Line Profile Measurements Research Articles

Application of high-resolution Fourier transform spectrometry to the study of glow discharge sources. Part 1. Excitation of iron and chromium spectra in a microwave boosted glow discharge source

A high-resolution ultraviolet–visible Fourier transform spectrometer has been used to record spectra from a Grimm-type glow discharge source with and without supplementary microwave excitation. Various cathodes were used (copper, aluminium, iron and chromium) with argon or neon as the carrier gas. True line profiles were recorded directly, so that line shapes could be studied easily. Close lines could be distinguished and identifications made unambiguously, even when major changes in relative intensities occurred. In this paper, information is presented on the effects of the excitation conditions on the iron and chromium spectra, using relative intensity measurements on a very large number of spectral lines. The results emphasize that any ‘excitation temperatures’ deduced from data on a limited number of lines are meaningless. The contribution of charge exchange processes to the excitation of ionic lines is discussed in detail. Line profile measurements will be reported in a subsequent paper.

High-resolution ultraviolet spectrograph for sounding rocket measurements of planetary emission line profiles

We constructed a high-resolution imaging spectrograph for use as a payload in a sounding rocket experiment. The spectrograph employs a modified Ebert-Fastie design with a LiF objective prism and a replica of an El echelle grating developed for the Space Telescope Imaging Spectrograph. The instrument has a 5-arcmin-long adjustable width entrance aperture with two identical secondary apertures separated from the primary by ±2 arcmin. The secondary apertures are intended for simultaneous measurement of the sky background. The spectrograph has been optimized for measurement of the 221st order of Lyman-α at a resolution of 0.03 to 0.04 A. The detector system is a two-dimensional photon counting device that employs a microchannel plate intensifier and a wedge and strip anode readout. The spectrograph is used as a focal plane instrument of the Jupiter Telescope, a Cassegrain telescope constructed exclusively for use as a sounding rocket payload. The Jupiter Telescope is self-pointed, employing image motion compensation to achieve 2- to 3-arc sec image quality. The telescope/spectrograph payload was launched from the White Sands Missile Range on May 4, 1991, to observe the H Lyman-α line profile spatially resolved across the disk of Jupiter in the North-South (polar) and East-West (equatorial) directions, and to measure the H Lyman-α emission line profile from interplanetary hydrogen associated with the local insterstellar medium.

Measurement of CO overtone line profiles in SVS 13

High-resolution spectra of the CO overtone emission in the infrared source SVS 13 are obtained and the individual vibration-rotation lines are resolved for the first time in a young stellar object. The observed FWHM velocity of the lines in the v = 2-0 band is 40 km/s. A fit of the v = 2-0 band head with a single temperature LTE slab model yields an optical depth of 0.3 in the R(51) line and a rotational temperature of about 3500 K. Given the best estimates for the orientation of the SVS 13 outflow, the observed line widths are much smaller than expected for either of the two most favored interpretations for the CO emission: a circumstellar disk or a high-velocity neutral wind.

OH product energy partitioning and absolute reactive cross section of the reaction H + H 2 O → OH + H 2

Using 193 nm photolysis of HBr, we have studied the reaction H+H 2 O→OH+H 2 at a center of mass energy of 2.52 eV. Laser induced fluorescence has been used to measure the nascent rotational quantum-state distribution and the translational energy of the OH product molecules. Within the experimental uncertainty no vibrational excitation of the OH products could be found ( v =1/ x =0<0.1). The degree of OH( v =0) rotational excitation is also very low. We found that only 4% of the total available reaction energy is channeled into OH rotation. The results of sub-Doppler measurements of the OH line profiles show that most of the available energy in the reaction ends up as c.m. translational energy of the products (67%). The population of two spin orbit multiplet states shows a slight preference for the low lying 2 Π 3/2 state. The ratio of the lambda doublet state population shows a preference for the (A′) state at high rotational quantum numbers. Together with the very low vibrational and rotational excitation of the OH products, this suggests that many of the reactive collisions are in character planar stripping collisions, with the OH bond acting as a spectator during the reaction. Using the H 2 O 2 photolysis at 193 nm as a reference source of well defined concentrations of OH radicals we determined an absolute reactive cross section: σ(2.52 eV)=(0.26±0.09) 2 . The experimental results show excellent agreement with predictions of dynamic calculations using a ab initio potential energy surface.

