scholarly journals 6Li in metal-poor halo stars: real or spurious?

2009 ◽  
Vol 5 (S265) ◽  
pp. 23-26 ◽  
Author(s):  
M. Steffen ◽  
R. Cayrel ◽  
P. Bonifacio ◽  
H.-G. Ludwig ◽  
E. Caffau
Keyword(s):  
Spectral Line ◽  
Isotopic Ratio ◽  
Line Profiles ◽  
Halo Stars ◽  
Convective Motions ◽  
Symmetric Line ◽  
Line Asymmetry ◽  
Red Wing

AbstractThe presence of convective motions in the atmospheres of metal-poor halo stars leads to systematic asymmetries of the emergent spectral line profiles. Since such line asymmetries are very small, they can be safely ignored for standard spectroscopic abundance analysis. However, when it comes to the determination of the 6Li/7Li isotopic ratio, q(Li)=n(6Li)/n(7Li), the intrinsic asymmetry of the 7Li line must be taken into account, because its signature is essentially indistinguishable from the presence of a weak 6Li blend in the red wing of the 7Li line. In this contribution we quantity the error of the inferred 6Li/7Li isotopic ratio that arises if the convective line asymmetry is ignored in the fitting of the λ6707 Å lithium blend. Our conclusion is that 6Li/7Li ratios derived by Asplund et al. (2006), using symmetric line profiles, must be reduced by typically Δq(Li) ≈ 0.015. This diminishes the number of certain 6Li detections from 9 to 4 stars or less, casting some doubt on the existence of a 6Li plateau.

scholarly journals 9. New Spectroscopic Results on Subluminous Stars, V

1971 ◽  
Vol 42 ◽  
pp. 46-60 ◽  
Author(s):  
J. L. Greenstein
Keyword(s):  
High Velocity ◽  
Classification Scheme ◽  
Ultraviolet Excess ◽  
Horizontal Branch ◽  
Line Profiles ◽  
Hydrogen Line ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Halo Stars

Determination of temperature and surface gravity by colors and hydrogen-line profiles have been carried out for hot halo stars. A narrow horizontal branch is found stretching to above 40000 K; the hot O subdwarfs show a nearly vertical sequence, dropping towards the hot white dwarfs.Spectra for 285 white dwarf stars have been obtained, and the classification scheme is reviewed. Theoretical problems of these spectra remain, largely, unsolved.The red subluminous stars found by Eggen were studied spectroscopically; among 68 stars only one new red degenerate star was found. The others are very metal-poor, high-velocity stars with large ultraviolet excess.

scholarly journals Measurement of Electron Density from Stark-Broadened Nanomaterial Plasma

2018 ◽  
Author(s):  
Ashraf M. EL Sherbini ◽  
Ahmed E. EL Sherbini ◽  
Christian G. Parigger
Keyword(s):  
Electron Density ◽  
Optical Emission Spectroscopy ◽  
Optical Breakdown ◽  
Optical Emission ◽  
Photon Absorption ◽  
Line Profiles ◽  
Balmer Series ◽  
Line Asymmetry ◽  
Atomic Lines

This work communicates results from optical emission spectroscopy following laser-induced optical breakdown at or near nanomaterial. Selected atomic lines of silver are evaluated for consistent determination of electron density. Comparisons are presented with Balmer series hydrogen results. Of particular interest are measurements free of self-absorption effects. For several silver lines, asymmetries are observed in the recorded line profiles. Electron densities of interest range from 0.5 to 3 × 1017 cm-3, for 5 nanosecond Q-switched Nd:YAG radiation at wavelengths of 1064, 532, and 355 nm, and for selected silver emission lines including 328.0, 338.2, 768.7, and 827.3 nm, and the hydrogen alpha Balmer series line at 656.3 nm. Line asymmetries are presented for the 328.0 nm Ag I line that is measured following generation of the plasma due to multiple photon absorption. This work explores electron density variations for different irradiance levels, and reports spectral line asymmetry of resonance lines for different laser fluence levels.

Determination of Particle Densities and Line Profiles in Plasmas by Resonance Interferometry: A Feasibility Study using Computer Simulated Refractivity Data

1995 ◽  
Vol 50 (10) ◽  
pp. 902-914 ◽  
Author(s):  
C. Haas ◽  
G. Pretzier ◽  
H. Jäger
Keyword(s):  
Spectral Line ◽  
Feasibility Study ◽  
Particle Density ◽  
Detection Limits ◽  
High Accuracy ◽  
Line Profiles ◽  
Actual Problem ◽  
Density Determination

AbstractThe principles of resonance interferometry are described with regard to two applications: High accuracy particle density determination within plasmas and interferometrical determination of spectral line profiles. The usability of this technique is investigated numerically, and physical limits are given for the regions in which resonance interferometry may be employed successfully. The discussion and the results are helt general for making it possible to decide whether or not to apply this method for an actual problem. An example (an object being longitudinally homogeneous with respect to the direction of light: end-on observation) shows how to use the presented results for calculating the detection limits of the method for a given object geometry.

