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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Demonstration of the frequency offset errors introduced by an incorrect setting of the Zeeman/magnetic field adjustment on the cesium beam frequency standard

The fine frequency setting of a cesium beam frequency standard is accomplished by adjusting the C field control with the appropriate Zeeman frequency applied to the harmonic generator. A novice operator in the field, even when using the correct Zeeman frequency input, may mistakenly set the C field to any one of seven major Beam I peaks (fingers) represented by the Ramsey curve. This can result in frequency offset errors of as much as 2.5 parts in ten to the tenth. The effects of maladjustment are demonstrated and suggestions are discussed on how to avoid the subtle traps associated with C field adjustments.

Kaufmann, D. C.↗
NASA NTRS1977

Feige 7 - A hot, rotating magnetic white dwarf

Results are reported for image-tube-scanner and digicon observations of Feige 7, a faint blue star identified as a probable white dwarf. It is found that this star is a magnetic white dwarf showing a very rich spectrum with Zeeman subcomponents of both hydrogen and neutral helium as well as periodic spectrum and circular-polarization variations. A polarization period of 2.2 hr is computed, and a surface magnetic-field strength of about 18 MG is determined by matching features of the absorption spectrum to Zeeman components. It is suggested that the only reasonable explanation for the periodic variations in circular polarization is an oblique rotator with the spin axis approximately in the plane of the sky and tilted by about 24 deg to the magnetic axis. An effective temperature in the range from 20,000 to 25,000 K is estimated, an absolute magnitude of about 10.5 is derived, and the atmosphere is shown to be helium-dominated. The evolution of Feige 7 is discussed in terms of possible magnetic-field effects on atmospheric composition, rotation velocity (5.5 km/s for a radius of 7000 km), and the origin of white-dwarf magnetic fields.

Liebert, J.↗
NASA NTRS1981

The ultraviolet spectrum of the magnetic degenerate star GD229

The ultraviolet spectrum obtained with the IUE satellite of the magnetic degenerate white dwarf star GD 229 is presented. The ultraviolet energy distribution measured by the short- and long-wavelength cameras covering the range 1170-3200 A, when combined with optical data, indicates a best fit blackbody temperature of 16,000 K, which is significantly lower than previous estimates. A broad absorption trough in the 2000-3000 A region is observed which may be produced by opacity in the fundamental cyclotron frequency for surface magnetic fields from 3.2 to 5 x 10 to the 8th gauss. The absence of a strong Lyman-alpha sigma + component suggests that the primary atmospheric constituent is not hydrogen, with various absorption features probably attributable to Zeeman components of neutral helium, or possibly Mg II, C II and other metal lines. The superposition of many strong Zeeman features is also an alternative interpretation of the absorption in the 2000-3000 A interval.

Green, R. F.↗
NASA NTRS1982

A technique for measuring magnetic fields on solar-type stars

A method is developed and tested by which magnetic-field strengths and area filling-factors of magnetic regions on late-type stars may be inferred from high-resolution, absorption-line profiles that have been broadened by the Zeeman effect. The technique involves fitting such profiles with a triplet of components, the shape of which is derived from profiles of lines of low Zeeman sensitivity. Tests of the systematic and random errors indicate that such magnetic flux measurements have an uncertainty of 20% for stars with field strengths of 2000 gauss if at least 10% of the stellar surface contains magnetic regions.

Marcy, G. W.↗
NASA NTRS1985

Futher identifications of hydrogen in Grw +708247

Numerous spectra of the magnetic white dwarf Grw +70 8247 were obtained with the double CCD spectrograph at Palomar with signal-to-noise ratio above 100. Five weak absorptions in the blue and four in the red are produced by hydrogen in a strong magnetic field. New, precise, multiparameter, variational energy levels yielding intensity and wavelength, from 100 to 600 MG are presented. A search for those Zeeman components with wavelengths nearly constant with field is carried out. Two such Zeeman components which are relatively sharp and strong Pi transitions, explain the Minkowski band, 4137 A (known since 1938), as the 2s0-4f0 and the 5855 A band as the 2s0-3p0. Both have minimum wavelengths at B of about 300 MG. Their absorptions resemble band heads degraded to the red, as observed. The mixed nature of the 4f0 level results in an intensity ratio (2s0-4f0)/(2s0-3p0) = 0.58 at 280 MG, high for a line forbidden at zero field. Profiles computed for a pole-on dipole, near log Bp = 8.5, fit the two observed lines. Other hydrogen transitions (including the core of Ly-alpha) are consistent with the field strength. Six models with a variety of Bp and inclination are illustrated to show the quality of fit to the observations.

