Macroturbulent Velocity Research Articles

Alpha Cygni as a radial-velocity variable

One hundred and twentythree radial velocities for α Cyg are derived between December 1977 and October 1982. These photospheric velocities are derived from NI lines near 8700 a. Semiregular variations in radial velocities are present with periods of 7 to 20 days. The range of variation of 14.3 kms−1 observed in the present radial velocities of α Cyg is close to the sum of the amplitudes (10.44 kms−1) of all the pulsation periods from 7 to 101 days (Lucy 1976a) and is also approximately equal to micro and macro-turbulent velocities.

?Crossing? method for studying the turbulence in solar and stellar atmospheres

A new ‘crossing’ method for the study of turbulent velocities in solar and stellar photospheres is considered. The method does not need knowledge of the abundance and oscillator strengths for determining the microturbulent velocity, if the macroturbulent velocity is adopted; or it allows investigation of the micro- and macro-velocities simultaneously, if the abundance and oscillator strengths are known. Using the crossing method for 200 lines of neutral iron we obtain microturbulent velocities for a large range of depths in the solar photosphere. The distribution of macroturbulent velocities with depth is also investigated. The total velocity field calculated from the obtained micro- and macro-velocities agrees with previous results from independent methods. This demonstrates the reliability of using the crossing method for separate determination of the micro- and macroturbulent velocities in solar and stellar atmospheres.

Measurements of rotation and turbulence in F, G, and K dwarfs

view Abstract Citations (130) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurements of rotation and turbulence in F, G and K dwarfs. Gray, D. F. Abstract Spectral line broadening in 18 F, G, and K dwarfs is analyzed for rotation and macroturbulence. Zeeman broadening is shown to have a significant effect on the derived parameters in late G and early K dwarfs. Support is found for the traditional (lower) v sin i scale. The rotation of the sun is probably normal compared to other stars. The average macroturbulence velocity decreases rapidly with advancing spectral type at the rate of 4 km/s per thousand degrees of effective temperature. The macroturbulence velocity is proportional to the granulation velocities for F and G stars. Publication: The Astrophysical Journal Pub Date: June 1984 DOI: 10.1086/162149 Bibcode: 1984ApJ...281..719G Keywords: Atmospheric Turbulence; Dwarf Stars; F Stars; G Stars; K Stars; Line Spectra; Stellar Rotation; Zeeman Effect; Angular Velocity; Doppler Effect; Fourier Transformation; Photosphere; Solar Rotation; Astrophysics full text sources ADS | data products SIMBAD (18)

The photospheric velocity field of Procyon

BUSS observations of the profiles of two well observed spectral lines in the ultraviolet spectrum of αCMi (Procyon; F5 IV–V) are analysed with a Fourier transform method in order to determine values of various parameters of the velocity field of the upper photosphere. We find a microturbulent line-of-sight velocity componentLμ = 0.9 ± 0.4 km s−1, a macroturbulent velocity componentLM = 5.3 ± 0.2 km s−1, and a rotational velocity componentvR sini=10.0±1.2 km s−1. In these calculations a single-moded sinusoidal isotropic macroturbulent velocity function was assumed. The result appears to be sensitive to the assumed shape of the macroturbulence function: for an assumed Gaussian shape the observations can be described withvR sini=4 km s−1 andLM = 11.6 ± 2.7 km s−1. A comparison is made with other results and theoretical predictions.

Stellar atmospheric velocity fields: The Beta Cephei variables γ Peg and β Cep

The shape parameters of a number of selected ultraviolet lines in BUSS-spectra of the Beta Cephei stars γ Peg and β Cep have been analyzed to determine the principal parameters of the atmospheric velocity field. We find for both stars a fairly high value (∼5 km s−1) for the microturbulent line-of-sight velocity component, which confirms an earlier result based on lower resolution UV spectra. Macroturbulent and rotational velocities are virtually zero in the atmosphere of γ Peg; for β Cep we findvrotsini=40 km s−1.

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.

