Differential Fe I Line Shifts as Convective Signatures in R = 40 000 Échelle Spectra?

1999 ◽  
Vol 170 ◽  
pp. 286-290
Author(s):  
Dag Gullberg
Keyword(s):  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Wavelength Shift ◽  
Cross Correlations

AbstractThe convection in stellar atmospheres causes spectral lines to be more or less blue-shifted. The differential wavelength shift between two groups of spectral lines could be used to characterize the convection. This paper describes such an effort using cross-correlations between R ≈ 40 000 échelle spectra and laboratory wavelength templates.

scholarly journals The relationship between photometric and spectroscopic oscillation amplitudes from 3D stellar atmosphere simulations

2021 ◽  
Author(s):  
Yixiao Zhou ◽  
Thomas Nordlander ◽  
Luca Casagrande ◽  
Meridith Joyce ◽  
Yaguang Li ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Three Dimensional ◽  
Quantitative Relationship ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Wavelength Shift ◽  
The Sun ◽  
Theoretical Derivation ◽  
Velocity Amplitude ◽  
Good Agreement

Abstract We establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, three-dimensional (3D), hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity amplitude for two case studies: the Sun and the red giant ε Tau. Luminosity amplitudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity amplitudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in BiSON and SONG observations. Consequently, the theoretical luminosity to radial velocity amplitude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm/[m s−1] from BiSON and SONG respectively, in good agreement with observations 19.1 and 21.6 ppm/[m s−1]. For ε Tau, we predict K2 and SONG ratios of 48.4 ppm/[m s−1], again in good agreement with observations 42.2 ppm/[m s−1], and much improved over the result from conventional empirical scaling relations which gives 23.2 ppm/[m s−1]. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.

The Use of Fabry-Perot Filters for Spectral Scanning

1969 ◽  
Vol 1 (6) ◽  
pp. 293-294
Author(s):  
M. D. Waterworth
Keyword(s):  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Resolving Power ◽  
Doppler Broadening ◽  
Collisional Broadening ◽  
Fabry Perot

In designing a stellar spectrograph, it is pointless to exceed the resolving power necessary to obtain all the information from the spectrum of a star. This is limited mainly by atomic thermal motions, giving rise to the Doppler broadening of spectral lines, by turbulence and rotation of the stellar atmospheres in which the lines are formed, and by collisional broadening.

scholarly journals The effect of hyperfine splitting on Stark broadening for three blue-green Cu i lines in laser-induced plasma

2019 ◽  
Vol 488 (4) ◽  
pp. 5594-5603 ◽  
Author(s):  
A M Popov ◽  
N I Sushkov ◽  
S M Zaytsev ◽  
T A Labutin
Keyword(s):  
Hyperfine Splitting ◽  
Stark Effect ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Stark Broadening ◽  
Laser Induced Plasma ◽  
Radiation Sources ◽  
And Shifts ◽  
First Time ◽  
Existing Data

ABSTRACT Stark effect is observed in many natural and artificial plasmas and is of great importance for diagnostic purposes. Since this effect alters profiles of spectral lines, it should be taken into account when assessing chemical composition of radiation sources, including stars. Copper is one of the elements which studies of stellar atmospheres deal with. To this end, UV and visible Cu lines are used. However, there is a lack of agreement between existing data on their Stark parameters. It is therefore of interest to obtain new experimental data on these lines and to compare them to previous results. In this work, we have estimated Stark widths and shifts for three blue-green lines at 5105.54, 5153.24, and 5218.20 Å (corresponding transitions are [3d104p] 2P° → [3d94s2] 2D and [3d104d] 2D → [3d104p] 2P°) observed in a ‘long-spark’ laser-induced plasma. For the first time, we have accurately estimated an impact of hyperfine splitting on the profile shapes of the studied lines taking also into account the isotope shifts. We have shown that both effects considerably influence shift and width of Cu i line at 5105.54 Å, and shifts of Cu i lines at 5153.24 and 5218.20 Å.

scholarly journals Three-dimensional simulations of scattering polarization and the Hanle effect in MHD chromospheric models

2014 ◽  
Vol 10 (S305) ◽  
pp. 360-367 ◽  
Author(s):  
J. Štěpán
Keyword(s):  
Recent Progress ◽  
Spectral Synthesis ◽  
Three Dimensional ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Line Formation ◽  
Spatially Resolved ◽  
Synthetic Spectra ◽  
Hanle Effect ◽  
Three Dimensional Simulations

AbstractScattering line polarization and the Hanle effect are among the most important mechanisms for diagnostics of the solar and stellar atmospheres. The fact that real stellar atmospheres are horizontally inhomogeneous makes the spectral synthesis and interpretation very challenging because the effect of thermodynamic fluctuations on spectral line polarization is entangled with the action of magnetic fields. This applies to the spatially resolved as well as to the averaged spectra. The necessary step towards the interpretation of such spectra is to study the line formation in sufficiently realistic 3D MHD models and compare the synthetic spectra with observations. This paper gives an overview of recent progress in the field of 3D NLTE synthesis of polarized spectral lines resulting from investigations with the radiative transfer code PORTA.

