scholarly journals Formation Depths of Spectral Lines in Cepheids

1995 ◽  
Vol 155 ◽  
pp. 373-374
Author(s):  
Michael D. Albrow ◽  
P. L. Cottrell
Keyword(s):  
Spectral Line ◽  
Velocity Fields ◽  
Radial Velocities ◽  
Spectral Lines ◽  
Line Formation ◽  
Ionisation Potential ◽  
Velocity Gradients ◽  
Different Levels ◽  
Line Depth

There has been a number of observational programmes that have endeavoured to investigate the atmospheric velocity fields in Cepheids (e.g., Sanford 1956, Wallerstein et al. 1992, Butler 1993). These studies measured the radial velocities of lines of different strength, excitation and ionisation potential as these provide an indication of line formation at different levels in the atmosphere. From these measurements, the presence of velocity gradients can be inferred, but determination of the magnitude of such gradients requires knowledge of the spectral line depth of formation. Through dynamical modelling we are endeavouring to ascertain what is actually being measured in the above observational programmes.

scholarly journals Tomography of cool giant and supergiant star atmospheres

2018 ◽  
Vol 610 ◽  
pp. A29 ◽  
Author(s):  
K. Kravchenko ◽  
S. Van Eck ◽  
A. Chiavassa ◽  
A. Jorissen ◽  
B. Freytag ◽  
...  
Keyword(s):  
Spectral Line ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Line Formation ◽  
Tomographic Method ◽  
1D Model ◽  
Supergiant Star

Context. Cool giant and supergiant star atmospheres are characterized by complex velocity fields originating from convection and pulsation processes which are not fully understood yet. The velocity fields impact the formation of spectral lines, which thus contain information on the dynamics of stellar atmospheres. Aim. The tomographic method allows to recover the distribution of the component of the velocity field projected on the line of sight at different optical depths in the stellar atmosphere. The computation of the contribution function to the line depression aims at correctly identifying the depth of formation of spectral lines in order to construct numerical masks probing spectral lines forming at different optical depths. Methods. The tomographic method is applied to one-dimensional (1D) model atmospheres and to a realistic three-dimensional (3D) radiative hydrodynamics simulation performed with CO5BOLD in order to compare their spectral line formation depths and velocity fields. Results. In 1D model atmospheres, each spectral line forms in a restricted range of optical depths. On the other hand, in 3D simulations, the line formation depths are spread in the atmosphere mainly because of temperature and density inhomogeneities. Comparison of cross-correlation function profiles obtained from 3D synthetic spectra with velocities from the 3D simulation shows that the tomographic method correctly recovers the distribution of the velocity component projected on the line of sight in the atmosphere.

scholarly journals Determination of metallicity of the HR7914 solar-like star

2003 ◽  
pp. 69-74 ◽  
Author(s):  
Oliver Vince ◽  
Istvan Vince
Keyword(s):  
Spectral Line ◽  
Stellar Atmosphere ◽  
Astronomical Observatory ◽  
Program Package ◽  
Spectral Lines ◽  
Iron Abundance ◽  
Microturbulent Velocity

By using the Blackwell program package by R.O. Gray, the metallicity of the HR7914 solar-like star was determined. The program package utilizes measured equivalent widths of several chosen neutral iron spectral lines from the observed spectra, appropriate atomic and spectral line parameters and adequate Kurucz?s stellar atmosphere models. The method is based on determination of the minimum dispersion of the iron abundance versus microturbulent velocity functions for the selected neutral iron spectral lines. The spectra were observed at National Astronomical Observatory Rozhen (NAO Rozhen), Bulgaria, using the 2m-telescope and Coude spectrograph. They were reduced with the IRAF program package. The measurement of the spectral line parameters was done with the SPE program package. The metallicity of the HR7914 solar-like star was determined to be 0.02.

scholarly journals Solar Oscillator Strengths as a Diagnostic Tool

1990 ◽  
Vol 138 ◽  
pp. 35-40
Author(s):  
E. A. Gurtovenko ◽  
R. I. Kostik ◽  
R. J. Rutten
Keyword(s):  
Spectral Line ◽  
Diagnostic Tool ◽  
Chemical Elements ◽  
Laboratory Data ◽  
Solar Spectrum ◽  
Oscillator Strengths ◽  
Small Subset ◽  
Solar Photosphere ◽  
Line Formation ◽  
Line Depth