On asymmetries of solar spectral lines

The profiles of 43 lines have been observed at the centre and near the limb of the solar disk. Their asymmetry decreases towards the limb, and increases with the equivalent width and the mean heigth of line formation; no relation was found between the asymmetry and the line excitation potential, nor with the degree of ionization, nor with the usually adopted macroturbulent velocity. The asymmetry appears to be due to radial movements.

The dependence of macroturbulence on luminosity in early K-type stars

view Abstract Citations (58) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The dependence of macroturbulence on luminosity in early K-type stars. Smith, M. A. ; Dominy, J. F. Abstract The velocity-dissection technique and Fourier techniques are applied to high-quality Reticon data in order to determine rotational and macroturbulent velocities for 17 early K stars and three late G stars of luminosity classes Ib, II, III, and IV. Several tests are made which indicate that the effects of various random and systematic errors are minor. The results suggest that rotational velocities cannot be discerned among early K subgiants and supergiants but are marginally detectable in some giants. This is explained in terms of present ideas concerning rotational deceleration due to evolutionary expansion. No evidence is found for large differences in the macroturbulence velocity distribution among late-type stars of luminosity classes Ib through V. The results obtained for the K1 giant Beta Cep confirm previous reports of a correlation between photospheric and chromospheric turbulence. Publication: The Astrophysical Journal Pub Date: July 1979 DOI: 10.1086/157209 Bibcode: 1979ApJ...231..477S Keywords: Early Stars; K Stars; Late Stars; Stellar Atmospheres; Stellar Luminosity; Stellar Rotation; Turbulent Flow; Chromosphere; G Stars; Photosphere; Spectral Resolution; Velocity Distribution; Astrophysics; K Stars:Luminosities; Late-Type Stars:Turbulence full text sources ADS | data products SIMBAD (21)

Macro-and micro-turbulent filter functions for weak lines in stellar atmospheres

Following a similar discussion given earlier for the solar case (De Jager, 1972) we compute in this paper spectral line profiles for the spatial wavelengths in which a stellar motion field can be decomposed, and thereafter the macro-and micro-turbulent filter functionsf M(θk) andf μ(θk), where θ is the optical scale height andf 2(k) dk the fraction of the energy of the turbulent motions between wavenumbersk andk+dk of the spectrum of turbulence that contributes to either kind of turbulence. If micro-and macro-turbulent velocity components are known for a certain star, and if the spectrum of turbulence is sharp enough, the ratiof M/f μ would enable one to derive the average size of the turbulent elements in the star's atmosphere. The computations apply to weak lines in idealized stellar atmospheres, and refer to two cases: isotropic turbulence, and radial pulsations. These filters can be suitably used in a diagnostic method for the analysis of the motion field in the solar and stellar atmospheres. Some examples of applications to stars of very different kinds are given.

Applications of Fourier analysis to broadening of stellar line profiles. III - Solar microturbulence and macroturbulence from iron lines

Kitt Peak solar profiles of iron lines obtained at ..mu.. = 0.63 were utilized to study the solar velocity field. The high quality of these data and the lack of influence of rotation make possible a modeling of the macroturbulent velocity distribution as well as a determination of the microturbulence. The analysis was performed by matching computed and observed criteria in both the wavelength and the Fourier transform domains. The principal ambiguities in evaluating microturbulence are caused by the uncertainty in the functional form of macroturbulence and in the value of the atomic damping constants. The form of the first sidelobe in the data transforms indicates the existence of a low (/sup 1///sub 4/ +- /sup 1///sub 4/ km s/sup -1/) microturbulence at intermediate photospheric regions which increases toward larger depths. Attempts were made to fit profiles with macroturbulences of a wide variety of functional forms. In the wavelength representation the Voigt distribution gives the best overall fit, whereas in the transform domain an exponential function matches the observed sidelobe best. A comparison of all the results shows only a small disparity in best-fit parameters around a mean of 2.0 km s/sup -1/. A triangular macrovelocity distribution which is similarmore » to that predicted by a radial-tangential model is recovered explicitly by deconvolution. However, for practical reasons a good one-parameter fit to it is provided by the exponential function. Because this function is very dissimilar to the rotation function, it should be possible to evaluate macroturbulence and rotation separately in sharp-lined late-type stars.« less

SPECTRUM SYNTHESIS AND THE SOLAR ABUNDANCE OF COBALT.