Quenching of Einstein coefficients by photons

Experimental evidence is presented for the change of Einstein's A coefficients for spontaneous transitions from the upper laser level of an argon in laser discharge due to the presence of a high-intensity laser flux. To demonstrate that this quenching effect cannot be attributed to a reduction in self-absorption of the strong spontaneous emission line, absorption and line profile measurements have been performed. Computer modelling of the reduction of self-absorption due to Rabi splitting also indicated that this effect is too small to explain the observed quenching of spontaneous line emissions.

An X-ray study of creep-deformation induced changes of the lattice mismatch in the γ′-hardened monocrystalline nickel-base superalloy SRR 99

X-ray line profile measurements were performed on monocrystalline specimens of the γ′-hardened nickel-base superalloy SSR 99 with axes close to the [001] direction. The aim was to measure the local lattice parameters in the γ-matrix and in the γ′-particles and to obtain information on the lattice mismatch and internal stresses. For this purpose, a special high-resolution double crystal diffractomoter with negligible instrumental line broadening was used. Measurements were performed on specimens in the initial state with cuboidal γ′-particles and on creep-deformed specimens containing the so-called γ/γ′-raft structure. In several cases the line profiles were measured as a function of the rocking angle, and the intensity distributions were mapped in reciprocal space around the (002) and (020) Bragg reflections. In the undeformed state these intensity distributionsindicate that the local lattice parameter varies spatially in the γ-phase. The line profiles of specimens in the initial state were asymmetric. A remarkable result obtained on creep-deformed specimes was that, whereas the asymmetry of the (020) line profiles was enhanced to the extent that a hump or a second peak appeared, the asymmetry of the (002) line profiles was reversed in sign. A quantitative evaluation yielded mean values of the constrained lattice mismatch which, in the case of creep-deformed specimens, differ significantly for the (001) and (010) lattice plane spacings. It is concluded that the orientation-dependent lattice spacings represent a triaxial state of residual stress which has its origin in the superposition of the originally present coherency stresses and the deformation-induced internal stresses. All observed features could be explained in detail in terms of a composite model of plastic deformation, which takes into account the dislocation networks deposited at the γ/γ′-interfaces during deformation.

A system for line profile studies at the 150-foot tower on Mount Wilson

We describe enhancements to the hardware and software for the 150-foot tower system on Mt. Wilson which make possible the acquisition of high precision line profile measurements. This system utilizes the 75-foot pit spectrograph with a photomultiplier detector system to scan line profiles repeatedly in order to study variations induced by the passage of waves vertically through the solar atmosphere. Oscillations of line profile parameters with an amplitude as low as 1.7 m s−1 have been detected with this system using integrated sunlight. Phase relations between oscillations of different parts of the line profile are appropriate to upward energy transport. Consistent with the previous conclusion by Mein and Schmieder (1981), we find that the magnitude of the energy transport is compatible with the 5-min oscillations making an important contribution to the heating of the low chromosphere.

Stark-broadening of the helium lines 447 and 492 nm at low electron densities

Stark-broadening of quasidegenerate He I lines at λ=447 and 492 nm has been investigated at low electron densities ranging from N e=1×10 20 to 3×10 21m -3. The electron density is determined by accurate laser interferometry with quadrature detection. Calculations have been performed according to the unified theory and the model microfield method. The line-profile measurements are compared with the calculations by a parametrization scheme. The influences of Doppler, ion-dynamical and instrument broadening are critically discussed. Different line profile parameters are examined in view of their applicability for diagnostic purposes.

Gamma-ray lines from SN1987A

Gamma-ray spectroscopy of SN1987A has provided us for the first time with a direct confirmation of the existence of explosive nucleosynthesis. Characteristic lines from the decay of radioactive 56Ni have been detected by both balloon and satellite-borne experiments. Lines at 847, 1238 and 2599 keV from excited levels of 56Fe (the final decay product of 56Ni) have been observed. Spherically symmetric, homogeneous models of SN1987A have been quite successful at providing a self-consistent explanation of the gamma-ray line intensity as a function of time. They have not, however, been successful at explaining the line profiles. The measured line profiles suggest the presence of red-shifts whereas the models predict blue shifts. Furthermore, the measured gamma-ray line widths, are characteristically a factor of two greater than the model predictions. The gamma-ray line profiles suggest that we are seeing a significant portion of the receding material on the back side of the shell. These lines are typically optically thick. To explain this apparent contradiction, it may be necessary to invoke fragmentation or non-spherical geometries.

