Lithium Line Research Articles

Stark-width regularities of neutral lithium lines within different spectral series

The e ects of upper level ionization potential on Stark widths of di erent spectral series of neutral potassium have been studied and discussed in this paper. Proton impact contribution to the Stark broadening show similar dependences as that of electron impact contribution. It is also shown that the term structure influences the Stark widths. Higher correlation between the empirical parameters were found when the temperature was increased. The deviation of the lowest transition from 4p-nd series trend can be explained by absence of close perturbing states to the emitting state. After establishing these dependences, the relations found were used for prediction of Stark widths for the missed lines, thus avoiding complicated calculation procedures.

X-Ray luminescence of polycrystalline TbO2-doped Li2B4O7

This paper examines the effect of doping level on the X-ray luminescence of TbO2-doped polycrystalline lithium tetraborate. It is shown that, when interpreting such spectra, it is convenient to proceed from the terms of free activator and constituent ions. We demonstrate that the emission lines of Tb3+ in doped polycrystalline lithium tetraborate are effectively excited in the band between 350 and 650 nm, which is predominantly due to electron transitions from the 5D3 and 5D4 excited states to spin-orbital levels of the 7FJ ground multiplet. The emission lines of lithium and boron in single-crystal and polycrystalline undoped lithium tetraborate are effectively excited in the band between 274 and 550 nm.

Spatial diagnostics of the laser induced lithium fluoride plasma

We present spatial characteristics of the lithium fluoride plasma generated by the fundamental and second harmonic of a Nd:YAG laser. The plume emission has been recorded spatially using five spectrometers covering the spectral region from 200 nm to 720 nm. The electron density is measured from the Stark broadened line profile of the line at 610.37 nm, whereas the plasma temperature has been determined using the Boltzmann plot method including all the observed spectral lines of lithium. Both the plasma parameters; electron density and plasma temperature decrease with the increase of the distance from the target surface. The thermal conduction towards the target, the radiative cooling of the plasma, and the conversion of thermal energy into kinetic energy are the main mechanisms responsible for the spatially decrease of the plasma parameters.

Binary-induced magnetic activity?

We present a first and detailed study of the bright and active K0IV-III star HD 123351. The star is found to be a single-lined spectroscopic binary with a period of 147.8919+-0.0003 days and a large eccentricity of e=0.8086+-0.0001. The rms of the orbital solution is just 47 m/s, making it the most precise orbit ever obtained for an active binary system. The rotation period is constrained from long-term photometry to be 58.32+-0.01 days. It shows that HD 123351 is a very asynchronous rotator, rotating five times slower than the expected pseudo-synchronous value. Two spotted regions persisted throughout the 12 years of our observations. Four years of Halpha, CaII H&K and HeI D3 monitoring identifies the same main periodicity as the photometry but dynamic spectra also indicate that there is an intermittent dependence on the orbital period, in particular for Ca ii H&K in 2008. Line-profile inversions of a pair of Zeeman sensitive/insensitive iron lines yield an average surface magnetic-flux density of 542+-72 G. The time series for 2008 is modulated by the stellar rotation as well as the orbital motion, such that the magnetic flux is generally weaker during times of periastron and that the chromospheric emissions vary in anti-phase with the magnetic flux. We also identify a broad and asymmetric lithium line profile and measure an abundance of log n(Li) = 1.70+-0.05. The star's position in the H-R diagram indicates a mass of 1.2+-0.1 Msun and an age of 6-7 Gyr. We interpret the anti-phase relation of the magnetic flux with the chromospheric emissions as evidence that there are two magnetic fields present at the same time, a localized surface magnetic field associated with spots and a global field that is oriented towards the (low-mass) secondary component.

Effect of transverse magnetic field on the laser-blow-off plasma plume emission in the presence of ambient gas

In the present paper we report the effect of variable magnetic field in the range of 0.04–0.2 T on the emission of two neutral Lithium lines Li I 670.8 nm and Li I 610.3 nm and one ionic line Li II 548.4 nm in the presence of ambient gas on the laser-blow-off plasma plume. Enhancement in the intensity associated with structures was observed in the temporal profile of neutrals, which is strongly dependent on the magnetic field intensity, distance from the target and background gas pressure. At 6 mm distance and 1.33 Pa argon pressure, apart from overall enhancement in the intensity of both the neutral lines, the results reveal some interesting features, e.g. disappearance of structures and narrowing of the temporal extent of 670.8 nm line at higher magnetic fields. On the other hand, the 610.3 nm line exhibits a significant enhancement in the intensity at the trailing part as the field is increased. At a shorter distance (2 mm) and for relatively higher pressures (133.3 Pa), the effect of field is not much prominent. Interestingly, the ionic spectral line does not exhibit any significant change with both, magnetic field and ambient gas. We explain the results by considering the role of various atomic processes viz. electron impact excitation, recombination and diffusion of ambient gas into plume in collisional and hydrodynamical regimes.

