Zeeman Splitting Of Spectral Lines Research Articles

A DZ white dwarf with a 30 MG magnetic field

ABSTRACTMagnetic white dwarfs with field strengths below 10 MG are easy to recognize since the Zeeman splitting of spectral lines appears proportional to the magnetic field strength. For fields ≳100 MG, however, transition wavelengths become chaotic, requiring quantum-chemical predictions of wavelengths and oscillator strengths with a non-perturbative treatment of the magnetic field. While highly accurate calculations have previously been performed for hydrogen and helium, the variational techniques employed become computationally intractable for systems with more than three to four electrons. Modern computational techniques, such as finite-field coupled-cluster theory, allow the calculation of many-electron systems in arbitrarily strong magnetic fields. Because around 25 per cent of white dwarfs have metal lines in their spectra, and some of those are also magnetic, the possibility arises for some metals to be observed in very strong magnetic fields, resulting in unrecognizable spectra. We have identified SDSS J114333.48+661531.83 as a magnetic DZ white dwarf, with a spectrum exhibiting many unusually shaped lines at unknown wavelengths. Using atomic data calculated from computational finite-field coupled-cluster methods, we have identified some of these lines arising from Na, Mg, and Ca. Surprisingly, we find a relatively low field strength of 30 MG, where the large number of overlapping lines from different elements make the spectrum challenging to interpret at a much lower field strength than for DAs and DBs. Finally, we model the field structure of SDSS J1143+6615 finding the data are consistent with an offset dipole.

HD 144941: the most extreme helium-strong star

Since its discovery about 50 yr ago, HD 144941 has generally been classified as a peculiar member of the extreme helium (EHe) supergiant stars, a very rare class of low-mass hydrogen-deficient stars. We report the detection of a strong longitudinal magnetic field based on spectropolarimetry with FORS2 on the ESO VLT with surface-averaged longitudinal field strengths as large as −9 kG. This is further constrained by the detection of Zeeman splitting of spectral lines to a field strength of at least 15 kG, explaining the recent finding of surface spots for this star. The quantitative analysis of the stellar atmosphere based on a hybrid non-local thermodynamic equilibrium approach and new optical spectra yields an effective temperature of 22 000 ± 500 K, a logarithmic surface gravity of 4.20 ± 0.10, and a surface helium fraction of 0.950 ± 0.002 by number. While the metal abundances are about a factor of 10 sub-solar in absolute number, the metal-to-hydrogen ratios are typical of massive early-type stars, indicating that helium fallback in a weak, fractionated stellar wind in the presence of a magnetic field took place – the canonical mechanism for the formation of the helium-strong phenomenon. Both the spectroscopic and the Gaia EDR3 parallax imply HD 144941 to be a luminous massive star. Kinematically, we argue that HD 144941 has reached its high Galactic latitude as a runaway star. We conclude that instead of being a comparatively high-gravity low-mass EHe star, HD 144941 is by far the most extreme member of the magnetic massive helium-strong stars, with almost all atmospheric hydrogen substituted by helium.

Detection of an extremely strong magnetic field in the double-degenerate binary merger product HD 144941

ABSTRACT HD 144941 is an extreme He (EHe) star, a rare class of subdwarf OB star formed from the merger of two white dwarf (WD) stars. Uniquely amongst EHe stars, its light curve has been reported to be modulated entirely by rotation, suggesting the presence of a magnetic field. Here, we report the first high-resolution spectropolarimetric observations of HD 144941, in which we detect an extremely strong magnetic field both in circular polarization (with a line-of-sight magnetic field averaged over the stellar disc 〈Bz〉 ∼−8 kG) and in Zeeman splitting of spectral lines (yielding a magnetic modulus of 〈B〉 ∼17 kG). We also report for the first time weak H α emission consistent with an origin and a centrifugal magnetosphere. HD 144941’s atmospheric parameters could be consistent with either a subdwarf or a main-sequence (MS) star, and its surface abundances are neither similar to other EHe stars nor to He-strong magnetic stars. However, its H α emission properties can only be reproduced if its mass is around 1 M⊙, indicating that it must be a post-MS object. Since there is no indication of binarity, it is unlikely to be a stripped star, and was therefore most likely produced in a WD merger. HD 144941 is therefore further evidence that mergers are a viable pathway for the generation of fossil magnetic fields.

