Line Profile Measurements Research Articles

Collision cross sections for the noble-gas broadening of the Cs 6S-7P doublet using photon echoes

Collisional cross sections and broadening constants are presented for each of the fine-structure components of the second resonance transition in caesium (6S12/-7P32,1/2/, 4555 AA, 4593 AA) perturbed by the five noble gases He-Xe. The results were obtained at perturber pressures of less than 0.5 Torr using the photon echo technique. The cross sections correspond closely with those obtained from spectral line profile measurements, but there are some significant discrepancies.

Mass loss in T Tauri stars - Observational studies of the cool parts of their stellar winds and expanding shells

view Abstract Citations (142) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass loss in T Tauri stars : observational studies of the cool parts of their stellar winds and expanding shells. Mundt, R. Abstract Extensive high-resolution and high signal-to-noise line profile measurements of 23 T Tauri stars are presented. Those stars showing indications for mass loss in the Na D lines were observed in H-alpha and Ca II K as well. Mass loss in these stars is found to be often indicated in the Na D lines by rather sharp blueshifted absorption lines. The observed line profiles strongly suggest that, at least in some stars, the winds are already accelerated to 150-350 km/s within 1.1-1.5 stellar radii. For the narrow, blueshifted Na D absorptions, two formation regions are discussed: (1) the distant, cold parts of the stellar wind, and (2) a stellar wind-driven shell. The descending material occasionally observed in some T Tauri stars is interpreted to be infalling matter recently ejected by these stars, and not matter left over from the star formation process. Publication: The Astrophysical Journal Pub Date: May 1984 DOI: 10.1086/162048 Bibcode: 1984ApJ...280..749M Keywords: Pre-Main Sequence Stars; Stellar Evolution; Stellar Mass Ejection; Stellar Spectra; Stellar Winds; T Tauri Stars; Absorption Spectra; H Alpha Line; Radial Velocity; Signal To Noise Ratios; Astrophysics full text sources ADS | data products SIMBAD (12)

Photon echo relaxation in caesium perturbed by noble gases

The collisional relaxation of photon echoes generated on the 6S built1 2 - 7P built3 2 (455 nm) transition in caesium has been observed and measured as a function of perturber pressure. Values for the collision cross-sections have been obtained using helium, neon, argon and krypton as perturbers. There is good agreement between these results and those obtained from high resolution measurements of pressure-broadened line profiles. The echoes were observed using the polarization rotation technique and all the measurements were made at perturber pressures below 0.5 torr.

Heterodyne spectroscopy for astrophysical applications using tunable laser sidebands at 10 microns

A heterodyne system was assembled from a microwave tunable sideband laser, a blackbody source, a gas cell, a CdHgTe photomixer and a filterbank. A measurement of line profiles of CH3F is presented and compared with absorption measurements. System sensitivity is sufficient for high resolution measurement of fine structure lines from astronomical objects, though falling short by a factor of 12, when compared with the most sensitive astronomical heterodyne spectrometers. The usefulness of such a system for astrophysical applications is discussed.

Analysis of Intensity Ratio for MgXII Lyα Components from Intercosmos 7 Observations

We discuss the Mg XII Lyα line profile measurements obtained, by means of Bragg crystal spectrometer aboard INTERCOSMOS 7 satellite. The design of this spectrometer allows to clearly resolve both components α½ and α3/2) of the Lyα spin doublet. The intensities of each of these components we derived by means of fitting two Voigt profiles to the measured Mg XII Lyα shape. More than 100 spectra were analyzed in this way providing the statistical information on the value of intensity ratio . Derived average value of a is close to the theoretically expected 0.5, but in many cases the value of a is significantly different from 0.5 (both lower and higher values occur). We present examples of the fit and the histograms showing correlations of a value with the values of other flare parameters. Present analysis consist the observational part of the larger paper under the preparation with Prof. R.W.P. McWhirter theoretical group.

Calculation of the combined Zeeman and translational Stark effect on the Hα-multiplet

The properties of the combined Zeeman and translational Stark effect on the hydrogen Balmer α line have been studied in detail under various plasma conditions. The applicability of the calculation method proposed here to transitions involving terms of hydrogenic atoms and hydrogen-like ions is suggested. Apart from its relevance for line profile measurements and particle beam diagnostics in Tokamaks some features concerning the application of the translational linear Stark effect in atomic and plasma physics are discussed.

