scholarly journals Hanle and Zeeman effects: from solar to stellar diagnostics

2013 ◽  
Vol 9 (S302) ◽  
pp. 130-133
Author(s):  
A. López Ariste
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Strong Field ◽  
Zeeman Effect ◽  
Stellar Atmospheres ◽  
Line Of Sight ◽  
Magnetic Topology ◽  
Hanle Effect ◽  
The Magnetic Field

RésuméWe suggest the use of the area asymmetries of the Stokes V profile of a line sensitive to the Zeeman effect to diagnose variatios of the magnetic field along the line of sight in stellar atmospheres. This tool could allow to disentangle the magnetic topology of the observed stellar features in analogy to the solar case: a fibril topology as in plage and netwrok magnetic fields vs. a homogeneous and strong field as in sunspots. We also suggest the use of the Hanle effect as a means to observe weak global dipoles.

scholarly journals The history of polarisation measurements: their role in studies of magnetic fields

2012 ◽  
Vol 10 (H16) ◽  
pp. 383-383
Author(s):  
R. Wielebinski
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Effect ◽  
Zeeman Effect ◽  
Line Of Sight ◽  
Radio Waves ◽  
New Methods ◽  
History Of ◽  
The Magnetic Field ◽  
Polarisation Measurements

Radio astronomy gave us new methods to study magnetic fields. Synchrotron radiation, the main cause of comic radio waves, is highly linearly polarised with the ‘E’ vector normal to the magnetic field. The Faraday Effect rotates the ‘E’ vector in thermal regions by the magnetic field in the line of sight. Also the radio Zeeman Effect has been observed.

scholarly journals Magnetic fields in star-forming systems – II: Examining dust polarization, the Zeeman effect, and the Faraday rotation measure as magnetic field tracers

2020 ◽  
Vol 500 (1) ◽  
pp. 153-176
Author(s):  
Stefan Reissl ◽  
Amelia M Stutz ◽  
Ralf S Klessen ◽  
Daniel Seifried ◽  
Stefanie Walch
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Zeeman Effect ◽  
Dominant Factor ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Magnetic Field Direction ◽  
Rotation Measure ◽  
The Magnetic Field

ABSTRACT The degree to which the formation and evolution of clouds and filaments in the interstellar medium is regulated by magnetic fields remains an open question. Yet the fundamental properties of the fields (strength and 3D morphology) are not readily observable. We investigate the potential for recovering magnetic field information from dust polarization, the Zeeman effect, and the Faraday rotation measure (RM) in a SILCC-Zoom magnetohydrodynamic (MHD) filament simulation. The object is analysed at the onset of star formation and it is characterized by a line-mass of about $\mathrm{\left(M/L\right) \sim 63\ \mathrm{M}_{\odot }\ pc^{-1}}$ out to a radius of $1\,$ pc and a kinked 3D magnetic field morphology. We generate synthetic observations via polaris radiative transfer (RT) post-processing and compare with an analytical model of helical or kinked field morphology to help interpreting the inferred observational signatures. We show that the tracer signals originate close to the filament spine. We find regions along the filament where the angular dependence with the line of sight (LOS) is the dominant factor and dust polarization may trace the underlying kinked magnetic field morphology. We also find that reversals in the recovered magnetic field direction are not unambiguously associated to any particular morphology. Other physical parameters, such as density or temperature, are relevant and sometimes dominant compared to the magnetic field structure in modulating the observed signal. We demonstrate that the Zeeman effect and the RM recover the line-of-sight magnetic field strength to within a factor 2.1–3.4. We conclude that the magnetic field morphology may not be unambiguously determined in low-mass systems by observations of dust polarization, Zeeman effect, or RM, whereas the field strengths can be reliably recovered.

scholarly journals 19. Astrophysical applications of selective magnetic rotation

1958 ◽  
Vol 6 ◽  
pp. 166-168
Author(s):  
Y. öhman
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Emission Lines ◽  
Absorption Lines ◽  
Magnetic Rotation ◽  
Double Refraction ◽  
Line Absorption ◽  
Complicated Process ◽  
The Magnetic Field

When measuring the magnetic fields of sunspots the astronomer assumes that the magnetic field revealed by the inverse Zeeman effect is the same as if the splitting were produced by emission lines instead of absorption lines. No doubt this is in general a very fair approximation, but we have reason to remember sometimes that line absorption in the presence of magnetic fields is a very complicated process. In the immediate neighbourhood of absorption lines effects of magnetic rotation of the plane of polarization and magnetic double refraction may appear in the spectrum.