Profiles of emission lines in active galactic nuclei - III. Observations of Ha, [N II] and [S II] profiles

Summary High-resolution (FWHM= 28 km s-1) observations of Ha, [N II] λ6548/6583 and [S II] λ6717/6731 emission lines in several southern active galactic nuclei (AGN) are presented. Deblending of the Hα + [N II] profiles was performed using, when available, the [0 III] λ5007 profile shape as a template. Line profile measurements, as well as line intensities, are tabulated. We found to be relatively common among the observed objects the existence of structure in the line cores, pointing to the complexity of the dynamics in the low-velocity emission region. Differences in profile shape and width amongst different lines are also common, indicating that often there is a superposition, on the spectrograph slit, of emission regions with different dynamics and excitation conditions. This superposition is quantified in the case of IC 5063. We found weak, broad Ha emission in IC 5063 and IC 5135. In NGC 2992, we were unable to confirm the presence of a broad Ha component with the same intensity as found by previous authors, which we ascribe to spectral resolution effects.

The Impact of CN Line Profile Measurements on the Cosmic Microwave Background Temperature

We present moderate to high signal-to-noise high-resolution (R ≈ 150,000–170,000) optical spectra toward ζ Oph. Gaussian fits to our data indicate a value of the line-width parameter b, of b = 1.4 ± 0.2 km s−1, along this line of sight. When CN is used as an indirect probe of the cosmic microwave background (CMB) temperature, the line profile is used to determine saturation corrections in the line. This affects column density calculations, which are reflected in the excitation temperature. Current measurements of the b-value along this line of sight range from 0.88 ± 0.02 km s−1 (Crane et al. 1986) to 1.3 ± 0.1 km s−1 (Hegyi, Traub, and Carleton 1972). The extreme range of these b-values yield saturation corrections to the CMB temperature that differ by 0.05 K, which is equal to the quoted precision of current measurements. Preliminary analysis of observations toward HD 29647 indicate that TCMB = 2.70 ± 0.14 K at 2.64 mm toward this line of sight.

A very fast molecular outflow from the proto-planetary nebula CRL 618

Observations of the CO(2-1) at 230.5 GHz and CO(3-2) were made using the 10.4 m telescope of the Hawaiian Caltech Submillimeter Observatory in 1988 and 1989. Measurement of sensitive line profiles from the highly evolved carbon star/proto-planetary nebula CRL 618 showed a very high velocity molecular outflow with V(0) greater than 190 km/sec. CRL 618 appears to be at the stage of beginning to ionize both the fast and slow molecular winds, as shown by the shapes of the millimeter-wavelength recombination lines by Martin-Pintado et al. (1988) and the width of the H-alpha line by Carsenty and Solf (1982). 25 refs.

Elastic Collision Studies in Caesium/noble Gas Systems Using Two-pulse Echoes

Abstract Measurements are presented of the collisional relaxation of two-pulse echoes on the 455 nm and 459 nm D-lines of atomic caesium perturbed by low pressures of He, Ar and Xe using the echo-polarisation rotation technique, with interpulse times up to approximately 200 ns. The line broadening constants are measured to about 3% and show significant discrepancies with line profile measurements. For τ ⩾ 100ns there is evidence for the diffractive velocity-changing aspects of the collisions. The mean collisional velocity changes and the cross-sections for diffractive velocity-changing collisions are estimated from the data. The results are found to be insensitive to variations of axial magnetic fields and optical densities.

Photoacoustic technique for the measurement of absorption line profiles

A spectrophone utilizing a resonant cylindrical cavity and operated by driving the first azimuthal mode of the cavity has been developed for the study of weak absorption lines of gases at pressures from 100 to 1300 Torr. Presented are the acoustic resonant amplification factor as a function of pressure, and a description of the noise sources inherent in this spectrophone. An example is given of the optical frequency resolution resulting when this spectrophone is used in conjunction with a tunable ring dye laser as a high resolution spectrometer.