scholarly journals Convection and 6Li in the atmospheres of metal-poor halo stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 215-220 ◽  
Author(s):  
Matthias Steffen ◽  
R. Cayrel ◽  
P. Bonifacio ◽  
H.-G. Ludwig ◽  
E. Caffau
Keyword(s):  
Effective Temperature ◽  
Hydrodynamical Model ◽  
Isotopic Ratios ◽  
Line Formation ◽  
Line Profiles ◽  
Halo Stars ◽  
Line Asymmetry ◽  
3Σ Criterion ◽  
Line Fitting ◽  
Synthetic Line

AbstractBased on 3D hydrodynamical model atmospheres computed with the CO5BOLD code and 3D non-LTE (NLTE) line formation calculations, we study the effect of the convection-induced line asymmetry on the derived 6Li abundance for a range in effective temperature, gravity, and metallicity covering the stars of the Asplund et al. (2006) sample. When the asymmetry effect is taken into account for this sample of stars, the resulting 6Li/7Li ratios are reduced by about 1.5% on average with respect to the isotopic ratios determined by Asplund et al. (2006). This purely theoretical correction diminishes the number of significant 6Li detections from 9 to 4 (2σ criterion), or from 5 to 2 (3σ criterion). In view of this result the existence of a 6Li plateau appears questionable. A careful reanalysis of individual objects by fitting the observed lithium 6707 Å doublet both with 3D NLTE and 1D LTE synthetic line profiles confirms that the inferred 6Li abundance is systematically lower when using 3D NLTE instead of 1D LTE line fitting. Nevertheless, halo stars with unquestionable 6Li detection do exist even if analyzed in 3D-NLTE, the most prominent example being HD 84937.

scholarly journals The origin and evolution of dense regions in the ISM, and their role in spectral features

2012 ◽  
Vol 8 (S292) ◽  
pp. 99-99
Author(s):  
Diego Falceta-Gonçalves
Keyword(s):  
Spectral Line ◽  
Numerical Simulations ◽  
Molecular Clouds ◽  
Spectral Features ◽  
Line Profiles ◽  
Origin And Evolution ◽  
Secular Evolution ◽  
Theoretical Assumptions ◽  
Order Of Magnitude

AbstractIn this work we discuss the turbulent evolution of molecular clouds and the formation of dense structures within. Typically, the clumps evolution occurs apart from the secular evolution of the turbulent mother cloud due to its high density and large inertia. Despite of current theoretical assumptions we show, by means of numerical simulations, that the clump lifetimes are greater than previously thought by more than an order of magnitude. The presence of dense and long-lived clumps modifies the spectral line profiles of clouds, which are strongly related to the determination of Larson's relations. We address the main modifications of these if a realistic distribution of dense structures is taken into account.

scholarly journals IAU Colloquium No. 8: Experimental Techniques for the Determination of Fundamental Spectroscopic Data

1971 ◽  
Vol 8 ◽  
pp. 48-60
Author(s):  
Bruce W. Shore
Keyword(s):  
Spectral Line ◽  
Energy Levels ◽  
Oscillator Strengths ◽  
Atomic Data ◽  
Fast Time ◽  
Line Profiles ◽  
Atomic Properties ◽  
University Of Edinburgh ◽  
Experimental Spectroscopy

The last ten years have brought significant changes to the venerable disciplines of astronomy and spectroscopy. Traditionally astronomers sought wavelength catalogues of identified spectra lines. Under this impetus spectroscopists laboured to provide very accurate wavelength measurements and estimates of emission line intensity. Physicists and astronomers alike are now recognizing interest not only in such properties of isolated atoms as energy levels (or spectral-line wavelengths) and oscillator strengths, but also those atomic properties which depend upon the surroundings of a radiating atom: spectral-line profiles, excitation rates, and level populations. In turn, new uses of lasers and interferometers, fast time resolution, and simple but significantly different absorption and emission samples are altering experimental spectroscopy almost beyond recognition. The present colloquium, chaired by A.H.Cook (University of Edinburgh) and held at Imperial College, London, on September 1-4 1970, aimed to identify the means by which astronomers can now obtain fundamental atomic data.

scholarly journals Assisting Extrasolar Planetary Detection Through the Determination of Stellar Space Orientations

1985 ◽  
Vol 112 ◽  
pp. 97-100 ◽  
Author(s):  
Laurance R. Doyle
Keyword(s):  
Spectral Line ◽  
Intensity Distribution ◽  
Orbital Plane ◽  
Speckle Interferometry ◽  
Line Of Sight ◽  
Line Profiles ◽  
Stellar Rotation ◽  
Short Term ◽  
Rotation Periods

Various methods outlined for indirect planetary detection would greatly benefit (in some cases require) the determination of the planetary orbital plane, which is theoretically equivalent to the stellar equatorial plane. Determining the stellar space orientation, therefore, would greatly benefit extrasolar planetary detection.We utilize stellar rotation periods determined from short-term variations in Call H&K sunspot emission combined with both stellar radii measurements and Doppler broadened spectral line profiles to get the stellar inclination to the line of sight.The clocklike, on the plane-of-the-sky component determination utilizes the concentration of sunspot associated plage areas at central stellar latitudes when viewed in Call H or K emission. One can perform Call H&K emission speckle interferometry to measure the clocklike angle of this stellar Call H&K emission band, modeling it as an elliptical intensity distribution. Both components should be determinable to within ten degrees for at least resolvable fifth magnitude stars.

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