Greenstein, J. L.↗
NASA NTRS1986

Measurements of magnetic fields in solar prominences

Magnetic fields can be measured, in solar prominences, by means of two different basic mechanisms that are responsible for the introduction (or the reduction) of a given amount of polarization in spectral lines: these are the Zeeman effect and the Hanle effect. Through the splitting of the magnetic components of a spectral line, the Zeeman effect is capable of introducing a certain amount of circular polarization across the line profile. The Hanle effect consist of a modification of the linear polarization that is induced in spectral lines by the anisotropic illumination of the prominence plasma by the photospheric radiation field. These two effects are briefly discussed.

Deglinnocenti, Egidio Landi↗
NASA NTRS1990

Linearly polarized radiation from astrophysical masers due to magnetic fields of intermediate strength

Previous solutions for polarization of astrophysical maser radiation due to closed-shell molecules in a magnetic field have potentially serious limitations. These solutions are mostly based on the approximation that the Zeeman frequency g-Omega is much greater than the rate for stimulated emission R and the rate for decay Gamma of the molecular state. Others are asymptotic solutions obtained for an angular momentum J = 1-0 transition. It has been unclear whether the polarizations due to plausible Zeeman splittings are adequately represented by the solutions obtained for g-Omega/Gamma much greater than 1 and g-Omega/R much greater than 1. Actual masing transitions tend to involve molecular states with angular momenta that are higher than J = 1 and 0. Numerical solutions for the linear polarization are presented here which do not have the foregoing restrictions on the g-Omega and which are not limited to a J = 1-0 transition.

Nedoluha, Gerald E.↗
NASA NTRS1990

Observations of the 12.3 micron Mg I emission line during a major solar flare

The extremely Zeeman-sensitive 12.32 micron Mg I solar emission line was observed during a 3B/X5.7 solar flare on October 24, 1989. When compared to postflare values, Mg I emission-line intensity in the penumbral flare ribbon was 20 percent greater at the peak of the flare in soft X-rays, and the 12 micron continuum intensity was 7 percent greater. The flare also excited the emission line in the umbra where it is normally absent. The umbral flare emission exhibits a Zeeman splitting 200 G less than the adjacent penumbra, suggesting that it is excited at higher altitude. The absolute penumbral magnetic field strength did not change by more than 100 G between the flare peak and postflare period. However, a change in the inclination of the field lines, probably related to the formation and development of the flare loop system, was seen.

Deming, Drake↗
NASA NTRS1991

High-resolution spectra of solar magnetic features. II - Magnetic fields of umbral brightenings

The spectra of Fe I and Fe II Zeeman-sensitive lines enhanced by video processing of CCD images are considered. The magnetic-field variation within umbras is obtained from the nearly complete Zeeman splitting of the Stokes I profile. It is shown that small brightenings within umbrae have magnetic fields nearly equal to or slightly smaller than that of the darker surroundings; these features are also nearly at rest with respect to their surroundings. It is noted that the absence of significant motions in umbral dots implies that radiation transports most of the energy at and immediately below the surface. The small size of the dots implies that, if convective plumes transport energy below the surface of sunspot umbrae, they should have both a lateral extent and a depth of their upper boundary comparable to or smaller than the size of the dot.