Introduction of Zeeman splitting in CHIANTI

High-resolution spectra emitted by laboratory plasmas provide invaluable diagnostic tools for the measurement of plasma properties. To be implemented, they require a large amount of atomic data and transition rates, which are available in several spectral codes. In this paper we present a new feature added to the CHIANTI code, which allows us to calculate the Zeeman splitting of spectral lines in the presence of a magnetic field with known intensity and orientation. When combined with the CHIANTI database and software to calculate level populations and line emissivities, this new feature returns the emissivities in all four Stokes parameters, that can be utilized for the measurement of the magnetic field inside laboratory plasma chambers, along with other plasma parameters. This new feature can be applied to the analysis of the emission of laboratory plasmas created in different devices.

Dependence of Zeeman splitting of spectral lines on the magnetic field magnitude for NO molecule

The paper presents an overview of experimental and theoretical results, which were obtained from the study of the dependence of Zeeman splitting of the vibrational-rotational lines of the 0–1 band of the nitric oxide molecule absorption spectra on the magnetic field magnitude. The experiments were performed at the Laboratory of Gas Lasers of P.N. Lebedev Physical Institute, Russian Academy of Sciences (FIAN). The method of laser magnetic resonance (LMR) with the use of a continuous-wave frequency-tunable CO laser were used to record the spectra. The theoretical analysis of LMR spectrograms was carried out at the Laboratory of Theoretical Spectroscopy of V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences (IAO SB RAS), where the numerical model was developed based on construction of the total effective Hamiltonian of the molecule accounting the interaction with an external magnetic field. The model allows calculation of LMR spectra under given conditions and description of the nonlinear dependence of splitting of rovibrational energy levels on the magnetic field magnitude. The comparison of calculated and experimental LMR spectrograms has shown that the numerical model adequately reproduces the positions of absorption peaks measured in a damped oscillating magnetic field.

Observation of Zeeman splitting of spectral lines and measurements of magnetic field pitch angle in KSTAR

The Zeeman splitting of the Da (656.10 nm) and the Hα (656.28 nm) spectral lines and the different impurities from deuterium/hydrogen discharges in the KSTAR tokamak plasma have been observed in the visible region of the spectrum. The internal magnetic field strength has been determined by analyzing the circular polarization of the spectral lines emitted by the plasma. The radial magnetic field is obtained by using the Abel inversion technique. In addition, the magneticfield pitch angle is derived from the polarization characteristics of the σ component of the Zeeman triplet of the H emission at 656.28 nm by using a polarization-sensitive spectroscope.

Зависимость зеемановского расщепления спектральных линий молекулы NO от величины магнитного поля

Зависимость зеемановского расщепления спектральных линий молекулы NO от величины магнитного поля

Least-squares deconvolution of the stellar intensity and polarization spectra

Least squares deconvolution (LSD) is a powerful method of extracting high-precision average line profiles from the stellar intensity and polarization spectra. Despite its common usage, the LSD method is poorly documented and has never been tested using realistic synthetic spectra. In this study we revisit the key assumptions of the LSD technique, clarify its numerical implementation, discuss possible improvements and give recommendations how to make LSD results understandable and reproducible. We also address the problem of interpretation of the moments and shapes of the LSD profiles in terms of physical parameters. We have developed an improved, multiprofile version of LSD and have extended the deconvolution procedure to linear polarization analysis taking into account anomalous Zeeman splitting of spectral lines. This code is applied to the theoretical Stokes parameter spectra. We test various methods of interpreting the mean profiles, investigating how coarse approximations of the multiline technique translate into errors of the derived parameters. We find that, generally, the Stokes parameter LSD profiles do not behave as a real spectral line with respect to the variation of magnetic field and elemental abundance. This problem is especially prominent for the Stokes I variation with abundance and Stokes Q variation with magnetic field. At the same time, the Stokes V LSD spectra closely resemble profile of a properly chosen synthetic line for the magnetic field strength up to 1 kG. We conclude that the usual method of interpreting the LSD profiles by assuming that they are equivalent to a real spectral line gives satisfactory results only in a limited parameter range and thus should be applied with caution. A more trustworthy approach is to abandon the single-line approximation of the average profiles and apply LSD consistently to observations and synthetic spectra.

Model atmospheres of magnetic chemically peculiar stars

In the last few years we have developed stellar model atmospheres which included effects of anomalous abundances and strong magnetic field. The full treatment of anomalous Zeeman splitting and polarized radiative transfer were introduced in the model atmosphere calculations for the first time. In this investigation we present results of modelling the atmosphere of one of the most extreme magnetic chemically peculiar stars, HD137509. This Bp SiCrFe star has the mean surface magnetic field modulus of about 29kG. We use the recent version of the line-by-line opacity sampling stellar model atmosphere code LLmodels, which incorporates the full treatment of Zeeman splitting of spectral lines, detailed polarized radiative transfer and arbitrary abundances. We compare model predictions with photometric and spectroscopic observations of the star, aiming to reach a self-consistency between the abundance pattern derived from high-resolution spectra and abundances used for model atmosphere calculation. Based on magnetic model atmospheres, we redetermined abundances and fundamental parameters of HD137509 using spectroscopic and photometric observations. This allowed us to obtain a better agreement between observed and theoretical parameters compared to non-magnetic models with individual or scaled-solar abundances. We confirm that the magnetic field effects should be taken into account in the stellar parameter determination and abundance analysis.