ABSTRACT The method of spectrum synthesis is applied to nine Co I lines for which high-resolution spectral data and center-limb comparisons are available. It is noted that the method does not give the elemental abundance, but rather the quantity log gf A, so that an accurate determination of the solar cobalt abundance depends on the establishment of good f-values for the relevant lines. The choice of the model atmosphere is discussed, the most probable micro- and macroturbulent velocities are postulated, and van der Waals interactions are taken into account. Observed and computed profiles at the disk center and the limb are compared for several lines. The failure of the spectral synthesis to represent the line profiles near the limb as well as they are represented at the center is attributed to deviations from local thermodynamic equilibrium. Previous solar cobalt-abundance determinations are reviewed, and it is concluded that the solar atmosphere and carbonaceous chondrites appear to show identical cobalt/silicon ratios within the precision permitted by the present f-values, model atmospheres, and damping-constant theory.

Atmospheric turbulence measured in stars above the main sequence

view Abstract Citations (104) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Atmospheric turbulence measured in stars above the main sequence. Gray, D. F. Abstract Measurements of broadened line profiles are analyzed to identify, measure, and separate macroturbulence from rotation. Evidence is presented for the possibility of more than one macroturbulence velocity distribution. Publication: The Astrophysical Journal Pub Date: November 1975 DOI: 10.1086/153960 Bibcode: 1975ApJ...202..148G Keywords: Atmospheric Turbulence; Line Spectra; Stellar Atmospheres; Stellar Rotation; Giant Stars; Spectral Line Width; Supergiant Stars; Velocity Distribution; Astrophysics full text sources ADS | data products SIMBAD (7)

The He II lines in the spectrum of zeta Puppis

Equivalents widths of He II lines in the series n=2,3,4 and 5 are compiled and compared with predictions from plane-parallel, static model atmospheres using a non-LTE theory of line formation. The agreement between observation and prediction for a (50,000,4.0) model atmosphere is good for the upper members of the n=3 and the n=5 series, but the two lines of the n=2 series which are observed and the upper members of the n=4 series (4$Yields$15,4$Yields$17, etc.) are stronger than predicted. Well-determined profiles of lines from the n=3 series indicate v sin i=200 km s$sup -1$. Profiles of the higher members of the n=4 series, however, do not match the predictions, the observed line cores being deeper than predicted. The n=4 level appears to be more overpopulated at moderate depths in the atmosphere than the non-LTE calculations with plane-parallel layers indicate. This may be due to an overlap of the H and He II lines in the even-even series caused by macroturbulent velocities of the hydrogen atoms and helium atoms. (AIP)

The solar neutral iron spectrum

The profiles of eighteen neutral iron lines of varying strengths were synthesized from disk center to the limb using source functions from detailed statistical equilibrium calculations. Emphasis is placed upon the analysis of the strong Fe i lines between 3500 A and 4500 A which are formed at and below the region of the initial temperature rise in the chromosphere. The major results are as follows: (1) We find an iron abundance of 1.5 × 1−5 relative to hydrogen (7.2 on a logarithmic scale with hydrogen equal to 12) that is independent of the assumed microturbulence model since it is based upon the far wing profiles of the strong lines. The far wings are formed in the photosphere where both the ionization and excitation equilibria are in detailed balance, so this abundance is directly comparable to other LTE abundances. (2) The strong line cores indicate that the chromospheric electron densities in the region of the initial temperature rise are similar to those derived by Henze (1969) from eclipse observations; i.e. higher than the HSRA model (Gingerich et al., 1971) by factors of two to five. We present (3) an anisotropic (angle-dependent) microturbulent velocity model, and (4) a mean macroturbulent velocity that aids in fitting the line cores. The formation of the two Fe i lines λ5232.95 and λ5250.21 is also discussed.

