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 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 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.

Association of calcium network brightness with polar magnetic fields

2018 ◽  
Vol 13 (S340) ◽  
pp. 198-199
Author(s):  
Nancy Narang ◽  
Kalugodu Chandrashekhar ◽  
Vaibhav Pant ◽  
Dipankar Banerjee
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Minimum ◽  
Polar Region ◽  
Polar Regions ◽  
The Sun ◽  
Photospheric Level ◽  
Good Proxy ◽  
Polar Magnetic Fields ◽  
The Magnetic Field

AbstractRecent dedicated HINODE polar region campaign revealed the presence of concentrated kilogauss patches of magnetic field in the polar regions of Sun which are also shown to be correlated with facular bright points at the photospheric level. In this work, we demonstrate that this spatial intermittency of the magnetic field persists even up to the chromospheric heights. Polar network bright points are the ones which are present in the polar regions of the Sun (above 70° latitudes). We use special HINODE campaigns devoted to observe polar regions of the Sun to study the polar network bright points during the phase of last extended solar minimum. We are able to find a considerable association between the polar network bright points and magnetic field concentrations which led us to conclude that these bright points can serve as a good proxy for polar magnetic fields where the direct and regular measurements of polar magnetic fields are not available (before 1970).

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.

scholarly journals Measurements of spatially unresolved magnetic fields of mixed polarity using observations of the Zeeman effect in the solar faculae

2018 ◽  
pp. 23-28
Author(s):  
V. Lozitsky
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Background Field ◽  
Magnetic Polarity ◽  
Half Width ◽  
Width Ratio ◽  
Disc Center ◽  
Mixed Polarity ◽  
The Magnetic Field

It is shown that it is quite possible to measure spatially unresolved magnetic fields of mixed polarity by the Zeeman effect if their intensity exceeds 150-200 G. This means that one can interconnect the ranges of the registration of these fields based on the Hanle and Zeeman effects. This thesis is illustrated by the results of calculations of the half-width of the Stokes profile I for the FeI 5247.1 and 5250.2 lines. Parameter I is sensitive to the presence of magnetic fields, regardless of whether they have the same magnetic polarity within the input aperture of the instrument, or the opposite one. According to the calculations, if the accuracy of the measurement of the half-width ratio of these two lines is increased to 0.5 %, then it is possible to measure the magnetic fields from 70-100 G. On the basis of the proposed method, an estimate of the intensity of the magnetic fields of mixed polarity in a solar faculae in the tail part of the active region NOAA 1809 was made, which on the day of observations, August 6, 2013, was located not far from the Sun’s disc center. The Echelle Zeeman-spectrogram of this region was obtained on the Horizontal Solar Telescope of Astronomical Observatory of Taras Shevchenko National University of Kyiv. The magnetic field in the faculae was measured in two ways: by shift of of the “center of gravity”of the profiles of the FeI 5247.1 and FeI 5250.2 Ǻ lines in the I + V i I – V spectra and also by the half-width ratio of the profiles I of these lines. The first method allows to measure the effective magnetic field Beff, which turned out to be 280 G by FeI 5250.2 and 360 G by FeI 5247.1. The corresponding ratio Beff (5247.1) / Beff (5250.2) ≈ 1.3 indicates the existence of the sub-telescopic flux tubes with kilogauss fields. However, the ratio of the half-width of the Stokes I profiles of these two lines is 1.08, which corresponds to the magnetic field ± 650 G, if magnetic field is purely longitudinal. Based on the analysis of these data as well as the results of other studies, one can conclude that in the investigated faculae there were probably three magnetic field field components: the fluxtubes with kG field Bfluxtube, the areas of background field Bbackgr of regular magnetic polarity, and the areas of subtelescopic fields Bmixpol of mixed magnetic polarity. In absolute value the magnetic flux of tangled mixed-polarity field exceeds the flux of entire regular field with the intensities of Bfluxtube and Bbackgr at least 2-fold.

scholarly journals The Measurement of Solar Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 3-23 ◽  
Author(s):  
Jacques M. Beckers
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Kinetic Energy ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
Zeeman Effect ◽  
Kinetic Energy Density ◽  
Solar Magnetic Fields ◽  
The Third ◽  
The Magnetic Field

The different methods which have been used, or which may be used in the future, to measure solar magnetic fields are described and discussed. Roughly these can be divided into three groups (a) those which use the influence of the magnetic field on the electromagnetic radiation, (b) those which use the influence of the field on the structure of the solar atmosphere (MHD effects), and (c) those which use theoretical arguments. The former include the Zeeman effect, the Hanle effect, the gyro and synchrotron radiations and the Faraday rotation of radiowaves. The second includes the alignment of details at all levels of the solar atmosphere, and the calcium network, and the third makes use, for example, of the assumption of equipartition between magnetic and kinetic energy density.

scholarly journals Observations of Magnetic Fields in Quiescent Prominences

1971 ◽  
Vol 43 ◽  
pp. 192-200 ◽  
Author(s):  
Einar Tandberg-Hanssen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Component ◽  
Zeeman Effect ◽  
Mean Value ◽  
Longitudinal Component ◽  
The Other ◽  
Magnetic Field Component ◽  
The Magnetic Field

The longitudinal component of the magnetic field, B∥, has been recorded in about 135 quiescent prominences observed at Climax during the period 1968–1969. The measurements were obtained with the magnetograph which records the Zeeman effect on hydrogen, helium and metal lines. The following lines were used, Hα; He I, D3, He I, 4471 Å; Na I, D1 and D2, and the observed magnetic field component in these prominences was independent of the line. The overall mean value of the field B∥ for all the prominences was 7.3G. As a rule, the magnetic field enters the prominence on one side and exits on the other, but in traversing the prominence material, the field tends to run along the long axis of the prominence.

scholarly journals Magnetic fields in AGB stars and (proto-) Planetary Nebulae

2008 ◽  
Vol 4 (S259) ◽  
pp. 47-52 ◽  
Author(s):  
Fabrice Herpin ◽  
A. Baudy ◽  
E. Josselin ◽  
C. Thum ◽  
H. Wiesemeyer
Keyword(s):  
Magnetic Field ◽  
Mass Loss ◽  
Zeeman Effect ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Asymptotic Giant Branch Star ◽  
High Mass Loss ◽  
Pn Stage ◽  
Draw Conclusion ◽  
The Magnetic Field

AbstractDuring its quick transition to the Planetary Nebula stage, the Asymptotic Giant Branch star will completely change its geometry. This AGB stellar evolution stage is characterized by a high mass loss driven by the radiation pressure. Strong magnetic field may rule the mass loss geometry and the global shaping of these objects. Following our previous work on the polarization of the SiO maser emission in a representative sample of O-rich evolved stars, we present here a study towards C-rich objects and PPN/PN objects to obtain unbiased conclusions. Using Xpol at the IRAM-30 m telescope, we have conducted CN N=1-0 observations to investigate the Zeeman effect in this molecule and draw conclusion on the evolution of the magnetic field and its influence during the transition of an AGB star to the PN stage. Following the analysis described by Crutcher et al. (1996) we derive an estimate of the magnetic field.

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.

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