LIF measurements on an atomic helium beam in the edge of a fusion plasma

A method for the absolute measurement of population densities of selected atomic helium levels, which has been applied on the tokamak TEXTOR at the Forschungszentrum Jülich in Germany, is presented. The method is based on the resonant excitation of selected levels by a high-power, narrow-band, pulsed laser beam saturating the optical pumping process. Observation of the fluorescence response is performed at the laser wavelength and elsewhere in the spectrum: this gives information on collisional population transfer between some excited levels. Data analysis, as required for the derivation of absolute population densities, includes due consideration of the Zeeman splitting of spectral lines in a strong magnetic field. The first results of the measured population densities are compared with those provided by simulation based on the collisional–radiative model for atomic helium in the edge of fusion plasmas. This code has been extended to include the laser interaction with atomic helium, in order to simulate the measured time traces of radiation from the laser-perturbed levels. A combination of this simulation procedure with laser-induced fluorescence measurements is suggested as a possible method for determining the electron density in the edge plasma.

Ultrahigh magnetic field diagnostic with spectral profile calculation

We report the theoretical results on use of neon as a tracer element to measure the multi-megagauss magnetic field, which is induced in the ultrahigh intense laser–matter interactions. The shape of Zeeman splitting of spectral line for 1s2p( 1P 1)→1s 2 transition of He-like neon are calculated for high-intensity laser produced quasi one-components plasma with the consideration of the electron collision broadening, electron collision shift and magnetic field splitting. The results show that all of the Zeeman splitting spectrum can be identified under Rayleigh criterion for the plasma with the electron temperature from 10 to 100 eV , the magnetic field from 10 6 to 10 8 G and the electron density 2×10 20 cm −3 . With both the electron temperature and magnetic field increasing, the requirement for the resolution power of the spectrometer decreases. If a spectrometer with the resolution power of 1/1000 is used, the measurement of the quasistatic magnetic field by Zeeman splitting of spectral lines is applicable when quasistatic magnetic field is larger than some tens of megaGauss.

Observation of Zeeman splitting of spectral lines from the JET plasma

Zeeman splitting of spectral lines from hydrogen and impurities in the JET Tokamak plasma has been observed in the visible region of the spectrum. An Optical Multichannel Analyser (OMA) coupled to a 1 m Czerny-Turner instrument is used to record several spectral lines simultaneously many times during a discharge. Tangential viewing optics enhance the influence of Zeeman splitting, especially when the impurities are located where the magnetic field is aligned along the viewing chord. To date, splitting of Halpha (6563 AA), CII (6578 AA and 6583 AA), CrI (4289 AA, 4274 AA and 4254 AA) and CIII (4794 AA, 4810 AA and 4819 AA) has been detected. The location of the impurities is determined from the magnitude of the splitting and the known toroidal field distribution. The effects of the magnetic field on the line profiles are best observed during the plasma initiation and termination phases where, for example, a large plasma incursion can result in the injection of impurities from the inner wall. The technique is of particular importance in determining the source of impurities (e.g. from the inside wall or the limiter at the outer periphery). The observations also highlight the importance of taking Zeeman splitting into account when making Doppler shift or broadening measurements in the visible spectrum.

Apparatus Drawings Project. Report Number 29. Accessory Apparatus for Large Electromagnet

The four devices described are designed to fit the large electromagnet, described earlier in this series, thus greatly enhancing its usefulness. (1) A magnetic force on a current-carrying conductor apparatus is intended for undergraduate laboratory investigations. A current of 50 amp in a magnetic field of 0.8 weber/m2 will produce a force on the conductor of nearly 3.2 newtons. The conductor current is normally obtained from lead storage cells. (2) An eddy current pendulum, 1 meter long, is used for lecture demonstrations. (3) Truncated square pyramidal pole faces provide the intense magnetic fields (about 1.3 weber/m2) required for a practical sophomore laboratory experiment on the Zeeman splitting of spectral lines. (4) The last device described is a single pole face specially tapered to produce a highly inhomogeneous magnetic field for experiments and demonstrations dealing with para- and dia-magnetism. Detailed information regarding construction of the apparatus is given.