Collisional effects on the rovibrational transitions of the HD fundamental band

The effect of collisions with self and buffer gases, Ar, Kr, and Xe, on the linewidth, line shape, and frequency of the rovibrational transitions of HD in its ground electronic state are studied with a high-resolution tunable laser difference-frequency spectrometer. Collisional narrowing, manifested in sub-Doppler width of the transitions, is observed (for the first time in HD) in both P and R branches of the infrared fundamental band. The measured line profiles and the pressure dependence of their widths are analyzed in the limits of strong and weak velocity-changing collisions. It is shown that both models fit the data equally well in the low pressure range (below about 300 Torr). The strong collision model, however, is found to be the best fit for HD/HD collisions in the entire 10–760 Torr pressure range. In the case of HD/buffer gas collisions, a model incorporating correlations between the velocity and state-changing collisions appears to be more appropriate. The dependence of collisional narrowing and broadening parameters on the rotational quantum number is reported and discussed.

Stigmatic coma free VUV devices for high resolution line profiles measurements

Optical devices for line profile measurements must have a symmetrical instrumental profile to allow the use of classical deconvolution methods. Such devices must be then coma free and simultaneously the astigmatic curvature must be eliminated. In a first approach we consider a modified version of a Rowland circle set-up, and in a second one, a new type of stigmatic and coma free spectrometer fitted with spherical holographic gratings each of them covering a restricted spectral range.

On the 2Σ potentials for the interaction of K(4P) and K(5P) with argon

In addition to recent experiments with differential scattering of K(4P) form Ar, blue-wing satellites for K(4P) and K(5P) have been measured at 729.7 and 403.97 nm, respectively (classical position). Both the scattering and the line profile measurements are simultaneously reproduced quite well by results from a model potential calculation. In this calculation the satellites are found at 727.8 and 404.14 nm, respectively. These are due to maxima in the corresponding Σ potentials located near 7 and 20 au, respectively.

The effect of rare-gas collisions on the wings of the potassium 4p2P3/2-7s2S1/2(5802 Å) transition

The potassium 4p 2P3/2-7s 2S1/2 (5802 A) transition when broadened by the noble gases exhibits satellites and line asymmetries which are clearly of a collisional origin. Measurements of complete line profiles are given for broadening by He, Ne, Ar, Kr and Xe within 16 cm-1 of the line centre at densities up to 1019 atoms cm-3 as observed for a microwave-excited electrodeless discharge. These are compared to computed unified theory line shapes and are found to agree when appropriate parameterised potentials are chosen for the potassium-noble-gas interactions. Such analyses yield experimental potentials for the 7s state that show extrema at interatomic separations from 14 to 18 A that are slightly repulsive for He and Ne, and attractive for Ar, Kr, and Xe. These features are not correctly predicted by the pseudopotential calculations of Pascale and Vandeplanque (1974) and are only qualitatively accounted for with potentials of the Fermi type.

Influence of supersaturated melt for InP growth on InP-InGaAsP interface of double-heterostructure laser wafers

Liquid-phase epitaxial growth with higher supersaturated InP growth melt could be successfully used in fabricating InGaAsP/InP double heterostructure (DH) lasers emitting in the 1.50–1.55-μm wavelength region. InP-InGaAsP interface characterization has been carried out with scanning electron microscope (SEM), transmission electron microscope, photoluminescence (PL) measurements, and Auger spectroscopy. From the dissolution depth measurements, it was found that there is a slight dissolution on the surface of the InGaAsP layer, even in the 1.3-μm wavelength region during an InP layer growth with 16° supersaturated melt. Although the amount of dissolution increases as the composition of the quaternary active layer becomes a longer wavelength, as a result of this dissolution, the transition region does not catastrophically affect the laser performances at a wavelength shorter than 1.55 μm. It was found that the InP-InGaAsP interface at 1.59-μm wavelength shows rugged configuration under high-resolution SEM observation and the half-width of PL spectrum becomes wider than that for DH wafers at a wavelength shorter than 1.55 μm. This was confirmed by Auger line profile measurements.

Line profile measurements of radiation from the magnetic field glow discharge source

Line profile measurements of radiation from the magnetic field glow discharge source

A method of data processing for improving precision of intensity measurements in inductively-coupled plasma emission spectrometry with a programmable monochromator

In the computer program described, a Gaussian curve is fitted to the measured line profile and peak intensity is determined from the calculated curve. Relative standard deviations are improved by 20% compared to normal measurements. Effects of the number of accumulations and slitwidths are discussed.

Determination of Cs(np)-Xe interactions from spectral line profile measurements

The 6s-7p, 8p and 9p absorption transitions in caesium perturbed by xenon foreign gas at a temperature of approximately 500K and densities up to 1.2*1019 atoms/cm3 have been observed with a high-resolution computer-controlled spectrometer. A Fourier analysis technique to deconvolve the asymmetric line core from instrumental and Doppler effects yields width, shift and asymmetry for the 7p an 8p doublets independent of the instrument and directly comparable with line-broadening calculations. Normalised profiles of the wings of the 7p and 8p transitions, and of the entire 9p contour are also given from measurements at sufficiently high resolution that instrumental effects are negligible. The observed line core-parameters and line profiles are compared with Anderson-Talman lineshape calculations (1956). The authors also note the observation of multiple-perturber satellites as predicted by the Anderson-Talman theory based on the assumption of additivity of the interaction.