The solar neutral iron spectrum

The profiles of eighteen neutral iron lines of varying strengths were synthesized from disk center to the limb using source functions from detailed statistical equilibrium calculations. Emphasis is placed upon the analysis of the strong Fe i lines between 3500 A and 4500 A which are formed at and below the region of the initial temperature rise in the chromosphere. The major results are as follows: (1) We find an iron abundance of 1.5 × 1−5 relative to hydrogen (7.2 on a logarithmic scale with hydrogen equal to 12) that is independent of the assumed microturbulence model since it is based upon the far wing profiles of the strong lines. The far wings are formed in the photosphere where both the ionization and excitation equilibria are in detailed balance, so this abundance is directly comparable to other LTE abundances. (2) The strong line cores indicate that the chromospheric electron densities in the region of the initial temperature rise are similar to those derived by Henze (1969) from eclipse observations; i.e. higher than the HSRA model (Gingerich et al., 1971) by factors of two to five. We present (3) an anisotropic (angle-dependent) microturbulent velocity model, and (4) a mean macroturbulent velocity that aids in fitting the line cores. The formation of the two Fe i lines λ5232.95 and λ5250.21 is also discussed.

The solar abundance of silver

Low noise, high resolution spectral scans have been obtained for the resonance lines of silver λ3280.7 and λ3382.9, observed at the centre of the solar disk. A double pass-monochromator is used in conjunction with the Snow telescope at Mount Wilson; the transparency of the sky is monitored during the observations in order to achieve required accuracy. The data are analyzed by the method of spectral synthesis wherein we employ a model atmosphere resembling Elste's (1968) model and checked by limb-darkening observations. The present kinematical model adopts a macroturbulent velocity of 2.2 km s−1 and no microturbulence. With this model line profiles can be reproduced without invoking implausibly large collisional damping constants. The silver abundance turns out to be {Ag}=log[N(Ag)/N(H)]+12;=0.85, a factor of four under the value found from the Type I carbonaceous chondrites.

The Distinction Between - and Macroturbulence in the Solar Photosphere Using Line Profiles

view Abstract Citations (32) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Distinction Between - and Macroturbulence in the Solar Photosphere Using Line Profiles Elste, Guenther H. E. Abstract On the basis of line-profile studies of sixty-two weak and medium-strong lines of Fe I, whose excitation potentials lie above 3 eV, a distinction between macro- and microturbulence is sought by comparing the observed relation between the half-widths and the equivalent widths with model computations. The shape of the lines near their cores as well as the curves of growth supports the result that the microturbulence velocity must be as low as 1 km/sec, while macroturbulent velocities of at least 1.5 km/sec are needed to explain the observations These conclusions are drawn from spectra of the center of the disk only. The more extensive study of the velocity field using the complete center-to4imb variation of the line profiles is in progress. Publication: The Astrophysical Journal Pub Date: June 1967 DOI: 10.1086/149210 Bibcode: 1967ApJ...148..857E full text sources ADS |

A systematic method for the analysis of high-resolution fraunhofer line profiles

A fraunhofer line profile depends on various parameters, partly related to the photospheric structure (T, Pg, Pe, vconv, vturb), partly to the atom or ion involved (such as oscillator strength, energy levels), partly also resulting from the interaction of the relevant kind of particles with the photosphere, and the photospheric radiation field. In this paper we shall mainly pay attention to the determination of: the macroturbulent (convective) velocities, vconv (τ); the damping constant γ (τ); the abundance, Ael; the distribution function ϕ(vconv, τ) of the convective velocities at each depth τ; the source function, S (τ); the microturbulent velocities, vturb (τ).

Turbulent Velocities in the Atmosphere of the Supergiant Canis Majoris

Equivalent widths, half-widths and central depths of Fe I and Fe II are measured from a high dispersion spectrum of the supergiant δ Canis Majoris. The equivalent widths of the Fe I lines are used in a curve of growth analysis to examine the dependence of the microturbulent velocity on excitation potential. The microturbulent velocity is found to be about 12 km/sec for lines of all excitation potentials. The macroturbulent velocity is derived from the half-widths and central depths of the Fe I lines. It is also found to be independent of excitation potential but the study of the central depths of the Fe I lines indicates a probable dependence of macro-turbulent velocity upon equivalent width. Some reasons are advanced as a possible explanation of this dependence.