Lithium line radiation in turbulent edge plasmas: Effects of low and high frequency temperature fluctuations

In lithium-wall-conditioned tokamaks, the line radiation due to the intrinsic impurities (Li/Li+/Li++) plays a significant role on the power balance. Calculations of the radiation losses are usually performed using a stationary collisional–radiative model, assuming constant values for the plasma parameters (Ne, Te,…). Such an approach is not suitable for turbulent plasmas where the various parameters are time-dependent. This is critical especially for the edge region, where the fluctuation rates can reach several tens of percents [e.g. J.A. Boedo, J. Nucl. Mater. 390–391 (2009) 29–37]. In this work, the role of turbulence on the radiated power is investigated with a statistical formalism. A special emphasis is devoted to the role of temperature fluctuations, successively for low-frequency fluctuations and in the general case where the characteristic turbulence frequencies can be comparable to the collisional and radiative rates.

Splitting of electron paramagnetic resonance lines of lithium–oxygen centers in isotopically enriched [formula omitted] single crystals

A significant narrowing of the electron paramagnetic resonance (EPR) and additional hyperfine structures of lithium–oxygen (Li–O) centers was observed in isotopically enriched 28Si single crystals. Unexpected splitting was found, reflecting the principal axis of the formally assigned trigonal g -tensors being tilted 3° from the 〈 111 〉 crystal axis, i.e., the g -tensor of the Li–O center actually has a monoclinic symmetry. Furthermore the splitting of the 7Li hyperfine lines into four components was observed at a temperature of 3.5 K.

The use of laser induced breakdown spectroscopy for the determination of Li in organic wash solutions during the preparation of lithium based oxide ceramics by sol–gel

Laser induced breakdown spectroscopy (LIBS) has been investigated for the determination of lithium in various streams generated during the preparation of lithium titanate microspheres employing internal gelation in Sol–gel. Important parameters including laser energy and acquisition delay were optimized to achieve the best signal to noise ratio during the LIBS analysis using filter paper as a solid support. The usefulness of different analytical emission lines of lithium was investigated. The developed LIBS methodology was found to be useful in developing the sol–gel process for preparing the lithium based microspheres for fusion based R&D programs.

A high-resolution spectroscopic survey of late-type stars: chromospheric activity, rotation, kinematics, and age

[NASA ADS]

Formation depths of lithium resonance absorption lines in the atmospheres of late-type stars and brown dwarfs

A numerical technique for determining absorption line formation depths in the atmospheres of late-type stars and substellar-mass subdwarfs is proposed. The technique is based on estimating individual absorptions contributed by certain layers of the stellar model atmosphere to the resulting equivalent width of a spectral line. In particular, the proposed technique can be used when considering lithium absorption lines formed at the background of molecular bands. The technique is applied to the formation of lithium lines in stellar atmospheres, specifically, in the atmosphere of the Sun (spectral type G2V) and those of the red giant star in the binary system RS Oph (M2III), the giant carbon star WZ Cas (C6), and the brown dwarf LP944-20 (M9V).

New results of the spectral observations of CP stars

AbstractThe lithium problem in Ap-CP stars has been, for a long time, a subject of debate. Individual characteristics of CP stars, such as high abundance of the rare-earth elements presence of magnetic fields, complicate structure of the surface distribution of chemical elements, rapid oscillations of some CP-stars, make the detection of the lithium lines and the determination of the lithium abundance, a difficult task. During the International Meeting in Slovakia in 1996, the lithium problem in Ap-CP stars was discussed. The results of the Li study carried out in CrAO Polosukhina (1973–1976), the works of Hack & Faraggiana (1963), Wallerstein & Hack (1964), Faraggiana et al. (1992–1996) formed the basis of the International project ‘Lithium in the cool CP-stars with magnetic fields’. The main goal of the project was, using systematical observations of Ap-CP stars with phase rotation in the spectral regions of the resonance doublet Li I 6708 Å and subordinate 6104 Å lithium lines with different telescopes, to create a database, which will permit to explain the physical origin of anomalous Li abundance in the atmospheres of these stars.