We briefly review the Kiev program for determining oscillator strengths of Fraunhofer lines from the optical solar spectrum, which has recently resulted in a compilation of solar gf-values for 1958 lines from 40 chemical elements (Gurtovenko and Kostik 1989). These gf-values were determined empirically by fitting solar lines using standard plane-parallel LTE modelling. Errors in this modelling propagate into the gf-values; reversely, the deviations in the latter may serve as diagnostics of the modelling and thus of spectral line formation in the solar photosphere. For a small subset, comparison with reliable laboratory data can be made; for other lines there is information in the differences between fits of the line area and of the line depth.

scholarly journals Observations of velocity fields in WN and Of stars

1979 ◽  
Vol 83 ◽  
pp. 475-478
Author(s):  
Virpi S. Niemelä
Keyword(s):  
Velocity Field ◽  
Large Scale ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Emission Lines ◽  
Temperature Structure ◽  
Early Type ◽  
Velocity Gradients ◽  
Early Type Stars

Systematic wavelength shifts of series of spectral line centers observed in many early type stars, generally interpreted as due to large scale motions, can give us information about the velocity gradients in stellar atmospheres. However, it should be borne in mind that the velocity gradients inferred from the observed displacements of spectral lines may not correspond to a unique alternative (e.g. see Karp 1978). Also, and especially when we are dealing with stars which have emission lines in their spectra, the structure of the velocity field depends on the assumed temperature structure of the atmosphere, i.e. in which atmospheric region do the lines originate.

scholarly journals The Magnetic and Velocity Fields and Brightness in the Solar Atmosphere

1971 ◽  
Vol 43 ◽  
pp. 274-278 ◽  
Author(s):  
S. I. Gopasyuk ◽  
T. T. Tsap
Keyword(s):  
Active Regions ◽  
Velocity Fields ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Solar Photosphere ◽  
Zero Line ◽  
Isotropic Distribution ◽  
The Mean ◽  
Different Levels ◽  
Made In

Simultaneous observations of the magnetic fields, the line-of-sight velocities and brightness were made in active and quiet regions with the Crimean double-magnetograph in the following lines: Hα, K3 Ca II, Hβ, Hγ, Hδ, MgI λ 5184 Å, CaI λ 4227 Å, D1 NaI, BaII λ 4554 Å, CaI λ 6103 Å, FeI λ 5250 Å.It is shown, that in the active regions the horizontal velocity is larger than the vertical one.The mean velocities in the quiet solar photosphere have an isotropic distribution (Gopasyuk and Kalman, 1971).The mean vertical velocities increase exponentially with height in active and quiet regions.The correlation between velocities at different levels in active and quiet regions decreases with the distance between the levels of the formation of spectral lines, and it disappears for the velocities recorded in λ 6103 Å and Hβ, for λ 5184 and Hα lines in active regions and for the velocities recorded in λ 5250 Å and Hα lines in quiet regions.The position of the maximal field strength within a magnetic hill coincides statistically with the zero line of the line-of-sight velocities for active as well as for quiet regions.

scholarly journals Benchmark stars, benchmark spectrographs

2020 ◽  
Vol 642 ◽  
pp. A182
Author(s):  
V. Adibekyan ◽  
S. G. Sousa ◽  
N. C. Santos ◽  
P. Figueira ◽  
C. Allende Prieto ◽  
...  
Keyword(s):  
Spectral Line ◽  
Line Width ◽  
Spectroscopic Data ◽  
Spectral Lines ◽  
High Quality ◽  
Ultrahigh Resolution ◽  
Stellar Spectroscopy ◽  
Spectral Reduction ◽  
Very High ◽  
Line Depth