High-resolution spectra of the luminous young stellar object V645 Cygni

The paper presents 6310-11,000 A spectra at 22, 75,and 90 km/s resolution of the two brightest knots (N0 and N1) near the luminous young stellar object V645 Cygni. The measured line profiles suggest a circumstellar disk plus bipolar wind model like those proposed for other premain-sequence stars. 68 refs.

Is Delta Scuti Star Seismology Possible?

AbstractThe direct fit of theoretical pulsation frequencies to the observations (i.e. stellar seismology) proved to be a very efficient tool in the study of solar oscillations. In the case of other multiperiodic variables, like δ Scuti stars, Ap stars and white dwarfs the method suffers from the disturbing abundance of possible nonradial modes. Colour and/or radial velocity (or line profile) measurements can narrow down the number of possibilities, but these kinds of data are not often available with the desired accuracy and sampling rate. Since pulsational frequencies are the most readily and accurately computed and measured quantities of pulsation, we address the question of the accurate fit of the nonradial pulsation frequencies to the observations in the case of δ Scuti stars.

L151-81A/B - A unique white dwarf binary with DB and DA components

view Abstract Citations (10) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS L151-81A/B: A Unique White Dwarf Binary with DB and DA Components Oswalt, Terry D. ; Hintzen, Paul M. ; Liebert, James W. ; Sion, Edward M. Abstract Spectroscopic observations of the wide binary L151-81A/B reveal that both components are white dwarfs with spectral types DB3 and DA4, the first such binary identified in a comprehensive survey of Luyten and Giclas common proper motion pairs. Assuming log g = 8, measurements of the helium line profiles in the DB primary yield Teff = 16,000 + or - 2,000, while the hydrogen profiles for the DA companion yield Teff =12,000 + or - 2,000. The existence of a helium-rich/hydrogen-rich degenerate pair offers several interesting tests of theoretical white dwarf formation channels and surface abundance evolution. Publication: The Astrophysical Journal Pub Date: October 1988 DOI: 10.1086/185293 Bibcode: 1988ApJ...333L..87O Keywords: Astronomical Photography; Binary Stars; Spectroscopic Analysis; Stellar Motions; Stellar Spectra; White Dwarf Stars; Helium; Hydrogen; Signal To Noise Ratios; Spectral Resolution; Astrophysics; STARS: BINARIES; STARS: PROPER-MOTION; STARS: SPECTRA; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (1)

Measurements of some plasma-broadened GeI spectral line profiles

The Stark widths and asymmetries of 10 GeI lines have been measured using a wall-stabilized arc, which was observed end-on at N e=5.7×10 16cm -3 and T=12,450 K.

Velocity dependence of impact line-broadening studied by resonant doppler-free two-photon laser spectroscopy

The velocity dependence of the collison broadening of the40Ca 4s 2 1 S 0→4s5p 1 P 1 →4s17d 1 D 2 transition by neon atoms has been studied. The experiment was performed exciting one velocity group of Ca atoms within the Doppler profile of the first transition and probing this group with a counterpropagating laser beam inducing the second transition. Using thermionic detection we have measured broadening rates for relative velocities between Ca and Ne atoms which corresponds to a temperature range of about 850 K (cell temperature) to 3000 K. The measured line-width was found to have very weak temperature dependence. This is attributed to the weak velocity dependence of polarization broadening of the final level which was found to be the major contribution to the broadening of the two-photon line. For large relative velocities significant asymmetries in the measured line profiles due to velocity changing collisions had to be taken into account.

Observation of Balmer-Alpha Line Profile of Hydrogen Atoms in Plasmas by Rapid-Frequency-Scan Laser Spectroscopy

The possibility of an instantaneous determination of the Balmer alpha (Hα) line profile of hydrogen atoms in large plasma devices by rapid-frequency-scan (RAFS) laser spectroscopy is discussed. A detailed analysis of the SN ratio shows that, although the SN ratio in Hα line profile measurements by RAFS is smaller than those in neutral hydrogen density measurements, a remarkable improvement can be obtained by the choice of the optimum saturation parameter and the long-pulse operation. Based on the experiment of the Hα profile measurement in a hydrogen DC glow discharge plasma by RAFS, the profile distortion in saturated excitation is evaluated. The SN ratio in the profile measurement by RAFS for Heliotron E plasma is estimated from the data on the neutral density measurement.