of absorption lines for I_2–planar laser-induced fluorescence measurement of temperature in a compressible flow

It is very important for I(2)-planar laser-induced fluorescence measurement of temperature in a compressible flow to choose a pair of absorption lines appropriate to the temperature range. The method for selection of suitable pairs of absorption lines of I(2) in the transition of B(3)II(ou) + (ν' = 43) ? X(1)Σ(g) + (ν" = 0)is described. By the use of many pairs of absorption lines, the temperature dependence of the ratio between the fluorescence signals is calculated theoretically and is also investigated in experiments in which several pairs are applied to determination of the temperature distribution of a supersonic free jet.

ESR Studies of Phosphoric Ion in α-Quartz

Measurements of electron spin resonance are carried out on X- and γ-ray irradiated single crystals of phosphorus-doped quartz. A pair of absorption lines showing hyperfine interaction with a nuclear spin of phosphoric ion is observed at room temperature. This ESR signal is ascribed to a paramagnetic center of C 2 symmetry having g and A tensor components of g 1 =2.0011, g 2 =2.0025, g 3 =2.0003 and | A 1 |=1065, | A 2 |=1049, | A 3 |=989 in units of 10 -4 cm -1 , respectively. The center is considered to be an s -like electron localized at a substitutional pentavalent phosphoric ion surrounded by four oxygen ions.

Some Spectral Effects in Atomic Absorption Spectrometry

Abstract There are several reports in the literature(1–3), where appreciable absorption occurs at widths far greater than the interval represented by the total half widths of the primary emission - flame absorption line pairs. This gives rise to spectral effects in atomic absorption spectrometry (AAS), many of which have been observed by various investigators(4–7). This note gives two new cases of spectral effects in AAS.