scholarly journals Magnetic fields of rapidly oscillating Ap stars

1993 ◽  
Vol 139 ◽  
pp. 132-132
Author(s):  
G. Mathys
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Rotation Frequency ◽  
Spectral Lines ◽  
Driving Mechanism ◽  
Line Splitting ◽  
Ap Stars ◽  
The Magnetic Field

Magnetic field appears to play a major role in the pulsations of rapidly oscillating Ap (roAp) stars. Understanding of the behaviour of these objects thus requires knowledge of their magnetic field. Such knowledge is in particular essential to interpret the modulation of the amplitude of the photometric variations (with a frequency very close to the rotation frequency of the star) and to understand the driving mechanism of the pulsation. Therefore, a systematic programme of study of the magnetic field of roAp stars has been started, of which preliminary (and still very partial) results are presented here.Magnetic fields of Ap stars can be diagnosed from the Zeeman effect that they induced in spectral lines either from the observation of line-splitting in high-resolution unpolarized spectra (which only occurs in favourable circumstances) or from the observation of circular polarization of the lines in medium- to high-resolution spectra.

scholarly journals Fast downflows in a chromospheric filament

2019 ◽  
Vol 15 (S354) ◽  
pp. 454-457
Author(s):  
K. Sowmya ◽  
A. Lagg ◽  
S. K. Solanki ◽  
J. S. Castellanos Durán
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Fields ◽  
Velocity Component ◽  
Field Vector ◽  
Line Of Sight ◽  
Plasma Velocity ◽  
Supersonic Velocities ◽  
Slow Velocity ◽  
The Magnetic Field

AbstractAn active region filament in the upper chromosphere is studied using spectropolarimetric data in He i 10830 Å from the GREGOR telescope. A Milne-Eddingon based inversion of the Unno-Rachkovsky equations is used to retrieve the velocity and the magnetic field vector of the region. The plasma velocity reaches supersonic values closer to the feet of the filament barbs and coexist with a slow velocity component. Such supersonic velocities result from the acceleration of the plasma as it drains from the filament spine through the barbs. The line-of-sight magnetic fields have strengths below 200 G in the filament spine and in the filament barbs where fast downflows are located, their strengths range between 100 - 700 G.

scholarly journals The magnetic field of the nearest cool star A Paradigm for Stellar Activity

1996 ◽  
Vol 176 ◽  
pp. 1-16
Author(s):  
Carolus J. Schrijver
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Differential Rotation ◽  
Stellar Atmospheres ◽  
The Sun ◽  
Flux Tubes ◽  
Cool Star ◽  
Temperature Regimes ◽  
The Magnetic Field ◽  
Selection Of

Looking at the Sun forges the framework within which we try to interpret stellar observations. The stellar counterparts of spots, plages, flux tubes, chromospheres, coronae, etc., are readily invoked when attempting to interpret stellar data. This review discusses a selection of solar phenomena that are crucial to understand stellar atmospheric activity. Topics include the interaction of magnetic fields and flows, the relationships between fluxes from different temperature regimes in stellar atmospheres, the photospheric flux budget and its impact on the measurement of the dynamo strength, and the measurement of stellar differential rotation.

scholarly journals Search for surface magnetic fields in Mira stars: first results on χ Cyg

2013 ◽  
Vol 9 (S302) ◽  
pp. 385-388 ◽  
Author(s):  
Agnès Lèbre ◽  
Michel Aurière ◽  
Nicolas Fabas ◽  
Denis Gillet ◽  
Fabrice Herpin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Stellar Atmosphere ◽  
Asymptotic Giant Branch ◽  
Photospheric Level ◽  
First Results ◽  
Weak Surface ◽  
Surface Fields ◽  
The Magnetic Field

AbstractSo far, surface magnetic fields have never been reported on Mira stars, while observational facilities allowing detection and measurement of weak surface fields through the Zeeman effect have become available. Then, in order to complete the knowledge of the magnetic field and of its influence during the transition from Asymptotic Giant Branch (AGB) to Planetary Nebulae (PN) stages, we have undertaken a search for magnetic fields at the surface of Miras. We present the first spectropolarimetric observations (performed with the Narval instrument at Télescope Bernard Lyot-TBL, Pic du Midi, France) of the S-type Mira star χ Cyg. We have detected a polarimetric signal in the Stokes V spectra and we have established its Zeeman origin. We claim that it is likely to be related to a weak magnetic field present at the photospheric level and in the lower part of the stellar atmosphere. The origin of this magnetic field is discussed in the framework of shock waves periodically propagating throughout the atmosphere of a Mira.