Ultra-lithium-deficient halo stars

AbstractWhile most warm halo dwarfs show lithium abundances at the level of the Spite Plateau, a small number (~5%) have undetectable lithium lines. The existence of these stars has long raised questions when interpreting the plateau abundances: are they an extreme example of a depletion mechanism that has affected the plateau stars, or do they have an entirely different history? We provide an overview of what is currently known about the lithium-poor halo stars and discuss a possible origin for the lithium deficiency in this unique group of stars.

Li-rich red giant branch stars in the Galactic bulge

We present Lithium abundance determination for a sample of K giant stars in the galactic bulge. The stars presented here are the only 13 stars with detectable Lithium line (6767.18 A) among ~400 stars for which we have spectra in this wavelength range, half of them in Baade's Window (b=-4) and half in a field at b=-6. The stars were observed with the GIRAFFE spectrograph of FLAMES@VLT, with a spectral resolution of R~20,000. Abundances were derived via spectral synthesis and the results are compared with those for stars with similar parameters, but no detectable Li line. We find 13 stars with a detectable Li line, among which 2 have abundances A(Li)>2.7. No clear correlations were found between the Li abundance and those of other elements. With the exception of the two most Li rich stars, the others follow a fairly tight A(Li)-T_eff correlation. It would seems that there must be a Li production phase during the red giant branch (RGB), acting either on a very short timescale, or selectively only in some stars. The proposed Li production phase associated with the RGB bump cannot be excluded, although our targets are significantly brighter than the predicted RGB bump magnitude for a population at 8 kpc

Lithium survey in evolved stars observed in the sacy project

AbstractThe primary goal of the sacy project (Search for Associations Containing Young Stars) was to identify possible associations of stars younger than the Pleiades association among optical counterparts of ROSAT X-ray-bright sources. The study of the chemical abundance in stars located in regions of stellar formation is extremely important to understand stellar nucleo-synthesis, the physical mechanisms controlling mixing in stellar interiors, and chemical enrichment in the Galaxy. The present work highights the first results of a chemical-abundance study of evolved stars identified in the sacy survey. For this, we performed a detailed spectroscopic analysis for the determination of atmospheric parameters and Li abundance for a sample of giant and subgiant stars. The observations were carried out with high resolution using the FEROS (R = 48 000) échelle spectrograph. We measured the stellar parameters (Teff, log g, vmic, [Fe/H]) from LTE analysis in the complete range of 420-1100 nm. Li abundance was derived from the region around the lithium line at 6707.78 Å for the entire sample of stars.

The theory of line shapes relevant to the spectra of cool stars

Accurate pressure broadened profiles of alkali resonance doublets are needed for modelling of the atmospheres of cool stars and for generating their synthetic spectra in the region 400–900 nm. When the usual impact theory of line broadening is used, the profile is simply Lorentzian and the widths and shifts of the lines can be calculated, provided that interaction potentials for the emitter–perturber system are available. However when the lines utterly dominate their region of the spectrum, it becomes important to also accurately represent the profile in the line wings, where the impact theory is no longer valid. The original development of line broadening theory by Baranger in 1958 is reexamined and calculations have been carried out in which it is shown that it is not necessary to invoke the impact approximation. To test the validity of different approximations, results for line widths and shifts are presented for the lithium and sodium resonance lines broadened by helium for 0.1 K ⩽ T ⩽ 3000 K.

Accurate Atomic Transition Probabilities for Hydrogen, Helium, and Lithium

We have carried out a comprehensive tabulation of the atomic transition probabilities for allowed and forbidden lines of hydrogen, helium and lithium, including LiII, as well as the hydrogen isotopes deuterium and tritium. Altogether, we tabulated about 3600 transitions and listed scaling relations for the hydrogenlike ions HeII and LiIII. The selected data are based on a critical evaluation of available literature sources and are all taken from recent advanced calculations. The tables are normally arranged in multiplets, and these are ordered in increasing excitation energies. For hydrogen, deuterium, and tritium, the energy levels are degenerate, i.e., all energy levels of the same principal quantum number essentially coincide. Thus, the principal tables for these species are for the average transition probabilities of lines between different principal quantum numbers.

Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association

The associations and moving groups of young stars are excellent laboratories for investigating stellar formation in the solar neighborhood. Previous results have confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of possible members of young stellar kinematic groups. A detailed study of the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, and identify the origin of these structures. We used stars possible members of the young (~ 10 - 650 Myr) moving groups from the literature. To determine the age of the stars, we used several suitable age indicators for young main sequence stars, i.e., X-ray fluxes and other photometric data. We also used spectroscopic data, in particular the equivalent width of the lithium line Li I and Halpha, to constrain the range of ages of the stars. By combining photometric and spectroscopic data, we were able to separate the young stars (10 - 650 Myr) from the old (> 1 Gyr) field ones. We found, in particular, that the Local Association is contaminated by old field stars at the level of ~30%. This value must be considered as the contamination for our particular sample, and not of the entire Local Association. For other young moving groups, it is more difficult to estimate the fraction of old stars among possible members. However, the level of X-ray emission can, at least, help to separate two age populations: stars with <200 Myr and stars older than this. Our results are consistent with a scenario in which the moving groups contain both groups of young stars formed in a recent star-formation episode and old field stars with similar space motion. Only by combining X-ray and optical spectroscopic data is it possible to distinguish between these two age populations.

Identification of spectral lines of elements using artificial neural networks

Artificial neural networks (ANNs) are relatively new computational tools that have found extensive utilization in solving many complex real-world problems. This paper describes how an ANN can be used to identify the spectral lines of elements. The spectral lines of Cadmium (Cd), Calcium (Ca), Iron (Fe), Lithium (Li), Mercury (Hg), Potassium (K) and Strontium (Sr) in the visible range are chosen for the investigation. One of the unique features of this technique is that it uses the whole spectrum in the visible range instead of individual spectral lines. The spectrum of a sample taken with a spectrometer contains both original peaks and spurious peaks. It is a tedious task to identify these peaks to determine the elements present in the sample. ANNs capability of retrieving original data from noisy spectrum is also explored in this paper. The importance of the need of sufficient data for training ANNs to get accurate results is also emphasized. Two networks are examined: one trained in all spectral lines and other with the persistent lines only. The network trained in all spectral lines is found to be superior in analyzing the spectrum even in a noisy environment.

6Li in the Atmosphere of GJ 117 Revisited

Detection of 6Li has been shown for energetic solar events, one chromospherically active binary, and several dwarf halo stars. We had previously found a 6Li/7Li = 0.03 ± 0.01 for active K dwarf GJ 117 using VLT UVES observations. Here we present high signal-to-noise (>1000) high spectral resolution observations taken with the McDonald Observatory's 2.7 m and echelle spectrometer of GJ 117. We have used the solar spectrum and template stars to eliminate possible blends, such as Ti I, in the 6Li spectral region. Our new analysis, using an updated PHOENIX model atmosphere, finds 6Li/7Li = 0.05 ± 0.02. In addition, bisector analysis showed no significant red asymmetries that would affect the lithium line profile. No changes above the statistical uncertainties are found between the VLT and McDonald data. The amount of 6Li derived for GJ 117 is consistent with creation in spallation reactions on the stellar surface, but we caution that uncertainties in the continuum level may cause additional uncertainty in the 6Li fraction.

The Metallicity and Lithium Abundances of the Recurring Novae T CrB and RS Oph

ABSTRACTWe report on high-resolution spectra of the two recurring novae, T CrB and RS Oph, obtained in 2004 when no outbursts were in progress. Selected regions of the spectra between 6500 and 8800 Å were measured for equivalent widths and analyzed for metallicity. Lines of Fe I, Ni I, Si I, and Ti I were used to establish the effective temperature. The metallicity as derived using models is near solar with an uncertainty estimated to be near a factor of 2 for both stars. Both stars show a strong lithium line at 6707.8 Å. Approximate Li abundances were derived using model atmospheres for a direct comparison with the nearby Fe I line at 6710.31 Å and the Ca I ground level line at 6572.78 Å. The Li abundances are near log N(Li) = 1.2 for RS Oph and 0.8 for T CrB on the scale of log N(H) = 12.0. Such Li abundances are high for single K and M giants. A survey of symbiotic stars with cool components of types K and M showed no recognizable Li line in 28 stars with high quality spectra. This makes the two repeating novae different from the other symbiotics that consist of a red giant and a white dwarf.