Lites, Bruce W.↗
NASA NTRS1991

Physics of the infrared spectrum

The IR bandpass is attractive for solar magnetic field studies in virtue of the proportionality to wavelength of the ratio of Zeeman splitting to line width. The large Zeeman splitting and optical thinness of the 12-micron observations render them especially useful for vector magnetic field derivations. The IR continuum, and many IR spectral lines, are formed in LTE and are useful in studies of the temperature structure of the solar atmosphere from the deepest observable photospheric layers to chromospheric altitudes. The far-IR continuum is an excellent thermometer for the upper photosphere and chromosphere.

Deming, Drake↗
NASA NTRS1992

The accretion halo in AM Herculis systems

Previous phase-resolved spectropolarimetric observations of the AM Herculis systems V834 Centauri (E1405-451) and EF Eridani have shown broad, Zeeman-shifted absorption features during the bright phases. These features are thought to be nonphotospheric in origin, and to arise from a cool 'halo' of unshocked gas surrounding the accretion shock on the surface of the white dwarf primary. Preliminary models for the accretion halo region are presented and these models are used to perform a more detailed analysis of the relevant data for these two systems than has previously been done. To explain the observed halo Zeeman features, geometries which are consistent with the presence of linearly extended cyclotron emission regions are required. Such regions have previously been deduced from different considerations by other investigators. The estimated masses for the accretion halo are comparable to the mass of the cyclotron emission region.

Achilleos, N.↗
NASA NTRS1992

Spatially extended measurements of magnetic field strength in solar plages

The study determines magnetic field strengths along one spatial dimension of a plage region from circularly polarized (Stokes V) spectra of a highly Zeeman-sensitive iron line at 6388.6/cm (1.565 micron). The measured fields are found to lie primarily in the range 1200-1700 G. The mean formal precision for a single determination is +/-65 G. More than 90 percent of the magnetic flux is kilogauss-strength fields. The field strength is coherently organized on spatial scales from 1 arcmin to the limit of angular resolution (2 arcsec). It is inferred from the amplitude of the V signal that the spatial filling factor of the strong-field elements can approach 0.5 within a 2-arcsec resolution element. Magnetic field strength and amplitude are correlated in the sense that locations with stronger mean fields have larger V amplitudes, but the relationship shows more scatter than can be explained by errors in measurement. The individual sigma-components of the V profile are broader than an average quiet-sun line profile would produce by an amount corresponding to 625 G or 4.1 km/s; Zeeman broadening due to a range of magnetic field strength within the resolution element is proposed as the likely explanation.

Rabin, Douglas↗
NASA NTRS1995

Instabilities and the transport of polarized astrophysical maser radiation

Time-dependent, radiative instabilities in the creation and transport of polarized astrophysical maser radiation in the presence of a magnetic field are calculated. The instabilities are similar to and occur under the same conditions as those found previously by Scappaticci & Watson for unpolarized maser radiation. The common limits in which the Zeeman splitting is much greater than, and much less than, the spectral line breadths are both considered in the current investigation. The resulting fluctuations in the emergent radiation are potentially relevant for the OH 1665 MHz masers which have been reported to fluctuate on timescales of 1000 s and which tend to be polarized. Instabilities occur and alter the transport of maser radiation only under a quite limited range of conditions. In particular, we find here that the instabilities do not occur for conditions that are appropriate for astrophysical masers with small Zeeman splittings such as the SiO and H2O masers. The time-independent, numerical solutions to the GKK equations of radiative transfer that have been obtained in previous investigations are thus essentially always valid except within a narrow range of conditions relevant for the OH masers.