scholarly journals A temperature dependence of the width of the atom spectral lines in stellar atmospheres

1998 ◽  
Vol 2 (1) ◽  
pp. 16-22
Author(s):  
I. O. Vakarchuk ◽  
R. E. Rykalyuk ◽  
L. M. Yankiv-Vitkovska
Keyword(s):  
Temperature Dependence ◽  
Stellar Atmospheres ◽  
Spectral Lines

scholarly journals Stark broadening of resonant Cr II 3d5–3d44p spectral lines in hot stellar atmospheres

2013 ◽  
Vol 432 (3) ◽  
pp. 2247-2251 ◽  
Author(s):  
Z. Simić ◽  
M. S. Dimitrijević ◽  
S. Sahal-Bréchot
Keyword(s):  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Stark Broadening

scholarly journals Simulation of the small-scale magnetism in main-sequence stellar atmospheres

2018 ◽  
Vol 614 ◽  
pp. A78 ◽  
Author(s):  
R. G. Salhab ◽  
O. Steiner ◽  
S. V. Berdyugina ◽  
B. Freytag ◽  
S. P. Rajaguru ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Spectral Type ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Small Scale ◽  
Positive Contribution ◽  
The Sun ◽  
Free Atmosphere ◽  
Paper Properties

Context. Observations of the Sun tell us that its granular and subgranular small-scale magnetism has significant consequences for global quantities such as the total solar irradiance or convective blueshift of spectral lines. Aims. In this paper, properties of the small-scale magnetism of four cool stellar atmospheres, including the Sun, are investigated, and in particular its effects on the radiative intensity and flux. Methods. We carried out three-dimensional radiation magnetohydrodynamic simulations with the CO5BOLD code in two different settings: with and without a magnetic field. These are thought to represent states of high and low small-scale magnetic activity of a stellar magnetic cycle. Results. We find that the presence of small-scale magnetism increases the bolometric intensity and flux in all investigated models. The surplus in radiative flux of the magnetic over the magnetic field-free atmosphere increases with increasing effective temperature, Teff, from 0.47% for spectral type K8V to 1.05% for the solar model, but decreases for higher effective temperatures than solar. The degree of evacuation of the magnetic flux concentrations monotonically increases with Teff as does their depression of the visible optical surface, that is the Wilson depression. Nevertheless, the strength of the field concentrations on this surface stays remarkably unchanged at ≈1560 G throughout the considered range of spectral types. With respect to the surrounding gas pressure, the field strength is close to (thermal) equipartition for the Sun and spectral type F5V but is clearly sub-equipartition for K2V and more so for K8V. The magnetic flux concentrations appear most conspicuous for model K2V owing to their high brightness contrast. Conclusions. For mean magnetic flux densities of approximately 50 G, we expect the small-scale magnetism of stars in the spectral range from F5V to K8V to produce a positive contribution to their bolometric luminosity. The modulation seems to be most effective for early G-type stars.

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 Theoretical transition probabilities, radiative lifetimes and Stark broadening parameters of singly ionized magnesium

2019 ◽  
Vol 490 (2) ◽  
pp. 1734-1737
Author(s):  
C Moreno-Díaz ◽  
A Alonso-Medina
Keyword(s):  
Transition Probabilities ◽  
Principal Quantum Number ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Atomic Data ◽  
Stark Broadening ◽  
Asymptotic Dependence ◽  
Radiative Lifetimes ◽  
Ionized Magnesium ◽  
Effective Principal

ABSTRACT The presence of spectral lines of singly ionized magnesium (Mg ii) in stellar atmospheres has been reported in different stars. Recently, the low-resolution spectrum obtained from Supernova 2014 J in M82, in which Mg ii absorption lines centred on 4400 Å as well as 7600 Å stand out, has been analysed. This is the motive for the atomic data calculations in this work, which are of much interest in the astrophysical area. In this article, ab initio relativistic Hartree–Fock calculations in an intermediate coupling formalism using Cowan’s code allowed us to obtain the required transition probabilities to calculate the theoretical radiative lifetimes for excited nS−, nP−, nD− and nF− states of singly ionized magnesium. An asymptotic dependence of lifetime (τnl) on the effective principal quantum number (n*) has been determined. Also, the Griem semi-empirical approach was used to obtain the theoretical Stark parameters (width and shift) of spectral lines; these data are displayed for an electron density of 1017 cm−3 and temperatures T = 10–100 (×103 K). We have compared the results of lifetimes for 16 levels and Stark parameters for seven spectral lines with previously reported experiments available in the literature. Finally, we discuss the behaviour of the Stark parameters versus temperature for three relevant spectral lines (2802.70, 2797.99 and 7868.04 Å).

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