scholarly journals Modeling surface magnetic fields in stars with radiative envelopes

2013 ◽  
Vol 9 (S302) ◽  
pp. 290-299
Author(s):  
Oleg Kochukhov
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Doppler Imaging ◽  
Magnetic Field Mapping ◽  
Ap Stars ◽  
Surface Fields ◽  
The Magnetic Field

AbstractStars with radiative envelopes, specifically the upper main sequence chemically peculiar (Ap) stars, were among the first objects outside our solar system for which surface magnetic fields have been detected. Currently magnetic Ap stars remains the only class of stars for which high-resolution measurements of both linear and circular polarization in individual spectral lines are feasible. Consequently, these stars provide unique opportunities to study the physics of polarized radiative transfer in stellar atmospheres, to analyze in detail stellar magnetic field topologies and their relation to starspots, and to test different methodologies of stellar magnetic field mapping. Here I present an overview of different approaches to modeling the surface fields in magnetic A- and B-type stars. In particular, I summarize the ongoing efforts to interpret high-resolution full Stokes vector spectra of these stars using magnetic Doppler imaging. These studies reveal an unexpected complexity of the magnetic field geometries in some Ap stars.

scholarly journals Vector magnetic field and vector current density in and around the δ-spot NOAA 10808

2010 ◽  
Vol 6 (S273) ◽  
pp. 338-338 ◽  
Author(s):  
Véronique Bommier ◽  
Egidio Landi Degl'Innocenti ◽  
Brigitte Schmieder ◽  
Bernard Gelly
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Simulated Annealing Algorithm ◽  
Zeeman Effect ◽  
Vector Current ◽  
Field Vector ◽  
Line Of Sight ◽  
Line Pair ◽  
Spot Center ◽  
The Magnetic Field

AbstractThe context is that of the so-called “fundamental ambiguity” (also azimuth ambiguity, or 180° ambiguity) in magnetic field vector measurements: two field vectors symmetrical with respect to the line-of-sight have the same polarimetric signature, so that they cannot be discriminated. We propose a method to solve this ambiguity by applying the “simulated annealing” algorithm to the minimization of the field divergence, added to the longitudinal current absolute value, the line-of-sight derivative of the magnetic field being inferred by the interpretation of the Zeeman effect observed by spectropolarimetry in two lines formed at different depths. We find that the line pair Fe I λ 6301.5 and Fe I λ 6302.5 is appropriate for this purpose. We treat the example case of the δ-spot of NOAA 10808 observed on 13 September 2005 between 14:25 and 15:25 UT with the THEMIS telescope. Besides the magnetic field resolved map, the electric current density vector map is also obtained. A strong horizontal current density flow is found surrounding each spot inside its penumbra, associated to a non-zero Lorentz force centripetal with respect to the spot center (i.e., oriented towards the spot center). The current wrapping direction is found to depend on the spot polarity: clockwise for the positive polarity, counterclockwise for the negative one. This analysis is made possible thanks to the UNNOFIT2 Milne-Eddington inversion code, where the usual theory is generalized to the case of a line (Fe I λ 6301.5) that is not a normal Zeeman triplet line (like Fe I λ 6302.5).

scholarly journals Investigation of Spatially Unresolved Magnetic Field Outside Sunspots Using Hinode/SOT Observations

2016 ◽  
Vol 12 (S325) ◽  
pp. 59-62
Author(s):  
Olga Botygina ◽  
Mykola Gordovskyy ◽  
Vsevolod Lozitsky
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Zeeman Effect ◽  
Active Regions ◽  
Line Ratio ◽  
Optical Telescope ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

AbstractThe structure of photospheric magnetic fields outside sunspots is investigated in three active regions using Hinode/Solar Optical Telescope(SOT) observations. We analyze Zeeman effect in FeI 6301.5 and FeI 6302.5 lines and determine the observed magnetic field value Beff for each of them. We find that the line ratio Beff(6301)/Beff(6302) is close to 1.3 in the range Beff < 0.2 kG, and close to 1.0 for 0.8 kG < Beff < 1.2 kG. We find that the observed magnetic field is formed by flux tubes with the magnetic field strengths 1.3 − 2.3 kG even in places with weak observed magnetic field fluxes. We also estimate the diameters of smallest magnetic flux tubes to be 15 − 20 km.

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