Wallin, Bradley K.↗
NASA NTRS2022

Coronal Polarimetry: Determining the Magnetic Origins of Coronal Mass Ejections

Synopsis: The mechanism for the release of stored magnetic energy in solar eruptions remains a major unsolved problem of Heliophysics. Choosing between triggers requires knowledge of pre-eruptive magnetic fields (B). Although linear polarization in visible/infrared (VIR) coronal emission lines reveals intriguing clues about coronal mass ejection (CME) precursor topology, small telescope apertures limit current capability for measuring vector field. Current coronal observations are insufficient to diagnose 3D coronal magnetic fields in CME precursors. Coronal cavities are the ideal candidates for CME precursor studies. BLOS in cavities is a direct measure of stored magnetic free energy, and the presence and location of topological X-points (reconnection locations) and O-points (circulation of B about axis) distinguish predictions of the flux rope-torus-instability and sheared-arcade-breakout CME models. - Finding: Coronal cavities are ubiquitous throughout the solar cycle, erupt as CMEs, and have coronal polarimetric signatures that distinguish between model predictions. - Recommendation: Coronal cavities should be targeted in a comprehensive multiwavelength study of CME precursors & associated eruption-driving mechanisms. Large ground-based VIR telescopes can measure both coronal magnetic field topology and strength through a combination of the saturated Hanle and BLOS -sensitive Zeeman effects. - Finding: The 4m Daniel K. Inouye Solar Telescope (DKIST) and proposed 1.5m Coronal Solar Magnetism Observatory Large Coronagraph (COSMO-LC) make a major leap forward in VIR coronal sensitivity, enabling measurement of vector B. - Recommendation: A dedicated coronal synoptic telescope with a large field-of-view (i.e., COSMO-LC) is needed to identify the dominant CME driving mechanisms, by measuring coronal magnetic fields from precursor state into eruption. In the UV, a new opportunity has arisen to make use of the strong H I Lyman-α coronal line, which obtains a measurement of B that is independent of the Zeeman effect. - Finding: Small-telescope spectropolarimetric capability in the unsaturated Hanle regime provides an independent and complementary coronal magnetic diagnostic to large ground-based telescope measurements. - Recommendation: The proposed 12-cm Coronal Lyman-α Resonance Observatory (CLARO) spectropolarimetric coronagraph demonstrates a path forward for space-based observations of the coronal magnetic field that should be incorporated into future missions away from the Sun-Earth line (e.g., COMPLETE).

magnetic energy↗
DOE OSTI2025

Anisotropic Response of Defect Bound States to the Magnetic Field in Epitaxial FeSn Films

Crystal defects, whether intrinsic or engineered, drive many fundamental phenomena and novel functionalities of quantum materials. Here, we report symmetry-breaking phenomena induced by Sn vacancy defects on the surface of epitaxial Kagome antiferromagnetic FeSn films using low-temperature scanning tunneling microscopy and spectroscopy. Near the single Sn vacancy, anisotropic quasiparticle interference patterns are observed in the differential conductance dI/dV maps, breaking the 6-fold rotational symmetry of the Kagome layer. Furthermore, the Sn vacancy defects induce bound states that exhibit anomalous Zeeman shift under an out-of-plane magnetic field, where the energy of the bound states moves linearly toward higher energy independent of the direction of the magnetic field. Under an in-plane magnetic field, the shift of the bound state energy also shows a 2-fold oscillating behavior as a function of the azimuth angle. These findings demonstrate defectenabled new functionalities in Kagome antiferromagnets for potential applications in nanoscale spintronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Frequency shifts in the electron paramagnetic resonance spectrum of 39 K due to spin-exchange collisions with polarized 3 He and precise 3 He polarimetry

The Zeeman splittings and electron paramagnetic resonance frequencies of alkali-metal atoms are shifted in the presence of a polarized noble gas. For a spherical geometry, the shift is enhanced over what is expected classically by a dimensionless atomic parameter 𝜅 0 that is unique to each alkali-metal-atom–noble-gas pair. Here, we present a precise measurement of 𝜅 0 for the 39 K − 3 He system with a relative accuracy of better than 1%. A critical component of achieving subpercent accuracy involved characterizing the shape of our samples using both MRI and CT medical-imaging techniques. The parameter 𝜅 0 plays an important role in establishing the absolute polarization of 3 He in a variety of contexts, including polarized targets for electron-scattering experiments and MRI of the gas space of the lungs. Our measurement more than doubles the accuracy possible when using 𝜅 0 for polarimetry purposes. Just as important, the work presented here represents a direct measurement of 𝜅 0 for the 39 K − 3 He system; previous values for 𝜅 0 in the 39 K − 3 He system relied on a chain of measurements that were benchmarked by previous measurements of 𝜅 0 in the Rb- 3 He system.

Zeeman effect↗