Context. Gaia benchmark stars are selected to be calibration stars for different spectroscopic surveys. Very high-quality and homogeneous spectroscopic data for these stars are therefore required. We collected ultrahigh-resolution ESPRESSO spectra for 30 of the 34 Gaia benchmark stars and made them public. Aims. We quantify the consistency of the results that are obtained with different high- (R ~ 115 000), and ultrahigh- (R ~ 220 000) resolution spectrographs. We also comprehensively studied the effect of using different spectral reduction products of ESPRESSO on the final spectroscopic results. Methods. We used ultrahigh- and high-resolution spectra obtained with the ESPRESSO, PEPSI, and HARPS spectrographs to measure spectral line characteristics (line depth; line width; and equivalent width, EW) and determined stellar parameters and abundances for a subset of 11 Gaia benchmark stars. We used the ARES code for automatic measurements of the spectral line parameters. Results. Our measurements reveal that the same individual spectral lines measured from adjacent 2D (spectrum in the wavelength-order space) echelle orders of ESPRESSO spectra differ slightly in line depth and line width. When a long list of spectral lines is considered, the EW measurements based on the 2D and 1D (the final spectral product) ESPRESSO spectra agree very well. The EW spectral line measurements based on the ESPRESSO, PEPSI, and HARPS spectra also agree to within a few percent. However, we note that the lines appear deeper in the ESPRESSO spectra than in PEPSI and HARPS. The stellar parameters derived from each spectrograph by combining the several available spectra agree well overall. Conclusions. We conclude that the ESPRESSO, PEPSI, and HARPS spectrographs can deliver spectroscopic results that are sufficiently consistent for most of the science cases in stellar spectroscopy. However, we found small but important differences in the performance of the three spectrographs that can be crucial for specific science cases.

scholarly journals Evaluation of a spectral line width for the Phillips spectrum by means of numerical simulation

2015 ◽  
Vol 22 (3) ◽  
pp. 325-335 ◽  
Author(s):  
A. O. Korotkevich ◽  
V. E. Zakharov
Keyword(s):  
Numerical Simulation ◽  
Kinetic Equation ◽  
Spectral Line ◽  
Line Width ◽  
Water Waves ◽  
Spectral Lines ◽  
Dynamical Equations ◽  
Spectral Line Width ◽  
Original Motivation ◽  
Different Levels

Abstract. The work aims to check one of the assumptions under which the kinetic equation for water waves was derived in order to understand whether it can be applied to the situations described by the Phillips spectrum. We evaluate a spectral line width of the spectrum from the simulations in the framework of primordial dynamical equations at different levels of nonlinearity in the system, corresponding to the weakly turbulent Kolmogorov–Zakharov spectra ω−4, Phillips spectra ω−5, and intermediate cases. The original motivation of the work was to check one of the assumptions under which the kinetic equation for water waves was derived in order to understand whether it can be applied to the Phillips spectrum. It is shown that, even in the case of relatively high average steepness, when the Phillips spectrum is present in the system, the spectral lines are still very narrow, at least in the region of the direct cascade spectrum. It allows us to state that, even in the case of the Phillips spectrum, one of the assumptions used for the derivation of the Hasselmann kinetic equation is still valid, at least in the case of moderate whitecapping.

The Interpretation of Line Profiles

1977 ◽  
Vol 36 ◽  
pp. 191-215
Author(s):  
G.B. Rybicki
Keyword(s):  
Magnetic Fields ◽  
Atomic Physics ◽  
Velocity Fields ◽  
Spectral Lines ◽  
Inhomogeneous Structure ◽  
The Sun ◽  
Line Profiles ◽  
Physical Phenomena

Observations of the shapes and intensities of spectral lines provide a bounty of information about the outer layers of the sun. In order to utilize this information, however, one is faced with a seemingly monumental task. The sun’s chromosphere and corona are extremely complex, and the underlying physical phenomena are far from being understood. Velocity fields, magnetic fields, Inhomogeneous structure, hydromagnetic phenomena – these are some of the complications that must be faced. Other uncertainties involve the atomic physics upon which all of the deductions depend.

On the Inhomogeneity of Chemical Composition over the Surface of 21 Per

1976 ◽  
Vol 32 ◽  
pp. 343-349
Author(s):  
Yu.V. Glagolevsky ◽  
K.I. Kozlova ◽  
V.S. Lebedev ◽  
N.S. Polosukhina
Keyword(s):  
Chemical Composition ◽  
Spectral Line ◽  
Variable Star ◽  
Radial Velocities ◽  
Crimean Astrophysical Observatory ◽  
Line Intensities ◽  
Magnetic Variable

SummaryThe magnetic variable star 21 Per has been studied from 4 and 8 Å/mm spectra obtained with the 2.6 - meter reflector of the Crimean Astrophysical Observatory. Spectral line intensities (Wλ) and radial velocities (Vr) have been measured.

Sign in / Sign up

Export Citation Format

Share Document