Turbulence in the Atmospheres of Eclipsing Binary Stars

Abstract:A review of the orbits and dimensions of the ζ Aurigae systems is given, based on photometric and spectrographic observations. The Ca II K-line has been studied intensively to determine the extent and uneven structure of the chromospheres of these stars; the multiple structure of this line observed at several eclipses confirms the presence of large-scale clouds in the atmospheres. Measurements of line profiles and equivalent widths show that macroturbulent velocities up to 10 km/sec in the upper chromosphere, and up to 20 km/sec. in the lower chromosphere are present. Microturbulent velocities in the lower chromosphere are about 10 km/sec. Recent ultraviolet observations indicate that the B star in the 32 Cygni system may be within the outer chromosphere of the giant component and its radiation may affect the chromospheric structure more than had previously been suggested.

ACCURACY OF LINE-PROFILE MEASUREMENTS.

ABSTRACT Comparisons are made among high-resolution line-profile measurements of Fe I 6065 and 6253 wavelengths in the spectrum of Arcturus. The line-profile measurements were made with four entirely different sets of equipment in order to have a leverage on external errors; three coude spectrographs and one Fourier transform spectrometer are used. The results indicate consistency in line shape to about 1% but zero-level differences of 2-5%. This represents a substantial improvement over the accuracy attained in the past decades. Reference profiles are tabulated for comparison by future observers.

Stratospheric sounding by infrared heterodyne spectroscopy

Intensity profiles of infrared spectral lines of stratospheric constituents can be fully resolved with a heterodyne spectrometer of sufficiently high resolution (∼5 MHz or 0.000167 cm−1 at 10 µ). The constituents' vertical distributions can then be evaluated accurately by analytic inversion of the measured line profiles. Estimates of the detection sensitivity of a heterodyne receiver are given in terms of minimum detectable volume mixing ratios of stratospheric constituents, indicating a large number of minor constituents which can be studied. Stratospheric spectral line shapes and the resolution required to measure them are discussed in light of calculated synthetic line profiles for some stratospheric molecules in a model atmosphere. The inversion technique for evaluation of gas concentration profiles is briefly described, and applications to synthetic lines of O3, CO2, CH4, and N2O are given. Some recent heterodyne measurements of CO2 and O3 absorption lines are analytically inverted, and the vertical distributions of the two gases are determined.

Simple fast-scanning Fabry-Perot spectrometer

A simple time-resolved Fabry-Perot spectrometer has been designed for the measurement of line profiles emitted by a pulsed plasma. The rotating mirror is used to scan the spatial image of the fringes. The intensity distribution of interference patterns can be observed within a scanning time of 25 nsec. The velocity of an accelerated copper plasma was measured by means of this system.

ON THE POSSIBILITY OF MEASURING STELLAR CONVECTION PARAMETERS.

ABSTRACT The detailed knowledge of solar convection now available is used to evaluate the possibility of deriving some of the surface convection parameters of other stars from line-profile measurements. A theory is outlined for computing integrated line profiles with convection, rotation, and limb darkening. This theory is employed to calculate line profiles for rotating convecting stars of the solar class for values of equatorial v sin i ranging from 0 to 10 km/s. Fourier sine transforms for solar-class stars are examined, and applications to stars not of the solar class are discussed. Several possible sources of line asymmetry are identified.

Analytical description of a Fabry-Perot spectrometer 4: Signal noise limitations in data retrieval; winds, temperature, and emission rate

A quantitative investigation of the effects of noise inherent in the signal received by the detector of a Fabry-Perot spectrometer has been carried out in detail. The study also includes the effects of the instrumental profile width and the presence of unwanted continuum radiation in the signal, such as background radiation and detector dark current. The results show the spectrum of the noise in the transform plane to have a quantitative description in terms of the instrumental and line shapes as well as the signal strength, or emission rate, of both the line profile and the unwanted radiation. The magnitude and shape of this noise spectrum not only limits in a known quantitative manner the amount of useful information available from a given measured profile, but it also provides information on the profile itself, thus allowing for more information to be obtained from the measurement than would otherwise be possible. A detailed example is given for the retrieval of winds, temperature, and emission rate from line profile measurements, and it is quantitatively shown how the (noise) limited information available from a measured profile appears as uncertainties of determination. These uncertainties are shown to be dependent on the signal strength, more correctly the noise inherent in this signal, as well as the shapes and relative widths of the line and instrumental profiles, with the temperature uncertainty showing the most sensitivity to these factors. Although in some cases the results are qualitatively obvious, their quantitative nature allows the design of experiments for least uncertainty and/or define the limitations inherent in such experiments.